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the sensitivity of xenopus laevis tadpole tail tissue to the action of thyroid hormones. 1977892410
biosynthesis, processing, and control of release of melanotropic peptides in the neurointermediate lobe of xenopus laevis.the neurointermediate lobes of dark-adapted toads xenopus laevis were incubated for 30 min in [3h]arginine and then "chased" for various time periods. by use of this pulse-chase paradigm there were detected 10 trichloroacetic acid (tca)-precipitable peptides separated on acid-urea polyacrylamide gels and one tca-soluble peptide separated by high-voltage electrophoresis (ph 4.9) with melanotropic activity. each of these peptides had a different degree of melanocyte stimulating hormone (msh) activ ...1977894250
in vivo repair of the 3'terminus of transfer rna injected into amphibian oocytes.yeast transfer rna specific for phenylalanine has been treated chemically to remove either one or two nucleotides of its 3' terminus and has been injected into xenopus laevis oocytes to test whether this rna can be repaired in vivo. the results obtained showed that oocytes could aminoacylate and thus repair trnaphe that has lost both its terminal adenosine and 3' phosphate. a similar result was obtained with trnaphe that had undergone two full cycles of 3' terminal nucleotide removal. the oocyte ...1977896475
regeneration of the tail of x-irradiated xenopus tadpoles.the effects of x-rays on the regeneration of the tail of xenopus laevis tadpoles have been studied. larvae of stage 52 were exposed in groups to irradiation either of the head or the body region with doses of 3,000 and 4,000 r. in both cases, the animals have regenerated the lost parts of their tails.1977899691
development of the myotomal neuromuscular junction in xenopus laevis: an electrophysiological and fine-structural study. 1977902924
slow mechanism for sodium permeability inactivation in myelinated nerve fibre of xenopus laevis.1. single myelinated nerve fibres were isolated and the nodal currents were recorded under potential clamp conditions. the effect of membrane potential on the na permeability (pna) mechanism was analysed. 2. the available pna increased slowly during negative polarization of the membrane. the time course of this change was about 10(3) times slower than the time course of the mechanism for the usual pna inactivation (h-system). the slow pna changes could be distinguished from changes in h because ...1977903895
treatment of skin-invading capillarid nematode in a colony of south african clawed frogs (xenopus laevis). 1977904298
the effect of tolbutamide on early embryos of xenopus laevis. 1977908419
purification of a dna-binding protein from xenopus laevis unfertilized eggs.a dna-binding protein from xenopus laevis unfertilized eggs has been purified to apparent homogeneity. it is a heat stable, lysine-rich protein and has a molecular weight corresponding to 8,200 daltons, measured by sodium dodecyl sulphate gel electrophoresis. the protein, which is active in a monomeric form, stimulates dna polymerase alpha, and binds to single and double stranded dna. one egg contains about 4 x 10(12) molecules (minimum estimate) of the protein; since we calculate that 4 x 10(8) ...1977909794
lipid and polypeptide components of the crystalline yolk system from xenopus laevis.the polypeptide and lipid components of the crystallinelipoprotein-phosphoprotein from the yolk system of xenopus laevis are described. this lipoprotein complex contains 17% lipid of which 75% is phospholipid. the phospholipid fraction consists of mostly phosphatidylcholine and phosphatidylethanolamine. the neutral lipid fraction contains mainly triglyceride. the phosphoprotein, phosvitin, has been separated from the lipoprotein, lipovitellin, by classical methods. three polypeptide chains can b ...1977914850
nuclear transplantation from intestinal epithelial cells of early and late xenopus laevis tadpoles.the aim of these experiments was to test whether the developmental potential of nuclei from intestinal epithelial cells of xenopus laevis tadpoles declined during the life of the functional larval gut. the results of transplantation of nuclei from three different stages of development were compared: stages 46-48, when feeding begins and while yolk is still present but before the formation of the typhlosole; stage 57, just prior to the onset of metamorphic reorganization; and stage 54, an interme ...1977915421
retinal growth in double dorsal and double ventral eyes in xenopus.the growth of normal and surgically produced compound dorsal and ventral retinae in xenopus laevis has been studied autoradiographically following injections of [3h] thymidine at stages 50 and 58. the animals were sacrificed 3 weeks after metamorphosis. the histogenetic pattern of the dorsal and ventral retinal halves was different at the three time points investigated, i.e. up to stage 50, between stages 50 and 58 and between stage 58 and 3 weeks after metamorphosis. asymmetrical dorsal retinal ...1977915422
toxicity of n-phenyl-alpha-naphthylamine and hydrazine to xenopus laevis embryos and larvae. 1977922193
isolation of globin messenger rna of xenopus laevis. 1977924017
kinetics of estrogen induction of xenopus laevis vitellogenin messenger rna as measured by hybridization to complementary dna. 1977925003
