Publications

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 ...	1976	947992
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 ...	1976	947996
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 ...	1976	948058
processes for sodium permeability inactivation in the myelinated nerve fibre of the frog (xenopus laevis).		1976	949010
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 ...	1976	949740
vital dye mapping of the gastrula and neurula of xenopus laevis. ii. prospective areas and morphogenetic movements of the deep layer.		1976	950072
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 ...	1976	953012
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 ...	1976	953737
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 ...	1976	953854
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 ...	1976	954087
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 ...	1976	954098
the size of the guanosine triphosphate pool active in the synthesis of stable rna by stage 6 oocytes of xenopus laevis.		1976	954858
hormone effects on male sex behavior in adult south african clawed frogs, xenopus laevis.		1976	955579
direct adaptation of cells to temperature: similar changes of ldh isozyme patterns by in vitro and in situ adaptations in xenopus laevis.		1976	963983
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 ...	1976	965920
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.	1976	965921
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 ...	1976	970983
arrangement of length heterogeneity in repeating units of amplified and chromosomal ribosomal dna from xenopus laevis.		1976	972392
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 ...	1976	973136
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 ...	1976	976269
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 ...	1976	978127
[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.	1976	983425
nuclear localization of dna polymerase alpha in xenopus laevis oocytes.		1976	985524
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 ...	1976	986165
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 ...	1976	986247
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 ...	1976	986250
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 ...	1976	986254
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 ...	1976	986255
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 ...	1976	986365
initiation of meiotic maturation in xenopus laevis oocytes by lanthanum.		1976	986558
the synthesis of freezing-point-depressing protein of the winter flounder pseudopleuronectus americanus in xenopus laevis oocytes.		1976	986821
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 ...	1976	986875
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 ...	1976	987857
morphological changes of the surface of the eggs of xenopus laevis in the course of development. 2. cytokinesis and early cleavage.		1976	988190
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 ...	1976	991238
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 ...	1976	991862
studies on the deiodination of thyroid hormones in xenopus laevis tadpoles.		1976	992332
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 ...	1976	993274
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 ...	1976	993831
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 ...	1976	994676
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 ...	1976	999136
dna-dependent rna polymerase c from xenopus laevis ovaries: formation of stable heparin-resistant dna-binding complexes.		1976	1001472
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 ...	1976	1010160
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 ...	1976	1010162
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 ( ...	1976	1010975
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.	1976	1010976
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 ...	1976	1010977
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); ...	1976	1010987
[histological studies on allografts and xenografts of lymphoid tissue in newts (triturus cristatus laur.) and xenopus (xenopus laevis daud.)].		1976	1013596
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 ...	1976	1015633
incorporation of (3h) leucine into the nucleoli of previtellogenic and early vitellogenic oocytes of xenopus laevis: a high resolution autoradiographic study.		1976	1015838
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 ...	1976	1018045
investigation of the mechanisms and consequences of steroid hormone action on vitellogenin synthesis in xenopus laevis.		1976	1020011
a recessive semi-lethal mutation, "distended lungs" (dl) affecting the tadpoles of xenopus laevis.		1976	1020625
[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)].		1976	1022319
[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 ...	1976	1023084
[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 ...	1976	1023086
[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 ...	1976	1023332
