| the oocyte as an endocytic cell. | oocytes of xenopus laevis grow primarily by sequestering vitellogenin (vtg) selectively from the maternal bloodstream. morphological observations have demonstrated that an endocytic system is responsible for vtg uptake. binding studies indicate the presence of 2-28 x 10(10) surface vtg receptors per oocyte. these are continuously internalized into endosomes whether or not they are occupied by vtg, and other macromolecules may become trapped in the process. vtg-containing endosomes give rise to d ... | 1983 | 6315318 |
| herpes simplex virus defective genomes: structure of hsv-1 ang defective dna of class ii and encoded polypeptides. | sequence organization and origin of hsv-1 strain angelotti (ang) class ii defective dna (hsv-1 ang ddna1) were examined in detail by establishing physical maps and by molecular cloning. ddna1 consists of concatemers of tandem repeat units in which sequences from the ul region spanning map coordinates 0.37 to 0.415 of standard hsv ang dna are covalently linked to trs/irs sequences. the size of the repeat unit was determined to be about 8.9 kilobase pairs (kb), comprising sequences of 7.3 kb from ... | 1983 | 6315866 |
| a hyperpolarization-activated chloride current in xenopus laevis oocytes under voltage-clamp. | voltage-clamp experiments have been performed on ovulated xenopus laevis oocytes. two kinds of oocytes were studied: mature oocytes presenting the white spot due to germinal vesicle breakdown (gvbd) were found to be essentially unexcitable; oocytes without the white spot appeared to possess ionic channels which open transiently on hyperpolarization. the current is carried by chloride ions and, in holtfreter's solution, has a reversal potential at approximately - 15 mv. | 1983 | 6316254 |
| the structure of rat 28s ribosomal ribonucleic acid inferred from the sequence of nucleotides in a gene. | the nucleotide sequence of a rat 28s rrna gene was determined. the 28s rrna encoded in the gene contains 4718 nucleotides and the molecular weight estimated from the sequence is 1.53 x 10(6). the guanine and cytosine content is 67%. the sequence of rat 28s rrna diverges appreciably from that of saccharomyces carlsbergensis 26s rrna (about 50% identity), but more closely approximates that of xenopus laevis 28s rrna (about 75% identity). rat 28s rrna is larger than the analogous nucleic acids from ... | 1983 | 6316273 |
| [electrotonic transmission between primary afferent fibers and the motor neurons of the isolated spinal cord of various representative amphibians]. | studies have been made of monosynaptic excitatory postsynaptic potentials elicited by stimulation of the posterior root in motoneurones of the isolated spinal cord of the frog rana ridibunda, toad bufo bufo, and clawed toad xenopus laevis. in all the amphibians studied, the early component of monosynaptic epsp was not blocked in ca-free medium containing 2 mm mn2+. it is suggested that electrical coupling in anuran amphibians reflects certain stage of evolution of the synaptic transmission in ve ... | 1983 | 6316697 |
| effects of physostigmine on the voltage dependent ionic conductances of skeletal muscle fibres. | the voltage dependent ionic conductances were studied by analysing the phase plane trajectories of action potentials evoked by electrical stimulation of the sartorius muscles of the frog (rana esculenta). the delayed outward potassium current was measured also under voltage clamp conditions on muscle fibres of either the frog (rana esculenta) or xenopus laevis. on analysing the effect of physostigmine decreasing the peak amplitude, the rate of both the rising and falling phases of the action pot ... | 1983 | 6316728 |
| xenopus mono(adenosine diphosphate ribosyl) transferase: purification, assay, and properties. | various tissues of xenopus laevis possess mono(adp-ribosyl) transferase activity. the xenopus liver enzyme was purified approximately 40,000-fold by sequential chromatography on phenyl sepharose, deae-sephadex, nad+-agarose, and con a-sepharose. the enzyme is relatively heat-stable, has no cation requirements, transfers monomers of adp-ribose from nad+ to arginine-rich histones h3 and h4, and is not dependent upon dna for activity. its mr was estimated to be 30 kilodaltons (kd). the amino acid a ... | 1983 | 6317632 |
| regulation of adenovirus transcription by an e1a gene in microinjected xenopus laevis oocytes. | the regulation of adenovirus type 5 gene expression by the e1a gene product was examined in microinjected xenopus laevis oocytes. chimeric genes were constructed which included the promoter region of early adenovirus type 5 gene 3 and the structural sequence which codes for the bacterial enzyme chloramphenicol-3-o-acetyltransferase (cat). a plasmid containing this chimeric gene as well as plasmids containing the e1a gene were coinjected into oocyte nuclei. the presence of the e1a gene was shown ... | 1983 | 6318084 |
| ras-related gene sequences identified and isolated from saccharomyces cerevisiae. | the oncogenes of harvey and kirsten murine sarcoma viruses (v-rash and v-rask) and their cellular homologues (c-rash and c-rask) constitute two members of the ras gene family. each functional member of the ras gene family encodes a 21,000 molecular weight protein (p21ras). ras genes have been detected in a wide variety of vertebrate species, including xenopus laevis (r. e. steele, personal communication), and in drosophila melanogaster. we report here the detection of ras-related genes in the ye ... | 1983 | 6318116 |
| fast ephemeral dna damage upon bap injection. | injection of high concentrations of benzo[a]pyrene (10-125 micrograms bap/g body weight) into young frogs (xenopus laevis), fish (gambusia affinis) or tissue culture cells (l 5178 y) in a state of logarithmic growth causes alterations in dna. in frogs these alterations reach a maximum at 60-90 min after application, then they decrease and become undetectable after 3 h. within 8-12 days after the single bap dose, a new wave of dna alterations can again be detected. parallel measurements of mixed ... | 1983 | 6320364 |
| amiloride and other blockers of electrolyte flux as inhibitors of progesterone-stimulated meiotic maturation in xenopus oocytes. | amiloride and seven of its analogues, as well as seven substances of other structural types, all of which control electrolyte transport, were tested for their effectiveness for inhibiting the progesterone-stimulated meiotic maturation cycle of oocytes from the amphibian xenopus laevis. data were also collected on the ability of the oocytes to recover from the drug's inhibitory effect and on the toxicity of each drug. the data revealed that up to a 14-fold difference exists in the inhibitory conc ... | 1984 | 6321028 |
| comparative analysis of the cdna sequences derived from the larval and the adult alpha 1-globin mrnas of xenopus laevis. | the complete nucleotide sequences of cloned cdna segments derived from the larval and the adult alpha 1-globin mrna of xenopus laevis have been determined. these sequences comprise part of the 5' noncoding region, the entire coding region and the 3' noncoding region, including the polyadenylation site. the larval sequence differs from the adult one by a much longer 3' noncoding region. the sequences diverge by 47%, but codon usage is similar. comparison of the amino acid sequences of vertebrates ... | 1984 | 6322851 |