a method for collecting naturally fertilized eggs of xenopus laevis immediately after laying. 1977926758
developmental changes in activity of choline acetyltransferase, acetyl-cholinesterase and glutamic acid decarboxylase in the central nervous system of the toad. xenopus laevis. 1976932736
new membrane formation and intercellular communication in the early xenopus embryo.the ionic permeability of the nonjunctional and newly formed junctional membranes was investigated in embryos of xenopus laevis up to the onset of the fifth cleavage. continuous measurements were made of the equivalent nonjunctional (r'o) and junctional resistances (r'i) in different pairs of adjacent cells separated by one of the four cleavage membranes formed in that period. the specific resistance of the nonjunctional membranes (ro) and of each cleavage membrane (ri) as a function of time wer ...1976933155
adult haemoglobin in developmentally retarded tadpoles of xenopus laevis.tadpoles of xenopus laevis reared in water containing 0-01% propylthiouracil continue to grow but fail to develop or metamorphose. the haemoglobin of such tadpoles has been extracted in buffer, converted to a cyanmet form, and run on polyacrylamide gels. the developmentally retarded tadpoles are found to possess adult-type haemoglobin rather than the tadpole type which normally characterizes their developmental stage.1976939939
nucleolar activity and rna metabolism in previtellogenic and vitellogenic oocytes of xenopus laevis. a biochemical and autoradiographical, light and em study. 1976943292
morphological changes of the surface of the egg of xenopus laevis in the course of development. iii. scanning electron microscopy of gastrulation. 1976943347
the effect of injected cytochalasin b on filament organization in the cleaving egg of xenopus laevis. 1976943569
an autoradiographic study of tritiated uridine incorporation into the larval ovary of xenopus laevis.the in vitro incorporation of 3h-5-uridine into the germinal and somatic cells of the larval ovary of xenopus laevis has been studied using both light and electron microscope autoradiography. incubation for only one hour in the presence of precursor revealed that the follicle cells are highly active in rrna synthesis, whereas substantial oogonial nucleolar labeling was not detected for several hours. semi-quantitative analysis of high-resolution autoradiograms indicated that the density of silve ...1976943967
ribosomes from xenopus laevis eggs and embryos in a cell-free protein-synthesizing system: translational regulation.three types of ribosomal preparations from xenopus laevis eggs and embryos were tested in a cell-free system to study possible translational regulation of protein synthesis as mediated by the ribosome during early amphibian development: type 1, a crude high-speed sediment, mainly containing monoribosomes completely dissociable by 0.5 m kc1; type ii, ribosomes washed with 0.5 m kc1; and type iii, ribosomes treated with puromycin - 0.5 m kc1. all three types showed an active response to the additi ...1976944101
comparison of exogenous energy sources for in vitro maintenance of follicle cell-free xenopus laevis oocytes.the purpose of these experiments was to determine which exogenous energy sources are suitable for isolated follicle cell-free oocytes from the frog, xenopus laevis. in order to compare prospective energy sources, follicle cell-free oocytes from 0.4 to 1.3 mm in diameter were incubated in a 1 mm concentration of each of a variety of energy sources and scored daily for the maintenance of morphological characteristics. vitellogenic oocytes placed in succinate or fumarate deteriorated at the same ti ...1976944165
the germinal vesicle nucleus of xenopus laevis oocytes as a selective storage receptacle for proteins.the amorphous nucleoplasm of the germinal vesicle nucleus of xenopus laevis oocytes has been selectively extracted under conditions which leave the nuclear formed elements morphologically intact. the nucleoplasm contains about 97% of the total nuclear proteins and on sds-polyacrylamide gels some 68 polypeptides can be distinguished. on the basis of solubility differences, the nucleoplasmic proteins can be classified into two categories. the first consists of soluble or easily solubilized protein ...1976944701
the effect of thymectomy at different stages of larval development on the immune response of the clawed toad to sheep erythrocytes.the role of the thymus during the first three weeks of larval life in the maturation of humoral immunity in the amphibian, xenopus laevis, is examined. thymectomy throughout this period dramatically affects the heterologous red cell response of young adults. sheep erythrocyte (srbc) administration elicited haemolytic antibody production in the blood and in the spleen (measured by the appearance of plaque forming cells) of control animals, but failed to do so in all thymectomized toadlets. moreov ...1976944762
cell-free translation of messenger rna from oocytes of xenopus laevis. 1976945202
control of 5s rna synthesis in xenopus laevis. 1976945465
nuclear swelling and chromatin decondensation can occur without cortical granule explosion in eggs of xenopus laevis. 1976945774
subunit homologies of lactate dehydrogenase (ldh) isoenzymes between amphibians (xenopus laevis) and mammals (wistar rat). 1976947661
