| synthesis and secretion of rat pancreatic proteins by xenopus laevis oocytes. | an in vivo translation system, the xenopus laevis oocyte, was employed to study the synthesis and secretion of pancreatic proteins. rna was purified from normal and diabetic rat pancreas and normal rat liver by use of guanidine isothiocyanate lysis and cesium chloride gradient centrifugation. the presence of functional mrna was documented by translation in a reticulocyte lysate that yielded precursors of all major secretory proteins, i.e., slightly higher mr than proteins synthesized in situ by ... | 1988 | 3186682 |
| gene expression in the embryonic nervous system of xenopus laevis. | development of the nervous system in the amphibian embryo is initiated during gastrulation by an inductive interaction between chordamesoderm and dorsal ectoderm. the induced ectoderm forms the neural plate while uninduced ectoderm generates epidermis. we screened for genes activated during gastrulation and expressed specifically in the nervous system of xenopus laevis in the expectation that clones representing such genes will constitute useful markers for the study of early neurogenesis. probe ... | 1988 | 3186710 |
| dexamethasone accelerates differentiation of a6 epithelia and increases response to vasopressin. | when seeded heavily on a porous tissue culture dish, a6 cells, derived from the kidney of xenopus laevis, form a highly differentiated epithelium within 4-6 days. when dexamethasone is added to the culture medium, morphological differentiation is completed by day 2, a time at which the control (untreated) is still a disorganized multilayer of cells. in addition to the morphologically evident monolayer of cuboidal cells, the accelerated differentiation is expressed as high transepithelial electri ... | 1988 | 3189533 |
| heat shock gene expression in xenopus laevis a6 cells in response to heat shock and sodium arsenite treatments. | continuous exposure of a xenopus laevis kidney epithelial cell line, a6, to either heat shock (33 degrees c) or sodium arsenite (50 microm) resulted in transient but markedly different temporal patterns of heat-shock protein (hsp) synthesis and hsp 70 and 30 mrna accumulation. heat-shock-induced synthesis of hsps was detectable within 1 h and reached maximum levels by 2-3 h. while sodium arsenite induced the synthesis of some hsps within 1 h, maximal hsp synthesis did not occur until 12 h. the p ... | 1988 | 3196465 |
| in vitro analysis of specificity during nerve-muscle synaptogenesis. | the early phase of synapse formation was studied in cultures of xenopus laevis spinal neurons and myotomal muscle cells. two early events are described: the pulsatile secretion of acetylcholine from the nerve terminal in response to myocytic or neuronal contacts, and the development of nerve-myocyte adhesion during the first few minutes of contact. the specificity in these early events in synaptogenesis was assessed with respect to the positional and clonal relationships of the neurons and myocy ... | 1988 | 3197513 |
| regional expression, pattern and timing of convergence and extension during gastrulation of xenopus laevis. | we show with time-lapse micrography that narrowing in the circumblastoporal dimension (convergence) and lengthening in the animal-vegetal dimension (extension) of the involuting marginal zone (imz) and the noninvoluting marginal zone (nimz) are the major tissue movements driving blastopore closure and involution of the imz during gastrulation in the south african clawed frog, xenopus laevis. analysis of blastopore closure shows that the degree of convergence is uniform from dorsal to ventral sid ... | 1988 | 3197629 |
| the behaviour and function of bottle cells during gastrulation of xenopus laevis. | the behaviour of bottle cells in normal and microsurgically altered gastrulae and in cultured explants of xenopus laevis was analysed, using time-lapse micrography, scanning electron microscopy (sem) and cell tracing with fluorescein dextran amine (fda). the results shed new light on the function of bottle cells. bottle cells forming in vivo show a predominantly animal-vegetal apical contraction and a concurrent apical-basal elongation, whereas those forming in cultured explants show uniform api ... | 1988 | 3197630 |
| temporal pattern of appearance and distribution of cholecystokinin-like peptides during development in xenopus laevis. | cholecystokinin (cck) radioimmunoassay and immunocytochemistry were used to localize the expression of cck-like peptides in the gut, brain, and skin of xenopus laevis during development from fertilization through metamorphosis to the adult form. cck-like peptides were first detected in the gut shortly before food was first observed in the lumen of the intestine. this cck-like immunoreactivity (cck-li) was localized in endocrine cells in the duodenal mucosa. gut cck-li decreased during metamorpho ... | 1988 | 3197950 |
| yolk proteins from nematodes, chickens, and frogs bind strongly and preferentially to left-handed z-dna. | yolk proteins purified from the nematode caenorhabditis elegans, from the frog xenopus laevis, and from chicken eggs all have the unexpected property of binding strongly and preferentially to a left-handed z-dna probe, brominated poly(dg-dc). we estimate that the nematode proteins bind to z-dna with an association constant of at least 10(4) (m-1) and that this association constant is at least 40-50-fold higher than the association constant to b-dna. thus, yolk proteins have a higher z-dna specif ... | 1988 | 3198611 |
| structure and organization of mouse u3b rna functional genes. | we report the isolation and primary structure of three genes encoding mouse u3b rna which are expressed after injection into xenopus laevis oocytes. over the u3b rna coding region, their sequences are perfectly identical, showing nine point differences with rat u3b, which do not alter the rna secondary structure. a comparison of the three mouse sequences for the gene flanks reveals the extensive divergence of the downstream regions, except for a few nucleotides adjacent to the u3 rna coding regi ... | 1988 | 3198636 |
| development of spinocerebellar afferents in the clawed toad, xenopus laevis. | the development of spinocerebellar projections in the clawed toad, xenopus laevis, was studied with horseradish peroxidase as an anterograde and retrograde tracer. early in development cells of origin of spinocerebellar projections were found, contralaterally, in or close to the medial motor column. in older tadpoles ipsilaterally projecting spinal neurons were also labeled from the cerebellum. these are virtually indistinguishable from the large primary motoneurons that occupy a very similar po ... | 1988 | 3198795 |
| destruction of a translationally controlled mrna in xenopus oocytes delays progesterone-induced maturation. | the maternal mrna d7 is a moderately abundant transcript in xenopus laevis whose expression is highest in, and perhaps restricted to, oogenesis and early embryogenesis. the nucleotide sequence of cloned d7 cdna was determined and shown to have the capacity to code for a 31-kd protein. this amino acid sequence was searched against a protein data base, and no homologous proteins were found. antibodies directed against d7 recognize in xenopus embryos a soluble, cytoplasmic protein with an apparent ... | 1988 | 3203907 |
