| involvement of endogenous galactoside-binding lectin of xenopus laevis in pattern formation of xenopus neurites in vitro. | galactoside-binding lectin has been purified from xenopus laevis embryos at the stage of neural crest migration. addition of this lectin to neurite cultures correlates with the appearance of fascicles of greater diameter and shorter length compared with controls. lectin-treated neurites are also more spread out on the substratum than their controls. the potent hapten inhibitor of the endogenous lectin, thiodigalactoside (tdg), was also added to these cultures. tdg-treated neurites are less well ... | 1989 | 2620261 |
| neural differentiation of xenopus laevis ectoderm takes place after disaggregation and delayed reaggregation without inducer. | when xenopus blastula or early gastrula ectoderm is disaggregated and cells are kept dispersed for up to 5 h prior to reaggregation, the resulting spheres will differentiate into large neural structures. in contrast, dissociated and immediately reaggregated ectoderm will only differentiate into ciliated epidermis (so-called 'atypical epidermis'). ectoderm treated with mesoderm-inducing xtc-conditioned medium during the period of reaggregation immediately after disaggregation will only form one- ... | 1989 | 2620262 |
| anion transport systems in the mouse erythrocyte: kinetic studies in situ and after expression of mouse erythroid band 3 protein in oocytes of xenopus laevis. | | 1989 | 2620762 |
| transport of glutamine in xenopus laevis oocytes: relationship with transport of other amino acids. | we have investigated transport of the amino acid glutamine across the surface membranes of prophase-arrested xenopus laevis oocytes. glutamine accumulation was linear with time for 30 min; it was stereospecific with a km of 0.12 +/- 0.02 mm and vmax of 0.92 +/- 0.17 pmol/oocyte.min for l-glutamine. transport of l-glutamine was na(+)-dependent, the cation not being replaceable with li+, k+, choline, tris(hydroxymethyl)-aminomethane (tris), tetramethylammonium (tma) or n-methyl d-glucamine (nmdg); ... | 1989 | 2621745 |
| cis- and trans-acting elements of the estrogen-regulated vitellogenin gene b1 of xenopus laevis. | vitellogenin genes are expressed under strict estrogen control in the liver of female oviparous vertebrates. gene transfer experiments using estrogen-responsive cells have shown that the 13 bp perfect palindromic element ggtcactgtgacc found upstream of the xenopus laevis vitellogenin gene a2 promoter mediates hormonal stimulation and thus, was called the estrogen-responsive element (ere). in the xenopus vitellogenin genes b1 and b2 there are two closely adjacent eres with one or more base substi ... | 1989 | 2626015 |
| neuroleptic modulation of oral dyskinesias induced in snakes by xenopus skin mucus. | the skin mucus of the african clawed frog xenopus laevis promotes escape from the american water snake nerodia sipedon by inducing oral dyskinesias. as xenopus mucus contains peptides and indoleamines with known neuroleptic properties, and because neuroleptics are the chief cause of drug-induced orofacial dyskinesias in humans, the hypothesis was tested that the neuroleptic haloperidol (hal) would induce oral dyskinesias when given alone and would potentiate dyskinesias in nerodia if injected pr ... | 1989 | 2626458 |
| preparation and characterization of cell-free protein synthesis systems from oocytes and eggs of xenopus laevis. | during the maturation of the oocytes of the frog xenopus laevis, the rate of protein synthesis shows a twofold increase. studies of the mechanisms involved in this stimulation have been seriously limited by the lack of an active cell-free translation system. we have now prepared such systems from oocytes, progesterone-matured oocytes and eggs of xenopus laevis by induction of lysis by centrifugation of whole cells. the extracts are highly active in incorporation of labelled amino acids and, in t ... | 1989 | 2627883 |
| expression of phenolic and tyrosyl ring iodothyronine deiodinases in xenopus laevis oocytes is dependent on the tissue source of injected poly(a)+ rna. | the phenolic (5' position) and tyrosyl (5 position) ring deiodinases which catalyze the peripheral metabolism of thyroid hormones have proven difficult to purify and characterize biochemically. the present studies used xenopus laevis oocytes as an in vivo translational assay system for detecting and quantitating mrna for these enzymes. the injection of poly(a)+ rna prepared from a human term placenta induced 5-deiodinase activity in oocytes. the expressed activity increased for up to 96 h after ... | 1989 | 2628739 |
| spatial aspects of neural induction in xenopus laevis. | a monoclonal antibody, 2g9, has been identified and characterised as a marker of neural differentiation in xenopus. the epitope is present throughout the adult central nervous system and in peripheral nerves. staining is first detected in embryos at stage 21 in the thoracic region. by stage 29 it stains the whole central nervous system, except the tail tip. the epitope is present in a 65k mr protein, and includes sialic acid. the antibody also reacts with neural tissue in mice and axolotls and n ... | 1989 | 2632233 |
| temporal and tissue-specific expression of the proto-oncogene c-fos during development in xenopus laevis. | we describe the isolation and complete sequence of the xenopus c-fos proto-oncogene. c-fos expression throughout xenopus development was analysed using a homologous probe derived from the cloned gene. c-fos rna is accumulated during oogenesis to reach a plateau of 2 x 10(5) transcripts per stage vi oocyte, suggesting an unusual stability of the c-fos message. the amount of rna per embryo decreases substantially after fertilisation to reach a level corresponding to less than 0.1 molecule per cell ... | 1989 | 2632235 |
| inducing factors and the control of mesodermal pattern in xenopus laevis. | the mesoderm of xenopus laevis and other amphibia is formed through an inductive interaction during which cells of the vegetal hemisphere act on cells of the animal hemisphere. two groups of factors mimic the effects of the vegetal hemisphere. one group consists of members of the fibroblast growth factor (fgf) family, while the other is related to transforming growth factor type beta (tgf-beta). in this paper we discuss the evidence that the fgf family represents 'ventral' mesoderm-inducing sign ... | 1989 | 2636136 |
| cholinoceptive properties of human primordial, preantral, and antral oocytes: in situ hybridization and biochemical evidence for expression of cholinesterase genes. | in addition to their well-known involvement in neuromuscular junctions and in brain cholinergic synapses, cholinergic mechanisms have been implicated in the growth and maturation of oocytes in various species. functional acetylcholine receptors were electrophysiologically demonstrated in amphibian and mammalian oocyte membranes, and activity of the acetylcholine-hydrolyzing enzyme, acetylcholinesterase (ache), was biochemically measured in the exceptionally big oocytes of the frog xenopus laevis ... | 1989 | 2641279 |
| structure of a major yolk glycoprotein and its processing pathway by limited proteolysis are conserved in echinoids. | to study the fate of the yolk glycoproteins found in eggs and embryos of the sea urchin, strongylocentrotus purpuratus, a polyclonal antibody to a 90-kda polymannose glycoprotein found in the embryo was prepared. immunoblot analysis of total proteins over the course of development showed that this antibody recognized a family of glycoproteins. concomitant with the disappearance of the major 160-kda yolk glycoprotein of the egg during embryogenesis, glycoproteins with a lower molecular mass appea ... | 1989 | 2645184 |
