| [regeneration of the optic nerve of xenopus laevis after argon laser injury]. | following mechanical lesion of the optic nerve (on), lower vertebrates are capable of regeneration of the on and regain visual function. we have studied, by light and electron microscopy, regeneration of the larval on of xenopus laevis after treatment with the argon laser. the laser energy is absorbed by the neurothelial pigment and provokes a burned crater and vesiculation in the interior of the on. in contrast to the mechanically induced process, axons regenerate, after laser treatment, within ... | 1992 | 1614133 |
| pattern perturbation in xenopus laevis forelimb regenerates following treatment with retinoic acid and carrier media. | | 1992 | 1614430 |
| functional reconstitution of a receptor-activated signal transduction pathway in xenopus laevis oocytes using the cloned human c5a receptor. | we have used the polymerase chain reaction to isolate and clone the cdna encoding the human c5a receptor, and have injected the cdna-derived receptor crna into xenopus laevis oocytes for functional characterization of the receptor protein. receptor activity was determined either electrophysiologically by measuring the agonist-dependent opening of [ca2+]i-dependent cl- channels, or by analysing the agonist-dependent efflux of 45ca2+ from the oocytes. using both methodologies, injection of pure c5 ... | 1992 | 1616822 |
| species differences in amphibian olfactory neuron reactivity to a monoclonal antibody. | a monoclonal antibody immunostained a subpopulation of olfactory sensory neurons in cryostat sections of the olfactory mucosa of the grass frog, rana pipiens, and the bullfrog, rana catesbeiana. however, in the olfactory tissues of the african clawed frog, xenopus laevis, only mucus and mucus-secreting components were stained, and no cell-specific immunoreactivity was seen in the tiger salamander, ambystoma tigrinum. this antibody is a useful marker of olfactory neuronal subpopulations in some a ... | 1992 | 1617462 |
| expression of a novel fgf in the xenopus embryo. a new candidate inducing factor for mesoderm formation and anteroposterior specification. | we have cloned and sequenced a new member of the fibroblast growth factor family from xenopus laevis embryo cdna. it is most closely related to both mammalian kfgf (fgf-4) and fgf-6 but as it is not clear whether it is a true homologue of either of these genes we provisionally refer to it as xefgf (xenopus embryonic fgf). two sequences were obtained, differing by 11% in derived amino acid sequence, which probably represent pseudotetraploid variants. both the sequence and the behaviour of in vitr ... | 1992 | 1618138 |
| relationship of neural cell adhesion molecules (n-cams) with adenylate cyclase. | bovine brain cdna cloned earlier and attributed to calmodulin-independent adenylate cyclase encodes the neural cell adhesion molecule (n-cam). the expression of n-cam mrna in xenopus laevis oocytes increases their basal adenylate cyclase activity. polyclonal antibodies against synthetic peptide a, vaenqqgkskaahfv (664-678 amino acid residues of bovine n-cam), containing sequence axxxxgks which is homologous to the nucleotide-binding consensus sequence gxxxxgks, inhibit the adenylate cyclase acti ... | 1992 | 1618305 |
| the cdna for the type i iodothyronine 5'-deiodinase encodes an enzyme manifesting both high km and low km activity. evidence that rat liver and kidney contain a single enzyme which converts thyroxine to 3,5,3'-triiodothyronine. | the enzymatic conversion of thyroxine (t4) to 3,5,3-triiodothyronine (t3) by iodothyronine 5'-deiodinase(s) is an obligate step in the physiologic action of thyroid hormones in most extrathyroidal tissues. in the rat liver and kidney, 5'-deiodinase processes having either high km (micromolar range) or low km (nanomolar range) values for thyroid hormone substrates have been described. the number of enzymes mediating these reactions, however, remains uncertain and controversial. to examine this qu ... | 1992 | 1618759 |
| sequence and specificity of a soluble lactose-binding lectin from xenopus laevis skin. | a 16-kda lactose-binding lectin comprises 5% or more of the soluble protein in xenopus laevis skin. this lectin is mainly localized in the cytoplasm of granular gland cells. in response to stress, the lectin along with a variety of toxic and antibiotic peptides are released onto the skin surface by holocrine secretion. we have purified the lectin, sequenced tryptic peptides using tandem mass spectrometry and edman degradation, and isolated full-length cdna using a deduced oligonucleotide. compar ... | 1992 | 1618791 |
| export of mrna from microinjected nuclei of xenopus laevis oocytes. | export of mrna from the nucleus to the cytoplasm was studied in mature xenopus laevis oocytes. in vitro transcribed, capped 32p-labeled mrna was microinjected into nuclei, and its appearance in the cytoplasm measured by counting radioactivity or by rna extraction and gel electrophoresis. both for a 5.0-kb transferrin receptor mrna and a 2.0-kb 4f2 antigen heavy chain mrna we found saturable transport with an apparent km of 3.6 x 10(8) molecules per oocyte nucleus. under non-saturating conditions ... | 1992 | 1618896 |
| distribution of type ii collagen mrna in xenopus embryos visualized by whole-mount in situ hybridization. | we have developed a whole-mount histochemical method to monitor the distribution of expressed genes within the intact, developing vertebrate embryo. background problems that result from alkaline phosphatase- or horseradish peroxidase-based stains have been minimized, enabling both early and late stages of xenopus embryogenesis to be monitored. the feasibility and utility of this non-isotopic method has been demonstrated by using a specific dna probe to localize xenopus laevis type ii collagen mr ... | 1992 | 1619277 |
| alternative 3' processing of xenopus alpha-tubulin mrnas; efficient use of a cauaaa polyadenylation signal. | the xenopus laevis alpha-tubulin gene x alpha t14 produces two mrnas of 1.7 and 2.15 kb and we have shown that this is due to the use, at approximately equal frequency, of alternative 3' processing sites. unusually, the hexanucleotide polyadenylation signal responsible for use of the downstream site, pa2, is cauaaa in contrast to the consensus aauaaa used at the upstream site, pa1. since such a variant hexanucleotide would normally be expected to reduce drastically the efficiency of 3' processin ... | 1992 | 1620589 |
| a device for quantitative measurement of the opacity of small animal lenses: application to xenopus laevis. | | 1992 | 1623949 |
| changing patterns of binocular visual connections in the intertectal system during development of the frog, xenopus laevis. iii. modifications following early eye rotation. | in the frog, xenopus laevis, a system of intertectal connections underlies the visual projection from an eye to its ipsilateral tectal lobe and is involved in the topographic representation of binocular visual space. rotation of one eye in early life may be followed by a radical rearrangement of the connections in this system. the modified pattern which later emerges is that which keeps the visual projection through the ipsilateral eye in topographic registration with the direct visual projectio ... | 1992 | 1623981 |
| analysis of the expression of a glucose-regulated protein (grp78) promoter/cat fusion gene during early xenopus laevis development. | developmental regulation of the expression of a glucose-regulated gene encoding a 78 kd protein, grp78, has been characterized by microinjection of a rat grp78/cat chimeric gene into early xenopus embryos. tunicamycin-induced expression of the chimeric gene during xenopus development was similar to the pattern of endogenous grp78 protein synthesis, with expression first being detected at gastrula and increasing at least until the tailbud stage. deletion analysis of the rat grp78 promoter reveale ... | 1992 | 1624059 |