dna-dependent rna polymerase c from xenopus laevis ovaries. ability to transcribe intact double-stranded dna.dna-dependent rna polymerase c, partially purified from xenopus laevis ovaries, has been resolved by deae-sephadex chromatography in two forms, eluting at 0.2 m and 0.3 m ammonium sulfate, respectively. both are sensitive to high concentrations of alpha-amanitin (200 mug/ml). their ionic strength dependence and divalent cation requirements are indistinguishable. quantitatively, rna polymerase c represents the major form of rna polymerase activity solubilized from the ovaries. both rna polymerase ...1976947751
melanoblast-tissue interactions and the development of pigment pattern in xenopus larvae.the melanophores of larval xenopus laevis are disparately distributed on the hypomere in that the upper region (uht) is densely pigmented, the median region (mht) is moderately pigmented, and the lower region (lht) is unpigmented. the roles of the melanoblasts and their tissue environment in determining the melanophore pattern was investigated by heterotopic transplantation of hypomeric tissues, culture of neural crest explants in vesicles derived from hypomeric tissues and radioactive marking o ...1976947992
stage-sensitivity and dose-response curve of u.v. effect on germ cell formation in embryos of xenopus laevis.ultraviolet light (u.v.) irradiation of the vegetal hemisphere of xenopus laevis eggs resulted in the elimination of primordial germ cells in tadpoles. quantitative studies were performed on this phenomenon. the stage sensitivity to u.v. inactivation of germ cell formation was obtained for the early developmental stages ranging from immediately after fertilization to small-cell blastula. it was found that u.v. irradiation at the stage immediately after fertilization was more injurious than irrad ...1976947996
measurement of potassium and chloride ion concentrations in the cupulae of the lateral lines of xenopus laevis.1. potential measurements were made with double barrel ion selective electrodes from the cupulae of lateral line organs in the aquatic toad xenopus laevis. 2. a positive endocupular potential (ecp) of 15-50 mv was recorded within the cupula, immediately above the hair cells. 3. increases in the cl- and k+ potentials were recorded when the ion selective electrodes touched the cupula. cupular cl- and k+ varied between 35 and 70 mm and 24 and 100 mm respectively. this variation existed between, rat ...1976948058
processes for sodium permeability inactivation in the myelinated nerve fibre of the frog (xenopus laevis). 1976949010
direct induction by estradiol on vitellogenin synthesis in organ cultures of male xenopus laevis liver.organ cultures of liver from untreated male xenopus respond to 17 beta-estradiol in the culture medium by synthesizing and secreting the yolk protein precursor vitellogenin. vitellogenin synthesis, as a primary response, is first detectable on the fourth day of culture, and comprises up to 12% of the protein synthesized on the eighth day. estradiol is required during the lag period of 4 days. tissue from male xenopus injected with 1 mg of estradiol 30 days before the start of culture responds mo ...1976949740
vital dye mapping of the gastrula and neurula of xenopus laevis. ii. prospective areas and morphogenetic movements of the deep layer. 1976950072
freeze-fracture electron microscopy of preexisting and nascent cell membrane in cleaving eggs of xenopus laevis.during cell division in the xenopus egg (diameter 1.25 mm) new cell membrane is formed in the furrow region (rate of growth approx 4-10(4) mum2/min). freeze-fracture electron microscopy has produced the following data. preexisting plasma membrane faces show a reversed polarity with respect to particle distribution, i.e. more particles are attached to the e-face (density 1600-2200 particles/mum2) than to the p-face (300 particles/mum2). a frequency histogram of 2331 measured intramembranous parti ...1976953012
neurite outgrowth from explanted xenopus retina: an effect of prior optic nerve section.experimental conditions are described for the in vitro study of explanted eyes from embryos of xenopus laevis and of retinas from older larvae. when eyes are explanted from embryos of stages 25-34, a rapid outgrowth of fibroblast-like and pigment cells is observed, upon which a neuritic outgrowth is eventually superimposed. outgrowth from the retina of later stage tadpoles (50-54) is not seen until about a week following explantation and resembles the mixed cell outgrowth observed in whole eye e ...1976953737
application of a multiwire proportional chamber to the detection of axoplasmic transport.a new technique for the detection of the axoplasmic transport of beta-radioactively labelled materials is described wherein a multiwire proportional chamber is used to measure the distribution of activity along peripheral nerve fibers which are maintained in vitro. the operating principles of the chamber are described and basic construction parameters given. potential radiolabels are discussed. two types of studies were performed at room temperature in vitro using sciatic nerves of the amphibian ...1976953854