| synacrosomal formation after cell fusion of round spermatids of xenopus laevis. | cell fusion was induced by hypotonic medium in pairs of spermatids which were derived from single secondary spermatocytes. in a pair of fused spermatids, a single acrosome (synacrosome) eventually formed whenever the cell fusion was induced during the course of acrosomal formation. direct observation of the process of synacrosomal formation was made on pairs of fused spermatids which had completed acrosomal formation. two patterns occurred, namely, fusion of two acrosomes or enlargement of one w ... | 1989 | 2647499 |
| amphibian (urodele) myotomes display transitory anterior/posterior and medial/lateral differentiation patterns. | myotome differentiation during mexican axolotl (ambystoma mexicanum) somitogenesis was analyzed by employing anti-actin and anti-myosin monoclonal antibodies as molecular probes. myotome differentiation occurs after segmentation and proceeds in the cranial-to-caudal direction along the somite file. within individual somites myotome differentiation displays distinct polarities. examination of the somite file at the tailbud stage revealed that soon after segmentation, actin/myosin accumulate predo ... | 1989 | 2647546 |
| nucleocytoplasmic transport of ribosomes in a eukaryotic system: is there a facilitated transport process? | we have examined the kinetics of the process by which ribosomes are exported from the nucleus to the cytoplasm using xenopus laevis oocytes microinjected into the germinal vesicle with radiolabeled ribosomes or ribosomal subunits from x. laevis, tetrahymena thermophila, or escherichia coli. microinjected eukaryotic mature ribosomes are redistributed into the oocyte cytoplasm by an apparent carrier-mediated transport process that exhibits saturation kinetics as increasing amounts of ribosomes are ... | 1989 | 2648382 |
| activation of glucose uptake by insulin and insulin-like growth factor i in xenopus oocytes. | xenopus laevis oocytes possess a glucose transport system that is activated 3- to 5-fold by insulin-like growth factor i (ka = 3 nm) and insulin (ka = 200-250 nm), properties suggesting activation mediated by an insulin-like growth factor i receptor. this activation increases the vmax of hexose uptake and has little or no effect on the km for deoxyglucose (km = 1-2 mm). activation by hormone requires about 60 min and is inhibited by cytochalasin b but not by cycloheximide. the dependence of hexo ... | 1989 | 2649887 |
| signals from the dorsal blastopore lip region during gastrulation bias the ectoderm toward a nonepidermal pathway of differentiation in xenopus laevis. | epi 1, a monoclonal antibody, was generated against an epidermal specific epithelial antigen; it does not stain neural epithelium. we have used epi 1 as a marker to determine when the spatial patterns delineating neural from nonneural epithelium become established. we used ventral ectoderm in a sandwich assay to show that signals from the central blastopore lip region, passing through the plane of the ectoderm sheet, define the pattern and boundary characteristics of epi 1 expression. the dorsal ... | 1989 | 2651180 |
| simple three-dimensional imaging of hrp-labelled neurons with the aid of an image processor. | a method is described for visualizing the three-dimensional structure of horseradish peroxidase-labelled neurons in the central nervous system of xenopus laevis tadpoles. the reconstruction is simple, and performed on a commercially available image processing system. minimal operational skill is required for using this method. also, various improvements were made where user's simplicity (user-friendliness), speed and required computer memory are concerned. in addition, the excellent properties o ... | 1989 | 2651674 |
| the micronucleus test in xenopus: a new and simple 'in vivo' technique for detection of mutagens in fresh water. | the aim of this study was to extend the micronucleus test to xenopus laevis to screen water for potential mutagens. up to now, the most commonly used methods for screening fresh water are the bacterial tests (ames tests). ames tests are well validated, but are merely in vitro bacterial assays which can only detect point mutations whereas the micronucleus test is an in vivo assay using a vertebrate species, and thus is able to detect both chromosome and genome mutations. this study was designed t ... | 1989 | 2654547 |
| detection of proto-oncogenes in the genome of the amphibian xenopus laevis. | the xenopus laevis genome was probed by southern blot analysis for the presence of sequences homologous to mammalian or avian proto-oncogenes. hybridization conditions were strictly defined with a known proto-oncogene to detect a positive signal with dna sequences having at least 60 to 64% homology. in such conditions thirteen genes representing different oncogene families exhibited positive hybridizations with specific dna restriction fragments. members of the protein kinase oncogene family wer ... | 1989 | 2654808 |
| genes encoding neuronal nicotinic acetylcholine receptors. | four genes (alpha 2, alpha 3, alpha 4, and beta 2), which encode proteins homologous to the torpedo electric organ and vertebrate muscle nicotinic acetylcholine receptors, have been identified by cloning rat brain cdnas. injection of transcripts derived from these cdnas into xenopus laevis oocytes results in the formation of three nicotinic acetylcholine receptors. two of these receptors, alpha 3/beta 2 and alpha 4/beta 2, have the characteristics of ganglionic nicotinic receptors. the third (al ... | 1989 | 2655998 |
| nucleolin from xenopus laevis: cdna cloning and expression during development. | nucleolin is a key nucleolar protein in higher eukaryotic cells and is involved directly in ribosome biogenesis. using an antiserum raised against hamster nucleolin, the homologous protein was detected in nucleoli of xenopus laevis hepatocytes as well as in the amplified nucleoli of oocytes. a cdna encoding xenopus nucleolin has been isolated and sequenced. the deduced protein sequence reveals similar domains in xenopus and in mammals, but they have undergone separate evolutions. in particular, ... | 1989 | 2656405 |
| the xenopus laevis u2 gene distal sequence element (enhancer) is composed of four subdomains that can act independently and are partly functionally redundant. | the sequences involved in enhancement of transcription of the xenopus u2 small nuclear rna gene by the distal sequence element (dse) of its promoter were analyzed in detail by microinjection of mutant genes into xenopus oocytes. the dse was shown to be roughly 60 base pairs long. within this region, four motifs were found to contribute to dse function: an atgcaaat octamer sequence, an spi binding site, and two additional motifs which, since they are related in sequence, may bind the same transcr ... | 1989 | 2657402 |
| expression of yeast invertase in oocytes from xenopus laevis. secretion of active enzyme differing in glycosylation. | in an effort to understand factors that control glycosylation of proteins and processing of carbohydrate chains, invertase from saccharomyces cerevisiae was expressed in a heterologous system. microinjection of invertase-specific in vitro transcripts into oocytes from xenopus laevis resulted in synthesis, glycosylation and secretion of enzymatically active invertase. it was found that although the number of carbohydrate chains acquired is the same as in yeast, the carbohydrate processing is diff ... | 1989 | 2659349 |