| some polypeptides in the nervous system of the marine worm, nereis diversicolor, are related to the sodium influx stimulating peptide of the pulmonate freshwater snail, lymnaea stagnalis. | total mrna, extracted from brain of the marine worm, nereis diversicolor (annelida, polychaeta), was translated either in vitro using a rabbit reticulocyte lysate or in ovo (xenopus laevis oocyte). the synthesized polypeptides were analyzed by electrophoresis and western blotting techniques using polyclonal antisera raised against three peptides: sodium influx stimulating peptide (sisp) sequences 10-19 and 67-76 and a monoclonal antibody raised against purified native sisp (1-77) of lymnaea stag ... | 1992 | 1624091 |
| regenerative responses in cultured hindlimb stumps of larval xenopus laevis. | the regenerative capacity of larval xenopus laevis hindlimbs amputated through the tarsalia at different stages of development and explanted in vitro was tested. in the first experimental series hindlimb stumps from stage 53, 54, 55, and 57 larvae (according to nieuwkoop and faber, '56) were cultured in leibovitz's l-15 medium supplemented with 10% fcs, and 0.04 u of insulin and 10(-8) mg of l-thyroxine per ml of medium. results showed that the distal part of the limb stumps from stages 53, 54, ... | 1992 | 1624916 |
| role of lys 558 and lys 869 in substrate and inhibitor binding to the murine band 3 protein: a study of the effects of site-directed mutagenesis of the band 3 protein expressed in the oocytes of xenopus laevis. | the effect of mutation of either lys 558 or lys 869 or both on mouse erythroid band 3 protein (ae1)-mediated 36cl- efflux and its inhibition by pyridoxal 5-phosphate (p5-p), dnds and h2dids were studied. regardless of the mutation, band 3 was always capable of executing cl- self-exchange. p5-p (5 mm, ph 7.6) produced irreversible inhibition in the wild type (kk) and in the mutant in which lys 558 (nk) or lys 869 (km) had been replaced by asparagine (n) or methionine (m), respectively. however, w ... | 1992 | 1625324 |
| wasting disease associated with cutaneous and renal nematodes, in commercially obtained xenopus laevis. | xenopus laevis, the south african clawed frog or toad, is a member of the family pipidae. now in high demand for research purposes, they are available commercially. its reported lifespan is up to fifteen years. investigators and caretakers are frustrated when commercially obtained, young frogs (four years or younger), not subjected to any studies, "waste" and die. the wasting syndrome is characterized by anorexia, color change, and "flaky skin." often the first sign of this syndrome is the prese ... | 1992 | 1626871 |
| expression of dna ligases i and ii during oogenesis and early development of xenopus laevis. | we have analyzed the expression of dna ligase i protein during oogenesis and early development of xenopus laevis. the protein is already present in stage i oocytes and then accumulates throughout oogenesis to reach a steady state level by stage vi. it remains at this level at least until tadpole stage. in stage vi oocytes dna ligase i protein is almost exclusively localized in the germinal vesicle. we have partially purified a dna ligase ii activity from stage vi oocytes, unfertilized eggs, and ... | 1992 | 1628756 |
| mrnp4, a major mrna-binding protein from xenopus oocytes is identical to transcription factor frg y2. | previous work has revealed a striking similarity between the sequence of mrnp4, a major mrna-binding protein of xenopus laevis oocytes and frg y2, a transcription factor specific for y-box-containing promoters. however, the apparent molecular mass of mrnp4 exceeds by 50-60% the cdna-deduced molecular mass of frg y2. to resolve this discrepancy we have measured the real molecular mass of mrnp4 by sedimentation equilibrium. the molecular mass of mrnp4 closely agrees with that of frg y2. we conclud ... | 1992 | 1629179 |
| xp2, a new member of the p-domain peptide family of potential growth factors, is synthesized in xenopus laevis skin. | similarly to epidermal growth factor (egf) and egf-like repeats, the "p-domain" represents a cysteine-rich module that has been detected in the past in a variety of polypeptides, as well as in high molecular weight proteins. here, a precursor for a secretory polypeptide (xp2) is characterized that consists of two p-domains. xp2 has been discovered in xenopus laevis with the help of the polymerase chain reaction. in contrast to all other p-domain peptides, it is synthesized in the skin but not in ... | 1992 | 1629230 |
| variants of the xenopus laevis ribosomal transcription factor xubf are developmentally regulated by differential splicing. | xubf is a xenopus ribosomal transcription factor of the hmg-box family which contains five tandemly disposed homologies to the hmg1 & 2 dna binding domains. xubf has been isolated as a protein doublet and two cdnas encoding the two molecular weight variants have been characterised. the major two forms of xubf identified differ by the presence or absence of a 22 amino acid segment lying between hmg-boxes 3 and 4. here we show that the mrnas for these two forms of xubf are regulated during develop ... | 1992 | 1630907 |
| posttranslational isoprenylation of rho protein is a prerequisite for its interaction with mastoparan and other amphiphilic agents. | the amphiphilic agents melittin, compound 48/80 and mastoparan inhibit adp-ribosylation of porcine brain rho protein by clostridium botulinum exoenzyme c3. however, adp-ribosylation of recombinant rhoa expressed in e.coli was not inhibited by these agents. accordingly, steady state gtp hydrolysis by recombinant rhoa was not stimulated by mastoparan, whereas gtp hydrolysis by porcine brain rho was stimulated 2.5-fold in the presence of this wasp venom. after microinjection of recombinant rhoa int ... | 1992 | 1632782 |
| structure and expression of xenopus prohormone convertase pc2. | the multifunctional prohormone, proopiomelanocortin (pomc), is processed in the melanotrope cells of the pituitary pars intermedia at pairs of basic amino acid residues to give a number of peptides, including alpha-melanophore-stimulating hormone (alpha-msh). this hormone causes skin darkening in amphibians during background adaptation. here we report the complete structure of xenopus laevis prohormone convertase pc2, the enzyme thought to be responsible for processing of pomc to alpha-msh. a co ... | 1992 | 1633858 |
| partial purification, from xenopus laevis oocytes, of an atp-dependent activity required for nucleosome spacing in vitro. | a critical feature of chromatin with regard to structure and function is the regular spacing of nucleosomes. in vivo, spacing of nucleosomes occurs in at least two steps, but the mechanism is not understood. in this report, we have mimicked the two-step process in vitro. a novel spacing activity has been partially purified from xenopus laevis ovaries. when this activity is added, either at the beginning or at the end of a nucleosomal assembly reaction, it can convert a dna template consisting of ... | 1992 | 1634540 |