| anucleolate frog embryos contain ribosomal dna sequences and a nucleolar antigen. | previous studies of xenopus laevis embryos homozygous for the nucleolar deletion mutation have concluded that these embryos contain few, if any, copies of the genes for the 18 s and 28 s ribosomal rnas. using hybridization to restriction endonuclease digests of dna it is found, in fact, that a small amount of ribosomal dna is still present in such embryos. the ribosomal dna in these embryos appears to include a few normal repeats together with a variety of unusual fragments containing either spa ... | 1984 | 6323234 |
| the nucleotide sequence of a rat 18 s ribosomal ribonucleic acid gene and a proposal for the secondary structure of 18 s ribosomal ribonucleic acid. | the nucleotide sequence of a rat 18 s rrna gene was determined. the 18 s rrna encoded in the gene contains 1874 nucleotides, and the molecular weight estimated from the sequence is 6.09 x 10(5). the sequences of rat and xenopus laevis 18 s rrnas are very similar; the only differences of consequence are the insertions between nucleotides 197 and 206 and between 258 and 279 of the rat nucleic acid of sequences rich in guanine and cytosine. a proposal is presented for the secondary structure of rat ... | 1984 | 6323401 |
| messenger rna from human brain induces drug- and voltage-operated channels in xenopus oocytes. | sodium channels and receptors to serotonin and kainate were 'transplanted' from human brain into frog oocytes, by isolating messenger rna from a fetal brain, and injecting it into xenopus laevis oocytes. the mrna was translated by the oocyte and induced the appearance of functional receptors and channels in its membrane. this approach renders drug- and voltage-operated channels of the human brain more amenable to detailed study. | 1984 | 6323990 |
| transcription of a cloned xenopus laevis h4 histone gene in the homologous frog oocyte system depends on an evolutionary conserved sequence motif in the -50 region. | a cloned xenopus laevis h4 histone gene has been expressed in the x.laevis oocyte nucleus. the homologous histone h4 gene can be correctly and efficiently expressed in the frog oocyte even in presence of bacterial vector dna. as revealed by both analytical gel electrophoresis and s1 mapping, two h4 mrnas are specified with different transcriptional efficiencies from the tandemly repeated promoter. results from deletion mapping of the sequences essential for promoting h4 transcription show that d ... | 1983 | 6324093 |
| persistence, methylation and expression of vitellogenin gene derivatives after injection into fertilized eggs of xenopus laevis. | we report the fate of different derivatives of the vitellogenin genes after injection into fertilized eggs of xenopus. we injected a constructed minigene as well as a 5' fragment of the a2 vitellogenin gene. the minigene survives in embryogenesis much better than the 5' a2 fragment and is retained more frequently and at a higher level in frog tissues. the mosaic distribution of the foreign dna in different frog tissues indicates that no integration occurred before the first cleavage stage. the p ... | 1984 | 6324111 |
| the methylation pattern of trna genes in xenopus laevis. | the methylation sensitive restriction enzymes hha i and hpa ii were used to analyse the methylation pattern of a trna gene cluster in germ line and somatic dna of xenopus laevis. a single tdna repeat containing 8 trna genes was studied and all copies were found to be fully modified in sperm dna. in the dna from erythroid cells, hepatocytes, kidney and brain, most tdna repeats were found to be fully modified. however, in a fraction of the repeats, specific demethylated sites can be detected, givi ... | 1984 | 6324123 |
| does timing of axon outgrowth influence initial retinotectal topography in xenopus? | the question of whether timing is involved in generating the topographic organization of the earliest embryonic projection from the retina to the tectum has been examined in xenopus laevis. first, the normal schedule of axonal outgrowth from the retina to the tectum was characterized. groups of axons originating from either dorsal or ventral extremes of the retina were labeled by in vitro incubation of sectors (one-quarter to one-third) of eye primordia in [3h]proline and their time courses of o ... | 1984 | 6325604 |
| isolation and characterization of calmodulin genes from xenopus laevis. | two cdnas derived from xenopus laevis calmodulin mrna have been cloned. both cdnas contain the complete protein-coding region and various lengths of untranslated segments. the two cdnas encode an identical protein but differ from each other by 5% nucleotide substitutions. the 5' and 3' untranslated regions, to the extent available, are highly homologous between the two cdnas. the predicted sequence of x. laevis calmodulin is identical to that of vertebrate calmodulins from mammals and chickens a ... | 1984 | 6325880 |
| organization of xenopus histone gene variants within clusters and their transcriptional expression. | using previously cloned xenopus nucleosomal core histone genes as hybridization probes, a genomic dna library of xenopus laevis was screened for histone gene clusters. from over 200 histone-gene containing clones identified, 36 were selected as possibly containing h1 histone genes by hybridization to a probe derived from a sea urchin h1 histone gene. these 36 clones were further analyzed by hybrid-selected translation for the definitive presence of h1 histone genes. the genes for three different ... | 1984 | 6326836 |
| cloning of an x. laevis gene expressed during early embryogenesis coding for a peptide region homologous to drosophila homeotic genes. | a xenopus laevis gene was cloned on the basis of cross-homology to a region conserved between several drosophila homeotic genes. it was shown to be expressed during early development, starting at late gastrulation and producing three transcripts under specific temporal control. the frog gene contains a region coding for 60 amino acids, which is extremely conserved when compared to drosophila homeotic genes in the region of the homeo domain. southern blot analysis indicates that there are at leas ... | 1984 | 6327066 |
| processing of the 3' sequence extensions upon the 5s rrna of a mutant yeast in xenopus laevis germinal vesicle extract. | a processing endonuclease acts to remove a short sequence from the 3' end of transcripts of the saccharomyces cerevisiae 5s ribosomal rna gene in generating the mature sequence of 5s rna. cells bearing the nuclear mutation rna82 .1 lack this activity and accumulate 5s forms with additional nucleotides at their 3' termini. 5s rnas labelled during short pulse- labellings of the mutant are essentially primary transcripts that mostly have the sequence u-u-a-u-u-u-c[u-u-u-u(u-u)] added to the 3' end ... | 1984 | 6327301 |
| dna methylation of three 5' c-c-g-g 3' sites in the promoter and 5' region inactivate the e2a gene of adenovirus type 2. | the e2a gene of human adenovirus type 2 (ad2) encodes the 72-kilodalton dna-binding protein. we previously described perfect inverse correlations between the methylation of all 5' c-c-g-g 3' sequences in the ad2 e2a gene in virus-transformed hamster cells containing viral dna sequences in an integrated state and the extent to which this gene is expressed. we subsequently showed that in vitro methylation of all 14 5' c-c-g-g 3' sequences in the cloned e2a gene by prokaryotic hpa ii dna methyltran ... | 1984 | 6328479 |
| properties of a cyclic nucleotide phosphodiesterase of amphibian oocytes that is activated by calmodulin and calcium, by tryptic proteolysis, and by phospholipids. | a calmodulin-ca2+-stimulated cyclic nucleotide phosphodiesterase (ec 3.1.4.17) which hydrolyzed both cgmp and camp has been purified about 2000-fold from ovaries of the amphibian xenopus laevis. gel filtration through sephadex g-200 indicated a molecular weight of 140,000. a single, major protein band of molecular weight 66,000 was observed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. in addition to the stimulation by calmodulin-ca2+, the enzyme was activated 5- to 10-fold by pr ... | 1984 | 6329099 |
