Publications
| Title | Abstract | Year Filter | PMID(sorted descending) Filter |
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| a rapid quantitative bioassay for evaluating the effects of ligands upon receptors that modulate camp levels in a melanophore cell line. | a new method for rapidly evaluating the effects of drugs on receptors that regulate intracellular camp in a cell line derived from xenopus laevis melanophores has been developed. melanophores were plated into sterile 96 well microtiter plates, and 3 days later the cells were treated with melatonin for 30 min to induce melanosome aggregation. subsequent exposure to msh or adrenergic agonists caused dose dependent pigment dispersion that peaked within 30 min. the cumulative pigment displacement fr ... | 1992 | 1337205 |
| the processing of beta-endorphin and alpha-melanotrophin in the pars intermedia of xenopus laevis is influenced by background adaptation. | beta-endorphin- and alpha-melanotrophin (alpha-msh)-related peptides were extracted from the pars intermedia of xenopus laevis maintained for 2, 4 or 6 weeks on a white background and for the same periods on a black background. the peptides were resolved under dissociating conditions by gel exclusion chromatography on sephadex g-50 and they were detected by radioimmunoassay with antibodies to beta-endorphin, alpha,n-acetyl beta-endorphin and alpha-msh. the beta-endorphin-related peptides separat ... | 1992 | 1336791 |
| protein kinase c activation antagonizes melatonin-induced pigment aggregation in xenopus laevis melanophores. | the pineal hormone, melatonin (5-methoxy n-acetyltryptamine) induces a rapid aggregation of melanin-containing pigment granules in isolated melanophores of xenopus laevis. treatment of melanophores with activators of protein kinase c (pkc), including phorbol esters, mezerein and a synthetic diacylglycerol, did not affect pigment granule distribution but did prevent and reverse melatonin-induced pigment aggregation. this effect was blocked by an inhibitor of pkc, ro 31-8220. the inhibitory effect ... | 1992 | 1334961 |
| primary structure of an apical protein from xenopus laevis that participates in amiloride-sensitive sodium channel activity. | high resistance epithelia express on their apical side an amiloride-sensitive sodium channel that controls sodium reabsorption. a cdna was found to encode a 1,420-amino acid long polypeptide with no signal sequence, a putative transmembrane segment, and three predicted amphipathic alpha helices. a corresponding 5.2-kb mrna was detected in xenopus laevis kidney, intestine, and oocytes, with weak expression in stomach and eyes. an antibody directed against a fusion protein containing a cooh-termin ... | 1992 | 1334959 |
| two isoforms of the thyrotropin-releasing hormone receptor generated by alternative splicing have indistinguishable functional properties. | two cdna clones encoding two different isoforms of the thyrotropin-releasing hormone receptor (trh-r) from gh3 rat anterior pituitary cells have been isolated. one isoform corresponds to the trh-r(412) receptor previously described (de la peña, p., delgado, l. m., del camino, d., and barros, f. (1992) biochem. j. 284, 891-899). the second one, named trh-r(387), contains a 52-base pair deletion, which yields a new variant of the receptor protein 25 amino acid shorter and which contains 12 new res ... | 1992 | 1334485 |
| p120, a novel substrate of protein tyrosine kinase receptors and of p60v-src, is related to cadherin-binding factors beta-catenin, plakoglobin and armadillo. | a novel protein tyrosine kinase (ptk) substrate, p120, has been previously implicated in ligand-induced signaling through the epidermal growth factor, platelet-derived growth factor and colony-stimulating factor 1 receptors, and in cell transformation by p60v-src. we have isolated a near full-length cdna encoding murine p120. the encoded protein lacks significant homology with any reported protein, but it contains four copies of an imperfect 42 amino acid repeat that occurs 12.5 times in the pro ... | 1992 | 1334250 |
| immunoblotting technique to study release of melanophore-stimulating hormone from individual melanotrope cells of the intermediate lobe of xenopus laevis. | the melanotrope cells in the pars intermedia in the pituitary of xenopus laevis synthesize and release the melanophore-stimulating hormone (alpha msh), a small peptide that causes skin darkening during the process of background adaptation. evidence has been found for a heterogeneity in biosynthetic activity of the melanotrope cells. in the present study two questions were addressed: (1) does the melanotrope cell population also show heterogeneous alpha msh-release, and (2) can this heterogeneity ... | 1992 | 1333944 |
| locations of contacts between individual zinc fingers of xenopus laevis transcription factor iiia and the internal control region of a 5s rna gene. | a set of mutants of transcription factor iiia (tfiiia) have been prepared in which successive zinc-finger domains have been deleted from the carboxyl terminus of the protein. these have been analyzed by hydroxyl radical footprinting to map the location of contacts to dna by individual zinc-finger domains of tfiiia. the results suggest that the nine zinc fingers of tfiiia are organized into three dna-binding domains of three fingers each. the spatial relationship between zinc-finger contacts to 5 ... | 1992 | 1332765 |
| a method for evaluating the effects of ligands upon gs protein-coupled receptors using a recombinant melanophore-based bioassay. | as an increasing number of medically important receptors that couple to stimulatory guanine nucleotide (gs) proteins are isolated and cloned, there is an equally escalating need for methods to rapidly and reproducibly evaluate potential ligands for their properties as agonists or antagonists. recently, a bioassay that can quickly and accurately determine the effects of numerous chemicals on a beta 1-like adrenergic receptor (ar) endogenous to melanophores derived from xenopus laevis was develope ... | 1992 | 1332547 |
| cl- channels in basolateral renal medullary membranes, vi. cl- conductance expression in xenopus oocytes. | cl- channels from basolateral membranes of the mammalian thick ascending limb of henle differ significantly, in certain of their functional characteristics, from cl- channels in apical membranes of secretory epithelia such as trachea or small intestine and from certain cl- channels in the central nervous system. yet there is no sequence information available about basolateral thick ascending limb cl- channels. as an initial step in the isolation of a cl- channel from the thick ascending limb of ... | 1992 | 1332508 |
| purification and characterization of joining peptide and n-terminal peptide of proopiomelanocortin from the pars distalis of the bullfrog pituitary. | the joining peptide (jp) and the n-terminal peptide of proopiomelanocortin (npp) were isolated from an acid-acetone extract of the distal lobe of the pituitary of the bullfrog, rana catesbeiana, and purified by gel filtration and reverse-phase high performance liquid chromatography. the amino acid sequence of the bullfrog jp resembled the sequences of the jps of rana ridibunda (86% similarity) and xenopus laevis (54% similarity), as deduced from the nucleotide sequences of their cdnas. the amino ... | 1992 | 1331997 |
| l-glutamate transporter derived from mrnas of primary glial cultures: expression in xenopus laevis oocytes. | a high-affinity sodium-dependent l-glutamate transporter was expressed in xenopus oocytes after microinjection of poly(a)+ rna from primary astrocyte cultures from rat brain cortex. mrna-induced l-glutamate transport was saturable by substrate and shows kinetic features similar to those found in intact glial cell preparations. l-glutamate accumulation was prevented by rising the external k+ concentration or by coincubation with l-, d-aspartate or d-glutamate. after fractionation by sucrose densi ... | 1992 | 1331663 |
