| selective enhancement of bovine papillomavirus type 1 dna replication in xenopus laevis eggs by the e6 gene product. | genetic analyses of bovine papillomavirus type 1 (bpv-1) dna in transformed mammalian cells have indicated that the e6 gene product is essential for the establishment and maintenance of a high plasmid copy number. in order to analyze the direct effect of the e6 protein on the replication of a bpv-1-derived plasmid, a cdna containing the bpv-1 e6 open reading frame was subcloned into an sp6 vector for the in vitro synthesis of the corresponding mrna. the sp6 e6 mrna was injected into xenopus laev ... | 1989 | 2540419 |
| action potentials and sodium inward currents of developing neurons in xenopus nerve-muscle cultures. | action potentials and voltage-gated na+ inward currents from cultured embryonic neurons of xenopus laevis were recorded using the patch-clamp technique in the whole cell configuration. neurons together with muscle cells were dissociated from embryos shortly after completion of gastrulation. under the voltage-clamp condition the voltage-gated na+ inward current was isolated from other currents by pharmacological means and by ion substitution. a small na+ current was observed in round cells withou ... | 1989 | 2540466 |
| inward rectifier produced by xenopus oocytes injected with mrna extracted from carp olfactory epithelium. | ionic channels encoded by mrna extracted from carp olfactory epithelium were investigated by injection into xenopus laevis oocytes. the oocytes expressed an inward rectifier k+ -channel, as detected under two-electrode voltage clamp conditions. the results were as follows. an inactivating inward current appeared on hyperpolarization and increased with increasing extracellular k+ concentrations. the 0 current potentials plotted as a function of log [k+]0 in the range between 2 to 20 mmk+ fell on ... | 1989 | 2541514 |
| properties of the beta 1- and beta 2-adrenergic receptor subtypes revealed by molecular cloning. | the beta 1- and beta 2-adrenergic receptor subtypes are biochemically and functionally similar, because both receptors mediate the catecholamine-dependent activation of adenylate cyclase through the gtp-binding protein, gs. pharmacologically, the two receptors can be distinguished on the basis of their relative affinities for the agonists epinephrine and norepinephrine as well as their affinities for several selective antagonists. the primary structures of the human beta 1- and beta 2-adrenergic ... | 1989 | 2541947 |
| changes in dna topology can modulate in vitro transcription of certain rna polymerase iii genes. | the role of dna supercoiling in eukaryotic gene expression is not fully understood. the objective of this study was to examine the regulation of in vitro chromatin assembly by topological alterations in the dna template using a cell-free extract from xenopus laevis oocytes (s-150). the results suggest that input dna topology may be a determining factor in controlling the transcriptional activity of the xenopus trna and one particular 5s gene. when the input topology is supercoiled, high levels o ... | 1989 | 2542762 |
| primary sequence of xenopus laevis na+-k+-atpase and its localization in a6 kidney cells. | polyclonal antibodies raised against the alpha- and beta-subunits of amphibian kidney na+-k+-atpase were used to screen an expression library from xenopus laevis kidney epithelial cells (a6 cell line). cdnas coding for each na+-k+-atpase subunit were identified and used to isolate near full-length cdnas. the complete nucleotide sequence and the deduced amino acid sequence were determined. the alpha-subunit is an alpha (alpha i)-isoform. the alpha- and beta-subunits are more closely related to th ... | 1989 | 2544104 |
| intracellular signals trigger ultrastructural events characteristic of meiotic maturation in oocytes of xenopus laevis. | oocytes of xenopus laevis were treated with agents which induce individual intracellular signals normally evoked during the process of meiotic maturation. ultrastructural analysis of these oocytes allowed identification of specific second messengers that individually trigger single ultrastructural changes characteristic of the meiotic maturation process: manipulation of intracellular camp levels induced changes in cortical granule position. cytoplasmic alkalinization triggered a disruption of th ... | 1989 | 2544275 |
| the cation-dependent mannose 6-phosphate receptor. structural requirements for mannose 6-phosphate binding and oligomerization. | the structural requirements for oligomerization and the generation of a functional mannose 6-phosphate (man-6-p) binding site of the cation-dependent mannose 6-phosphate receptor (cd-mpr) were analyzed. chemical cross-linking studies on affinity-purified cd-mpr and on solubilized membranes containing the receptor indicate that the cd-mpr exists as a homodimer. to determine whether dimer formation is necessary for the generation of a man-6-p binding site, a cdna coding for a truncated receptor co ... | 1989 | 2544594 |
| sodium and potassium currents recorded during an action potential. | a simple method was used to measure directly sodium and potassium currents underlying the action potential in single nerve fibres of xenopus laevis. a short rectangular stimulus under current-clamp conditions elicited an action potential which was digitally stored and later used as command when voltage-clamping the same fibre. the currents thus obtained nearly reproduced the original rectangular stimulus. adding first 100 nm ttx and subsequently 100 nm ttx plus 10 mm tea to the extracellular rin ... | 1989 | 2546753 |
| purification of a p47 phosphoprotein from xenopus laevis oocytes and identification as an in vivo and in vitro p34cdc2 substrate. | this paper describes the purification of a 47 kda protein from xenopus laevis oocytes that becomes phosphorylated when the oocytes undergo meiotic maturation. this protein (p47) is part of a high molecular mass complex containing at least two other proteins of molecular mass 30 and 36 kda. this complex can be isolated from stage vi oocytes before maturation. we obtained a pattern for phosphopeptides in p47 phosphorylated in vivo very similar to that of the purified protein phosphorylated in vitr ... | 1989 | 2546822 |
| extranuclear estrogen-regulated destabilization of xenopus laevis serum albumin mrna. | the present study examined 1) whether the estrogen-regulated destabilization of albumin mrna occurs in the nuclear or extranuclear fraction of the liver cell, and 2) whether the selective posttranscriptional regulation of albumin mrna stability might result from covalent changes introduced in the processing or polyadenylation of the primary transcript. the disappearance of albumin mrna after estrogen is restricted to the extranuclear fraction of the cell. transient changes in steady state levels ... | 1989 | 2547154 |
| calcium channels in skeletal muscle fibres of the frog. | the vaseline gap voltage clamp technique was used to study slow and fast calcium currents in phasic and tonic muscle fibres of the frogs rana temporaria (r.t.) and xenopus laevis (x.l.). at physiological ca2+ and na+ concentrations three inward currents could be recorded in r.t. twitch muscle fibres: a fast ca current, a slow ca current, and a non-specific (ins) current carried by na ions. the last current appeared as a sole component at a low threshold membrane potential (mp -55 mv) and was pre ... | 1989 | 2547359 |
| evidence for intracellular sodium pumps in permeabilized xenopus laevis oocytes. | ouabain binding was studied in xenopus laevis oocytes permeabilized by detergents. the behaviour of markers showed that 10 microm-digitonin selectively disrupts the plasma membrane. in the presence of atp, oocytes permeabilized at 10 microm-digitonin bound no more ouabain molecules than were required to abolish active 86rb+ uptake in the intact cells. however, the ouabain binding capacity increased approx. 2-fold when inner membranes were disrupted by sds or excess digitonin, as judged from the ... | 1989 | 2548475 |
