Publications
| Title | Abstract | Year(sorted ascending) Filter | PMID Filter |
|---|
| activin as a cell differentiation factor. | activin, originally discovered as a polypeptide hormone that is capable of stimulating follicle-stimulating hormone secretion from pituitary cells in vitro, has recently been found to have a much wider range of biological activities. there are a number of reports of activin action as a cell differentiation factor on various types of cells rather than as a modulator of hormone secretion, as predicted initially, based on its structural similarity to transforming growth factor-beta. studies of the ... | 1990 | 1966558 |
| expression of class ii major histocompatibility complex antigens on adult t cells in xenopus is metamorphosis-dependent. | class ii major histocompatibility complex (mhc) antigens are expressed predominantly on b lymphocytes and macrophages of tadpoles of the south african clawed frog, xenopus laevis, as is the pattern in lymphocyte populations of most mammals. however, unlike most mammals, young postmetamorphic frogs show expression of class ii mhc antigens on a high proportion of thymocytes and most peripheral t and b lymphocytes. using the j-strain of xenopus and the anticlass ii monoclonal antibody, 14a2, we hav ... | 1990 | 1967017 |
| npxy, a sequence often found in cytoplasmic tails, is required for coated pit-mediated internalization of the low density lipoprotein receptor. | rapid internalization of the cell surface low density lipoprotein (ldl) receptor requires the first 22 amino acids of the cytoplasmic domain (residues 790-811), which must include an aromatic residue at position 807. in the human ldl receptor, this position is part of a tetrameric sequence, npvy. a similar tetramer, npxy (where x stands for any amino acid), is conserved in ldl receptors from six species (including xenopus laevis) and in two members of the ldl receptor gene family, human ldl rece ... | 1990 | 1968060 |
| a slowly inactivating potassium current in native oocytes of xenopus laevis. | membrane currents were recorded in voltage-clamped oocytes of xenopus laevis in response to voltage steps. we describe results obtained in oocytes obtained from one donor frog, which showed an unusually large outward current upon depolarization. measurements of reversal potentials of tail currents in solutions of different k+ concentration indicated that this current is carried largely by k+ ions. it was strongly reduced by extracellular application of tetraethylammonium, though not by ba2+ or 4 ... | 1990 | 1968644 |
| [modification of pattern formation along the anterior-posterior axis by introduction of excess amount of homeobox mrnas in xenopus laevis embryos]. | 1990 | 1969669 | |
| expression of rat liver canalicular sulfate carrier in xenopus laevis oocytes. | poly(a)+ rna (mrna)extracted from rat liver was injected into xenopus laevis oocytes and the expression of sulfate transport was determined by measuring [35s] sulfate uptake. compared to water-injected oocytes, which exhibited virtually no sulfate uptake, injection of rat liver mrna resulted in a time- and dose-dependent increase in uptake of sulfate. depending on the method used for the isolation of the mrna, sulfate uptake was stimulated after injection (40 ng after 6 days) between 8- and 72-f ... | 1990 | 1970568 |
| amphibian experimental systems: developmental neurobiology and behavioral endocrinology in the clawed frog, xenopus laevis. | 1990 | 1974779 | |
| xenopus laevis oocytes injected with mammalian pituitary mrna as a model system for study of thyrotropin-releasing hormone action. | 1990 | 1974807 | |
| neural expression of the xenopus homeobox gene xhox3: evidence for a patterning neural signal that spreads through the ectoderm. | the xenopus laevis homeobox gene xhox3 is expressed in the axial mesoderm of gastrula and neurula stage embryos. by the late neurula-early tailbud stage, mesodermal expression is no longer detectable and expression appears in the growing tailbud and in neural tissue. in situ hybridization analysis of the expression of xhox3 in neural tissue shows that it is restricted within the neural tube and the cranial neural crest during the tailbud-early tadpole stages. in late tadpole stages, xhox3 is onl ... | 1990 | 1974841 |
| genes and mechanisms involved in early embryonic development in xenopus laevis. | our laboratory is studying genes involved in the regulation of the balance between cell growth and differentiation during embryonic development in xenopus. we have analyzed the developmental expression of the proto-oncogenes c-myc, and kiras 2b, the proliferating cell nuclear antigen (pcna), and the tumor suppressor gene p53. these genes, usually expressed during cell proliferation, are expressed in the oocyte in large quantities, but the majority of their maternal rnas are degraded by the gastr ... | 1990 | 1975504 |
| glycine stimulates calcium-independent release of 3h-gaba from isolated retinas of xenopus laevis. | a perfusion system was used to monitor the release of [3h]-gaba from isolated retinas of xenopus laevis. measurable release was stimulated by glycine at concentrations as low as 200 microm. glycine-stimulated release was blocked by strychnine, and was not reduced in "calcium-free" ringer's solution (0 ca2+/20 mm mg2+). glutamate also stimulated calcium-independent release, using concentrations as low as 100 microm. in contrast, release stimulated by 25 mm potassium was reduced by 80% in calcium- ... | 1990 | 1980204 |
| a slow and a fast secretory compartment of pomc-derived peptides in the neurointermediate lobe of the amphibian xenopus laevis. | 1. peptide release from the neurointermediate lobe of xenopus laevis has been studied using dual pulse-chase incubation, superfusion and hplc techniques. 2. lobes release pulse-labelled material in two phases, the first phase lasting about 6 hr, the second persisting up to 14 hr. 3. in both phases similar, pomc-derived peptides are released. their release can be inhibited by dopamine. 4. when release during the first phase is inhibited, newly synthesized peptides are shunted into the second rele ... | 1990 | 1980877 |
| the xenopus laevis hox 2.1 homeodomain protein is expressed in a narrow band of the hindbrain. | the expression pattern of the xenopus homeodomain protein hox 2.1 during development was determined using an affinity-purified antibody directed against a carboxyterminal peptide. nuclear staining was detected in a very narrow band of the hindbrain. this pattern was compared to that of the previously described xenopus gene xihbox 1 in serial sections and found to be more anterior than the xihbox 1 long protein expression but overlapping with that of the short protein. xenopus hox 2.1 protein exp ... | 1990 | 1981142 |
| movements of the large intestine in the anuran larvae, xenopus laevis. | 1. the contractile behavior of the large intestine of xenopus laevis tadpoles was studied. 2. the large intestine is divided into a colon and rectum, and shows three types of movements: rhythmic ascending (antiperistaltic) waves of contraction originating at the anal end of the large bowel, rhythmic longitudinal contractions in the rectum and colon, and irregular contractions. the first two patterns occur in the large bowel in situ and thus appear mature. the last one occurred only in older prep ... | 1990 | 1981343 |