| planar induction of anteroposterior pattern in the developing central nervous system of xenopus laevis. | it has long been thought that anteroposterior (a-p) pattern in the vertebrate central nervous system is induced in the embryo's dorsal ectoderm exclusively by signals passing vertically from underlying, patterned dorsal mesoderm. explants from early gastrulae of the frog xenopus laevis were prepared in which vertical contact between dorsal ectoderm and mesoderm was prevented but planar contact was maintained. in these, four position-specific neural markers (engrailed-2, krox-20, xlhbox 1, and xl ... | 1992 | 1636091 |
| secretory and inductive properties of drosophila wingless protein in xenopus oocytes and embryos. | like its vertebrate homologues, xenopus wnt-8 and murine wnt-1, we find that drosophila wingless (wg) protein causes axis duplication when overexpressed in embryos of xenopus laevis after mrna injection. in many cases, the secondary axes contain eyes and cement glands, which reflect the induction of the most dorsoanterior mesodermal type, prechordal mesoderm. we show that the extent of axis duplication is dependent on the embryonic site of expression, with ventral expression leading to a more po ... | 1992 | 1638990 |
| genomic potential of erythroid and leukocytic cells of rana pipiens analyzed by nuclear transfer into diplotene and maturing oocytes. | in order to determine whether differentiated somatic cells maintain genetic totipotency, nuclear transplantations from several differentiated somatic cell types into eggs and oocytes were performed previously in rana pipiens and xenopus laevis. the formation of postneurula embryos and tadpoles under the direction of the test nuclei demonstrated their genetic multipotency. in addition, rana erythrocyte nuclei transplanted to oocytes directed more extensive tadpole development than those injected ... | 1992 | 1639224 |
| activation of xenopus laevis eggs in the absence of intracellular ca activity by the protein phosphorylation inhibitor, 6-dimethylaminopurine (6-dmap). | xenopus laevis eggs pricked or microinjected with water or saline in medium containing a limited quantity of free ca (1.0 to 2.0 microm) remain unactivated for at least 6 hr, even after transfer to oocyte medium containing ca at higher concentrations (0.5-1.0 mm). these injected eggs, when later pricked in oocyte medium or exposed to a23187 or urethane are fully capable of activation. this confirms the observations of wangh ('89). however, eggs injected in this ca-limited medium (calm) with 6-dm ... | 1992 | 1640202 |
| [isolation and control of the functional quality of mrna of bovine leukocyte interferon]. | for the construction of the cdna library total cellular rna was separated from bovine leucocytes induced with ndv (inductor of interferons) for five hours. guanidinisothiocyanate and ultracentrifugation in the gradient of cscl were used for the separation of the total rna (chirgwin et al., 1979). bands 18s and 28s were detected in the samples of rna by electrophoresis in an mops buffer (fig. 1). mrna was separated from the mixture of rna via affinity chromatography on oligo(dt)-cellulose (aviv a ... | 1992 | 1641951 |
| regulation of c-erba-alpha messenger rna species in tadpole erythrocytes by thyroid hormone. | putative thyroid hormone (th) nuclear receptors have been detected in several tissues of rana catesbeiana tadpoles. t3 receptor number (sites per nucleus) in red blood cells (rbcs) and tail increases substantially just before metamorphic climax or in response to exogenous th; in contrast, receptor number in liver remains relatively constant. th receptors in mammals and birds are thought to be encoded by a c-erba gene. in the present study, two c-erba cdnas, one prepared from xenopus laevis oocyt ... | 1991 | 1645454 |
| differential mechanisms for the n-acetylation of alpha-melanocyte-stimulating hormone and beta-endorphin in the intermediate pituitary of the frog, xenopus laevis. | immunohistochemical analysis of the pituitary of xenopus laevis revealed the colocalization of alpha-melanocyte-stimulating-hormone (msh)-related immunoreactivity and n-acetyl-beta-endorphin-related immunoreactivity in the cells of the intermediate pituitary. in order to determine whether the immunoreactive n-acetylated beta-endorphin is released in parallel with the immunoreactive alpha-msh, intermediate pituitaries were incubated in l-15 medium for 24 h. the medium and an acid extract of the i ... | 1991 | 1646412 |
| in vitro translation and expression of renal intrinsic factor-cobalamin receptor. | the primary translation product of intrinsic factor (if)-cobalamin receptor (ifcr) mrna from rat kidney is a single polypeptide chain of mr = 215,000. when expressed in xenopus laevis oocytes the ifcr binding activity is expressed with mrna of a size between 5 to 7 kb. these results suggest that ifcr mrna transcripts are present in the renal tissue and encode a single chain, large molecular weight precursor. furthermore, xenopus oocytes can be used as a screening system in the expression cloning ... | 1991 | 1646608 |
| release of acetylcholine by xenopus oocytes injected with mrnas from cholinergic neurons. | xenopus laevis oocytes were injected with poly(a)+ mrnas extracted from the electric lobes of torpedo marmorata. the electric lobes contain the perikarya of approximately 120,000 cholinergic neurons that innervate the electric organs and are homologous to motor neurons. the injected oocytes accumulated acetylcholine and were able to synthesize [14c]acetylcholine from 1-[14c]acetate. with kcl depolarization and upon treatment with a ca2+ ionophore, they released their endogenous as well as the ra ... | 1991 | 1646712 |
| hormone-regulated k+ channels in follicle-enclosed oocytes are activated by vasorelaxing k+ channel openers and blocked by antidiabetic sulfonylureas. | follicular oocytes from xenopus laevis contain k+ channels activated by members of the recently recognized class of vasorelaxants that include cromakalim and pinacidil and blocked by antidiabetic sulfonylureas, such as glibenclamide. these channels are situated on the adherent follicular cells and are not present in denuded oocytes. cromakalim-activated k+ channels are also activated by increases in intracellular camp, and camp-activated k+ channels are blocked by glibenclamide. although cromaka ... | 1991 | 1647032 |
| a perichromosomal region contains proteins phosphorylated during mitosis in xenopus laevis cells. | an antibody that recognizes the phosphorylated form of nucleoplasmin has identified another nuclear protein whose antigenic form is regulated in a mitosis-specific manner, with a dramatic increase in binding occurring in all mitotic cells. the protein is localised around the periphery of condensed chromosomes during mitosis in a manner analogous to another nucleoplasmin-related polypeptide no38. mitosis-specific expression of the antigenic site is dependent on phosphorylation of the polypeptide; ... | 1991 | 1647398 |
| the cell cycle dependence of protein synthesis during xenopus laevis development. | the regulation of early embryonic development in the amphibian xenopus laevis depends largely upon translational and post-translational regulatory mechanisms to direct the complex cytodifferentiations that take place during early cleavage and blastula formation. the cell cycle dependence of protein synthesis was examined in developing xenopus embryos as well as in cycling cell-free lysates from xenopus eggs. in both cases m-phase and the activation of the m-phase kinase were found to be correlat ... | 1991 | 1647990 |
| the 165-kda dna topoisomerase i from xenopus laevis oocytes is a tissue-specific variant. | two forms of topoisomerase i can be purified from xenopus laevis. a protein with a molecular mass of 165 kda has been identified as topoisomerase i in ovaries (richard and bogenhagen, 1989. j. biol. chem. 264, 4704-4709). when a similar purification is performed using liver tissue, topoisomerase i is purified as a 110-kda protein. separate rabbit antisera were raised against oocyte and liver topoisomerase i polypeptides. each antiserum reacts in immunoblotting or immunoprecipitation procedures o ... | 1991 | 1647991 |