| isolation of a mitochondrial dna topoisomerase from human leukemia cells. | mitochondria from human acute lymphoblastic leukemia cells contain an atp-independent dna topoisomerase which can relax negative and positive supercoils. this enzyme has been purified 200-fold by carboxymethyl-cellulose or double stranded dna-cellulose chromatography. in contrast to the molecular weights reported for mitochondrial topoisomerases in other systems, the native leukemia enzyme has a molecular weight of 132,000 daltons as determined by gel permeation chromatography in buffer containi ... | 1984 | 6329201 |
| initiation of sv40 dna replication after microinjection into xenopus eggs. | we have examined the capacity of xenopus laevis eggs to support replication of microinjected sv40 dna. as previously reported, microinjected dna undergoes semi-conservative replication. unlabeled sv40 dna was microinjected with [3h]dttp and, after a 3 h incubation period, the dna was recovered and adsorbed to bnd-cellulose. elution with an nacl gradient removes molecules that are entirely double-stranded but not those with single-stranded regions. the latter dna population is eluted with caffein ... | 1984 | 6329301 |
| microsomal monooxygenase system in frog livers. | liver microsomes prepared from four species of frog, rana catesbeiana, rana nigromaculata , bufo bufo japonicus, and xenopus laevis, contained cytochrome p-450 and showed nad(p)h-dependent monooxygenase activities to several foreign chemical compounds tested. the oxidations of the chemical compounds by frog liver microsomes showed significant variations among frog species. the oxidation of 7-ethoxycoumarin was much faster than that by rat liver microsomes. the oxidation of benzo(a)pyrene was sig ... | 1984 | 6329594 |
| the unmethylated state of the promoter/leader and 5'-regions of integrated adenovirus genes correlates with gene expression. | an inverse correlation has been established between the levels of dna methylation at 5'-ccgg-3' (mspi/hpaii) sites in specific genes of integrated viral dna in adenovirus type 12 (ad12)-transformed hamster cell lines and the extent to which these genes are expressed ( sutter and doerfler , 1979, 1980). in general, early genes are transcribed into mrna, while late genes are permanently switched off in these cell lines. adenovirus type 2 genes methylated in vitro at 5'-ccgg-3' sites are not transc ... | 1982 | 6329677 |
| 18s coding sequences in amplified ribosomal dna from xenopus laevis oocytes are highly homogeneous, unmethylated, and lack major open reading frames. | we have used two approaches to search for sequence variants in the 18s coding region of amplified ribosomal dna (rdna) from xenopus laevis oocytes. first, using clones derived from amplified rdna, we compared the equivalent of a complete 18s coding region from two clones and short regions from two other clones with the 18s sequence previously determined from a "reference" clone. the respective sequences in all the clones were identical. secondly, we examined greater than 60% of the 18s sequence ... | 1982 | 6329693 |
| a prokaryotic trnatyr gene, inactive in xenopus laevis oocytes, is activated by recombination with an eukaryotic trnapro gene. | eukaryotic tdna promoters are composed of two essential regions contained within the coding sequence (box a and box b). due to the highly conserved structure of prokaryotic and eukaryotic trna, most prokaryotic trna genes are expected to be active templates in eukaryotic transcriptional systems. in this paper we show that escherichia coli tdnatyr is not transcribed in the nucleus of xenopus laevis oocytes. by in vitro construction of hybrid molecules between inactive prokaryotic tdnatyr from e. ... | 1982 | 6329706 |
| cloning and structure of the human immune interferon-gamma chromosomal gene. | two clones containing the human immune interferon-gamma (ifn-gamma) chromosomal gene were isolated from a human dna library present in lambda charon4a phage. dna from these clones specified biologically active interferon upon injection into the nuclei of xenopus laevis oocytes. analysis of the clones revealed that they were derived from the same chromosomal segment. restriction fragments that hybridized with 32p-labeled cdna probes were subcloned into plasmids and the complete sequence of the if ... | 1982 | 6329718 |
| the organization of ribosomal genes in vertebrates. | the organization of the repeat unit of the ribosomal genes has been determined in 15 different species of vertebrates. the ecori and bamhi restriction maps of the rdna from single individuals of different species of fishes, amphibians, and reptiles have been analysed. two rdna clones from xenopus laevis (representing one complete repeat unit) were used as probes in southern blots to detect restriction fragments containing ribosomal genes. the results obtained indicate that the transcribed region ... | 1982 | 6329726 |
| characterization of highly and moderately repetitive 500 bp eco ri fragments from xenopus laevis dna. | three different types of repetitive eco ri fragments, which comigrate within a visible band of approximately 500 bp at gel electrophoresis of xenopus laevis dna eco ri digests have been cloned and sequenced. these sequences are designated as repetitive eco ri monomers: rem 1, rem 2 and rem 3. the sequences contain direct repeats, inverted repeats and palindromic elements. genomic organization of the most abundant sequence (rem 1; 0.4% of total dna) is that of an interspersed sequence. rem 2 (0.0 ... | 1984 | 6330690 |
| mitogen-induced b-cell differentiation in xenopus laevis. | spleen cells from the south african clawed toad xenopus laevis proliferate vigorously upon pokeweed mitogen (pwm) stimulation, as measured by 3h-thymidine uptake. the peak response is observed after 6-8 days of culture, and both light- and electron-microscopy examinations of stimulated cells reveal the presence of a large number of lymphoblasts. beside proliferation, pwm induces the in vitro differentiation of a large proportion of lymphoblasts into immunoglobulin (ig)-producing plasmablasts, as ... | 1984 | 6334001 |
| [appearance of secondary melanophore reactions in the ontogeny of anuran amphibia]. | the development of physiological reactions of the dermal melanophores has been studied in rana temporaria, r. ridibunda and xenopus laevis. in these species, the background (secondary) reactions of melanophores appeared at different stages of larval development but their appearance was always timed with the eye slit closure. | 1984 | 6334263 |
| birefringent periodicities in amphibian rod outer segments. | birefringence variations, seen as regularly spaced altering light and dark rings (bands), have been observed along the length of unfixed, freshly isolated rod outer segments (ros) of both rana pipiens and xenopus laevis. in our hands, the spatial frequency of the banding pattern is from 1.3-1.6u/band in rana pipiens and 1.8-2.2u/band in xenopus laevis ros, both corresponding closely to determinations we made in the same animals of the quantity of new ros disks added each day. to further probe th ... | 1984 | 6334590 |
| early development of descending pathways from the brain stem to the spinal cord in xenopus laevis. | the early development of descending pathways from the brain stem to the spinal cord has been studied in xenopus laevis tadpoles. the relatively protracted development of this permanently aquatic amphibian as well as its transparency during development make this animal particularly attractive for experimental studies. between the 5th and 10th myotome the spinal cord was crushed with a thin needle and dry horseradish peroxidase (hrp) crystals were applied. after a survival time of one day the tadp ... | 1984 | 6335361 |
