| assay for characterization of human follicular oocyte maturation inhibitor using xenopus oocytes. | human follicular fluid from healthy mature graafian follicles and from pathologic ovarian cyst fluid was found to be inhibitory to progesterone-induced meiotic maturation of oocytes from the south african clawed toad, xenopus laevis. human follicular fluid but not human serum, collected from the same individuals, demonstrated a linear dose-response inhibition on the maturation of oocytes in the xenopus assay system. these findings indicate that the human follicular and cyst fluids contain oocyte ... | 1983 | 6860740 |
| cytogenetics of xenopus laevis. i. g-banding pattern of xenopus laevis chromosomes. | although karyotype analyses by g-band staining have been used routinely in mammals, birds and reptiles, few have been reported in amphibia. we succeeded, however, in differential chromosome staining of some chromosomes of the african clawed toad, xenopus laevis, by using the trypsin technique. | 1983 | 6861972 |
| isolation and characterization of a 7 s rnp particle from mature xenopus laevis oocytes. | mature oocytes of xenopus laevis contain a 7 s rnp particle consisting of two components, ribosomal 5 s rna and a protein of mr approximately 45000. the structure of the free 5 s rrna and the 7 s rnp complex has been studied by diethylpyrocarbonate modification of adenines. a74, a77, a90, a100, a101 and a103 of the 5 s rrna are protected upon association of the protein. | 1983 | 6862025 |
| the origin of the mesoderm in an anuran, xenopus laevis, and a urodele, ambystoma mexicanum. | we have investigated whether superficial cells of the blastula contribute to mesodermal structures in the anuran xenopus laevis and the urodele ambystoma mexicanum. the superficial cells alone of late blastulae of both embryos were labelled with bolton-hunter reagent and the embryos were allowed to develop. the progeny of the labelled cells were identified at later stages and the results demonstrate that superficial cells of xenopus blastulae make no significant contribution to the mesoderm, whe ... | 1983 | 6862108 |
| effects of temperature on the replication of chromosomal dna of xenopus laevis cells. | dna fibre autoradiography has been used to study the effects of temperature on the replication of chromosomal dna of xenopus laevis cells in tissue culture at 18, 23 and 28 degrees c. pulse/stepdown labelling shows that the dna replicates bidirectionally. origin-to-origin distances (initiation intervals) vary, but the range of and the mean initiation intervals at all three temperatures are much the same. the mean interval between initiation points is of the order of 60 to 66 microns. staggering ... | 1983 | 6863405 |
| nucleotide sequences of h1 histone genes from xenopus laevis. a recently diverged pair of h1 genes and an unusual h1 pseudogene. | four clones containing h1 histone gene sequences were previously isolated from a xenopus laevis genomic library (1) and we now present the complete nucleotide sequences of these h1 genes and their flanking regions. two of these genes code for minor h1 proteins, probably h1c, when expressed in the oocyte transcription/translation system and are present on clones with almost identical overall organization. however, at the nucleotide level these genes differ in showing base insertions and deletions ... | 1983 | 6866767 |
| non-lymphoid cells of the anuran spleen: an ultrastructural study in the natterjack, bufo calamita. | the present study is concerned with the ultrastructure of the spleen in the natterjack, bufo calamita (anura, bufonidae), with special emphasis on the structure and function of the non-lymphoid elements occurring in the red and white pulp. the organ consists of two clearly distinguishable areas, the white and the red pulp, separated by a prominent marginal zone. thus, the pattern of lymphocytic arrangement in the spleen of bufo calamita corresponds to a follicular model and is similar to that re ... | 1983 | 6869311 |
| an unusual excitatory action of adenosine on the ventricular muscle of the south african clawed toad (xenopus laevis). | the effects of adenyl compounds and some of their analogues were examined on atrial and ventricular muscle of xenopus laevis. in contrast to all heart muscle preparations studied previously, adenosine produced excitation of the ventricle of xenopus. 2-chloroadenosine, atp, beta, gamma-methylene atp (appcp) and alpha, beta-methylene atp (apcpp) also elicited excitation of xenopus ventricles; the order of potency being 2-chloroadenosine greater than atp greater than or equal to adenosine greater t ... | 1983 | 6873160 |
| the differentiation of the olfactory placode in xenopus laevis: a light and electron microscope study. | | 1983 | 6875050 |
| compartmental relationships between anuran primary spinal motoneurons and somitic muscle fibers that they first innervate. | the compartmental and clonal relationships between primary motoneurons and the myotubes they innervate have been studied in xenopus laevis embryos by initiating clones at blastula stages (32 to 512 cells) with intracellular injections of horseradish peroxidase (hrp). primary motoneurons and ventral myotome belong to the posterior-ventral compartment, whereas sensory neurons and dorsal myotome belong to the posterior-dorsal compartment (jacobson, m. (1983) j. neurosci. 3: 1019-1038). the pathways ... | 1983 | 6875662 |
| specific interaction of proteins with 5 s rna and trna in the 42 s storage particle of xenopus oocytes. | during early oogenesis in amphibia, most of the 5 s rna and trna is stored in a ribonucleoprotein particle that sediments at 42 s. in xenopus laevis the 42 s particle contains two major proteins: of mr 48 000 (p48) and 43 000 (p43). it is shown that heterogeneity in composition of the 42 s particle reflects a changing situation whereby initially, both 5 s rna and trna are complexed with p48 (1 molecule 5 s rna: 1 molecule p48; 2 or 3 molecules trna: 1 molecule p48), but later, trna becomes incre ... | 1983 | 6882765 |
| pattern regulation in isolated halves and blastomeres of early xenopus laevis. | xenopus embryos at the 2-cell stage were cut into right and left halves, those at the 4-cell stage into dorsal and ventral halves or individual blastomeres, and those at the 8-cell stage into lateral, animal and vegetal halves. defect embryos, that is, 8-cell embryos from which a particular pair of blastomeres had been removed, were also prepared. these halves, blastomeres and defect embryos were cultured in 50% leibovitz (l-15) medium supplement was determined from their macroscopic appearance ... | 1983 | 6886596 |