| melatonin receptor mrna expression in xenopus oocytes: inhibition of g-protein-activated response. | melatonin is the major endocrine product of the pineal gland in the mammalian brain and plays a variety of roles in photoperiodic functions. in order to investigate melatonin receptors, poly(a)+ rna was extracted from pars tuberalis of the ovine pituitary and injected into oocytes of xenopus laevis. after 3-5 days of incubation, functional melatonin receptors were expressed. receptors were revealed by their inhibitory effect upon oscillatory currents resulting from alf4-induced activation of g-p ... | 1991 | 1648693 |
| genes encoding receptors for insulin and insulin-like growth factor i are expressed in xenopus oocytes and embryos. | insulin and insulin-like growth factor i (igf-i) initiate their metabolic, growth, and differentiation effects through binding to the insulin receptor and the igf-i receptor, two members of the tyrosine kinase family of receptors. to study the role of these peptides and receptors in early development, we used the polymerase chain reaction and embryo-derived rna to generate partial cdna sequences of the insulin receptor and igf-i receptor from the amphibian xenopus laevis. three unique tyrosine k ... | 1991 | 1648732 |
| characterization of the defect in the na(+)-phosphate transporter in vitamin d-resistant hypophosphatemic mice. | hypophosphatemic vitamin d-resistant rickets is the most common form of vitamin d-resistant rickets in man. the hypophosphatemic mouse model (hyp) is phenotypically and biochemically similar to the human disease. biochemically, hypophosphatemia is the hallmark of this disorder. the cause of the hypophosphatemia is thought to be secondary to a defect in the renal and/or intestinal na(+)-phosphate transporter. the current studies were designed to investigate and characterize the localization of th ... | 1991 | 1649826 |
| segregation of nmda and non-nmda receptors at separate synaptic contacts: evidence from spontaneous epsps in xenopus embryo spinal neurons. | many excitatory amino acid (eaa)-mediated synaptic potentials are dual-component as a result of the simultaneous activation of n-methyl-d-aspartate (nmda) and non-nmda receptor subtypes, the two major classes of eaa receptor in vertebrates. this raises the question of whether the two receptor types are located separately or together at individual synaptic contacts. support for the segregation of nmda and non-nmda receptors in discrete anatomical patches arises from the observation that the fast ... | 1991 | 1650276 |
| study of frog (rana esculenta) proopiomelanocortin processing in the intermediate pituitary. identification of alpha-melanotropin, beta-melanotropin, lys-gamma-melanotropin, and corticotropin-like intermediate lobe peptide. | the proteolytic processing of frog (rana esculenta) proopiomelanocortin in melanotropic cells of the intermediate pituitary gland has been examined through purification of the mature fragments by reverse-phase high-pressure liquid chromatography and microsequencing of isolated peptides. alpha-melanotropin, beta-melanotropin, lys-gamma-melanotropin, corticotropin-like intermediate lobe peptide, and hinge peptide have been isolated and chemically characterized. the results show a high preservation ... | 1991 | 1651291 |
| effects of calcitonin gene-related peptide and efferent nerve stimulation on afferent transmission in the lateral line organ. | 1. calcitonin gene-related peptide (cgrp) is a 37-amino acid peptide immunolocalized in efferent fibers innervating hair-cell organs, including the lateral line organ of xenopus laevis. cgrp, applied in nanomolar concentrations, increased the spontaneous discharge rate in afferent fibers innervating hair cells of the lateral line organ. 2. the increase in spontaneous discharge rate with application of cgrp was associated with an increase in the rate of occurrence of spontaneous excitatory postsy ... | 1991 | 1651373 |
| simple luminometric assay to detect phosphoinositol-linked receptor expression in xenopus oocytes. | a simple and sensitive method to measure the expression of phosphoinositol-linked receptors in xenopus laevis oocytes is described. oocytes are co-injected with the calcium photoprotein aequorin and rna, encoding the receptor of interest. the binding of ligand to the expressed receptor increases intracellular calcium that induces the aequorin to luminesce. with an autosampler-equipped luminometer, this provides a fully automated assay of receptor expression of oocytes. this method was applied to ... | 1991 | 1652262 |
| coordinated expression of 7b2 and alpha msh in the melanotrope cells of xenopus laevis. an immunocytochemical and in situ hybridization study. | 7b2 is a highly conserved protein present in many secretory cells. using in situ hybridization techniques and immunocytochemistry, parameters concerning the biosynthesis and storage of the 7b2 protein were studied in the pituitary gland and median eminence of the clawed toad xenopus laevis, in relation to the physiological process of background adaptation. 7b2-like immunoreactivity was present in the median eminence, in the neural and anterior pituitary lobes and, particularly, in the melanotrop ... | 1991 | 1652364 |
| conditions for a backward-running na+/k+ pump in xenopus oocytes. | current generated by the electrogenic na+/k+ pump protein was determined in oocytes of xenopus laevis as strophantidine-sensitive current measured under voltage clamp. under conditions of reduced intracellular [na+] and [atp], both to values below 1 mm, and in extracellularly k(+)-free medium, the na+/k+ pump seems to operate in a reversed mode pumping na+ into the cell and k+ out of the cell. this is demonstrated by strophantidine-induced hyperpolarization of the membrane and inward-directed cu ... | 1991 | 1654105 |
| role of gtpase activating protein in mitogenic signalling through phosphatidylcholine-hydrolysing phospholipase c. | recent evidence has accumulated showing that activation of plc-catalysed hydrolysis of phosphatidylcholine (pc-plc) is a critical step in mitogenic signal transduction both in fibroblasts and in oocytes from xenopus laevis. the products of ras genes activate pc-plc, bind guanine nucleotides, have intrinsic gtpase activity, and are regulated by a gtpase-activating protein (gap). it has been suggested that, in addition to its regulatory properties, gap may also be necessary for ras function as a d ... | 1991 | 1655413 |
| functional expression of n-terminal truncated alpha-subunits of na,k-atpase in xenopus laevis oocytes. | n-terminal deletion mutants of na,k-atpase alpha 1 isoforms initiating translation at met34 (alpha 1t1) or at met43 (alpha 1t2) were expressed in x. laevis oocytes. compared to beta 3 crna injected controls, the co-expression of alpha 1wt, alpha 1t1, alpha 1t2 with beta 3 subunits results in a 2- to 3-fold increase of ouabain binding sites, parallelled by a concomitant increase in na,k-pump current. the apparent k1/2 for potassium activation of the alpha 1t2/beta 3 na,k-pumps is significantly hi ... | 1991 | 1655538 |
| the receptor for yolk lipoprotein deposition in the chicken oocyte. | the final rapid growth phase of the chicken oocyte is characterized by massive uptake of hepatically synthesized yolk precursor proteins from the plasma. the two major yolk-forming components, very low density lipoprotein (vldl) and vitellogenin (vtg), have been shown to interact with a 95-kda protein present in detergent extracts of ovarian membranes; this protein is absent in hens of a mutant nonlaying chicken strain (nimpf, j., radosavljevic, m., and schneider, w. j. (1989) j. biol. chem. 264 ... | 1991 | 1655760 |