| effect of temperature and zn2+ on isometric contractile properties and electrical phenomena of frog (rana) and xenopus skeletal muscle fibers. | effects of temperature and zn2+ on the isometric contractile properties of toe muscle fibers of rana catesbeiana and xenopus laevis were studied. the maximum twitch tension almost doubled when the temperature was lowered from 20 to 4 degrees c in rana muscles but not in xenopus muscles, although the duration of action potential in xenopus muscle was increased slightly more than that seen in the rana species. the maximum rate of rise of tension was greater in xenopus muscle than in the rana muscl ... | 1984 | 6335672 |
| corticotropin-releasing factor (crf)-like immunoreactivity in the vertebrate endocrine pancreas. | the light microscopic immunocytochemical localization of corticotropin-releasing factor (crf) is described in the endocrine pancreas of several species representing the major classes of vertebrates: fishes (channel catfish, ictalurus punctatus), amphibians (african clawed toad, xenopus laevis), reptiles (chameleon, anolis carolinensis), birds (chicken, gallus domesticus), and several mammals (rat, mouse, cat, rhesus monkey, and man). the crf-containing cells are scattered over the entire islet t ... | 1983 | 6340106 |
| ontogeny and characterization of mitogen-reactive lymphocytes in the thymus and spleen of the amphibian, xenopus laevis. | the ontogeny of the proliferative response of xenopus thymocytes to the t-cell mitogens concanavalin a (con a) and phytohaemagglutinin and to the b-cell mitogen e. coli lipopolysaccharide (lps) is examined during the first 2 years of life. responses after metamorphosis are compared with those occurring in the spleen. during much of larval life, mitogen-treated thymocytes display no sign of elevated [3h]tdr uptake. a low level in vitro response to con a and lps emerges transiently just prior to m ... | 1983 | 6343233 |
| maturation-promoting factor induces nuclear envelope breakdown in cycloheximide-arrested embryos of xenopus laevis. | we have studied the effect of maturation-promoting factor (mpf) on embryonic nuclei during the early cleavage stage of xenopus laevis development. when protein synthesis is inhibited by cycloheximide during this stage, the embryonic cell cycle arrests in an artificially produced g2 phase-like state, after completion of one additional round of dna synthesis. approximately 100 nuclei can be arrested in a common cytoplasm if cytokinesis is first inhibited by cytochalasin b. within 5 min after injec ... | 1983 | 6345556 |
| the thymus dependency of transplantation allotolerance in the metamorphosing frog xenopus laevis. | larval as well as adult frogs (xenopus laevis) are immunocompetent. yet, whereas adults will vigorously reject mhc-incompatible skin grafts, metamorphosing larvae may not. previous studies have revealed that this graft survival reflects an immunologically specific host tolerance. the role of the thymus in the acquisition of this tolerance to mhc-disparate skin allografts by metamorphosing outbred and inbred frogs has been investigated. when thymectomy was performed during midlarval or late larva ... | 1983 | 6346599 |
| response to skin grafts exchanged among siblings of larval and adult gynogenetic diploids in xenopus laevis. | gynogenetic diploid individuals were produced in an anuran amphibian, xenopus laevis, and their response to skin grafts exchanged among siblings was studied. all skin grafts exchanged among nongynogenetic sibling froglets, as well as those from genetically unrelated donors, were rejected within 30 days. more than half (57%) of the gynogens that received grafts from sibling partners exhibited a prolonged survival (over 30 days), including long-term survival of over 120 days in 13%. the skin graft ... | 1983 | 6346617 |
| specific in vivo and nonspecific in vitro alloreactivities of adult frogs (xenopus laevis) that were thymectomized during early larval life. | thymectomy of very young xenopus larvae abrogated in vitro proliferative responses to phytohemagglutinin (pha) and allogeneic leukocytes. thymectomized (txd) frogs, however, still rejected first-set skin allografts chronically and second-set grafts (but not third-party grafts) more rapidly. the specific second-set rejection reaction by txd frogs was transferable in vivo to secondary txd hosts (with major histocompatibility complex identical to the cell donor) by the subcutaneous injection of a m ... | 1983 | 6347694 |
| allograft rejection in xenopus laevis following larval thymectomy. | xenopus laevis thymectomized at stages 41 through 49 accept first set allografts, while animals thymectomized at stage 51 or older reject allografts in times similar to intact animals. however, thymectomy at progressively earlier stages results in a greater proportion of animals unable to reject second set grafts. in some animals, the allograft response remains deficient even after multiple challenges. the results indicate that alloreactive cells are thymus dependent, and suggest that the thymus ... | 1983 | 6347739 |
| isolation of chlamydia psittaci from naturally infected african clawed frogs (xenopus laevis). | an inclusion-forming agent was isolated from the livers of commercially raised african clawed frogs (xenopus laevis) involved in an epizootic of high morbidity and mortality. original isolation was made in mccoy cells. this agent was identified as chlamydia psittaci based on the formation of typical intracytoplasmic inclusions which developed within 48 h, were not stained by iodine, and were resistant to sulfadiazine. the isolate from one particular frog (designated as strain 178) was further st ... | 1983 | 6347897 |
| mitochondrial transfer rna genes from fungi (aspergillus nidulans) and plants (lupinus luteus) are transcribed in xenopus laevis oocyte nuclei. | three plasmids containing aspergillus nidulans mitochondrial transfer rna genes were microinjected into the nucleus of xenopus laevis oocytes. plasmids that contained a single trnacys gene or two trna genes (arg and asn) yielded trna-sized transcripts. plasmids containing cloned lupinus mitochondrial trna genes were also transcribed and processed in x. laevis nuclei. | 1983 | 6350603 |
| steroidal and peptidic control mechanisms in membrane of xenopus laevis oocytes resuming meiotic division. | stage 5-6 xenopus laevis oocytes are arrested in the prophase of the first meiotic division, and can be studied in vitro after removal from their follicle cell environment. while they do not mature spontaneously, they demonstrate germinal vesicle (nucleus) breakdown (gvbd) if exposed to approximately 1 microm progesterone, the hormone released in vivo at the time of ovulation and maturation. they become an egg ready to be fertilized. the progesterone-oocyte interaction, contrary to what is obser ... | 1983 | 6350717 |
| induction of germinal vesicle breakdown in xenopus laevis oocytes: response of denuded oocytes to progesterone and insulin. | denuded oocytes freed of their vitelline envelope have been prepared by two methods, enzymatically with pronase and manually by microdissection. the response of denuded oocytes to progesterone, in terms of germinal vesicle breakdown (gvbd), was similar to that obtained with defolliculated oocytes (separated with collagenase from follicle cells, but still keeping their vitelline membrane). the same conclusion was drawn with respect to morphological features of the oocyte surface observed by trans ... | 1983 | 6352367 |