| the xenopus laevis ribosomal gene promoter contains a binding site for nuclear factor-1. | nuclear factor i (nf1) is a dna binding protein that is known to function in the replication of adeno virus and also binds to many promoters recognized by rna polymerase ii. we have found that there is also an nf1 binding site within the ribosomal gene promoter from xenopus laevis as well as in several other promoters recognized by rna polymerase i. the function of a binding site for a polymerase ii transcription factor within a promoter recognized by polymerase i is not known. however, its pres ... | 1988 | 3205719 |
| erythroid specific activation of the xenopus laevis adult alpha-globin promoter in transient heterokaryons. | insertion of 1.5 kb of the 5' flanking region of the adult alpha-globin gene of x. laevis in front of the cat structural gene promotes synthesis of cat in transiently transfected x. laevis kidney cells. fusion of transiently transfected kidney cells with erythroblasts isolated from anaemic frogs stimulates cat expression 3-4 fold in the resulting transient heterokaryons. the stimulation is specific for the alpha-globin promoter and is obtained after fusion with erythroid cells but not with hepat ... | 1988 | 3205739 |
| the xenopus laevis mitochondrial protein mtdbp-c cooperatively folds the dna in vitro. | the binding of the xenopus laevis mitochondrial protein mtdbp-c to dna was studied by equilibrium density banding, agarose gel electrophoresis and electron microscopy. the results obtained show that the mtdbp-c binds cooperatively to dna irrespective of whether the dna is supercoiled, relaxed or linear and it induces the formation of superhelical turns locally leading to the formation of a highly folded structure. it appears that this protein could be involved in the compaction of dna in the mit ... | 1988 | 3208753 |
| effects of increasing ploidy on the lumbar lateral motor column and hindlimb of newly metamorphosed xenopus laevis: a comparison of diploid and triploid siblings. | this study was undertaken to determine how increasing ploidy in xenopus laevis affected the size of the lumbar lateral motor column (l-lmc) motoneuron population, the size of representative hindlimb muscles, and the relationship between these features in animals at the completion of metamorphosis. triploids were produced by exposing fertilized diploid eggs to increased hydrostatic pressure. in the triploids, l-lmc motoneuron number was significantly reduced and motoneuron nuclear cross-sectional ... | 1988 | 3209744 |
| water depth alters respiratory behaviour of xenopus laevis. | | 1988 | 3209976 |
| effect of sequence differences between somatic and oocyte 5s rna genes on transcriptional efficiency in an oocyte s150 extract. | the differential expression of the xenopus laevis somatic and oocyte 5s rna genes is partially, but not solely, due to several base differences near the 5' boundary of the internal control region. a hybrid oocyte 5s gene with somatic-type base changes at +47, +53, +55, and +56 had intermediate transcriptional activity in oocyte s150 extracts. these base substitutions also resulted in increased affinity for a factor(s), other than tfiiia, which forms a stable complex with the 5s gene. | 1988 | 3211136 |
| [the action of serotonin and its analogs on the in vitro maturation of amphibian oocytes]. | indolylalkylamines (5-ht, 5-chlorotryptamine, 5-ethyltryptamine) suppress or block the progesterone-induced oocyte maturation in bufo viridis and xenopus laevis and disturb cytoskeletal rearrangements associated with oocytes involved, together with the other transmitter systems, in modulation of progesterone effect. | 1988 | 3211454 |
| introduction of an intervening sequence into a human serine suppressor trna gene: effects on gene expression in vitro and in vivo. | the 13 nucleotide xenopus laevis tyrosine trna gene intervening sequence was into a human serine suppressor trna gene which lacked an intron, by site-directed mutagenesis. analysis of the products of in vitro transcription in a hela cell extract indicates that the intervening sequence is accurately removed to generate a mature sized rna identical to that obtained from an intron-less gene. analysis of the transcripts obtained in vitro and in vivo shows that the u in the cua anticodon sequence is ... | 1988 | 3211744 |
| lumbar lateral motor column development in triploid xenopus laevis. | the effects of increasing ploidy on the development of the lumbar lateral motor column (l-lmc) in xenopus laevis were investigated in order to determine how early events contribute to producing the significant difference in the average number of motoneurons present in diploid and triploid animals after cell death (sperry: j. comp. neurol. 277:499-508, '88). from naturally occurring diploid and experimentally produced triploid siblings at two stages prior to significant amounts of neuronal cell d ... | 1988 | 3216051 |
| preparation of shadowed nuclear envelopes from xenopus oocyte germinal vesicles for electron microscopy. | methods for examining the structure of the nuclear envelope of oocytes of xenopus laevis by electron microscopy using metal shadowing have been developed and evaluated. minor modifications were made to existing methods for preparing specimens by freeze drying, mainly to eliminate unnecessary steps and a rapid method for examining the structure and arrangement of nuclear envelope components, based on dehydration in an ethanol series followed by amyl acetate and then air drying, was also developed ... | 1988 | 3216383 |
| immuno-electron microscopic identification of human estrogen receptor-dna complexes at the estrogen-responsive element and in the first intron of a xenopus vitellogenin gene. | using an extract of nuclei from the estrogen-responsive human breast cancer cell line mcf-7, protein-dna complexes were assembled in vitro at the 5' end of the xenopus laevis vitellogenin gene b2 that is normally expressed in liver after estrogen induction. the complexes formed were analyzed by electron microscopy after labeling by the indirect colloidal gold immunological method using a monoclonal antibody specific for the human estrogen receptor. as identified by its interaction with protein a ... | 1988 | 3216393 |
| a novel synergistic stimulation of na+-transport across frog skin (xenopus laevis) by external cd2+- and ca2+-ions. | isolated skin of the clawed frog xenopus laevis was mounted in an ussing-chamber. the transcellular sodium-current (ina) was identified either as amiloride-blockable (10(-3) mol/l) short-circuit current (isc), or by correcting isc for the shunt-current obtained with mucosal tris. a dose of 10 mmol/l cd2+ applied to the mucosal side increased the current by about 70%. the half-maximal effect was reached at a cd2+-concentration of 2.6 mmol/l (in nacl-ringer). the quick and fully reversible effect ... | 1988 | 3217238 |
| [axonal projections of the cells of the dorsal ganglia in the lumbar segments of the spinal cord in tadpoles of the toad xenopus laevis]. | using anterograde labeling by horseradish peroxidase, studies have been made on the formation of axonal projections of cells of the dorsal ganglia in lumbar segments of xenopus tadpoles at different stages of development of their hindlimbs. it was shown that at the early stages of premetamorphosis, primary afferents grow into the spinal cord and form collaterals directed into the grey matter. during prometamorphosis, the axons reach lateral motor nucleus. at final stages of prometamorphosis, whe ... | 1988 | 3218403 |