| analysis of the mechanism of isoniazid-induced developmental toxicity with frog embryo teratogenesis assay: xenopus (fetax). | the developmental toxicity of isoniazid (inh) and the metabolites acetylhydrazide (ah) and isonicotinic acid (ina) were examined with the frog embryo teratogenesis assay-xenopus (fetax). late xenopus laevis blastulae were exposed to inh, ah, and ina for 96 h in two separate static-renewal tests with and without the presence of three differently induced metabolic activation systems (mas). the mas consisted of uninduced, aroclor 1254-induced, and inh-induced rat liver microsomes. addition of the i ... | 1990 | 1982910 |
| preparation and rapid resolution of xenopus phosvitins and phosvettes by high-performance liquid chromatography. | the presence of acidic phosivitins phosvettes in xenopus laevis yolk platelets and their purification by (nh4)2so4 precipitation of associated lipovitellin were documented by polyacrylamide gel electrophoresis followed by staining with stains-all. procedures were further developed to resolve the various entities present in the crude phosvitin/phosvette fraction by size-exclusion, anion-exchange, and hydrophobic interaction chromatography, using a pharmacia fplc system, and their resolution was d ... | 1990 | 2077049 |
| the vocal motor neurons of xenopus laevis: development of sex differences in axon number. | sex differences in the number of muscle fibers in the larynx of clawed frogs (xenopus laevis) develop after metamorphosis. in order to examine possible contributions of neural innervation to this process, we prepared sections of the laryngeal nerve from tadpole stage 56, when the sexes can first be distinguished, through adulthood, and counted axons on electron micrographs. the adult number of axons is achieved by a sexually differentiated pattern of axonal addition and loss. axon numbers are hi ... | 1990 | 2077103 |
| downregulation of the translation elongation factor 2 kinase in xenopus laevis oocytes at the final stages of oogenesis. | phosphorylation of translation elongation factor 2(eef-2) by a specific ca2+/calmodulin-dependent eef-2 kinase plays an important role in the regulation of protein synthesis in mammalian cells. we show here that an eef-2 kinase similar to the mammalian enzyme is present in tissues of the amphibian xenopus laevis. we investigated changes in the activity of eef-2 kinase in extracts of xenopus oocytes at different stages of oogenesis. the eef-2 kinase activity was constant from stage i to stage iv ... | 1990 | 2078557 |
| regional neural induction in xenopus laevis. | during development of the xenopus embryo, the formation of the nervous system depends on an inductive interaction between mesoderm and ectoderm. the result is a neural tube that is regionally differentiated along the anterior-posterior axis from forebrain to spinal cord. the discovery of genes whose transcripts can be used as molecular markers for different regions of the nervous system has permitted reassessment of the existing theories of neural tissue formation. although the neural inducing m ... | 1990 | 2080914 |
| the mechanics of notochord elongation, straightening and stiffening in the embryo of xenopus laevis. | we have examined the biomechanical development of the notochord of xenopus early tail-bud embryos by: (1) quantifying morphological and mechanical changes in the embryo during stages 20-28, and (2) conducting manipulative experiments to elucidate mechanical roles of various components of the notochord. the notochord, which is composed of a stack of flat cells surrounded by a connective tissue sheath, elongates dramatically and begins straightening between stages 21 and 25. at this time the fiber ... | 1990 | 2081454 |
| histones in xenopus laevis' early development: the race against time. | using cloned histone gene variants, the expression of three types of histone gene clusters was studied at the rna level during early development in xenopus laevis. for each histone class the number of mrna molecules per embryo strongly decreased upon ovulation and steadily increased during early development, with a slight decrease at the neurula stage. variation of the stringency of hybridization revealed that none of the histone genes probed is specifically and uniquely expressed at any time po ... | 1990 | 2082927 |
| extracellular matrix components prevent neural differentiation of disaggregated xenopus ectoderm cells. | neuralization (archencephalic brain formation) takes place after dissociation and delayed reaggregation of animal caps of early gastrula without inducer (grunz, h. and l. tacke: cell differ. dev. 28, 211-218 (1989)). this autoneuralization can be prevented by the cell supernatant from dissociated ectoderm of xenopus laevis, which contains extracellular matrix components. after phenol extraction of the supernatant, the aqueous phase does no longer show inhibitory activity. it can be concluded fro ... | 1990 | 2083395 |
| tissue interactions involving cranial neural crest in cartilage formation in xenopus laevis (daudin). | deletion experiments in neurula stage embryos of xenopus laevis provide an approximate anuran fate map of the chondrogenic cranial neural crest which is similar to maps produced for other vertebrates. crest cells in the transverse (rostral) neural fold do not contribute to the skeleton; other cranial crest cells contribute to the larval cranial and visceral skeletons in a rostral to caudal sequence. grafting experiments show that contact with stomodeal (pharyngeal) endoderm is necessary to elici ... | 1990 | 2083397 |
| two types of intrinsic muscarinic responses in xenopus oocytes. ii. hemispheric asymmetry of responses and receptor distribution. | fully grown xenopus laevis oocytes display marked morphological asymmetry. the giant cell is divided into animal (pigmented) and vegetal hemispheres. we have developed methodology aimed at easy determination of hemispheric responses to the application of acetylcholine (ach) and determination of the distribution of muscarinic receptors. oocytes of common donors exhibit muscarinic responses that are similar when either the animal or the vegetal hemisphere of the cell is exposed to ach. oocytes of ... | 1990 | 2084615 |
| ferromagnetic isolation of endosomes: a novel method for subcellular fractionation of xenopus oocytes. | a novel method has been developed using ferric particles to label endosomes, and to achieve magnetic sorting of the various endocytic compartments involved in lipoprotein uptake into cells. ferric particles conjugated to a receptor-recognized ligand are bound to coated membrane pits and become internalized into the cytoplasm inside coated vesicles. after apparent fusion of the vesicles to tubular endosomes, the conjugates accumulate and finally discharge into multivesicular endosomes. pulse-chas ... | 1990 | 2085692 |
| a monoclonal antibody against the human il-2 receptor binds to paraformaldehyde-fixed but not viable frog (xenopus) splenocytes. | others have reported that a monoclonal anti-human il-2 receptor antibody (anti-cd25) specifically binds a membrane receptor on xenopus laevis pha-induced and paraformaldehyde-fixed splenic blasts. in this paper, we present evidence suggesting that this binding is an artifact of membrane damage. specifically, significant binding of anti-cd25 could only be achieved if the lymphoblasts were acid-washed and/or paraformaldehyde-fixed prior to being incubated with the fluoresceinated antibody. for exa ... | 1990 | 2086450 |
| microinjection of alpha-toxin from clostridium novyi type a promotes meiotic maturation in xenopus laevis oocytes. | microinjection of purified alpha-toxin into xenopus laevis oocytes induced meiotic maturation provided insulin was present in the medium. induction of maturation as indicated by breakdown of the germinal vesicle depended on the amount of intracellular alpha-toxin (with a detection limit of 2 ng/oocyte) and on the concentration of insulin. the hormone concentrations used were inactive when given alone and so was alpha-toxin (1 micrograms/ml) applied from the outside. the results demonstrate an in ... | 1990 | 2087699 |