| a study of the growth cones of developing embryonic sensory neurites. | the scanning electron microscope was used to examine the growth cones of sensory neurites on the basal lamina of the trunk skin and on the myotomes in dissected embryos of the amphibian, xenopus laevis. on the myotomes growth cones are large and flat with extensive lamellipodia and many filopodia. on the skin growth cones are smaller and have simpler processes particularly in more ventral positions. where growth cones contact each other or other neurites they are very intimately apposed and show ... | 1983 | 6886615 |
| the early development of the primary sensory neurones in an amphibian embryo: a scanning electron microscope study. | we have described the development of the primary sensory system of the trunk region of xenopus laevis embryos from larval stages 21 to 32. the system is based upon rohon-beard and extramedullary cells, which have central axons forming a dorsolateral spinal tract and peripheral neurites which innervate the skin. the pioneer axons of the central tract grow along the outer surface of the cord at stage 22. these pioneer axons may be used by secondary axons as a growth substrate. as the tract forms i ... | 1983 | 6886616 |
| developmental changes in the distribution of acetylcholine receptors in the myotomes of xenopus laevis. | the acquisition and distribution of nerve fibres and of acetylcholine (ach) receptors were examined in the myotomes of xenopus laevis during normal development. this muscle is well-suited for investigating temporal relationships during neuromuscular synaptogenesis because the age of the xenopus embryo at the onset of innervation can be assessed with an accuracy of about one hour. myotomal nerve fibres were visualized after staining them with nitroblue tetrazolium and ach receptors were examined ... | 1983 | 6887034 |
| structural analysis of repetitive sequence elements transcribed in early development of xenopus laevis. | a cdna library prepared from mrna of xenopus laevis embryos was screened with a genomic dna fragment containing various transcribed repetitive sequence elements. comparison of the nucleotide sequence of two isolated cdnas and their genomic relatives allows one to define two transcribed repetitive sequence elements. one of them belongs to a highly reiterated family and consists of a tandem array of homologous subunits of 77-80 bp. the other is reiterated approximately 2200 times, has a size of 26 ... | 1983 | 6888377 |
| assembly, glycosylation, and secretion of the oligomeric rat prostatic binding protein in xenopus oocytes. | prostatic binding protein (pbp), a hormonally controlled oligomeric glycoprotein secreted by the rat ventral prostate, is composed of three different polypeptide chains, c1, c2, and c3. microinjection of prostate mrna into xenopus laevis oocytes results in the synthesis, processing, and correct assembly of these three components, and also in the export of pbp into the medium. the glycosylation of component c3--the only glycopeptide of pbp--by the oocyte enzymes does not lead to the same result a ... | 1982 | 6889597 |
| expression of ribosomal-protein genes in xenopus laevis development. | using probes to xenopus laevis ribosomal-protein (r-protein) mrnas, we have found that in the oocyte the accumulation of r-protein mrnas proceeds to a maximum level, which is attained at the onset of vitellogenesis and remains stable thereafter. in the embryo, r-protein mrna sequences are present at low levels in the cytoplasm during early cleavage (stages 2-5), become undetectable until gastrulation (stage 10) and accumulate progressively afterwards. normalization of the amount of mrna to cell ... | 1982 | 6889922 |
| retinal protein synthesis in relationship to environmental lighting. | a series of in vivo and in vitro experiments using xenopus laevis juvenile toads was conducted to probe the relationship between environmental lighting and protein synthesis in the retina. autoradiographic and biochemical analyses indicated that measurable changes in protein synthesis did not occur during a normal diurnal cycle when animals were conditioned to 12 hr light followed by 12 hr darkness each day (ld). however, when retinas from animals maintained in continuous darkness (dd) for 3 day ... | 1982 | 6890049 |
| transcription of complementary repeat sequences in amphibian oocytes. | repeat sequences are transcribed in the germinal vesicles of amphibian oocytes. in the hnrna population both complements of the repeats are found and can be readily detected because they form intermolecular duplex structures. the structure and formation of duplex regions have been studied in the hnrna of xenopus laevis, triturus cristatus, amphiuma means and necturus maculosus, a series of amphibians of increasing genome size (c-value). in t. cristatus, the duplex structures are mostly 600-1200 ... | 1982 | 6890891 |
| soluble acidic complexes containing histones h3 and h4 in nuclei of xenopus laevis oocytes. | oocyte nuclei of xenopus laevis contain nucleosomal-core histones in large amounts and in a soluble, non-chromatin-bound form. supernatant fractions (100,000 x g) from isolated nuclei are enriched in complexes containing histones h3 and h4, which are of distinct size (5.6s by sucrose gradient centrifugation, approximate molecular weight of 270,000 by gel filtration) and negatively charged (isoelectric at ph 4.4). these complexes bind to deae-sephacel and can be separated from nucleoplasmin. in d ... | 1982 | 6891289 |
| the heat-shock response in xenopus oocytes is controlled at the translational level. | xenopus laevis oocytes respond to high temperature (greater than 31 degrees c) by the synthesis of one major (70 kilodalton) protein and by a gradual reduction in the rate of normal protein synthesis. in contrast with most other cells, the heat-shock response of xenopus oocytes is controlled exclusively at the translational level. enucleated or alpha-amanitin-injected oocytes synthesize normal levels of heat-shock protein. thus high temperature induces the translation of preformed heat-shock mrn ... | 1982 | 6891290 |
| insensitivity to cytochalasin b of surface contractions keyed to cleavage in the xenopus egg. | in fertilized eggs of xenopus laevis a marked flattening of the pigmented animal hemisphere has been observed. the flattening begins 15-20 minutes before the appearance of the cleavage furrow. as the furrow develops, the pigmented surface relaxes and rounds up. the initial appearance of the furrow is thus shown to be a combination of furrow deepening and rounding up of adjacent pigmented surfaces. it is demonstrated that the flattening is not caused by gravity or osmotic mechanisms and that inte ... | 1982 | 6892157 |