| site-directed in vitro replacement of nucleosides in the anticodon loop of trna: application to the study of structural requirements for queuine insertase activity. | we have investigated the specificity of the enzymes q-insertase and mannosyl-q transferase that replace the guanosine at position 34 (wobble base) in the anticodon of several trnas by q or mannosyl-q derivatives. we have restructured in vitro the normal anticodon of yeast trna-asp-guc, yeast trnaargicg and yeast trnaleuuag. with yeast trna-asp-guc, we have replaced one or several nucleotides in the vicinity of g34 by one of the four canonical nucleotides or by pseudouridylic acid; we have also c ... | 1983 | 6354708 |
| development of the lateral line system in xenopus laevis. i. normal development and cell movement in the supraorbital system. | during development of xenopus laevis, the supraorbital lateral line system (i.e. the parietal and supraorbital lines of organs and the anterior auditory group of organs) is all derived from a single primordium located in the ear region of the epidermis. the primordium elongates first by active movement along the dorsal margin of the eye. individual primary organs are then formed by progressive fragmentation of the streak-like primordium. after fragmentation, passive displacement of the organs du ... | 1983 | 6355359 |
| [intercellular relay interactions in explants of amphibian embryonic tissues. i. intercellular relay interactions in normal explant morphogenesis]. | in the explants of lateral mesoderm, together or without the overlaying ectoderm, taken from the neurula-early tail bud of amphibian embryos (xenopus laevis, rana temporaria) within 5-30 min, several types of cytological transformations have been observed, some of these being: formation of a microfilamentous layer under the naked explant surface, morphological polarization, and unilateral spreading of cells. these processes are described at the light and electron microscopy levels. it is suggest ... | 1983 | 6356533 |
| mitogenic responses of frog lymphocytes to crude and purified preparations of bacterial lipopolysaccharide (lps). | we have compared in vitro mitogenic responses of frog (xenopus laevis and rana pipiens) lymphocytes to various preparations of lipopolysaccharide (lps). commercial lps prepared from e. coli (phenol extraction) and from s. abortus-equi (phenol and tca extraction procedures) was mitogenic for frog lymphocytes. after reextraction of these lps preparations with phenol-water, the remaining lps was either considerably less mitogenic or not mitogenic. purified e. coli 055:b5 lps, prepared by phenol wat ... | 1983 | 6357879 |
| tolerance maintenance depends on persistence of the tolerizing antigen: evidence from transplantation studies on xenopus laevis. | in order to assess the role of antigen persistence in the tolerant state, tolerance was induced in xenopus laevis by the embryonic transplantation of whole eyes or tail tissue. both types of transplants were seen to heal in and persist, with no signs of immunological incompatibility. at metamorphosis, tail resorption occurred and grafted tail tissue was lost. eye transplants were maintained through metamorphosis in most eye grafted animals. eye graft recipients which had maintained the transplan ... | 1983 | 6357880 |
| the number of synaptic boutons terminating on xenopus cardiac ganglion cells is directly correlated with cell size. | the relationship between the size of parasympathetic neurones and the number of synaptic boutons terminating upon them has been studied in the cardiac ganglion of xenopus laevis. synaptic boutons were visualized by impregnation with zinc iodide and osmium (zio), which by electron microscopy was shown to stain heavily all synaptic boutons in six preparations. light microscopic examination of the unipolar ganglion cells in intact tissue reveals that larger neurones have more synaptic boutons. the ... | 1983 | 6358464 |
| detergent-soaked hrp-chips: a new method for precise and effective delivery of small quantities of the tracer to nervous tissue. | we dissolved horseradish peroxidase (hrp) in a 5% aqueous detergent solution (nonidet p-40) and dried it to a solid mass which was then fragmented into small chips of convenient size. these were applied to the cut or crushed oculomotor nerves of xenopus laevis tadpoles. this method combines the advantages of solid hrp (high concentration) and the presence of a detergent (enhanced uptake). moreover, as compared to chips of hrp alone, addition of the detergent facilitated the manipulation of the c ... | 1983 | 6358709 |
| sequence analysis of 28s ribosomal dna from the amphibian xenopus laevis. | we have determined the complete nucleotide sequence of xenopus laevis 28s rdna (4110 bp). in order to locate evolutionarily conserved regions within rdna, we compared the xenopus 28s sequence to homologous rdna sequences from yeast, physarum, and e. coli. numerous regions of sequence homology are dispersed throughout the entire length of rdna from all four organisms. these conserved regions have a higher a + t base composition than the remainder of the rdna. the xenopus 28s rdna has nine major a ... | 1983 | 6359063 |
| alcohol dehydrogenase isozymes in the clawed frog, xenopus laevis. | alcohol dehydrogenase (adh; ec 1.1.1.1) activity in xenopus laevis was highest in liver tissue, with decreasing activities in kidney, heart, and gut tissues, respectively. essentially no activity was found among other tissues screened, including lung, ovary, eye, and testes. also, there was no apparent sexual dimorphism of adh activity in either liver or kidney tissue. all adh isozymes were inhibited by 10 mm pyrazole, and no eye-specific retinol dehydrogenase activity was detected on starch gel ... | 1983 | 6362654 |
| mitochondrial dna-binding proteins that bind preferentially to supercoiled molecules containing the d-loop region of xenopus laevis mtdna. | from the bulk of the xenopus laevis mitochondrial proteins insoluble in 1% triton x-100 + 1m nacl, we have isolated, by dna-cellulose chromatography, a protein fraction enriched in dna-binding proteins. this fraction contains proteins showing a specific affinity for supercoiled dna molecules containing the mitochondrial dna displacement-loop region, as measured by filter binding and competition assays. | 1983 | 6362668 |
| stabilization of the maturation promoting factor (mpf) from xenopus laevis oocytes. protection against calcium ions. | maturation promoting factor (mpf) activity was recovered from progesterone-matured xenopus oocytes cytosol, fractionated by polyethylene glycol-20,000 or ethanolic precipitation. an improved stabilization of the biological activity was obtained by adding adenosine 5'-o-(3-thiotriphosphate) (atp-gamma-s) (50 microm) to the preparation buffers. neither ca2+ ions nor calmodulin inhibit the partially purified mpf. | 1983 | 6362894 |
| construction of a uga suppressor trna by modification in vitro of yeast trnacys. | in this paper we describe the construction of a yeast trnacys uga suppressor. after specific hydrolysis of the parent molecule, the first base of the anticodon gca was replaced by a uracil. the resulting molecule, harboring a uca anticodon, was injected into xenopus laevis oocytes in order to test its biological activities. the level of aminoacylation was similar to that of the parent molecule. readthrough of the uga termination codon in beta-globin mrna, coinjected with the trna, indicated supp ... | 1984 | 6363071 |