low molecular weight viral rnas transcribed by rna polymerase iii during adenovirus 2 infection.nuclei isolated from human cells productively infected with adenovirus 2 have been shown to synthesize four low molecular weight rna species which hybridize efficiently to viral dna. one species corresponds to the 5.5s or va rna (ohe, weissman, and cooke, 1969), and is designated v156. the other three species are novel and have been designated v200, v140, v130, since they are approximately 200, 140, and 130 nucleotides in length, respectively. these viral rnas retain their distinct electrophoret ...1976954087
a reinvestigation of 5' leads to 3' polarity in 40s ribosomal rna precursor of xenopus laevis.the 5' leads to 3' polarity of the 40s precursor rrna molecule relative to the location of the 18s and 28s rna regions in the precursor has been reinvestigated. fragments of rdna derived by the restriction endonuclease ecori and cloned in e. coli were partially digested with the exonuclease induced by bacteriophage lambda and with exonuclease iii from e. coli. the resulting rdna fragments with single-stranded tails were hybridized separately with 18s and 28s rrna, and the formation of the hybri ...1976954098
the size of the guanosine triphosphate pool active in the synthesis of stable rna by stage 6 oocytes of xenopus laevis. 1976954858
hormone effects on male sex behavior in adult south african clawed frogs, xenopus laevis. 1976955579
direct adaptation of cells to temperature: similar changes of ldh isozyme patterns by in vitro and in situ adaptations in xenopus laevis. 1976963983
induction of meiosis by injection of heterologous protein kinase and phosphorylase kinase in xenopus laevis oocytes.meiosis reinitiation has been triggered by injection of beef heart protein kinase or rabbit phosphorylase kinase into xenopus laevis oocytes. successful injections are followed by germinal vesicle breakdown, chromosome condensation, formation of a normal meiotic spindle, and appearance of an amplifiable maturation promoting factor. meiosis reinitiation does not occur when the enzymes are introduced into the oocytes simultaneously with egta or after pretreatment with cycloheximide. antipain, an a ...1976965920
electrophoretic introduction of calcium ions into the cortex of xenopus laevis oocytes triggers meiosis neinitiation.meiosis reinitiation has been triggered via electrophoretic driving of ca++ into the cortex of xenopus laevis oocytes freed from functional follicle cells by collagenase treatment. mg++ could not be substituted for ca++. ca++ induced maturation resembles progesterone induced maturation in so far both are inhibited by cycloheximide, give rise to amplifiable mpf in the cytoplasm of treated oocytes and allow chromosome condensation and the formation of a normal meiotic spindle.1976965921
the deleterious effects of fungicides and herbicides on xenopus laevis embryos.groups of 30 xenopus laevis embryos, at "tail-bud" stage (nieukoop-faber stages 22-24) were exposed to 0.1-2 ppm concentrations of various pesticides for 1 to 10 days. the pesticides used were chloranil and dichlone (both are fungicidal and herbicidal); diquat (herbicide); and nabam (fungicide). the parameters examined were mortality, gross morphology, histology, and behavior. chloranil (1.25 to 1.75 ppm) treated embryos showed abnormalities of the otolith, optic cup, and general pigmentation. t ...1976970983
arrangement of length heterogeneity in repeating units of amplified and chromosomal ribosomal dna from xenopus laevis. 1976972392
ribosomal genes of xenopus laevis: evidence of nucleosomes in transcriptionally active chromatin.most of the reiterated ribosomal genes in the somatic cells of larvae of a mutant of xenopus laevis appear to be protected from short-term nuclease digestion by being packaged in the form of chromatin subunits or nucleosomes. since these mutant animals probably require all of their ribosomal genes to be active in order to maintain viability, at least some of the transcriptionally active gene sequences are probably associated with chromatin subunits. thus, association of dna with nucleosomes may ...1976973136
the arrangement of 18-s and 28-s ribosomal ribonucleic acids within the 40-s precursor molecule of xenopus laevis.the arrangement of 18-s rrna and 28-s rrna within their 40-s common precursor molecule (pre-rrna) of xenopus laevis was investigated by electron microscopic analysis of secondary structure of nascent pre-rrna chains of oocytes, and by 5'-end analysis of 18-s rrna and 28-s rrna hybridized to the ecori fragment of rdna cloned as plasmid pcd42. secondary structure mapping of phenol-extracted rna from nucleolar cores revealed complete pre-rrna chains or molecules at various stages of processing and ...1976976269
observations on the migration and proliferation of gonocytes in xenopus laevis.the process of primordial germ cell formation in the normal course of development of xenopus laevis was examined with a light microscope on paraffin and epon sections of embryos or tadpoles, extending over the period from the gastrula to the feeding tadpole stage. positional changes of gonocytes with development were nearly the same as those reported on the same species by blackler (1958) and whitington & dixon (1975). the following points were newly demonstrated. gonocytes which have been locat ...1976978127