| actin synthesis during the early development of xenopus laevis. | cytoskeletal beta and gamma-actin are amongst the most rapidly made proteins of oocytes, blastulae and late embryonic stages of xenopus laevis but, relative to other proteins, the rate of synthesis is low in the egg or cleaving embryo, although the messenger rna is present in comparable amounts at the different stages. actin synthesis therefore involves post-transcriptional regulation. alpha-actin, the actin class characteristics of straited muscle cells, is first detectable in late gastrulae an ... | 1980 | 6893718 |
| a dna binding protein from xenopus laevis oocyte mitochondria. | | 1981 | 6894896 |
| methylation of adenovirus genes in transformed cells and in vitro: influence on the regulation of gene expression? | an inverse correlation has been described between the levels of dna methylation in specific segments of adenovirus dna integrated into the genomes of transformed and tumor cells and the extent to which these segments are expressed as messenger rna. in the adenovirus type 2 (ad2)-transformed hamster cell lines he2 and he3, the virus-specific dna binding protein (dbp) is not expressed, and the dna in the dbp gene is completely methylated in all 5'-ccgg-3' sites. at least part of the late promoter/ ... | 1981 | 6895196 |
| the role of estrogen receptor in xenopus laevis vitellogenin gene expression. | administration of estradiol 17 beta [estra-1,3,5(10)-triene-3,17-beta-diol] to male xenopus laevis induces the massive synthesis by the liver of the egg yolk precursor phospholipoglycoprotein, vitellogenin, and its cognate mrnas. restimulation of male x. laevis that have been previously induced to synthesize vitellogenin mrna but are inactive in vitellogenin mrna synthesis at the time of restimulation with estrogen results in more rapid accumulation of vitellogenin mrna and more efficient transc ... | 1982 | 6896404 |
| a gradient of poly(a)+ rna sequences in xenopus laevis eggs and embryos. | | 1982 | 6896500 |
| h3 and h4 histone cdna sequences from xenopus: a sequence comparison of h4 genes. | ovarian poly (a) + rna from xenopus laevis and xenopus borealis was used to construct two cdna libraries which were screened for histone sequences. cdna clones to h4 mrna were obtained from both species and an h3 cdna clone from xenopus laevis. the complete dna sequences of these clones have been determined and are presented. these new sequences are compared with other h3 and h4 dna sequences both in the coding and 3' noncoding regions. we find that there is considerable non-random codon usage i ... | 1982 | 6896750 |
| estrogen dramatically decreases albumin mrna levels and albumin synthesis in xenopus laevis liver. | the levels of albumin mrna in xenopus laevis liver were measured at various times after injection of estradiol using two different methods involving hybridization of cloned albumin cdna to total liver rna. the absolute levels of albumin mrna fell by more than 95% during the first 4 days following estrogen treatment, then slowly returned to normal levels over the following 12 days. albumin synthesis paralleled the albumin mrna levels during the first 8 days after injection; but, 16 and 32 days af ... | 1982 | 6897244 |
| structural analysis of a cdna clone from xenopus laevis containing a repetitive sequence element. | | 1982 | 6897540 |
| the minimum intragenic sequences required for promotion of eukaryotic trna gene transcription. | transcription of eukaryotic trna genes is controlled by two intragenic regions, the d-control region (which in the trna codes for the d-stem and -loop) and the t-control region (which in the trna codes for the t psi c loop). to determine whether these sequences alone are sufficient to promote trna gene transcription in vitro, the two control regions of a drosophila trnaarg gene were cloned separately from the context of the parental dna (these constructions are called trna minigenes). the trna m ... | 1982 | 6924209 |
| progesterone induces a rapid increase in [ca2+]in of xenopus laevis oocytes. | progesterone causes a rapid increase in the intracellular free calcium level in fully grown amphibian oocytes. when albino xenopus laevis oocytes were microinjected with the ca-specific photoprotein aequorin, the calcium-induced luminescence from this protein increased at 40-60 sec after the addition of progesterone and returned to the control level within 5-6 min. no further change in the aequorin glow could be detected through the remainder of the maturation period. this transient increase in ... | 1980 | 6929506 |
| proteins iodinated by the chloramine-t method appear to be degraded at an abnormally rapid rate after endocytosis. | proteins labeled with either (3)h by reductive methylation or (125)i by the chloramine-t method were incubated with xenopus laevis oocytes; the incorporation and acid precipitability of the proteins were then studied. the uptake rates of both specifically incorporated (vitellogenin) and nonspecifically incorporated proteins (bovine serum albumin and x. laevis serum proteins lacking albumin) were not influenced by the method of labeling. however, (125)i-labeled proteins were apparently degraded a ... | 1980 | 6929509 |
| transcription units of chicken ovalbumin gene observed after injection of cloned complete genes into xenopus oocyte nuclei. | the organization of transcription of a well-characterized protein encoding gene was studied by microinjection and electron microscopy. circular recombinant dna molecules containing the complete chicken ovalbumin sequences (7.7 kilobases, contained in 11.5 kilobases of chicken dna) were microinjected into germinal vesicles of living oocytes of the clawed toad xenopus laevis, and their transcription was studied in nuclear spread preparations. evaluation of spread chromatin showed a limited number ... | 1980 | 6934527 |
| photoreactivation of uv induced cell killing, chromosome aberrations, sister chromatid exchanges, mutations and pyrimidine dimers in xenopus laevis fibroblasts. | fibroblasts from xenopus laevis, which possess photoreactivating enzyme were used to study the influence of photoreactivating light on the frequency of pyrimidine dimers in dna, chromosomal aberrations, sister chromatid exchanges, cell killing and the induction of gene mutations (ouabain-resistance) induced by 254 nm ultraviolet irradiation. the frequency of all biological endpoints studied were reduced following exposure to photoreactivating light parallel to the reduction in the frequencies of ... | 1980 | 6936598 |
