| embryotoxic effects of environmental chemicals: tests with the south african clawed toad (xenopus laevis). | in the course of the investigations reported below, it was shown that p-chloroaniline has a lethal effect on the embryos of xenopus laevis at a concentration of 100 ppm and is development inhibiting (teratogenic) at concentrations of 1 and 10 ppm, respectively. in the case of aniline, a significant development-inhibiting effect was observed at a concentration as low as 1 ppm. a toxic effect was caused by concentrations between 30 and 40 ppm during embryogenesis and by concentrations above 40 ppm ... | 1987 | 3608894 |
| electron microscopic visualization of protein-dna interactions at the estrogen responsive element and in the first intron of the xenopus laevis vitellogenin gene. | stable protein-dna complexes can be assembled in vitro at the 5' end of xenopus laevis vitellogenin genes using extracts of nuclei from estrogen-induced frog liver and visualized by electron microscopy. complexes at the three following sites can be identified on the gene b2: the transcription initiation site, the estrogen responsive element (ere) and in the first intron. the complex at the transcription initiation site is stabilized by dinucleotides and thus represents a ternary transcription co ... | 1987 | 3608991 |
| regulation and subcellular distribution of a protein methyltransferase and its damaged aspartyl substrate sites in developing xenopus oocytes. | a protein methyltransferase which recognizes racemized and isomerized aspartyl residues in proteins has been identified in both the cytoplasm and nucleus of xenopus laevis oocytes by enzymatic and immunochemical assays. the methyltransferase activity is maintained at a constant concentration of approximately 0.2 microm throughout vitellogenesis. two forms of the enzyme can be identified on immunoblots by their cross-reactivity with an antibody prepared against the purified enzyme from bovine bra ... | 1987 | 3611066 |
| kinetic and electrophoretic analysis of transmethylation reactions in intact xenopus laevis oocytes. | transmethylation reactions in fully grown xenopus oocytes were analyzed following the microinjection of s-adenosyl-l-[methyl-3h]methionine (adomet). the size of the endogenous adomet pool, measured by cation exchange high pressure liquid chromatography is 5.91 pmol/oocyte. the adomet pool turns over with a half-time of 2 h, at a rate of 2.07 pmol/h/oocyte. fractionation experiments indicate that approximately one-third of the adomet in oocytes is utilized for protein carboxylmethylation reaction ... | 1987 | 3611067 |
| contractile properties and myosin isoenzymes of various kinds of xenopus twitch muscle fibres. | single twitch muscle fibres have been isolated from various parts of the iliofibularis muscle of xenopus laevis. after measurements of their isotonic contractile properties, myosin extraction was performed on individual fibres and the extract analysed by various forms of gel electrophoresis. in agreement with previous results three major fibre types, types 1, 2, and 3 could be discerned. both mechanical data and native isomyosin patterns indicated a further subdivision of types 1 and 2 into subt ... | 1987 | 3611330 |
| the early development of neurons with gaba immunoreactivity in the cns of xenopus laevis embryos. | we have used an antibody to glutaraldehyde fixation complexes of gamma-amino butyric acid (gaba) to stain the developing central nervous system of xenopus laevis embryos. neuronal somata, growth cones, axons, and dendrites were found with gaba-like immunoreactivity. transmission electron microscope (tem) observations were made of axons and synapses. by observation of the earliest stages of differentiation of neurons, seven classes of putative gabaergic interneurons were discerned. 1) ascending n ... | 1987 | 3611420 |
| protamine polymorphism in xenopus laevis laevis. | protamines from individual frogs of the subspecies xenopus laevis laevis were compared by electrophoresis on polyacrylamide gels containing acetic acid, urea, and triton x-100 to determine if the expression of protamine genes differs among individuals. two electrophoretic bands, sp2a and sp2b, appeared to be expressed as allelic variants. of 33 frogs, 19 expressed only sp2a, 11 expressed both sp2a and sp2b, and three expressed only sp2b. electrophoretic analysis of partial v8 protease digests co ... | 1987 | 3612054 |
| ultrastructural changes in the intestinal connective tissue of xenopus laevis during metamorphosis. | ultrastructural changes in the intestinal connective tissue of xenopus laevis during metamorphosis have been studied. throughout the larval period to stage 60, the connective tissue consists of a few immature fibroblasts surrounded by a sparse extracellular matrix: few collagen fibrils are visible except close to the thin basal lamina. at the beginning of the transition from larval to adult epithelial form around stage 60, extensive changes are observed in connective tissue. the cells become mor ... | 1987 | 3612815 |
| epidermal capillariasis in south african clawed frogs (xenopus laevis). | significant morbidity and mortality of south african clawed frogs, xenopus laevis, can be caused by parasitism of the epidermis by a capillarid nematode. these worms produce an erosive dermatitis that is complicated by infection with gram-negative microorganisms. the nematode apparently has a direct life cycle that can be completed within the epidermis of the frog. these characteristics are suggested by the lack of an intermediate host and failure to detect visceral migration. another unique fea ... | 1987 | 3613514 |
| visual experience and the maturation of the ipsilateral visuotectal projection in xenopus laevis. | the effect of visual deprivation upon the maturation of the ipsilateral visuotectal projection has been studied in xenopus laevis. this topographically ordered projection is polysynaptic. the first stage involves the retinal projection to the contralateral optic tectum. the tectum projects to the nucleus isthmi on the same side. the final stage is the crossed isthmotectal projection from the nucleus isthmi to the tectum ipsilateral to the eye. the topographic precision of connections at various ... | 1987 | 3614642 |
| dna sequence of the first exon and 5' flanking region of the 68-k serum albumin gene of xenopus laevis. | | 1987 | 3615206 |
| a possible role of the glomus cell in controlling vascular tone of the carotid labyrinth of xenopus laevis. | to clarify the physiological significance of the g-s connection (intimate apposition of the glomus cell to the smooth muscle) in the xenopus carotid labyrinth, experiments were carried out morphologically and physiologically. results obtained are as follows. efferent electrical stimulation of the glossopharyngeal nerve resulted in concentrating dense-cored vesicles on the peripheral region of the glomus cell, and a decrease of vesicles as a whole. in the carotid labyrinth perfused artificially, ... | 1987 | 3617052 |
| kinetic behavior of 30s rrna intermediate labeled in developing embryonic cells of xenopus laevis. | in xenopus neurula cells, "30s" rna was found to be labeled with 3h-uridine after a relatively short labeling period. results obtained from cumulative labeling and pulse-labeling and chase experiments with cells from late gastrulae, yolk plug-stage embryos, and neurulae showed that the 30s rna is an intermediate in rrna processing and is derived from 40s pre-rrna and processed to 28s rrna. the half-life of the 30s rrna intermediate was about 7.5 min or less at the three stages examined. | 1987 | 3621362 |