[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 ...	1976	1023333
[electronmicroscopical, functional morphological, morphometric analysis of anterior pituitary of xenopus leavis (anura)].		1976	1023590
[relationships between endocardial cushion development and hemodynamics in embryonic heart. experimental study on xenopus laevis larvae].		1976	1024374
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 ...	1976	1027717
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 ...	1976	1028946
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 ...	1976	1030707
amino acid uptake in xenopus laevis oocytes.		1976	1033078
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 ...	1976	1033208
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 ...	1976	1033986
uv effect on germ cell determinant and a proposed scheme for germ cell formation process in embryos of xenopus laevis.		1976	1035637
microinjection of trna into amphibian oocytes.	the microinjection technique affords us the possibility to introduce purified components into living cells and to answer the question of what effects the change introduced has on cellular metabolism. this technique can therefore be used to test the hypothesis that transfer rna plays a regulatory role in cellular protein synthesis. prior to these experiments it is important, however, to test whether transfer rna microinjected into amphibian oocytes is stable and functional inside this cells. thes ...	1976	1036012
evidence that the fertilization envelope blocks sperm entry in eggs of xenopus laevis: interaction of sperm with isolated envelopes.		1976	1036730
nature of progesterone action on amino acid uptake by isolated full-grown oocyte of xenopus laevis.	l-leucine uptake into full-grown oocytes of xenopus laevis is a saturable process which is na+ dependent and presumably coupled to na+ gradient. our results indicate that progesterone (10(-6) m) blocks abruptly, around the germinal vesicle breakdown, the saturable transport of l-leucine. p-chloromercuribenzoate (10(-4) m) induces maturation and after a short lag of time strongly inhibits l-leucine uptake. cycloheximide prevents progesterone-induced maturation and permeability changes.	1976	1247560
in situ hybridization of "nick-translated" 3h-ribosomal dna to chromosomes from salamanders.	a technique is described for preparation of 3h-labelled dna by nick-translation employing deoxyribonuclease i and dna polymerase i. the labelled dna can be obtained in high yield with specific activities of 10(6) cpm/mug or more. ribosomal dna, isolated from ovaries of young xenopus laevis, and whole dna from plethodon cinereus were labelled in this way. the rdna was used for in situ hybridization to meiotic chromosomes from p. cinereus, p. vehiculum and p. dunni. autoradiographs of in situ hybr ...	1976	1248332
31p nuclear-magnetic-resonance studies on the developing embryos of xenopus laevis.	the concentrations of nucleoside triphosphate, inorganic phosphate and the yolk proteins, phosvitin and lipovitellin, have been monitored in living embryos of xenopus laevis by 31p nuclear magnetic resonance (nmr) spectroscopy. the nucleoside triphosphate levels remain relatively constant at about 3.5-4.5 nmol/embryo at least until the 'spontaneous movement' stage of development. by the swimming tadpole stage an inorganic phosphate resonance representing about 30 nmol/embryo becomes evident in t ...	1976	1248465
characterization of polysomes from xenopus liver synthesizing vitellogenin and translation of vitellogenin and albumin messenger rna's in vitro.	1. conditions are described for the isolation of polysomes from the liver of xenopus laevis. the method involves homogenization of liver in 0.2 m tris-hcl ph 8.5, treatment with 2% triton x-100 and subsequent sucrose density gradient fractionation of polysomes from a 10000 x g supernatant. 2. vitellogenin synthesis was induced in male xenopus liver by oestradiol treatment. polysomes were isolated and vitellogenin-synthesizing polysomes characterized by their association with monospecific 125 i- ...	1976	1248478
incorporation of (5-3h) uridine into ribonucleotide pools and rna during thyroxine-induced metamorphosis of xenopus laevis tadpoles.	incorporation of [3h] uridine into the ribonucleoside triphosphates utp and ctp, total rna, and nuclear and cytoplasmic rna was followed in xenopus laevis tadpole liver during thyroxine (t4)-induced metamorphosis. pool sizes of utp and ctp were found to remain unchanged, although turnover the ribonucleoside triphosphates was found to be greatly stimulated after 4 days of hormone treatment. the time course of labeling of the 40-s pre-rrna was very similar to that of utp in both thyreostatic and t ...	1976	1248666
progesterone biosynthesis and metabolism by ovarian follicles and isolated oocytes xenopus laevis.		1976	1252564
histogenesis of retina in the clawed frog with implications for the pattern of development of retinotectal connections.		1976	1252942
electron microscope analysis of amplifying ribosomal dna from xenopus laevis.		1976	1253845