| a mosaicism in the higher order structure of xenopus oocyte nucleolar chromatin prior to and during ribosomal gene transcription. | we report an analysis by electron microscopy of the differences in the folding of ribosomal gene and adjacent nontranscribed spacer dna of xenopus laevis oocytes into supranucleosomal chromatin structures. the chromatin structures identified in gene and spacer regions of transcriptionally active nucleoli (from stage 5 oocytes) were compared with those found in nucleoli prior to transcription (from stage 2 oocytes) to determine whether changes in the chromatin structure occur when transcription i ... | 1981 | 6939485 |
| in vitro transcription of cloned 5s rna genes of the newt notophthalmus. | recombinant plasmids that carried genes coding for 5s ribosomal rna of the newt, notophthalmus viridescens, were transcribed in vitro with extracts of xenopus laevis oocyte nuclei. plasmids containing multiple repeats of the 5s gene and spacer directed accurate transcription of 5s rna (120 bases). individual repeat units were recloned by inserting sau 3a restriction fragments into the bam hi site of plasmid pbr322. because each repeat was cut by the enzyme within the coding region, the inserts h ... | 1981 | 6945306 |
| 31p nmr reveals increased intracellular ph after fertilization in xenopus eggs. | 31p nmr spectra of mature eggs of the frog (xenopus laevis) were taken prior to and after both fertilization and activation by a ca2+/h+ ionophore (a23187). the eggs were constantly perfused with fresh well-buffered solution during the experiments, and the intracellular ph (phi) was determined from the ph-dependent chemical shift of the internal pi peak. the detection of this pi peak in the presence of overlapping yolk phosphoprotein signals was accomplished by a t2 experiment which discriminate ... | 1981 | 6945594 |
| transformation of frog embryos with a rabbit beta-globin gene. | in order to study the fate and possible expression of foreign dna during embryogenesis of the frog xenopus laevis, we have injected a rabbit beta-globin gene into fertilized xenopus eggs. frog embryo dna was extracted at various stages of development, fractionated by agarose gel electrophoresis, transferred to nitrocellulose filters, and hybridized to labeled beta-globin recombinant plasmid dna. it was found that the injected dna replicated extrachromosomally, reaching, at gastrula stage, a leve ... | 1981 | 6946453 |
| modulation of the neural control of the clasp reflex in male xenopus laevis by androgens: a multidisciplinary study. | the neural control of the clasp reflex in male xenopus laevis has been studied by using anatomical, electrophysiological, and biochemical techniques. neurons in spinal segment 2 of castrated males accumulate label after injection of [3h]-dihydrotestosterone; these neurons are distributed within the rostral portions of the motoneuronal pools of the sternoradialis and flexor carpi radialis muscles. in vitro recordings from the nerve to the sternoradialis muscle in the isolated spinal cord preparat ... | 1981 | 6946519 |
| internal control regions for transcription of eukaryotic trna genes. | we have identified the region within a eukaryotic trna gene required for initiation of transcription. these results were obtained by systematically constructing deletions extending from the 5' or the 3' flanking regions into a cloned drosophila trnaarg gene by using nuclease bal 31. the ability of the newly generated deletion clones to direct the in vitro synthesis of trna precursors was measured in transcription systems from xenopus laevis oocytes, drosophila kc cells, and hela cells. two contr ... | 1981 | 6947245 |
| mapping of transcription initiation and termination signals on xenopus laevis ribosomal dna. | we have injected cloned derivatives of xenopus laevis ribosomal genes into x. laevis oocyte nuclei and examined the resulting transcription complexes in the electron microscope. from this work we conclude that the promoter lies somewhere within a region between -320 nucleotides upstream and +113 nucleotides downstream from the site of transcription initiation. this assignment agrees with inferences based on sequence conservation. it further suggests that the duplicated initiation region sequence ... | 1982 | 6948303 |
| hybridization-selected translation of bombyx mori high-cysteine chorion proteins in xenopus laevis oocytes. | xenopus laevis oocytes were injected with poly(a)+-mrna isolated from chorionating follicular epithelium of the domesticated silk moth (bombyx mori). on two-dimensional gel electrophoresis, the resultant translation products comigrated with authentic, secreted, chorion standards, demonstrating that the frog oocyte system synthesizes and correctly process virtually all major chorion components. a cdna clone has been shown to contain sequences complementary to those of mrnas encoding b mori high-c ... | 1982 | 6951160 |
| expression of a cloned adenovirus gene is inhibited by in vitro methylation. | in many viral and nonviral eukaryotic systems, an inverse correlation has been observed between the extent of dna methylation at 5'-c-c-g-g-3' sites and the extent of expression of specific genes as mrna. the e2a region of adenovirus serotype 2 (ad2) dna encodes the ad2-specific dna binding protein required for viral dna replication. in three lines of ad2 transformed hamster cells (he1, he2, and he3), multiple copies of the major part of the ad2 genome persist in an integrated state. cell lines ... | 1982 | 6951163 |
| relationship between the two components of the split promoter of eukaryotic trna genes. | plasmids containing eukaryotic trna genes are faithfully transcribed in the nucleus of xenopus laevis oocytes [cortese, r., melton, d. a., tranquilla, t. & smith, j. d. (1978) nucleic acids res. 5, 4593-4611]. it has been established that two separated regions within the coding sequence of a trna gene are essential and sufficient for promotion of transcription [hofstetter, h., kressmann, a. & birnstiel, m. l. (1981) cell 24, 573-585; ciliberto, g., castagnoli, l., melton, d. a. & cortese, r. (19 ... | 1982 | 6952243 |
| in vitro replication of recombinant plasmids carrying chromosomal segments of xenopus laevis. | recombinant plasmids carrying a segment of xenopus laevis chromosomal dna were constructed with plasmid pbr322 as the vector. a recombinant plasmid pxy65 carrying a 3.2-kilobase bamhi segment of the chromosome of x. laevis has been found to contain a repetitive sequence dispersed throughout the x. laevis chromosomes. this plasmid initiated replication in vitro when the supercoiled circular molecules were incubated in a replication system. the other recombinant plasmids tested and the pbr322 vect ... | 1982 | 6954512 |