| e-series prostaglandins activate camp-mediated potassium currents in follicle-enclosed xenopus oocyte. | receptor-mediated responses to prostaglandins e1 and e2 are shown by electrophysiological methods in follicle-enclosed oocytes of xenopus laevis. in voltage-clamped oocytes, prostaglandins e1 and e2 elicited an outward hyperpolarizing current. this outward membrane current was caused by an increase in k+ conductance. the prostaglandin-induced current was augmented by adenylate cyclase activator, forskolin, and by phosphodiesterase inhibitor, theophylline, indicating that adenosine 3', 5'-cyclic ... | 1989 | 2548500 |
| intracellular magnesium blocks sodium outward currents in a voltage- and dose-dependent manner. | tail currents through na+ channels have been measured in inside-out patches from xenopus laevis oocytes injected with cdna-derived mrna coding for the rat brain type ii na+ channel. it is shown that intracellular mg2+ blocks outward currents in a voltage- and dose-dependent manner with a half blocking concentration between 3 and 4 mm at 0 mv and a voltage dependence of e-fold per 49 mv. | 1989 | 2548634 |
| quantal charge redistributions accompanying the structural transitions of sodium channels. | asymmetric displacement currents, ig, associated with the gating of nerve sodium channels have been recorded in cell-attached macropatches of xenopus laevis oocytes injected with exogenous mrna coding for rat-brain-ii sodium channels. the ig properties were found to be similar to those of gating currents previously observed in native nerve preparations. ig fluctuations were measured in order to ascertain the discreteness of the conformational changes which precede the channel opening. the auto-c ... | 1989 | 2548829 |
| control of melanoblast differentiation in amphibia by alpha-melanocyte stimulating hormone, a serum melanization factor, and a melanization inhibiting factor. | a ventrally localized melanization inhibiting factor (mif) has been suggested to play an important role in the establishment of the dorsal-ventral pigment pattern in xenopus laevis [fukuzawa and ide:dev. biol., 129:25-36, 1988]. to examine the possibility that melanoblast expression might be controlled by local putative mif and melanogenic factors, the effects of alpha-melanocyte stimulating hormone (alpha-msh), a serum melanization factor (smf) from x. laevis or rana pipiens, and mif on the "ou ... | 1989 | 2549532 |
| identification of the atp + mg-dependent and polycation-stimulated protein phosphatases in the germinal vesicle of the xenopus oocyte. | two protein phosphatase activities were characterized in the germinal vesicle of xenopus laevis oocytes after manual dissection of the nucleus. one enzyme can be classified as an active form of the atp + mg-dependent (amd) phosphatase, the other as a polycation-stimulated (pcs) phosphatase. the activity of the pcs phosphatase is localized exclusively in the soluble compartment of the nucleus (nucleoplasm). the catalytic subunit of the amd phosphatase activity is associated either with the nuclea ... | 1989 | 2549958 |
| microinjection of inositol 1,2-(cyclic)-4,5-trisphosphate, inositol 1,3,4,5-tetrakisphosphate, and inositol 1,4,5-trisphosphate into intact xenopus oocytes can induce membrane currents independent of extracellular calcium. | inositol phosphate action in an intact cell has been investigated by intracellular microinjection of eight inositol phosphate derivatives into xenopus laevis oocytes. these cells have calcium-regulated chloride channels but do not have a calcium-induced calcium release system. microinjection of inositol 1,3,4,5-tetrakisphosphate (ip4), inositol 1,2-(cyclic)-4,5-trisphosphate (cip3), inositol 1,4,5-trisphosphate (ip3), or inositol 4,5-bisphosphate [(4,5)ip2], open chloride channels to induce a me ... | 1989 | 2550488 |
| composite transposable elements in the xenopus laevis genome. | members of two related families of transposable elements, tx1 and tx2, were isolated from the genome of xenopus laevis and characterized. in both families, two versions of the elements were found. the smaller version in each family (tx1d and tx2d) consisted largely of two types of 400-base-pair tandem internal repeats. these elements had discrete ends and short inverted terminal repeats characteristic of mobile dnas that are presumed to move via dna intermediates, e.g., drosophila p and maize ac ... | 1989 | 2550791 |
| oligonucleotide-targeted degradation of u1 and u2 snrnas reveals differential interactions of simian virus 40 pre-mrnas with snrnps. | we have investigated the roles of u1 and u2 snrnp particles in sv40 pre-mrna splicing by oligonucleotide-targeted degradation of u1 or u2 snrnas in xenopus laevis oocytes. microinjection of oligonucleotides complementary to regions of u1 or u2 rnas either in the presence or absence of sv40 dna resulted in specific cleavage of the corresponding snrna. unexpectedly, degradation of u1 or u2 snrna was far more extensive when the oligonucleotide was injected without, or prior to, introduction of vira ... | 1989 | 2550896 |
| melanin concentrating hormone. v. isolation and characterization of alpha-melanocyte-stimulating hormone from frog pituitary glands. | the structure of alpha-melanocyte-stimulating hormone (alpha-msh) has been determined in the pars intermedia of the frog rana ridibunda. pulse-chase labeling of frog neurointermediate lobes with selective amino acids revealed that the composition of frog alpha-msh is similar to that of alpha-msh from all mammalian species yet studied. tryptic mapping of nexly synthetized alpha-msh generated two fragments with the following amino acid composition: (t1) trp, pro, lys, gly, val and (t2) tyr, arg, p ... | 1989 | 2552247 |
| selective expression of an amiloride-inhibitable na+ conductance from mrna of respiratory epithelium in xenopus laevis oocytes. | poly(a)+rna was prepared from primary cultures of human nasal polyp epithelia and from native bovine tracheal epithelia. six to fifty nanograms mrna were injected into prophase-arrested immature xenopus laevis oocytes. one to four days later the oocytes were probed with electrophysiological techniques for induction of novel ion conductances. oocytes injected with mrna had lower membrane potentials (vm) and resistances (rm) than controls. by use of step changes in extracellular na+ concentration ... | 1989 | 2552830 |
| vertebrate and yeast calmodulin, despite significant sequence divergence, are functionally interchangeable. | yeast strains relying solely on vertebrate (xenopus laevis) calmodulin, expressed under control of a yeast (gal1) promoter, grew at the same rate as yeast cells containing their endogenous calmodulin. therefore, the ability to perform essential functions has been conserved between yeast and vertebrate calmodulins, suggesting that calmodulin performs the same (or overlapping) roles in yeast as it does in higher eukaryotes. successful substitution of vertebrate for yeast calmodulin also suggests t ... | 1989 | 2554295 |
| molecular basis of functional diversity of voltage-gated potassium channels in mammalian brain. | cloning and sequencing of cdnas isolated from a rat cortex cdna library reveals that a gene family encodes several highly homologous k+ channel forming (rck) proteins. functional characterization of the channels expressed in xenopus laevis oocytes following microinjection of in vitro transcribed rck-specific rnas shows that each of the rck proteins forms k+ channels that differ greatly in both their functional and pharmacological properties. this suggests that the molecular basis for the diversi ... | 1989 | 2555158 |