in vivo and in vitro hormonal effects on the metabolism of immature oocytes of xenopus laevis.		1976	1254084
the ionic basis of the resting potential and a slow depolarizing response in rohon-beard neurones of xenopus tadpoles.	1. rohon-beard cells in the spinal cord of xenopus laevis tadpoles have been studied in animals 4-days to 2-weeks-old (nieuwkoop & faber, 1956, stages 45-49). these neurones have an unusually large resting membrane potential of -88 mv, in ringer solution containing 3-0 mm k+. 2. their resting potential (r..) depends on the concentration gradient of k+ across the cell membrane. these cells follow the prediction of the nernst equation for a k+-selective electrode, down to external k+ concentration ...	1976	1255512
low resistance junctions between mesoderm cells during development of trunk muscles.	1. electrical connexions between mesoderm cells have been examined during the formation of somites in xenopus laevis, bombina orientalis and ambystoma mexicanum. 2. in xenopus the resting potentials of presumptive myotome cells (-65 + 2 mv, s.e. of mean) and somite muscle cells (-65 +/- 0-6 mv s.e. of mean) were 40 mv, greater than dermatome cells (-25 +/- 0-6 mv, s.e. of mean). similar differences were found in bombina and ambystoma. 3. in all three species cells of the dermatome layer of the m ...	1976	1255515
iodination of xenopus laevis histone f2a1 in chromatin.	the reaction of calf thymus and xenopus laevis histones with radioactive iodine has been studied under various conditions that affect chromatin structure. all histones from both species contain at least one tyrosine residue and, in a denaturing solvent, all the the histones react with iodine. histone f2a1 has been studied in detail. calf thymus f2a1 is known to contain four tyrosyls and all four react with iodine. in high voltage paper electrophoresis, the tyrosine-containing peptides from calf ...	1976	1259948
protein incorporation by isolated amphibian oocytes. v. specificity for vitellogenin incorporation.	macromolecules of vitellogenin were sequestered by xenopus laevis oocytes 20-50 times (on a molar basis) more rapidly than other proteins tested. selectivity for vitellogenin did not appear to involve molecular size or charge. the km for vitellogenin incorporation was at least several orders of magnitude less than that for bovine serum albumin (bsa). at concentrations less than 10 mg-ml-1, bsa did not measurably compete with vitellogenin; a slight, apparent competition observed above a bsa conce ...	1976	1262394
morphology and kinetics of spermatogenesis in xenopus laevis.	the light microscopic characteristics of spermatogenic stages of the germ cell line in the anuran, xenopus laevis, have been described as they appear in both nuclear squash preparations and plastic embedded thick sections of intact testes. tritiated thymidine autoradiography was employed to unequivocally identify stages. using this methodology, it was determined that the premeiotic dna synthetic period occurs in a cell which is morphologically indistinguishable from a late secondary spermatogoni ...	1976	1262821
nucleotide sequences within the ribosomal ribonucleic acids of hela cells, xenopus laevis and chick embryo fibroblasts.		1976	1263259
oogenesis in xenopus laevis (daudin). iii. localization of negative charges on the surface of developing oocytes.		1976	1263301
genomic transcriptional activity and the structure of chromatin.	nucleic acid hybridisation has shown that micrococcal nuclease-derived chromatin subunits from the cells of xenopus laevis contain fragments of ribosomal 28s, 18s and 5s rnas within the population of 200 base-pair pieces of dna. subunits from cultured embryonic cells actively transcribing ribosomal rna contain only 70-74% of the cistrons present in undigested wild-type dna, while subunits from adult erythrocytes not active in rna transcription contain close to 90% of the ribosomal cistrons in na ...	1976	1264202
utrastructure of the cement gland of xenopus laevis.	to establish a morphological baseline for experimental studies of differentiation using the cement gland as a model, the following observations are added to those on record. the elongated cells of xenopus laevis cement glands have an internal organization displaying five distinct zones differing in structure and specialized function. the apical zone contains packed secretion vesicles apparently belonging to two different types. the transit zone appears to be devoid of major biosynthetic activity ...	1976	1267966
analysis of moving supernumerary limbs of xenopus laevis.		1976	1269564
polyadenylic acid-containing rna and its polyadenylic acid sequences newly synthesized in isolated embryonic cells of xenopus laevis.		1976	1269831
stereological analysis of the effects of 6-hydroxydopamine on the ultrastructure of the melanocyte-stimulating hormone cell of the pars intermedia of the pituitary of xenopus laevis.		1976	1269902