| the thyroid hormone receptor gene (c-erba alpha) is expressed in advance of thyroid gland maturation during the early embryonic development of xenopus laevis. | the c-erba proto-oncogene encodes the thyroid hormone receptor, a ligand-dependent transcription factor which plays an important role in vertebrate growth and development. to define the role of the thyroid hormone receptor in developmental processes, we have begun studying c-erba gene expression during the ontogeny of xenopus laevis, an organism in which thyroid hormone has well-documented effects on morphogenesis. using polymerase chain reactions (pcr) as a sensitive assay of specific gene expr ... | 1991 | 1656222 |
| inhibition of chromatin assembly in xenopus oocytes correlates with derepression of the mouse mammary tumor virus promoter. | the mouse mammary tumor virus (mmtv) promoter is positively regulated by glucocorticoid hormone via binding of glucocorticoid receptor to a specific response element. upon addition of hormone, a nucleosome containing the glucocorticoid response element is removed or structurally altered, suggesting that the nucleosome interferes with transcription. accordingly, inhibition of chromatin assembly should relieve the repression and result in an increased constitutive activity. we have tested this hyp ... | 1991 | 1656227 |
| indirect action of elevated potassium and neuropeptide y on alpha msh secretion from the pars intermedia of xenopus laevis: a biochemical and morphological study. | a number of neurochemical messengers have been shown to act directly on the melanotrope cells of the pars intermedia of xenopus laevis to regulate alpha msh secretion. in the present study the possibility that the melanotropes are also indirectly controlled has been examined. for this purpose, the characteristics of alpha msh release from superfused intact lobes, cultured lobe and isolated melanotropes were compared after treatment with elevated potassium. isolated melanotropes responded with an ... | 1991 | 1656300 |
| adrenocorticotropin receptors: functional expression from rat adrenal mrna in xenopus laevis oocytes. | the adrenocorticotropin (acth) receptor, which binds corticotropin and stimulates adenylate cyclase and steroidogenesis in adrenocortical cells, was expressed in xenopus laevis oocytes microinjected with rat adrenal poly(a)+ rna. expression of the acth receptor in individual stage 5 and 6 oocytes was monitored by radioimmunoassay of ligand-stimulated camp production. injection of 5-40 ng of adrenal mrna caused dose-dependent increases in acth-responsive camp production. these were detected at 48 ... | 1991 | 1656448 |
| immunolocalization of n-acetylgalactosaminylphosphotransferase in the adult retina and subretinal space. | the cell surface n-acetylgalactosaminylphosphotransferase (galnacptase) modulates n-cadherin-mediated adhesion among embryonic chick retinal cells (balsamo et al., 1990). we are investigating the potential role of this transferase in modulating adhesive interactions in the adult retina. using a previously characterized monoclonal anti-galnacptase, we have used immunohistochemical and immunoblot techniques to localize and characterize the transferase in the retinas of the post metamorphic frog (x ... | 1991 | 1657627 |
| native yeast telomeres are sufficient to stabilize linear dna in xenopus laevis oocytes. | we have constructed a linear plasmid in yeast containing the entire bovine papillomavirus genome and tested its physical stability following microinjection into stage vi oocytes of xenopus laevis. our results show that unmodified telomeres, in contrast to the yeast-passaged telomeres, drastically affect the stability of the injected linear plasmid. plasmids carrying unmodified tetrahymena thermophila telomeric sequences are rapidly degraded in oocytes. when these plasmids are passed through yeas ... | 1991 | 1657721 |
| molecular cloning and expression of platelet-activating factor receptor from human leukocytes. | the cdna for a platelet-activating factor (paf) receptor was cloned from a human leukocyte cdna library using a 0.8-kilobase pair fragment of the guinea pig lung paf receptor cdna (honda, z., nakamura, m., miki, i., minami, m., watanabe, t., seyama, y., okado, h., toh, h., ito, k., miyamoto, t., and shimizu, t. (1991) nature 349, 342-346). the cdna (1.8-kilobase pairs) had an open reading frame encoding 342 amino acid residues with a calculated mr of 39,203. the clone was shown to code for a paf ... | 1991 | 1657923 |
| characterization of an endogenous na+/h+ antiporter in xenopus laevis oocytes. | the amiloride-sensitive na+/h+ antiporter in defolliculated oocytes of xenopus laevis was characterized by measurements of 22na+ influx and apparent h+ efflux. uptake of 22na+ was linear over a 90-min incubation period and was inhibited approximately 80% with 5 x 10(-4) mol l-1 amiloride. amiloride-sensitive sodium uptake was reduced following collagenase treatment or oocyte aging. k0.5 for amiloride inhibition was 4.13 x 10(-6) +/- 1.33 x 10(-6)mol l-1 and the km for na+ was 4.25 x 10(-3) mol l ... | 1991 | 1658182 |
| sodium dependence of the epithelial sodium conductance expressed in xenopus laevis oocytes. | the epithelial na+ conductance was expressed in xenopus laevis oocytes by injection of size-fractionated mrna of bovine tracheal epithelium. fractionation was achieved by sucrose density gradient centrifugation. successful expression was analysed by recording current/voltage (i/v) curves in the presence and absence of amiloride (10 mumol/l). the newly expressed conductance was half-maximally inhibited by 44 nmol/l amiloride and exhibited a selectivity for na+ over k+ of 140:1. i/v curves obtaine ... | 1991 | 1658728 |
| [from ovocyte to biochemistry of the cell cycle]. | the cell division cycle in eukaryotes contains up to three major transition points; the conversion of quiescent cells to a stage of active proliferation, the initiation of dna synthesis (s phase) and the induction of mitosis in cells with newly replicated genome (m phase). within the past years two strategies, have converged to identify, genetically and biochemically a key protein kinase p34 cdc2 that governs the entry into mitosis. in the fission yeast schizosaccharomyces pombe a number of muta ... | 1991 | 1659057 |
| the bovine mannose 6-phosphate/insulin-like growth factor ii receptor. localization of mannose 6-phosphate binding sites to domains 1-3 and 7-11 of the extracytoplasmic region. | the extracytoplasmic region of the 270-kda mannose 6-phosphate/igf-ii receptor is composed of 15 repeating domains and is capable of binding 2 mol of mannose 6-phosphate (man-6-p). to localize the man-6-p binding domains, bovine receptor was subjected to partial proteolysis with subtilisin followed by affinity chromatography on pentamannosyl phosphate-agarose. eleven proteolytic fragments ranging in apparent molecular mass from 53 to 206 kda were isolated. sequence analysis of six of the fragmen ... | 1991 | 1660469 |
| presence of vi-transposon-like elements in the proopiomelanocortin gene a of xenopus laevis does not affect gene activity. | restriction mapping of the two proopiomelanocortin (pomc) genes of the south african clawed toad xenopus laevis revealed that pomc gene a is much larger than pomc gene b. here we report that this size difference is mainly due to the presence of four vitellogenin (vi)-transposon-like elements in pomc gene a, while vi elements are absent from pomc gene b. alignment of these elements with other vi elements revealed a consensus sequence of 463 bp, which is bounded by a 16 bp inverted repeat and flan ... | 1991 | 1662768 |