| quantitation of type ii topoisomerase in oocytes and eggs of xenopus laevis. | we have generated a monoclonal antibody and a polyclonal antiserum specific for xenopus laevis topoisomerase ii. using quantitative immunoprecipitation and western blotting techniques, we have determined the content of topoisomerase ii in x. laevis oocytes during oogenesis and in unfertilized eggs. an average stage i oocyte contains 6 pg of topoisomerase ii. the content of topoisomerase ii per oocyte increases throughout oogenesis to 1.5 ng per stage vi oocyte. the topoisomerase ii protein in st ... | 1989 | 2555235 |
| metabolism of inositol pentakisphosphate to inositol hexakisphosphate in xenopus laevis oocytes. | the formation and metabolism of inositol pentakis-and hexakisphosphates (insp5 and insp6) were investigated in xenopus laevis oocytes. after [3h]inositol injection, [3h]insp5 and subsequently [3h]insp6 increased progressively over 72 h. in intact oocytes, [3h]insp5 was progressively converted to [3h]insp6 from 6 to 72 h of incubation and was not metabolized to lower inositol phosphates. in contrast, [3h]insp6 remained unmetabolized for up to 72 h. these data are consistent with the kinetics of t ... | 1989 | 2555344 |
| a role for the beta-subunit in the expression of functional na+-k+-atpase in xenopus oocytes. | in all cellular systems studied so far, the catalytic alpha- and the glycosylated beta-subunit of na+-k+-atpase are coordinately synthesized and are assembled into stoichiometric alpha, beta-complexes. in contrast to these data, in this study we show that the fully grown oocyte of xenopus laevis synthesizes much less beta-subunit than alpha-subunit. the alpha-subunit produced in excess over the beta-subunit is membrane associated but highly trypsin sensitive and can be compared with the immature ... | 1989 | 2556932 |
| calcium-dependent chloride currents elicited by injection of ethanol into xenopus oocytes. | electrophysiological techniques were used to study the response of native xenopus laevis oocytes to intracellular injection and bath application of ethanol. injection of ethanol produced dose-dependent transient inward currents accompanied by large current fluctuations, with estimated intracellular concentrations ranging from 10 to 300 mm. the response duration varied between 2 and 15 min, with an onset delay of 2-15 s. the inward current sometimes consisted of a fast and a slow component. bath ... | 1989 | 2557132 |
| long-term starvation in xenopus laevis daudin--iii. effects on enzymes in several tissues. | 1. adult, female xenopus laevis were subjected to 12 months of starvation. 2. starvation resulted in a continuous reduction in the activity of both hepatic and renal glucose-6-phosphate dehydrogenase. 3. fructose-1,6-diphosphatase was significantly reduced at months 10 and 12 in the liver, and at months 4, 10, and 12 in the kidney. 4. pyruvate kinase activity of muscle and liver decreased during the experimental period whereas the renal enzyme remained essentially unchanged. 5. both hepatic and ... | 1989 | 2558003 |
| aldosterone induces a rapid increase in the rate of na,k-atpase gene transcription in cultured kidney cells. | aldosterone (300 nm) induces a 4-fold increase over a 6-hr stimulation in a6 kidney cells from xenopus laevis in the abundance of mrna beta 1 and a 2-fold in that of mrna alpha 1 coding for each na,k-atpase subunit, which is in agreement with a previous report. after a 3-hr stimulation already, aldosterone elicited a significant increase of mrna beta 1 (2.51-fold +/- 0.47, n = 3, p less than 0.05) and a nonsignificant increase of mrna alpha 1 (1.26-fold +/- 0.30, n = 3, ns). increasing doses of ... | 1989 | 2558308 |
| temperature dependence of gating current in myelinated nerve fibers. | asymmetrical displacement currents and na currents of single myelinated nerve fibers of xenopus laevis were studied in the temperature range from 5 to 24 degrees c. the time constant of the on-response at e = 4 mv, tau on, was strongly temperature dependent, whereas the amount of displaced charge at e = 39 mv, qon, was only slightly temperature dependent. the mean q10 for tau on-1 was 2.54, the mean q10 for qon was 1.07. the time constant of charge immobilization, tau i, at e = 4 mv varied signi ... | 1989 | 2559205 |
| u2 snrna sequences that bind u2-specific proteins are dispensable for the function of u2 snrnp in splicing. | previously we showed that microinjection of purified u2 snrna from hela cells into xenopus laevis oocytes, depleted of their endogenous u2 snrnps by oligonucleotide-targeted degradation, led to assembly of hybrid snrnps that were fully functional for splicing of sv40 late pre-mrna. we have extended these results by examining features of u2 rna that are required for its role in splicing. injection of xenopus u2 snrna transcribed in vitro by t7 rna polymerase, differing in sequence from authentic ... | 1989 | 2559872 |
| effects of aldosterone on (na+ + k+)-atpase of amphibian sodium-transporting epithelial cells (a6) in culture. | stimulation by aldosterone of sodium reabsorption can be reproduced on a cell line, a6, derived from the renal tissue of xenopus laevis. these cells organize themselves as a polarized epithelium carrying out unidirectional sodium transport, reflected by the short-circuit current (isc). isc response to aldosterone starts to be apparent after a latency period of 2-3 h; the full hormonal effect takes much longer. on the other hand, (na+ + k+)-atpase activity and density in ouabain binding sites did ... | 1989 | 2560522 |
| chloride channels mediate the response to gonadotropin-releasing hormone (gnrh) in xenopus oocytes injected with rat anterior pituitary mrna. | functional expression of receptors for gnrh was studied using xenopus laevis oocytes injected with poly(a)+ mrna extracted from rat anterior pituitary glands. whole-cell currents were monitored using two-electrode voltage-clamp techniques. in oocytes which responded to both gnrh and trh, the gnrh response showed a longer latency and time-to-peak than the trh response. the response to gnrh or an agonist of gnrh receptors, buserelin (1 nm-1 microm) consisted of current fluctuations and occurred in ... | 1989 | 2560805 |
| expression of n-cam precedes neural induction in pleurodeles waltl (urodele, amphibian). | the appearance and localization of n-cam during neural induction were studied in pleurodeles waltl embryos and compared with recent contradictory results reported in xenopus laevis. a monoclonal antibody raised against mouse n-cam was used. in the nervous system of pleurodeles, it recognized two glycoproteins of 180 and 140x10(3) m(r) which are the pleurodeles equivalent of n-cam-180 and -140. using this probe for immunohistochemistry and immunocytochemistry, we showed that n-cam was already exp ... | 1989 | 2562662 |
| duplicated homeobox genes in xenopus. | multiple kinds of clones and restriction fragment polymorphisms are frequently encountered when analyzing genes of the tetraploid frog xenopus laevis. two types of cdna clone have been isolated for homeobox gene 2. analysis of their corresponding genomic clones confirmed the existence of clearly distinct restriction maps; in addition the nearby presence of two additional homeoboxes suggests that this region is homologous to the hox 2 gene complex of mammals. we asked whether the genetic polymorp ... | 1989 | 2563247 |
| steady-state levels of pro-dynorphin-related end-products from the brain of the amphibian, xenopus laevis. | steady-state analyses of prodynorphin-derived opioid peptides were conducted on acid extracts of the brain of the frog. xenopus laevis. radioimmunoassays specific for dynorphin a(1-17), dynorphin a(1-8), alpha-neoendorphin and dynorphin b coupled with gel filtration chromatography and reverse phase high performance liquid chromatography were used. the major prodynorphin-related end-product detected was alpha-neoendorphin. interestingly, leu-enkephalin was also detected. since the xenopus proenke ... | 1989 | 2564304 |
