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crystalline lipoprotein-phosphoprotein complex in oocytes from xenopus laevis: determination of lattice parameters by x-ray crystallography and electron microscopy. 19751206699
the cement gland of xenopus laevis as an experimental model for embryonic differentiation. iii. histochemical and ultrastructural studies on cement glands differentiated in vitro. 19751211950
mitotic activity of germ cells during normal development of xenopus laevis tadpoles.data on the spatio-temporal pattern of germ cell proliferation in xenopus laevis tadpoles were obtained, tracing the germ cells from the cloacal position forward. this spatial pattern in germ cell distribution and its change during normal development clearly coincided with histological observations of germ gland development. by application of regression lines to the analysis of this complex pattern, an interesting conclusion about the mitotic activity of germ cells was suggested. while the mitot ...19751214114
isolation and structure of a new active peptide xenopsin on rat stomach strip and some biogenic amines in the skin of xenopus laevis. 19751218451
[metaplastic transformation of the tissue of the eye in tadpoles and adult xenopus laevis frogs].the pigment epithelium of the tadpoles and adults x. laevis, as well as of other anurans and cyprinids, is not capable of transformation into the retina without the special influences of agents produced by the retina. when implanting a layer of pigmented epithelium of tadpoles with the bruch's membrane into the cavity of lensless eye of a tadpole, the transformation of pigment epithelium into retina proceeded in 40% of cases and when implanting the pigment epithelium of adults without the bruch' ...19751230674
effects of 5-bromodeoxyuridine on the development of xenopus laevis. ii. stages of differentiation. 19751232721
effects of 5-bromodeoxyuridine on the development of xenopus laevis eggs. i. early stages of development. 19751233854
excitatory and depressant effects of dieldrin and aldrin-transdiol in the spinal cord of the toad (xenopus laevis).an investigation was made into the action of the insecticide dieldrin and one of its metabolites, aldrin-transdio, on the isolated spinal cord of the toad, xenopus laevis. conventional electrophysiological techniques were used for stimulating and recording of dorsal and ventral spinal roots. an augmentation of polysynaptic reflex activity along with a marked reduction of orthodromic postsynaptic inhibition could be demonstrated in preparations isolated from dieldrin-poisoned animals. however, ap ...19751234759
melatonin content of cat cerebrospinal fluid and blood following intravenous injection of melatonin as measured by xenopus laevis skin melanophore test.melatonin content of the cerebrospinal fluid (csf), serum and choroid plexus was measured in untreated and melatonin-injected cats using the xenopus laevis melanophore-contracting bioassay. csf and choroid plexus had a considerable melanophore contracting activity in the untreated animals. intravenously injected melatonin considerably enhanced the melanophore-contracting activity of the csf and choroid plexus. two hours later, melatonin was still present at high concentrations in these tissues, ...19751235454
aster formation in eggs of xenopus laevis. induction by isolated basal bodies.we have assayed various materials for their ability to induce aster formation by microinjection into unfertilized eggs of xenopus laevis. we have found that purified basal bodies from chlamydomonas reinhardtii and tetrahymena pyriformis induce the formation of asters and irregular cleavage furrows within 1 h after injection. other microtubule structures such as flagella, flagellar axonemes, cilia, and brain microtubules are completely ineffective at inducing asters or cleavage furrows in unferti ...19751236852
studies on maturation in xenopus laevis oocytes. iii. energy production and requirements for protein synthesis.the following results were obtained: 1) the oxygen comsumption of progesterone-stimulated x. laevis oocytes increases at the time of germinal vesicle (gv) breakdown. 2) continous treatment with 1 mm kcn, 1 mm and 0.1 mm dnp completely inhibits gv breakdown. 3) pretreatment experiments with kcn, dnp and cycloheximide show that binding of progesterone to the plasma membrane and the specific hormone receptor requires neither energy, nor protein synthesis. 4) 1 h pulses of dnp (1mm) or cycloheximide ...19751237439
the effect of u.v. irradiation of the vegetal pole of xenopus laevis eggs on the presumptive primordial germ cells.the initial effect of u.v. irradiation of the vegetal pole was to inhibit cleavage in the vegetal hemisphere although karyokinesis was not substantially affected. in this way a syncytium formed in the vegetal hemisphere which broke down into individual cells some time between morula and late blastula. the movement of the germ plasm from the peripheral cortical regions into the interior of the egg was not appreciably delayed although aggregation of the germ plasm did not take place until the indi ...19751237530