| synthesis and partial maturation of the alpha- and gamma-subunits of the mouse submaxillary gland nerve growth factor in xenopus laevis oocytes. | sera raised against the alpha-, beta- and gamma-subunits of the mouse 7 s ngf were used to characterize translation products coded by submaxillary gland mrnas microinjected into xenopus oocytes. anti-beta ngf sera did not cross-react with any material. in contrast, the precursors of the alpha- and gamma-subunits, as well as that of renin were identified. use of tunicamycin, and a comparison of the translation products obtained in oocytes or in the reticulocyte lysate indicated that oocytes achie ... | 1984 | 6363124 |
| structure and transmembrane nature of the acetylcholine receptor in amphibian skeletal muscle as revealed by cross-reacting monoclonal antibodies. | a collection of 126 monoclonal antibodies (mabs) made against acetylcholine receptors (achrs) from the electric organs of torpedo californica or electrophorus electricus was tested for cross-reactivity with achrs in cryostat sections of skeletal muscle from rana pipiens and xenopus laevis by indirect immunofluorescence. 49 mabs (39%) cross-reacted with achrs from rana, and 25 mabs (20%) cross-reacted with achrs from xenopus. mabs specific for each of the four subunits of electric organ achr (alp ... | 1984 | 6363425 |
| pronounced structural similarities between the small subunit ribosomal rna genes of wheat mitochondria and escherichia coli. | we present here the nucleotide sequence of the small subunit (18s) rrna gene from wheat mitochondria. aside from five discrete variable domains, this gene and the analogous (16s) rrna gene in escherichia coli show essentially a one-to-one correspondence in their potential secondary structures, with regions accounting for 86% of the bacterial 16s rrna having a strict secondary structure counterpart in the mitochondrial 18s rrna. primary sequence identity between the two rrnas ranges from 73% to 8 ... | 1984 | 6364144 |
| a survey of h1o-and h5-like protein structure and distribution in higher and lower eukaryotes. | a survey of h1o and h5-like proteins has been conducted through a range of higher and lower eukaryotic species. all mammals examined possessed h1o proteins, although in variable amounts, and the protein's structure was well conserved, though not invariant. the testis-specific histone hlt (from rat) did not have an h1o-like structure and it appears that h1o does not occur in spermatocytes in any form. the results also show that xenopus laevis contains h1o-like proteins, but lower, non-vertebrate ... | 1984 | 6365542 |
| electron microscopic immunolocalization of a karyoskeletal protein of molecular weight 145 000 in nucleoli and perinucleolar bodies of xenopus laevis. | amplified nucleoli of xenopus laevis oocytes contain a major karyoskeletal protein of mr 145 000 insoluble in low- and high-salt buffer as well as in non-denaturing detergents. electron microscopic localization on native and high-salt extracted nucleoli using specific murine antibodies against this polypeptide and gold-coupled antibodies for visualization reveals that the mr 145 000 protein is located in coils of filaments of ca 4 nm diameter. in addition, this protein occurs in the medusoid fil ... | 1984 | 6365576 |
| the effect of insulin on intracellular ph and ribosomal protein s6 phosphorylation in oocytes of xenopus laevis. | both insulin and progesterone are capable of stimulating germinal vesicle breakdown (gvbd) of large, stage vi oocytes of xenopus laevis. numerous studies have shown an increase in intracellular ph (phi) and ribosomal protein s6 phosphorylation prior to gvbd in oocytes treated with progesterone. in this study the effect of insulin and progesterone on phi and s6 phosphorylation was compared. both hormones increased phi and s6 phosphorylation to similar levels and the time course of phi change was ... | 1984 | 6365656 |
| induction of germinal vesicle breakdown in xenopus laevis oocytes: synergistic action of progesterone and insulin. | progesterone is the hormone that reinitiates the meiotic division of amphibian oocytes and insulin and insulin-like growth factors are also active on defolliculated oocytes in vitro. we have studied xenopus laevis oocytes (stage 5-6) of different hormonal sensitivities, obtained from unstimulated and from human chorionic gonadotrophin-stimulated females. some oocytes from unstimulated females were also precultured with a subthreshold level of progesterone. a dose-dependent potentiating effect of ... | 1984 | 6368732 |
| enzymatic conversion of adenosine to inosine in the wobble position of yeast trnaasp: the dependence on the anticodon sequence. | we have investigated the specificity of the trna modifying enzyme that transforms the adenosine at position 34 (wobble position) into inosine in the anticodon of several trnas. for this purpose, we have constructed sixteen recombinants of yeast trnaasp harboring an axy anticodon (where x or y was one of the four nucleotides a, g, c or u). this was done by enzymatic manipulations in vitro of the yeast trnaasp, involving specific hydrolysis with s1-nuclease and rnaase a, phosphorylation with t4-po ... | 1984 | 6369251 |
| ribonucleoprotein particles from xenopus eggs and embryos. neural-archencephalic-inducing activity of the protein moiety. | ribonucleoprotein particles were isolated from unfertilized eggs and gastrula stages of xenopus laevis. the particles from both stages induce in gastrula ectoderm the formation of large foreheads (neural-archencephalic-inducing activity), whereas ribosomal subunits have no inducing activity. the inducing activity of particles from both stages is largely abolished after treatment with proteolytic enzymes and to some extent with ribonuclease. the protein moiety of gastrula ribonucleoprotein partic ... | 1984 | 6370694 |
| inactivation of mitotic factors by ultraviolet irradiation of hela cells in mitosis. | extracts from mitotic hela cells, when injected into fully grown xenopus laevis oocytes, exhibit maturation-promoting activity (mpa) indicated by germinal vesicle breakdown (gvbd) and chromosome condensation. recently, we observed that the mpa of mitotic cell extracts is neutralized by the inhibitors of mitotic factors (imf) in hela cells, which are activated at telophase and remain active throughout the g1 period. the activity of the imf coincides with the process of chromosome decondensation, ... | 1984 | 6371031 |
| the identification of a tissue-restricted plasma membrane marker in xenopus laevis embryos by using a monoclonal antibody. | a library of monoclonal antibodies raised against partially purified membrane fractions from xenopus laevis oocytes has been produced. one of these antibodies has been cloned and characterized in detail. it was found to be specific for a membrane-bound antigen of apparent mr, 55,000. the distribution of the antigen has been studied by indirect immunofluorescence on sections of x. laevis embryos and has been found to be highly specific for some ectodermal and endodermal tissues. it was not presen ... | 1984 | 6373020 |
| secondary structure of mouse 28s rrna and general model for the folding of the large rrna in eukaryotes. | we present a secondary structure model for the entire sequence of mouse 28s rrna (1) which is based on an extensive comparative analysis of the available eukaryotic sequences, i.e. yeast (2, 3), physarum polycephalum (4), xenopus laevis (5) and rat (6). it has been derived with close reference to the models previously proposed for yeast 26s rrna (2) and for prokaryotic 23s rrna (7-9). examination of the recently published eukaryotic sequences confirms that all pro- and eukaryotic large rrnas sha ... | 1984 | 6374617 |