| dna primase activity associated with dna polymerase alpha from xenopus laevis ovaries. | one of the two forms of dna polymerase alpha from ovaries of the frog xenopus laevis catalyzed ribonucleoside triphosphate-dependent dna synthesis on single-stranded circular fd phage dna templates. dna synthesis was dependent on atp and added template. ctp, gtp, and utp stimulated dna synthesis but were not required and could not substitute for atp. dna synthesis was not inhibited by alpha-amanitin. neither poly(dt) nor double-stranded dna served as template. analysis of [32p]-dtmp-labeled prod ... | 1982 | 6961403 |
| the hatching enzyme from xenopus laevis: limited proteolysis of the fertilization envelope. | hatching in the amphibian xenopus laevis involves release of an embryo-secreted hatching enzyme, a protease, which weakens the envelope surrounding the embryo. the envelope is not totally solubilized, which infers that only selected envelope components are hydrolyzed by the enzyme. the susceptibility of the glycoprotein components composing the envelope to hydrolysis by the hatching enzyme was investigated. isolated envelopes in various physical states, ie, particulate and solubilized, were trea ... | 1981 | 6965088 |
| survey of the numbers and species of amphibia used in the united kingdom in 1977. | this survey suggests that about 115 000 amphibia, of which more than half were rana temporaria, were supplied for use in teaching and research in the uk during 1977. as only 27 000 were recorded as being used by universities, polytechnics and research institutes, probably mostly for teaching, it must be assumed that the majority are used for teaching purposes in schools. there has been an increase in the proportion of amphibia supplied by recognised suppliers, and also in that being 'purpose-bre ... | 1980 | 6965743 |
| lymphocyte reactivity to "t" and "b" cell mitogens in xenopus laevis: studies on thymus and spleen. | | 1980 | 6966237 |
| investigation of the determinants of nuclear pore number. | to assess the functional significance of nuclear pore complexes, we have investigated whether the number of pores per nucleus is determined by such factors as the nuclear volume, nuclear surface area, dna content, or aspects of nuclear activity. comparisons were made between cell types chosen to permit observation of differences in nuclear pore number as a function of differences in the other qualities measured. the number of nuclear pores was determined by freeze-etching and measurements of nuc ... | 1980 | 6966999 |
| responses of msh and prolactin cells to 5-hydroxytryptophan (5-htp) in amphibians and teleosts. | injection of 5-hydroxytryptophan (5-htp), a precursor of serotonin, induces dispersion of melanin in the amphibians, pleurodeles waltlii (urodela) and xenopus laevis (anura), in the goldfish, carassius auratus, and in the carp, cyprinus carpio. it is accompanied by a dispersion of erythrophore pigments. in the pituitaries of pleurodeles and goldfish, a stimulation of msh cells, characterized by a significant nuclear hypertrophy, is also observed; in carassius, msh cells may become degranulated. ... | 1980 | 6967354 |
| highly conserved lipoprotein assembly in teleost and amphibian yolk-platelet crystals. | ohlendorf et al. have reported that yolk-platelet crystals in the frog, xenopus laevis, were orthorhombic (space group p21221) and consisted of elongated asymmetric units (approximately 5.5 x 11.5 x 25 nm). the presence of an orthorhombic lattice in amphibian yolk platelets fulfilling the symmetry requirements of crystals had been missed in earlier structural interpretations. a comparative study of teleost, urodele and anuran yolk-platelet crystals performed in our laboratory has shown the wides ... | 1981 | 6969859 |
| [vestibular apparatus study of the toad, xenopus laevis, and rats under prolonged weightlessness]. | fertilized eggs of the clawed toad xenopus laevis were placed aboard of orbital laboratory of "salut-6" spacecraft where they developed for 20 days at temperature 15 degrees c. the larvae were fixed in weightlessness. light and electronmicroscopic studies revealed undisturbed structure on the saccular and utricular maculae and otolith membranes. some ultrastructural abnormalities were found in the inner ear of adult rats after 20 days of weightlessness ("kosmos-936"). | 1980 | 6970471 |
| a hormonal component in central vestibular compensation. | in developing clawed toads xenopus laevis, the compensation mechanism of behavioural defects caused by unilateral labyrinthectomy consists of two components, a vestibular one and a hormonal one. thyroxine accelerates this compensation. | 1980 | 6971023 |
| an atlas of notochord and somite morphogenesis in several anuran and urodelean amphibians. | a scanning electron microscopic, comparative survey of notochord and somite formation including some details of change in cell morphology and arrangement, was made of selected stages of two species of anuran amphibians (xenopus laevis and rana pipiens) and two species of urodeles (ambystoma mexicanum and pleurodeles waltlii). the ectoderm or neural plate was removed from fixed embryos and the dorsal aspect of the developing notochord and somite mesoderm was photographed. micrographs of comparabl ... | 1980 | 6971322 |
| ultrastructural events during early gonadal development in rana pipiens and xenopus laevis. | the establishment of the undifferentiated gonad was studied in xenopus laevis and rana pipiens using high resolution techniques. it was found that the cells of the so-called "mesonephric blastema" had no structural resemblance to the cells of the gonadal medulla in both species. furthermore, there was no morphological evidence that would suggest a migration of the former cells towards the incipient gonad at the time of its appearance. however, the basal lamina of the coelomic epithelium was inte ... | 1981 | 6973296 |
| cholesterol-induced in vitro maturation of oocytes of acipenser stellatus, xenopus laevis, and rana temporaria. | | 1981 | 6973502 |
| translation of lymphocyte mrna into biologically-active interleukin 2 in oocytes. | a variant line of murine t lymphoma el4 produces high levels of the lymphokine interleukin 2 (il 2) when it is stimulated with phorbol myristate acetate. we have extracted poly a+ rna from the stimulated cells and injected it into xenopus laevis oocytes. the injected oocytes synthesize a material with biologic and biochemical properties of murine il 2. namely, it stimulates the continued growth of a cloned, cytotoxic t cell line (the t cell growth factor assay) and it chromatographs on a gel fil ... | 1981 | 6975322 |