| hormone-sensitive stages in the sexual differentiation of laryngeal muscle fiber number in xenopus laevis. | the number of muscle fibers in the vocal organ of the adult male african clawed frog, xenopus laevis, exceeds that of adult females. this sex difference is the result of rapid fiber addition in males between the end of metamorphosis, post-metamorphic stage 0 (pm0) and pm2. at pm0, male and female frogs have similar numbers of laryngeal muscle fibers. males then add more muscle fibers than females and achieve an adult value that is 1.7 times the female number. males castrated at pm0 have the same ... | 1990 | 2088715 |
| correlated onset and patterning of proopiomelanocortin gene expression in embryonic xenopus brain and pituitary. | to identify cellular interactions that underlie the spatially appropriate transcription of neural genes, we characterized the embryonic development of proopiomelanocortin (pomc) gene expression in xenopus laevis using in situ hybridization histochemistry. this has led to the establishment of a unique model system for studying how a neuropeptide gene program in four distinct cell groups is set up in pituitary and forebrain. the embryonic onset and patterning of pomc expression was found to be spa ... | 1990 | 2088717 |
| the pattern of early cleavage of the marsupial frog gastrotheca riobambae. | comparison of early development of the marsupial frog gastrotheca riobambae with xenopus laevis suggests that the cleavage pattern of xenopus and the tight coupling of events at the midblastula transition are features of the accelerated development of small amphibian eggs with aquatic reproduction, rather than generalized features of amphibian development. the large eggs of the marsupial frog gastrotheca riobambae not only display an atypical holoblastic pattern of cleavage and a very slow rate ... | 1990 | 2088720 |
| expression of the n-myc proto-oncogene during the early development of xenopus laevis. | the n-myc proto-oncogene is expressed in a wide range of tissues during mammalian embryogenesis. this observation, along with the oncogenic capacity of this gene, has led to the suggestion that n-myc plays an important role in early development. however, due to the complexity of the expression pattern and the difficulty of manipulating mammalian embryos, little progress has been made towards understanding the developmental function of this gene. to enable a more detailed analysis of the role of ... | 1990 | 2088727 |
| post-transcriptional regulation of ornithine decarboxylase in xenopus laevis oocytes. | the level at which ornithine decarboxylase expression is regulated in growing oocytes has been investigated. immunoprecipitation of the in vivo labelled proteins showed that ornithine decarboxylase accumulated less rapidly in stage iv oocytes than in previtellogenic stage i + ii oocytes. quantitative northern analysis showed that ornithine decarboxylase mrna is abundant in oocytes (about 8 x 10(8) transcripts/cell) and this number does not significantly change during oogenesis. polysome analysis ... | 1990 | 2088731 |
| isolation of a vegetalizing inducing factor after extraction with acid ethanol. concentration-dependent inducing capacity of the factor. | a vegetalizing factor has been isolated from chicken embryos by an improved method. the factor is extracted with acid/ethanol and finally purified by four consecutive steps of reversed phase hplc. the molecular mass is about 25 kda. the factor dissociates after reduction with dithiothreitol into two subunits of about 13 kda. the factor was tested on triturus alpestris by the implantation method, and on isolated ectoderm of xenopus laevis in solution. the factor induces as the crude fractions all ... | 1990 | 2090330 |
| ultrastructural comparison between regenerating and developing hindlimbs of xenopus laevis tadpoles. | hindlimbs of xenopus laevis tadpoles at stages 50 to 55 of embryonic development were amputated in order to study the fine structure associated with ontogenetic decline in regenerative ability of this anuran. regenerating hindlimbs were compared with their contralateral developing limb so as to determine the similarities and differences in ectodermal-mesenchymal ultrastructural relationships in these systems. prior to stage 53, mesenchymal cells in regenerating limbs, as well as mesenchyme cells ... | 1990 | 2092016 |
| protein kinase c acts downstream of calcium at entry into the first mitotic interphase of xenopus laevis. | transit into interphase of the first mitotic cell cycle in amphibian eggs is a process referred to as activation and is accompanied by an increase in intracellular free calcium [( ca2+]i), which may be transduced into cytoplasmic events characteristic of interphase by protein kinase c (pkc). to investigate the respective roles of [ca2+]i and pkc in xenopus laevis egg activation, the calcium signal was blocked by microinjection of the calcium chelator bapta, or the activity of pkc was blocked by ... | 1990 | 2100203 |
| a cytoplasmic determinant for dorsal axis formation in an early embryo of xenopus laevis. | in xenopus laevis, dorsal cells that arise at the future dorsal side of an early cleaving embryo have already acquired the ability to cause axis formation. since the distribution of cytoplasmic components is markedly heterogeneous in an egg and embryo, it has been supposed that the dorsal cells are endowed with the activity to form axial structures by inheriting a unique cytoplasmic component or components localized in the dorsal region of an egg or embryo. however, there has been no direct evid ... | 1990 | 2100253 |
| inhibition of proteoglycan synthesis eliminates left-right asymmetry in xenopus laevis cardiac looping. | the heart of any vertebrate is formed from an apparently symmetric cardiac tube that loops consistently in the same direction along the left-right axis of the embryo. in the amphibian xenopus laevis, inhibition of proteoglycan synthesis by p-nitrophenyl-beta-d-xylopyranoside during a narrow period of development from late gastrula to early neurula specifically eliminated the looping of the cardiac tube. most of the proteoglycans synthesized during this period were heparan sulfate proteoglycans. ... | 1990 | 2100995 |
| identification of a soluble precursor complex essential for nuclear pore assembly in vitro. | we analysed the soluble form in which the nuclear pore complex protein p68 is stored in xenopus laevis eggs and its involvement in pore complex assembly processes. we have shown previously that p68, which is the major wheat germ agglutinin (wga)-binding glycoprotein of nuclear pore complexes from xenopus oocytes, is located in the pore channel and participates in mediated transport of karyophilic proteins. using a monoclonal antibody directed against p68 (pi1) we removed this protein from xenopu ... | 1990 | 2101351 |
| characterization of a second highly conserved b-type lamin present in cells previously thought to contain only a single b-type lamin. | previous analyses of the nuclear lamina of mammalian cells have revealed three major protein components (lamins a, b and c) that have been identified by protein sequence homology as members of the intermediate filament (if) protein family. it has been claimed that mammalian cells contain either all three lamins or lamin b alone. using monoclonal antibodies specific for b-type lamins and cdna cloning we identified a second major mammalian b-type lamin (murine lamin b2), thus showing that lamin co ... | 1990 | 2102682 |