[transfer of behavior patterns through transplantation of anlagen of neuro-anatomic structures in amphibian larva. 1. xenoplastic exchange of medulla anlagen between xenopus laevis and hymenochirus boettgeri (amphibia, anura)].by transplantation of parts of the neural plate (latter medulla oblongata) from xenopus laevis (daud.) to hymenochirus boettgeri (torn.) larval chimaeras were obtained, which showed donorlike rhythmical movements of the mouth and pharyngeal region, movements which the host species lacks. nevertheless, some of these tadpoles were still able to catch small prey in a reaction which is typical for the host and lacking in the donor.1976983425
nuclear localization of dna polymerase alpha in xenopus laevis oocytes. 1976985524
isolation, physicochemical properties, and the macromolecular composition of the vitelline and fertilization envelopes from xenopus laevis eggs.as a step toward defining in molecular terms the sperm-triggered block to polyspermy reaction established by the egg at fertilization, vitelline (ve) and fertilization (fe) envelopes were isolated from eggs of the sounth african clawed toad xenopus laevis and some of their physicochemical properties determined. envelopes were isolated after lysis of the fertilized or unfertilized eggs by sieving techniques; isolated envelopes retained their in situ morphology as determined by electron microscopy ...1976986165
repeating units of xenopus laevis oocyte-type 5s dna are heterogeneous in length.the restriction enzymes hind iii and hae iii cleave xenopus laevis 5s dna at one and three sites, respectively, in each repeating unit of approximately 700 base pairs. the cleavage sites for both enzymes have been located within the repeating unit by denaturation mapping of the restriction fragments. the hind iii products and one of the hae iii fragments are variable in length, indicating heterogeneity in the length of the repeating unit in 5s dna. this length heterogeneity is confined to the ma ...1976986247
a study of foldback dna.nuclear dna from eucaryotes contains a significant fraction which forms duplexes very rapidly and also independently of the dna concentration. this fraction can be isolated by adsorption to hydroxylapatite and has been called foldback dna (britten and smith, 1970). here we extend previous studies to show that the foldback fraction is due to the existence of a finite number of foldback foci in each genome equivalent of dna, approximately 10(5) in the case of xenopus laevis. more significantly, we ...1976986250
the 5' leads to 3' polarity of the xenopus ribosomal rna precursor molecule.evidence is presented that in xenopus laevis the 18s rrna sequence is proximal to the 5' end of the rrna precursor molecule and the 28s secquence is proximal to the 3' end. this assignment was made by digesting amplified ribosomal gene transcription complexes with ecori restriction endonuclease and spreading the cleaved transcription complexes for electron microscopy. from the known location of the ecori cutting sites within the transcribed region and the length of nascent chains on the cleaved ...1976986254
sequences of 5s ribosomal rna from xenopus mulleri and the evolution of 5s gene-coding sequences.sequences for 5s rna from somatic cells and oocytes of xenopus mulleri are presented. comparison with sequences previously given for xenopus laevis indicates that the somatic 5s rna genes of each species are more closely related to each other than either is to its own set of oocyte genes, suggesting that somatic and oocyte genes within each species are evolving independently. however, detailed analysis of sequence variants in each species suggests that there is a mechanism which allows occasiona ...1976986255
defined nutrient medium for the in vitro maintenance of xenopus laevis oocytes.a procedure is described for the isolation and culture of large numbers of follicle cell-free xenopus laevis oocytes in all stages of development. the isolation procedure involves the incubation of pieces of ovary in a calcium-free solution or2 containing 0.2% collagenase. a defined nutrient medium for the maintenace of the oocytes in vitro is presented. it is shown that this medium, referred to as dnom, can maintain certain morpological and functional characteristics of oocytes for periods up t ...1976986365
initiation of meiotic maturation in xenopus laevis oocytes by lanthanum. 1976986558
the synthesis of freezing-point-depressing protein of the winter flounder pseudopleuronectus americanus in xenopus laevis oocytes. 1976986821
isolation and some properties of dna coding for trna1met from xenopus laevis.dna containing the reiterated genes for trna1met has been partially purified from xenopus laevis by centrifugation in actinomycin c1-cscl and ag+-cs2so4 gradients. these gradients separate the trna1met genes from those coding for trna2met and trnaval, thus confirming our earlier suggestion that these genes are not intermingled with each other (clarkson, birnstiel, and purdom, 1973a). the gradients also demonstrate the existence of a minor 5s dna fraction which appears to differ from that previou ...1976986875