| analysis of autofeedback mechanisms in the secretion of pro-opiomelanocortin-derived peptides by melanotrope cells of xenopus laevis. | the secretion of most pituitary hormones is under the control of feedback mechanisms. the feedback control of alpha-melanophore-stimulating hormone (alpha-msh) from melanotrope cells is controversial. the possible existence of an autofeedback exerted by alpha-msh or other pomc-derived peptides on melanotrope cells of the amphibian xenopus laevis has been investigated. alpha-msh or its potent agonist 4-norleucine,7-d-phenylalanine-alpha-msh has no effect on the release of radiolabeled pomc-derive ... | 1992 | 1330808 |
| choroid plexus, ependyma and arachnoidea express receptors for vitamin d: differences between "seasonal" and "non-seasonal" breeders. | autoradiographic studies with [3h]1,25-dihydroxyvitamin d3 demonstrated nuclear high affinity binding sites (receptors) in epithelial cells of choroid plexus, ependyma and arachnoid in "seasonal" breeders of various vertebrate phyla, namely xiphophorus helleri, hyla crucifer, xenopus laevis, bufo woodhousei, chrysemys scripta, anolis carolinensis, nerodia sipedon and phodopus sungorus, but vitamin d receptors were undetectable in these tissues in non-seasonal breeders, such as zebra finch, labor ... | 1992 | 1329147 |
| the protein-phosphatase inhibitor okadaic acid mimics msh-induced and melatonin-reversible melanosome dispersion in xenopus laevis melanophores. | the present study describes the ability of 315 nm okadaic acid to induce melanosome dispersion in cultured xenopus laevis melanophores. this effect of okadaic acid is similar to that of a-melanocyte stimulating hormone (msh) and can be reversed by melatonin treatment; it indicates that a member of the protein-phosphatase 1 or 2a families must be active for maintenance of the aggregated state. higher concentrations of okadaic acid (1 microm) attenuate the response of xenopus melanophores to melat ... | 1992 | 1329076 |
| molecular cloning and expression of cdna encoding the murine gonadotropin-releasing hormone receptor. | the primary structure of the gonadotropin-releasing hormone (gnrh) receptor was determined by sequencing a functional receptor cdna isolated by expression cloning from an immortalized murine gonadotroph (alpha t3) cell line. positive clone pools from a cdna library were detected by screening expressed rna in aequorin-injected xenopus laevis oocytes, in which receptor-mediated calcium responses were monitored as light emission during stimulation by gnrh. the isolated receptor cdna encodes a 327-a ... | 1992 | 1328228 |
| inositol lipid hydrolysis contributes to the ca2+ wave in the activating egg of xenopus laevis. | we have used fluorescence ratio-imaging of fura-2 in the activating egg of xenopus laevis to study the wave of increased intracellular free ca2+ concentration ([ca2+]i) while monitoring that of cortical granule exocytosis. naturally matured eggs were dejellied, injected with fura-2, and activated by the iontophoresis of 1-30 ncoul of inositol-1,4,5-trisphosphate which triggers an immediate increase in free [ca2+]i at the injection site. the ca2+ rise spreads throughout the egg, reaching the oppo ... | 1992 | 1327924 |
| regulation mechanisms of intracellular ph of xenopus laevis oocyte. | intracellular ph values (phi) of xenopus oocytes were optically measured using a fluorescent dye, 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (bcecf). the oocytes were loaded with dye by incubation with a membrane-permeable form (bcecf-am). mean phi of the oocytes in ph 7.6 solution was 7.69. increasing ambient pco2 rapidly decreased phi and estimated buffering power was 23.8 mm/ph unit. changing ambient hco3- from 5 to 30 mm did not alter phi. after incubation in a na(+)-free solution, n ... | 1992 | 1327152 |
| isolation, characterization, and localization of the inositol 1,4,5-trisphosphate receptor protein in xenopus laevis oocytes. | inositol 1,4,5-trisphosphate (ins(1,4,5)p3) induces ca2+ oscillations and waves in xenopus laevis oocytes. microsomes from oocytes exhibit high-affinity binding for ins(1,4,5)p3, and demonstrate ins(1,4,5)p3-induced ca2+ release. the ins(1,4,5)p3 receptor (insp3r) was purified from oocyte microsomes as a large tetrameric complex and shown to have a monomer molecular mass of 256 kda, compared with 273 kda for the brain insp3r. binding to the oocyte receptor is highly specific for ins(1,4,5)p3 and ... | 1992 | 1326534 |
| microinjection of cloned proviral rous sarcoma virus dnas into xenopus laevis one cell embryos. | plasmid patv8 carrying rous sarcoma virus (rsv) dna with one long terminal repeat (ltr) or plasmid paprc carrying complete rsv proviral dna was injected into fertilized eggs of xenopus laevis. the fate of the exogenous dnas was followed during embryogenesis. in both cases a new form of dna, comigrating with endogenous dna, began to appear shortly after the injection. this new form represented a linear dimer of the injected plasmid that had formed by ligation of linear monomers of the plasmid dna ... | 1992 | 1326446 |
| properties of the guinea-pig lung platelet-activating factor receptor encoded by the cloned cdna. | platelet-activating factor (paf) is a naturally occurring phospholipid possessing proinflammatory and shock-inducing activities. although paf exerts these functions via specific receptors, the molecular structures of the receptor has not been clarified. we have isolated a cdna coding for paf receptor through expression cloning. the paf receptor expressed in xenopus laevis oocytes and cos-7 cells showed pharmacological properties consistent with those in previous reports. sequence analysis reveal ... | 1992 | 1326344 |
| inositol monophosphatase is a highly conserved enzyme having localized structural similarity to both glycerol 3-phosphate dehydrogenase and haemoglobin. | the cdna coding for an inositol monophosphatase in the oocytes of the african clawed frog, xenopus laevis, has been isolated and sequenced. the predicted primary structure of this enzyme is markedly conserved when it is compared with its mammalian functional homologues; up to 84% of the amino acid residues are identical, and conservative substitutions increase the similarity to 95%, suggesting that this sequence represents the most parsimonious primary structure for the protein to maintain not o ... | 1992 | 1325777 |
| molecular dissection of a specific nuclear domain: the chromatin region of the ribosomal gene cluster in xenopus laevis. | molecular dissection of the nuclear domain corresponding to the ribosomal chromatin cluster was investigated. the experimental scheme was based on the ability of restriction enzymes to digest the whole genome without affecting this region (several megabases in length). such a strategy involved the judicious choice of restriction enzymes, which is possible in xenopus laevis, where the rdna sequence is known and the repeated units are organized into one unique cluster. sali, xhoi, and ecorv digest ... | 1992 | 1324846 |
| a single-stranded dna binding protein required for mitochondrial dna replication in s. cerevisiae is homologous to e. coli ssb. | it has previously been shown that the mitochondrial dna (mtdna) of saccharomyces cerevisiae becomes thermosensitive due to the inactivation of the mitochondrial dna helicase gene, pif1. a suppressor of this thermosensitive phenotype was isolated from a wild-type plasmid library by transforming a pif1 null strain to growth on glycerol at the non-permissive temperature. this suppressor is a nuclear gene encoding a 135 amino acid protein that is itself essential for mtdna replication; cells lacking ... | 1992 | 1324172 |