| regulation of beta-adrenergic response in xenopus laevis oocytes. | | 1991 | 1663058 |
| systems for the study of nuclear assembly, dna replication, and nuclear breakdown in xenopus laevis egg extracts. | | 1991 | 1664032 |
| the hydrolysis of phosphatidylinositol 4-phosphate in membranes of xenopus laevis oocytes: characteristics of a phosphomonoesterase. | 1. phosphatidylinositol 4-phosphate (ptdins4p) is degraded by isolated membranes from xenopus laevis oocytes. 2. incubation of [4-32p]ptdins4p with membranes yields only radioactive inorganic phosphate, indicating the presence of a phosphomonoesterase. 3. membranes hydrolyze ptd[2-3h]ins4p to produce mainly ptd[2-3h]ins in the lipid phase. in this incubation [3h]inositol and inositol monophosphate appear in the water phase. 4. membrane incubations of ptd[2-3h]ins4p carried out in the presence of ... | 1991 | 1664308 |
| type iii phosphodiesterase plays a necessary role in the growth-promoting actions of insulin, insulin-like growth factor-i, and ha p21ras in xenopus laevis oocytes. | three phosphodiesterase (pde) type iii inhibitors were tested and found to inhibit xenopus oocyte maturation induced by insulin with apparent ic50 values of 2.2 +/- 0.2 microm cl-930, 25 +/- 3 microm imazodan (cl-914), and 786 +/- 237 microm piroximone (mdl 19,205). the same rank order of potencies was observed for inhibition of insulin-like growth factor-i (igf-i)-induced oocyte maturation, with ic50 values of 5.5 +/- 0.9 microm cl-930, 54 +/- 4 microm imazodan, and 1190 +/- 395 microm piroximo ... | 1991 | 1665204 |
| [two types of nondepolarizing-activated calcium channels on the spinal cholinergic neurons from embryonic xenopus laevis]. | single calcium channel current was studied on the identified spinal cholinergic neurons from embryonic xenopus laevis with patch clamp method. the results indicate that some calcium channels show opening activity at resting membrane potential. according to the characteristics of conductance and kinetics of such channels, they could be divided into two types: a stretch sensitive type-ns with a slope conductance of 7.5 ps (mean open time 0.58 ms at resting membrane potential) and a type-nl with a ... | 1991 | 1665590 |
| aggregation of pigment granules in single cultured xenopus laevis melanophores by melatonin analogues. | 1. isolated melanophores were differentiated from aggregates of neural crest obtained from neurula stage xenopus laevis embryos after 2 days in culture. 2. condensation of pigment granules in these cells by melatonin (5-methoxy n-acetyltryptamine, amt) and various novel analogues was monitored with an image analysis system to quantitate the area occupied by pigment in individual cells. 3. melanophores exposed to vehicle (a maximum of 0.1% meoh) showed little (less than 5%) change in pigment area ... | 1991 | 1667293 |
| nephroblastoma in the clawed frog xenopus laevis. | one 2.5-3 year old female clawed frog (xenopus laevis), out of a consignment of 4,000 frogs, was found to have an abnormal abdominal growth, weighing 7.9 g. the growth was examined histologically and on the basis of the abundant stroma and serially-arranged tubules nephroblastoma was diagnosed. the growth is not considered to be transmissible. | 1991 | 1667587 |
| oscillatory muscarinic acetylcholine responses of xenopus oocytes are desensitized by protein kinase c and sensitized by protein phosphatase 2b. | the oscillatory current response to acetylcholine (ach) in xenopus laevis oocytes, mediated by endogenous muscarinic ach receptors, is known to be mildly desensitized by repetitive ach applications. pretreatment of oocytes with staurosporine (an inhibitor of protein kinases) was found not only to abolish this desensitization but also to positively and progressively potentiate oscillatory ach responses. this sensitization by staurosporine was suppressed by 12-o-tetradecanoylphorbol 13-acetate (an ... | 1991 | 1667757 |
| pathways of degradation and mechanism of action of antisense oligonucleotides in xenopus laevis embryos. | recently, we described a new class of antisense oligonucleotides that can be used to direct the cleavage of mrnas in xenopus laevis embryos by rnase h (dagle et al., nucleic acids res. 18, 4751-4757). in this study, we have examined several factors that determine the activity of these derivatives. in embryos, oligodeoxyribonucleotides were found to be rapidly degraded by a 3' exonuclease. modification of 3'-terminal phosphodiester linkages as phosphoramidates blocks this activity. the predominan ... | 1991 | 1668307 |
| different forms of soluble cytoplasmic mrna binding proteins and particles in xenopus laevis oocytes and embryos. | to gain insight into the mechanisms involved in the formation of maternally stored mrnps during xenopus laevis development, we searched for soluble cytoplasmic proteins of the oocyte that are able to selectively bind mrnas, using as substrate radiolabeled mrna. in vitro mrnp assembly in solution was followed by uv-cross-linking and rnase digestion, resulting in covalent tagging of polypeptides by nucleotide transfer. five polypeptides of approximately 54, 56 60, 70, and 100 kd (p54, p56, p60, p7 ... | 1991 | 1670777 |
| distinct, developmentally regulated brain mrnas direct the synthesis of neurotransmitter transporters. | the xenopus laevis oocyte expression system was utilized to define developmental and structural properties of neurotransmitter transporter mrnas and the pharmacological characteristics of encoded carriers independent of the complexities of brain tissue preparations. poly(a)+ rna from dissected brain regions of neonatal and adult rats was microinjected into xenopus oocytes and the expression of na(+)-dependent neurotransmitter transporters determined 48 h later. transport studies conducted with o ... | 1991 | 1671586 |
| functional expression of the intestinal peptide-proton co-transporter in xenopus laevis oocytes. | the expression of the intestinal peptide-proton cotransporter was examined in xenopus laevis oocytes by microinjection of poly(a)+ mrna prepared from rabbit intestinal mucosal cells. the concomitant expression of the glucose-sodium co-transporter was used as the control for the effectiveness of the expression technique. there was significant endogenous activity of gly-sar uptake in water-injected oocytes, but the uptake activity increased nearly 3-fold in poly(a)+ mrna-injected oocytes. the expr ... | 1991 | 1672128 |
| analysis of ccaat box transcription factor binding activity during early xenopus laevis embryogenesis. | unfertilized eggs and pre-midblastula (mbt) stage xenopus embryos were found to contain a large pool of maternally derived ccaat box-binding transcription factor (cbtf). dna mobility shift experiments using embryonic extracts prepared with either low or high salt buffers suggest that xenopus cbtf may not interact with embryonic dna until the late blastula stage, a time point coincident with the increase in zygotic transcription. additionally, photoaffinity-labeling experiments revealed that both ... | 1991 | 1674922 |
| ubiquitous myod transcription at the midblastula transition precedes induction-dependent myod expression in presumptive mesoderm of x. laevis. | we have used a quantitative reverse transcription-polymerase chain reaction assay to detect myod mrna during early embryonic development of xenopus laevis. we find that during a short period of time following the midblastula transition myod becomes transcriptionally activated at a low level ubiquitously throughout the embryo. restriction of myod expression to muscle precursor cells appears as a subsequent event, in which the process of mesoderm induction stabilizes transcription only in the marg ... | 1991 | 1675156 |