| particular processing of pro-opiomelanocortin in xenopus laevis intermediate pituitary. sequencing of alpha- and beta-melanocyte-stimulating hormones. | alpha- and beta-melanocyte-stimulating hormones (alpha-msh and beta-msh) have been isolated from xenopus laevis neurointermediate pituitary and microsequenced. intracellular alpha-msh is not n-acetylated after proteolytic processing of pro-opiomelanocortin in contrast to mammalian alpha-mshs. there is a high preservation of the melanotropic amino acid sequence common to all mshs although in xenopus beta-msh a histidine residue replaces the glutamic acid residue found in position 8 of mammalian b ... | 1989 | 2564347 |
| involvement of proliferating cell nuclear antigen (cyclin) in dna replication in living cells. | proliferating cell nuclear antigen (pcna) (also called cyclin) is known to stimulate the activity of dna polymerase delta but not the other dna polymerases in vitro. we injected a human autoimmune antibody against pcna into unfertilized eggs of xenopus laevis and examined the effects of this antibody on the replication of injected plasmid dna as well as egg chromosomes. the anti-pcna antibody inhibited plasmid replication by up to 67%, demonstrating that pcna is involved in plasmid replication i ... | 1989 | 2564636 |
| pharmacological alterations of the activity of afferent fibers innervating hair cells. | to determine whether some of the substances that may be present in hair-cell sensory organs could affect neural activity in afferent fibers, we examined 56 compounds for the ability to alter the discharge rate of afferent fibers innervating hair cells in the lateral line organ of xenopus laevis, the african clawed frog. these compounds included amino acids, glutamyl dipeptides, standard neurotransmitter candidates, and other constituents of tissues and body fluids. substances found to be excitat ... | 1989 | 2565327 |
| quantitation and subcellular localization of proliferating cell nuclear antigen (pcna/cyclin) in oocytes and eggs of xenopus laevis. | proliferating cell nuclear antigen (pcna/cyclin) is a 36-kda polypeptide present in the nuclei of mitotically active cells. it is known to be involved in dna replication through an association with dna polymerase delta. we examined the total content as well as the subcellular distribution of pcna in the oocyte and the egg of xenopus laevis by employing immunocytological staining and immunoblot analysis. while oocytes are not capable of replicating chromosomes, pcna is abundant in the nucleus (ab ... | 1989 | 2566509 |
| cytochalasin d inhibits l-glutamate-induced disc shedding without altering l-glutamate-induced increase in adhesiveness. | excitatory amino acid-stimulated disc shedding is correlated with the appearance of microfilament-rich ensheathing processes of the retinal pigment epithelium (rpe) and increased apparent adhesiveness between photoreceptors and rpe in explanted eyecups of xenopus laevis. we have compared the time course of disc shedding and increased retinal adherence during l-glutamate treatment. increased adherence was measured on the basis of the tendency of the apical rpe domains to partition with isolated n ... | 1989 | 2567678 |
| potassium-induced release of endogenous glutamate and two as yet unidentified substances from the lateral line of xenopus laevis. | the release of endogenous glutamate and other primary amines from the lateral-line of xenopus laevis was studied using an in vitro superfusion technique and high performance liquid chromatography. potassium stimulation (50 mm kcl) applied to 60 or 120 lateral-line organs dissected from the skin and pooled in a perfusion chamber induced the release of glutamate and aspartate. the release of aspartate was smaller than that of glutamate and more variable. a variable release of two, as yet, unidenti ... | 1989 | 2570615 |
| ionic and charge-displacement currents evoked by temperature jumps in xenopus oocytes. | membrane currents were recorded in voltage-clamped oocytes of xenopus laevis. currents were produced in response to temperature jumps imposed by a heating lamp. responses were larger when the animal (pigmented) hemisphere of the oocyte was illuminated as compared to the vegetal hemisphere; they arose because of a thermal effect as they were attenuated by removal of infrared wavelengths. the temperature jump responses comprised two distinct components: (i) a slow maintained current, which inverte ... | 1989 | 2571159 |
| translation of poly(a)+ mrna encoding cfu-s proliferation stimulator of human fetal liver origin in xenopus laevis oocytes. | using the sodium dodecyl sulfate/chloroform/phenol method, total rna was extracted from human fetal liver tissue with a yield of 870-1060 micrograms/g of tissue; mrna was obtained after chromatography on an oligo(dt)-cellulose column. experimental studies demonstrated the translation of a poly(a)+ mrna encoding proliferation stimulator of human fetal liver origin in xenopus laevis oocytes. | 1989 | 2572442 |
| xlhbox 8: a novel xenopus homeo protein restricted to a narrow band of endoderm. | we report the isolation of a new homeobox gene from xenopus laevis genomic dna. the homeodomain sequence is highly diverged from the prototype antennapedia sequence, and contains a unique histidine residue in the helix that binds to dna. the homeodomain is followed by a 65 amino acid carboxyterminal domain, the longest found to date in any vertebrate homeobox gene. we have raised specific antibodies against an xlhbox 8-beta-gal fusion protein to determine the spatial and temporal expression of t ... | 1989 | 2574662 |
| expression of an engrailed-related protein is induced in the anterior neural ectoderm of early xenopus embryos. | we have used a monoclonal antibody directed against the c-terminus of the drosophila invected homeodomain to detect a nuclear protein in brain cells of xenopus laevis embryos. we refer to this antigen as the xenopus en protein. the en protein is localized at midneurula stage to a band of cells in the anterior portion of the neural plate, on each side of the neural groove. later in development, the expression coincides with the boundary of the midbrain and hindbrain, and persists at least to the ... | 1989 | 2574664 |
| two tfiiia activities regulate expression of the xenopus 5s rna gene families. | immunoblotting experiments with polyclonal and monoclonal anti-transcription factor iiia (tfiiia) antibodies reveal different electrophoretic forms of tfiiia in extracts from immature and mature oocytes of xenopus laevis. the well-characterized 39-kd tfiiia species is present in approximately 10(12) copies per cell in stage i-iii previtellogenic oocytes and declines in abundance by 10- to 20-fold during oogenesis. an immunologically related protein of apparent molecular mass of 42 kd is present ... | 1989 | 2575558 |
| bimodal and graded expression of the xenopus homeobox gene xhox3 during embryonic development. | a xenopus laevis homeobox gene, xhox3, has been isolated using the homeobox of the drosophila pair-rule gene even skipped as a hybridization probe. xhox3 is first transcribed at the midblastula transition; rna levels peak at the early neurula stage and decrease thereafter. during the early period of xhox3 expression, the gastrula and neurula stages, transcripts are found in a graded fashion along the anteroposterior (a-p) axis in the mesoderm and are most concentrated at the posterior pole. in t ... | 1989 | 2576399 |
| translation in a cell-free system, and in xenopus oocytes, of mrna which specify a cadmium-binding protein in nereis diversicolor (annelida, polychaeta). | the presence in the marine worm nereis diversicolor of a low molecular mass protein with the capacity to bind cadmium has been previously demonstrated. poly(a)(+)-mrna were extracted from coelomocytes of nereis diversicolor and were translated either in vitro, using a rabbit reticulocyte lysate, or in vivo into xenopus laevis oocytes. analysis of synthesized polypeptides by enzyme-linked immunosorbent assay (elisa) and by western blotting, using a specific monoclonal anti-mp ii antibody, showed ... | 1989 | 2576641 |