| early appearance of and neuronal contribution to agrin-like molecules at embryonic frog nerve-muscle synapses formed in culture. | antibodies against chicken and torpedo agrin were used for immunofluorescent staining in order to assess the spatial distribution and temporal appearance of agrin-like molecules at newly formed synaptic contacts in cultures of embryonic xenopus nerve and muscle cells. the antibodies stained xenopus neuromuscular junctions and removed ach receptor (achr)-aggregating activity from extracts of xenopus brain. immunofluorescence was observed at almost all nerve-induced achr aggregates, even at microa ... | 1992 | 1322981 |
| stimulation of mitogen-activated protein kinase by oncogenic ras p21 in xenopus oocytes. requirement for ras p21-gtpase-activating protein interaction. | p21ras plays an important role in the control of cell proliferation. the molecular mechanisms implicated are unknown. we report that the injection of oncogenic lys12 ras into xenopus laevis oocytes promoted the activation of mitogen-activated protein kinase (map kinase) after a lag of about 90 min. map kinase activity was 10-fold higher 4 h after injection of oncogenic lys12 ras than after injection of nononcogenic gly12 ras. the stimulated map kinase activity remained at a plateau for at least ... | 1992 | 1322893 |
| modulation of cardiac ca2+ channels in xenopus oocytes by protein kinase c. | l-type calcium channel was expressed in xenopus laevis oocytes injected with rnas coding for different cardiac ca2+ channel subunits, or with total heart rna. the effects of activation of protein kinase c (pkc) by the phorbol ester pma (4 beta-phorbol 12-myristate 13-acetate) were studied. currents through channels composed of the main (alpha 1) subunit alone were initially increased and then decreased by pma. a similar biphasic modulation was observed when the alpha 1 subunit was expressed in c ... | 1992 | 1321730 |
| thymus ontogeny in frogs: t-cell renewal at metamorphosis. | metamorphosis in amphibians presents a unique problem for the developing immune system. because tadpoles are free-living, they need an immune system to protect against potential pathogens. however, at metamorphosis, they acquire a variety of new adult-specific molecules to which the tadpole immune system must become tolerant. we hypothesized that xenopus laevis tadpoles may avoid potentially destructive antiself responses by largely discarding the larval immune system at metamorphosis and acquir ... | 1992 | 1320967 |
| nppb block of ca(++)-activated cl- currents in xenopus oocytes. | nppb (5-nitro-2-(3-phenylpropylamino)-benzoate), a member of the novel class of cl- channel blockers related to diphenylamine-2-carboxylate, was studied for its effect on the ca(++)-activated cl- current (icl(ca)) in frog (xenopus laevis) oocytes. icl(ca) was activated by bath application of 5 mm ca++ to oocytes that had been ca++ permeabilized with the ca++ ionophore a23187. in order to prevent the inactivation of icl(ca) that occurs with repetitive applications of ca++, oocytes were also treat ... | 1992 | 1320252 |
| angiotensin ii and acetylcholine differentially activate mobilization of inositol phosphates in xenopus laevis ovarian follicles. | angiotensin ii (aii) evokes a ca(2+)-dependent cl- current in xenopus laevis ovarian follicles that appears to involve a pertussis-toxin-sensitive g protein mediating phosphoinositide hydrolysis and ca2+ mobilization from intracellular stores. follicle responses to aii closely resemble the two-component response stimulated by acetylcholine (ach) in this tissue. intraoocyte injections of phytic acid, heparin, and inositol 1,4,5-trisphosphate [ins(1,4,5)p3], acting as inhibitors of ins(1,4,5)p3-in ... | 1992 | 1320248 |
| effect of putative melatonin receptor antagonists on melatonin-induced pigment aggregation in isolated xenopus laevis melanophores. | the ability of putative melatonin receptor antagonists to antagonise melatonin-induced aggregation of pigment granules in cultured neural crest xenopus laevis melanophores was examined. neither ml 23 (n-(2,4-dinitrophenyl)-5-methoxytryptamine) nor 6-methoxy-2-benzoxazolinone showed agonist or antagonist activity. n-acetyltryptamine and n-butanoyltryptamine were partial agonists; both compounds aggregated pigment granules in some cells, but also reversed melatonin-induced pigment agreggation in a ... | 1992 | 1319920 |
| antitumor activity of magainin analogues against human lung cancer cell lines. | magainin 1 and magainin 2, originally isolated from african clawed frog xenopus laevis skin, inhibit the growth of bacteria and fungi. synthetic magainin a (mag a) and magainin g (mag g) are more potent against bacteria and protozoa. in order to determine the antitumor activity of these analogues, we have tested these two analogues against six small cell lung cancer (sclc) cell lines nci-h82, nci-h526, nci-h678, nci-h735, nci-h841, and nci-h889, which were known to differ by more than 10-fold in ... | 1992 | 1319823 |
| localization of binding sites for atrial natriuretic factor and angiotensin ii in the central nervous system of the clawed toad xenopus laevis. | the distribution of binding sites for atrial natriuretic factor (anf) and angiotensin ii (a ii) was investigated in the central nervous system (cns) of the clawed toad xenopus laevis by means of in vitro autoradiography using [125i]-rat anf(99-126) or [125i] [val5] a ii and [125i]human a ii as labeled ligands. the highest densities of specific anf-binding were detected in the nucleus habenularis, thalamic regions, hypophyseal pars nervosa and nucleus interpeduncularis. moderate anf-binding was f ... | 1992 | 1318168 |
| complementation of formyl peptide receptor-mediated signal transduction in xenopus laevis oocytes. | formyl-methionine-containing peptides (e.g. fmet-leu-phe) stimulate a variety of neutrophil functions by interacting with specific cell surface receptors which are coupled via g-proteins to stimulation of phospholipase c. two markedly distinct cdnas coding for formyl peptide receptors have recently been isolated from a rabbit and a human cdna library respectively. to examine the hitherto unknown signal transduction properties of the formyl peptide receptor encoded by the human cdna, we have used ... | 1992 | 1318022 |
| beta-subunit expression is required for camp-dependent increase of cloned cardiac and vascular calcium channel currents. | in contrast to vascular smooth muscle (vsm), camp-dependent phosphorylation increases l-type voltage dependent ca(2+)-channel (l-vdcc) activity in heart. to investigate whether this difference depends on the tissue-specific alpha 1-subunit of the l-vdcc or its regulation by other subunits, we used a xenopus laevis oocyte expression system. injection of camp into oocytes expressing cardiac alpha 1 or vsm alpha 1 alone had no effect on l-vdcc activity. however, camp increased l-vdcc activity 2-fol ... | 1992 | 1317953 |
| multiple genes for xenopus activin receptor expressed during early embryogenesis. | four distinct cdnas for activin receptor designated as xstk2, 3, 8 and 9 have been cloned from a xenopus laevis cdna library. the protein structures deduced from the cdnas have shown that they all have a putative extracellular ligand-binding domain, a single transmembrane domain and cytoplasmic ser/thr kinase domain, except that xstk2 is extremely similar to the xstk3 gene but lacks a carboxyl-terminal part of the kinase motif. northern blot analysis showed that all transcripts are maternally in ... | 1992 | 1317302 |