| cytostatic factor (csf) activity in cytosols extracted from xenopus laevis eggs. | cytostatic factor (csf), found in the cytoplasm of unfertilized eggs of amphibians, causes metaphase arrest when microinjected into cleaving blastomeres. although csf from rana pipiens eggs has been extracted and characterized, little is known about csf extracted from eggs of other species. we investigated the conditions required to preserve csf activity in cytosols extracted from xenopus laevis eggs and found that it was necessary to expose the eggs to co2 prior to extraction and that the extra ... | 1990 | 2105220 |
| talin and vinculin in the oocytes, eggs, and early embryos of xenopus laevis: a developmentally regulated change in distribution. | we have investigated the expression and distribution of talin and vinculin in the oocytes, eggs, and embryos of xenopus laevis. antibodies to the previously characterized avian proteins stain several different xenopus cell types identically by immunofluorescence: adhesion plaques of cultured kidney (a6) cells, the cell peripheries of oviduct cells, and the postsynaptic neuromuscular junctions of tadpole tail muscle fibers. these antibodies also identify cognate proteins of the appropriate sizes ... | 1990 | 2105901 |
| eleven distinct vh gene families and additional patterns of sequence variation suggest a high degree of immunoglobulin gene complexity in a lower vertebrate, xenopus laevis. | lower vertebrate species, including xenopus laevis, exhibit restricted antibody diversity relative to higher vertebrates. we have analyzed more than 180 vh gene-containing recombinant clones from an unamplified spleen cdna library by selective sequencing of jh and ch positive clones following iterative hybridization screening with family-specific vh probes, 11 unique families of vh genes, each associated with a unique genomic southern blot hybridization pattern, are described and compared. consi ... | 1990 | 2110243 |
| effects of divalent cations on the frequency of spontaneous action potentials from the lateral line organ of xenopus laevis. | the effect of superfusion of the internal surface of the skin of xenopus laevis with saline containing co2+, ca2+, mg2+, or ba2+, on the frequency of spontaneous action potentials of the lateral line nerve, was studied to investigate the role of extracellular ca2+ in spontaneous neural activity. addition of divalent cations to frog saline, either singly or as a mixture of two different ions, produced concentration-dependent suppression of spontaneous rate. the rank order of potency for suppressi ... | 1990 | 2110846 |
| structural modifications induced by the mtdbp-c protein in the replication origin of xenopus laevis mitochondrial dna. | the structure of the non-coding region of xenopus laevis mitochondrial dna has been studied by electron microscopy analysis of dna molecules end-labelled with streptavidin-ferritin. we have shown that the effect of a protein modifying the shape of the dna double-helix can be studied and precisely located by this method. it was found that the non-coding region contains curved segments and that the mitochondrial protein mtdbp-c preferentially enhances the curvature of the promoters-replication ori ... | 1990 | 2111178 |
| activin-like factor from a xenopus laevis cell line responsible for mesoderm induction. | induction of mesoderm during early amphibian embryogenesis can be mimicked in vitro by adding growth factors, including heparin-binding and type-beta transforming growth factors (tgf-beta), to isolated ectoderm explants from xenopus laevis embryos. although the mesoderm-inducing factor (mif) from x. laevis xtc cells (xtc-mif) has properties similar to tgf-beta, this factor is still unidentified. recently, we obtained a number of homogeneous cell lines from the heterogeneous xtc population, which ... | 1990 | 2113616 |
| alternating zinc-finger motifs in the human male-associated protein zfy. | zfy, a putative transcription factor encoded by the human y chromosome, contains a distinctive two-finger repeat: odd-numbered and even-numbered cc/hh metal-binding motifs exhibit systematic alternation in sequence pattern. such alternation, which is not generally observed in zinc-finger proteins, has also been described in an extensive family of kruppel-like genes in xenopus laevis and in the aids-associated human dna-binding protein hiv-ep1. the strict conservation of a two-finger repeat among ... | 1990 | 2116899 |
| repair of acetyl-aminofluorene modified pbr322 dna in xenopus laevis oocytes and eggs; effect of diadenosine tetraphosphate. | using xenopus laevis oocytes and unfertilized eggs, we have developed a system which allows the study of dna repair upon microinjection of pbr 322 dna which has been previously modified in vitro by n-acetyl-aminofluorene, under controlled conditions. in unfertilized eggs, an efficient repair of pbr-18aaf dna takes place, leading to a restoration of the transforming activity of the plasmid dna towards escherichia coli. the repaired dna is even efficiently replicated, the egg being "activated" by ... | 1990 | 2116915 |
| molecular cloning and sequence determination of four different cdna species coding for alpha-subunits of g proteins from xenopus laevis oocytes. | a cdna library prepared from xenopus laevis oocytes in lambda gt10 was screened with a mixture of three oligonucleotide probes designed to detect sequences found in different mammalian genes coding for alpha-subunits of g-proteins. in addition to a clone coding for a g alpha o-type subunit previously reported [(1989) febs lett. 244, 188-192] four additional clones have been found coding for different g alpha protein subunits. by comparison with mammalian alpha-subunits, these oocyte cdnas corres ... | 1990 | 2116977 |
| the changing distribution of neurons in the inner nuclear layer from metamorphosis to adult: a morphometric analysis of the anuran retina. | the generation and changing distribution of neurons of the inner nuclear layer (inl) in the retina of two anuran species, bufo marinus and xenopus laevis, were studied from metamorphosis to adult. morphometric studies were undertaken at six developmental stages in bufo and four in xenopus. the number and thickness of neurons in the inl were established in 29 predetermined retinal locations from serial sections of the eyes cut vertically or horizontally. the total number of neurons in the inl inc ... | 1990 | 2118741 |
| the organization of the cortical endoplasmic reticulum in xenopus eggs depends on intracellular ph: artefact of fixation or not? | the cortical endoplasmic reticulum (cer), which develops and becomes organized during oocyte maturation in xenopus laevis (anuran amphibians), has been thought to be essential for the propagation of the activating signal at the time of fertilization, possibly by regulating intracellular ca2+ (ca2+i) (charbonneau and grey, dev. biol. 102, 90-97, 1984). the present paper demonstrates that changing intracellular ph (phi) has an influence on the structure and organization of the cer in unactivated x ... | 1990 | 2119869 |
| a fluorescent analogue of hydrin 1: a new probe for vasotocin receptors. | hydrin 1 is the biosynthetic precursor of vasotocin in xenopus laevis. we have synthesized deamino and fluorescein analogues of hydrin 1 and characterized their physiological action in the urinary bladder of the toad, bufo marinus. 1-deamino-hydrin 1 (d-hydrin) was more potent than vasotocin in stimulating osmotic water flow across intact bladders and more potent than vasotocin in displacing tritium-labeled vasopressin [( 3h]avp) from cell membranes. 1-deamino-[11-lysine (fluorescein)]-hydrin 1 ... | 1990 | 2121046 |