| specific changes in axonally transported proteins during regeneration of the frog (xenopus laevis) optic nerve. | labeled proteins in intact and regenerating optic nerves of juvenile xenopus clawed frogs were examined at three different time points (2 to 4 hr, 18 hr, and 5 to 9 days) following [35s]methionine injection into the eye. the distal axon tips of optic nerves were transected at the margin of the tectal lobe and regeneration of the nerve was followed by three methods: autoradiography, tissue section counting following [3h]proline injection into the eye, and electrophysiological mapping of the visua ... | 1985 | 2578186 |
| 2'-fluoro-2'-deoxycytidine triphosphate as a substrate for rna- and dna-dependent dna polymerases. | the ability of the analog 2'-fluoro-2'-deoxycytidine triphosphate (dcfltp) to be used as a substrate in the reactions catalyzed by xenopus laevis oocytes dna polymerase alpha and amv reverse transcriptase has been studied. the apparent km values for dctp and dcfltp, using activated dna as templates, were 0.6 microm and 7 mm with dna polymerase alpha and 0.14 microm and 7 microm with amv reverse transcriptase, respectively. as observed with dctp, aphidicolin was a noncompetitive inhibitor in the ... | 1985 | 2578819 |
| 2'-fluoro-2'-deoxypolynucleotides as templates and inhibitors for rna- and dna-dependent dna polymerases. | poly(2'-fluoro-2'-deoxyadenylic acid) (poly(dafl)) and poly(2'-deoxycytidylic acid) (poly(dcfl)) were tested as templates in dna synthesis reactions catalyzed by xenopus laevis oocytes dna polymerase alpha, mouse cell dna polymerase gamma and avian myeloblastis virus (amv) reverse transcriptase. poly(dafl).(dt)12 can fully substitute for poly(ra).(dt)12 as template with dna polymerase gamma, to 50% with reverse transcriptase, but was poorly recognized by dna polymerase alpha. dna synthesis by re ... | 1985 | 2578820 |
| beta-adrenergic induced k+ current in xenopus oocytes: role of camp, inhibition by muscarinic agents. | the k+ current induced by isoprenaline acting on beta-adrenergic receptors in xenopus laevis has been studied in oocytes still surrounded by their follicular cells and inner ovarian epithelium. forskolin, an adenylate cyclase activator, induced a similar k+ current and when used at subliminal concentration it potentiated the current induced by isoprenaline. inhibition of phosphodiesterase by methylisobutylxanthine also enhanced the response to isoprenaline. 8-br-camp, a permeant analogue of camp ... | 1985 | 2579401 |
| in vitro activation of human sperm induced by amphibian egg extract. | in this paper we characterize a system for the activation of human sperm using cell-free extracts from xenopus laevis eggs. we characterize the kinetics of sperm activation in terms of morphological and dna synthetic parameters. we have optimized some of the components which are necessary for chromatin decondensation and present data to demonstrate that the in vitro process is efficient over a wide range of salt concentrations and amounts of supplementary reducing agents. | 1985 | 2579835 |
| gating kinetics of nonjunctional acetylcholine receptor channels in developing xenopus muscle. | the development of nonjunctional acetylcholine (ach) receptor gating kinetics was studied in myotomal muscle of xenopus laevis by spectral analysis of ach-induced noise. the results are consistent with the idea that there is a developmental shift in relative numbers of receptors with fast and slow gating kinetics. for about the first 20 hr following the onset of ach sensitivity, the majority of channel openings contributing to the ach noise were slow, having an apparent mean open time of about 3 ... | 1985 | 2580068 |
| three functions of sodium channels in the toad node of ranvier are altered by trimethyloxonium ions. | voltage-clamped nodes of ranvier of the toad xenopus laevis were treated with trimethyloxonium ions (tmo) which are known to methylate carboxyl groups. tmo did not affect potassium channels but the sodium system was modified in three ways: a) the current was reduced, b) channels were rendered insensitive to tetrodotoxin (ttx) and c) the inactivation of all channels, ttx-resistant or not, was slowed in a potential range between 50 and 110 mv. steady-state inactivation, however, was not changed. p ... | 1985 | 2580267 |
| light and temperature modulated staining of the rod outer segment distal tips with lucifer yellow. | external application of the dye lucifer yellow to isolated retinas of xenopus laevis causes a specific staining of the distal tips of the rod outer segment (ros). staining occurs most frequently in the distal 4 micron of the ros and does not diffuse throughout the ros cytosol. in contrast, damaged ros fill with the dye and exhibit a diffuse fluorescence. retinas from constant light-treated animals show a greater frequency of labeling when isolated in the light than when isolated in the dark afte ... | 1985 | 2581915 |
| rna directed synthesis of catalytically active drosophila sn-glycerol-3-phosphate dehydrogenase in xenopus oocytes. | xenopus laevis oocytes injected with poly(a)+ rna isolated from drosophila melanogaster direct the synthesis of catalytically active glycerol-3-phosphate dehydrogenase (nad+) (ec 1.1.1.8). the de novo synthesized enzyme reflects the electrophoretic properties appropriate to the stock of flies from which the injected rna was isolated and is electrophoretically distinct from endogenous xenopus activity. immunoprecipitation of 35s-labeled translation products has demonstrated two immunologically re ... | 1985 | 2581943 |
| imaging of cell membraneous and cytoskeletal structures with a scanning tunneling microscope. | the first observation of unstained cell membraneous structures by a scanning tunneling microscope is reported. an adhesive preparation method was used for imaging human medulloblastoma cells from the cell line te 671 and oocytes from the clawed toad xenopus laevis. the images show filaments, stacks of molecules and hilly structures. the possible identify of the filamentous structures is discussed, although the observed structures cannot yet be fully characterized. the work suggests possible futu ... | 1989 | 2583291 |
| genetic mapping in xenopus laevis: eight linkage groups established. | inheritance of alleles at 29 electrophoretically detected protein loci and one pigment locus (albinism) was analyzed in xenopus laevis by backcrossing multiply heterozygous individuals generated by intersubspecies hybridization. pairwise linkage tests revealed eight classical linkage groups. these groups have been provisionally numbered from 1 to 8 in an arbitrarily chosen order. linkage group 1 includes alb-2 (albumin), adh-1 (alcohol dehydrogenase), np (nucleoside phosphorylase), and ap (perio ... | 1989 | 2583481 |
| quick-freeze, deep-etch, rotary-shadow views of the extracellular matrix and cortical cytoskeleton of xenopus laevis eggs. | the quick-freeze, deep-etch, rotary-shadow technique provides a powerful tool to study the structural dynamics of extracellular matrices. using this technique, we show that the extracellular investments of the xenopus laevis egg are multilayered and securely anchored to the egg surface. the cortical cytoskeleton within the egg contains embedded cortical granules with surrounding endoplasmic reticulum and is capped by a thin reticular sheet that contacts the inner surface of the plasma membrane. ... | 1989 | 2585120 |