| initiation of translation of human rhinovirus rna: mapping the internal ribosome entry site. | in order to map the 3' boundary of the segments needed for translation initiation at the correct site on human rhinovirus 2, deletions were made from the 3' end of the viral 5'-untranslated region. these truncated viral segments were placed immediately upstream of a reporter gene, a derivative of the influenza virus ns cdna, either as monocistronic constructs or as dicistronic constructs in which the upstream cistron was the xenopus laevis cyclin b2 cdna. in vitro transcripts of these clones wer ... | 1992 | 1316679 |
| mutation of a cysteine in the first transmembrane segment of na,k-atpase alpha subunit confers ouabain resistance. | the cardiac glycoside ouabain inhibits na,k-atpase by binding to the alpha subunit. in a highly ouabain resistant clone from the mdck cell line, we have found two alleles of the alpha subunit in which the cysteine, present in the wild-type first transmembrane segment, is replaced by a tyrosine (y) or a phenylalanine (f). we have studied the kinetics of ouabain inhibition by measuring the current generated by the na,k-pump in xenopus oocytes injected with wild-type and mutated alpha 1 and wild-ty ... | 1992 | 1316269 |
| expression of xmyod protein in early xenopus laevis embryos. | a monoclonal antibody specific for xenopus myod (xmyod) has been characterized and used to describe the pattern of expression of this myogenic factor in early frog development. the antibody recognizes an epitope close to the n terminus of the products of both xmyod genes, but does not bind xmyf5 or xmrf4, the other two myogenic factors that have been described in xenopus. it reacts in embryo extracts only with xmyod, which is extensively phosphorylated in the embryo. the distribution of xmyod pr ... | 1992 | 1315678 |
| immunolocalization and expression of functional and nonfunctional cell-to-cell channels from wild-type and mutant rat heart connexin43 cdna. | the carboxyl terminal cytoplasmic domain of distinct gap junction proteins may play an important role in assembly of functional channels as well as differential responsiveness to ph, voltage, and intracellular second messengers. oligonucleotide-directed site-specific mutagenesis in a paired xenopus laevis oocyte expression system was used to examine the expression of mrnas encoding wild-type and carboxyl terminal mutant connexin43 (cx43) proteins. oocytes were stripped, injected with mrna or dis ... | 1992 | 1315637 |
| cloning of a second type of activin receptor and functional characterization in xenopus embryos. | a complementary dna coding for a second type of activin receptor (actriib) has been cloned from xenopus laevis that fulfills the structural criteria of a transmembrane protein serine kinase. ectodermal explants from embryos injected with activin receptor rna show increased sensitivity to activin, as measured by the induction of muscle actin rna. in addition, injected embryos display developmental defects characterized by inappropriate formation of dorsal mesodermal tissue. these results demonstr ... | 1992 | 1313188 |
| requirements for phosphorylation of map kinase during meiosis in xenopus oocytes. | mitogen-activated protein (map) kinases are activated in response to a variety of extracellular stimuli by phosphorylation on tyrosine and threonine residues. xp42 is a xenopus laevis map kinase that is activated during oocyte maturation. modified forms of xp42 that lacked enzymatic activity or either of the phosphorylation sites were expressed in xenopus oocytes. when meiotic maturation was induced with progesterone, each mutant xp42 was phosphorylated, indicating that at least one kinase was a ... | 1992 | 1313186 |
| proton transport mechanism in the cell membrane of xenopus laevis oocytes. | mechanisms of h+ transport across the plasma cell membrane of prophase-arrested oocytes of xenopus laevis were investigated by testing the effect of ion substitutions and inhibitors on cytoplasmic ph (phi), membrane potential (vm) and membrane resistance (rm). during superfusion with control solution of ph = 7.4, phi was 7.49 +/- 0.12 (n = 15), vm was -61.9 +/- 7.8 mv (n = 34) (cytoplasm negative), and rm was 2.9 +/- 1.5 m omega (n = 19). these data confirm that h+ ions are not distributed at el ... | 1992 | 1313170 |
| regulation of endogenous and expressed na+/k+ pumps in xenopus oocytes by membrane potential and stimulation of protein kinases. | modulation of the current generated by the na+/k+ pump by membrane potential and protein kinases was investigated in oocytes of xenopus laevis. in addition to a positive slope region in the current-voltage (i-v) relationship of the na+/k+ pump, a negative slope region has been described in these cells (lafaire & schwarz, 1986) and has been attributed to a voltage-dependent apparent km value for pump stimulation by external [k+] (rakowski et al., 1991). to study this feature in more detail, xenop ... | 1992 | 1313113 |
| voltage-dependent stimulation of na+/k(+)-pump current by external cations: selectivity of different k+ congeners. | currents generated by the endogenous na+/k+ pump in the oocytes of xenopus laevis were determined under voltage-clamp as currents activated by different k+ congeners. the voltage dependence of the pump current reflects voltage-dependent steps in the reaction cycle. the decrease of k(+)-activated pump current at positive potentials has been attributed to voltage-dependent stimulation by the external k+ (rakowski, vasilets, latona and schwarz (1991) j. membr. biol. 121, 177-187). in na(+)-free sol ... | 1992 | 1312862 |
| multiple retinoid-responsive receptors in a single cell: families of retinoid "x" receptors and retinoic acid receptors in the xenopus egg. | in a search for nuclear hormone receptors expressed in early development we found that xenopus laevis eggs contain mrnas from two retinoic acid receptor genes (xrar alpha and xrar gamma) and two retinoid "x" receptor genes (xrxr alpha and xrxr gamma). we also show that rxrs are members of a family of at least three genes, thus expanding the number of genes encoding retinoic acid-responsive transcription factors to six. with the exception of xrxr gamma, these maternal mrnas are degraded before ga ... | 1992 | 1312717 |
| the fms-like tyrosine kinase, a receptor for vascular endothelial growth factor. | the fms-like tyrosine kinase (flt) is a transmembrane receptor in the tyrosine kinase family. expression of flt complementary dna in cos cells conferred specific, high-affinity binding of vascular endothelial growth factor, also known as vascular permeability factor (vegf-vpf), a factor that induces vascular permeability when injected in the guinea pig skin and stimulates endothelial cell proliferation. expression of flt in xenopus laevis oocytes caused the oocytes to release calcium in response ... | 1992 | 1312256 |
| demonstration of coexisting catecholamine (dopamine), amino acid (gaba), and peptide (npy) involved in inhibition of melanotrope cell activity in xenopus laevis: a quantitative ultrastructural, freeze-substitution immunocytochemical study. | this quantitative ultrastructural immunocytochemical study demonstrates the coexistence of a catecholamine [dopamine (da)], an amino acid (gaba), and a neuropeptide [neuropeptide y (npy)] in axon varicosities innervating the pars intermedia of xenopus laevis. the varicosities are assumed to control the pars intermedia melanotrope cells, which regulate skin color during the physiological process of background adaptation. varicosity profiles appear to abut melanotrope cells and folliculostellate c ... | 1992 | 1312137 |
| molecular characterisation, expression and localisation of human neurokinin-3 receptor. | the complete amino acid sequence of the human neurokinin-3 receptor was deduced by dna sequence analysis of human genomic fragments. comparison of the predicted primary structure with those for the human neurokinin receptors 1 and 2 shows a highly conserved pattern of seven hydrophobic regions with maximum divergence occurring at the amino- and carboxy-termini. the position of intron-exon junctions are identical to those in other reported neurokinin genes. using a chimeric genomic-cdna gene, the ... | 1992 | 1312036 |