on the existence of polyadenylated histone mrna in xenopus laevis oocytes.in a variety of systems, histone mrna has been shown to lack poly(a) (adesnik and darnell, 1972; grunstein et al., 1973). we have found, however, that in xenopus laevis oocytes, poly (a)-containing mrna codes for histones, in a wheat germ cell-free system, based on the following criteria: first, co-migration with authentic x. laevis oocyte histones on polyacrylamide gels; second, no detectable incorporation of tryptophan; third, differential incorporation of lysine and methionine into histone fr ...1976987857
morphological changes of the surface of the eggs of xenopus laevis in the course of development. 2. cytokinesis and early cleavage. 1976988190
effects of light and dark upon photoreceptor synapses in the retina of xenopus laevis.photoreceptor synapses in xenopus retina were studied after exposure to day/night cycles and continuous light or dark. in the rods, dense-core vesicles appear alongside the synaptic ribbons in animals exposed to light. in dark-adapted rods, electron-dense material is present in the synaptic clefts, but no dense-core vesicles are found associated with the synaptic ribbons. cone photoreceptors do not show these ultrastructural changes in response to light and dark. prolonged exposure to light (21 ...1976991238
reiteration frequency of the histone genes in the genome of the amphibian, xenopus laevis.radioactive rna was obtained from xenopus laevis gastrula-stage embryos which had been labelled by microinjection of [3h]uridine. a 9-12-s rna fraction was isolated by phenol extraction of whole embryos followed by sucrose gradient centrifugation of the rna and polyacrylamide gel electrophoresis. this rna was identified as histone mrna on the basis of its chemical and physical properties. on polyacrylamide gels the labelled rna could be subfractionated into different components with electrophore ...1976991862
studies on the deiodination of thyroid hormones in xenopus laevis tadpoles. 1976992332
the relationship of ribosomal rna synthesis to the formation of segregated nucleoli and nucleolus-like bodies.the relationship of ribosomal rna (rrna) synthesis to nucleolar ultrastructure was studied in partial nucleolar mutants of xenopus laevis. these mutations are the result of a partial deletion of rrna genes and therefore alow studies on nucleolar structure and function without using drugs that inhibit rrna synthesis. ultrastructural studies demonstrated that normal embryos have reticulated nucleoli that are composed of a loose meshwork of granules and fibrils and a typical nucleolonema. in contra ...1976993274
photoreceptor thresholds and visual pigment levels in normal and vitamin a-deprived xenopus tadpoles.1. measurements of the aspartate-isolated piii component of the electroretinogram (erg) were used to estimate photoreceptor threshold in dark-adapted tadpoles of the clawed toad, xenopus laevis raised on a normal diet. spectral sensitivity functions established that the rod mechanism governed absolute dark thresholds from stage 40 to the end of premetamorphic development. 2. parallel measures of rod outer-segment dimensions and visual pigment levels demonstrated a) that visual pigment concentrat ...1976993831
effective stimulus for the xenopus laevis lateral-line hair-cell system.an in vitro preparation of the lateral-line organ of the african clawed toad xenopus laevis was used to evaluate the properties of the physiological stimuli which are most effective in evoking neural responses in this simple hair-cell system. changes in the mean firing rate and the amount of modulation of the neural activity in the fibers innervating the hair cells were determined during the presentation of well-controlled pressure or water-movement stimuli in a specially designed chamber that p ...1976994676
physiological basis of cochlear transduction and sensitivity.experiments were conducted in the guinea pig cochlea and the xenopus laevis lateral line organ to obtain information about the electrical impedance properties of the cochlea, the sources and characteristics of the cochlear potentials, and to determine if hair cells are electrically excitable. the significance of the resting and evoked cochlear potentials in the transduction process leading to excitation of the acoustic nerve fibers was evaluated by comparing the results of electrophysiological e ...1976999136
dna-dependent rna polymerase c from xenopus laevis ovaries: formation of stable heparin-resistant dna-binding complexes. 19761001472
protein labelling patterns in oocytes of xenopus laevis.soluble and microsomal proteins synthesized at various stages of oogenesis in xenopus laevis were compared by 3h and 14c dual-isotope labelling with subsequent mixing and analysis on sodium dodecyl sulfate (sds)-polyacrylamide gels. the results indicated that the proteins labelled in all the stages of oogenesis studied are remarkably similar. however, the patterns in the small and medium-sized oocytes are more similar to one another than to the patterns characteristic of large oocytes. the great ...19761010160
on the diversity of sperm histones in the vertebrates. i. changes in basic proteins during spermiogenesis in the newt notophthalmus viridescens.sperm histones display great variability in contrast to the conservation of most classes of somatic histones. to study this paradox, this series of papers examines the variation of histone patterns in the testis and sperm of vertebrates, particularly amphibians and reptiles, and attempts to relate such variation to genetically based sex determination as hypothesized by bloch [genetics supplement 61, 93 (1969)]. in the present study we have investigated spermiogenesis in the newt notophthalmus vi ...19761010162
