| central organization of wave localization in the clawed frog, xenopus laevis. i. involvement and bilateral organization of the midbrain. | the central nervous organization of water wave localization in the clawed frog xenopus laevis was investigated by performing behavioral tests on frogs that had various brain ablations. the criterion of localization was the orientation of response turns toward the origin of stimulus waves. after complete midbrain ablation, xenopus still detected impinging waves but could not localize them. after thalamopretectal ablation, however, xenopus localized waves with normal accuracy. thus, wave localizat ... | 1988 | 3046708 |
| central organization of wave localization in the clawed frog, xenopus laevis. ii. midbrain topology for wave directions. | the organization of water wave localization within the midbrain of the clawed frog xenopus was investigated by performing behavioral tests on frogs that had partial midbrain ablations. the criterion of localization was the orientation of turns toward the origin of impinging waves. all lesion effects became apparent as localization failure within an angular sector of wave direction. the sectors were contralateral to the lesion and of various sizes, some comprising the complete hemifield. localiza ... | 1988 | 3046709 |
| effects of thyroxine-driven precocious metamorphosis on maturation of adult-type allograft rejection responses in early thyroidectomized frogs. | in contrast to the adult pattern of allograft reactivity, larval south african clawed frogs (xenopus) either become tolerant of adult major histocompatibility complex (mhc) disparate skin grafts or reject them slowly. larvae fail to reject grafts that are incompatible at minor histocompatibility (h) loci (mhc-identical); rather, they become immunologically tolerant. we report here that early thyroidectomized (thyroidx) larvae, forced to metamorphose precociously on a regimen of thyroxine (t4) tr ... | 1988 | 3046979 |
| two distinct regions of the murine p53 primary amino acid sequence are implicated in stable complex formation with simian virus 40 t antigen. | we mapped regions of the mouse p53 primary amino acid sequence implicated in stable complex formation with simian virus 40 t antigen. a number of mutant p53 proteins failed to complex stably with t antigen in vivo but formed stable complexes with t antigen in in vitro association assays. in contrast to an earlier report (t.-h. tan, h. wallis, and a. j. levine, j. virol. 59:574-583, 1986), our study showed that two distinct regions of p53 primary amino acid sequence, highly conserved between mous ... | 1988 | 3047431 |
| excitatory amino acids and rod photoreceptor disc shedding: analysis using specific agonists. | l-glutamate and l-aspartate stimulate photoreceptor disc shedding. in order to evaluate the possible involvement of a receptor, we examined the effects of specific excitatory amino acid agonists on rod photoreceptor disc shedding and neural retinal toxicity. using eyecups from both xenopus laevis and rana pipiens, we found that kainate, quisqualate, and n-methyl-d-aspartate (nmda) were all neurotoxic, but that kainate caused a more extensive inner retinal lesion. kainate also caused disc sheddin ... | 1988 | 3053226 |
| proteinase ysce of yeast shows homology with the 20 s cylinder particles of xenopus laevis. | proteinase ysce of the yeast saccharomyces cerevisiae has been compared with the 20 s cylinder particles of xenopus laevis. both proteins are characterized by a similar group of 10-12 polypeptides with molecular masses ranging between 21 and 38 kda. antibodies generated against the 20 s xenopus cylinder particles show cross-reactivity with yeast proteinase ysce subunits. the xenopus particles and yeast proteinase ysce exhibit an identical image in electron microscopy. both proteins appear as hol ... | 1988 | 3053244 |
| immunocytochemical evidence for the colocalization of neurotensin/xenopsin- and gastrin/caerulein-immunoreactive substances in xenopus laevis gastrointestinal tract. | distribution and association of neurotensin (nt)- and xenopsin (xp)-like peptides were investigated using immunocytochemical techniques in the amphibian gut. antisera against both groups of peptides showed an identical distribution pattern of nt- and xp-positive cells in xenopus laevis gastrointestinal tract. immunolabeling of consecutive semithin sections revealed the coexistence of nt- and xp-like substances within cells of the stomach and small intestine. recent reports of the colocalization ... | 1988 | 3053328 |
| the distribution of nucleoplasmin in early development and organogenesis of xenopus laevis. | the fate of the germinal vesicle-derived protein, nucleoplasmin, was followed in embryos and tadpoles of xenopus using monoclonal antibodies and indirect immunofluorescent staining. nucleoplasmin was found in all nuclei up to feeding tadpole stages. thereafter its level decreased in all nuclei. it was not detected in nuclei of advanced tadpoles or of adults. contrasting with another protein, n1, that was previously monitored in the nuclei of dividing gonia of both sexes, nucleoplasmin was only d ... | 1988 | 3058314 |
| cytoskeletons of retinal pigment epithelial cells: interspecies differences of expression patterns indicate independence of cell function from the specific complement of cytoskeletal proteins. | in vertebrate tissue development a given cell differentiation pathway is usually associated with a pattern of expression of a specific set of cytoskeletal proteins, including different intermediate filament (if) and junctional proteins, which is identical in diverse species. the retinal pigment epithelium (rpe) is a layer of polar cells that have very similar morphological features and practically identical functions in different vertebrate species. however, in biochemical and immunolocalization ... | 1988 | 3058315 |
| presence of microtubules in isolated cortices of prophase i and metaphase ii oocytes in xenopus laevis. | an extensive array of microtubules has been shown to exist in the cortex of xenopus laevis oocytes both at the prophase i and metaphase ii stages. the cortical microtubules were visualized after the oocyte cortex was squashed and immunostained using anti-tubulin antibody. they are cold- and nocodazole-sensitive; their stability to both treatments decreases after meiotic maturation. biochemical extraction of manually isolated oocyte cortices, in a microtubule-stabilizing buffer, confirms these cy ... | 1988 | 3058316 |
| insulin and progesterone activate a common synthetic ribosomal protein s6 peptide kinase in xenopus oocytes. | a synthetic peptide arg-arg-leu-ser-ser-leu-arg-ala, the structure of which is based on that of a phosphorylated sequence in ribosomal protein s6, was employed as a probe for stimulated kinase activity in xenopus laevis oocytes induced to mature with insulin or progesterone. insulin elicited an early (20-30 min) 3-fold stimulation of s6 peptide phosphorylating activity that was not evident with progesterone. however, both hormones produced a delayed 7-12-fold stimulation of s6 peptide phosphoryl ... | 1988 | 3058511 |
| gene expression in amphibian embryogenesis. | the study of molecular events during the embryogenesis of xenopus laevis has advanced as a result of the availability of molecular markers, i.e., nucleic acid and antibody probes for genes that are expressed in a temporally and spatially regulated fashion during development. in this article we summarize results on the localized expression of keratin genes and on the reconstruction of regulated transcription of the gastrula/neurula-specific dg42 gene. furthermore, we discuss experiments that inve ... | 1988 | 3061595 |