| xenopus oocyte k+ current. i. fsh and adenosine stimulate follicle cell-dependent currents. | ovarian follicles of xenopus laevis frogs consist of a single large oocyte surrounded by follicle cells attached to the oocyte by gap junctions. adenosine has been found to activate an outward k+ current in follicles. this response is reduced by microinjection of protein kinase inhibitor (pki), suggesting that adenosine 3',5'-cyclic monophosphate (camp) mediates the response. to investigate this further, we verified previous studies that indicate that several methods of elevating camp in follicl ... | 1990 | 2122736 |
| selective carboxyl methylation of structurally altered calmodulins in xenopus oocytes. | the eucaryotic protein carboxyl methyltransferase specifically modifies atypical d-aspartyl and l-isoaspartyl residues which are generated spontaneously as proteins age. the selectivity of the enzyme for altered proteins in intact cells was explored by co-injecting xenopus laevis oocytes with s-adenosyl-l-[methyl-3h]methionine and structurally altered calmodulins generated during a 14-day preincubation in vitro. control experiments indicated that the oocyte protein carboxyl methyltransferase was ... | 1990 | 2123492 |
| localization of endogenous galactoside-binding lectin during morphogenesis of xenopus laevis. | a monoclonal antibody has been produced against xenopus laevis galactoside-binding neural-crest-stage lectin. this antibody inhibits lectin-mediated hemagglutination. using this antibody in conjunction with immunohistochemical techniques, lectin deposition has been studied in embryos and tadpoles at different stages of morphogenesis, from initial neural crest migration, up to the formation of a swimming tadpole. lectin levels change during development in different regions of the embryo and tadpo ... | 1990 | 2123609 |
| dystrophin as a focal adhesion protein. collocalization with talin and the mr 48,000 sarcolemmal protein in cultured xenopus muscle. | monoclonal antibodies against dystrophin and the postsynaptic 58 kda protein from torpedo electric organ were used to localize homologs of these proteins in cultured skeletal muscle (xenopus laevis). the xenopus homolog is an mr 48,000 protein and, like dystrophin, is a sarcolemmal protein. both proteins localized precisely to talin-positive sites, hence with each other, on the substrate-apposed sarcolemma. therefore, the first sites of appearance of dystrophin on cultured muscle cells are focal ... | 1990 | 2123804 |
| ribosomal 5s rna from xenopus laevis oocytes: conformation and interaction with transcription factor iiia. | this review describes extensive studies on 5s rrna from x laevis oocytes combining conformational analyses in solution (using a variety of chemical and enzymatic probes), computer modeling, site-directed mutagenesis, crosslinking and tfiiia binding. the proposed 3-dimensional model adopts a y-shaped structure with no tertiary interactions between the different domains of the rna. the conserved nucleotides are not crucial for the tertiary folding but they maintain an intrinsic structure in the lo ... | 1990 | 2124147 |
| developmental expression of the xenopus laevis fos protooncogene. | we have isolated the xenopus laevis homologue of the protooncogene fos. nucleotide sequence analysis of the complementary dna revealed a coding domain for a 370-amino acid protein which shares extensive sequence homology with the avian and mammalian fos protein. during xenopus development, the fos mrna is present in the oocyte and egg stages and declines to relatively low levels by the mid-blastula transition. transient expression of fos can be seen during the late neurula and again at the tadpo ... | 1990 | 2127691 |
| expression of receptor for alpha-latrotoxin in xenopus oocytes after injection of mrna from rat brain. | alpha-latrotoxin, the major toxin of black widow spider venom, was suggested to bind to the specific receptor on the membrane of presynaptic cells and to activate a nonselective cation channel. the aim of this investigation was to express the receptor to alpha-latrotoxin in the membrane of xenopus laevis oocytes. responses to alpha-latrotoxin were studied using a double microelectrode voltage-clamp technique on x. laevis oocytes previously injected with poly(a+)-rna from rat brain. alpha-latroto ... | 1990 | 2129054 |
| mesoderm-inducing factor from bovine amniotic fluid: purification and n-terminal amino acid sequence determination. | bovine amniotic fluid contains a protein capable of inducing mesoderm formation from animal cap cells isolated from xenopus laevis embryos at the late blastula stage. the procedure for purification of this protein is described and includes the following steps: cm-cellulose cation-exchange chromatography, chromatography on hydroxylapatite, reverse-phase hplc, size exclusion hplc, and a second reverse-phase hplc. a partially purified preparation of a mesoderm-inducing factor with high mesoderm-ind ... | 1990 | 2133067 |
| translational regulation of the expression of ribosomal protein genes in xenopus laevis. | the mrnas coding for ribosomal proteins (rp-mrna) are subjected to translational control during xenopus oogenesis and embryogenesis, and also during nutritional changes in xenopus cultured cells. this regulation, which appears to respond to the cellular need for new ribosomes, operates by changing the fraction of rp-mrna engaged on polysomes, each translated rp-mrna molecule always remaining fully loaded with ribosomes. all rp-mrnas analyzed up to now show this translational behavior, and also s ... | 1990 | 2133662 |
| molecular cloning of xenopus fibrillarin, a conserved u3 small nuclear ribonucleoprotein recognized by antisera from humans with autoimmune disease. | autoantibodies against u3 small nuclear ribonucleoprotein are associated with scleroderma autoimmune disease. they were shown to react with fibrillarin, a 34- to 36-kilodalton protein that has been detected in all eukaryotes tested from humans to yeasts. we isolated a 1.6-kilobase cdna encoding fibrillarin from a xenopus laevis cdna library. the protein contains a 79-residue-long gly-arg-rich domain in its n-terminal region and a putative rna-binding domain with ribonucleoprotein consensus seque ... | 1990 | 2136767 |
| expression of a human cocaine-sensitive dopamine transporter in xenopus laevis oocytes. | the human dopamine transporter was expressed in xenopus laevis oocytes following injection of mrna isolated from human brain substantia nigra. the specific accumulation of [3h]dopamine into these oocytes was time and na+ dependent. furthermore, [3h]dopamine accumulation was prevented by coincubation of oocytes with dopamine (100 microm) or with the dopamine uptake inhibitors gbr 12909 (1 microm) or cocaine (3 microm). in contrast, oocyte injection of mrna isolated from human globus pallidus, an ... | 1990 | 2137162 |
| potential for two isoforms of the a1 ribonucleoprotein in xenopus laevis. | we have identified the xenopus cognates for the rna-binding protein a1. this protein has previously been shown to be one of the components of the heterogeneous nuclear ribonucleoprotein (hnrnp) complex in rat and human cells. we have isolated several xenopus clones from oocyte, tailbud embryo, and leg muscle cdna libraries and determined their nucleotide sequences. potentially, two different a1 isoforms are expressed in xenopus; they have been termed xa1a and xa1b. besides insertions and deletio ... | 1990 | 2137612 |