| the lampbrush chromosomes of xenopus laevis: preparation, identification, and distribution of 5s dna sequences. | details are given of a technique for making permanent preparations of the lampbrush chromosomes of xenopus laevis. stained preparations allow all 18 bivalent chromosomes to be identified, and a working map showing the major features has been constructed. fifteen of the xenopus chromosomes have one telomere conspicuously larger than the other; the two smallest chromosomes, and one other, lack large telomeres. similar preparations, extracted with rnase and denatured, have been hybridized in situ w ... | 1987 | 3622079 |
| cerulein mrna and peptide alpha-amidation activity in the skin of xenopus laevis: stimulation by norepinephrine. | the skin of xenopus laevis, because of its high concentrations of amidated peptides, is an excellent model for the study of neuropeptide biosynthesis. in this paper we determined levels of the mrnas which encode cerulin and characterized the enzymatic activity which likely produces the carboxyl terminal alpha-amide moiety of cerulein. this enzyme is stimulated by the addition of cuso4 and ascorbate and requires the presence of molecular oxygen and is thus similar to the peptidyl-glycine alpha-am ... | 1987 | 3623070 |
| the primary structure of rat ribosomal protein l5. a comparison of the sequence of amino acids in the proteins that interact with 5 s rrna. | the covalent structure of rat ribosomal protein l5, which associates with 5 s rrna in the organelle, was deduced from the sequence of nucleotides in a recombinant cdna (pl5-6-4) and confirmed from the sequences of amino acids in portions of the protein. ribosomal protein l5, encoded by pl5-6-4, contains 296 amino acids and has a molecular weight of 34,298. however, a second recombinant cdna, pl5-8-5, encodes a protein with an additional methionyl residue at position 236 and may be the product of ... | 1987 | 3624282 |
| the nature of developmental restrictions in xenopus laevis embryos. | | 1986 | 3625118 |
| ammonium ion as a possible regulator of the commencement of rrna synthesis in xenopus laevis embryogenesis. | recently, we have shown that ammonium salts and amines at an external concentration of 3 mm selectively inhibit rrna synthesis in xenopus disaggregated neurula cells. we studied here the change in the amount of ammonia within the embryo and its inhibitory action on the commencement of rrna synthesis which normally occurs at the blastula stage of development. ammonia exists at ca. 50 ng/egg (or ca. 3.0 mm at an intra-egg concentration) in the unfertilized egg. this level was maintained during cle ... | 1986 | 3635478 |
| biochemical research on oogenesis. binding of trna to the nucleoprotein particles of xenopus laevis previtellogenic oocytes. | in previtellogenic oocytes of xenopus laevis, nearly all trna is included in nucleoprotein particles (thesaurisomes) sedimenting at 42 s. we evaluate the possibility of a trna exchange between the particles and the ribosomes during protein synthesis. we find that the particles take up trna after a very short incubation in vitro. in the absence of atp, the particles preferentially bind charged trna. in the presence of atp, more trna binds to the particles, and the sedimentation coefficient of the ... | 1987 | 3643212 |
| acceleration of the rate of processing of 40 s pre-rrna during xenopus laevis embryogenesis. | processing of 40 s pre-rrna into 18 and 28 s mature rrnas was studied in xenopus embryonic cells by pulse-chase experiments using actinomycin d as a transcription-inhibitor. gel electrophoretic analyses revealed that the rate of processing was accelerated due to a shortening of the half-life of 40 s pre-rrna from 19 min at the gastrula stage to 9 min at and after the neurula stage. the step under developmental control appeared to be the cleavage of 40 s pre-rrna into 18 s rrna and the 34 s rrna ... | 1987 | 3647911 |
| regional specification within the mesoderm of early embryos of xenopus laevis. | we have further analysed the roles of mesoderm induction and dorsalization in the formation of a regionally specified mesoderm in early embryos of xenopus laevis. first, we have examined the regional specificity of mesoderm induction by isolating single blastomeres from the vegetalmost tier of the 32-cell embryo and combining each with a lineage-labelled (fda) animal blastomere tier. whereas dorsovegetal (d1) blastomeres induce 'dorsal-type' mesoderm (notochord and muscle), laterovegetal and ven ... | 1987 | 3652971 |
| mode of action of ammonia and amine on rrna synthesis in xenopus laevis embryonic cells. | recently, we found that rrna synthesis in dissociated embryonic cells of xenopus laevis is selectively inhibited by ammonium salts added to their surrounding medium. similar effects were also observed in cells treated with amines. in this report, we analysed in more detail the effects of an ammonium salt and trimethylamine on rrna synthesis in xenopus embryonic cells cultured under several different conditions. results obtained showed that ammonia and trimethylamine inhibit formation of 40s pre- ... | 1987 | 3652983 |
| lithium inhibits morphogenesis of the nervous system but not neuronal differentiation in xenopus laevis. | xenopus embryos treated with 100 mm-lithium from the 2- to 4-cell stage to the early blastula stage (4h) failed to neurulate and developed without a discernible anteroposterior axis. the internal structure of defective embryos was grossly disorganized, but immunohistochemical staining with cell-type-specific antibodies revealed differentiated nerve and muscle cells. quantitative assay in tissue cultures from control and acutely abnormal lithium-treated embryos showed that neural differentiation ... | 1987 | 3653007 |
| dynamics of the control of body pattern in the development of xenopus laevis. iv. timing and pattern in the development of twinned bodies after reorientation of eggs in gravity. | the mesendodermal anatomy of twinned larval axes is described in relation to the normal single pattern, when twinning has been caused by experimental tilting of eggs before first cleavage. the formation of two origins for gastrulation movements (dorsal lips) and their relatively rapid spread and coalescence to give a circular blastopore, is a predictor of twin formation in individual embryos after treatment. the anatomy of twins where development has been disturbed from the outset in this way is ... | 1987 | 3653010 |
| a processed gene coding for a sarcomeric actin in xenopus laevis and xenopus tropicalis. | a processed gene potentially coding for a sarcomeric actin has been identified in xenopus laevis and in the more primitive species x. tropicalis. the peptides encoded in these two species differ by two out of 377 amino acid residues. on the basis of the amino acid substitutions, the encoded peptide was identified as an alpha-skeletal actin in x. laevis and as an alpha-cardiac actin in x. tropicalis. northern blot analysis and s1 mapping experiments suggest that in x. tropicalis the gene is expre ... | 1987 | 3653078 |