in vitro differentiation of a homogeneous cell population--the epidermis of xenopus laevis.a simple culture technique is described for obtaining homogeneous populations of differentiating epidermal cells from adult amphibian skin. this population of cells continues its normal differentiation, namely keratinization, in vitro. by the third day of culture more than 99-9% of the cells in the population contain immunoreactive keratin. during the next 5-7 days of culture these cells synthesize increasing amounts of a tissue-specific keratin-like protein until this protein constitutes more t ...19751237533
circular ribosomal dna and ribosomal dna: replication in somatic amphibian cells.pulse labelled rdna from cultured somatic cells of xenopus laevis was examined by electron microscope autoradiography. the pattern of replication closely resembles that of bulk chromosomal dna and differs considerably from rdna synthesis during amplification in the oocyte. - about 0.15% of the rdna molecules in the purified preparations were circular. the presence of interlocked circles of equal size indicates that the circles are not in vitro cyclization artefacts, but may represent free rrna g ...19751238239
effects of differences in mitotic activity, stage of cell cycle, and degree of specialization of donor cells on nuclear transplantation in xenopus laevis. 19751238302
intermolecular renaturation of hairpin loops leads to stable and specific aggregates of 28-s rrna and precursor rrnas from xenopus laevis.under certain extraction conditions, 28-s rrna of xenopus laevis can form specific dimers by intermolecular renaturation of a particular hairpin loop near the b end of the molecules. this was demonstrated by electron microscopy of isolated aggregates under conditions where rrna shows a reproducible pattern of secondary structure. in 50% formamide, 15 mm sodium chloride, 1.5 mm trisodium citrate, ph 7.0, the aggregates dissociate into their monomers at a temperature (61 degrees c) at which the mo ...19751239380
inhibitor of ribosomal rna synthesis in xenopus laevis embryos. iv. the release of inhibitor from cultured cells. 19751239392
inhibitor of ribosomal rna synthesis in xenopus laevis embryos. v. inability of inhibitor to repress 5s rna synthesis. 19751239394
[heat production and respiration of the oocyte of xenopus laevis l. in various stages of oogenesis].the data are given on the respiration and heat production intensity in the x. laevis oocytes by which the value and patterns of change of psiu-function (function of bound dissipation) during oogenesis are calculated. all 3 values were shown to decrease rapidly from the stage of previtellogenesis till the stage of mature oocyte what agrees with the thermodynamic theory of development.19751241800
nature of progesterone action on amino acid uptake by isolated full-grown oocyte of xenopus laevis.l-leucine uptake into full-grown oocytes of xenopus laevis is a saturable process which is na+ dependent and presumably coupled to na+ gradient. our results indicate that progesterone (10(-6) m) blocks abruptly, around the germinal vesicle breakdown, the saturable transport of l-leucine. p-chloromercuribenzoate (10(-4) m) induces maturation and after a short lag of time strongly inhibits l-leucine uptake. cycloheximide prevents progesterone-induced maturation and permeability changes.19761247560
in situ hybridization of "nick-translated" 3h-ribosomal dna to chromosomes from salamanders.a technique is described for preparation of 3h-labelled dna by nick-translation employing deoxyribonuclease i and dna polymerase i. the labelled dna can be obtained in high yield with specific activities of 10(6) cpm/mug or more. ribosomal dna, isolated from ovaries of young xenopus laevis, and whole dna from plethodon cinereus were labelled in this way. the rdna was used for in situ hybridization to meiotic chromosomes from p. cinereus, p. vehiculum and p. dunni. autoradiographs of in situ hybr ...19761248332
31p nuclear-magnetic-resonance studies on the developing embryos of xenopus laevis.the concentrations of nucleoside triphosphate, inorganic phosphate and the yolk proteins, phosvitin and lipovitellin, have been monitored in living embryos of xenopus laevis by 31p nuclear magnetic resonance (nmr) spectroscopy. the nucleoside triphosphate levels remain relatively constant at about 3.5-4.5 nmol/embryo at least until the 'spontaneous movement' stage of development. by the swimming tadpole stage an inorganic phosphate resonance representing about 30 nmol/embryo becomes evident in t ...19761248465
characterization of polysomes from xenopus liver synthesizing vitellogenin and translation of vitellogenin and albumin messenger rna's in vitro.1. conditions are described for the isolation of polysomes from the liver of xenopus laevis. the method involves homogenization of liver in 0.2 m tris-hcl ph 8.5, treatment with 2% triton x-100 and subsequent sucrose density gradient fractionation of polysomes from a 10000 x g supernatant. 2. vitellogenin synthesis was induced in male xenopus liver by oestradiol treatment. polysomes were isolated and vitellogenin-synthesizing polysomes characterized by their association with monospecific 125 i- ...19761248478