| selenocysteine trna[ser]sec gene is ubiquitous within the animal kingdom. | recently, a mammalian trna which was previously designated as an opal suppressor seryl-trna and phosphoseryl-trna was shown to be a selenocysteyl-trna (b. j. lee, p. j. worland, j. n. davis, t. c. stadtman, and d. hatfield, j. biol. chem. 264:9724-9727, 1989). hence, this trna is now designated as selenocysteyl-trna[ser]sec, and its function is twofold, to serve as (i) a carrier molecule upon which selenocysteine is biosynthesized and (ii) as a donor of selenocysteine, which is the 21st naturall ... | 1990 | 2139169 |
| an abundant and ubiquitous homo-oligomeric ring-shaped atpase particle related to the putative vesicle fusion proteins sec18p and nsf. | we have discovered a ring-shaped particle of 12.5 nm diameter, 14.5s and apparent molecular weight of approximately 570,000 that displays 6-fold radial symmetry and is composed of a single kind of an acidic (pi approximately 5.5) polypeptide of mr 97,000 (p97). using antibodies to this protein we have detected its occurrence in a wide range of cells and tissues of diverse species from frog to man, including highly specialized cells such as mammalian erythrocytes and spermatozoa. in xenopus laevi ... | 1990 | 2140770 |
| activation in vitro of rna polymerase ii and iii directed transcription by baculovirus produced e1a protein. | the baculovirus expression system has been successfully used to overproduce a number of different protein products. in this report we describe the construction of a recombinant baculovirus containing the adenovirus e1a 13s cdna sequence. infection of insect cells with this virus results in the production of phosphorylated e1a protein. the phosphorylation pattern appears to be similar to the complex pattern associated with e1a protein synthesis in mammalian cells. purified baculovirus generated e ... | 1990 | 2140886 |
| plasmid and bacteriophage lambda-dna show differential replication characteristics following injection into fertilized eggs of xenopus laevis: dependence on period and site of injection. | the fate of dna injected into in vitro fertilized eggs of xenopus laevis during subsequent early embryogenesis was investigated by changing the time period and the area of injection. form i/ii plasmid dna was found to be preferentially replicated in embryos which had been injected 60-65 min after fertilization into the animal half of the fertilized egg, irrespective of the presence of a eukaryotic origin of replication sequence element in the dna probe used for injection. in the experiments wher ... | 1990 | 2140953 |
| development and innervation of the abdominal muscle in embryonic xenopus laevis. | the morphogenesis and innervation of the ventral abdominal musculature in xenopus embryos was examined using microscopic techniques. muscle development begins at nieuwkoop and faber stage 31, when aggregates of undifferentiated cells form on the ventrolateral margins of rostral trunk myotomes. during subsequent stages, aggregates form and detach from progressively more caudal myotomes to form a series of seven discrete cell clusters (anlagen). the anlagen migrate ventrally in a cell-free space b ... | 1990 | 2141230 |
| the degradation sequence of adenovirus e1a consists of the amino-terminal tetrapeptide met-arg-his-ile. | the adenovirus e1a gene product is a potent transcriptional activator and nuclear oncoprotein. like other regulatory proteins, e1a has a short half-life, in the range of 30 to 120 min. this short half-life, which was measured in cells synthesizing e1a, is not observed in cells injected with e1a protein made in bacteria or in vitro. in these cases, e1a is essentially refractory to degradation. in an attempt to reconcile this apparent paradox, we suggested that e1a was marked for degradation durin ... | 1990 | 2146491 |
| vitellogenesis in xenopus laevis and chicken: cognate ligands and oocyte receptors. the binding site for vitellogenin is located on lipovitellin i. | vitellogenesis is the process of yolk formation in rapidly growing oocytes of oviparous species. the transport of yolk precursor proteins from the blood plasma into the oocyte is achieved by receptor-mediated endocytosis. although the xenopus oocyte is one of the prime experimental systems for expression of foreign genes and their products, the receptor for the main vitellogenic protein, vitellogenin, from this extensively utilized cell has not been identified. here we have applied ligand and im ... | 1990 | 2153117 |
| downregulation of surface sodium pumps by endocytosis during meiotic maturation of xenopus laevis oocytes. | during meiotic maturation, plasma membranes of xenopus laevis oocytes completely lose the capacity to transport na and k and to bind ouabain. to explore whether the downregulation might be due to an internalization of the sodium pump molecules, the intracellular binding of ouabain was determined. selective permeabilization of the plasma membrane of mature oocytes (eggs) by digitonin almost failed to disclose ouabain binding sites. however, when the eggs were additionally treated with 0.02% sodiu ... | 1990 | 2154110 |
| expression of biologically active human platelet-derived growth factor (pdgf) b-receptor in xenopus laevis oocytes. | platelet-derived growth factor (pdgf) consists of three different isoforms, pdgf-aa, pdgf-ab and pdgf-bb, which bind to at least two types of receptors: the b-receptor, to which only pdgf-bb binds, and the a/b receptor, to which all three isoforms bind. microinjection of synthetic mrna in xenopus laevis oocytes was used to obtain cell-surface expression of the human pdgf b-receptor. the production of receptor molecules of correct size (190 kd) was demonstrated by specific immunoprecipitation; th ... | 1990 | 2154197 |
| formation of inositol pentakisphosphate by ovarian follicles of xenopus laevis from metabolism of inositol (1,4,5)trisphosphate and inositol (1,3,4,5)tetrakisphosphate and from receptor activation. | small amounts of a higher inositol phosphate with chromatographic properties of [3h]inositol (1,3,4,5,6)pentakisphosphate were formed from [3h]inositol (1,4,5)trisphosphate added to homogenates of ovarian follicles of xenopus laevis, and from [3h]inositol (1,3,4,5)tetrakisphosphate after injection into follicular oocytes. other intermediate forms of inositol tetrakisphosphate were not detectable. [3h]inositol (1,3,4,5,6)pentakisphosphate prepared from chicken erythrocytes was metabolized in homo ... | 1990 | 2154206 |
| nucleotide sequence determination of mouse, chicken and xenopus laevis rig cdnas: the rig-encoded protein is extremely conserved during vertebrate evolution. | mouse, chicken and xenopus laevis homologues to rig (rat insulinoma gene) cdna were isolated and their nucleotide sequences were determined. each homologue encoded a 145-amino acid protein; the amino acid sequence remained invariant in the murine and avian genes, and there were only 6 amino acid substitutions in the salientian gene. the evolutionary rate calculated for rig mrna was sufficiently low to be viewed as evidence that rig is vital to vertebrate species. southern blot analysis indicated ... | 1990 | 2154983 |
| absence of substantial bending in xenopus laevis transcription factor iiia-dna complexes. | the extent and location of dna-bending induced in the xenopus laevis transcription factor iiia-oocyte 5s rna gene complex was determined by the gel retardation method. the electrophoretic mobilities of tfiiia complexed with restriction fragments of 160, 177, 282 and 300 bp that contain the sequence of the major oocyte 5s rna gene were compared. in these fragments the 120-bp gene is positioned either in the middle or at the end. minor differences in the mobility of the complexes indicate that the ... | 1990 | 2155404 |