| hyperdorsoanterior embryos from xenopus eggs treated with d2o. | excessively dorsalized embryos of xenopus laevis develop from eggs treated with 30-70% d2o for a few minutes within the first third of the cell cycle following fertilization. as the concentration of d2o and the duration of exposure are increased, the anatomy of these embryos shifts in the direction of enlarged dorsal and anterior structures and reduced ventral and posterior ones. twinning of dorsoanterior structures is frequent. intermediate forms include embryos with large heads but no trunks o ... | 1989 | 2659411 |
| stimulation of protein synthesis in stage iv xenopus oocytes by microinjected insulin. | the effects of intracellular insulin on protein synthesis were examined in intact cells and isolated, undiluted cellular components. [35s]methionine incorporation into protein was measured in stage iv oocytes from xenopus laevis maintained under paraffin oil. radiolabel and insulin were introduced into the cytoplasm by microinjection. after a short delay (approximately 15 min), injected insulin stimulated the rate of methionine incorporation. stimulation was dose-dependent, increasing with injec ... | 1989 | 2659587 |
| isolation and characterization of two different insulins from an amphibian, xenopus laevis. | the south african clawed toad, xenopus laevis, is a versatile laboratory model of vertebrate development. to study the role of insulin during embryogenesis, we have recently cloned preproinsulin cdnas from this species. unexpectedly, we identified two preproinsulin cdnas corresponding to two different nonallelic genes that code for similar but distinctly different insulins. we now report the isolation, amino acid sequence, and characterization of both of these insulins from pancreatic extracts o ... | 1989 | 2661211 |
| evidence for a pertussis toxin-sensitive g protein involved in the control of meiotic reinitiation of xenopus laevis oocytes. | meiotic reinitiation of xenopus laevis oocytes is induced in vitro by progesterone or insulin. the hormonal effect is inhibited in a dose-dependent manner by the injection of the a protomer of pertussis toxin (islet-activating protein, iap) into the oocytes. this inhibition occurs only before the appearance of a maturation-promoting activity in the cytoplasm. furthermore, injection of the toxin a protomer into recipient oocytes does not inhibit the induction of maturation obtained through inject ... | 1989 | 2661247 |
| mitosis-specific monoclonal antibody mpm-2 inhibits xenopus oocyte maturation and depletes maturation-promoting activity. | mpm-2, a monoclonal antibody specific for cells in mitosis, recognizes a family of proteins that share a common phosphorylated epitope. in this study we have shown that during the maturation of xenopus laevis oocytes induced by progesterone, phosphorylation of mpm-2 antigens coincided with the appearance of mpf activity. when mpm-2 (0.7-1.4 micrograms per oocyte) was injected into oocytes prior to progesterone stimulation, mpf activity failed to appear and induction of maturation was inhibited a ... | 1989 | 2662192 |
| analysis of 3'-untranslated regions of seven c-myc genes reveals conserved elements prevalent in post-transcriptionally regulated genes. | we have characterized the complete sequence of two c-myc cdnas from the amphibian xenopus laevis, and could thus compare the 3'-non-coding sequences of 7 myc cdnas from 6 species spread over 350 million years of evolution. although the size of these sequences is heterogeneous, we identified three completely conserved sequences of 10, 11 and 12 contiguous nucleotides. we observed that two of these elements may be contained in conserved stem-loop structures previously implicated in mrna turnover. ... | 1989 | 2666167 |
| mitochondrial rna polymerase: dual role in transcription and replication. | mitochondrial rna polymerases from humans, xenopus laevis and saccharomyces cerevisiae are very similar in protein composition and function. they consist of a nonspecific core rna polymerase and a protein factor that confers promoter selectivity on the core component, and they participate in transcription as well as in dna replication. amino acid sequence comparisons indicate that the yeast mitochondrial core component is related to bacteriophage t3 and t7 rna polymerases; mitochondrial and phag ... | 1989 | 2667219 |
| the distribution of fibronectin and laminin in the somitogenesis of xenopus laevis. | | 1989 | 2668088 |
| evolutionary conservation of the biochemical properties of p53: specific interaction of xenopus laevis p53 with simian virus 40 large t antigen and mammalian heat shock proteins 70. | we have investigated the biochemical properties of xenopus laevis p53. with an in vitro binding assay, we can detect a specific association between x. laevis p53 and simian virus 40 large t antigen. furthermore, x. laevis p53 expressed in monkey cos cells is stably associated with this viral antigen. like mammalian p53, x. laevis p53 in complex with simian virus 40 large t antigen exhibits a 20-fold increase of its half-life. on the other hand, x. laevis p53 is unable to associate either in vivo ... | 1989 | 2668561 |
| sequence requirements for synthetic peptide-mediated translocation to the nucleus. | the abilities of 18 synthetic peptides to target a carrier protein to the nucleus following microinjection into the cytoplasm of hela cells were determined. eight of the sequences chosen for synthesis were based on published nuclear targeting regions as determined by gene fusion and deletion experiments. six of these sequences were found to be effective when mimicked by a synthetic peptide and conjugated to a carrier protein. one additional peptide was based on a region of lamin l1, a nuclear pr ... | 1989 | 2668735 |
| expression of human and murine interleukin-5 in eukaryotic systems. | a cdna coding for murine interleukin-5 (il-5) was isolated from the el4.exc5 cell line. with the exception of a single amino acid substitution at position 79 (arg----his), it is identical to a published sequence. the coding sequence for human il-5 was synthesized chemically, allowing the introduction of strategically located restriction enzyme cleavage sites. both cdnas were expressed in various eukaryotic systems. deletion of the 3' untranslated region of the murine il-5 gene led to a 5- to 10- ... | 1989 | 2670497 |
| proteases released from xenopus laevis eggs at activation and their role in envelope conversion. | during fertilization of the xenopus laevis egg, the egg envelope is converted so that further sperm contact with the egg is prevented. in this study two envelope conversion reactions were investigated, envelope hardening and limited hydrolysis of two structurally related envelope glycoproteins. both of these reactions were shown to be sensitive to protease inhibitors. in an attempt to identify egg proteases involved in envelope conversion, the medium around activated dejellied eggs was collected ... | 1989 | 2670636 |
| xenopus laevis skin arg-xaa-val-arg-gly-endoprotease. a highly specific protease cleaving after a single arginine of a consensus sequence of peptide hormone precursors. | comparison of the precursor sequence for several peptide hormones of xenopus laevis skin revealed a consensus sequence around a single arginine cleavage site which is 100% conserved on four residues arg-xaa-val-arg-gly (rxvrg). a tetradecapeptide substrate (asp-val-asp-glu-arg-asp-val-arg-gly-phe-ala-ser-phe-leu-nh2) was used as a probe to purify and characterize the putative processing endoprotease. a hydrophobic enzyme was purified at least 9000-fold from xenopus skin exudate by a four-step pr ... | 1989 | 2670921 |