| monoclonal antibodies to a mr 68,000 pore complex glycoprotein interfere with nuclear protein uptake in xenopus oocytes. | using a monoclonal antibody (pi1) raised against mouse lymphocyte nuclear matrix fractions we have identified a n-acetylglucosamine (glcnac)-containing glycoprotein of mr 68,000 as a component of the nuclear pore complexes of xenopus laevis oocytes. the antigenic determinant recognized by antibody pi1 comprises both the sugar moiety and protein sequences since, on the one hand, added glcnac competed effectively for antibody binding and, on the other hand, the antibody reacted in immunoblots with ... | 1988 | 3064988 |
| immunoglobulin fc receptor molecules on xenopus laevis splenocytes. | the existence of membrane-associated fc receptors for igy (fc nu r) or igm (fc mu r) was demonstrated on a large percentage of xenopus splenocytes. the fc receptors were detected by direct fluorescent staining in which the spleen cells were incubated with fluorescein isothiocyanate (fitc)-conjugated antigen-complexed igy antibodies or with fitc-conjugated heat-aggregated igm. results showed that 28.9% (sd +/- 5.1) and 5.3% (sd +/- 2.2) of the cells bear fcnu or fc mu receptors, respectively. the ... | 1988 | 3065222 |
| characterization of proteolytic activities in embryos of xenopus laevis. | 1. proteolytic activities in early embryos of xenopus laevis exhibited maximum levels at ph 3.2, 5.6 and 7.2 when 3h-bsa was used as substrate, and the maximum proteolytic activity at ph 3.2 was several thousand-fold higher during the tail bud stage than in the unfertilized egg. 2. the proteolytic activity at ph 3.2 was separated into two fractions by gel chromatography. one fraction corresponded to a mol. wt of about 40,000 and its activity was inhibited by thiol protease inhibitors. the other ... | 1988 | 3066576 |
| patterns of n-cam expression during myogenesis in xenopus laevis. | the neural cell adhesion molecule (n-cam) is seen in the membrane of nerves and muscles from several vertebrate species. using indirect immunofluorescence, we have examined the expression of this protein during embryonic and postembryonic myogenesis in the african clawed frog, xenopus laevis. while good staining for n-cam was seen in neuronal tissues at all stages examined, no staining of embryonic muscle was observed, including both mononucleated and polynucleated myoblasts. in contrast, limb m ... | 1988 | 3073079 |
| transdifferentiation of ocular tissues in larval xenopus laevis. | transdifferentiation phenomena offer a useful opportunity to study experimentally the mechanisms on which cell phenotypic stability depends. the capacities of vertebrate eye tissues to reprogram cell differentiation are well known in avian and mammalian embryos, and in larval and adult newt. from research into the capacity of anuran eye tissues to reprogram differentiation into a new pathway, considerable data have accumulated concerning the transdifferentiative capacities of eye tissues in larv ... | 1988 | 3073094 |
| the expression of epidermal antigens in xenopus laevis. | five kinds of monoclonal antibodies that are specific for the epidermis of xenopus embryos were produced. epidermis-specific antibodies were used to investigate the spatial and temporal expressions of epidermal antigens during embryonic and larval development. the cells that were recognized by the antibodies at the larval stage are as follows: all of the outer epidermal cells and cement gland cells were recognized by the antibody termed xepi-1, all of the outer and inner epidermal cells, except ... | 1988 | 3075541 |
| specificity and retinotectal projections of quarter-eye fragments in xenopus laevis. | three quarters of the eye anlage in xenopus embryos of stage 33/34 were eliminated in three different sets of experiments. the remaining quadrant originated from the nasoventral part of the retina, from its ventral portion, or from the temporo-ventral area of the retina. all the fragments developed into small eyes of normal shape. the retinotectal connections did not deviate from those found in the control groups, even though mirror-image duplication was fairly frequent. for all fragments the te ... | 1988 | 3077005 |
| regulation of transcript encoding the 43k subsynaptic protein during development and after denervation. | the postsynaptic membrane of vertebrate neuromuscular synapses is enriched in the four subunits of the acetylcholine receptor (achr) and in a peripheral membrane protein of mr = 43 x 10(3) (43k). although achrs are virtually restricted to the postsynaptic membrane of innervated adult muscle, developing and denervated adult muscle contain achrs at nonsynaptic regions. these nonsynaptic achrs accumulate because the level of mrna encoding achr subunits increases in response to a loss of muscle cell ... | 1988 | 3077352 |
| localization of c-myc expression during oogenesis and embryonic development in xenopus laevis. | the expression of the proto-oncogene c-myc during oogenesis and embryonic development was followed by in situ hybridization using a cytological protocol adapted to amphibian embryos. the c-myc rna was highly expressed in the cytoplasm of young oocytes and was further diluted during oocyte growth without specific localization. from the neurula stage on, new myc transcripts were detected and the whole embryo appeared positive with antisense myc rna probes relative to control sense rna probes. in a ... | 1988 | 3077353 |
| regulatory factors of embryonic stem cells. | the analysis of factors which regulate cell proliferation and differentiation in early mammalian development has been facilitated by the existence of cell lines derived from pluripotential stem cells of the early embryo; embryonal carcinoma (ec) cells and embryonic stem (es) cells. ec cells have proved to be a useful source of embryonic growth factors. a potent mitogen, ecdgf has been isolated from ec cell conditioned medium. ecdgf appears to be a novel member of the heparin binding growth facto ... | 1988 | 3077939 |
| developmental regulation of translation by the 5' noncoding region of murine c-myc mrna in xenopus laevis. | the translational efficiency of chloramphenicol acetyltransferase (cat) mrna containing a 5' noncoding sequence derived from exon 1 of the murine c-myc gene (360cat) has been examined at different stages of xenopus egg development. in contrast to its reduced translation in the xenopus oocyte, 360cat mrna is translated as efficiently as cat mrna when injected into either mature xenopus eggs or xenopus embryos. no significant alteration of 360cat mrna stability was observed up to 10 h post-fertili ... | 1988 | 3078957 |
| mauthner neurons survive metamorphosis in anurans: a comparative hrp study on the cytoarchitecture of mauthner neurons in amphibians. | giant medullary neurons were revealed in adult xenopus laevis and rana esculenta following hrp injections to the spinal cord. these neurons were identified as mauthner neurons because (1) they have the same position and orientation as the larval mauthner neurons, i.e., they lie at the level of the viiith nerve root. (2) they have two large dendritic trees that for each species are similar to those of the larval mauthner neurons, (3) they are clearly distinguishable from other large reticular neu ... | 1986 | 3081602 |