| the spatio-temporal framework of melanogenic induction in pigmented retinal cells of xenopus laevis. | using methods involving transplantation of neuroectoderm and eye rudiments between ap/ap mutants and +/+ embryos of xenopus laevis, new aspects of melanogenic induction have been ascertained. the possibility of separate induction of a melanocyte cell type and of the product of terminal differentiation in it-melanosomes, has been demonstrated. melanogenic induction starts at the late gastrula stage. it has an irreversible character which has been shown using the technique of double transplantatio ... | 1980 | 6975795 |
| experiments on anuran limb buds and their significance for principles of vertebrate limb development. | a standard set of six experiments performed on the limb buds of two species of anurans - rana temporaria and xenopus laevis - are described. the experiments are limb-bud amputation, distal to proximal shifts, proximal to distal shifts, inversion of the dorsoventral axis inversion of the anteroposterior axis and inversion of both axes. the results are compared to those previously reported for urodeles and chicks to determine whether any principles of vertebrate limb development can be formulated. ... | 1981 | 6975797 |
| uptake and localization of 3h-2 deoxy-d-glucose by retinal photoreceptors. | following dark incubation of isolated retinas of xenopus laevis in ringer solution supplemented with 3h-2-deoxy-d-glucose (2dg), virtually all of the uptake of the label was by the inner segments and synaptic bases of the photoreceptor cells. autoradiographs prepared from conventionally fixed tissue showed the same cellular distribution of label as those prepared from identically incubated, unfixed, freeze-dried retinas. however, fixation removed about 77% of the total counts. this fixation-labi ... | 1982 | 6976980 |
| amphibian neurotensin (nt) is not xenopsin (xp): dual presence of nt-like and xp-like peptides in various amphibia. | to clarify whether xenopsin (xp) is the amphibian counterpart of mammalian neurotensin (nt), extracts of skin, brain, and intestine from representative amphibians were subjected to immunochemical, chromatographic, and biological analyses. the results indicated the dual presence of nt- and xp-like peptides in extracts of tissues from xenopus laevis, rana catesbeiana, rana pipiens, bufo marinus, bufo americanus, and necturus maculosus, which were separated during gel chromatography on sephadex g-2 ... | 1982 | 6977439 |
| autoradiographic study on the distribution of thymus-derived and thymus-independent lymphocytes in the spleen of xenopus laevis. | non-thymectomized and early-thymectomized xenopus laevis were injected with 3h-thymidine, and labelled lymphocytes from thymus, spleen, and peripheral blood were transferred to histocompatible recipients to study their distribution by autoradiography. an extremely high proportion of labelled thymocytes was localized in the splenic red pulp of both non-thymectomized and thymectomized recipients after transfer. labelled splenic lymphocytes were localized in a significantly higher density in the sp ... | 1982 | 6978268 |
| histones synthesized for use in early development of xenopus laevis are stored as a complex with antigenic properties similar to those of the octamer core of nucleosomes. | serum of patients with systemic lupus erythematosus (sle) contains crossreacting autoantibodies which recognize histones in nucleosomes or when they are induced to form octamers in solution in the presence of 2 m nacl, but not when they are dissociated free in solution at physiological ionic strength. we have found that histones stored in eggs of xenopus laevis for use in rapid nuclear synthesis during early development react with this antibody. this reaction has been observed by radioimmunoassa ... | 1982 | 6979546 |
| biophysics of underwater hearing in anuran amphibians. | a standing wave tube apparatus was used to determine the biophysical basis of underwater hearing sensitivity in 3 species of rana and in xenopus laevis. a speaker inside the base of a vertical, water-filled 3 m steel pipe produced standing waves. pressure and particle motion were measured with a hydrophone and geophone respectively and were spatially 90 degrees out of phase along the length of the tube. microphonic responses were recorded from the inner ear of frogs lowered through pressure and ... | 1982 | 6980964 |
| transport and phosphorylation of 2-deoxy-d-glucose by amphibian retina. effects of light and darkness. | we studied the uptake of 2-deoxy-d-glucose (2dg) and the synthesis of its phosphorylated product 2dg-6-phosphate (2dg-6p) by the retinas of the clawed frog (xenopus laevis) and the bullfrog (rana catesbeiana). autoradiographs showed that most of the retinal 2dg uptake is by the photoreceptor layer. the 2dg accumulation by isolated xenopus retinas was time and concentration dependent. the kt for transport was 5.05 mm; vmax was 6.99 x 10(-10) mol . mg-1 tissue wet weight min-1. the km for 2dg-6p f ... | 1982 | 6981682 |
| potassium permeability in thin amphibian myelinated fibres. | potential clamp analysis of thin (10-12 micrometers) myelinated fibres from amphibia (xenopus laevis and rana temporaria) showed that they had a large delayed k-permeability (pk) and a pk/pna-ratio of 0.32, which is similar to the ratio in large (25-30 micrometers) frog fibres. these results agree with earlier evidence of a large delayed pk in 10-15 micrometers rana fibres; a recent description of a size-dependent difference in pk was thus not confirmed. the large pk (0.32 cm3s-1 x 10(-9) in 10- ... | 1982 | 6981796 |
| development of peroxisomes in amphibians. ii. cytochemical and biochemical studies on the liver, kidney, and pancreas. | the ontogeny of catalase-containing organelles was studied by cytochemical and biochemical methods in the liver, kidney, and pancreas during the development of rana catesbeiana. the biochemical differentiation of peroxisome in the liver and kidney was compared to that of xenopus laevis. catalase activity was localized after incubation in dab medium and studied biochemically by a spectrophotometric method. in rana catesbeiana the number of catalase-positive organelles per cell section is low in a ... | 1982 | 6982309 |
| karyophilic proteins: polypeptides synthesized in vitro accumulate in the nucleus on microinjection into the cytoplasm of amphibian oocytes. | the specific nucleocytoplasmic compartmentalization of proteins has been examined for some major soluble acidic nuclear proteins in oocytes of different amphibia. proteins synthesized and radioactively labeled by translation in vitro, by using mrna from ovaries of the frog xenopus laevis, were injected into the cytoplasm of living oocytes of xenopus or of the salamander pleurodeles waltlii. at various times after injection, nucleus and cytoplasm were manually separated and endogenous and injecte ... | 1982 | 6982470 |