| periodic dna synthesis in cell-free extracts of xenopus eggs. | cell-free extracts prepared from unfertilized eggs of xenopus laevis support dna synthesis on sperm pronuclei. continuous labelling studies using [3h]dctp and pulse labelling studies using [32p]dctp demonstrate that synthesis occurs in short bursts of 40 min, which are punctuated by periods of 20-40 min during which no synthesis occurs. density substitution experiments using bromodeoxyuridine demonstrate that this synthesis involves the initiation of replication and reveals that re-initiation ev ... | 1987 | 3653080 |
| autoantibodies in hypertrophic cardiomyopathy and their clinical significance. | data concerning autoantibodies in hypertrophic cardiomyopathy are rare and controversial and only the results of indirect immunofluorescence methods are available in the literature. the aim of this study was to determine the frequency and clinical significance of autoantibodies in hypertrophic cardiomyopathy by means of the western blot which is a highly sensitive immunological technique. sera from twelve (48.0%) of the whole group of 25 patients with hypertrophic cardiomyopathy reacted with act ... | 1987 | 3653127 |
| a quantitative analysis of cellular and matrix changes in meckel's cartilage in xenopus laevis. | the changes in cell population and matrix volume fraction in meckel's cartilage during metamorphic climax have been assessed using standard stereological techniques. the period of climax has been divided into three phases, a preliminary 'lag' phase (nf stages 57-60), a 'division' phase (nf stages 60-62) when the cell population rises rapidly and a 'synthesis' phase (nf stages 62-66) when the matrix content of the tissue also increases dramatically. these changes along with the membranous ossific ... | 1987 | 3654355 |
| presumptive mesoderm cells from xenopus laevis gastrulae attach to and migrate on substrata coated with fibronectin or laminin. | during amphibian gastrulation, presumptive mesoderm cells migrate from the blastopore towards the animal pole along the inner surface of the ectodermal layer. their natural substratum is a network of anastomosing extracellular matrix fibrils, which contains fibronectin and laminin, as shown by immunostaining. if the fibril network is transferred onto a coverslip from the ectodermal layer, dissociated mesodermal cells readily attach to such conditioned surfaces and show active migration in a medi ... | 1986 | 3654774 |
| level of histone h4 mrna in xenopus laevis embryonic cells cultured in the absence of cell adhesion. | the amount of histone h4 mrna per embryo was followed during early development of xenopus laevis by northern blot analyses using a cloned histone h4 cdna as the probe. the h4 mrna content was nearly constant until the blastula stage, increased greatly at the gastrula stage and then decreased at the neurula stage. experiments with actinomycin d suggested that most h4 mrna molecules detected at the late gastrula and neurula stages were maintained depending on new transcription of h4 genes during t ... | 1986 | 3655646 |
| sequence of a 3.18 kb tandem repeat of xenopus laevis dna containing 8 trna genes. | | 1987 | 3658682 |
| linker scanner mutagenesis of the xenopus laevis ribosomal gene promoter. | we have assayed a series of linker scanner mutants which cover the xenopus laevis ribosomal gene promoter at approximately ten base pair intervals. all of these mutations adversely affect promoter activity with the exception of one mutation which stimulates activity. thus, none are neutral. we show that most of the mutations can be partially rescued by ligating a block of enhancer elements upstream of the promoter. in addition, we have made extracts from liver nuclei which produce dnasei protect ... | 1987 | 3658698 |
| observations on the structure of two human 7sk pseudogenes and on homologous transcripts in vertebrate species. | a comparison of the sequence of two human 7sk rna pseudogenes, covering approx. 190 and 240 base-pairs of the structural gene, is presented. both repeated elements are flanked by direct repeats and begin at the 5' end of the gene. each terminates approx. 90 base-pairs short of the 3' end, the latter representing a continuous sequence and the former carrying an internal deletion of about 40 base-pairs, this region being flanked in the progenitor gene by short repeated sequences. southern blotting ... | 1987 | 3663152 |
| in vivo phosphorylation of titin and nebulin in frog skeletal muscle. | titin and nebulin are two major protein components of the sarcomere matrix in striated muscles. purified titin and nebulin from frog (xenopus laevis) skeletal muscle are similar in size and in amino acid composition to their mammalian or avian counterparts. both proteins contain substantial amounts of protein-bound phosphate: about 5 to 6 per titin subunit and 8 to 9 per nebulin subunit. injection of radioactive inorganic phosphate into the dorsal lymph sacs of xenopus laevis resulted in the sig ... | 1987 | 3663225 |
| fate map for the 32-cell stage of xenopus laevis. | a complete fate map has been produced for the 32-cell stage of xenopus laevis. embryos with a regular cleavage pattern were selected and individual blastomeres were injected with the lineage label fluorescein-dextran-amine (fda). the spatial location of the clones was deduced from three-dimensional (3d) reconstructions of later stages and the volume of each tissue colonized by labelled cells in each tissue was measured. the results from 107 cases were pooled to give a fate map which shows the fa ... | 1987 | 3665770 |
| thesaurin a, the major protein of xenopus laevis previtellogenic oocytes, present in the 42 s particles, is homologous to elongation factor ef-1 alpha. | we have purified in sds x.laevis thesaurin a (mr 50,000) which is part of the 42 s storage particles. its n-terminal amino acid is blocked and several peptides obtained by v8 protease treatment were purified and sequenced. as expected from one of the functional roles of the 42 s particles (trna binding, protection against deacylation and exchange with the ribosome), the amino acid sequence of thesaurin a was found to be closely related to that of the elongation factor ef-1 alpha. we suggest that ... | 1987 | 3666148 |
| decay of the oocyte-type heat shock response of xenopus laevis. | xenopus oocytes have a complex heat shock response. during transition of the oocyte into fertilized egg, the heat shock response undergoes several qualitative and quantitative changes culminating in its complete extinction. heat shock induces oocytes to synthesize four heat shock proteins (hsps): 83, 76, 70, and 57. after ovulation, two additional proteins (hsps 22 and 16) are inducible. the heat shock response of spawned eggs can be modified by changing the ionic configuration of the external m ... | 1987 | 3666305 |
| inductive interactions in the spatial and temporal restriction of lens-forming potential in embryonic ectoderm of xenopus laevis. | the process of lens cell determination in amphibians is currently viewed as one involving a series of inductive interactions. on the basis of previous investigations, these interactions are thought to begin during gastrulation when the presumptive foregut endoderm and then the heart mesoderm come into contact with the presumptive lens ectoderm. this earlier period of induction is followed by the later interaction of the optic vesicle with the lens-forming ectoderm. transplantation experiments we ... | 1987 | 3666306 |