| valproate reduces excitability by blockage of sodium and potassium conductance. | effects of the antiepileptic drug valproate on sodium and potassium currents in the nodal membrane of peripheral nerve fibers of xenopus laevis were determined by voltage- and current-clamp experiments. under voltage-clamp conditions, a reduction of both sodium and potassium conductance (in a ratio of 2:1) was observed. typically, 2.4 mm (400 mg/l) valproate reduced the sodium current 54% and the potassium current 26%, at a membrane potential of 5 mv. valproate did not affect the leakage conduct ... | 1986 | 3084227 |
| a mass spectrometric method for the identification of novel peptides in xenopus laevis skin secretions. | the peptides secreted by the south african frog xenopus laevis were screened systematically using a strategy based on fabms. hplc of crude and sephadex g-10 chromatographed secretions showed that many more peptides were present in these secretions than those previously identified, i.e., xenopsin, caerulein, trh, and pgla. fractions from the hplc were analyzed directly by fabms to determine the molecular weights of these novel peptides. subsequent analyses, using a combination of fabms, manual ed ... | 1986 | 3084710 |
| the cellular distribution of histone h5 in embryonic and adult tissues of xenopus laevis and chicken. | the cellular distribution of histone h5 in embryonic and adult tissues of xenopus laevis and chicken has been established with monoclonal antibodies to histone h5. both in xenopus and in chicken, the protein has presumably a more widespread cellular distribution than hitherto expected but is absent in most embryonic tissues. at least in xenopus its presence seems not to be restricted to amitotic cells. arguments will be put forward histone h5 in these animals should be considered as a h1(0) type ... | 1986 | 3085145 |
| spatial domains within the early xenopus laevis embryo revealed by in situ hybridization and monoclonal antibodies. | | 1986 | 3085157 |
| cell surface carbohydrate involvement in controlling the adhesion and morphology of neural crest cells and melanophores of xenopus laevis. | pieces of dorsal neural tube (stages 22-23) or late neural crest tissue (stages 24-26) of xenopus laevis were cultured. migratory cells moved out of explants to form an outgrowth of multipolar melanophores on the substratum. treatment with beta-galactosidase (0.1-0.4 u/ml) to remove cell surface galactose was correlated with detachment of melanophores. in the presence of lower concentrations of this enzyme the shapes of these cells were converted to arborized, spidery morphologies and cell movem ... | 1986 | 3086486 |
| aerobic and anaerobic correlates of mechanical work by gastrocnemius muscles of the aquatic amphibian xenopus laevis. | isolated, saline-perfused gastrocnemius muscles of xenopus laevis were used to assess the relationships between aerobic and anaerobic metabolism during conditions of rest, isotonic contraction and recovery. the major part (85%) of the energy used during 25 min of isotonic contractions in the saline-perfused muscles was from anaerobic rather than aerobic sources. however, the small contribution made by oxidative metabolism during activity can be attributed, in part at least, to limitations impose ... | 1986 | 3088193 |
| processing of the thyrotropin releasing hormone (trh) precursor in xenopus skin and bovine hypothalamus: evidence for the existence of extended forms of trh. | acid extracts of xenopus laevis skin were fractionated by gel filtration on sephadex g50 ion-exchange chromatography and reverse-phase high performance liquid chromatography (hplc). peptides related to thyrotropin releasing hormone (trh) were identified in the eluted fractions by trypsin digestion and radioimmunoassay (ria) using antibodies to the trh tripeptide pglu-his-pro amide or to a trh-related pentapeptide pglu-his-pro-gly-lys. in addition to the tripeptide hormone, evidence was obtained ... | 1986 | 3088682 |
| the vitelline envelope to fertilization envelope conversion in eggs of xenopus laevis. | fertilization of the xenopus laevis egg causes the conversion of the vitelline envelope to the fertilization envelope, a change reflected in the loss of sperm penetrability of the egg and the appearance of an electron-dense layer on the outer aspect of the fertilization envelope. as seen by one-dimensional gel electrophoresis, two components with molecular weights of 69,000 and 64,000 in the vitelline envelope were converted to 66,000 and 61,000 in the fertilization envelope. by two-dimensional ... | 1986 | 3089852 |
| determination of human factor viii (ahg-associated protein)--antigen in endothelial cells from xenopus laevis (xth cells). evaluation of a sensitive elisa technique. | ahg-associated protein (ahg-a.p.), the antigen of the blood-clotting factor viii complex, is a specific endothelial cell marker. primary (p-xth) and established (xth-2) endothelial cells from the hearts of xenopus laevis tadpoles were assayed for the presence of this marker by means of immunological cross-reaction (recognition of common antigenic sites) with antiserum against human ahg-a.p. radial immunodiffusion and rocket immunoelectrophoresis proved to be insufficiently sensitive, whereas imm ... | 1986 | 3091251 |
| the synthesis and expression of hla-a and -b antigens in xenopus laevis oocytes. | purified mrna's encoding the hla-a and -b antigen heavy chains or beta 2-microglobulin were prepared from human b lymphoid cells by positive hybridization selection procedures. the role of chain association in the biosynthesis and intracellular transport of hla-a and -b antigens was investigated by injecting these mrna species into xenopus laevis oocytes and following the fates of the translated products by immunoprecipitation. when mrna encoding beta 2-microglobulin from the b lymphoblastoid ce ... | 1986 | 3092030 |
| subunit structure of a cortical granule lectin involved in the block to polyspermy in xenopus laevis eggs. | the cortical granule lectin of xenopus laevis eggs is a large molecular mass glycoprotein involved in the post-fertilization block to polyspermy. we have investigated the subunit structure of this lectin and found that the native molecule contains 10-12 monomers, each of which has considerable charge and size heterogeneity due to glycosylated side chains. in addition, significant amino acid sequence homology is indicated by peptide mapping of subunits separated by isoelectric focusing. | 1986 | 3093279 |
| isolation and characterization of a lectin from the cortical granules of xenopus laevis eggs. | a cortical granule lectin was isolated from eggs of the south african clawed toad xenopus laevis. the lectin was released from the cortical granules by activation of dejellied eggs with the ca2+ ionophore a23187. the lectin was purified by affinity chromatography with its natural ligand, the egg jelly coat, chemically coupled to a sepharose matrix. the purified lectin was homogeneous by the criteria of isoelectric focusing (pi = 4.6), immunodiffusion, and immunoelectrophoresis but existed in two ... | 1986 | 3098282 |
| periodic changes in the rigidity of activated anuran eggs depend on germinal vesicle materials. | the eggs of xenopus laevis and bufo bufo japonicus matured in vitro by progesterone were denuded and activated by electrical shock or pricking, and their diameters were determined periodically until the postactivation time equivalent to the 8- to 16-cell stage. normally matured eggs showed a quick rounding-up and flattening immediately after activation (activation response), followed by a periodic flattening and rounding-up (postactivation response) corresponding to the intervals of early cleava ... | 1986 | 3098597 |