| dna cloning and amino acid sequence determination of a major constituent protein of mammalian nucleoli. correspondence of the nucleoplasmin-related protein no38 to mammalian protein b23. | using a cdna probe encoding the nucleolar protein no38 of xenopus laevis, we have isolated clones that code for the corresponding mammalian protein from cdna libraries of mouse embryonal carcinoma and fetal liver cells. the murine cdna-derived amino acid sequence defines a polypeptide of 292 amino acids (including the initial methionine) of a total molecular weight of 32,560 and identifies a single approximately 1.5 kb mrna on northern blot hybridization. this polypeptide, which is highly homolo ... | 1988 | 3219912 |
| promoter sequences required for transcription of xenopus laevis histone genes in injected frog oocyte nuclei. | amphibian oogenesis is accompanied by the accumulation of histone mrna and proteins in the absence of ongoing dna replication. to begin an analysis of the mechanisms by which histone gene expression is regulated during frog oogenesis and embryogenesis, we used oocyte injection to examine the upstream sequences required for transcription of genes encoding each of the five histone classes. we found that sequences necessary for maximal levels of transcription are located 100 to 200 base pairs upstr ... | 1988 | 3221862 |
| observation on the basal lamina of duodenal epithelial cells during metamorphosis of xenopus laevis. | | 1988 | 3222037 |
| developmental expression of a neurofilament-m and two vimentin-like genes in xenopus laevis. | a hamster vimentin cdna probe has been used to isolate and characterize three xenopus laevis intermediate filament genes, named xif1, xif3 and xif6. of these, xif6 shows 89% homology at the amino acid level to a portion of porcine neurofilament-m. xif6 is transcribed solely in nervous tissue of embryos, commencing at the late neural tube stage. expression is totally dependent on an interaction between mesoderm and ectoderm during gastrulation and can be used as a marker of neural induction. xif1 ... | 1988 | 3224553 |
| vimentin expression in oocytes, eggs and early embryos of xenopus laevis. | immunocytochemical studies using a monoclonal anti-porcine vimentin antibody reveal a well-organized pattern of staining in xenopus laevis oocytes, eggs and early embryos. the positions of xenopus vimentin and desmin in two-dimensional (2d) polyacrylamide gels were first established by immunoblotting of muscle triton extracts with anti-intermediate filament antibodies (anti-ifa), which cross-react with all intermediate filament proteins (ifps). the anti-porcine vimentin reacts with vimentin and ... | 1988 | 3224554 |
| voltage dependence of na/k pump current in xenopus oocytes. | stage v and vi (dumont, j.n., 1972, j. morphol. 136:153-180) oocytes of xenopus laevis were treated with collagenase to remove follicular cells and were placed in k-free solution for 2 to 4 days to elevate internal [na]. na/k pump activity was studied by restoring the eggs to normal 3 mm k barth's solution and measuring membrane current-voltage (i-v) relationships before and after the addition of 10 microm dihydroouabain (dho) using a two-microelectrode voltage clamp. two pulse protocols were us ... | 1988 | 3225842 |
| a quantitative comparison of osteoclasts in the teeth of the anuran amphibian xenopus laevis. | an image-analysing computer was used to measure transectional areas of osteoclast cytoplasm and nuclei, the number of nuclei per osteoclast transection, odontoblast height and dentine thickness on serial sections of resorbing, erupting and ankylosed teeth from 3 groups of female frogs of different snout-vent lengths. all parameters except nuclear size were increased significantly between the small and large frogs, suggesting that larger teeth are resorbed by larger osteoclasts. because more time ... | 1988 | 3228388 |
| the jelly layers and cortex of the unfertilized xenopus laevis egg: carbohydrate, phospholipid and protein analysis. | differences in the carbohydrate composition were found in the jellies and the cortex of the unfertilized xenopus laevis egg using lectins and blood group antibodies. blood group h trisaccharide was detected in the outer jelly and "a-like" oligosaccharide was found in the inner jelly. the blood group a trisaccharide was detected in the vitelline envelope and the cortex. the plasma membranes were isolated and partially purified by differential centrifugation on sucrose cushion. the phospholipid co ... | 1988 | 3229420 |
| mitotic activity in the epidermal cells of regenerating hind limbs of xenopus laevis larvae after amputation at different levels. an autoradiographic study. | | 1988 | 3229686 |
| horseradish peroxidase study of tectal afferents in xenopus laevis with special emphasis on their relationship to the lateral-line system. | afferent projections to the tectum opticum of the clawed toad xenopus laevis were studied by injections of horseradish peroxidase (hrp) into the tectum. cells were labelled in the following nuclei, listed from rostral to caudal: nucleus entopeduncularis anterior, nucleus anterior thalami, nucleus posterior thalami, nucleus ventromedialis thalami, nucleus ventrolateralis thalami pars dorsalis, nucleus lateralis thalami pars posterodorsalis, nucleus neuropilis postthalamici, nucleus lentiformis me ... | 1988 | 3233482 |
| the role of external tensions in differentiation of xenopus laevis embryonic tissues. | explants extirpated from xenopus laevis embryos at the early gastrula stage were placed on pieces of hydrophilized latex film which were then either stretched or remained intact. in explants cultivated on the intact films most cells emigrated out of the explants and remained undifferentiated, whereas the explants on the films stretched for 10 min or more developed a normal set of rudiments. in the explants of suprablastoporal zone stretched perpendicularly to the cranio-caudal direction, the axi ... | 1988 | 3233534 |
| purification and characterization of cytoplasmic creatine kinase isozymes of xenopus laevis. | the soluble creatine kinase isozymes ck-ii, ck-iii, and ck-iv from xenopus laevis have been purified to apparent homogeneity and their subunits characterized by means of molecular weight, peptide pattern, and dissociation-reassociation experiments. ck-iii and ck-iv are homodimeric isozymes whose subunits are distinct in both molecular weight (42,000 and 41,000, respectively) and staphylococcus aureus v8 peptide pattern. in dissociation-reassociation experiments, those two subunits do form active ... | 1988 | 3242493 |
| amino acid sequence and molecular characterization of murine lamin b as deduced from cdna clones. | the nuclear lamina is the karyoskeletal structure, intimately associated with the nuclear envelope, that is widespread among the diverse types of eukaryotic cells. a family of proteins, termed lamins, has been shown to be a prominent component of this lamina, and various members of this family are differentially expressed in different cell types. in mammals, three major lamins (a, b, c) have been identified, and in all cells so far examined lamin b is constitutively expressed while lamins a and ... | 1988 | 3243285 |