| neural crest development in the xenopus laevis embryo, studied by interspecific transplantation and scanning electron microscopy. | the xenopus borealis quinacrine marker and scanning electron microscopy have been used to study the appearance, migration, and homing of neural crest cells in the embryo of xenopus. the analysis shows that the primordium of the neural crest develops from the nervous layer of the ectoderm and consists of three segments at early neurula stages. this primordium is located in the lateral halves of the neural folds behind the prospective eye vesicles. the histological and experimental evidence shows ... | 1987 | 3666314 |
| vocalizations by a sexually dimorphic isolated larynx: peripheral constraints on behavioral expression. | the clawed frog xenopus laevis uses sexually dimorphic vocalizations, mate calling and ticking, to advertise reproductive state. the basic unit of vocalization is a brief click, produced by the movement of cartilagenous disks located within the larynx. the rate of click production in the male-specific mate call (71 hz) is an order of magnitude faster than the rate of click production in female typical ticking (6 hz). to determine if vocalization rate is constrained by the periphery, male and fem ... | 1987 | 3668623 |
| androgen regulation of muscle fiber type in the sexually dimorphic larynx of xenopus laevis. | we used histochemical techniques [assays for adenine triphosphatase (atpase) and succinate dehydrogenase (sdhase) activity] to identify muscle fiber types in the larynx of xenopus laevis. male muscle is made up of one fiber type, medium-sized fibers (approximately 9 microns2) that stain lightly for acid-stable atpase and intensely for sdhase activity. in contrast, the female has 3 fiber types: small fibers (approximately 6 microns2) that stain intensely for atpase and sdhase, medium-sized fibers ... | 1987 | 3668624 |
| cytoplasmic effect on gene function in xenopus laevis. | the pigmentation gene of xenopus laevis is dominant and that of albino ap mutant recessive. heterologous haploid hybrids are produced by uv inactivation of the egg nuclei during second polar body formation in the mutant sperm-fertilized xenopus eggs. during development of these hybrids, melanin appeared in the eye and melanophores in the skin at stages comparable to those of the wild type, but much earlier than in the albino mutant. the number and intensity of pigment cells are intermediate betw ... | 1987 | 3672098 |
| a nerve growth factor-induced gene encodes a possible transcriptional regulatory factor. | nerve growth factor (ngf) is a trophic agent that promotes the outgrowth of nerve fibers from sympathetic and sensory ganglia. the neuronal differentiation stimulated by this hormone was examined in the ngf-responsive cell line pc12. differential hybridization was used to screen a complementary dna library constructed from pc12 cells treated with ngf and cycloheximide. one of the complementary dna clones that was rapidly induced by ngf was found to have a nucleotide sequence that predicts a 54-k ... | 1987 | 3672127 |
| a comparative sem-study on the teeth of 10 anuran species. | teeth of 10 anuran species have been investigated by means of scanning electron microscopy (sem). generally a great variability of the structure of dentine crowns and the zone of division was noted not only between the single species, but also within one species on the same dentigerous bone. 4 species (hyla cinerea, rana ridibunda, r. hosei, ptychadena spec.) mostly have more or less bladed bicuspid and clearly divided teeth corresponding to the "lissamphibia"-pattern. 2 species (xenopus laevis, ... | 1987 | 3674455 |
| development of the connective tissue in the digestive tract of the larval and metamorphosing xenopus laevis. | developmental changes, until the completion of metamorphosis, of the connective tissue of the digestive tract in the south african clawed frog xenopus laevis were examined by light and scanning electron microscopy. during the pre- and prometamorphosis (stages 50 through 59) the layer of connective tissue was prominent in the typhlosole, while that in the rest of the intestine and stomach remained very thin. most of the connective tissue cells were fibroblasts and were concentrated mainly in the ... | 1987 | 3674459 |
| synthesis and expression of functional angiotensin ii receptors in xenopus oocytes injected with rat brain mrna. | xenopus laevis oocytes were injected with poly(a)+ mrna isolated from rat brain and superfused in a medium containing either serotonin, angiotensin ii or bradykinin. applications of serotonin or angiotensin ii to injected oocytes elicited, in a dose-dependent manner, changes in membrane potential. the angiotensin ii receptor was desensitized fairly rapidly in the continued presence of the agonist. no response was obtained with bradykinin. the selectivity of the angiotensin ii-induced response wa ... | 1987 | 3676711 |
| conserved exon-intron organization in two different caerulein precursor genes of xenopus laevis. additional detection of an exon potentially coding for a new peptide. | from a genomic library of xenopus laevis, two genes coding for different preprocaeruleins have been isolated and sequenced. these correspond to the type i and type iii precursors analyzed previously at the cdna level [richter, k., egger, r. and kreil, g. (1986) j. biol. chem. 261, 3676-3680]. the type iii gene comprises eight exons; the type i apparently contains eight exons as well, of which six have been sequenced. the genetic information for the dekapeptide caerulein is present on small exons ... | 1987 | 3678233 |
| the compatibility of xenopus antibody and homoiothermic complement. | adult xenopus laevis serum containing an anti-chicken erythrocyte antibody exhibits complement (c) activity by both the classical and the alternative pathways. lytic activity is removed by heating serum to 50 degrees c for at least 20 min; it is also removed by polysaccharides and by 7.5 mm edta. the optimum temperature for xenopus c activation is 25 degrees c. the ability of xenopus antibody against chicken erythrocytes to co-operate with homoiothermic c in in vitro by lysis of chicken erythroc ... | 1987 | 3678560 |
| comparison of the organization and fine structure of a chicken and a xenopus laevis vitellogenin gene. | the structural organization and the coding nucleotide sequence of the xenopus laevis a2 and the chicken major vitellogenin genes have been compared. both genes show the same exon-intron organization. however, the degree of homology between the nucleotide and derived amino acid sequences varies extensively along the genes. several of the 35 exons are quite similar, and a unique cysteine motif in the lipovitellin ii domain is conserved between the two genes. in contrast, one internal region is qui ... | 1987 | 3680202 |
| expression of human cathepsin d in xenopus oocytes: phosphorylation and intracellular targeting. | we have obtained expression of a cdna clone for human cathepsin d in xenopus laevis oocytes. biosynthetic studies with [35s]methionine labeling demonstrated that most of the cathepsin d remained intracellular and underwent proteolytic cleavage, converting a precursor of mr 47,000 d to a mature form of mr 39,000 d with processing intermediates of mr 43,000-41,000 d. greater than 90% of the cathepsin d synthesized by oocytes bound to a mannose 6-phosphate (man-6-p) receptor affinity column, indica ... | 1987 | 3680368 |