| functional reconstitution of fmet-leu-phe receptor in xenopus laevis oocytes. | fmet-leu-phe (fmlp) receptors were functionally reconstituted into xenopus laevis oocytes by microinjection with rna isolated from promyelocytic leukemia cells (hl-60) differentiated with 750 microm n6, o2-dibutyryl cyclic adenosine 3',5'-monophosphate. fmlp-induced ca2+ mobilization was monitored by measurement of photon emission elicited by aequorin coinjected with rna into albino x. laevis oocytes. maximal expression of the fmlp receptor was achieved 48 h after microinjection of rna. dose-res ... | 1990 | 2156834 |
| calcium wave evoked by activation of endogenous or exogenously expressed receptors in xenopus oocytes. | the mrna encoding the cloned substance k receptor was microinjected into xenopus laevis oocytes. after expression of the mrna, ca2+ was imaged in the oocytes with a digital imaging fluorescence microscopy system using the ca2(+)-sensitive dyes fura-2 and fluo-3. application of substance k caused a dose-related wave of ca2+ mobilization to spread from a focus and to elevate the ca2+ concentration in the oocyte. activation of endogenous muscarinic or angiotensin ii receptors in noninjected oocytes ... | 1990 | 2157216 |
| orthopoxvirus gene expression in xenopus laevis oocytes: a component of the virion is needed for late gene expression. | we have examined the feasibility of using xenopus laevis oocytes microinjected with rabbit poxvirus as a system to study poxvirus gene expression. the injection of either intact virus or subviral cores resulted in accurate synthesis of viral proteins. this expression was dependent on the multiplicity of injected virus, with the optimal injected dose being equivalent to approximately 300 pfu per oocyte. extensive viral gene expression including late viral protein synthesis was observed when intac ... | 1990 | 2157885 |
| characterization of a na(+)-k(+)-2cl- cotransport system in oocytes from xenopus laevis. | in order to characterize the transport systems mediating k+ uptake into oocytes, flux studies employing 86rb were performed on xenopus oocytes stripped of follicular cells by pretreatment with ca2(+)-mg2(+)-free barth's medium. total rb+ uptake consisted of an ouabain-sensitive and an ouabain-insensitive flux. in the presence of 100 mmol/l nacl and 0.1 mmol/l ouabain the ouabain-insensitive flux amounted to 754.7 +/- 59.9 pmol/oocyte per h (n = 30 cells, i.e., 10 cells each from three different ... | 1990 | 2158348 |
| oxytocin receptors from llc-pk1 cells: expression in xenopus oocytes. | two selective radioligands for oxytocin receptors, [3h]-[4-threonine,7-glycine]oxytocin [( 3h]-[thr4,gly7]ot) and 125i-[1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(o-methyl)tyrosine, 4-threonine, 8-ornithine, 9-tyrosine amide]-oxytocin (125i-ota), were used to characterize oxytocin receptors from two pig kidney-derived cell lines, llc-pk1 and llc-pk1l. [3h]-[thr4,gly7]ot and 125i-ota bind with high affinity (mean kd values of 14 and 0.06 nm, respectively) to the same popula ... | 1990 | 2158746 |
| postnatal development of voltage-dependent calcium channels in the mouse brain disclosed by the xenopus oocyte assay. | we assessed the ontogeny of murine voltage-dependent calcium channels by extracting mrna from brains of mice at different postnatal ages and injecting the mrna into oocytes of the frog, xenopus laevis. voltage-dependent ca2(+)-activated cl- channels were measured to assess the presence of ca2(+) channels. when compared with water-injected oocytes (controls), an increase in ca2(+) channels was not detected until postnatal day 7. the number of ca2+ channels peaked between 9 and 18 days and began t ... | 1990 | 2159399 |
| functional expression of ca2(+)-mobilizing alpha-thrombin receptors in mrna-injected xenopus oocytes. | alpha-thrombin (th) initiates a program of intracellular events that lead to dna replication in quiescent ccl39 chinese hamster lung fibroblasts via membrane receptors that have yet to be characterized at a molecular level. functional th receptors were expressed in xenopus laevis oocytes following injection of poly(a)+ rna from th-responsive ccl39 cells; their presence was demonstrated by th-stimulated 45ca2+ efflux or ca2(+)-dependent cl- channel activation. in voltage clamp experiments on micr ... | 1990 | 2159419 |
| isolation and characterization of a tyrosyl phosphatase activator from rabbit skeletal muscle and xenopus laevis oocytes. | ptpa, a specific phosphotyrosyl phosphatase activator of the pcsh2 and pcsl protein phosphatases, was purified up to apparent homogeneity from xenopus laevis ovaries and rabbit skeletal muscle and highly purified from dog liver. ptpa appears as a 40-kda protein in gel filtration, as well as in sucrose gradient centrifugation, and as a 37-39-kda protein doublet in sds-page. its estimated cellular concentration of 0.75 microm in oocytes or 0.25 microm in rabbit skeletal muscle is suggestive of an ... | 1990 | 2159785 |
| metabolism of the biologically active inositol phosphates ins(1,4,5)p3 and ins(1,3,4,5)p4 by ovarian follicles of xenopus laevis. | the metabolism of biologically active inositol phosphates in developed ovarian follicles from xenopus laevis was investigated. techniques used were microinjection of tracer into the intact oocyte coupled by gap junctions to follicle cells, as well as addition of tracer to homogenates of ovarian follicles and to homogenates of oocytes stripped of outer follicle-cell layers. metabolism was similar to that previously described for other types of cell and tissue, with several unusual features. homog ... | 1990 | 2160808 |
| molecular biology of mammalian amino acid receptors. | the amino acid receptor proteins are ubiquitous transducers of most excitatory and inhibitory synaptic transmission in the brain. in july 1987 two reports appeared describing the molecular cloning of a pair of subunits of the gabaa receptor (7) and one subunit of the glycine receptor (13). these papers sparked wide interest and led quickly to the concept of a ligand-gated receptor-ion channel superfamily that includes nicotinic acetylcholine receptors as well as certain amino acid receptors. the ... | 1990 | 2161372 |
| regulation of na+ channels in frog lung epithelium: a target tissue for aldosterone action. | sodium transport across isolated lung tissue of the frog xenopus laevis was measured in ussing chambers under voltage-clamp conditions. perfusing the lungs with nacl-ringer's solutions on both sides, a basal distinct amiloride-blockable na+ current was present. incubating the lungs with 1 mumol/l aldosterone from the pleural side raised the short circuit current after a 1-h latent period. maximal values were reached after 4-5 h of aldosterone treatment, at which time the transepithelial na+ curr ... | 1990 | 2162035 |
| morphology of the pars intermedia and the melanophore-stimulating cells in xenopus laevis in relation to background adaptation. | the melanophore-stimulating hormone (msh) cells of the amphibian pars intermedia secrete the peptide alpha-melanophore-stimulating hormone (alpha-msh), which induces pigment dispersion in dermal melanophores. the purpose of the present study was to determine (1) whether prolonged activation of the secretory activity of the pars intermedia is associated with hypertrophy, hyperplasia, or both and (2) whether the msh cells function as a homogeneous or heterogeneous population in meeting the physiol ... | 1990 | 2162308 |