| characterization of protein kinase c in xenopus oocytes. | protein kinase c (pkc) was partially purified from xenopus laevis oocytes by ammonium sulfate fractionation followed by deae-cellulose and hydroxyapatite column chromatography. in the latter chromatography, two distinct pkc activities were identified. both pkc fractions contained an 80 kda protein which was recognized by three antisera raised against the conserved regions of mammalian pkc. however, specific antisera against alpha, beta i, beta ii, and gamma-subspecies of rat pkc did not recogniz ... | 1992 | 1310011 |
| reducing inositol lipid hydrolysis, ins(1,4,5)p3 receptor availability, or ca2+ gradients lengthens the duration of the cell cycle in xenopus laevis blastomeres. | we have microinjected a mab specifically directed to phosphatidylinositol 4,5-bisphosphate (pip2) into one blastomere of two-cell stage xenopus laevis embryos. this antibody binds to endogenous pip2 and reduces its rate of hydrolysis by phospholipase c. antibody-injected blastomeres undergo partial or complete arrest of the cell cycle whereas the uninjected sister blastomeres divided normally. since pip2 hydrolysis normally produces diacylglycerol (dg) and inositol 1,4,5-triphosphate (ins[1,4,5] ... | 1992 | 1309810 |
| a cdc2-related kinase oscillates in the cell cycle independently of cyclins g2/m and cdc2. | the eg1 gene in xenopus laevis is related in sequence to the cdc2+ gene. we show here that the eg1 gene product (cdk2) possesses histone h1 protein kinase activity and binds to pstair antibodies as well as to sepharose beads linked to the 13-kda product of the suc 1 gene (p13suc1). eg1 protein kinase is active only in an mr approximately 200,000 complex with other proteins but is not associated with any of the three known xenopus mitotic cyclins or with any newly synthesized protein in egg extra ... | 1992 | 1309805 |
| the guanine nucleotide-binding protein gs activates a novel calcium transporter in xenopus oocytes. | calcium influx is an important aspect of receptor-mediated signal transduction, yet limited information is available regarding the pathways of calcium influx into nonexcitable cells. we show that treatment of oocytes from xenopus laevis with cholera toxin, a potent activator of the guanine nucleotide-binding protein gs, specifically stimulates a sustained inward whole cell flux of calcium through a novel membrane transporter. the calcium is distributed into a mobilizable pool. the flux is voltag ... | 1992 | 1309778 |
| expression of functional bradykinin receptors in xenopus oocytes. | mrna prepared from various tissues and cultured cells was injected into xenopus laevis oocytes. three to five days after injection, the response of the oocytes to the peptide bradykinin was monitored. the oocytes were voltage clamped and the membrane currents generated on application of agonist were recorded. mrna from ng108-15, rat uterus, and human fibroblast cell line wi38 gave similar responses to bradykinin (1 microm), with an initial inward current (10-20 na) followed by a prolonged period ... | 1992 | 1309236 |
| nucleotide sequence of the 18s ribosomal ribonucleic acid gene from two teleosts and two sharks and their molecular phylogeny. | the 18s rrna sequence was determined for two teleostean fish species, fundulus heteroclitus and sebastolobus altivelis, and two sharks, squalus acanthias and echinorhinus cookei. to study the molecular phylogeny of these taxa, the sequences were compared with 18s rrna sequences of the coelacanth latimeria chalumnae, the frog xenopus laevis, and humans. maximum parsimony analysis of the sequences resulted in a single most parsimonious tree that is in agreement with the expected phylogeny. the cor ... | 1992 | 1308203 |
| recombinant pdgf from lower vertebrates: receptor binding and immunochemical analysis with metabolically labeled growth factor. | we used a baculovirus vector/insect host cell system to express cdna clones of pdgf a genes from mouse and frog (xenopus laevis). the insect host cells process pdgf a subunits from either frogs or mice into biologically active aa homodimers with yields in the range of 0.5-1.0 mg/liter of culture medium. the recombinant pdgfs can be metabolically labeled with 35s-cysteine for use in radioreceptor and radioimmunoassays. neutralizing polyclonal antisera can be raised against the mouse and frog pdgf ... | 1992 | 1306683 |
| teratogenicity of cadmium chloride in the south african frog, xenopus laevis. | the teratogenicity of cadmium chloride was tested by the fetax (frog embryo teratogenesis assay: xenopus) procedure. in five assays, groups of xenopus embryos were grown in media containing concentrations of 0.75-56 mumol/l; controls were incubated in medium without cadmium chloride. exposures began 5 h post-fertilization and ended 101 h post-fertilization. in control groups, > 95% of embryos survived at 101 h and the incidence of malformations was < 7%. in cd(2+)-exposed groups, concentration-d ... | 1992 | 1303948 |
| expression of cloned aromatic l-amino acid decarboxylase in xenopus laevis oocytes. | sense mrna coding for bovine adrenal medulla aromatic l-amino acid decarboxylase (aadc) was expressed following microinjection into xenopus laevis oocytes. the expressed enzyme activity was stereoselective for l-5-hydroxytryptophan and l-dopa and blocked by nsd-1015 an inhibitor of aadc. heating the expressed enzyme at 55 degrees c resulted in a parallel loss of activity towards both substrates. our findings are consistent with the prevailing notion that a single enzyme is able to decarboxylate ... | 1992 | 1303156 |
| mechanism of release of ca2+ from intracellular stores in response to ionomycin in oocytes of the frog xenopus laevis. | 1. the mechanism of ca2+ release from intracellular stores was studied in defolliculated xenopus laevis oocytes by measuring whole-cell currents using the two-electrode voltage-clamp method. 2. the extracellular application of ionomycin, a selective ca2+ ionophore, evoked an inward current consisting of a spike-like fast component followed by a long-lasting slow component with few superimposed current oscillations (fluctuations). the ionomycin response occurred in a dose-dependent manner and was ... | 1992 | 1302268 |
| xenopus gastrulation without a blastocoel roof. | the objective of this paper is to determine the function in gastrulation of several of the five major regional morphogenetic processes in the african clawed frog, xenopus laevis. these regional processes are (1) epiboly of the animal cap (ac); (2) migration of the mesoderm on the roof of the blastocoel; (3) convergence and extension of the dorsal, noninvoluting marginal zone (nimz); (4) formation of the bottle cells at the site of blastopore formation; and (5) convergence and extension of the in ... | 1992 | 1301081 |
| mesoderm-inducing factors and the control of gastrulation. | one of the reasons that we know so little about the control of vertebrate gastrulation is that there are very few systems available in which the process can be studied in vitro. in this paper, we suggest that one suitable system might be provided by the use of mesoderm-inducing factors. in amphibian embryos such as xenopus laevis, gastrulation is driven by cells of the mesoderm, and the mesoderm itself arises through an inductive interaction in which cells of the vegetal hemisphere of the embryo ... | 1992 | 1299357 |