| growth of anuran oocytes in serum-supplemented medium. | appropriately-sized oocytes from xenopus laevis can be grown in vitro in vitellogenin-containing serum for up to 2 weeks. the source of serum appears to be unimportant. rates of oocyte growth are somewhat better than those achieved in the presence of vitellogenin alone. rana pipiens oocytes grow about twice as fast as x. laevis oocytes under identical conditions. the oocyte culture conditions described appear to be applicable to amphibian oocytes in general. | 1980 | 6984201 |
| the action of low-intensity pulsed ultrasound on amphibian embryonic tissues. | amphibian embryos at different stages of development, and ectomesodermal explants (small pieces of embryonic tissue extirpated from lateral parts of the embryos just after neurulation), have been irradiated with continuous and pulsed ultrasound at a frequency of 0.88 mhz, spatial and temporal average intensities being within the range 0.025-0.1 w cm2. ultrasound pulse repetition frequencies were varied within 10-1000 hz, duty factor being constant and equal to 0.5. destruction of embryonic tissu ... | 1982 | 6984549 |
| immunological identification and localization of the predominant nuclear protein of the amphibian oocyte nucleus. | nuclei of vitellogenic oocytes of the frog, xenopus laevis, contain a prominent protein, representing about 10% of nuclear protein, which is characterized by a polypeptide of m(r) 30,000. this protein is highly phosphorylated and acidic, displays several isoelectric variants with pi values ranging from 4.7 to 5.3, shows a high thermostability, is not stably complexed with other proteins, and is readily extracted in buffer solutions. guinea pig antibodies against this protein have allowed its spe ... | 1980 | 6987661 |
| development of the mitochondrial mass and accumulation of mtdna in previtellogenic stages of xenopus laevis oocytes. | the development of the mitochondrial mass of the previtellogenic oocytes of xenopus laevis has been analysed by a morphometric method and it has been correlated with the growth of the occyte itself. the study which was performed with oocytes from females of very different ages shows that the relative size of the mitochondrial mass in the smallest oocytes decreases gradually with the age of the females. cytophotometric analysis of the feulgen-stained mitochondrial mass enabled the mtdna content o ... | 1980 | 6988447 |
| effects of n-methyl-n-nitrosourea on the lymphoid tissues and skin allograft response of xenopus laevis. | | 1980 | 6995191 |
| initiation of ribosomal rna chains in homogenates of oocyte nuclei. | we have studied rna synthesis in homogenates of nuclei manually isolated from mature oocytes of xenopus laevis. transcription of the endogenous template is completely resistant to alpha-amanitin and represents primarily transcription of the amplified ribosomal genes. three lines of evidence demonstrate that rna polymerase i is reinitiating rna chains in this system. first, transcription continues in the homogenates for at least 8 h. during this time, 50 to 100 rna copies are synthesized per gene ... | 1980 | 6995456 |
| xenopus laevis larval thymocytes do not express surface immunoglobulin. | | 1980 | 6996841 |
| partial purification and characterization of the maturation-promoting factor from eggs of xenopus laevis. | | 1980 | 7000582 |
| molecular cloning of cdna sequences coding for the major alpha- and beta-globin polypeptides of adult xenopus laevis. | this report describes the synthesis and cloning of almost complete dna copies of the mrnas encoding the major alpha-globin and major beta-globin of x. laevis. double-stranded globin cdna was inserted into the psti site of the plasmid pbr322 and two cloned recombinants (designated pxg6c1 and pxg8d2) were selected. these were shown to contain almost complete copies of x. laevis globin mrna. restriction enzyme maps were determined for each cdna sequence using the established method of partial diges ... | 1980 | 7001356 |
| the role of zinc and follicle cells in insulin-initiated meiotic maturation of xenopus laevis oocytes. | | 1980 | 7001631 |
| more ribosomal spacer sequences from xenopus laevis. | the base sequence analysis of a xenopus laevis ribosomal dna repeat (7) has been extended to cover almost the entire non-transcribed and external transcribed spacer. a compilation of these sequences is presented. all the repetitive and non-repetitive sequence elements of the spacer are identified and their evolution discussed. comparison of the x.laevis and s.cerevisiae (25,26) ribosomal dnas shows about 80% sequence conservation in the 18s gene but no sequence conservation, from the available d ... | 1980 | 7003549 |
| rental projections in the adult xenopus laevis: a study with cobalt filling technique. | cobaltic-lysine complex was used to show retinal projections in adult xenopus laevis. retinal fibres partially decussate in the chiasma, and terminate on both sides in the nucleus ovoidalis, lateral geniculate complex, pretectal area, optic tectum, and in the basal optic nucleus. cobalt filled fibres were found in the preoptic area, dorsal hypothalamic area, and in the periventricular region close to the wall of the third ventricle. | 1980 | 7008512 |
| development of an amphibian neuromuscular junction in vivo and in culture. | during normal development presumptive synaptic sites in the myotomes of xenopus laevis begin to acquire a high density of ach receptors within as little as 2 h after the arrival of the nerve fibres. synaptic function also begins very shortly after the arrival of the nerve fibres. initially synaptic currents are some eight times longer lasting than at maturity and are not prolonged by anticholinesterase. during the first day after nerve-muscle contact is made there is a considerable decrease in s ... | 1980 | 7009778 |
| the secondary structure of the protein l1 binding region of ribosomal 23s rna. homologies with putative secondary structures of the l11 mrna and of a region of mitochondrial 16s rrna. | an heterologous complex was formed between e. coli protein l1 and p. vulgaris 23s rna. we determined the primary structure of the rna region which remained associated with protein l1 after rnase digestion of this complex. we also identified the loci of this rna region which are highly susceptible to t1, s1 and naja oxiana nuclease digestions respectively. by comparison of these results with those previously obtained with the homologous regions of e. coli and b. stearothermophilus 23s rnas, we po ... | 1981 | 7010313 |