| expression of the four subunits of the torpedo californica nicotinic acetylcholine receptor in saccharomyces cerevisiae. | yeast expression vectors were constructed containing complementary dna encoding the alpha-, beta-, gamma-, and delta-subunits of the torpedo californica nicotinic acetylcholine receptor under the control of the saccharomyces cerevisiae alcohol dehydrogenase promoter. all four plasmids were integrated into the yeast genome of a single yeast cell. the resulting yeast strain synthesized polypeptides novel to yeast that had the molecular weights and antigenic properties similar to the authentic t. c ... | 1989 | 2670931 |
| magainins and the disruption of membrane-linked free-energy transduction. | magainins, a family of positively charged peptides, are partly if not wholly responsible for antimicrobial activity in skin extracts of xenopus laevis. we report here that members of the magainin family--i.e., the 21-amino acid peptide pgla and the 23-amino acid peptide magainin 2 amide (pgsa)--dissipate the electric potential across various energy-transducing membranes and thus uncouple respiration from other free-energy-requiring processes. we propose that this is a likely mechanism for the an ... | 1989 | 2671997 |
| measurement of erythroid band 3 protein-mediated anion transport in mrna-injected oocytes of xenopus laevis. | | 1989 | 2674617 |
| a purified complex from xenopus oocytes contains a p47 protein, an in vivo substrate of mpf, and a p30 protein respectively homologous to elongation factors ef-1 gamma and ef-1 beta. | a high molecular mass complex isolated from xenopus laevis oocytes contains three main proteins, respectively p30, p36 and p47. the p47 protein has been reported to be an in vivo substrate of the cell division control protein kinase p34cdc2. from polypeptide sequencing, we now show that the p30 and the p47 correspond to elongation factor ef-1 beta and ef-1 gamma. furthermore, the p30 and p36 proteins were phosphorylated in vitro by casein kinase ii. | 1989 | 2676593 |
| embryonic development of xenopus studied in a cell culture system with tissue-specific monoclonal antibodies. | an in vitro microculture system of early gastrula cells of xenopus laevis has been developed; deep layer cells from the lateral marginal zone (prospective somite region) or ventral ectoderm (prospective epidermis region) were fully dissociated, and the desired number of each (1-100) was distributed into a microculture well and cultured under appropriate conditions. when examined with the tissue-specific mabs (mu1 for muscle and e3 for epidermis, respectively), a substantial portion of the deep l ... | 1989 | 2680422 |
| functional expression of the yes proto-oncogene protein in xenopus oocytes injected with chicken cerebellar mrna. | using monospecific antibodies raised against the amino terminal domain of viral-yes protein, we precipitated a 58 kd protein-tyrosine kinase from the brain of xenopus laevis frog. by a number of criteria, including pattern of expression in various tissues and one-dimensional peptide mapping, we concluded that pp58 is very likely the authentic amphibian yes protein because it is more similar to the chicken yes protein than to any other known tyrosine kinases. the pp58c-yes is expressed in adult b ... | 1989 | 2681802 |
| nuclear factors specifically bind to upstream sequences of a xenopus laevis ribosomal protein gene promoter. | the upstream region of the xenopus laevis l14 ribosomal protein gene was deleted starting from the 5' extremity in order to define the promoter length necessary to express a linked reporter cat gene. the functional analysis indicated that a sequence located between -63 and -49 from the capsite is important for an efficient promoter activity. band shift and exoiii protection assays evidenced the binding to this region of a factor, called xrpfi, present in the crude nuclear extract from x.laevis o ... | 1989 | 2682523 |
| biochemical characterization of the p34cdc2 protein kinase component of purified maturation-promoting factor from xenopus eggs. | genetic studies in the fission yeast schizosaccharomyces pombe and biochemical data in oocytes and eggs of xenopus laevis have implicated the product of the cdc2+ gene as critical for the g2 to m transition in the cell cycle. the product of the cdc2+ gene is a 34-kda serine/threonine protein kinase, designated p34cdc2, that is a component of purified maturation-promoting factor (mpf) and also of purified mammalian growth-associated histone h1 kinase. the biochemical properties of p34cdc2 h1 kina ... | 1989 | 2684959 |
| translocation of a store of maternal cytoplasmic c-myc protein into nuclei during early development. | the c-myc proto-oncogene is expressed as a maternal protein during oogenesis in xenopus laevis, namely, in nondividing cells. a delayed translation of c-myc mrna accumulated in early oocytes results in the accumulation of the protein during late oogenesis. the oocyte c-myc protein is unusually stable and is located in the cytoplasm, contrasting with its features in somatic cells. a mature oocyte contains a maternal c-myc protein stockpile of 4 x 10(5) to 6 x 10(5) times the level in a somatic gr ... | 1989 | 2685563 |
| structure of a ribosomal protein gene in mucor racemosus. | as an extension of our analysis of the translational apparatus of mucor racemosus we have isolated a gene encoding a ribosomal protein of mucor. based on a method developed for s. cerevisiae, we identified by hybrid selection and in vitro translation a lambda-charon 4a clone containing the genomic copy of a mucor ribosomal protein. the gene consisted of two exons of 57 and 387 nucleotides. the two exons were separated by an 131 nucleotide intron. the processed transcript was 714 nucleotides in l ... | 1989 | 2685758 |
| identification of a widespread nuclear actin binding protein. | the many different cellular functions so far shown to involve actin and to be regulated by specific actin binding proteins are located primarily, if not exclusively, in the cytoplasm. actin is also found in the nucleus of various cells, but because of the problems of cell fractionation the significance of nuclear actin has remained unclear. the large amphibian oocyte nucleus (germinal vesicle), however, can be isolated manually with little cytoplasmic contamination. this nucleus contains high co ... | 1989 | 2689884 |
| multiple modifications in the phosphoproteins bound to stored messenger rna in xenopus oocytes. | messenger rna molecules accumulated in amphibian oocytes are stabilized and blocked from translation through association with a defined set of phosphoproteins. phosphoproteins of 60 kda and 56 kda (pp60 and pp56) isolated from messenger ribonucleoprotein particles of xenopus laevis oocytes can be bound in vitro to mrna sequences. after phospholabelling in vitro, both pp60 and pp56 show a range of ionic forms, which resolve on two-dimensional gel electrophoresis as a series of pairs with identica ... | 1989 | 2690959 |
| expression of a functional glucose transporter in xenopus oocytes. | a cdna encoding the rat brain glucose transporter was inserted between the 5' and 3' untranslated regions from the xenopus globin gene and downstream of an sp6 rna polymerase start site. rna synthesized from this vector was microinjected into oocytes from xenopus laevis; this resulted in expression of the glucose transporter, as determined by both immunoblotting and the appearance of transport activity. the properties of the transporter were those expected from previous studies: it was glycosyla ... | 1989 | 2692709 |