| cytoplasmic membrane transplants in early xenopus embryos indicate cell-cycle-specific effects. | fragments of rough endoplasmic reticulum or golgi complex isolated from normal adult rat liver homogenates were injected into one cell of cleaving two-cell xenopus laevis embryos and the effects on development were monitored during early cleavage by morphological analysis. scanning electron microscopy revealed the formation of large cells on the injected side of the embryos. such large cells were not present in controls and thus were considered to have been formed as a consequence of delayed cle ... | 1992 | 1299267 |
| examination of the dna sequence-specific binding properties of heat shock transcription factor in xenopus laevis embryos. | the binding of heat shock transcription factor (hsf) to the heat shock element (hse) is necessary for transcriptional activation of eukaryotic heat shock protein (hsp) genes. the properties of xenopus embryo hsf were examined by dna mobility shift analysis employing a synthetic oligonucleotide corresponding to the proximal hse in the promoter of the xenopus hsp70b gene. heat shock induced activation of hsf binding in xenopus neurulae was not affected by an inhibition of protein synthesis, indica ... | 1992 | 1297327 |
| patterns of cell motility in the organizer and dorsal mesoderm of xenopus laevis. | in a companion paper (shih, j. and keller, r. (1992) development 116, 901-914), we described a sequence of cell behaviors, called mediolateral intercalation behavior (mib), that produces mediolateral cell intercalation, the process that drives convergence and extension of the axial and paraxial mesoderm of xenopus. in this paper, we describe the pattern of expression of mib in the mesoderm during gastrulation, using video image processing and recording of cell behavior in 'shaved', open-faced ex ... | 1992 | 1295744 |
| cell motility driving mediolateral intercalation in explants of xenopus laevis. | in xenopus, convergence and extension are produced by active intercalation of the deep mesodermal cells between one another along the mediolateral axis (mediolateral cell intercalation), to form a narrower, longer array. the cell motility driving this intercalation is poorly understood. a companion paper shows that the endodermal epithelium organizes the outermost mesodermal cells immediately beneath it to undergo convergence and extension, and other evidence suggests that these deep cells are t ... | 1992 | 1295743 |
| the epithelium of the dorsal marginal zone of xenopus has organizer properties. | we have investigated the properties of the epithelial layer of the dorsal marginal zone (dmz) of the xenopus laevis early gastrula and found that it has inductive properties similar to those of the entire spemann organizer. when grafts of the epithelial layer of the dmz of early gastrulae labelled with fluorescein dextran were transplanted to the ventral sides of unlabelled host embryos, they induced secondary axes composed of notochord, somites and posterior neural tube. the organizer epitheliu ... | 1992 | 1295742 |
| the developmental mutants of xenopus. | the 32 developmental mutants found in our laboratory have appeared in the course of the genetic analysis of adult xenopus laevis issued from nuclear transfers, and of their progeny. these experiments originally were devised more than thirty years ago to test whether somatic nuclei had undergone irreversible changes during differentiation or whether they had remained totipotent. in the majority of cases, the mutations were carried by wild-caught imported frogs or their laboratory-bred progeny; ho ... | 1992 | 1295559 |
| [oocyte maturation and activation in the common frog and the clawed toad under the action of divalent cations]. | maturation of rana temporaria and xenopus laevis oocytes was induced by solutions containing mn2+ and co2+ ions. completion of oocyte maturation was estimated by the following criteria: (1) appearance of the maturation promoting factor (mpf) in the oocyte cytoplasm and (2) oocyte capacity to activation and formation of male pronuclei from the injected sperm nuclei. x. laevis oocytes matured under the effect of co2+ ions were shown to contain mpf. oocytes of both species matured under the effect ... | 1992 | 1294929 |
| [a comparative analysis of notochord formation in amphibian embryos]. | we studied the origin, structure, and development of the notochord in pleurodeles waltlii (urodela) and xenopus laevis (anura) embryos. the notochord rudiment is formed in both species at the early gastrula stage as a cluster of polarized chorda-mesoderm cells located along the sagittal plane of the embryo. in pl. waltlii the notochord rudiment is separated from the gastrocoele roof as a result of contraction of apical cell surfaces. the contraction wave spreads forward and backward along cranio ... | 1992 | 1294926 |
| fate of ciliated epidermal cells during early development of xenopus laevis using whole-mount immunostaining with an antibody against chondroitin 6-sulfate proteoglycan and anti-tubulin: transdifferentiation or metaplasia of amphibian epidermis. | xenopus embryonic epidermis changes its cellular composition during development: the appearance of ciliated epidermal cells before hatching is a remarkable characteristic. in this study, the functional change of ciliated cells to mucus-secreting cells was examined with immunocytochemistry using anti-tubulin and anti-chondroitin 6-sulfate (c6s). before hatching, most epidermal cells were labeled with anti-c6s in a granular fashion. immunoelectron microscopy revealed that the anti-c6s-positive str ... | 1992 | 1293075 |
| a tea-insensitive flickering potassium channel active around the resting potential in myelinated nerve. | a novel potassium-selective channel which is active at membrane potentials between -100 mv and +40 mv has been identified in peripheral myelinated axons of xenopus laevis using the patch-clamp technique. at negative potentials with 105 mm-k on both sides of the membrane, the channel at 1 khz resolution showed a series of brief openings and closings interrupted by longer closings, resulting in a flickery bursting activity. measurements with resolution up to 10 khz revealed a single-channel conduc ... | 1992 | 1291683 |
| sequential up-regulation of thyroid hormone beta receptor, ornithine transcarbamylase, and carbamyl phosphate synthetase mrnas in the liver of rana catesbeiana tadpoles during spontaneous and thyroid hormone-induced metamorphosis. | during both spontaneous and thyroid hormone (th)-induced metamorphosis, the rana catesbeiana tadpole undergoes postembryonic developmental changes in its liver which are necessary for its transition from an ammonotelic larva to a ureotelic adult. although this transition ultimately results from marked increases in the activities and/or de novo synthesis of the urea cycle enzymes, the precise molecular means by which th exerts this tissue-specific response are presently unknown. recent reports, u ... | 1992 | 1291156 |
| n-cadherin transcripts in xenopus laevis from early tailbud to tadpole. | cadherins are ca(++)-dependent cell adhesion molecules which play a key role in morphogenesis and histogenesis. two mrnas clones (8 and 9) corresponding to two n-cadherin pseudo-allelic genes are present in xenopus laevis. we report here that these transcripts share a highly homologous coding region but diverge in the non-coding region. we have determined the pattern of n-cadherin expression at the mrna level by in situ hybridization with a riboprobe complementary to the ec5 domain of xenopus n- ... | 1992 | 1286211 |
| translational control by poly(a) elongation during xenopus development: differential repression and enhancement by a novel cytoplasmic polyadenylation element. | one characteristic of oocyte maturation and embryogenesis in xenopus laevis is the activation of translationally repressed (masked) maternal mrnas by cytoplasmic poly(a) elongation. at maturation, poly(a) elongation is controlled by two cis-acting elements in the 3'-untranslated regions (utrs) of responsive mrnas, the hexanucleotide aauaaa and the cytoplasmic polyadenylation element (cpe), consisting of uuuuuau or other similar sequences. to investigate poly(a) elongation and translational activ ... | 1992 | 1285126 |