| expression sequences and distribution of two primary cell adhesion molecules during embryonic development of xenopus laevis. | studies of chicken embryos have demonstrated that cell adhesion molecules are important in embryonic induction and are expressed in defined sequences during embryogenesis and histogenesis. to extend these observations and to provide comparable evidence for heterochronic changes in such sequences during evolution, the local distributions of the neural cell adhesion molecule (n-cam) and of the liver cell adhesion molecule (l-cam) were examined in xenopus laevis embryos by immunohistochemical and b ... | 1987 | 3680386 |
| disappearance of rohon-beard neurons from the spinal cord of larval xenopus laevis. | rohon-beard neurons are primary sensory cells located in the spinal cord of embryonic lower vertebrates. the kinetics of their normal, gradual, but complete disappearance in xenopus tadpoles has been followed. levels of acid phosphatase activity, a common histochemical correlate of cell death, were assayed and found to increase at the time of onset of disappearance of rohon-beard cells. ultrastructural examination revealed the presence of numerous secondary lysosomes, swelling of endoplasmic ret ... | 1987 | 3680623 |
| factors guiding optic fibers in developing xenopus retina. | we have characterized, by electron microscopy, the growth of pioneering axons from the retina into the visual pathway during early development of xenopus laevis. the subsequent development of following fibers from the growing retinal margin as they accumulated in the ganglion cell fiber layer (gcfl) of the retina was also studied. extracellular channels bordered by neuroepithelial cells appear in the developing retina in a dorsal to ventral gradient before any pioneering axons are seen. pioneeri ... | 1987 | 3680626 |
| relationship between natural variations in motoneuron number and body size in xenopus laevis: a test for size matching. | during normal development, tadpoles of xenopus laevis demonstrate large variations in body size that are carried through metamorphosis. this variation in size exists at the stages when lumbar lateral motor column (l-lmc) motoneurons are produced and when neuronal cell death in this neuron population occurs. body size, hindlimb size, motoneuron number, and motoneuron size (i.e., neuron nuclear cross-sectional area) were measured in animals from three developmental stages: one prior to significant ... | 1987 | 3680631 |
| healing and growth of half-eye "compound eyes" in xenopus: application of an interspecific cell marker. | surgically constructed compound eyes have been widely used to examine the development of retinotectal projections in amphibians. such studies have been limited, however, by the lack of an adequate cellular marker with which to assess the contributions of grafted and host tissues to the later larval and adult retina. we have followed the growth of graft- and host-derived ocular tissues in interspecific compound eyes prepared by orthotopic and heterotopic exchanges of half-eye fragments between pi ... | 1987 | 3681411 |
| a complex array of sequences enhances ribosomal transcription in xenopus laevis. | the ribosomal dna spacer in xenopus laevis was shown in previous studies to be involved in regulating the expression of the ribosomal genes. here transcription enhancement by this spacer has been studied in some detail, to fully identify the sequences involved and to determine their relative importance in this phenomenon. it is shown that the 60/81 base-pair (bp) repeats, which were reported to be enhancer elements, act as part of a mode of enhancement whose effect is amplified by the spacer pro ... | 1987 | 3681979 |
| transcriptionally inactive oocyte-type 5s rna genes of xenopus laevis are complexed with tfiiia in vitro. | an extract from whole oocytes of xenopus laevis was shown to transcribe somatic-type 5s rna genes approximately 100-fold more efficiently than oocyte-type 5s rna genes. this preference was at least 10-fold greater than the preference seen upon microinjection of 5s rna genes into oocyte nuclei or upon in vitro transcription in an oocyte nuclear extract. the approximately 100-fold transcriptional bias in favor of the somatic-type 5s rna genes observed in vitro in the whole oocyte extract was simil ... | 1987 | 3683391 |
| magnetic effects on tail-fin melanophores of xenopus laevis tadpoles in vitro. | | 1987 | 3683589 |
| the enhancement of ribosomal transcription by the recycling of rna polymerase i. | it has been suggested that the tandemly repeated ribosomal genes of eukaryotes may be subject to a special mechanism of transcriptional enhancement, called readthrough enhancement, in which transcription factors are recycled. recent experiments with the mouse ribosomal genes, although consistent with this possibility, were unable to distinguish between true readthrough enhancement and promoter occlusion. to test directly for readthrough enhancement, the pre-ribosomal rna of xenopus laevis was pr ... | 1987 | 3684604 |
| observations on the development of cerebellar afferents in xenopus laevis. | the development of cerebellar afferents has been studied in the clawed toad, xenopus laevis, from stage 46 to 64, with the horseradish peroxidase retrograde tracer technique. already in stage 48 tadpoles, i.e. before the formation of the limbs, a distinct set of cerebellar afferents was found. vestibulocerebellar (mainly arising bilaterally in the nucleus vestibularis caudalis) and contralateral olivo-cerebellar projections dominate. secondary trigeminocerebellar (from the descending nucleus of ... | 1987 | 3688451 |
| the development of the merkel cells in the tentacles of xenopus laevis larvae. | the merkel cells in the larval tentacles of xenopus laevis were examined by tem. different forms of merkel cells were found, depending on the age of the larvae or the location in the tentacles. these forms have the appearance of intermediate states between merkel cells and superficial epidermal cells; thus an epidermal origin for the merkel cells seems more likely than an immigration from the neural crest. the forms differ in (1) their location in the epidermis, (2) their shape, (3) the number a ... | 1987 | 3688453 |
| cloning and sequence of cdna encoding a peptide c-terminal alpha-amidating enzyme from xenopus laevis. | the c-terminal alpha-amide formation of the peptides is one of the most important events of prohormone processing. we have recently isolated an alpha-amidating enzyme, ae-i, from xenopus laevis skin, which is the only enzyme ever purified to homogeneity. in this study, we report cloning and sequence of cdna encoding ae-i. our results indicate that enzyme ae-i is initially synthesized as a precursor with 400 amino acid residues, which is further processed to the mature enzyme consisting of 344 re ... | 1987 | 3689360 |
| functional characterization of x. laevis u5 snrna genes. | xenopus laevis u5 snrna genes are found in several genomic arrangements, represented by a predominant tandem repeat of 583 bp and other minor repeats. several copies of the major tandem repeat have been cloned and expressed in xenopus oocytes. the transcripts assemble into u5 snrnps which are recognized by anti-sm antibodies. we have identified functional elements in the u5 gene promoter. although similar in organization to other u snrna gene promoters, u5 contains significant differences and is ... | 1987 | 3691481 |