| functional expression of b2 bradykinin receptors from balb/c cell mrna in xenopus oocytes. | the murine balb/c 3t3 fibroblast clone sv-t2 (3t3 cells) expresses receptors for the nonapeptide bradykinin. in these cells, bradykinin stimulates both inositol phosphate (insp) formation and arachidonic acid release by independently activating phospholipase c and phospholipase a2, respectively. these actions of bradykinin are mediated by a receptor(s) coupled to pertussis toxin-insensitive guanine nucleotide-binding proteins. bradykinin-stimulated increases in insp lead to the mobilization of i ... | 1990 | 2163013 |
| characterization of a maternal type vi collagen in xenopus embryos suggests a role for collagen in gastrulation. | we characterized a novel extracellular matrix element that is present in the earliest developmental stages of xenopus laevis, and is recognized by an mab 3d7. based on amino acid composition, breakdown patterns by bacterial collagenases, and the molecular weights of the components of the antigen (240, 200, and 140 kd), we found it very similar to mammalian collagen type vi. the antigen is evenly distributed in unfertilized eggs. shortly after fertilization, it becomes localized intracellularly i ... | 1990 | 2164030 |
| action of light on frog pigment cells in culture. | solar radiation induces numerous biologic effects in skin but the mechanism underlying these responses is poorly understood. to study the etiology of these phenomena, we investigated the effect of light on cultured xenopus laevis melanophores. visible light stimulated a marked increase in intracellular camp levels within the first minute of irradiation. this light-induced elevation in camp was blocked by melatonin and was not seen in fibroblasts irradiated in a similar manner. these data show th ... | 1990 | 2165596 |
| restoration of the plasticity of binocular maps by nmda after the critical period in xenopus. | visual input during a critical period of development plays a major role in the establishment of orderly connections in the developing visual system. in xenopus laevis, the matching of visual maps from the two eyes to the optic tectum depends on binocular visual input during the critical period, which extends from late tadpole to early juvenile stages. alterations in eye position, which produce a mismatch of the tectal maps, normally evoke a compensatory adjustment in the map of the ipsilateral e ... | 1990 | 2166343 |
| regulation of oogenesis: the piscine receptor for vitellogenin. | the receptor-mediated uptake of vitellogenin (vtg), a plasmatic lipophosphoglycoprotein, is crucial for oocyte growth in egg-laying animals. the plasma membrane receptor for vtg was characterized from oocytes of coho salmon, oncorhynchus kisutch. in direct binding studies, the receptor exhibited high affinity (kd, 180 nm) for salmonid vtg, and by ligand blotting with radiolabelled vtg it was visualized as a protein with an apparent mr of 100,000, under non-reducing conditions. the fish vtg recep ... | 1990 | 2167133 |
| micromolar free calcium exposes ouabain-binding sites in digitonin-permeabilized xenopus laevis oocytes. | as demonstrated previously, digitonin-permeabilized xenopus oocytes have a large internal pool of sodium pumps which are inaccessible to cytosolic ouabain [schmalzing, kröner & passow (1989) biochem. j. 260, 395-399]. access to internal ouabain-binding sites required permeabilization of inner membranes with sds. in the present study, micromolar free ca2+ was found to stimulate ouabain binding in the digitonin-permeabilized cells (k0.5 0.5 microm-ca2+, h 1.9, average of seven experiments) without ... | 1990 | 2167664 |
| ca-sensitive sodium absorption in the colon of xenopus laevis. | transepithelial electrogenic na transport (ina) was investigated in the colon of the frog xenopus laevis with electrophysiological methods in vitro. the short circuit current (isc) of the voltage-clamped tissue was 24.2 +/- 1.8 microa.cm-2 (n = 10). about 60% of this current was generated by electrogenic na transport. removal of ca2+ from the mucosal ringer solution stimulated ina by about 120%. ina was not blockable by amiloride (0.1 mmol.l-1), a specific na-channel blocker in epithelia, but a ... | 1990 | 2167905 |
| sn-1,2-diacylglycerol levels increase in progesterone-stimulated xenopus laevis oocytes. | full-grown xenopus laevis oocytes resume meiosis from prophase arrest in response to progesterone stimulation. recent studies have shown that the tumor promoter, 12-o-tetradecanoylphorbol 13-acetate (tpa), a very potent activator of protein kinase c, can also induce the resumption of meiosis in amphibian oocytes. we have investigated the possibility that sn-1,2-diacylglycerol (dag), the intracellular activator of protein kinase c, may be involved in the pathway normally used by progesterone. we ... | 1990 | 2167919 |
| activation of two different receptors mobilizes calcium from distinct stores in xenopus oocytes. | acetylcholine (ach) and thyrotropin-releasing hormone (trh) utilize inositol 1,4,5-trisphosphate (ip3) as a second messenger and evoke independent depolarizing membrane electrical responses accompanied by characteristic 45ca efflux profiles in xenopus laevis oocytes injected with gh3 pituitary cell mrna. to determine whether this could be accounted for by mobilization of calcium from functionally separate stores, we measured simultaneously 45ca efflux and membrane electrical responses to ach and ... | 1990 | 2168222 |
| a possible role of the beta-subunit of (na,k)-atpase in facilitating correct assembly of the alpha-subunit into the membrane. | mrnas from the alpha- and beta-subunits (mrna alpha and mrna beta, respectively) of torpedo californica (na,k)-atpase were injected into xenopus laevis oocytes either separately or in combination, and the properties of the two subunits synthesized were studied. the alpha-subunit synthesized in oocytes injected with mrna alpha alone was recovered in both the membrane and cytosol fractions and was susceptible to tryptic attack. when mrna beta was coinjected with mrna alpha, almost all the alpha-su ... | 1990 | 2168428 |
| microinjected gtp-gamma-s inhibits progesterone-induced maturation of xenopus oocytes. | gtp-gamma-s inhibits progesterone-induced maturation of xenopus laevis oocytes and induces a rise in their camp levels. gtp-gamma-s does not inhibit mpf-induced maturation. although gtp-gamma-s prevents the progesterone-induced increases in protein synthesis and phosphorylation, it has no effect on the basal rates of either. gtp-gamma-s also prevents the initial dag drop induced by progesterone. gdp-beta-s effects are ambiguous, but it seems not to affect progesterone-induced maturation. these r ... | 1990 | 2170213 |
| expression of epithelial na channels in xenopus oocytes. | epithelial na channel activity was expressed in oocytes from xenopus laevis after injection of mrna from a6 cells, derived from xenopus kidney. poly a(+) rna was extracted from confluent cell monolayers grown on either plastic or permeable supports. 1-50 ng rna was injected into stage 5-6 oocytes. na channel activity was assayed as amiloride-sensitive current (ina) under voltage-clamp conditions 1-3 d after injection. ina was not detectable in noninjected or water-injected oocytes. this amilorid ... | 1990 | 2170563 |
| expression of neurotrophic activity in xenopus oocytes injected with mrna from wounded rat cerebral cortex. | injury to the cerebral cortex of the rat brain has been shown to induce the expression of neurotrophic factors for dissociated peripheral and central neurons in culture. we confirm this phenomenon and report that xenopus laevis oocytes injected with mrna extracted from wounded rat cortex expressed similar neurotrophic activity. to detect the low amounts of neurotrophic factors that could be expected from the oocyte translation system, a miniaturization of the assay for neurotrophic and cell-surv ... | 1990 | 2170801 |