| the egg of xenopus laevis: a model system for studying cell activation. | | 1989 | 2692788 |
| development of xenopus laevis skin glands producing 5-hydroxytryptamine and caerulein. | the granular glands in xenopus laevis skin are known to contain large quantities of biogenic amines and bioactive peptides which closely resemble mammalian brain-gut peptides. we studied the development of glands producing 5-hydroxytryptamine (5-ht) and caerulein using immunohistochemistry, hplc-fluorometric systems and ria. the immunoreactivities of 5-ht and caerulein were first detected in the spherical gland rudiments in the stratum spongiosum at st. 58 (nieuwkoop and faber stage), or at the ... | 1989 | 2692831 |
| rudimentary phosvitin domain in a minor chicken vitellogenin gene. | we have determined the nucleotide sequence and the derived amino acid sequence of the phosphoprotein-encoding region of the chicken vitellogenin iii gene. the sequence of this minor vitellogenin could be aligned with exon 22 up to exon 27 of the previously sequenced major vitellogenin ii gene (van het schip et al., 1987). the exon 23 and 25 sequences are rich in serine codons (26% and 41%, respectively), and this region encodes at least one of the small egg yolk phosphoproteins. the major egg yo ... | 1989 | 2701940 |
| onchocerca volvulus heat shock protein 70 is a major immunogen in amicrofilaremic individuals from a filariasis-endemic area. | infestation with organisms causing lymphatic filariasis (i.e. wuchereria bancrofti and brugia malayi) results in a variety of clinical presentations. it is possible that some of the variation is due to differences in host response to parasite. to determine whether individuals who live in an endemic area but differ in their clinical manifestations respond to different filarial antigens, we screened onchocerca volvulus expression libraries with sera from a number of individuals belonging to differ ... | 1989 | 2704388 |
| stimulation of endogenous dopamine release and metabolism in amphibian retina by light- and k+-evoked depolarization. | the release and metabolism of dopamine (da) in retina was assessed using an in vitro eye cup preparation of the african clawed frog. the concentration of da in the incubation medium and of 3,4-dihydroxyphenylacetic acid (dopac) and da in retinas was measured by high-performance liquid chromatography with electrochemical detection (hplc-ed). k+-induced depolarization stimulated da overflow from the eye cups into the incubation medium and increased tissue dopac levels in dark-adapted retinas. basa ... | 1989 | 2706474 |
| low-concentration n-acetylaspartylglutamate suppresses the climbing fiber response of purkinje cells in guinea pig cerebellar slices and the responses to excitatory amino acids of xenopus laevis oocytes injected with cerebellar mrna. | whether n-acetylaspartylglutamate (naag) at micromolar concentrations shows a modulatory action on the synaptic transmission mediated by excitatory amino acids was investigated using guinea pig cerebellar slices and the xenopus laevis oocytes injected with mrna from guinea pig cerebellum. the climbing fiber response consisted of an excitatory postsynaptic potential (epsp) and a plateau potential intracellularly recorded from purkinje cell dendrite was depressed by 30 microm naag; the epsp was de ... | 1989 | 2706484 |
| changing patterns of binocular visual connections in the intertectal system during development of the frog, xenopus laevis. ii. abnormalities following early visual deprivation. | during normal metamorphic and post-metamorphic growth of the frog, xenopus laevis, there is a major and orderly remodelling of the pattern of neuronal connections in the intertectal system. these changes preserve the spatial registration of binocular visual inputs to each optic tectum in the face of continuous changes in relative eye alignment (grant and keating 1989). we suggested that visual experience might be utilised by the intertectal system to effect the maturational remodelling of its co ... | 1989 | 2707345 |
| changing patterns of binocular visual connections in the intertectal system during development of the frog, xenopus laevis. i. normal maturational changes in response to changing binocular geometry. | during metamorphic and post-metamorphic life in the frog. xenopus laevis, growth-related changes in skull shape produce radical alterations in the spatial relationship between the two eyes. these changes in binocular visual geometry were measured using optical techniques. between the onset of metamorphic climax at stage 60 and adulthood (2 or more years post-metamorphosis) each eye migrates nasally by 55 degrees and dorsally by 50 degrees with respect to the major body axes of the animal. as a r ... | 1989 | 2707359 |
| the mrna encoding elongation factor 1-alpha (ef-1 alpha) is a major transcript at the midblastula transition in xenopus. | a xenopus laevis gastrula cdna library has been screened in order to identify sequences that are expressed early in development. we find that the mrna encoding translation elongation factor 1-alpha (ef-1 alpha) is synthesized in very large amounts in the early embryo. transcription of ef-1 alpha mrna commences at the midblastula transition (mbt), and new ef-1 alpha protein is synthesized very soon after this, as determined by the association of ef-1 alpha mrna with polysomes. the nucleotide sequ ... | 1989 | 2707491 |
| serotoninergic neurons in the retina of xenopus laevis: selective staining, identification, development, and content. | uptake of 3h-serotonin followed by autoradiography, and uptake of the serotonin analog 5,7-dihydroxytryptamine (5,7-dht), with subsequent staining, were each used to define a unique set of neurons in the retina of the african clawed frog, xenopus laevis. both techniques demonstrated the same population of neurons, on the basis of perikaryal size, shape, and position within the retina. two classes of amacrine cells accumulated 5,7-dht at the proximal (vitread) margin of the inner nuclear layer; t ... | 1989 | 2708578 |
| developmental toxicity testing with fetax: evaluation of five compounds. | the teratogenic potential of five compounds was evaluated with fetax (frog embryo teratogenesis assay: xenopus). early embryos of xenopus laevis were exposed for 96 h to 6-aminonicotinamide (6-an), isoniazid (inh), urethane, nitrilotriacetate (nta) or sodium cyclamate, in two separate static-renewal tests of each compound. based on teratogenic index values, growth endpoints and the types and severity of the induced malformations, 6-an, inh and urethane scored as having strong teratogenic potenti ... | 1989 | 2714209 |
| in vitro synthesis of vertebrate u1 snrna. | we have developed a dna-dependent in vitro transcription system for vertebrate snrna genes. by isolating the nuclei (germinal vesicles, gvs) of xenopus laevis oocytes under oil to maintain the in vivo composition of their internal milieu, we are able to prepare nuclei that retain their ability to synthesize snrnas efficiently. homogenates of these gvs synthesize correctly initiated and terminated u1 snrna using exogenous x.laevis u1 genes as templates. the templates may be either injected into t ... | 1989 | 2714253 |
| the novel pituitary polypeptide 7b2 is a highly-conserved protein coexpressed with proopiomelanocortin. | in the amphibian intermediate pituitary gland the biosynthetic activity for production of the precursor protein proopiomelanocortin (pomc) can be physiologically manipulated; pomc synthesis is high in animals adapted to a black background and low in white-adapted animals. in order to study genes associated with pomc gene expression we applied a differential hybridization technique involving screening of a pituitary cdna library with probes derived from rna of inactive and physiologically activat ... | 1989 | 2714283 |