the response of the brachial ventral horn or xenopus laevis to forelimb amputation during development.the normal development of the brachial ventral horn of the frog xenopus laevis and the response of the brachial ventral horn to complete forelimb extirpation at five developmental stages were assessed histologically. differentiation of brachial ventral horn neurons occurred in pre-metamorphic tadpoles between stages 52/53 and 57. mean cell number in the brachial ventral horn reached a peak of 2576 (s.e.m. equals +/- 269, n equals 2) per side of the spinal cord at stage 55 and decreased to 1070 ( ...19761010975
scanning electron microscopy of lithium-induced exogastrulae of xenopus laevis.lithium-induced exogastrulae are abnormal embryos which fail to complete gastrulation and do not form normal neural structures. scanning electron microscopy has been used to compare the surface structure of the ectoderm cells of exogastrulae with that of the ectoderm cells of normal embryos and has shown that the appearance of ciliated cells is delayed in exogastrulae. in addition, the structure of endoderm cells, which remain exposed in these embryos, has been studied.19761010976
injected nuclei in frog oocytes: fate, enlargement, and chromatin dispersal.a method is described by which nuclei associated with some cytoplasm can be rapidly prepared from a suspension of cells. the method involves the use of lysolecithin and bovine serum albumin. oocytes of xenopus laevis were injected with about 200 nuclei perpared from human hela cells by this method. nuclei were deposited in oocyte cytoplasm, in the oocyte nucleus, or in the dispersed contents of a ruptured oocyte nucleus. injected hela nuclei enlarge up to several hundred times in volume in the c ...19761010977
ultrastructural analysis of some functional aspects of xenopus laevis pancreas during development and metamorphosis.morphological studies using both light and electron microscope were carried out with the aim of characterizing cells present in the larval and adult pancreas of xenopus laevis. the following cell types have been seen: (1) exocrine cells, with a very well developed r.e.r. (rough endoplasmic reticulum), well defined golgi complexes and numerous large secretory granules (a cells); (2) cells without either r.e.r. or secretory granules but with a large number of well developed mitochondria (b cells); ...19761010987
[histological studies on allografts and xenografts of lymphoid tissue in newts (triturus cristatus laur.) and xenopus (xenopus laevis daud.)]. 19761013596
the distribution of intercellular gap junctions in the developing retina and pigment epithelium of xenopus laevis.the distribution of gap junctions in the developing retina and pigment epithelium of xenopus has been examined from optic vesicle to photoreceptor outer segment stages. in the retina and pigment epithelium walls of the optic vesicle gap junctions are found between ventricular cells in the apical contact zone and close to the outside wall; a neural tube type of distribution. optic cup formation brings the retina and pigment epithelium into contact and gap junctions form between them. after the st ...19761015633
incorporation of (3h) leucine into the nucleoli of previtellogenic and early vitellogenic oocytes of xenopus laevis: a high resolution autoradiographic study. 19761015838
circus movements and blebbing locomotion in dissociated embryonic cells of an amphibian, xenopus laevis.circus movements, which involve the circumferential rotation of a hyaline cytoplasmic protrusion, occur in cells obtained by edta dissociation of gastrula-stage xenopus laevis embryos. only a few dissociated blastula-stage cells show circus movements, more early gastrula-stage cells show them, and nearly all late gastrula-stage cells show them. circus movements cease in cells prior to mitosis and begin again in daughter cells after mitosis is completed. in early gastrulae, only 17% of prospectiv ...19761018045
investigation of the mechanisms and consequences of steroid hormone action on vitellogenin synthesis in xenopus laevis. 19761020011
a recessive semi-lethal mutation, "distended lungs" (dl) affecting the tadpoles of xenopus laevis. 19761020625
[comparison of the formation of the mesonephric, medullary, and adrenal blastema of common toad embryos, bufo bufo l., and the clawed toad, xenopus laevis duad. (anuran amphibians)]. 19761022319
[role of bruch's membrane in the process of metaplasia of the ocular pigmented epithelium of xenopus laevis].the metaplasia of pigmented epithelium into retina with the formation of nuclear and reticular layers took place in the experiments with wrapping a sheet of pigmented epithelium from tadpoles up in the bruch's membrane of adult frogs x. laevis. the implant with de novo formed retina resembled the inverted eye. in those experiments where the bruch's membrane of tadpoles came into contact with that of adults only depigmentation of the pigmented epithelium cells was observed. the pigmented epitheli ...19761023084