| elicitation of weak immune response in larval and adult xenopus laevis by allografted pituitary. | to test the claim that tolerance to organ-specific self antigens is established during the ontogenic development of the immune system, pituitary anlagen were removed from early tailbud embryos of xenopus laevis, and the resulting hypophysectomized tadpoles were grafted with pituitaries after the tadpoles had become immunocompetent. the result was that none of the histocompatible or allogeneic pituitary grafts was rejected throughout an observation period of 100 days. subsequent experiments revea ... | 1984 | 6382714 |
| subcellular distribution of ribosomal proteins s6 and el12. analysis by autoradiography and immunofluorescence of sections from oocytes of xenopus laevis. | the process of ribosome assembly in eukaryotes was studied by injecting tritium-labeled ribosomal proteins s6 and el12 into oocytes of xenopus laevis. the subcellular distribution of the two proteins was visualized by means of autoradiography in sections of oocytes. protein s6 but not el12 was found in the nucleus where it accumulated at the nucleoli. in the presence of actinomycin d the accumulation of s6 at the nucleoli was reduced. in-situ immunofluorescence studies indicated that s6 is locat ... | 1984 | 6383624 |
| interaction of metabolic inhibitors with actin fibrils. | the dependence of the arrangement of fibrillar actin in cultured endothelial cells on metabolic conditions was investigated with cellular elements derived from the heart of xenopus laevis tadpoles. either primary culture or an established cell line (xth-2) were used in these studies. the metabolic stage of the cells was influenced by inhibiting respiration and lactate production. the actin pattern was revealed either by indirect immunofluorescence or by tetramethylrhodaminyl (tritc)-phalloidin f ... | 1984 | 6386168 |
| collagen transition types during osteogenesis in xenopus laevis. an immunofluorescence study with heterologous antisera. | | 1984 | 6386627 |
| oocytes and early embryos of xenopus laevis contain intermediate filaments which react with anti-mammalian vimentin antibodies. | previous studies have shown that xenopus oocytes possess a cortical shell, which includes actin-containing microfilaments and cytokeratin-containing intermediate filaments. in this paper we show that oocytes of xenopus laevis also contain filaments throughout their cytoplasm which are stained by several anti-vimentin antibody preparations. we also show that dramatic changes in pattern of these filaments occur during oocyte differentiation, first during vitellogenesis, and then during maturation ... | 1984 | 6389749 |
| structural requirements for the interaction of 5s rrna with the eukaryotic transcription factor iiia. | in order to study the binding of the eukaryotic transcription factor iiia to heterologous 5s rrnas with a low degree of overall sequence conservation (less than 20%) we have utilized a transcription competition assay involving eubacterial, archaebacterial and eukaryotic 5s rrnas. all the molecules inhibit xenopus 5s rrna transcription specifically, which suggests that only a small amount of specific conserved rna sequences, if indeed any, are essential for the interaction of the transcription fa ... | 1984 | 6390342 |
| post-translational modification of exogenous proteins in xenopus laevis oocytes. | | 1984 | 6397378 |
| karyoskeletal proteins and the organization of the amphibian oocyte nucleus. | we have investigated the existence of structural components in the nucleus of the oocyte of xenopus laevis and other amphibia that are insoluble in non-denaturing detergents and buffers of low and high ionic strength. these cells are particularly suitable for such studies as they have a high frequency of extrachromosomal amplified nucleoli and pore complexes of the nuclear envelope. using biochemical and immunological techniques, we have shown these structures to contain only two major proteins. ... | 1984 | 6397470 |
| changes in antibody and complement production in xenopus laevis during postmetamorphic development revealed in a primary in vivo or in vitro antibody response. | xenopus laevis (g-line) mounts a primary plaque forming cell (pfc) response either in vivo or in vitro following challenge with foreign erythrocytes. methods are described for generating and assaying the response, which specify criteria such as antigen dose, antigen choice, response kinetics, and complement source. the results suggest that at the peak of the primary response (approximately day 6), animals of different ages produce predominantly different 'classes' of antibody which display marke ... | 1984 | 6398353 |
| restoration of the antibody response to sheep erythrocytes in thymectomized xenopus implanted with mhc-compatible or mhc-incompatible thymus. | these experiments make use of an amphibian model system for investigating the role of the thymus in t helper cell education. clawed toads (xenopus laevis), thymectomized at 7 days, are unable to mount an antibody response to thymus-dependent antigens, such as sheep red blood cells (srbc). when thymectomized larvae are implanted with larval thymuses (either irradiated or non-irradiated), incompatible at the major histocompatibility complex (mhc) or with mhc-compatible or -incompatible 'adult' thy ... | 1984 | 6398354 |
| multiple forms of dna-dependent rna polymerases in xenopus laevis. rapid purification and structural and immunological properties. | dna-dependent rna polymerases i, ii, and iii (ec 2.7.7.6) were isolated from xenopus laevis ovaries. the soluble enzymes were precipitated with polyethyleneimine and subjected to chromatography on heparin-sepharose, deae-sephadex, and phosphocellulose. rna polymerase i was subjected to an additional chromatographic step on cm-sephadex. the procedure required 40 h and produced purified rna polymerase forms ia, iia, and iii in yields of 5 to 40%. the specific activities of rna polymerases iia and ... | 1983 | 6401728 |
| microinjection of purified ornithine decarboxylase into xenopus oocytes selectively stimulates ribosomal rna synthesis. | this study has utilized stage vi oocytes of xenopus laevis which have amplified the rdna gene 1,000-fold to assess whether the microinjection of ornithine decarboxylase (orndcase) would stimulate [alpha-32p]guanosine incorporation into 45s and 18s/28s rna selectively. the injection of purified orndcase into individual oocytes resulted in a greater than 2-fold increase in the incorporation of [32p]guanosine into 45s rna and 18s/28s rna with no increased incorporation into low molecular weight rna ... | 1983 | 6402779 |
| effects of diltiazem on skinned skeletal muscle fibers of the african clawed toad. | to examine the effects of diltiazem and its l-cis isomer (which possesses only a weak ca++-antagonistic action) on the contractile system and the sarcoplasmic reticulum of skeletal muscle, we used skinned fibers isolated from iliofibularis muscle of the african clawed toad, xenopus laevis. diltiazem showed the following effects: an increase in the ca++ sensitivity of the contractile system, a decrease in the maximal tension developed in a saturating concentration of ca++, an inhibition of ca++ u ... | 1983 | 6403257 |
| developmentally regulated rna binding proteins during oogenesis in xenopus laevis. | during oogenesis, xenopus oocytes synthesize and accumulate all types of rna. in particular, they store poly(a+) rna to such an extent that only about 5% is actually translated in the oocyte. using a protein blotting and in vitro binding assay, we have identified proteins which are associated with poly(a+) rna and perhaps other rnas as well. two groups of binding proteins were identified. the first group accumulates during oogenesis, generally is less than 50,000 molecular weight, and sediments ... | 1983 | 6403538 |