incorporation of (5-3h) uridine into ribonucleotide pools and rna during thyroxine-induced metamorphosis of xenopus laevis tadpoles.incorporation of [3h] uridine into the ribonucleoside triphosphates utp and ctp, total rna, and nuclear and cytoplasmic rna was followed in xenopus laevis tadpole liver during thyroxine (t4)-induced metamorphosis. pool sizes of utp and ctp were found to remain unchanged, although turnover the ribonucleoside triphosphates was found to be greatly stimulated after 4 days of hormone treatment. the time course of labeling of the 40-s pre-rrna was very similar to that of utp in both thyreostatic and t ...19761248666
progesterone biosynthesis and metabolism by ovarian follicles and isolated oocytes xenopus laevis. 19761252564
histogenesis of retina in the clawed frog with implications for the pattern of development of retinotectal connections. 19761252942
electron microscope analysis of amplifying ribosomal dna from xenopus laevis. 19761253845
in vivo and in vitro hormonal effects on the metabolism of immature oocytes of xenopus laevis. 19761254084
the ionic basis of the resting potential and a slow depolarizing response in rohon-beard neurones of xenopus tadpoles.1. rohon-beard cells in the spinal cord of xenopus laevis tadpoles have been studied in animals 4-days to 2-weeks-old (nieuwkoop & faber, 1956, stages 45-49). these neurones have an unusually large resting membrane potential of -88 mv, in ringer solution containing 3-0 mm k+. 2. their resting potential (r..) depends on the concentration gradient of k+ across the cell membrane. these cells follow the prediction of the nernst equation for a k+-selective electrode, down to external k+ concentration ...19761255512
low resistance junctions between mesoderm cells during development of trunk muscles.1. electrical connexions between mesoderm cells have been examined during the formation of somites in xenopus laevis, bombina orientalis and ambystoma mexicanum. 2. in xenopus the resting potentials of presumptive myotome cells (-65 + 2 mv, s.e. of mean) and somite muscle cells (-65 +/- 0-6 mv s.e. of mean) were 40 mv, greater than dermatome cells (-25 +/- 0-6 mv, s.e. of mean). similar differences were found in bombina and ambystoma. 3. in all three species cells of the dermatome layer of the m ...19761255515
iodination of xenopus laevis histone f2a1 in chromatin.the reaction of calf thymus and xenopus laevis histones with radioactive iodine has been studied under various conditions that affect chromatin structure. all histones from both species contain at least one tyrosine residue and, in a denaturing solvent, all the the histones react with iodine. histone f2a1 has been studied in detail. calf thymus f2a1 is known to contain four tyrosyls and all four react with iodine. in high voltage paper electrophoresis, the tyrosine-containing peptides from calf ...19761259948
protein incorporation by isolated amphibian oocytes. v. specificity for vitellogenin incorporation.macromolecules of vitellogenin were sequestered by xenopus laevis oocytes 20-50 times (on a molar basis) more rapidly than other proteins tested. selectivity for vitellogenin did not appear to involve molecular size or charge. the km for vitellogenin incorporation was at least several orders of magnitude less than that for bovine serum albumin (bsa). at concentrations less than 10 mg-ml-1, bsa did not measurably compete with vitellogenin; a slight, apparent competition observed above a bsa conce ...19761262394
morphology and kinetics of spermatogenesis in xenopus laevis.the light microscopic characteristics of spermatogenic stages of the germ cell line in the anuran, xenopus laevis, have been described as they appear in both nuclear squash preparations and plastic embedded thick sections of intact testes. tritiated thymidine autoradiography was employed to unequivocally identify stages. using this methodology, it was determined that the premeiotic dna synthetic period occurs in a cell which is morphologically indistinguishable from a late secondary spermatogoni ...19761262821
nucleotide sequences within the ribosomal ribonucleic acids of hela cells, xenopus laevis and chick embryo fibroblasts. 19761263259
oogenesis in xenopus laevis (daudin). iii. localization of negative charges on the surface of developing oocytes. 19761263301
genomic transcriptional activity and the structure of chromatin.nucleic acid hybridisation has shown that micrococcal nuclease-derived chromatin subunits from the cells of xenopus laevis contain fragments of ribosomal 28s, 18s and 5s rnas within the population of 200 base-pair pieces of dna. subunits from cultured embryonic cells actively transcribing ribosomal rna contain only 70-74% of the cistrons present in undigested wild-type dna, while subunits from adult erythrocytes not active in rna transcription contain close to 90% of the ribosomal cistrons in na ...19761264202