| a possible role for a mammalian facilitative hexose transporter in the development of resistance to drugs. | we show that d- but not l-hexoses modulate the accumulation of radioactive vinblastine in injected xenopus laevis oocytes expressing the murine mdr1b p-glycoprotein. we also show that x. laevis oocytes injected with rna encoding the rat erythroid/brain glucose transport protein (glut1) and expressing the corresponding functional transporter exhibit a lower accumulation of [3h]vinblastine and show a greater capacity to extrude the drug than do control oocytes not expressing the rat glut1 protein. ... | 1991 | 1675425 |
| chronic effects of nmda and apv on tectal output in xenopus laevis. | in the south african clawed-toed frog xenopus laevis, visual experience plays a crucial role in the formation of matching binocular maps in the tectum. the ipsilateral eye's projection, relayed through the crossed isthmotectal projection, displays marked plasticity in response to altered visual input during a critical period of development. this plasticity and the events responsible for the end of the critical period are mediated by n-methyl-d-aspartate (nmda) receptor function. we have previous ... | 1991 | 1675586 |
| endogenous l-glutamate transport in oocytes of xenopus laevis. | the existence of an endogenous na(+)-glutamate cotransporter in the oocytes of xenopus laevis is demonstrated. the transporter does not accept d-glutamate as substrate. the dependence on substrate displays two saturating components with low (k1/2 = 9 mm) and high (k1/2 = 0.35 microm) affinities for l-glutamate. the dependence on external na+ exhibits a saturating component with a k1/2 value of about 5 mm and a component that has not saturated up to 110 mm na+. in voltage-clamped oocytes, it is p ... | 1991 | 1676599 |
| functional expression of h1-histaminergic receptors in xenopus laevis oocytes injected with bovine adrenal medullary mrna. | we prepared poly (a)+ mrna from bovine adrenal medulla and electrophysiologically examined the expression of h1-histaminergic receptors in xenopus laevis oocytes. histamine dose-dependently induced inward currents in oocytes injected with the mrna, but not in those injected with water or the non-injected oocytes. this response was also induced by h1-agonists and antagonized by h1-antagonists, while both an h2-agonist and an antagonist had no effect. these results clearly demonstrate that h1-hist ... | 1991 | 1676766 |
| a comparison of the xenopus laevis oocyte acetylcholinesterase with the muscle and brain enzyme suggests variations at the post-translational level. | 1. xenopus laevis oocytes express endogenously two components of the cholinergic system: the muscarinic receptors and the acetylcholinesterase (ache). 2. a biochemical characterization of this enzyme was carried out. 3. the results established that the activity found in the oocytes correspond to 'true' ache with a molecular weight of 65,000 da and a sedimentation coefficient of 3-4 s. 4. the enzyme aggregates in the absence of detergent suggesting that it possess an hydrophobic character; despit ... | 1991 | 1676945 |
| an analysis of the biochemical and biosynthetic properties of dentin phosphoprotein. | dentin phosphoprotein (dpp) and dephosphorylated dpp (dep-dpp) were isolated from developing bovine incisor and purified by deae-sephacel and sepharose cl-6b chromatography. intact dpp showed partial resistance to proteolytic cleavage; while dep-dpp was completely susceptible to protease digestion. this result suggested that phosphate residues within dpp molecule may protect its structural integrity. dpp was also very sensitive to heat. when dpp was heated at 100 degrees c in the presence of sod ... | 1991 | 1677156 |
| organizer-specific homeobox genes in xenopus laevis embryos. | the dorsal blastopore lip of the early xenopus laevis gastrula can organize a complete secondary body axis when transplanted to another embryo. a search for potential gene regulatory components specifically expressed in the organizer was undertaken that resulted in the identification of four types of complementary dnas from homeobox-containing genes that fulfill this criterion. the most abundant of these encodes a dna-binding specificity similar to that of the drosophila melanogaster anterior mo ... | 1991 | 1677215 |
| retinoic acid perturbs the expression of xhox.lab genes and alters mesodermal determination in xenopus laevis. | retinoic acid (ra) treatment of xenopus laevis embryos leads to anterior truncation of the body axis (durston et al. 1989; sive et al. 1990). these initial studies suggested that ra may play a role in the patterning of the primary body axis. at least one target of ra was shown previously to be dorsal ectoderm. in this report we extend this observation and also ask whether ra alters the determination and inducing capacity of mesodermal tissue. to facilitate this analysis we isolated the homeo-dom ... | 1991 | 1678362 |
| retinoic acid can mimic endogenous signals involved in transformation of the xenopus nervous system. | in the frog xenopus laevis, signals from the mesoderm divert part of the ectoderm from an epidermal to a neural fate. in the course of neural induction, the neurectoderm also acquires anterior-posterior polarity. in this report, the early expression of two genes, xlhbox6 and the neurofilament gene xif6, is examined. the pattern of expression of the two genes seen in the tailbud embryo develops progressively over a 4 hr period following gastrulation. physiological concentrations of retinoic acid ... | 1991 | 1678613 |
| progressively restricted expression of a new homeobox-containing gene during xenopus laevis embryogenesis. | we have isolated cdnas encoding a novel xenopus homeodomain-containing protein homologous to the mouse hox-7.1 and the drosophila muscle segment homebox (msh). northern blot and rnaase protection experiments established that transcripts of the frog gene, termed xhox-7.1, first appear at about the beginning of gastrulation. after a rapid increase, mrna levels plateau between the neurula and middle-tailbud stages, and decrease steadily thereafter. in situ hybridization localized the xhox-7.1 messa ... | 1991 | 1679007 |
| [power spectra of the inter-cycle heart fluctuations in xenopus laevis (l.), conscious or pithed, exposed to temperature changes and pharmacological treatments]. | spectral analysis of spontaneous heart rate fluctuations, a powerful noninvasive tool for quantifying autonomic nervous system activity, was assessed in xenopus laevis, intact or spinalized, at different temperatures and by use of pharmacological tools. as expected, increasing the body temperature resulted in a positive chronotropic effect, both in the conscious and the spinalized preparations. characteristic modifications of the spontaneous heart rate fluctuations were detected in both the expe ... | 1991 | 1679636 |
| development of the xenopus laevis hatching gland and its relationship to surface ectoderm patterning. | an antibody that recognizes tyrosine hydroxylase can be used as a marker for hatching gland cells in xenopus embryos. using this marker, we have shown that hatching gland cells are induced at the end of gastrulation and that presumptive hatching gland cells are localized to the anterior neural folds in xenopus. the movements of neurulation bring the hatching gland cells together to form a characteristic y pattern on the dorsoanterior surface of the head. the y pattern delineates several zones of ... | 1991 | 1680048 |