| meckel's cartilage in xenopus laevis during metamorphosis: a light and electron microscope study. | meckel's cartilage, in xenopus laevis prior to metamorphosis, is a tissue exhibiting very large lacunae, separated by thin rims of matrix, presenting a net-like appearance, similar to that of cartilage in invertebrates. the cells on the periphery of the tissue are rather more flattened, and more closely packed. on the lateral aspects of the cartilage distinct columns of apparently dividing cells are evident. during metamorphic climax, the amount of matrix separating the lacunae increases, with a ... | 1986 | 3693112 |
| neurogenesis in the vocalization pathway of xenopus laevis. | we examined possible contributions of neurogenesis to sex differences in the vocalization pathway of the south african clawed frog, xenopus laevis. birthdates of neurons were obtained from autoradiograms of animals receiving tritiated thymidine from gastrulation through 1 month after metamorphosis. thymidine availability studies showed that 80% of the [3h]-thymidine injected into embryos and tadpoles was incorporated into the dna of dividing cells within 3 hours. we observed 3 patterns of neurog ... | 1987 | 3693599 |
| [rearrangement of the morphological structure and degradation of the extracellular matrix in amphibian embryos after short-term disruption of cell contacts]. | the changes in cell structure of explants of presumptive early gastrula mesoderm of xenopus laevis and dynamics of extracellular matrix formation has been studied for 6 h after their isolation. after 6 h, control explants of any dorsoventral level turned into dense spheric homogeneous cell clusters. explants of dorsal and lateral sectors, treated with medium without ca2+ and mg2+ for 30 s, bent and separated into several layers, and in ventral sector explants, cavities, surrounded by polarized c ... | 1987 | 3696679 |
| characterization of a stable, major dna polymerase alpha species devoid of dna primase activity. | we have purified from xenopus laevis ovaries a major dna polymerase alpha species that lacked dna primase activity. this primase-devoid dna polymerase alpha species exhibited the same sensitivity as the dna polymerase dna primase alpha to buadatp and bupdgtp, nucleotide analogs capable of distinguishing between dna polymerase delta and dna polymerase dna primase alpha. the primase-devoid dna polymerase alpha species also lacked significant nuclease activity indicative of the alpha-like (rather t ... | 1987 | 3697091 |
| dopamine receptor-mediated inhibition of serotonin n-acetyltransferase activity in retina. | the possible involvement of catecholamines in the regulation of serotonin n-acetyltransferase (nat) activity in retina of the african clawed frog was investigated using an in vitro eye cup preparation. dopamine (10 microm) and norepinephrine (50 microm) had no significant effect on nat activity of eye cups incubated in the light. however, dopamine inhibited the increase of retinal nat activity that occurs in eye cups incubated in darkness; the ed50 for dopamine was 0.3 microm. the effect of dopa ... | 1986 | 3697740 |
| the ontogeny of androgen receptors in the cns of xenopus laevis frogs. | androgenic steroids have been implicated in the development of sex differences in xenopus laevis frogs. in order to determine when neurons first acquire the ability to concentrate androgen, we prepared autoradiograms of cns in developing frogs following injection of tritiated dihydrotestosterone (dht). x. laevis tadpoles and juveniles from stage 60 to 2 months post-metamorphosis (pm) were injected with [3h]dht. brain and spinal cord autoradiograms from these animals were examined for the presenc ... | 1986 | 3697774 |
| development of pronuclei from human spermatozoa injected microsurgically into frog (xenopus) eggs. | human spermatozoa were demembranated with triton x-100 (tx) and injected into the mature eggs of xenopus laevis. the nuclei of these spermatozoa decondensed and developed into pronuclei. chromosomes did not appear in the eggs until the end of a 5-hr incubation period. when the demembranated human spermatozoa were further treated with dithiothreitol (dtt) before they were injected into the eggs, the sperm nuclear decondensation and pronuclear development took place considerably faster than in spe ... | 1986 | 3701290 |
| naturally occurring and induced ganglion cell death. a retinal whole-mount autoradiographic study in xenopus. | the retina in frogs grows continuously throughout the whole life of the animal by the addition of rings of cells at the ciliary margin. naturally occurring neuron death cannot, consequently, be established by counting surviving neurons. a new approach, retinal whole-mount auto-radiography was introduced in this study to estimate cell loss occurring in the ganglion cell layer over a long period of time. 3h-thymidine injection at stage 53 (midlarval stage) labels a ring of cells, thereby marking t ... | 1986 | 3706775 |
| observations on the mitochondrial distribution in normal, rotated and cold-treated 2-cell stage embryos of xenopus laevis. | the distribution of mitochondrial profiles at the level of the frontal plane dividing dorsal and ventral halves of the xenopus 2-cell stage embryo was studied. it was found that the mitochondria are distributed asymmetrically in the two embryo sides which appear non-equivalent in terms of mitochondrial density. egg rotation experiments indicated that the observed asymmetry is coupled with sidedness and essential to it. cold shock of the eggs resulted in a disturbed mitochondrial distribution, su ... | 1986 | 3708695 |
| activation of ribosomal protein s6 phosphorylation during meiotic maturation of xenopus laevis oocytes: in vitro ordered appearance of s6 phosphopeptides. | during meiotic maturation of xenopus laevis stage 6 oocytes into unfertilized eggs, 40s ribosomal protein s6 undergoes multiple phosphorylation. extracts prepared from unfertilized eggs are up to 10-fold more efficient in phosphorylating s6 than those prepared from immature oocytes. when analyzed by deae chromatography the s6 kinase activity elutes as a single peak. if extracts from unfertilized eggs are prepared in the absence of beta-glycerol phosphate, a putative phosphatase inhibitor, there ... | 1986 | 3709523 |
| acquisition of developmental autonomy in the equatorial region of the xenopus embryo. | this paper describes a continuing effort to define the location and mode of action of morphogenetic determinants which direct the development of dorsal body axis structures in embryos of the frog xenopus laevis. earlier results demonstrated that presumptive endodermal cells in one vegetal quadrant of the 64-cell embryo can, under certain experimental conditions, induce partial or complete body axis formation by progeny of adjacent equatorial cells. (r.l. gimlich and j.c. gerhart, 1984, dev. biol ... | 1986 | 3709967 |
| axis determination in polyspermic xenopus laevis eggs. | polyspermic xenopus laevis eggs can be identified easily because of regions of pigment accumulation and white stripes, which arise by a nocodazole-sensitive process. eggs containing up to four sperm are capable of forming a single embryonic axis. dispermic eggs display two regions of pigment accumulation, one around each sperm entry point (sep), and one white stripe between the seps. such eggs with a 180 degree separation between the seps were bisected before first cleavage along the white strip ... | 1986 | 3709970 |