utrastructure of the cement gland of xenopus laevis.to establish a morphological baseline for experimental studies of differentiation using the cement gland as a model, the following observations are added to those on record. the elongated cells of xenopus laevis cement glands have an internal organization displaying five distinct zones differing in structure and specialized function. the apical zone contains packed secretion vesicles apparently belonging to two different types. the transit zone appears to be devoid of major biosynthetic activity ...19761267966
analysis of moving supernumerary limbs of xenopus laevis. 19761269564
polyadenylic acid-containing rna and its polyadenylic acid sequences newly synthesized in isolated embryonic cells of xenopus laevis. 19761269831
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. 19761269902
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 ...19761270438
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 ...19761270975
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 ...19761270976
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 ...19761272264
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 ...19761274627
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 ...19761276984
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 ...19921279162
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 ...19921279339
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 ...19921279355
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 ...19921279413
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 ...19921279699
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. ...19921280323
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 ...19921280546
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 ...19921280940
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 ...19921281263
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 ...19921281451
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 ...19921281856
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 ...19921282474
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 ...19921282859
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 ...19921283395
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- ...19921283455
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 ...19921284029
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 ...19921284237
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 ...19921284470
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 ...19921285126
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- ...19921286211
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 ...19921291156
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 ...19921291683
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 ...19921293075
[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 ...19921294926
[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 ...19921294929
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 ...19921295559
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 ...19921295742
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 ...19921295743
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 ...19921295744
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 ...19921297327
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 ...19921299267
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 ...19921299357
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 ...19921301081
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 ...19921302268
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 ...19921303156
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 ...19921303948
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 ...19921306683
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 ...19921308203
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 ...19921309236
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 ...19921309778
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 ...19921309805
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] ...19921309810
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 ...19921310011
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 ...19921312036
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 ...19921312137
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 ...19921312256
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 ...19921312717
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 ...19921312862
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 ...19921313113
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 ...19921313170
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 ...19921313186
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 ...19921313188
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 ...19921315637
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 ...19921315678
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