| identification of highly acidic peptides from processing of the skin prepropeptides of xenopus laevis. | the skin secretion of the frog xenopus laevis has been fractionated by reverse-phase hplc and the most polar components studied by fast-atom-bombardment mass spectrometry (fab/ms). esterification of the hydrophilic peptides with methanol and ethanol was employed to improve the sensitivity of the technique. a number of small, highly acidic peptides have been identified, and alcoholysis of the peptide bonds within a number of these permitted their sequencing by fab/ms. the sequences confirmed that ... | 1989 | 2714285 |
| spermatogenic cell-somatic cell interactions are required for maintenance of spermatogenic cell glutathione. | sertoli cells play a major role in the regulation of spermatogenic cell energy metabolism and differentiation. this study demonstrates that sertoli cells are essential for the maintenance of spermatogenic cell glutathione (gsh), an important intracellular reductant and detoxicant. primary spermatocytes and round spermatids isolated from xenopus laevis contained 1.5 +/- 0.1 mm gsh, but sperm lacked detectable gsh. during a 5-day culture period, isolated spermatocytes and spermatids lost 80% of th ... | 1989 | 2720029 |
| dominant and specific repression of xenopus oocyte 5s rna genes and satellite i dna by histone h1. | the genome of xenopus laevis contains two large families of class iii genes (oocyte 5s rna and satellite i dna) that are repressed in somatic cells. both gene families are actively transcribed in a soluble extract of x.laevis oocyte nuclei, using chromatin deficient in histone h1 as a template. the addition of histone h1, to this transcriptionally active chromatin, results in the dominant and selective repression of oocyte 5s rna genes and satellite i dna. somatic 5s rna genes remain active foll ... | 1989 | 2721490 |
| xlgv7: a maternal gene product localized in nuclei of the central nervous system in xenopus laevis. | the xenopus oocyte nucleus (gv) is a storehouse for a large number of proteins that are used during early development. we have cloned and characterized a cdna coding for a maternal gene product that is localized in the gv and then becomes highly enriched in the nuclei of the central nervous system (cns) of tadpoles and adult frogs. this cdna (xlgv7) is 2.1 kb and hybridizes to a 2.4-kb rna species on northern blots. southern blots of genomic dna suggest that this gene is a member of a multigene ... | 1989 | 2721962 |
| xenopus laevis contains two nonallelic preproinsulin genes. cdna cloning and evolutionary perspective. | we undertook the cloning of preproinsulin cdnas from the south african clawed toad, xenopus laevis, in order to study the role of insulin during embryogenesis in this species. we found that x. laevis contains two different preproinsulin cdnas, both of which code for peptides containing 106 amino acids of typical structure but which differ by eight amino acids: one in the signal peptide, two in the b-chain, four in the c-peptide, and one in the a-chain. southern blot analysis indicates that the t ... | 1989 | 2722842 |
| expression of myosin heavy chain transcripts during xenopus laevis development. | in amphibians, the composition and pattern of expression of the myosin heavy chain (myhc) gene family are mostly unknown. to understand better the regulation of this complex family, we screened cdna libraries from swimming tadpole and adult leg muscle rna and have isolated and partially sequenced clones for several myhcs. two of these, e3 and e19, first appear in mesoderm at late gastrula stage and are coexpressed with muscle actin. they increase in abundance in trunk and tail myotome until meta ... | 1989 | 2731640 |
| the development of retinal ganglion cells deprived of their targets. | the influence of central targets on the morphological differentiation of retinal ganglion cells was investigated in xenopus laevis. since the ganglion cells mature into distinct morphological subtypes after their axons have reached their central targets, it is possible that the target tissues may influence or specify this aspect of neuronal cell development. to test this idea, xenopus eyebuds were target-deprived by transplantation to the flank region of host embryos where they developed ectopic ... | 1989 | 2731644 |
| expression and tissue-specific assembly of human butyrylcholine esterase in microinjected xenopus laevis oocytes. | cholinesterases represent a ubiquitous, polymorphic family of acetylcholine hydrolyzing enzymes. the multileveled tissue-specific heterogeneity which characterizes these enzymes makes the cholinesterases an appropriate model for studying the mechanisms involved in regulating divergent pathways in protein biogenesis. for this purpose, a cdna coding for human butyrylcholine esterase (buche) was subcloned into the sp 6 transcription vector. synthetic mrna transcribed from this construct was microni ... | 1989 | 2732242 |
| characterization of early dna synthesis in xenopus eggs after injection of circular plasmid dna. | circular plasmid dna is known to replicate when injected into unfertilized eggs of xenopus laevis. we characterized early dna synthesis which precedes the replication. incorporation of a radioactive precursor into covalent closed circular dna becomes detectable as early as 2 minutes after injection. judging from the sensitivity to aphidicolin, replicative dna polymerase alpha or delta is involved in this reaction. however, analysis of density-labeled product as well as detection of newly synthes ... | 1989 | 2734101 |
| the constituents of storage granules in the dermal glands of xenopus laevis. structure of a basic polypeptide deduced from cloned cdna. | mature dermal glands of xenopus laevis contain storage granules with a characteristic ellipsoid shape. a few major proteins are present in these granules, including two with the same amino-terminal sequence and apparent molecular masses of 26 and 28 kda. using antibodies against these proteins, positive clones were isolated from a cdna expression library prepared from skin of x. laevis. one cdna encodes a preprotein with a typical signal sequence and a mature part of 187 amino acids. the protein ... | 1989 | 2737290 |
| transcriptional characteristics of in vitro assembled chromatin assayed by microinjection into xenopus laevis oocytes. | plasmid dna was in vitro assembled into chromatin using an s-150 extract of xenopus laevis oocytes. by varying the assembly temperature and dna concentration it is possible to generate fully or partially assembled molecules. the fate of the in vitro preassembled molecules injected into x. laevis oocyte nuclei and their transcriptional activity were studied. completely reconstituted molecules underwent a rearrangement of their chromatin structure after injection and showed reduced transcriptional ... | 1989 | 2737294 |
| a new family of growth factor-like peptides. 'trefoil' disulphide loop structures as a common feature in breast cancer associated peptide (ps2), pancreatic spasmolytic polypeptide (psp), and frog skin peptides (spasmolysins). | four peptides present in completely different biological sources have been shown to exhibit a large degree of structural similarity. the peptides include: (i) a 60 amino acid residue breast cancer associated ps2 peptide isolated from human gastric juice and the culture media of the human breast cancer cell line mcf-7; (ii) a 106 amino acid residue pancreatic spasmolytic polypeptide (psp) isolated from porcine pancreas and pancreatic juice; and (iii) a 49 and 50 amino acid residue peptide predict ... | 1989 | 2737304 |