| identification and developmental expression of the xenopus laevis cystic fibrosis transmembrane conductance regulator gene. | an amphibian homologue of the human cystic fibrosis transmembrane conductance regulator (cftr) gene has been isolated from xenopus laevis by polymerase chain reaction (pcr) amplification. the 4455bp sequence encodes a predicted polypeptide of 1485 amino acids which has an overall homology at the amino acid level of 77% identity and 88% similarity with human cftr. comparison of these evolutionarily diverse cftr sequences has structure-function implications. investigation of the expression of the ... | 1992 | 1284470 |
| spatially restricted expression of fibroblast growth factor receptor-2 during xenopus development. | the fibroblast growth factors (fgfs) play a role in xenopus laevis embryonic development, particularly in the induction of ventral-type mesoderm. we have isolated a full-length cdna from xenopus that we have designated xenopus fibroblast growth factor receptor-2 (xfgfr-2), with significant amino acid sequence similarity to the previously described bek gene (fgfr-2). we expressed the xfgfr-2 cdna in cos1 cells and showed that it functions as an fgf receptor by binding radiolabeled fgf-2. rna gel ... | 1992 | 1284237 |
| the cloning and characterization of a localized maternal transcript in xenopus laevis whose zygotic counterpart is detected in the cns. | we have cloned a cdna (xlan4) from a xenopus laevis oocyte cdna library whose cognate mrna is localized in the animal pole region of full grown oocytes. the cdna can be translated in vitro to produce a predicted size protein of 35 kda and, is also expressed in e. coli as a fusion protein. the conceptual protein encoded by the xlan4 cdna is 17.5% proline rich and possesses several pest sequences found in proteins with short half-lives. the xlan4 mrna is 2.6 kb and during early development its tit ... | 1992 | 1284029 |
| suppression of a ligand operated membrane current by the epileptogenic agent pentylenetetrazol in oocytes of xenopus laevis after injection of rat brain rna. | the effects of the epileptogenic substance pentylenetetrazol (ptz) on ligand operated membrane channels were studied. for this purpose serotonin (5-ht) sensitive channels were expressed in rna injected oocytes of xenopus laevis. with simultaneous application of both substances, the response to 5-ht was reduced and eventually abolished by ptz with increasing concentrations (5-100 mm). a reduction of the 5-ht response also appeared when ptz was applied in various intervals (15 and 240 s) before 5- ... | 1992 | 1283455 |
| ultrastructure of sarcoballs on the surface of skinned amphibian skeletal muscle fibres. | the formation of sarcoballs on the surface of skinned fibres from semitendinosus muscles of xenopus laevis, and the sarcoplasmic reticulum content of the structures, have been studied using conventional electron microscopic techniques and immunoelectron microscopy. examination of the fibres showed many membrane-bound blebs projecting from the surface in areas where vesicles of internal membranes (including sarcoplasmic reticulum, t-tubules and mitochondria) were clustered in interfilament spaces ... | 1992 | 1283395 |
| expression of tenascin mrna in mesoderm during xenopus laevis embryogenesis: the potential role of mesoderm patterning in tenascin regionalization. | in xenopus embryos, the extracellular matrix (ecm) protein tenascin (tn) is expressed dorsally in a very restricted pattern. we have studied the spatial and temporal expression of tn mrna in tailbud-stage embryos by rnaase protection and in situ hybridization using a cdna probe for xenopus tn obtained by pcr amplification. we report that tn transcripts are principally expressed in cells dispersed around the neural tube and notochord as well as in myotome and sclerotome cells. no tn mrna could be ... | 1992 | 1282859 |
| distribution of nonmuscle actin during xenopus laevis development. | using antisera specific for the n-terminal peptides of nonmuscle isoforms of actin we studied these proteins in the developing egg and embryo of xenopus laevis. the antisera did not crossreact with muscle actin and did not react with the other nonmuscle isoform. by immunofluorescence we found a large maternal actin store in the oocyte, in the balbiani body and the nucleoli, respectively. in the blastula, nonmuscle actin was preferentially expressed in the mitotic apparatus of the individual blas ... | 1992 | 1282474 |
| spinal cord and ganglia regeneration in larval xenopus laevis following unilateral ablation. | the experiments were carried out on larvae of xenopus laevis at stage 48 (acc. to nieuwkoop and faber, 1956). two different kinds of experiments were performed. experiment i: unilateral ablation of either a brachial or lumbar segment of the spinal cord and simultaneous removal of the related ganglia. experiment ii: simple unilateral removal of either brachial or lumbar spinal ganglia. the results obtained in experiment i show that not only an extensive restitution of the ablated spinal cord does ... | 1992 | 1281856 |
| muscle-specific expression of srf-related genes in the early embryo of xenopus laevis. | we have isolated two members of the rsrf protein family, sl-1 and sl-2, in xenopus laevis. both proteins contain srf-type dna binding domains and are related to the human protein, rsrfc4. sl-1 constitutes a novel member of the rsrf family whilst sl-2 is similar to human rsrfc4 throughout its length. sl-1 protein recognizes the consensus dna sequence cta(a/t)4tar in vitro and can bind to the same regulatory sites as other a/t-rich sequence-specific binding activities, such as the muscle-specific ... | 1992 | 1281451 |
| functional expression of renal organic anion transport in xenopus laevis oocytes. | secretion of organic anions by the kidney plays a critical role in the elimination of toxic agents from the body. recent findings in isolated membranes and intact tissue have demonstrated the participation of multiple transport proteins in this process. as a first step toward molecular characterization of these proteins through expression cloning, the studies reported below demonstrate functional expression of both fumarate- and lithium-sensitive glutarate and probenecid-sensitive p-aminohippura ... | 1992 | 1281263 |
| decondensation of human sperm nuclei and hp1 protamine degradation from normospermia and asthenospermia in xenopus egg extracts. | the process of human sperm decondensation has been studied in vitro in cytoplasmic extracts prepared from unfertilized xenopus laevis eggs. the chromatin decondensation-recondensation cycle was divided into four stages according to chromatin appearance. spermatozoa from normospermia and asthenospermia were evaluated according to their capacity to reach these stages, and their dna integrity was assessed by acridine orange (ao) staining. we observed a significant difference between normospermia an ... | 1992 | 1280940 |
| time course of glutamate receptor expression in individual oocytes of xenopus laevis after injection of rat brain rna. | 1. the receptor for the neurotransmitter glutamate was functionally expressed in oocytes of xenopus laevis after microinjection of rat brain rna. the functional differentiation of this receptor type was further analyzed. 2. the development of the sensitivity to the agonists showed a time course which was differential for the various ligands in individual oocytes. 3. sensitivity appeared after one day for kainate (ka), after two days for alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (ampa ... | 1992 | 1280546 |