| determination of the intracellular state of soluble macromolecules by gel filtration in vivo in the cytoplasm of amphibian oocytes. | a method to examine the diffusible state and the sizes of major cytoplasmic proteins in a living cell is described. small (40-300 microns) commercially available gel filtration beads of a broad range of mr exclusion limits were microsurgically implanted into the cytoplasm of oocytes of the frog, xenopus laevis, usually after metabolic labeling of oocyte proteins with [35s]methionine. after equilibration in vivo for several hours, the appearance of the implanted cells, notably the bead-cytoplasm ... | 1986 | 3711142 |
| membrane protein redistribution during xenopus first cleavage. | a large increase in surface area must accompany formation of the amphibian embryo first cleavage furrow. the additional membrane for this areal expansion has been thought to be provided entirely from cytoplasmic stores during furrowing. we have radioiodinated surface proteins of fertilized, precleavage xenopus laevis embryos and followed their redistribution during first cleavage by autoradiography. near the end of first cleavage, membrane of the outer, pigmented surface of the embryo and a shor ... | 1986 | 3711145 |
| the coelomic envelope to vitelline envelope conversion in eggs of xenopus laevis. | an amphibian egg recovered from the body cavity is enclosed by a coelomic egg envelope. upon transport down the oviduct, the envelope is converted to the vitelline envelope. the coelomic and vitelline envelopes are distinct in terms of sperm penetrability, ultrastructural morphology, and radioiodination profiles. in this study, the macromolecular compositions of these two envelopes were determined. isolated envelopes were compared by one- and two-dimensional gel electrophoresis, peptide mapping, ... | 1986 | 3711153 |
| visual deprivation and the maturation of the retinotectal projection in xenopus laevis. | there has been a resurgence of interest, recently, in the possible role of neural activity in the ordering of synaptic connections in the lower vertebrate retinotectal system. blockade of all neural activity, by chronic administration of tetrodotoxin (ttx), during the regeneration of the optic nerve in goldfish has been found to prevent the re-emergence of a fully ordered retinotectal projection. we sought to determine the effects of visual deprivation, a less radical perturbation of neural acti ... | 1986 | 3711779 |
| localization of specific mrna sequences in xenopus laevis embryos by in situ hybridization. | in situ hybridization of cloned cdna probes to frozen sections of xenopus laevis stage-42 tadpoles has been used to determine the tissue localization of several mrnas. nine out of sixteen probes tested hybridized to most or all tadpole tissues; seven probes exhibited tissue-specific hybridization. the non-tissue-specific sequences hybridized to rna species that are also present in maternal rna while the tissue-specific sequences hybridized to embryonic rna species induced after gastrulation and ... | 1986 | 3711782 |
| an examination of the evidence for the existence of preformed pathways in the neural tube of xenopus laevis. | we have examined the neural tube in xenopus laevis tadpoles to investigate the anatomical guidance elements which may be present in the presumptive marginal zone. with appropriate fixation protocols the neuroepithelial cells appeared in contact; electron microscopic observations failed to show any specialized intercellular spaces preceding the growing axons. the first fibres were found in the intercellular clefts between the neuroepithelial cells near the surface of the neural tube. reconstructi ... | 1986 | 3711784 |
| comparison of the effects of vitamin a on limb development and regeneration in xenopus laevis tadpoles. | the purpose of these experiments was to compare the effects of vitamin a on developing and regenerating limbs in xenopus laevis tadpoles. each tadpole had one hindlimb amputated to induce regeneration while the contralateral developing limb was left intact. tadpoles at stages 50 through 54 were treated by immersion in retinol palmitate at doses ranging from 0.3 to 75 i.u. ml-1, for periods ranging from 1 to 14 days. developing limbs usually became hypomorphic as a result of the treatment, with r ... | 1986 | 3711790 |
| the effects of local application of retinoic acid on limb development and regeneration in tadpoles of xenopus laevis. | vitamin a can have different effects on developing and regenerating limbs depending on the mode of administration. previous work has demonstrated the differential effect of retinol palmitate on limb development and regeneration in xenopus laevis. the purpose of the present investigation was to determine the effects of vitamin a on limb development and regeneration in xenopus when administered by a local implantation method. xenopus tadpoles had both hindlimbs implanted with either a block of sil ... | 1986 | 3711791 |
| further studies on the melanophores of periodic albino mutant of xenopus laevis. | it is still unknown why dermal melanophores disappear during larval development, and why no or very few epidermal melanophores appear during and after metamorphosis, in xenopus laevis showing periodic albinism (ap). to elucidate these points, we investigated the occurrence of depigmentation in mutant (ap/ap) melanophores during in vitro proliferation and the incidence of melanophore differentiation from mutant melanoblasts in the skin in vitro. during in vitro proliferation of mutant melanophore ... | 1986 | 3711792 |
| pattern formation in 8-cell composite embryos of xenopus laevis. | we have shown in defect experiments that an 8-cell embryo of xenopus laevis consists of three kinds of cells, that is, animal, vegetal dorsal and vegetal ventral cells, and that cells of different kinds are distinctly different in their developmental capacity. complete pattern formation occurs in any defect embryo which contains at least two animal, one vegetal dorsal and one vegetal ventral cell. in the present transplantation experiments, we replaced one or two cells of one 8-cell embryo by th ... | 1986 | 3711793 |
| behavioral development in the absence of neural activity: effects of chronic immobilization on amphibian embryos. | embryos of xenopus laevis and ambystoma mexicanum were continually immobilized from premotile stages of development to stages at which normally reared embryos were swimming well. immobilization was achieved through exposure to solutions of chloretone, lidocaine, or alpha-bungarotoxin. at a number of stages after recovery from the drugs, spontaneous and stimulated behaviors were extensively quantified. immobilization of ambystoma embryos resulted in temporary defects in musculoskeletal developmen ... | 1986 | 3711983 |
| anatomical and physiological development of the xenopus embryonic motor system in the absence of neural activity. | embryos of xenopus laevis were continually immobilized by immersion in solutions of either chloretone or lidocaine, from the late neural-fold stage to the approximate time of hatching. such treatment has been shown to result in only transient quantitative effects on swimming behavior. chronic immobilization was without either immediate or long-term effect on the ventral root output exhibited during "fictive" swimming episodes. development under these conditions of diminished or absent neural act ... | 1986 | 3711984 |