| gas exchange, storage and transport in voluntarily diving xenopus laevis. | a closed, extracorporeal loop, containing oxygen and carbon dioxide electrodes, was developed in order to make continuous measurements of lung gas po2 (pao2) and pco2 (paco2) in undisturbed xenopus laevis. pulmonary r values (delta paco2/delta pao2) are about 0.8 during periods of lung ventilation in resting animals, but they fall very rapidly as a voluntary dive proceeds. in fact, the instantaneous r values for lung eventually fall to zero during a voluntary dive, since pao2 continues to declin ... | 1986 | 3100713 |
| globin evolution in the genus xenopus: comparative analysis of cdnas coding for adult globin polypeptides of xenopus borealis and xenopus tropicalis. | globin mrnas of xenopus borealis and xenopus tropicalis have been cloned and sequenced. the nucleotide and derived amino acid sequences were compared with each other and with already available data from xenopus laevis. this analysis rendered clear evidence that the common ancestor of x. laevis and x. borealis, but not of x. tropicalis, had lost one amino acid of the beta-globins prior to a genome duplication event that preceded the segregation of the former two species. replacement-site substitu ... | 1986 | 3100812 |
| lipid metabolic pathways operating in amphibian full-grown oocytes. | the utilization of (2-3h)-glycerol in lipid biosynthesis was analyzed in bufo arenarum and xenopus laevis full-grown oocytes. the precursor was more actively incorporated in xenopus laevis oocytes. neutral glycerides were the lipids displaying the highest levels of radioactivity followed by phosphatidylcholine and phosphatidylethanolamine. after reincubation of prelabeled oocytes in a saline buffer solution, a net fall in labeled phosphatidic acid concomitant with an increase in phosphatidylchol ... | 1987 | 3103976 |
| assessment of trh as a potential msh release stimulating factor in xenopus laevis. | this study considers the possible involvement of the tripeptide trh (thyrotropin releasing hormone) in the physiological regulation of melanophore stimulating hormone (msh) secretion from the pars intermedia of the toad, xenopus laevis. trh was shown to stimulate release of msh from superfused neurointermediate lobes obtained from white-background adapted animals, but had no effect on secretion from lobes of black-background adapted animals. immunohistochemical analysis revealed a rich trh-conta ... | 1987 | 3106938 |
| [a variety of human autoantibodies recognizes in hela cells 2 proteins related to the tfiiia factor of xenopus laevis which regularizes the transcription of ribosomal 5s rna]. | using the sera from two patients with autoimmune disorders, we have identified by immunoprecipitation of hela cell extracts two proteins with apparent molecular masses of 37 kda (p 37) and 32 kda (p 32). these proteins are associated with 5 s rna. they are antigenetically related to xenopus laevis 5 s rna transcription factor tfiiia, which is very abundant in early oocytes of this species. in contrast to what is observed in x. laevis oocytes, the tfiiia-related proteins of hela cells are present ... | 1987 | 3107764 |
| toad splenocytes bind human il-2 and anti-human il-2 receptor antibody specifically. | human r-dna il-2 and fluorescent (fl) mouse anti-human il-2 receptor antibody have been tested separately and in competition with each other for their capacities to bind to the splenocytes of xenopus laevis, the south african clawed toad. binding by fl*-mouse anti-dnp antibody of the same subclass (igg1, kappa) was used as a control. the results of visual tests using ril-2 coated fluorescent covaspheres demonstrate that the human mediator will bind cells of the toad spleen. moreover, the mediato ... | 1987 | 3108143 |
| intracellular ph and buffer power of type 1 and 2 fibres from skeletal muscle of xenopus laevis. | intracellular ph (phi) and buffering power of type 1 and type 2 fibres from the iliofibularis muscle of the clawed frog, xenopus laevis, have been measured using ph-sensitive microelectrodes. in phosphate buffered ringer's solution (extracellular ph 7.25, 20-22 degrees c), mean phi and its variance were similar in the two fibre types (6.86 +/- sd 0.15 +/- sem 0.03, n = 24, type 1, and 6.86 +/- sd 0.12 +/- sem 0.03, n = 15, type 2). on changing to ringer's solution containing co2 and hco3- (extra ... | 1987 | 3108853 |
| single olfactory organ associated with prosencephalic malformation and cyclopia in a xenopus laevis tadpole. | a cyclops xenopus laevis tadpole with a single olfactory organ is described. at a stage comparable to 48, the telencephalon was severely atrophic and only the region where the olfactory fibres terminated appeared to have the cytoarchitecture of the olfactory bulb. in this animal the central nervous system (cns) appeared normally developed only posterior to the preoptic area. the hypothesis of a diencephalic origin of the region where the olfactory fibres terminated is discussed in the light of o ... | 1987 | 3111639 |
| chromatin decondensation and dna synthesis in human sperm activated in vitro by using xenopus laevis egg extracts. | an in vitro sperm activation system was used to study nuclear swelling-chromatin decondensation and dna synthesis; processes that occur in vivo following fertilization. lysolecithin-permeabilized human sperm were incubated in xenopus laevis egg extract and examined by using phase-contrast light microscopy, electron microscopy, and autoradiography. during a 3-hour incubation, the activated sperm nuclear chromatin underwent a decondensation-recondensation cycle during which dna was synthesized. th ... | 1987 | 3112302 |
| nucleotide sequences of variable region segments of the immunoglobulin heavy chain of xenopus laevis. | | 1987 | 3112743 |
| enzymatic formation of queuosine and of glycosyl queuosine in yeast trnas microinjected into xenopus laevis oocytes. the effect of the anticodon loop sequence. | the eukaryotic trna-guanine transglycosylases (queuine insertases) catalyse an exchange of guanine for queuine in position 34, the wobble nucleoside, of trnas having a gun anticodon where n (position 36) stands for a, u, c or g. in trnaasp (anticodon quc) and trnatyr (anticodon q psi a) from certain eukaryotic cells, the nucleoside q-34 is further hypermodified into a glycosylated derivative by trna-queuine glycosyltransferase. in order to gain insight into the influence of the nucleosides in po ... | 1987 | 3117541 |
| biochemical research on oogenesis: protein synthesis in whole cells and in cell-free extracts of xenopus laevis immature ovaries. | nearly all trna molecules in previtellogenic oocytes of xenopus laevis are included in nucleoprotein particles sedimenting at 42s. the trna-binding sites of these particles have several properties in common with those of the ribosomes. this suggests that the 42s particles might behave like unprogrammed ribosomes and be the site of a template-independent polymerization of amino acids. we expected this reaction to be insensitive to protein synthesis inhibitors, such as cycloheximide and puromycin. ... | 1987 | 3118963 |
| biochemical research on oogenesis: protein synthesis by purified 42s particles from xenopus laevis and tinca tinca previtellogenic oocytes. | when incubated with atp and a labeled amino acid, the 42s particles from early oocytes of xenopus laevis and tinca tinca incorporate radioactivity into trna and into a high molecular mass material which can be identified as protein. this incorporation is totally independent of ribosomes of cytosolic, mitochondrial or bacterial origin. the incorporated amino acids are linked to a broad spectrum of proteins by covalent bonds. simple treatments such as incubation in buffer or addition of synthetic ... | 1987 | 3118964 |