| retinoic acid causes an anteroposterior transformation in the developing central nervous system. | all-trans retinoic acid (ra) is well known as a biologically active form of vitamin a and a teratogen. the identification of nuclear receptors for this ligand suggests strongly that it is an endogenous signal molecule, and measurements of ra and teratogenic manipulations suggest further that ra is a morphogen specifying the anteroposterior axis during limb development. besides the limb, ra and other retinoids affect development of other organs, including the central nervous system (cns). none of ... | 1989 | 2739735 |
| experimental reversal of the normal dorsal-ventral timing of blastopore formation does not reverse axis polarity in xenopus laevis embryos. | during gastrulation in xenopus laevis, the dorsal lip of the blastopore normally appears before the ventral lip. metabolic gradient models propose that the dorsal lip develops from the region of highest metabolic activity and somehow dominates other regions to prevent them from becoming dorsal. to test these ideas, i applied a temperature gradient of 12 degrees c across the embryo. localized heating of the prospective ventral vegetal region from early in the first cleavage period until gastrulat ... | 1989 | 2744238 |
| clonal analysis of mesoderm induction in xenopus laevis. | acidic fibroblast growth factor (afgf) has been used to induce mesoderm from single animal pole cells of midblastula stage xenopus embryos. the cells are individually cultured in a completely defined medium and are able to differentiate as small clones in a high proportion of cases. fgf-treated cells can give rise to several mesodermal cell types, while untreated cells show only epidermal or neural differentiation. mesodermal differentiation can occur in clones of as few as eight cells, indicati ... | 1989 | 2744244 |
| further study on the changes in the concentration of prolactin-binding sites in different organs of xenopus laevis male and female, kept under dry conditions and then returned to water (their natural habitat). | the binding of 125i-labeled ovine prolactin (125i-oprl) to membranes from the kidney and liver of xenopus laevis male and female specimens (experiment i) and from the kidney, epidermis, and liver of female specimens (experiment ii) (1) kept in an aquatic environment, (2) exposed for 2 weeks to dehydrating conditions, and (3) then placed back into their aquaria after exposure to dehydrating conditions (experiment ii) was studied. no significant sex differences in prl binding to kidney, epidermis, ... | 1989 | 2744411 |
| positive and negative regulation of the gene for transcription factor iiia in xenopus laevis oocytes. | expression of the positively acting 5s gene-specific transcription factor, tfiiia, is regulated during development, with highest levels of mrna and protein occurring during oogenesis. by analysis of tfiiia promoter mutants microinjected into late stage xenopus oocytes, we have determined dna sequences required for the transcription of this gene and we have identified proteins that bind to these regulatory sequences. a negative element lies between positions -306 and -289. three positive-acting s ... | 1989 | 2744458 |
| expression of the thyroid sodium/iodide symporter in xenopus laevis oocytes. | poly(a+) rna isolated from frtl-5 cells (a continuous line of cultured and fully functional rat thyroid cells (ambesi-impiombato, f. s., parks, l. a. m., and coons, h. g. (1980) proc. natl. acad. sci. u. s. a. 77, 3455-3459] was injected into xenopus laevis oocytes, and the expression of the na+/i- symporter in the plasma membrane was assayed by measuring the na+-dependent clo4--sensitive uptake of 125i. expression of the na+/i- symporter was detected as a 7-fold average increase in transport ov ... | 1989 | 2745421 |
| xenopus laevis serum albumin: sequence of the complementary deoxyribonucleic acids encoding the 68- and 74-kilodalton peptides and the regulation of albumin gene expression by thyroid hormone during development. | in adult xenopus serum, albumin gene expression is regulated by estrogen through the selective destabilization of its mrna during the vitellogenic response. the present study reports the cdna sequence of both the 68k and 74k xenopus albumin mrnas, their derived amino acid sequence, and the regulation of albumin gene expression during embryogenesis. albumin mrna has a 39 nucleotide 5' untranslated region terminating in a consensus translation initiation site. the derived amino acid sequence yield ... | 1989 | 2747653 |
| analysis of oxygen binding by xenopus laevis hemoglobin: implications for the root effect. | we have measured oxygen binding properties for red cell suspensions and stripped hemolysate of xenopus laevis (xl) in order to answer the question whether xl hemoglobin exhibits a root effect. the present results show that under physiological conditions xl red cells do not exhibit all the criteria for a root effect. compared to human hb a, stripped xl hemoglobin has a low oxygen affinity, a normal alkaline bohr effect and a lower interaction with 2,3-diphosphoglycerate, its physiological alloste ... | 1989 | 2749024 |
| primary structure from amino acid and cdna sequences of two cu,zn superoxide dismutase variants from xenopus laevis. | a mixture of two different amino acid sequences was discovered in cu,zn superoxide dismutase purified from the amphibian xenopus laevis. no n-terminal post-translational modification was found. the high number of substitutions in the sequence suggested that protein heterogeneity was a product of gene duplication. this was confirmed by isolation of two different cdna clones. nucleotide sequence analysis allowed the primary structure of the two peptide chains to be unambiguously assigned. the obse ... | 1989 | 2751312 |
| progressive determination during formation of the anteroposterior axis in xenopus laevis. | the cement gland is an ectodermal organ in the head of frog embryos, lying anterior to any neural tissue. as analyzed by specific rna expression, cement gland, like neural tissue, was induced by the dorsal mesoderm. interestingly, mesoderm with the highest cement gland-inducing potential lay posterior to the ectoderm fated to form this organ, indicating that its induction occurred at a distance from the inducer source. cement gland induction first occurred during early gastrulation. however, mos ... | 1989 | 2752418 |
| site selection by xenopus laevis rnaase p. | investigation of the mechanism of cleavage site selection by xenopus rnaase p reveals that the acceptor stem, a 7 bp helix common to all trna precursors, is required for cleavage. we propose that xenopus rnaase p recognizes conserved features of the mature trna and that the cleavage site is selected by measuring the length of the acceptor stem. in support of this, we demonstrate that insertion of 2 bp in the acceptor stem of yeast pre-trna(3leu) relocates the cleavage site 2 bases 3' to the orig ... | 1989 | 2752421 |
| morphology of afferent synapses in the mauthner cell of larval xenopus laevis. | the fine structure of the afferent synapses on the mauthner cell of larval xenopus laevis has been studied as a first step toward comparing the fine structure of the afferent synaptic apparatus before and after metamorphosis. there are various types of afferent endings on this cell, some of which are confined to specific cellular regions, while others are distributed over most of the large surface of the neuron. four different main types of endings have been observed: club endings, round-vesicle ... | 1989 | 2754034 |