| the role of glycosaminoglycans in anuran pigment cell migration. | the migratory pathways of neural crest-derived pigment cells were examined in two anurans, xenopus laevis and discoglossus pictus, and correlated with the distribution of glycosaminoglycans (gag) in the extracellular matrix (ecm) of these pathways. in xenopus, melanophores in the trunk reach the dermis by initially migrating ventrally, between the neural tube and somites, and then by migrating through the somites to reach the subectodermal space. in discoglossus, melanophores, iridophores, and x ... | 1986 | 3723060 |
| ocular migration and the metamorphic and postmetamorphic maturation of the retinotectal system in xenopus laevis: an autoradiographic and morphometric study. | the growth of the retina and tectum during larval life in xenopus has previously been studied extensively. these two structures continue to grow in metamorphosing and postmetamorphic animals. during these later stages there are marked changes in eye position. we have used histogenetic and morphometric techniques to monitor retinal and tectal growth in xenopus aged from stage 58 of larval life to ten years postmetamorphosis. the relative eye migration was quantified with optical techniques. an at ... | 1986 | 3723067 |
| diagnostic exercise: death of african clawed frogs. | | 1986 | 3724055 |
| metabolism of cerebrosides and sulfatides in the nervous system of xenopus tadpole during metamorphosis. | xenopus laevis tadpoles undergoing metamorphosis were used to study the turnover of cerebrosides and sulfatides in the nervous system of the frog. tadpoles at the beginning of metamorphosis were treated by intraperitoneal injection with [u-14c]glucose and radioactivity incorporated into galactosphingolipids of brain and tail was measured after various times. the specific activity of brain cerebrosides increased rapidly for the first 24 hr after injection, reached a plateau after 48 hr, and then ... | 1986 | 3724962 |
| peptide c-terminal alpha-amidating enzyme purified to homogeneity from xenopus laevis skin. | the c-terminal alpha-amide formation of the peptides is one of the most important events of prohormone processing. in this study, we have developed a simple and sensitive assay for monitoring alpha-amidating activity by using radioiodinated ac-tyr-phe-gly as a substrate. by utilizing this assay, an alpha-amidating enzyme was first purified to homogeneity from xenopus laevis skin. the purified enzyme has a single polypeptide chain with an apparent molecular weight of 39,000 and its n-terminal seq ... | 1986 | 3729962 |
| preservation of xenopus laevis rdna-containing plasmid, pxlr101a, injected into the fertilized egg of xenopus laevis. | a circular rdna-containing recombinant plasmid, pxlr101a, and its vector pbr322 were microinjected into the cytoplasm of fertilized xenopus laevis eggs. the dnas extracted from injected embryos at various stages of development were analyzed by hybridization with 32p-labeled pbr322 as the probe. neither pxlr101a nor pbr322 were replicated, but they were maintained until the tailbud stage, disappearing during the muscular response stage. when pxlr101a-injected embryos were raised until the 2-week- ... | 1986 | 3731283 |
| myoblasts and notochord influence the orientation of somitic myoblasts from xenopus laevis. | the orientation of developing myoblasts extending a bipolar axis in the presence of explanted myoblasts or whole notochord has been studied in vitro. myoblasts tended to elongate perpendicular to the lines of diffusion of substances from these tissues. a slow-release source of agar impregnated with medium conditioned by segmented somitic myoblast or notochord also caused myoblasts to elongate perpendicular to the lines of diffusion from the source. medium conditioned by neural tube cells or unse ... | 1986 | 3734680 |
| effects of antiestrogens on the induction of vitellogenin and its mrna in xenopus laevis. | the egg yolk protein precursor vitellogenin is induced by estrogen in the liver of male xenopus laevis. the large rise in serum vitellogenin is accompanied by a corresponding increase in intracellular levels of vitellogenin and its mrna. in the present study this model system was used to examine the subcellular sites of action of triphenylethylene antiestrogens (e.g. tamoxifen). tamoxifen was extensively metabolized to 4-hydroxytamoxifen in xenopus and both of these antiestrogens were used in th ... | 1986 | 3736040 |
| morphology of endoplasmic reticulum and golgi elements following microinjection of rat liver microsomes into xenopus laevis oocyte cytoplasm. | fragments of rough endoplasmic reticulum and golgi complex purified from rat liver homogenates were injected into xenopus oocytes and the sites of microinjection analysed by electron microscopy at different times post-injection. the in vivo incubated fragments were located by their proximity to a microinjection vacuole, and identified by their association with specific morphological markers (peroxisomal cores associated with rough microsomes and lipoprotein particles with golgi derivatives). typ ... | 1986 | 3743670 |
| cytophotometric evidence of variation in genome size of desmognathine salamanders. | the amount of dna per haploid genome, the c-value, is often directly correlated with nuclear and cell volume, but inversely correlated with cell replication rate. also, rates of cellular growth sometimes appear to be correlated with organismal developmental rates and life history patterns. among vertebrates, salamanders exhibit the greatest variation in genome size. in the present study we have examined interspecific and intraspecific variation in blood cell dna levels in the genus desmognathus, ... | 1986 | 3744902 |
| descending projections and excitation during fictive swimming in xenopus embryos: neuroanatomy and lesion experiments. | we describe the distribution of "descending" interneurons in late xenopus laevis embryos after retrograde filling with horseradish peroxidaze via their ipsilateral, descending axons in the spinal cord. these multipolar neurons, with dendrites spread throughout the marginal zone, form a longitudinal column extending from midtrunk spinal cord into the brainstem to the level of the vagus. in the hindbrain these neurons are part of the uncrossed reticulospinal projection. they are most numerous in t ... | 1986 | 3745515 |
| optic fibers follow aberrant pathways from rotated eyes in xenopus laevis. | the rotated eye paradigm has been a major experimental test of the neuronal specificity model for the development of ordered retinotectal connections in amphibians. in most studies, however, no optic fiber pathways were traced from rotated eyes and correlated with visuotectal projections. as an initial approach to this question, optic fibers from eyes rotated at different embryonic stages were traced with 3h-proline autoradiography. three experimental series were prepared: in situ eye rotations, ... | 1986 | 3745520 |
| nuclear factor iii, a novel sequence-specific dna-binding protein from hela cells stimulating adenovirus dna replication. | dissection and reconstitution of the adenovirus dna replication machinery has led to the discovery of two hela nuclear proteins which are required in conjunction with three viral proteins. one of these, nuclear factor i (nf-i), recognizes an internal region of the origin between nucleotides 25 and 40 and by binding to one side of the helix stimulates the initiation reaction up to 30-fold. nfi-binding sites have been observed upstream of several cellular genes, such as chicken lysozyme, human igm ... | 1986 | 3748145 |