| biochemical research on oogenesis: distribution of trna-linked peptides and proteins in previtellogenic oocytes of xenopus laevis. | peptides and proteins were detected in the deacylation products of trna purified from the 42s particles and from the messenger ribonucleoprotein particles (mrnps) present in the previtellogenic oocytes of xenopus laevis. only a small fraction of particle trna carries a peptide or protein chain. the bulk of particle trna is simply aminoacylated. the trna-linked peptide chains of the particles appear to turn over more slowly in vivo than aminoacyl trna. these chains could arise in the particles by ... | 1987 | 3118965 |
| the nuclear migration signal of xenopus laevis nucleoplasmin. | nucleoplasmin is the most abundant protein in the nucleus of xenopus laevis oocytes. its ability to target to the nucleus when microinjected into the cytoplasm has been the subject of many studies central to our understanding of how proteins segregate into nuclei. using a cdna clone we constructed beta-galactosidase-nucleoplasmin hybrids in modified bacterial expression vectors. the fusion proteins were expressed in escherichia coli, purified and injected into the cytoplasm of x. laevis oocytes. ... | 1987 | 3119324 |
| dna synthesis in a mitochondrial lysate of xenopus laevis oocytes. h strand replication in vitro. | conditions for efficient replication in vitro of mitochondrial dna l strand into h strand products have been established. gel electrophoresis and hybridization analyses of the products show that neosynthesized h strands are progressively elongated from the d-loop region, and some of them are synthesized as full-length molecules. evidence for initiation of these h strands de novo is presented. in contrast, there is no detectable l strand synthesis in vitro in this system. this may prove useful fo ... | 1987 | 3119861 |
| gtp-binding proteins gi and go transplanted onto xenopus oocyte by rat brain messenger rna. | after injection with messenger rna (mrna) isolated from rat brain, xenopus laevis oocytes acquired electrophysiological responsiveness to externally perfused acetylcholine (ach) or serotonin (5-ht), and elevated responsiveness to internally applied guanosine 5'-(3-o-thio)triphosphate (gtp gamma s). compared with the membranes of native oocytes, those of mrna-injected oocytes contained increased amounts of 39 and 41 kda proteins, which could be [32p]adp-ribosylated by pertussis toxin (ptx). the a ... | 1987 | 3123009 |
| thymosin beta 4xen: a new thymosin beta 4-like peptide in oocytes of xenopus laevis. | two new thymosin beta 4-like peptides have been detected in ovaries of xenopus laevis and rana esculenta. previously, it was reported that thymosin beta 4 can be found in various species, from mammals to amphibians, e.g., in x. laevis [s. erickson-viitanen, s. ruggieri, p. natalini, and b.l. horecker (1983) arch. biochem. biophys. 221, 570-576]. however, oocytes and spleen from r. esculenta contain no thymosin beta 4 but a similar peptide without methionine. the peptide from r. esculenta elutes ... | 1988 | 3124756 |
| antimicrobial properties of peptides from xenopus granular gland secretions. | previously, we described a family of novel broad spectrum antimicrobial peptides, magainins, from the skin of xenopus laevis. in this report we show that at least two other xenopus peptides, present in the skin and its secretions, pgla and a peptide released from the xenopsin precursor, exhibit antimicrobial properties comparable to the magainins. the identification of these newer members provides insight into the structural diversity of vertebrate antimicrobial peptides. | 1988 | 3125066 |
| comparison of benzo[a]pyrene-diol-epoxide binding to histone h2a with different carboxy-terminal regions. | we have compared (+/-)-7r,8t-dihydroxy-9t,10t-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (bpde-i) binding to three vertebrate histones h2a with different c-terminal regions. hplc analyses of core histones prepared from nuclei exposed to [3h]bpde-i showed that rat liver and chicken erythrocyte histones h2a were heavily labeled by [3h]bpde-i, but xenopus laevis liver histone h2a was not. this result was confirmed by hplc analyses of v8-protease digests of bpde-i bound to histone h2a purified from the t ... | 1988 | 3125994 |
| bufo japonicus japonicus and xenopus laevis laevis egg jellies contain structurally related antigens and cortical granule lectin ligands. | the antigenic relationship of the egg jelly coat glycoproteins from bufo japonicus japonicus and xenopus laevis laevis was investigated using agar double diffusion methods. the presence of ligands in the jelly coats for the cortical granule lectin from x.l. laevis eggs was also investigated. anti-jelly serum for both anuran species crossreacted with the jelly coat from the other species with precipitin patterns of identity. each egg jelly coat of both species contained two ligands for the cortic ... | 1988 | 3127533 |
| in vitro analysis of germ cell genotoxicity in testis explant cultures: spermatid micronucleus assays. | explant cultures of testes from the frog xenopus laevis have been employed to evaluate the application of testis culture to the routine screening of potential germ cell genotoxicants. testis explants were incubated with varied concentrations of 3 model mutagens (9,10-dimethyl-1,2-benzanthracene, cyclophosphamide, adriamycin) and solvent controls. round spermatids were isolated from testes cultured 2-30 days after exposure to each mutagen. the spermatids were then stained with hoechst 33258 and s ... | 1988 | 3127703 |
| the involvement of inositol 1,4,5-trisphosphate and calcium in the two-component response to acetylcholine in xenopus oocytes. | 1. the membrane response to acetylcholine (ach), inositol 1,4,5-trisphosphate (ip3) and intracellular ca2+ was studied in xenopus laevis oocytes under voltage-clamp conditions. 2. shallow, submembranal injections of ip3 in the animal hemisphere of the oocyte evoked a two-component response comprised of a rapid, transient component followed by a slow, sustained component. 3. when the injection pipette was inserted further into the cell (to 300 microns below the cell membrane), the fast component ... | 1987 | 3128657 |
| transcription of the drosophila melanogaster 5s rna gene requires an upstream promoter and four intragenic sequence elements. | linker-scanning (ls) mutations were constructed spanning the length of the drosophila melanogaster 5s rna gene. in vitro transcription analysis of the ls 5s dnas revealed five transcription control regions. one control region essential for transcription initiation was identified in the 5'-flanking sequence. the major sequence determinants of this upstream promoter region were located between coordinates -39 and -26 (-30 region), but important sequences extended to the transcription start site at ... | 1988 | 3130565 |
| [modification of the periodic albinism mutation in the xenopus laevis]. | | 1988 | 3131093 |
| excessive numbers of axons after early enucleation and blockade of metamorphosis in the oculomotor nerve of xenopus laevis. | the number of axons in the oculomotor (om) nerve of xenopus laevis tadpoles was counted in unoperated and in unilaterally enucleated animals, raised in 0.4 g/l thiourea (tu), a thyroid-blocking agent, which arrested their development at premetamorphosis. in unoperated animals the number of axons starts to decrease with metamorphosis. when raised in tu, the tadpoles do not metamorphose and show no axon loss; rather, there is a moderate increase in axon number (13%) after 6 months of thiourea-trea ... | 1988 | 3133082 |