| developmental expression and 5s rrna-binding activity of xenopus laevis ribosomal protein l5. | ribosomal protein l5 binds specifically to 5s rrna to form a complex that is a precursor to 60s subunit assembly in vivo. analyses in yeast cells, mammalian cells, and xenopus embryos have shown that the accumulation of l5 is not coordinated with the expression of other ribosomal proteins. in this study, the primary structure and developmental expression of xenopus ribosomal protein l5 were examined to determine the basis for its distinct regulation. these analyses showed that l5 expression coul ... | 1989 | 2586520 |
| a nuclear factor i-like activity and a liver-specific repressor govern estrogen-regulated in vitro transcription from the xenopus laevis vitellogenin b1 promoter. | a hormone-controlled in vitro transcription system derived from xenopus liver nuclear extracts was exploited to identify novel cis-acting elements within the vitellogenin gene b1 promoter region. in addition to the already well-documented estrogen-responsive element (ere), two elements were found within the 140 base pairs upstream of the transcription initiation site. one of them, a negative regulatory element, is responsible for the lack of promoter activity in the absence of the hormone and, a ... | 1989 | 2586526 |
| development of early swimming in xenopus laevis embryos: myotomal musculature, its innervation and activation. | the development of the axial musculature, its innervation and early locomotion in xenopus laevis embryos are described. between stages 17 and 40 some 45 myotomes are formed on each side of the body. during this period the animals develop from non-motile to free swimming embryos. using fluorescein-conjugated bungarotoxin the acquisition of acetylcholine receptor-sites was studied. at stage 25 (early flexure stage) bound bungarotoxin was confined to the first seven intermyotomal clefts, in free sw ... | 1989 | 2586744 |
| [the spatio-temporal distribution of single-stranded breaks in nuclear dna in sections of clawed toad embryos during gastrulation and neurulation]. | spatial and temporal pattern and quantities of nicks in nuclear dna during gastrulation and neurulation was studied using nick-translation in sections of xenopus laevis embryos. specific changes in the number of nicks in different mesoderm and ectoderm regions were detected during embryogenesis. dorso-ventral gradient of nuclear labelling was observed in mesoderm and inner ectoderm layer of early and middle gastrula. the gradient was inverted during transition from gastrula to neurula. at the sa ... | 1989 | 2587008 |
| ribosome loading, but not protein synthesis, is required for estrogen stabilization of xenopus laevis vitellogenin mrna. | we have examined the effect of protein synthesis and of ribosome loading on the estrogen-mediated stabilization of hepatic xenopus laevis vitellogenin mrna. removal of estradiol-17 beta from the culture medium, which destabilizes vitellogenin mrna, does not alter the density of ribosomes on polysomal vitellogenin mrna, or change the proportion of vitellogenin mrna associated with the endoplasmic reticulum. cycloheximide, which inhibits elongation, without changing the density of ribosomes on vit ... | 1989 | 2587251 |
| initiation and termination of human u1 rna transcription requires the concerted action of multiple flanking elements. | sequences in the 5' flanking region of small nuclear rna (snrna) genes are responsible for recognition of 3' end signals. formation of the pre-u1 3' end occurs at the downstream signal closest to the promoter, probably by transcription termination. we have analyzed promoter elements for their participation in formation of the 3' ends of pre-u1 rna. to do this, a human u1 rna gene with deletions in individual promoter elements was microinjected into xenopus laevis oocytes and the resulting rnas w ... | 1989 | 2587258 |
| structure and functional expression of a cloned xenopus thyroid hormone receptor. | a clone corresponding to a thyroid hormone receptor was isolated from a xenopus laevis cdna library prepared from folliculated oocytes. the cdna encodes a protein of 418 amino acid residues with a domain structure, including a putative dna binding region with two zinc fingers, similar to other members of the v-erba-related superfamily of receptors. the encoded protein resembles the tr alpha 1-type receptor of the rat. when expressed in cos cells the protein product binds triiodothyronine with a ... | 1989 | 2587261 |
| factors influencing the heat shock response of xenopus laevis embryos. | we have further characterized the heat shock response of xenopus laevis embryos. xenopus embryos respond to heat shock by consistently synthesizing four major heat shock proteins (hsps) of 62, 70, 76, and 87 kilodaltons. in addition to these hsps, heat-shocked embryos also exhibit the synthesis of several minor hsps. the synthesis of these hsps is often variable. we have monitored the effects of different temperatures and lengths of heat shock on the pattern and intensity of hsp synthesis. in ge ... | 1989 | 2590525 |
| studies on the atp requirements of in vitro chromatin assembly. | to gain a more complete understanding of the process of in vitro chromatin assembly, an examination of the energy requirements of nucleosome formation must be undertaken. the experiments outlined in this manuscript address this issue by making use of the xenopus laevis s-150 cell-free extract. the s-150 catalyzes chromatin assembly on circular dna templates dependent either on the exogenous addition of atp or regeneration of endogenous atp. we define two distinct, but temporally ordered, phases ... | 1989 | 2590528 |
| expression of microinjected hsp 70/cat and hsp 30/cat chimeric genes in developing xenopus laevis embryos. | the expression of microinjected chimeric genes containing drosophila hsp 70 and xenopus hsp 70 and hsp 30 promoters linked to the reporter gene coding for bacterial chloramphenicol acetyltransferase (cat) was examined during early development of xenopus laevis. heat-inducible expression of fusion genes containing either the drosophila hsp 70 promoter (1100 bp) or the xenopus hsp 70 promoter (750 bp) was first detectable after the midblastula stage of development. this coincides with the embryoni ... | 1989 | 2591315 |
| characterization of neutral and cationic amino acid transport in xenopus oocytes. | amino acid transport was characterized in stage 6 xenopus laevis oocytes. most amino acids were taken up by the oocytes by way of both na+-dependent and saturable na+-independent processes. na+-dependent transport of 2-aminoisobutyric acid (aib) was insensitive to cis- or trans-inhibition by the system a-defining substrate 2-(methylamino)-isobutyric acid (meaib), although threonine, leucine, and histidine were found to be effective inhibitors, eliminating greater than 80% of na+-dependent aib up ... | 1989 | 2592432 |
| immunocytochemical reactivity of xenopus laevis retinal rods and cones with several monoclonal antibodies to visual pigments. | immunocytochemical reactions with several antibodies to visual pigments were used to study visual cells of the xenopus laevis retina. monoclonal antibodies to bovine opsin "e," 1d4, and 4b4 (reactive with the n- and c-terminus and with the loop connecting transmembrane segments 5-6, respectively) and to chicken visual pigments cos-1 and os-2 (binding to mammalian red/green and blue cones, respectively), as well as a rabbit antifrog opsin serum 11-7, were applied to semithin and thin sections of ... | 1989 | 2592607 |
| differential gene expression in the anterior neural plate during gastrulation of xenopus laevis. | we have isolated three cdna clones that are preferentially expressed in the cement gland of early xenopus laevis embryos. these clones were used to study processes involved in the induction of this secretory organ. results obtained show that the induction of this gland coincides with the process of neural induction. genes specific for the cement gland are expressed very early in the anterior neural plate of stage-12 embryos. this suggests that the anteroposterior polarity of the neural plate is ... | 1989 | 2598814 |