| melanophore differentiation in xenopus laevis, with special reference to dorsoventral pigment pattern formation. | during the development of xenopus laevis, after stage 26, a large number of dopa-positive cells were observed in the ventral region. electron microscopic observations revealed that these cells became localized in the epidermal layer and contained premelanosomes. in cultured ventral skin, fully matured melanophores appeared. these results strongly suggest that a large number of melanoblasts are present in the ventral epidermis and remain there without final differentiation into melanized melanoph ... | 1983 | 6411851 |
| [inhibitory effect of lectins extracted from arachis hypogea and soybeans on germ cell migration in the embryo of xenopus laevis (amphibia, anura)]. | effect of injection of arachis hypogea (pna) and soybean (sba) lectins on the migration of xenopus primordial germ cells (pgcs) were investigated. pna inhibited almost entirely the pgcs migration, more than sba. our results indicated that the inhibition of the migration could be a consequence of the lectin-induced alterations of cell surface properties. | 1983 | 6412978 |
| characterization of trna precursor splicing in mammalian extracts. | transcription of a xenopus laevis trnatyr gene and splicing of the transcript have been studied in hela cell extracts. this trnatyr gene has a 13-base intervening sequence and is expressed as mature trna when transfected into mammalian cells. the trnatyr gene is transcribed under conditions of low concentrations of magnesium and atp, but is processed by splicing only when both of these cofactors are added at higher concentrations. the endonucleolytic activity of the trna-splicing system in the h ... | 1983 | 6413507 |
| 5'-flanking sequences that inhibit in vitro transcription of a xenopus laevis trna gene. | two series of deletion mutants have been constructed in the 5'-flanking dna of a variant methionine trna gene of x. laevis. when assayed in homologous cell-free extracts, mutants of both series are expressed at very different levels and they initiate transcription at either or both of the two major sites used by the wild-type gene. no similarities are evident in the 5'-flanking regions of well expressed mutants, but two dna segments are identified that inhibit transcription. the most inhibitory ... | 1983 | 6414719 |
| analysis of the chromatin assembled in germinal vesicles of xenopus oocytes. | we have injected circular dna, labeled with 32p at a single restriction site, into germinal vesicles of xenopus laevis oocytes in order to study the nucleosome arrangement on the assembled minichromosomes. two types of genes were used in these studies, the somatic 5 s rna gene unit of xenopus borealis and the histone gene unit of drosophila melanogaster. we find that injections of labeled dna alone, at 1 ng dna per oocyte, results in irregularly spaced nucleosomes and partially supercoiled dna m ... | 1983 | 6415291 |
| [comparative effects of an extract of anguilla stannius corpuscles and of an active fragment of human parathyroid hormone (1-34 hpth) on an anuran batracian, xenopus laevis]. | parathyrin of the corpuscles of stannius (pcs), glands which are restricted to holostei and teleostei, resembles mammalian parathyroid hormone secreted by the parathyroids. these glands made their first phylogenic appearance with amphibians, whereas the stannius corpuscles disappeared. we have compared, in the clawed toad, xenopus laevis, the effects of injections of extracts of corpuscles of stannius and of the active synthetic fragment of parathyrin (1-34 hpth). both hormones elicited hypocalc ... | 1983 | 6416629 |
| xenopus laevis lectin is localized at several sites in xenopus oocytes, eggs, and embryos. | the endogenous lectin of xenopus laevis oocytes, unfertilized eggs, and blastula-stage embryos was immunohistochemically localized using a highly specific antiserum. each tissue was examined with several techniques, including paraformaldehyde or glutaraldehyde fixation, frozen or plastic sections, and immunofluorescence or immunoperoxidase staining. in oocytes and unfertilized eggs, lectin was detected in association with yolk platelets, cortical granules, and the vitelline envelope. in embryos, ... | 1983 | 6417146 |
| the cytostatic effect of the cytoplasm of mature, non-activated and cleaving eggs of rana temporaria, acipenser stellatus and xenopus laevis. | corroborated here is the fact, earlier established by chulitskaya and felgengauer (1977), that the cytoplasm of mature non-activated eggs of rana temporaria and acipenser stellatus, unlike that of rana pipiens, exerts no cytostatic effect on the nuclei of the cleaving embryo, but acquires such a capacity after being treated with egta. egta treatment imparts cytostatic properties also to the cytoplasm of cleaving embryos. revealed is the dependence of the cytostatic effect and death of injected e ... | 1983 | 6420076 |
| the onset of activation responsiveness during maturation coincides with the formation of the cortical endoplasmic reticulum in oocytes of xenopus laevis. | immature, stage vi oocytes of xenopus laevis fail to activate (i.e., to propagate a cortical reaction and elevate a fertilization envelope) when pricked or exposed to a23187. we determined the times during maturation when immature oocytes treated with progesterone in vitro developed the capacity to respond to pricking and to ionophore. responsiveness to ionophore first appears at about 3.5-4.5 hr after progesterone treatment; all oocytes are activated by 8-9 hr after progesterone. the capacity t ... | 1984 | 6421640 |
| [does masui's ca-sensitive cytostatic factor exist in the cytoplasm of mature nonactivated eggs of acipenser stellatus, rana temporaria and xenopus laevis?]. | the cytoplasm of mature non-activated and cleaving eggs of a. stellatus and r. temporaria had no cytostatic effect. the cytoplasm treated with egta, being injected in one of two blastomeres of the cleaving egg of the same species, inhibits fully or partially the cleavage. the nuclei in the "arrested" blastomeres had, however, vesicular structure but were not blocked at metaphase, as could be expected if the cleavage was inhibited by a cytostatic factor described by masui (1974). the portion of p ... | 1984 | 6422374 |
| xenopus laevis 18s ribosomal rna: experimental determination of secondary structural elements, and locations of methyl groups in the secondary structure model. | 18s ribosomal rna from x. laevis was subjected to partial digestion with ribonucleases a or t1 under a variety of conditions, and base-paired fragments were isolated. sequence analysis of the fragments enabled five base-paired secondary structural elements of the 18s rna to be established. four of these elements (covering bases 221-256, 713-757, 1494-1555 and 1669-1779) confirm our previous secondary structure predictions, whereas the fifth (comprising bases 1103-1125) represents a phylogenetica ... | 1984 | 6424099 |
| biosynthesis of thyrotropin releasing hormone in the skin of xenopus laevis: partial sequence of the precursor deduced from cloned cdna. | skin of xenopus laevis contains relatively large quantities of thyrotropin releasing hormone (trh). total mrna isolated from skin was cloned in the plasmid puc8. among 1400 cdna clones, one was found with an insert of 478 nucleotides coding for the amino-terminal part of prepro-trh. this clone was detected using a mixture of two synthetic undecanucleotides for colony hybridization. the single open reading frame starts with a methionine residue and a stretch of hydrophobic amino acids, as is typi ... | 1984 | 6425056 |