| computer modeling from solution data of spinach chloroplast and of xenopus laevis somatic and oocyte 5 s rrnas. | detailed atomic models of a eubacterial 5 s rrna (spinach chloroplast 5 s rrna) and of a eukaryotic 5 s rrna (somatic and oocyte 5 s rrna from xenopus laevis) were built using computer graphic. both models integrate stereochemical constraints and experimental data on the accessibility of bases and phosphates towards several structure-specific probes. the base sequence was first inserted on to three-dimensional structural fragments picked up in a specially devised databank. the fragments were mod ... | 1989 | 2754730 |
| effect of dna conformation on the transcription of mitochondrial dna. | the importance of the conformation of the dna template for in vitro transcription experiments was investigated using a mitochondrial rna polymerase preparation from xenopus laevis oocyte mitochondria. a premature termination transcription assay has been devised and the levels of the formation of transcriptional complexes have been identified using agarose gel electrophoresis. it was found that accurate initiation of transcription from in vivo promoter sequences was enhanced by supercoiling and t ... | 1989 | 2759085 |
| maximum rate of oxygen consumption and quantitative histochemistry of succinate dehydrogenase in single muscle fibres of xenopus laevis. | three different types of single living muscle fibre were dissected from the iliofibularis muscle of xenopus laevis. the fibres were mounted in a glass chamber and their rate of oxygen consumption was determined as a function of twitch frequency at 20 degrees c. the rate of oxygen consumption increased with twitch frequency until it levelled off and reached a maximum. the maximum rate of oxygen consumption varied between fibres (0.019 to 0.161 nmol o2 s-1 mm-3) and was reached at different twitch ... | 1989 | 2760192 |
| toxic and developmental effects of organophosphorus insecticides in embryos of the south african clawed frog. | four organophosphorus insecticides and the active metabolites of two phosphorothionate insecticides were tested for their toxic and teratogenic effects on embryos of xenopus laevis. all compounds caused dose-dependent developmental defects, such as abnormal pigmentation, abnormal gut development, notochordal defects and reduced growth. malathion, malaoxon, parathion, and paraoxon produced severe defects, while monocrotophos and dicrotophos produced considerably milder defects. all compounds redu ... | 1989 | 2760412 |
| expression of the poly(a)-binding protein during development of xenopus laevis. | we have isolated and sequenced cdna clones encoding the poly(a)-binding protein of xenopus laevis oocytes. polyclonal antiserum was raised against a fusion protein encoding 185 amino acids of the xenopus poly(a)-binding protein. this antiserum localizes the poly(a)-binding protein to subcellular sites associated with protein synthesis; in the retina, immunoreactive protein is detected in the synthetically active inner segment of the photoreceptor but not in the transductive outer segment. transc ... | 1989 | 2761544 |
| an oocyte-expressed alpha-tubulin gene in xenopus laevis; sequences required for the initiation of transcription. | we have studied the expression of x alpha t14, a member of the alpha-tubulin multigene family in xenopus laevis. small amounts of x alpha t14 rna are detectable in a range of cell types, but much higher levels are present in ovary and tissue culture cells. in oocytes x alpha t14 transcripts accumulate during early vitellogenesis but their level declines in more advanced stages. faithful and efficient initiation of transcription occurred on cloned x alpha t14 injected into oocytes even at low tem ... | 1989 | 2762119 |
| differential replication of circular dna molecules co-injected into early xenopus laevis embryos. | replication of co-injected supercoiled dna molecules in fertilized xenopus eggs was monitored through the blastula stage of development. the extent of replication, as measured by 32p-dtmp incorporation into form i dna, was directly proportional to the number of molecules, rather than the size, of the plasmid injected. although only a small fraction of molecules of either template was replicated, incorporation was predominantly into full length daughter molecules. over at least a 20-fold concentr ... | 1989 | 2762153 |
| cis-acting elements of the sea urchin histone h2a modulator bind transcriptional factors. | functional tests, performed by microinjection into xenopus laevis oocytes, show that a dna fragment containing the modulator of the early histone h2a gene of paracentrotus lividus enhances transcription of a reporter gene when located, in the physiological orientation, upstream of the tk basal promoter. gel retardation and dnase i footprinting assays further reveal that the h2a modulator contains at least two binding sites [upstream sequence elements 1 and 2 (use 1 and use 2)] for nuclear factor ... | 1989 | 2762313 |
| activation of masked neural determinants in amphibian eggs and embryos and their release from the inducing tissue. | the neural-archencephalic (forehead) inducing activity of the microsomes and the high speed supernatant from xenopus laevis ovaries and eggs was tested on gastrula ectoderm of triturus alpestris. both fractions have a very small inducing activity which increases considerably after autolysis or treatment with dissociating agents. a comparison with the inducing activity of the high speed supernatant from gastrulae suggests that neural inducing factors are synthesized in the ovary, stored in a mask ... | 1989 | 2766041 |
| replicating premeiotic germ cells of the mouse contain a novel dna primase stimulatory factor. | a protein factor that stimulates dna primase activity associated with dna polymerase alpha has been identified in mouse germ cell populations enriched in spermatogonia and preleptotene spermatocytes. the partially purified factor enhances dna primase activity from homologous cell types as well as dna primase activity from xenopus laevis oocytes in a poly dt or m 13 directed reaction. the factor does not stimulate dna polymerase alpha activity in a gapped salmon sperm or poly dt-ra directed react ... | 1989 | 2766046 |
| cell intercalation during notochord development in xenopus laevis. | morphometric data from scanning electron micrographs (sem) of cells in intact embryos and high-resolution time-lapse recordings of cell behavior in cultured explants were used to analyze the cellular events underlying the morphogenesis of the notochord during gastrulation and neurulation of xenopus laevis. the notochord becomes longer, narrower, and thicker as it changes its shape and arrangement and as more cells are added at the posterior end. the events of notochord development fall into thre ... | 1989 | 2769201 |
| regional identity is established before gastrulation in the xenopus embryo. | regional differences in cell recognition properties along the animal-vegetal axis of xenopus laevis embryos were investigated by using an in vitro cell sorting assay. dissociated cells were obtained from defined regions of blastula- and early gastrula-stage embryos. binary combinations of cells from different regions, or from the same region at different ages, were aggregated in stationary culture. labelling of one population in each pair with a cell-autonomous dye allowed the degree of sorting ... | 1989 | 2769203 |