| the specification of heart mesoderm occurs during gastrulation in xenopus laevis. | the establishment of heart mesoderm during xenopus development has been examined using an assay for heart differentiation in explants and explant combinations in culture. previous studies using urodele embryos have shown that the heart mesoderm is induced by the prospective pharyngeal endoderm during neurula and postneurula stages. in this study, we find that the specification of heart mesoderm must begin well before the end of gastrulation in xenopus embryos. explants of prospective heart mesod ... | 1989 | 2598816 |
| developmental expression of cu,zn superoxide dismutase in xenopus. constant level of the enzyme in oogenesis and embryogenesis. | cdna clones for xenopus laevis cu,zn-superoxide dismutase were isolated, sequenced and used as probes to study the expression of the corresponding gene during oogenesis and embryogenesis; cu,zn-superoxide dismutase activity was also monitored throughout development. it has been observed that its mrna is actively synthesized during early oogenesis, reaching a maximum level at stage ii, and is utilized through oogenesis. this results in an accumulation of enzyme activity during oocyte growth, para ... | 1989 | 2598938 |
| an increase in the intracellular ph of fertilized eggs of xenopus laevis is associated with inhibition of protein and dna syntheses and followed by an arrest of embryonic development. | in many systems, events participating in cell division are controlled by intracellular ph (phi). in xenopus eggs, fertilization is accompanied by an increase in phi which occurs concomitantly with an increase in protein synthesis and a reinitiation of dna synthesis, leading the embryo to cell division. in this paper, we have shown that increasing phi of fertilized eggs from 7.8 to 8.2 by using weak bases produced an arrest in embryonic development. such a change in phi was accompanied by a sever ... | 1989 | 2599030 |
| whole-cell currents in olfactory receptor cells of xenopus laevis. | olfactory mucosae of xenopus laevis were dissociated without enzymatic treatment and the isolated olfactory neurones were studied with the tight-seal whole-cell recording configuration of the patch clamp technique. in the voltage clamp, five current components could be distinguished: a fast, ttx-sensitive na+-current, a small and slow inward current carried by ca2+ ions, a ca2+-dependent k+-current, a k+-current which activates rapidly at voltages more positive than -20 mv and quickly inactivate ... | 1989 | 2599033 |
| dynamics of background adaptation in xenopus laevis: role of catecholamines and melanophore-stimulating hormone. | the pars intermedia of the pituitary gland in xenopus laevis secretes alpha-melanophore-stimulating hormone (alpha-msh), which causes dispersion of pigment in dermal melanophores in animals on a black background. in the present study we have determined plasma levels of alpha-msh in animals undergoing adaptation to white and black backgrounds. plasma values of black-adapted animals were high and decreased rapidly after transfer to a white background, as did the degree of pigment dispersion in der ... | 1989 | 2599346 |
| dna polymerase gamma from xenopus laevis. i. the identification of a high molecular weight catalytic subunit by a novel dna polymerase photolabeling procedure. | dna polymerase gamma has been purified over 10,000-fold from mitochondria of xenopus laevis ovaries. we have developed a novel technique which specifically photolabels dna polymerases. this procedure, the dna polymerase trap, was used to identify a catalytic subunit of 140,000 da from x. laevis dna polymerase gamma. additional catalytically active polypeptides of 100,000 and 55,000 da were identified in the highly purified enzyme. these appear to be products of degradation of the 140,000-da subu ... | 1989 | 2600077 |
| dna polymerase gamma from xenopus laevis. ii. a 3'----5' exonuclease is tightly associated with the dna polymerase activity. | xenopus laevis dna polymerase gamma co-purifies with a tightly associated 3'----5' exonuclease. the purified enzyme lacks 5'----3' exonuclease and endonuclease activity. the ratio of the 3'----5' exonuclease activity to dna polymerase gamma activity remains constant over the final three chromatographic procedures. in addition, these activities co-sediment under partially denaturing conditions in the presence of ethylene glycol. the associated 3'----5' exonuclease activity removes a terminally mi ... | 1989 | 2600078 |
| determination of ionic permeability coefficients of the plasma membrane of xenopus laevis oocytes under voltage clamp. | 1. a method of estimating absolute ionic permeability coefficients which does not depend on the use of impermeant substitutes is reported. 2. the method is based on a pump leak model of the xenopus laevis oocyte membrane. the procedure consists of measuring, in the same experiment, the pump current and the currents generated under voltage clamp by the partial substitution of one or two ions at a time. for each experimental condition, the measured currents are substituted in a goldman-hodgkin-kat ... | 1989 | 2600847 |
| electrophysiological investigation of the amino acid carrier selectivity in epithelial cells from xenopus embryo. | the electrical responses induced by external applications of neutral amino acids were used to determine whether different carriers are expressed in the membrane of embryonic epithelial cells of xenopus laevis. competition experiments were performed under voltage-clamp conditions at constant membrane potential. gly, l-ala, l-pro, l-ser, l-asn and l-gln generate electrical responses with similar apparent kinetic constants and compete for the same carrier.they are [na]o and voltage-dependent, insen ... | 1989 | 2600961 |
| degradation of linear dna by a strand-specific exonuclease activity in xenopus laevis oocytes. | linear dna injected into xenopus laevis oocyte nuclei recombines with high efficiency if homologous sequences are present at overlapping molecular ends. we found that injected linear dna was degraded by a 5'----3' strand-specific exonuclease activity during incubation in the oocyte nucleus to leave a heterogeneous population of 3'-tailed molecules. decreasing the concentration of dna injected increased the heterogeneity and the average rate of degradation. the 3' tails created were relatively st ... | 1989 | 2601699 |
| human transcription factor tfiiic2 specifically interacts with a unique sequence in the xenopus laevis 5s rrna gene. | transcription factor tfiiic2 derived from human cells is required for trna-type gene transcription and binds with high affinity to the essential b-box promoter element of trna-type genes. although 5s rrna genes contain no homology with the trna-type gene b box, we show that tfiiic2 is also required for xenopus laevis 5s rrna gene transcription. tfiiic2 protected an approximately 30-base-pair (-10 to +18) region of a xenopus 5s rrna gene from dnase i digestion. this region, which spanned the tran ... | 1989 | 2601702 |
| the xenopus ribosomal dna 60- and 81-base-pair repeats are position-dependent enhancers that function at the establishment of the preinitiation complex: analysis in vivo and in an enhancer-responsive in vitro system. | although it is generally believed that the 60- and 81-base-pair (60/81-bp) repeats of the xenopus laevis ribosomal dna (rdna) spacer are position-independent transcriptional enhancers, this has not been shown directly. we have now developed a critical assay which proves that the 60/81-bp repeats do, in fact, stimulate transcription from promoters in cis and that they function in both orientations and when up to 1 kilobase pair from the initiation site. however, contrary to the widely accepted vi ... | 1989 | 2601710 |