[proliferative potentials of xenopus laevis tadpole and toad optic thalamus nerve tissue cells following injury].after the injury of the thalamus right hemisphere in tadpoles and young frogs x. laevis, 3h-thymidine incorporated in the cells of the thalamus ventricular zone, but not in the middle and large neurons of the type of neurons of the trigeminal nerve mesencephalic nucleus and the large ganglion cells of vi and viii layers of the thalamus cortex. the brain trauma in tadpoles resulted in the activation of cell proliferation in the ventricular zone, whereas in young frogs the proliferation of glyocyt ...19761023086
[quantitative limits of the feulgen reaction: analysis of interference caused by dehistonization and denaturation and renaturation treatments].the feulgen reaction intensity (measured with a microdensitometer vickers m86 on the nucleus of erytrocytes of xenopus laevis daud.) is increased after dehistonization according to brody (1974) only if the dehistonization is made before the fixation in acetic acid. the denaturation and renaturation treatments which should act specifically on the screws of the dna and therefore should not affect the feulgen reaction, act in a specific manner, probably going away another histonic components. on th ...19761023332
[some cytochemical characteristics of the chromatin in the erythrocytes of xenopus laevis daud].the xenopus laevis daud. genome offers a stimulating model of a chromatin (davidson et al., 1975) in which a high ratio of repetitious dna sequences has been recorded (45% of total genome according to davidson et al., 1975). we have studied cytochemically this model "in situ", on the erythrocytes of air-dried smears of peripheral blood. the cells, which are non-dividing and not engaged in dna reduplication, constitute almost hypothetically a homogeneous class constantly in g1 phase of the cellul ...19761023333
[electronmicroscopical, functional morphological, morphometric analysis of anterior pituitary of xenopus leavis (anura)]. 19761023590
[relationships between endocardial cushion development and hemodynamics in embryonic heart. experimental study on xenopus laevis larvae]. 19761024374
demonstration of thymus-independent immune system in xenopus laevis. response to polyvinylpyrrolidone.larvae of xenopus laevis were thymectomized at stage 45 (4 days old), and raised beyond metamorphosis. thymectomized toads, when injected with polyvinylpyrrolidone (pvp), produced the same titres of antibodies as non-thymectomized animals, providing strong evidence that the thymus-independent immune response is present in this anuran. antibodies were of exclusively high molecular weight, heat-stable, and 2-mercaptoethanol sensitive. after immunization, lymphoid accumulations were evident in the ...19761027717
early changes in the ultrastructure of the pars intermedia of the pituitary of xenopus laevis after change of background color.stereological analysis of the secretory cells of the pars intermedia of xenopus laevis over a period of 3 days following the transfer of animals from a white to a black background has revealed that significant alterations in the ultrastructural appearance of these cells can be detected 8 h after the transfer. in particular, changes in the secretory granules and the rough endoplasmic reticulum were found to correlate well with previous reports concerning the melanocyte-stimulating hormone (msh) c ...19761028946
functional significance of the variations in the geometrical organization of tight junction networks.using freeze-fracture techniques, we have examined the morpholog of tight junction networks found along the length of the alimentary tract of xenopus laevis before and after metamorphosis. we have developed the hypothesis, based on these observations, that the geometrical organization of the network determined by the stress-induced shape changes normally experienced by the cells linked by the network. consistent with this theory, tight junctions can be classified into two distinct types of netwo ...19761030707
amino acid uptake in xenopus laevis oocytes. 19761033078
translation and stability of human globin mrna in xenopus oocytes.human globin messenger rna (mrna) prepared from erythroid cells of patients with sickle cell anemia has been translated in xenopus laevis oocytes. addition of hemin to the injected mrna causes total globin synthesis to increase and the ratio of alpha- to betas-globin synthesis (alpha/betas ratio) to approach unity. to determine the effect of the length of the poly-(a) segment on human globin mrna stability, 10 s globin mrna was fractionated into poly-(a)-poor fractions by oligo (dt)-cellulose co ...19761033208
protein synthesis and germ plasm in cleavage embryos of xenopus laevis.(3h) leucine was injected into unfertilized eggs, fertilized eggs, and stage 2-12 embryos of x. laevis. incorporation of the leucine into protein by blastomeres containing germ plasm was studied autoradiographically. eggs, both fertilized and unfertilized, actively synthesized protein, ad did embryos from stage 2 onwards. probably all blastomerers containing germ plasm were labelled. in embryos from stages 4-12, the germ plasm itself was also labelled, and this result suggests that the germ plas ...19761033986
uv effect on germ cell determinant and a proposed scheme for germ cell formation process in embryos of xenopus laevis. 19761035637
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