| development and characterization of commissural interneurones in the spinal cord of xenopus laevis embryos revealed by antibodies to glycine. | by using an antibody to glutaraldehyde fixation products of glycine we have been able to observe the development of a defined population of spinal interneurones in the cns of xenopus laevis embryos. the first glycine immunoreactive (gly) somata appeared at stage 22 in the caudal hindbrain within a few hours of neural tube closure. the population then increased by extending caudally into the spinal cord and by infill. it was followed up to the time of hatching, stage 37/38. by observing gly cells ... | 1988 | 3246217 |
| purification, partial characterization and biological effects of the xtc mesoderm-inducing factor. | the mesoderm of xenopus laevis is formed through an inductive interaction in which a signal from the vegetal hemisphere of the blastula acts on overlying animal pole cells. we have recently reported that the xenopus xtc cell line secretes a mesoderm-inducing factor (mif) which may resemble the natural signal. in this paper, we describe the purification and biological effects of xtc-mif. xtc-mif is a hydrophobic protein with an isoelectric point of 7.8 and an apparent relative molecular mass (mr) ... | 1988 | 3246228 |
| patterns of junctional communication during development of the early amphibian embryo. | cell-cell communication through gap junctions was examined in xenopus laevis embryos between the 16-cell and early blastula stages using lucifer yellow, fluorescein, lead edta and dicyanoargentate as probes of junctional permeability. injections were made into cells whose position was identified with respect to the primary cleavage axis and the grey crescent. fitc dextrans revealed cytoplasmic bridges between the injected cell and its sister only. in the animal pole at the 16-cell stage at the f ... | 1988 | 3248524 |
| development of myotomal cells in xenopus laevis larvae. | electron microscopic appearances of xenopus laevis axial myotome cells were examined through stages 22-41 (nieuwkoop & faber, 1956). differentiated contractile structures were not observed in myotome cells at or before stage 22. at stages 24-25, myofibrils appeared both as disordered strands in association with tubular membranes, and in different degrees of assembly into ordered sarcomeres. by stage 28, all contractile organelles observed were organised into sarcomeres. the latter extended the l ... | 1988 | 3248960 |
| electrophysiology and dye-coupling are sexually dimorphic characteristics of individual laryngeal muscle fibers in xenopus laevis. | sex differences at the laryngeal neuromuscular junction of xenopus laevis were examined by recording intracellularly from muscle fibers in response to nerve stimulation. male laryngeal muscle contains 2 physiologically distinct fiber types. type i fibers generate postsynaptic potentials in response to low-magnitude stimulus pulses and action potentials in response to higher-magnitude stimulus pulses. type ii muscle fibers require repetitive stimulation for action potential production, probably b ... | 1988 | 3249234 |
| formation of visual pigment chromophores during the development of xenopus laevis. | retinoids in the eyes of xenopus laevis at several developmental stages, were analyzed by high-performance liquid chromatography (hplc). at stage 37/38, larval eyes contained mainly all-trans isomers of retinal, 3-dehydroretinal, retinyl ester and 3-dehydroretinyl ester. ratios of all-trans 3-dehydroretinal to retinal and of all-trans 3-dehydroretinyl ester to retinyl ester were almost 1 at the stage. with the advance of development, the amounts of all-trans retinal and 3-dehydroretinal decrease ... | 1988 | 3254649 |
| expression of size-selected messenger rna encoding the brain and adrenal gland angiotensin-ii receptor in xenopus laevis oocytes. | the expression of the rat angiotensin-ii receptor has been studied in xenopus oocytes. poly(a)+ rna isolated from the brain and adrenal gland was injected into oocytes, and the expression of the receptor in the oocyte plasma membrane was assayed by measuring the change in membrane potential in the presence of angiotensin-ii. expression of the angiotensin-ii receptor was detected 1.0-1.5 days after messenger rna (mrna) injection, and the degree of membrane depolarization was proportional to the a ... | 1988 | 3256274 |
| cloning of the mitochondrial genome of rana catesbeiana and the nucleotide sequences of the nd2 and five trna genes. | the entire mitochondrial genome of rana catesbeiana was cloned into a plasmid vector pbr322 at the unique bamhi site and the nucleotide sequences of the nd2 gene and of its flanking genes were determined. the nd2 gene was encoded by 1,033 base pairs and, as deduced from the nucleotide sequence, the nd2 product consisted of 344 amino acids with a molecular weight of 37,561. this gene was flanked on the 5' side by the trna genes for isoleucine, glutamine, and methionine and on the 3' side by those ... | 1988 | 3260590 |
| dependency of the force-velocity relationships on mg atp in different types of muscle fibers from xenopus laevis. | mgatp binding to the actomyosin complex is followed by the dissociation of actin and myosin. the rate of this dissociation process was determined from the relationship between the maximum velocity of shortening and the mgatp concentration. it is shown here that the overall dissociation rate is rather similar in different types of muscle fibers. the relation between mgatp concentration and the maximum shortening velocity was investigated in fast and slow fibers and bundles of myofibrils of the il ... | 1988 | 3260802 |
| oxygen consumption of single muscle fibres of rana temporaria and xenopus laevis at 20 degrees c. | 1. oxygen consumption of contracting single muscle fibres of rana temporaria and xenopus laevis was investigated at 20 degrees c. 2. single fibres of the tibialis anterior muscle of rana and the iliofibularis muscle of xenopus were mounted in a chamber containing ringer solution. the solution was stirred and its partial pressure of oxygen (po2) was continuously measured polarographically. 3. steady-state rates of oxygen consumption (vo2) of single fibres were determined as a function of twitch f ... | 1988 | 3261341 |
| stabilization and enhancement of primary cytostatic factor (csf) by atp and naf in amphibian egg cytosols. | amphibian zygotes microinjected with the cytoplasm or cytosol of unactivated eggs are arrested at metaphase of mitosis. the activity responsible for this effect has been designated primary "cytostatic factor (csf)." primary csf disappears from the cytoplasm after egg activation, as well as from cytosols after addition of ca2+. in the present study, using fresh cytosols of rana pipiens eggs, a unit of csf activity was defined as the dose required to arrest 50% of the recipients, and the specific ... | 1988 | 3261698 |
| induction of odorant-evoked current transients in xenopus oocytes injected with mrna isolated from the olfactory mucosa of rana pipiens. | total mrna isolated from the olfactory mucosa of the frog, rana pipiens, and from rat pup brains was microinjected into mature oocytes isolated from xenopus laevis. both populations of voltage-clamped oocytes as well as controls were non-responsive to an odorant mixture and other ligands two days later. on the 3rd day, oocytes microinjected with rat brain mrna responded to 5-hydroxytryptamine but not to an odorant mixture, while oocytes injected with rana pipiens olfactory mucosal mrna responded ... | 1988 | 3263588 |