| cytoskeletal actin gene families of xenopus borealis and xenopus laevis. | we have sequenced the coding and leader regions, as well as part of the 3' untranslated region, of a xenopus borealis type 1 cytoskeletal actin gene [defined according to the arrangement of acidic residues at the n-terminus; vandekerckhove et al. (1981) j mol biol 152:413-426]. the encoded amino acid sequence is the same as the avian and mammalian beta (type 1) cytoskeletal actins, except for an isoleucine at position 10 (as found in the mammalian gamma cytoskeletal actins), and an extra amino a ... | 1988 | 3133485 |
| isolation and structural analysis of a ribosomal protein gene in d.melanogaster. | by using the cdna clone containing the sequence for the l1 ribosomal protein gene of xenopus laevis as probe (1), we have isolated positive phages from a drosophila melanogaster genomic library. the drosophila genomic fragment, which gives the hybridization signal with the xenopus cdna, was sequenced: a region of 369 bp is 70% homologous to the sequence of x. laevis l1 cdna. the gene was localized in situ at position 98ab of the right arm of the third polytene chromosome. by s1 mapping and heter ... | 1988 | 3133637 |
| characterization of protein synthesis initiation factor 2 from xenopus laevis oocytes. | the protein synthesis initiation factor 2 (eif2) from xenopus laevis oocytes has been extensively purified and characterized. depending upon the purification scheme, eif2 containing three subunits (alpha, beta and gamma) with mr of 160,000, or two subunits (alpha and gamma) with mr 90,000 can be obtained. the key step for obtaining the three subunit factor is the addition of 30 mm benzamidine to the initial homogenization, since this compound protects the highly sensitive beta subunit from prote ... | 1988 | 3134946 |
| the finger motif defines a multigene family represented in the maternal mrna of xenopus laevis oocytes. | we have screened xenopus laevis cdna and genomic libraries for finger motif encoding sequences by use of a synthetic oligonucleotide probe coding for a stretch of conserved amino acids, the h/c-link, which joins individual finger loops in several multi-fingered proteins. our studies reveal that a large number of different cdna clones encode amino acid sequences predicting multiple units of the metal-coordinating finger structure. derived proteins are different from each other as well as from the ... | 1988 | 3139407 |
| studies on the mechanism of the reversal of rapid organelle transport in myelinated axons of xenopus laevis. | rapid organelle transport was studied by computer- and video-enhanced microscopy in the region of localized lesions in single myelinated axons of xenopus laevis. localized lesions were created that were either impermeable to small ions in the bathing medium or were permeable to agents with molecular weights up to 10,000. providing the axons were bathed in a suitable "internal" medium, organelle transport continued to within a few micrometers of the lesion whether the lesion was permeable or not. ... | 1988 | 3141070 |
| proteasomes (multi-protease complexes) as 20 s ring-shaped particles in a variety of eukaryotic cells. | latent multicatalytic protease complexes, named proteasomes, were purified to apparent homogeneity from various eukaryotic sources, such as human, rat, and chicken liver, xenopus laevis ovary, and yeast (saccharomyces cerevisiae), and their functional and structural properties were compared. they showed latency in breakdown of [methyl-3h]casein, but were greatly activated in various ways, such as by addition of polylysine. they all degraded three types of fluorogenic oligopeptides at the carboxy ... | 1988 | 3141402 |
| phylogenetic conservation of brain microtubule-associated proteins map2 and tau. | the major rat brain microtubule-associated proteins, map2 and tau, exhibit various properties that implicate them in the mechanisms underlying the growth of axons and dendrites during neuronal development. to determine if these properties represent fundamental morphogenetic mechanisms, we have examined the phylogenetic conservation of these proteins in xenopus laevis, quail and rat with respect to their molecular form, cytological distribution and developmental expression. in all three species, ... | 1988 | 3143928 |
| structure-activity relationships for osteolathyrism: ii. effects of alkyl-substituted acid hydrazides. | a series of 8 alkyl-substituted acid hydrazides were assayed for their toxicity and teratogenicity using early embryos of the frog xenopus laevis. each acid hydrazide was able to induce the connective tissue defect osteolathyrism. the 96-h toxicity (log lc50) and 96-h teratogenicity (log ec50) endpoints are correlated with hydrophobicity measured by the fragment substitution constant (fr). these relationships suggest the rate limiting step is the ability of the chemical to reach the site of acti ... | 1988 | 3144058 |
| proto-oncogenes and embryonic development. | the role of proto-oncogenes in embryonic development was investigated using one of the most characterized vertebrates, the amphibian xenopus laevis. genes which belong to the major proto-oncogene families have been detected in xenopus genome. the developmental control of the myc gene was assayed using a characterized xenopus myc probe and specific antibodies. the myc gene is highly expressed as a stable maternal mrna in oocyte, and an unfertilized egg contains 5 x 10(5)-fold the myc rna content ... | 1988 | 3145024 |
| pseudouridine modification in the trna(tyr) anticodon is dependent on the presence, but independent of the size and sequence, of the intron in eucaryotic trna(tyr) genes. | in saccharomyces cerevisiae, pseudouridine formation in the middle position of the trna(tyr) anticodon (psi 35) is dependent on the presence of the intron in the trna(tyr) gene (johnson and abelson, nature 302:681-687, 1983). drosophila melanogaster trna(tyr) genes contain introns of three size classes: 20 or 21 base pairs (bp) (six genes), 48 bp (one gene), and 113 bp (one gene). as in yeast, removal of the intron led to loss of psi 35 in the anticodon when transcription was assayed in xenopus ... | 1988 | 3145410 |
| primary structure and evolutionary relationship between the adult alpha-globin genes and their 5'-flanking regions of xenopus laevis and xenopus tropicalis. | to investigate the evolution of globin genes in the genus xenopus, we have determined the primary structure of the related adult alpha i- and alpha ii-globin genes of x. laevis and of the adult alpha-globin gene of x. tropicalis, including their 5'-flanking regions. all three genes are comprised of three exons and two introns at homologous positions. the exons are highly conserved and code for 141 amino acids. by contrast, the corresponding introns vary in length and show considerable divergence ... | 1988 | 3148743 |
| lectin binding on carbohydrate compounds of the flask cells in the claw-frog kidney. | the carbohydrate compounds of the mucus of flask cells in the kidney of claw-frogs (xenopus laevis) were analysed through lectin binding studies. after removing epoxy resin semithin sections were incubated with 7 lectins (wga, rca i, pna, lch, uea, lpa) marked by horseradish peroxidase and 2 unmarked lectins (vaa, con a). the glycosaminoglycans in the canalicular lumen of flask cells showed a strong reaction with wga and rca, whereas the binding of pha, con a, and lch was weaker. no reaction was ... | 1988 | 3149443 |