| expression of the mouse macrophage cystine transporter in xenopus laevis oocytes. | system xc- mediates transport of cystine and glutamate across the mammalian plasma membrane in a na(+)-independent manner. this transport activity can be induced in mouse peritoneal macrophages during culture by diethylmaleate, a sulfhydryl-reactive agent. we injected mrna from such macrophages into xenopus oocytes and demonstrated the expression of system xc-, i.e., a na(+)-independent, glutamate-inhibitable cysteine transport system. the expressed cystine transport activity depended on the ass ... | 1991 | 1680312 |
| morphology and retinal distribution of tyrosine hydroxylase-like immunoreactive amacrine cells in the retina of developing xenopus laevis. | the development of neurons immunoreactive to tyrosine hydroxylase (th-ir) in the retina of xenopus laevis was investigated from stage 53 tadpoles to adult, by using an antibody against tyrosine hydroxylase. at all developmental stages, most of the immunoreactive somata were located in the inner nuclear layer, and a few in the ganglion cell layer. immunoreactive processes arborized in the scleral and vitreal sublaminae of the inner plexiform layer, indicating that these cells were bistratified am ... | 1991 | 1681761 |
| the effect of clofibrate on amphibian hepatic peroxisomes. | liver peroxisomes of two anuran amphibian species, rana esculenta and xenopus laevis, were studied in untreated and in clofibrate-treated adults by means of complementary technical approaches, ie, ultrastructural cytochemistry, cell fractionation and marker enzyme activity assays. in untreated adults, hepatic peroxisomes were found to be very scarce in xenopus when compared to rana. activities of catalase, d-amino acid oxidase and of the three first enzymes of the peroxisomal beta-oxidation syst ... | 1991 | 1681969 |
| resetting the circadian clock in cultured xenopus eyecups: regulation of retinal melatonin rhythms by light and d2 dopamine receptors. | a circadian oscillator is located within the eye of xenopus laevis. this oscillator regulates retinal melatonin synthesis, stimulating it at night. the primary goal of the studies reported here was to define input pathways to this circadian oscillator as a step toward identification of circadian clock mechanisms. a flow-through superfusion culture system was developed to monitor circadian rhythms of melatonin release from individual eyecups. this system was used to determine the effects of light ... | 1991 | 1682423 |
| rdna intergenic region from arabidopsis thaliana. structural analysis, intraspecific variation and functional implications. | the ribosomal gene intergenic region from arabidopsis thaliana contains four clusters of mutually unrelated repeated sequences. by comparison with the respective regions in two other brassicaceae, raphanus and sinapis, the putative promoter sequence for rna polymerase i was located. the homologies suggest that the rna polymerase i promoter in brassicaceae ranges further upstream than in animals. upstream duplications of at least a part of the promoter region were found to be located between indi ... | 1991 | 1682499 |
| xenopus borealis and xenopus laevis 28s ribosomal dna and the complete 40s ribosomal precursor rna coding units of both species. | we have determined the nucleotide sequence of xenopus borealis 28s ribosomal dna (rdna) and have revised the sequence of xenopus laevis 28s rdna (ware et al., nucl. acids res. 11, 7795-7817 (1983)). in the regions encoding the conserved structural core of 28s rrna (2490 nucleotides) there are only four differences between the two species, each difference being a base substitution. in the variable regions, also called eukaryotic expansion segments (ca. 1630 nucleotides) there are some 61 differen ... | 1991 | 1682930 |
| the development of swimming rhythmicity in post-embryonic xenopus laevis. | the post-embryonic development of 'fictive' swimming in immobilized xenopus laevis tadpoles has been examined during the first day of larval life. in xenopus embryos (stage 37-38; nieuwkoop & faber 1956), the rhythmic ventral root activity underlying swimming occurs as single brief (ca. 7 ms) compound impulses on each cycle. however, by stage 42 (about 24 h after hatching), ventral root discharge consists of bursts lasting around 20 ms per cycle. in addition to increased burst duration in each c ... | 1991 | 1685239 |
| an endogenous carrier-mediated uptake system for folate in oocytes of xenopus laevis. | we investigated the existence of an endogenous uptake system for folate in xenopus laevis oocytes. this was done by performing uptake measurements using [3h]folic acid. uptake of folic acid was linear with time for 4 h of incubation, and was similar in collagenase-treated and non-treated oocytes. the uptake process was carrier-mediated, as suggested by the saturation of folic acid uptake with concentration, and by the ability of unlabelled folic acid and its related compounds to significantly in ... | 1991 | 1685241 |
| why are several inhibitory transmitters present in the innervation of pituitary melanotrophs? actions and interactions of dopamine, gaba and neuropeptide y on secretion from neurointermediate lobes of xenopus laevis. | the aim of the present experiments was to determine whether some rationale for the presence of the several inhibitory neurotransmitters in the innervation to the toad melanotroph might be found in differences in their individual effects or in possible cooperative interactions affecting secretion. measurements of peptide release from isolated, perifused neurointermediate lobes of the toad xenopus laevis showed that each of the three identified inhibitory transmitters, dopamine, gaba and npy, was ... | 1991 | 1686069 |
| teratogenicity of cobalt chloride in xenopus laevis, assayed by the fetax procedure. | the teratogenicity of cobalt chloride (cocl2) was tested by the fetax (frog embryo teratogenesis assay: xenopus) procedure in the south african frog, xenopus laevis. in five assays, beginning at 5 h post-fertilization, groups of xenopus embryos were incubated for 96 h in media that contained cocl2 at concentrations ranging from 1.8 x 10(-6) to 1.8 x 10(-2) mol/l; control groups were incubated in the same medium without added cocl2. at 101 h post-fertilization, surviving embryos were counted, fix ... | 1991 | 1686677 |
| insulin, glucagon and somatostatin localization in the pancreas of metamorphosed xenopus laevis. | the current study was designed to determine if insulin, glucagon and somatostatin-containing cells are present in the pancreas of adult xenopus laevis. localization methods utilized included cytochemical aldehyde fuchsin (af) staining as well as the immunochemical peroxidase antiperoxidase (pap) procedure for light microscopy. the results show numerous large clusters of af-positive cells within a network of highly vascularized acinar tissue. pap immunochemical localization with insulin antibody ... | 1991 | 1686682 |
| activation of the 5-ht1c receptor expressed in xenopus oocytes by the benzazepines sch 23390 and skf 38393. | 1. a cloned 5-ht1c receptor expressed in xenopus laevis oocytes was used to characterize the action of four dopamine d1-selective benzazepines at the 5-ht1c receptor. additionally, the apparent binding of the d1-selective benzazepines to 5-ht1c receptors was measured in the choroid plexus of the pig. 2. in voltage-clamped oocytes expressing the cloned 5-ht1c receptor, 5-hydroxytryptamine (5-ht) elicited a characteristic inward current response with an ec50 of 13 nm. sch 23390 acted as a stereose ... | 1991 | 1687364 |