| comparative studies of the haemagglutination of adult and umbilical cord erythrocytes by animal lectins. | 1. the sugar specificities of four lactose-binding lectins were studied through the agglutination of adult and/or umbilical cord human erythrocytes (ahrbc and/or chrbc). 2. rana catesbeiana egg lectin specifically agglutinated both intact blood group a-ahrbc and intact blood group a-chrbc. 3. rana catesbeiana liver lectin agglutinated intact a-ahrbc much more strongly than intact a-chrbc. 4. xenopus laevis skin lectin nonspecifically agglutinated ahrbc and chrbc. 5. plecoglossus altivelis egg le ... | 1988 | 3265660 |
| kinetics of histone gene expression during early development of xenopus laevis. | using literature data for transcriptional and translational rate constants, gene copy numbers, dna concentrations, and stability constants, we have calculated the expected concentrations of histones and histone mrna during embryogenesis of xenopus laevis. the results led us to conclude that: (i) for x. laevis the gene copy number of the histone genes is too low to ensure the synthesis of sufficient histones during very early development, inheritance from the oocyte of either histone protein or h ... | 1988 | 3267765 |
| mesoderm induction in xenopus laevis: responding cells must be in contact for mesoderm formation but suppression of epidermal differentiation can occur in single cells. | when xenopus embryos are cultured in calcium- and magnesium-free medium (cmfm), the blastomeres lose adhesion but continue dividing to form a loose heap of cells. if divalent cations are restored at the early gastrula stage the cells re-adhere and eventually form muscle (a mesodermal cell type) as well as epidermis. if, however, the cells are dispersed during culture in cmfm, muscle does not form following reaggregation although epidermis does. this suggests that culturing blastomeres in a heap ... | 1988 | 3268406 |
| molecular cloning and sequence analysis of two distinct types of xenopus laevis protein kinase c. | two distinct types of protein kinase c cdna clones were isolated from a xenopus laevis oocyte cdna library, and the complete nucleotide sequences were determined. the sequences encode a single open reading frame with a domain structure that consists of four constant (designated c1-c4) and five variable (designated v1-v5) regions. comparison of the two sequences shows good homology at the nucleotide and deduced amino acid level. the differences reside primarily in the variable regions. each clone ... | 1988 | 3272298 |
| the xenopus laevis estrogen receptor: sequence homology with human and avian receptors and identification of multiple estrogen receptor messenger ribonucleic acids. | we have isolated and sequenced a cdna clone encompassing the entire protein coding region of the xenopus laevis estrogen receptor (xer). the xenopus er, the first steroid hormone receptor to be sequenced from a cold-blooded organism, exhibits two regions of striking amino acid homology with the human and avian ers. in the putative dna binding region, the amino acid sequence of the xer differs from those of the human and avian ers at only one of 83 amino acids. the putative hormone binding region ... | 1987 | 3274894 |
| the metabolism of ribosomal proteins microinjected into the oocytes of xenopus laevis. | when the total proteins from xenopus laevis 60 s ribosomal subunits (tp60) were 3h-labeled in vitro and injected back into x. laevis oocytes, most 3h-tp60 are integrated into the cytoplasmic 60 s subunits via the nucleus during 16 h of incubation. in the oocytes whose rrna synthesis is inhibited, 3h-tp60 are rapidly degraded with a half-life of 2-3 h. this degradation ceased as soon as rrna synthesis was resumed, suggesting that ribosomal proteins unassociated with nascent rrna are unstable in t ... | 1988 | 3275544 |
| antimicrobial activity of synthetic magainin peptides and several analogues. | we have previously reported the isolation of two broad-spectrum antimicrobial peptides ("magainins") from the skin of the african clawed frog xenopus laevis. these natural peptides are active against many species of bacteria and fungi and also induce osmotic lysis of protozoa. in this report we demonstrate that synthetic magainin peptides appear to be indistinguishable from the natural products with respect to chromatographic properties and biological activity. these studies demonstrate conclusi ... | 1988 | 3277183 |
| mutational analysis of the tobacco mosaic virus 5'-leader for altered ability to enhance translation. | mutational analysis of the 5'-untranslated leader sequence (omega) of tobacco mosaic virus (tmv) was carried out to determine those sequences necessary for the translational enhancement associated with omega. five deletion mutants, a single base substitution, and a 25 base replacement mutant were tested for alterations in omega's ability to enhance expression of beta-glucuronidase (gus) mrna in tobacco mesophyll protoplasts and escherichia coli or chloramphenicol acetyltransferase (cat) mrna in ... | 1988 | 3278300 |
| early cross-striation formation in twitching xenopus myocytes in culture. | spontaneous release of neurotransmitter has been demonstrated in various types of synapses. its physiological significance, however, is still unknown. in nerve-muscle cultures of embryonic xenopus laevis, we observed that acetylcholine, which is released spontaneously at the synaptic terminal, caused frequent twitches of muscle cells. these muscle cells developed cross-striations earlier than neighboring non-twitching cells. this effect of innervation was unaffected by tetrodotoxin but was block ... | 1988 | 3279423 |
| a second antigenic heat shock protein of plasmodium falciparum. | we describe here an antigen of plasmodium falciparum, defined by a cdna clone designated ag361. the antigen is a soluble cytoplasmic 70-kd polypeptide present in all isolates analyzed and in all stages of asexual development in the blood. the antigen is a natural immunogen, although it lacks repeating epitopes of many p. falciparum antigens. ag361 shares extensive sequence homology with the hsp70 proteins of xenopus laevis, drosophila melanogaster, escherichia coli, and man, as well as a previou ... | 1988 | 3282854 |
| the entire mesodermal mantle behaves as spemann's organizer in dorsoanterior enhanced xenopus laevis embryos. | the body plan of xenopus laevis can be respecified by briefly exposing early cleavage stage embryos to lithium. such embryos develop exaggerated dorsoanterior structures such as a radial eye and cement gland (k.r. kao, y. masui, and r.p. elinson, 1986, nature (london) 322, 371-373). in this paper, we demonstrate that the enhanced dorsoanterior phenotype results from an overcommitment of mesoderm to dorsoanterior mesoderm. histological and immunohistochemical observations reveal that the embryos ... | 1988 | 3282938 |
| coupled transcription-translation of silkworm cytoplasmic polyhedrosis virus injected into oocytes of the frog, xenopus laevis. | the cytoplasmic polyhedrosis virus of the silkworm, bombyx mori, contains a ten-segmented, double-stranded rna genome and five species of polypeptides, v1 (mr 146,000), v2 (mr 140,000), v3 (mr 128,000)), v4 (mr 62,000), and v5 (mr 32,000). the virus contains an rna-dependent rna polymerase that transcribes the duplex genome rna to form mrna either in the infected animals or under appropriate conditions in vitro. we co-microinjected the virus, [alpha-32p]gtp and actinomycin d into oocytes of the ... | 1988 | 3283114 |