| multiple soluble vertebrate galactoside-binding lectins. | all vertebrates synthesize soluble galactoside-binding lectins. many are expressed at high levels in the embryo and at lower levels in the adult, whereas others show an inverse pattern of expression. most lectins tend to be concentrated in one or a number of specific cell types. in the past few years, the multiplicity of these lectins has become more apparent. for example, in xenopus laevis 3 galactoside-binding lectins, 2 with a preference for alpha-galactosides, have been purified and partiall ... | 1988 | 3149527 |
| membrane morphogenesis in retinal rod outer segments: inhibition by tunicamycin. | isolated xenopus laevis retinas were incubated with 3h-labeled mannose or leucine in the presence or absence of tunicamycin (tm), a selective inhibitor of dolichyl phosphate-dependent protein glycosylation. at a tm concentration of 20 micrograms/ml, the incorporation of [3h]mannose and [3h]leucine into retinal macromolecules was inhibited by approximately 66 and 12-16%, respectively, relative to controls. cellular uptake of the radiolabeled substrates was not inhibited at this tm concentration. ... | 1985 | 3155750 |
| suppression in xenopus laevis: thymus inducer, spleen effector cells. | studies were carried out on suppressor function in the amphibian xenopus laevis, the south african clawed toad. suppression by the thymus of haemagglutinin (ha) production by spleen is antigen-dependent, partially specific and not mhc-restricted in this species (ruben, buenafe & seivert, 1983). three questions were considered in this study. does the thymus effect suppression by stimulating peripheralized spleen effector cells, or do effector cells reside within the thymus? do macrophages partici ... | 1985 | 3156089 |
| xenopus mhc class ii molecules. i. identification and structural characterization. | class ii antigens from the xenopus laevis mhc (f haplotype) were identified by using a rabbit antihuman class ii beta-chain serum (anti-p29boost). this xenoantiserum inhibits bidirectional xenopus mlr (but not pha-stimulation), recognizes the same molecules as certain mhc-linked xenopus alloantisera, and immunoprecipitates class ii molecules from xenopus cells consistent with the tissue distribution of mammalian class ii molecules. the xenopus class ii molecules are composed of two different cha ... | 1985 | 3156930 |
| membrane assembly in retinal photoreceptors. ii. immunocytochemical analysis of freeze-fractured rod photoreceptor membranes using anti-opsin antibodies. | we have used a cytochemical technique for labeling freeze-fractured tissues (pinto da silva, p., c. parkison, and n. dwyer (1981) proc. natl. acad. sci. u.s.a. 78: 343-347) to examine the distribution of immunoreactive opsin in rod photoreceptor membranes. aldehyde-fixed retinas of african clawed frogs (xenopus laevis) embedded in a cross-linked protein matrix were frozen and fractured at -196 degrees c, then thawed and labeled with biotinylated sheep anti-cow opsin igg followed by avidin-ferrit ... | 1985 | 3156972 |
| isolation and characterization of the human tissue-type plasminogen activator structural gene including its 5' flanking region. | mrna specific for tissue type plasminogen activator (t-pa) is induced in hela cells by the tumor promoter phorbol myristate acetate (waller, e.k., and schleuning, w.d. (1985) j. biol. chem. 260, 6354-6360). to study the underlying mechanism, a cdna library was constructed from phorbol myristate acetate stimulated hela cell mrna and screened with two t-pa mrna specific oligonucleotides (edlund, t., ny, t., rånby, m., heden, l.-o., palm, g., holmgren, e., and josephson, s. (1983) proc. natl. acad. ... | 1985 | 3161893 |
| expression of epi 1, an epidermis-specific marker in xenopus laevis embryos, is specified prior to gastrulation. | the induction of morphologically observable neural structures occurs as the result of tissue interactions between chordamesoderm and overlying ectoderm beginning at gastrulation. since the future dorsal, and hence neural, side of the embryo is determined around the time of fertilization, we questioned whether the presumptive neural epithelium might have received some developmental instructions prior to contact with the migrating chordamesoderm. epi 1, a cell surface antigen present only on epide ... | 1988 | 3166428 |
| identification of domains involved in nuclear uptake and histone binding of protein n1 of xenopus laevis. | the karyophilic protein n1 (590 amino acids) is an abundant soluble protein of the nuclei of xenopus laevis oocytes where it forms defined complexes with histones h3 and h4. the amino acid sequence of this protein, as deduced from the cdna, reveals a putative nuclear targeting signal as well as two acidic domains which are candidates for the interaction with histones. using two different histone binding assays in vitro we have found that the deletion of the larger acidic domain reduces histone b ... | 1988 | 3168999 |
| effect of ultraviolet light on the expression of genes for human u1 rna. | two types of uv-light-induced inhibitions of the synthesis of small nuclear rna species u1, u2, u3, u4, and u5 were described previously: an immediate inhibition and a separate, delayed suppression that requires 1-2 hr of postirradiation cell incubation and uv doses that are about tenfold lower. in the present report, u1 rna transcription in isolated nuclei from hela cells, assayed by rnaase t1 protection, reproduced the delayed inhibition. the sizes of the protected rna fragments suggest that i ... | 1988 | 3170658 |
| video microscopic image processing facilitates the evaluation of light microscopic autoradiography at high magnification. | light microscopic autoradiographs of 3h-thymidine labelled unstained semithin sections of xenopus laevis embryonic nuclei were examined with conventional nomarski differential interference contrast, phase-contrast and video microscopy. whereas at low magnification it was possible to obtain a photograph of the nuclear structure and the silver grains in one focal plain, at high magnification, with small depths of focus, a satisfactory image was not attainable. therefore, we stored the images of th ... | 1988 | 3172186 |
| a third striated muscle actin gene is expressed during early development in the amphibian xenopus laevis. | during early embryonic development in the frog xenopus laevis, several muscle-specific actin genes encoding distinct actin protein isoforms are activated in cells of the embryonic muscle. in addition to the cardiac (or alpha 1) and skeletal (or alpha 2) actin genes, a third muscle-specific actin gene is expressed in the same embryonic tissue. we have determined the complete nucleotide sequence of this third gene and examined its expression in embryonic and adult tissues. during embryogenesis, th ... | 1988 | 3172214 |
| merkel cells and the mechanosensitivity of normal and regenerating nerves in xenopus skin. | we have investigated some of the physiological, morphological and trophic characteristics of the merkel cell-neurite complexes in the skin of xenopus laevis. the merkel cells, which are specialized sensory cells, occur in groups of 2-4 around the openings of the cutaneous gland ducts. a voltage-controlled mechanical stimulator was used to determine the distribution of mechanosensory thresholds across the skin; an analysis of the results revealed the presence of a single population of rapidly ada ... | 1988 | 3173695 |
| oocyte and somatic 5s ribosomal rna and 5s rna encoding genes in xenopus tropicalis. | we have investigated the structure of oocyte and somatic 5s ribosomal rna and of 5s rna encoding genes in xenopus tropicalis. the sequences of the two 5s rna families differ in four positions, but only one of these substitutions, a c to u transition in position 79 within the internal control region of the corresponding 5s rna encoding genes, is a distinguishing characteristic of all xenopus somatic and oocyte 5s rnas characterized to date, including those from xenopus laevis and xenopus borealis ... | 1988 | 3174434 |