| biochemical and cytological changes associated with expression of deregulated pp60src in xenopus oocytes. | we have examined the effects of xenopus pp60c-src with constitutive kinase activity on the morphology and maturation of xenopus laevis oocytes. when rna encoding this deregulated variant was injected into stage vi oocytes, we observed a gross alteration in the cortex of the oocyte. this alteration involved aggregation of pigment and invagination of the cortex in a large area proximal to the site of injection. this phenomenon was not seen in oocytes injected with rna encoding wild-type pp60c-src. ... | 1992 | 1280323 |
| structure, expression, and functional analysis of a na(+)-dependent glutamate/aspartate transporter from rat brain. | transport systems specific for l-glutamate and l-aspartate play an important role in the termination of neurotransmitter signals at excitatory synapses. we describe here the structure and function of a 66-kda glycoprotein that was purified from rat brain and identified as an l-glutamate/l-aspartate transporter (glast). a glast-specific cdna clone was isolated from a rat brain cdna library. the cdna insert encodes a polypeptide with 543 amino acid residues (59,697 da). the amino acid sequence of ... | 1992 | 1279699 |
| induction of micronuclei in tadpoles of rana temporaria and xenopus laevis by the pyrethroid fastac 10 ec. | the mutagenic properties of the pyrethroid fastac 10 ec were estimated using the micronucleus test in tadpoles of rana temporaria and xenopus laevis. the frequency of erythrocytes with micronuclei was examined in blood smears obtained from animals kept for 14 days in water containing 3 different concentrations of fastac 10 ec. the study was accompanied by a positive control using the known mutagens cyclophosphamide and n-methyl-n-nitrosourea. the results obtained showed that at high concentratio ... | 1992 | 1279413 |
| expression of a glutamate-activated chloride current in xenopus oocytes injected with caenorhabditis elegans rna: evidence for modulation by avermectin. | membrane currents were recorded from xenopus laevis oocytes injected with c. elegans poly(a)+ rna. in such oocytes glutamate activated an inward membrane current that desensitized in the continued presence of glutamate. glutamate-receptor agonists quisqualate, kainate, and n-methyl-d-aspartate were inactive. the reversal potential of the glutamate-sensitive current was -22 mv, and exhibited a strong dependence on external chloride with a 48 mv change for a 10-fold change in chloride. the chlorid ... | 1992 | 1279355 |
| dynamics of cyclic-amp efflux in relation to alpha-msh secretion from melanotrope cells of xenopus laevis. | an important factor in regulating secretion from endocrine cells is the cytoplasmic concentration of cyclic-amp. many regulatory substances are known to either stimulate or inhibit the production of this second messenger through activation of their receptors. in the present study, we have monitored changes in cyclic-amp efflux from melanotrope cells of xenopus laevis in response to established neurochemical regulators of alpha-msh secretion. in vitro superfusion of neurointermediate lobes allows ... | 1992 | 1279339 |
| calcium channel currents in xenopus oocytes injected with rat skeletal muscle rna. | 1. ba2+ currents (iba) through voltage-dependent ca2+ channels were studied in xenopus laevis oocytes injected with heterologous rna extracted from skeletal muscle (skm) of young rats, using the two-electrode voltage clamp technique. 2. with 40 or 50 mm-extracellular ba2+, native oocytes of most frogs displayed iba between -5 and -20 na at 0 mv. however, in 'variant' native oocytes of four frogs, iba exceeded -30 na and reached up to -100 na. in oocytes injected with skm rna, iba of up to -250 n ... | 1992 | 1279162 |
| lipid composition of developing xenopus laevis embryos. | the total lipid content, amount of phospholipid, proportions of major polar and neutral lipid classes, and the overall fatty acid composition were examined in xenopus laevis embryos. no obvious differences were observed in any of the parameters between fertilization and hatching or between eggs produced by different females. the average lipid content per egg was 113 mug, 31.6 mug of which was phospholipid. the major phospholipids were phosphatidylcholine and sphingomyelin. the major fatty acids ... | 1976 | 1276984 |
| the effects of neuraminidase and protamine chloride on potential clamp parameters of the node of ranvier (xenopus laevis). | the effects of neuraminidase and protamine chloride on the ionic currents associated with step changes in membrane potential were studied. neuraminidase (a hydrolase which cleaves glycosidically bound sialic acid) had negligible effects on the permeability properties. the polycation protamine chloride decreased the sodium as well as the potassium currents. the sodium equilibrium potential decreased during the experiments which indicates a gain in internal sodium concentration. the analysis showe ... | 1976 | 1274627 |
| synthesis of human placental lactogen in xenopus oocytes. | oocytes from xenopus laevis were injected with polysomes from normal human term placenta. synthesis of the protein hormone human placental lactogen (hpl) in the oocytes was demonstrated by specific immunoprecipitation with anti-hpl serum. analysis of the immunoprecipitates on sds-polyacrylamide gel revealed one peak, with a migration distance corresponding exactly to that of [14c]-radioacetylated hpl added as a marker. two days after injection the mrna was still able to direct the synthesis of h ... | 1976 | 1272264 |
| the formation of the gonadal ridge in xenopus laevis. ii. a scanning electron microscope study. | this paper studies the surface morphology of the developing gonadal ridge in x. laevis between stages 44 and 49 (nieuwkoop & faber, 1956). during this period the primordial germ cells (pgcs) move laterally from the dorsal mesentery of the gut to the position of the presumptive gonadal ridge. as they do so the coelomic lining cells lateral to the mesentery differentiate into a specialized, longitudinally orientated band, stretching nearly the full length of the dorsal mesentery on each side. the ... | 1976 | 1270976 |
| the formation of the gonadal ridge in xenopus laevis. i. a light and transmission electron microscope study. | in xenopus laevis tadpoles, between stages 44 and 49 (nieuwkoop & faber, 1956), the primordial germ cells (pgcs) migrate from the dorsal mesentery of the gut to the site of the presumptive gd gonadal ridge. this paper describes the process at the light- and electronmicroscope levels. the pgcs in the mesentery, which at first are very large and yolk-laden, seem to lie entirely within the cellular matrix of the mesentery, although this is not obvious in light micrographs. where the pgcs bulge out ... | 1976 | 1270975 |
| in vitro translation and estradiol-17beta induction of xenopus laevis vitellogenin messenger rna. | administration of estradiol-17beta to male xenopus laevis induces synthesis and secretion by the liver of the egg yolk precursor protein vitellogenin. rna extracted from livers of estradiol-17beta-treated xenopus laevis directs the synthesis of the entire 200,000-dalton vitellogenin monomer in a cell-free protein synthesizing system derived from rabbit reticulocytes. vitellogenin synthesized in vitro was isolated and quantitated by indirect immunoprecipitation and identified by comparison to aut ... | 1976 | 1270438 |
| stereological analysis of the effects of 6-hydroxydopamine on the ultrastructure of the melanocyte-stimulating hormone cell of the pars intermedia of the pituitary of xenopus laevis. | 1976 | 1269902 | |
| polyadenylic acid-containing rna and its polyadenylic acid sequences newly synthesized in isolated embryonic cells of xenopus laevis. | 1976 | 1269831 |