| amphibian oocyte maturation induced by extracts of physarum polycephalum in mitosis. | the orderly progression of eukaryotic cells from interphase to mitosis requires the close coordination of various nuclear and cytoplasmic events. studies from our laboratory and others on animal cells indicate that two activities, one present mainly in mitotic cells and the other exclusively in g1-phase cells, play a pivotal role in the regulation of initiation and completion of mitosis, respectively. the purpose of this study was to investigate whether these activities are expressed in the slim ... | 1988 | 3286658 |
| effect of anti-er antibodies within the er lumen of living cells. | we describe the production and partial characterization of 12 monoclonal antibodies raised against a preparation of endoplasmic reticulum membranes obtained from xenopus laevis liver. four of the antibodies cross-react with liver melanocytes; two of the antibodies recognize extracellular antigens, whilst the remaining six recognize antigens present in hepatocytes. the concentrations of these latter antigens increase markedly in livers stimulated by estrogen. western blotting analysis revealed th ... | 1988 | 3288484 |
| formation of flagella during interphase in secondary spermatocytes from xenopus laevis in vitro. | in cell culture, single motile flagella, 1 micron in length, were observed to grow from secondary spermatocytes of xenopus laevis within 2-3 hours after telophase i, at 22 degrees c. about 90% of the secondary spermatocytes formed flagella as observed by phase-contrast microscopy. the flagella grew up to 2-6 microns in length during interphase ii, which lasted about 18 hours. the presence of the "9 + 2" microtubular structure of the flagellar axonemes of secondary spermatocytes was confirmed by ... | 1988 | 3290387 |
| phosphorylation activity associated with plasma membrane-cortical granule complex of xenopus laevis oocytes. | plasma membrane-cortical granule complexes from xenopus laevis oocytes were isolated by a differential centrifugation procedure. membrane preparations incorporated 32p from [gamma-32p]atp predominantly into three protein bands of mr 128,000, 54,000 and 29,000, as determined by sodium dodecyl-polyacrylamide gel electrophoresis. progesterone and insulin, added in vitro to membranes, did not produce any change in this phosphorylation pattern, contrary to some previously published results. the avail ... | 1988 | 3291866 |
| oncogenic ras protein induces meiotic maturation of amphibian oocytes in the presence of protein synthesis inhibitors. | microinjection of the activated ras oncogenic protein can induce the meiotic maturation of xenopus laevis oocytes, a process that can also be triggered by progesterone or high concentrations of insulin. cycloheximide and puromycin, well-known inhibitors of protein synthesis, block the maturation process induced by progesterone and insulin but do not affect the maturation caused by h-raslys12 protein microinjection. theophylline, an inhibitor of camp phosphodiesterase that also affects oocyte pro ... | 1988 | 3292293 |
| differential expression of the ca2+-binding protein parvalbumin during myogenesis in xenopus laevis. | we have used immunocytological techniques to examine the developmental expression of the ca2+-binding protein parvalbumin in xenopus laevis embryos. western blot experiments show that at least three different forms of parvalbumin are expressed during embryogenesis; the tadpole tail expresses one form, adult brain expresses another, mylohyoid muscle expresses both, and gastrocnemius and sartorius muscles express these two plus a third form. parvalbumin (pv) is first detectable by immunofluorescen ... | 1988 | 3294065 |
| the processing and secretion of rat serum albumin by oocytes from xenopus laevis. | microinjection of rat liver mrna into xenopus oocytes led to the synthesis of intracellular proalbumin and the secretion of mature albumin into the incubation medium. the ionophore monensin abolished the secretion of albumin but not the processing of the precursor. a variety of protease inhibitors were added to the incubation medium but there was no detectable inhibition of proalbumin cleavage. | 1987 | 3297791 |
| a change of the hepatocyte population is responsible for the progressive increase of vitellogenin synthetic capacity at and after metamorphosis of xenopus laevis. | synthesis of the egg yolk precursor protein, vitellogenin, can be induced in adult, but not in larval, amphibian hepatocytes by estrogen treatment. the transition process for this inducibility of hepatocytes during development of xenopus laevis was examined, using primary cultures of hepatocytes. this was found to occur at about the metamorphic climax of stage 62, although the level of vitellogenin production was very limited at this stage. this low level seemed due neither to insufficient estra ... | 1987 | 3297851 |
| specific cell surface labels in the visual centers of xenopus laevis tadpole identified using monoclonal antibodies. | monoclonal antibodies (mabs) against the optic tectum of xenopus tadpoles were generated and screened by the immunofluorescent staining of frozen sections of tadpole brains. mab-a5 stains the 8th and 9th plexiform layers of the optic tectum, whereas mab-b2 stains all but the eighth and ninth plexiform layers of the optic tectum. mab-a5 antigen is also detectable in the nucleus of belonci, the corpus geniculatum thalamicum, the pretectal area, and the basal optic nucleus, all targets of the optic ... | 1987 | 3297854 |
| a distant enhancer element is required for polymerase iii transcription of a u6 rna gene. | u rnas are highly abundant small nuclear rnas involved in the processing of messenger rna. most u rna genes are thought to be transcribed by rna polymerase ii (pol ii). however, evidence has recently been presented that u6 rna genes are transcribed by rna polymerase iii (pol iii). in the light of these results it was surprising to find that the 5' flanking region of a mouse u6 rna gene includes a perfect copy of the octamer sequence motif, atttgcat, found in many rna polymerase ii transcription ... | 1987 | 3299107 |
| magainins, a class of antimicrobial peptides from xenopus skin: isolation, characterization of two active forms, and partial cdna sequence of a precursor. | a family of peptides with broad-spectrum antimicrobial activity has been isolated from the skin of the african clawed frog xenopus laevis. it consists of two closely related peptides that are each 23 amino acids and differ by two substitutions. these peptides are water soluble, nonhemolytic at their effective antimicrobial concentrations, and potentially amphiphilic. at low concentrations they inhibit growth of numerous species of bacteria and fungi and induce osmotic lysis of protozoa. the sequ ... | 1987 | 3299384 |
| the in vivo stability, maturation and aminoacylation of anticodon-substituted escherichia coli initiator methionine trnas. | we have constructed eight anticodon-modified escherichia coli initiator methionine (fmet) trnas by insertion of synthetic ribotrinucleotides between two fragments ('half molecules') derived from the initiator trna. the trinucleotides, namely cau (the normal anticodon), caa, cac, cag, gaa, gac, gag and gau, were joined to the 5' and 3' trna fragments with t4 rna ligase. the strategy of reconstruction permitted the insertion of radioactive 32p label between nucleotides 36 and 37. trnas were microi ... | 1987 | 3301339 |
| [the suitability of xenopus laevis as an alternative to european frogs caught in open country for student training]. | | 1987 | 3304948 |