| trans activation of rat phosphoenolpyruvate carboxykinase (gtp) gene expression by micro-coinjection of rat liver mrna in xenopus laevis oocytes. | to study the liver-specific trans activation of the rat phosphoenolpyruvate carboxykinase (pepck) gene, the pepck promoter was linked to a reporter gene and was microinjected into xenopus laevis oocytes alone or in conjunction with rat liver poly(a)+ rna. the rat liver mrna markedly enhanced the expression of the pepck-chimeric construct. this effect appeared to be sequence specific, as it was dependent on the presence of the intact promoter. moreover, the rna effect was limited to mrna preparat ... | 1989 | 2601721 |
| presence of high molecular weight glycans on the surface of germ and embryonic cells of xenopus laevis. | xenopus laevis male germ cells, fertilized eggs and gastrula cells were labelled with 3h labelled sodium borohydride reduction after galactose oxidase treatment. after pronase digestion, the bulk of the label is carried by high molecular weight glycans (greater than or equal to 6,000 d). the high molecular weight of these labelled glycans and their susceptibility to degradation by endo-beta-galactosidase suggest that they may be related to the polylactosaminoglycans. | 1989 | 2605647 |
| synthesis of a thymosin beta 4-like peptide, deacetyl-thymosin beta xen4, and its restorative effect on depressed lymphocyte blastogenic response to phytohemagglutinin (pha) in uremic patients. | an analog of thymosin beta xen4 isolated from oocytes of xenopus laevis, deacetyl-thymosin beta xen4, was synthesized by assembling 6 peptide fragments, followed by deprotection with 1 m trifluoromethanesulfonic acid-thioanisole (molar ratio, 1:1) in trifluoroacetic acid in the presence of dimethylselenium. finally, the deprotected peptide was incubated with dithiothreitol to reduce sulfoxide on the methionine side chain. the synthetic tritetracontapeptide was found to have a restoring effect on ... | 1989 | 2605693 |
| a transcription factor, tfis, interacts with both the promoter and enhancer of the xenopus rrna genes. | an activity that binds sequence specifically to the enhancer of the xenopus laevis rrna genes has been highly purified. this activity stimulates transcription of coinjected rrna templates in xenopus oocytes and has been named tfis, as it binds to the enhancer sequences within the intergenic spacer. in addition to its enhancer binding activity, tfis binds to the promoter of the xenopus rrna genes, as predicted by models for enhancer action. dnase i footprinting on promoter mutants suggests that t ... | 1989 | 2606346 |
| the xenopus ribosomal gene enhancers bind an essential polymerase i transcription factor, xubf. | we purified xubf on the basis of its ability to specifically bind the enhancer elements of the xenopus laevis rrna genes. xubf also binds to both upstream and downstream regions of the x. laevis ribosomal gene promoter and is essential for polymerase i transcription. unexpectedly, xubf binds to both upstream and downstream regions of the human ribosomal gene promoter, producing footprints that are indistinguishable from the footprints produced by hubf, a previously described polymerase i transcr ... | 1989 | 2606347 |
| [intragenomic polymorphism of the primary structure of 5s rrna gene variants of the loach (misgurnus fossilis l.). determination of the transcriptional activity]. | the primary structure of 12 cloned repeats of loach oocyte 5s rrna genes was determined. the heterogeneity of nucleotide sequences was revealed in the coding regions and spacer of the genes. the results of the study on in vivo transcriptional activity of the cloned 5s rrna gene variants are consistent with the localisation of site specific base substitutions in the coding part affecting the transcription. we have compared the nucleotide sequences of loach 5s rrna gene variants and of xenopus lae ... | 1989 | 2608037 |
| identification of two steroid-responsive promoters of different strength controlled by the same estrogen-responsive element in the 5'-end region of the xenopus laevis vitellogenin gene a1. | a structural and functional analysis of the 5'-end region of the xenopus laevis vitellogenin gene a1 revealed two transcription initiation sites located 1.8 kilobases apart. a rna polymerase ii binding assay indicates that both promoters form initiation complexes efficiently. in vitro, using a transcription assay derived from a hela whole-cell extract, the upstream promoter is more than 10-fold stronger than the downstream one. in contrast, both promoters have a similar strength in a hela nuclea ... | 1989 | 2608051 |
| observation on the basal lamina of duodenal mesothelial cells during metamorphosis of xenopus laevis. | morphologic changes in the basal lamina of duodenal mesothelial cells during metamorphosis of xenopus laevis were observed. in the prometamorphosis stage (stage 56-59), the basal lamina was almost completely flat; the lamina densa of the basal lamina was a 50 nm layer of high electron density. in the early stages of metamorphic climax (stage 60-62), the basal lamina showed occasional slight folding (stage 60), with the lapse of time, the folding became continuous and deeper. the development of a ... | 1989 | 2608259 |
| the development of the xenopus retinofugal pathway: optic fibers join a pre-existing tract. | the developing optic nerve and tract have received considerable attention in recent years, but the cellular and subcellular microenvironment of the growing axons has not been described. in the belief that such a description is essential (though certainly not sufficient) for an understanding of pathway formation, we have examined the normal development of the retinofugal projection of xenopus laevis. optic fibers were labeled anterogradely at the retina with horseradish peroxidase (hrp) or the ca ... | 1989 | 2612377 |
| evaluation of the developmental toxicity of five compounds with the frog embryo teratogenesis assay: xenopus (fetax) and a metabolic activation system. | the potential teratogenic hazard of five compounds was evaluated using the frog embryo teratogenesis assay--xenopus (fetax) and a metabolic activation system. embryos of the south african clawed frog, xenopus laevis, were exposed to (i) three compounds suspected to be proteratogenic in mammalian test systems--[2-acetylaminofluorene (2-aaf), rifampicin (ra) and benzo[a]pyrene (bp)] for 96 h; (ii) one compound unaffected by mixed-functional oxidase (mfo) metabolism--znso4; (iii) one compound thoug ... | 1989 | 2613998 |
| a comparison of the distribution of muscle type in the tadpole tails of xenopus laevis and rana temporaria: an histological and ultrastructural study. | the types and the distribution of muscle fibres were analysed and compared in the tails of xenopus laevis and rana temporaria tadpoles. the filter feeding tadpoles of x. laevis were found to have both white muscle fibres adjacent to the notochord used for normal locomotory swimming and a superficial layer of small red fibres. the red fibres are probably used for the continuous flickering movement of the tail associated with the maintenance of the mid-water filter feeding position. r. temporaria, ... | 1989 | 2617517 |
| the anatomical substrate for telencephalic function. | the basic thesis for this study was that the telencephalon is needed to make decisions in new situations. subsidiary hypotheses were that the telencephalon consists of: (a) a sensorimotor system which generates motor activity from sensory input and (b) a selection system which makes choices from possible motor programs. it was postulated that the selection system should fulfil the following requirements: be accessible for past and present events, have the capacity to process this information in ... | 1989 | 2618850 |