| transient administration of estradiol-17 beta establishes an autoregulatory loop permanently inducing estrogen receptor mrna. | a single transient dose of estradiol-17 beta is sufficient to elicit the permanent induction of hepatic estrogen receptor mrna, which is induced 18-fold (from 0.13 to 2.4 molecules per cell) and then remains fully induced for at least 125 days. in primary liver cultures, extremely low concentrations of estradiol-17 beta, which are below the kd of the xenopus laevis estrogen receptor, maintain persistent induction of estrogen receptor mrna but not of estrogen-inducible vitellogenin mrna. these da ... | 1988 | 3174624 |
| [behavioral reactions of the clawed toad xenopus laevis to l- and d-isomers of amino acids]. | studies on the action of l- and d-isomers of amino acids upon motor activity in the clawed toad revealed that most effective among them are basic amino acids (all of them being essential) and hydrophobic amino acids (mainly essential ones). positive correlation was found between the effectiveness of hydrophobic amino acids on the motor activity of animals and their effectiveness with respect to taste receptors. the data obtained indicate the role of the olfactory receptors in realization of the ... | 1988 | 3176774 |
| site selection by the trna splicing endonuclease of xenopus laevis. | to investigate the mechanism by which the purified xenopus trna splicing endonuclease recognizes its splice sites, we utilized yeast pre-trna(3leu) and pre-trna(phe) variants constructed by in vitro mutagenesis. we found that the endonuclease interacts with conserved features of the mature trna domain. in particular, u8 and c56 may be examples of contact points between protein and rna. given that there are no conserved sequences at the splice junctions, the specificity of cutting at both splice ... | 1988 | 3180224 |
| reinvestigation of the role of the optic vesicle in embryonic lens induction. | the induction of the lens by the optic vesicle in amphibians is often cited as support for the view that a single inductive event can lead to determination in a multipotent tissue. this conclusion is based on transplantation experiments whose results indicate that many regions of embryonic ectoderm which would normally form epidermis can form a lens if brought into contact with the optic vesicle. although additional evidence argues that during normal development other tissues, acting before the ... | 1988 | 3181032 |
| cdna cloning of the developmentally regulated lamin liii of xenopus laevis. | lamins are nucleoskeletal proteins which form intermediate type filaments in close association with the inner nuclear envelope membrane. based on molecular and biochemical properties the lamins were grouped as type-a and type-b lamins, respectively. i have cloned the cdna encoding lamin liii of xenopus which is the lamin protein present in oocyte nuclei and in cleavage nuclei. the data presented here indicate that a pool of maternal lamin liii rna is synthesized very early in oogenesis and that ... | 1988 | 3181134 |
| in vitro formation of the "s" layer, a unique component of the fertilization envelope in xenopus laevis eggs. | the extracellular matrix (ecm) of unfertilized xenopus laevis eggs consists of an elaborate filamentous network in the perivitelline space (ps) and a thick fibrillar vitelline envelope (ve), with a thin layer of horizontal filaments (hf) separating the two. at fertilization this ecm is converted into the fertilization envelope (comprised of the fertilization (f) layer and altered ve), and a third layer, the smooth (s) layer, is formed at the upper boundary of the ps (larabell and chandler, 1988) ... | 1988 | 3181634 |
| a role for glyceraldehyde-3-phosphate dehydrogenase in the development of thermotolerance in xenopus laevis embryos. | during heat shock, xenopus laevis embryos exhibit an increase in the rate of accumulation of lactate and a loss of atp relative to non-heat-shocked control embryos. these results suggest that heat shock stimulates a shift in energy metabolism to anaerobic glycolysis while at the same time causing an increase in the demand for atp. we have evidence indicating that the embryo may meet such demands placed on it by increasing the levels of some glycolytic enzymes. in this report, we show that heat s ... | 1988 | 3182940 |
| evidence that regenerative ability is an intrinsic property of limb cells in xenopus. | xenopus laevis exhibits an ontogenetic decline in the ability to regenerate its limbs: young tadpoles can completely regenerate an amputated limb, whereas post metamorphic froglets regenerate at most a cartilagenous "spike." we have tested the regenerative competence of normally regenerating limb buds of stage 52-53 xenopus tadpoles grafted onto limb stumps of postmetamorphic froglets. the limb buds become vascularized and innervated by the host and, when amputated, regenerate limbs with normal ... | 1988 | 3183582 |
| s6 phosphorylation is regulated at multiple levels in xenopus laevis oocytes. | it is known that the 40s ribosomal protein s6 undergoes a dramatic increase in its level of phosphorylation during xenopus oocyte meiotic maturation in response to progesterone stimulation. during prophase arrest, the majority of s6 has 0 moles phosphate per mole protein; this increases to 4-5 moles phosphate per mole protein by the time of germinal vesicle breakdown (gvbd). our in vitro and in vivo studies indicate that the accumulation of phosphate on s6 is the net result of a 4-5-fold increas ... | 1988 | 3183597 |
| characterization of the repressed 5s dna minichromosomes assembled in vitro with a high-speed supernatant of xenopus laevis oocytes. | we describe an in vitro system, based on the xenopus laevis oocyte supernatant of glikin et al. (g. glikin, i. ruberti, and a. worcel, cell 37:33-41, 1984), that packages dna into minichromosomes with regularly spaced nucleosomes containing histones h3, h4, h2a, and h2b but no histone h1. the same supernatant also assembles the 5s rna transcription complex; however, under the conditions that favor chromatin assembly, transcription is inhibited and a phased nucleosome forms over the 5s rna gene. ... | 1988 | 3185548 |
| sequence elements essential for function of the xenopus laevis ribosomal dna enhancers. | the intergenic spacer region of the xenopus laevis ribosomal dna contains multiple elements which are either 60 or 81 base pairs long. clusters of these elements have previously been shown to act as position- and distance-independent enhancers on an rna polymerase i promoter when located in cis. by a combination of deletion and linker scanner mutagenesis we show that the sequences essential for enhancer function are located within a 56-base-pair region that is present in both the 60- and 81-base ... | 1988 | 3185550 |
| lack of axon regeneration of isthmic neurons in juvenile xenopus. | in young adult xenopus laevis frogs the axons of isthmic neurons projecting to the contralateral tectum were severed at the postoptic commissure and the survival of such neurons was studied between 2 and 26 weeks after the operation. pyknotic neurons were first observed in the isthmic nucleus 2 weeks after axotomy. the continued neuron loss resulted in the decrease from 2920 in intact animals to 1520 surviving isthmic neurons in animals 26 weeks after the operation. these findings suggest that ( ... | 1988 | 3185983 |