| distribution of synaptic specializations along isolated motor units formed in xenopus nerve-muscle cultures. | the capacity of individual muscle cells and neurons to establish synaptic specializations along the entire extent of their neurite-muscle contacts was assessed in culture. spinal cord neurons derived from embryos of xenopus laevis were plated at low density in cultures of xenopus myotomal muscle cells in order to obtain isolated motor units whose neuron and muscle cells were not contacted by any other neuron. these isolated motor units were examined for localization of acetylcholine receptors (a ... | 1987 | 3305801 |
| cytoarchitecture of the xenopus thymus following gamma-irradiation. | this paper describes in vitro and in vivo attempts to deplete the 4- to 8-month-old xenopus laevis (j strain) thymus of its lymphocyte compartment. gamma irradiation (2-3000 rad) of the excised thymus, followed by two weeks in organ culture, is effective in removing lymphocytes, but causes drastic reduction in size and loss of normal architecture. in contrast, in vivo whole-body irradiation (3000 rad) and subsequent in situ residence for 8-14 days proves successful in providing a lymphocyte-depl ... | 1987 | 3308399 |
| a constitutive nucleolar protein identified as a member of the nucleoplasmin family. | using monoclonal antibodies we have localized a polypeptide, appearing on gel electrophoresis with a mr of approximately 38,000 and a pi of approximately 5.6, to the granular component of the nucleoli of xenopus laevis oocytes and a broad range of cells from various species. the protein (no38) also occurs in certain distinct nucleoplasmic particles but is not detected in ribosomes and other cytoplasmic components. during mitosis no38-containing material dissociates from the nucleolar organizer r ... | 1987 | 3308448 |
| cytoskeletal changes during oogenesis and early development of xenopus laevis. | the frog oocyte is well known for studies on the control of gene expression, but has been used much less in studies on the cytoskeleton. however, frog oocytes are very large single cells, whose cytoplasmic movements and asymmetries are fundamental to the correct development of the subsequent embryo. one particular example of asymmetrically distributed cytoplasm is germ plasm, thought to be important in the formation of the germ line. data are presented that show that germ plasm is highly concent ... | 1986 | 3308916 |
| antibodies to xenopus egg s6 kinase ii recognize s6 kinase from progesterone- and insulin-stimulated xenopus oocytes and from proliferating chicken embryo fibroblasts. | ribosomal protein s6 becomes highly phosphorylated during progesterone- or insulin-induced maturation of xenopus laevis oocytes. we have previously purified an mr 92,000 protein as one of the major s6 kinases from xenopus unfertilized eggs. in this paper we confirm by renaturation of activity from a sodium dodecyl sulfate-polyacrylamide gel that this protein is an s6 kinase. this enzyme, termed s6 kinase ii (s6 k ii), was used for the preparation of polyclonal antiserum. immunocomplexes formed w ... | 1987 | 3313008 |
| primary structures of three highly acidic ribosomal proteins s6, s12 and s15 from the archaebacterium halobacterium marismortui. | the amino acid sequences of three extremely acidic ribosomal proteins, s6, s12, and s15, from halobacterium marismortui have been determined. the sequences were obtained by the sequence analysis of peptides derived by enzymatic digestion with trypsin. stapylococcus aureus protease and chymotrypsin, as well as by cleavage with dilute hcl. the proteins, s6, s12 and s15, consist of 116, 147 and 102 amino acid residues, and have molecular masses of 12,251, 16,440 and 11,747 da, respectively. compari ... | 1987 | 3315748 |
| serum immunoreactive insulin levels in intact and regenerating postmetamorphic xenopus laevis. | in order to confirm the presence of immunoreactive insulin (iri) in the serum of postmetamorphic xenopus laevis, radioimmunoassay (ria) methods were used. the concentration of hormone found in samples of blood serum taken from nonanaesthetized intact male and female animals by the guillotine method was 10.46 +/- 0.76 microu/ml. significantly higher iri concentrations were found in our intact animals anaesthetized in ms 222 at ph 3.5 (21.9 microu/ml) compared with intact controls anaesthetized in ... | 1987 | 3316480 |
| the histone h1(0)/h5 variant and terminal differentiation of cells during development of xenopus laevis. | the maintenance of the differentiated condition is supposed to be associated with the presence of a histone of the h1(0)/h5 subclass. if the h1(0)/h5 variant has an important role in differentiation distinct from that of h1, it should display differential expression in time and position during development. here we report that this prediction is verified during xenopus laevis development, in which tadpoles exhibit a very characteristic, developmentally regulated pattern of histone h1(0)/h5 expres ... | 1987 | 3327718 |
| preliminary characterization of maturation-promoting factor from yeast saccharomyces cerevisiae. | it has been known for some time that maturation-promoting factor (mpf) appears in a wide variety of eukaryotic cells at m phase and exerts equal m-phase-promoting activity in both meiotic cells and mitotic cells in a non-specific manner. mpf was extracted from cdc20 mutant cells of the yeast saccharomyces cerevisiae synchronized at m phase by incubation at the restrictive temperature. when injected into immature oocytes of xenopus laevis, yeast mpf caused meiosis reinitiation in a dose-dependent ... | 1987 | 3329198 |
| endogenous lectin secretion into the extracellular matrix of early embryos of xenopus laevis. | an endogenous galactoside-binding lectin with subunit molecular weight of 43,000-45,000, previously detected in unfertilized eggs of xenopus laevis, persists at high levels in embryos through gastrulation. during embryonic development the lectin is found in cytoplasmic vesicles, and then is secreted into extracellular matrix which is prominent around the blastopore and on the roof of the blastocoel. the lectin is also found in the extracellular material in the developing neural fold. the presenc ... | 1988 | 3334717 |
| involvement of a calcium-phospholipid-dependent protein kinase in the maturation of xenopus laevis oocytes. | it has been described that phosphorylation, and dephosphorylation, of specific proteins is associated with key events of the cell cycle and is likely to be due to activation of kinase(s). from our results, the presence of calcium-phospholipid-dependent protein kinase (pkc) was clearly demonstrated in both the cytosolic and particulate fractions of immature xenopus laevis oocytes and in the cytosolic fraction of mature oocytes. however, it was less active in metaphase ii- than in prophase i-arres ... | 1988 | 3338563 |
| a two-dimensional nmr study of the antimicrobial peptide magainin 2. | using two-dimensional nmr spectroscopy, a complete 1h resonance assignment has been obtained for the peptide magainin 2 recently isolated from xenopus laevis. it is demonstrated that this peptide adopts an alpha-helical structure with amphiphilic character when dissolved in a mixture of trifluoroethanol (tfe) and h2o. the transition to the alpha-helical conformation occurs at very low concentrations of tfe. | 1988 | 3338566 |