| genetic control of t helper cell function in the clawed toad xenopus laevis. | the genetic control of the collaboration between xenopus t and b cells has been analyzed in vivo using cells from five strains of major histocompatibility complex-defined xenopus. when carrier (fowl gamma-globulin)-primed t cells and hapten (dinitrophenylated keyhole limpet hemocyanin)-primed b cells differed by minor histocompatibility antigens or by only one haplotype of the major histocompatibility complex, the collaboration was efficient in the sense that large numbers of plaques, low-molecu ... | 1981 | 7011821 |
| further studies on acid proteolytic activity in the fore gut of xenopus laevis larvae. | | 1980 | 7011857 |
| nucleotide sequence of xenopus laevis 18s ribosomal rna inferred from gene sequence. | 18s ribosomal rna in xenopus laevis is 1,825 nucleotides long, as inferred from sequence analysis of an 18s gene. all the 40 rrna methyl groups can be located in the sequence. comparison with the yeast (saccharomyces cerevisiae) 18s sequence reveals extensive regions of high homology interspersed with tracts having little or no homology. regions of high homology contain almost all the rna methyl groups. major regions of low homology area considerably richer in c + g in xenopus than in yeast. | 1981 | 7015146 |
| tetanus toxin: a marker of amphibian neuronal differentiation in vitro. | tetanus toxin may be used to specifically mark neurones in cultures of mammalian and chick nervous tissue. we have prepared cultures of neural ectoderm and underlying mesoderm from late neurula xenopus laevis embryos, and shown that in this amphibian species, neurones are labelled by tetanus toxin. aggregate cultures of ectoderm and mesoderm from late blastula embryos were than examined to determine whether tetanus toxin might be used to mark neuronal precursor cells. our observations suggest th ... | 1981 | 7015184 |
| ultrastructural identification of gastrin-like immunoreactive nerve fibres in the brain of xenopus laevis by means of colloidal gold or ferritin immunocytochemical methods. | | 1981 | 7016332 |
| the pure inhibitor of camp-dependent protein kinase initiates xenopus laevis meiotic maturation. a 4-step scheme for meiotic maturation. | the availability of the pure inhibitor of camp-dependent protein kinase prompted a re-examination of the inhibitor-induced meiotic maturation of xenopus laevis oocytes. injection of the inhibitor (1.5 microm) triggered 100% germinal vesicle breakdown faster than progesterone and slower than the maturation-promoting factor: at 0.15 microm, the inhibitor still triggered 100% meiosis, but with a much slower kinetics. in contrast, injection of 24 microm calmodulin resulted in less than 50% gvbd, and ... | 1981 | 7016632 |
| origin of replication from xenopus laevis mitochondrial dna promotes high-frequency transformation of yeast. | a specific fraction of chromosomal dna from both yeast and a wide variety of other eukaryotes, but not from escherichia coli, promotes high-frequency transformation in yeast. the plasmids containing these sequences are maintained as extra-chromosomal molecules in transformed cells. these results suggest that similar or identical sequences are used for the initiation of dna replication in eukaryotes. to test this hypothesis, several foreign eukaryotic dnas implicated directly or indirectly in the ... | 1981 | 7019920 |
| ph changes associated with meiotic maturation in oocytes of xenopus laevis. | | 1981 | 7021268 |
| prolonged survival of major histocompatibility complex-disparate skin allografts transplanted to the metamorphosing frog, xenopus laevis. | | 1981 | 7022797 |
| usage of the three termination codons in a single eukaryotic cell, the xenopus laevis oocyte. | oocytes from xenopus laevis were injected with purified amber (uag), ochre (uaa), and opal (uga) suppressor trnas from yeasts. the radioactively labeled proteins translated from the endogenous mrnas were then separated on two-dimensional gels. all three termination codons are used in a single cell, the xenopus laevis oocyte. but a surprisingly low number of readthrough polypeptides were observed from the 600 mrnas studied in comparison to uninjected oocytes. the experimental data are compared wi ... | 1981 | 7024919 |
| actin in xenopus development: indirect immunofluorescence study of actin localization. | actin was studied in xenopus unfertilized eggs and early developmental stages. immunochemical proof is given of structural differences between xenopus laevis muscle actin and nonmuscle cell actin. actin localization and changes of actin aggregation during xenopus development were observed using indirect immunofluorescence. we have also tried to explain the presence of an actin shell around the yolk platelets that appeared in our experiments. | 1981 | 7030842 |
| secondary lens formation from the cornea following implantation of larval tissues between the inner and outer corneas of xenopus laevis tadpoles. | secondary lens formation from the cornea of larval xenopus laevis has been used as a measure of the lens-inducing capacities of various larval xenopus tissues. the experimental design employed involved implantation of selected body tissues between the inner and outer cornea of stage-50 tadpole eyes, in such a way that the integrity of the inner cornea and eye cup was not disrupted. implantation of retina, pituitary, limb blastema or limb bud resulted in secondary lens formation from the outer co ... | 1981 | 7031166 |
| locomotion of xenopus epidermis cells in primary culture. | the locomotion of single epidermis cells, grown out from xenopus laevis tadpole tails has been investigated by time-lapse cinemicrography using phase-contrast and reflection-contrast optics. the cells develop a large, mostly 200-250 nm thick, lamella, which adheres homogeneously to the supporting coverglass and exceeds the projection area of the cell body. from the comparison of ric-pictures taken at high (1.06) and low (0.62) numerical aperture of illumination (i.n.a.) we deduce that at low i.n ... | 1981 | 7037800 |
| immunological localization of the major architectural protein associated with the nuclear envelope of the xenopus laevis oocyte. | | 1982 | 7042377 |
| is there really actin around xenopus laevis yolk platelets? | our previous immunofluorescence experiments (1) on actin localization in xenopus development showed a fluorescent halo around xenopus yolk platelets. this fact suggests the presence of a sort of actin covering of the yolk platelet; we have called this structure the 'actin-shell'. in this work, by the use of a dnase i-fluorochrome complex, we were able clearly to demonstrate the presence of the actin-shell around xenopus yolk platelets. a proposal about the function of the actin-shell is made; it ... | 1982 | 7042383 |