| a possible maternal-effect mutant of xenopus laevis i. cytological and biochemical analyses of the unfertilized eggs and embryos. | in an effort to define the cause of the developmental arrest of offspring from a certain xenopus female (designated as no. 65), we have examined eggs and embryos from the female both cytologically and biochemically. light and electron microscopic observations revealed that all of the blastomeres from embryos of female no. 65 had multiple small spherical nuclei, while wild-type counterparts had a single lobulated nucleus. two-dimensional gel electrophoretic analyses demonstrated that a major acid ... | 1988 | 3338624 |
| intramolecular recombination between partially homologous sequences in escherichia coli and xenopus laevis oocytes. | we describe a system to analyze the individual contribution of a single physical dna end on intramolecular recombination between partially homologous sequences. we took advantage of this partial sequence divergence to measure the distance separating the dna end from the final recombination event. we show that a single physical dna end stimulates recombination when located in a region of homology. recombination frequency decreases gradually with the distance from the dna end. a recombinational ho ... | 1987 | 3306681 |
| freeze-fracture analysis of structural reorganization during meiotic maturation in oocytes of xenopus laevis. | during meiotic maturation, the cortex of oocytes of xenopus laevis undergoes structural reorganization, visualized in this study by freeze-fracture electron microscopy. in the full-grown but immature oocyte, annulate lamellae are dispersed throughout the subcortex of the egg, 5 to 20 micron from the plasma membrane. the annulate lamellae consist of well-organized stacks of membrane with visible pores. stimulation of meiotic maturation by progesterone leads to disruption of the annulate lamellae ... | 1988 | 3342433 |
| persistent estrogen induction of hepatic xenopus laevis serum retinol binding protein mrna. | administration of estradiol-17 beta to male xenopus laevis induces the hepatic mrna coding for the serum retinol binding protein (rbp) approximately 10-fold, both in vivo and in primary liver cultures. estrogen induction of rbp mrna is completely blocked by the anti-estrogen, hydroxytamoxifen. testosterone administration reduces the elevated level of rbp mrna observed in livers of female x. laevis to the constitutive level seen in livers of control male animals, and partially blocks the estrogen ... | 1988 | 3343247 |
| interleukins and t-cell ontogeny in xenopus laevis. | | 1987 | 3295893 |
| xenopus laevis in developmental and molecular biology. | xenopus laevis is a prime system for the study of embryogenesis in vertebrates. both prelocalized information in the egg and inductive interactions between cells contribute to the ordered increase in complexity during development. embryonic induction, discovered in amphibians, is being studied intensely in xenopus; recent work suggests a role for growth factors in this process. contributions of the xenopus system to the analysis of ribosomal and 5s rna genes, and the diverse and highly productiv ... | 1988 | 3287620 |
| development of voltage-dependent calcium, sodium, and potassium currents in xenopus spinal neurons. | action potentials of embryonic nerve and muscle cells often have a different ionic dependence and longer duration than those of mature cells. the action potential of spinal cord neurons from xenopus laevis exhibits a prominent calcium component at early stages of development that diminishes with age as the impulse becomes principally sodium dependent. whole-cell voltage-clamp analysis has been undertaken to characterize the changes in membrane currents during development of these neurons in cult ... | 1988 | 3346722 |
| the development of primary afferents to the lumbar spinal cord in xenopus laevis. | the development of dorsal root ganglia (drg) and the primary afferent system of the hindlimb was studied during metamorphosis in xenopus laevis larvae. the first drg cells appeared at stage 40 and at stage 48 the first primary afferent fibers entered the lumbar spinal cord where they bifurcated into ascending and descending branches. primary afferent fibers and the dendrites of the secondary motoneurons contacted first in a lateral (state 56) and later (stage 58) in a dorsomedial terminal field. ... | 1988 | 3347369 |
| role of the 3'-poly(a) sequence in translational regulation of mrnas in xenopus laevis oocytes. | we investigated the effect of 3'-noncoding and poly(a) sequences on the translation and stability of membrane-bound mrna (maize zein) and free mrna (xenopus beta-globin) by injecting sp6 transcripts into stage 6 xenopus oocytes. with zein mrna, the presence or absence of a 3'-noncoding or poly(a) sequence had little effect on mrna stability over 24 h, and the 3'-noncoding sequence played essentially no role in mrna translation. with short periods of incubation, e.g. 1-2 h, the presence or absenc ... | 1988 | 3356706 |
| morphology of the caudal spinal cord in rana (ranidae) and xenopus (pipidae) tadpoles. | using a variety of neuroanatomical and histological techniques, we compare the spinal cord and peripheral nerve distribution in the tails of larvae from xenopus laevis and three species of rana. the relatively large, postsacral spinal cord of xenopus contains abundant motoneurons and their axons. spinal nerves exit from the spinal cord in a regular array, one nerve per myotome, from the cervical region to near the end of the tail. somata of motoneurons innervating caudal myotomes are found along ... | 1988 | 3356808 |
| a monoclonal antibody specific for an epidermal cell antigen of xenopus laevis: electron microscopic observations using a gold-labeling method. | a monoclonal antibody (epi-1), raised against the supernatant of a homogenate of xenopus laevis larvae at the tailbud stage (stage 36/37), interacts specifically with a 250 kd epidermal antigen of xenopus. an immunocytochemical gold-labeling technique was used to investigate changes in antigen distribution during epidermal development of xenopus laevis. specific immunolabeling was initially detected over the endoplasmic reticulum in the outer epithelial cells of the late gastrula stage (stage 12 ... | 1988 | 3356895 |
| nucleotide sequence determination and secondary structure of xenopus u3 snrna. | using a combination of rna sequencing and construction of cdna clones followed by dna sequencing, we have determined the primary nucleotide sequence of u3 snrna in xenopus laevis and xenopus borealis. this molecule has a length of 219 nucleotides. alignment of the xenopus sequences with u3 snrna sequences from other organisms reveals three evolutionarily conserved blocks. we have probed the secondary structure of u3 snrna in intact xenopus laevis nuclei using single-strand specific chemical reag ... | 1988 | 3357768 |
| a comparison of the solution structures and conformational properties of the somatic and oocyte 5s rrnas of xenopus laevis. | the secondary and tertiary structures of xenopus oocyte and somatic 5s rrnas were investigated using chemical and enzymatic probes. the accessibility of both rnas towards single-strand specific nucleases (t1, t2, a and s1) and a helix-specific ribonuclease from cobra venom (rnase v1) was determined. the reactivity of nucleobase n7, n3 and n1 positions towards chemical probes was investigated under native (5 mm mgcl2, 100 mm kcl, 20 degrees c) and semi-denaturing (1 mm edta, 20 degrees c) conditi ... | 1988 | 3357778 |