in vitro translation and estradiol-17beta induction of xenopus laevis vitellogenin messenger rna.	administration of estradiol-17beta to male xenopus laevis induces synthesis and secretion by the liver of the egg yolk precursor protein vitellogenin. rna extracted from livers of estradiol-17beta-treated xenopus laevis directs the synthesis of the entire 200,000-dalton vitellogenin monomer in a cell-free protein synthesizing system derived from rabbit reticulocytes. vitellogenin synthesized in vitro was isolated and quantitated by indirect immunoprecipitation and identified by comparison to aut ...	1976	1270438
the formation of the gonadal ridge in xenopus laevis. i. a light and transmission electron microscope study.	in xenopus laevis tadpoles, between stages 44 and 49 (nieuwkoop & faber, 1956), the primordial germ cells (pgcs) migrate from the dorsal mesentery of the gut to the site of the presumptive gd gonadal ridge. this paper describes the process at the light- and electronmicroscope levels. the pgcs in the mesentery, which at first are very large and yolk-laden, seem to lie entirely within the cellular matrix of the mesentery, although this is not obvious in light micrographs. where the pgcs bulge out ...	1976	1270975
the formation of the gonadal ridge in xenopus laevis. ii. a scanning electron microscope study.	this paper studies the surface morphology of the developing gonadal ridge in x. laevis between stages 44 and 49 (nieuwkoop & faber, 1956). during this period the primordial germ cells (pgcs) move laterally from the dorsal mesentery of the gut to the position of the presumptive gonadal ridge. as they do so the coelomic lining cells lateral to the mesentery differentiate into a specialized, longitudinally orientated band, stretching nearly the full length of the dorsal mesentery on each side. the ...	1976	1270976
synthesis of human placental lactogen in xenopus oocytes.	oocytes from xenopus laevis were injected with polysomes from normal human term placenta. synthesis of the protein hormone human placental lactogen (hpl) in the oocytes was demonstrated by specific immunoprecipitation with anti-hpl serum. analysis of the immunoprecipitates on sds-polyacrylamide gel revealed one peak, with a migration distance corresponding exactly to that of [14c]-radioacetylated hpl added as a marker. two days after injection the mrna was still able to direct the synthesis of h ...	1976	1272264
the effects of neuraminidase and protamine chloride on potential clamp parameters of the node of ranvier (xenopus laevis).	the effects of neuraminidase and protamine chloride on the ionic currents associated with step changes in membrane potential were studied. neuraminidase (a hydrolase which cleaves glycosidically bound sialic acid) had negligible effects on the permeability properties. the polycation protamine chloride decreased the sodium as well as the potassium currents. the sodium equilibrium potential decreased during the experiments which indicates a gain in internal sodium concentration. the analysis showe ...	1976	1274627
lipid composition of developing xenopus laevis embryos.	the total lipid content, amount of phospholipid, proportions of major polar and neutral lipid classes, and the overall fatty acid composition were examined in xenopus laevis embryos. no obvious differences were observed in any of the parameters between fertilization and hatching or between eggs produced by different females. the average lipid content per egg was 113 mug, 31.6 mug of which was phospholipid. the major phospholipids were phosphatidylcholine and sphingomyelin. the major fatty acids ...	1976	1276984
[the tail of the tadpole of alytes obstetricans in organ culture with or without the addition of thyroxine. ultrastructural controls].	the tail of the alytes obstetricans tadpole, isolated at different stages (end of proclimax and climax), was studied in organ culture. the addition of thyroxine at a concentration of 5.10(-7) induces an involution slower than in vivo. besides, this regression is comparatively slower in similar conditions, than in xenopus laevis. this delay could be explained by the important volume and the very developed musculature of this anuran tail. ultrastructural controls reveal the form of the muscles, th ...	1976	139991
synthesis of the mitochondrial inner membrane in cultured xenopus laevis oocytes.	the purpose of this study was to investigate the contribution of mitochondrial and cytoplasmic protein synthesis to the biogenesis of cytochrome oxidase (ferrocytochrome c:oxygen oxidoreductase ec 1.9.3.1) and rutamycin-sensitive adenosine triphosphatase (atp phosphohydrolase ec 3.6.1.3) in cultured oocytes of the toad, xenopus laevis. x. laevis cytochrome oxidase was purified over 23-fold with respect to specific activity and over 29-fold with respect to specific heme a content from oocyte subm ...	1976	184093
dna-relaxing activity and endonuclease activity in xenopus laevis oocytes.	complex simian virus 40 dna produced by a soluble cell-free extract derived from stage 6 oocytes of xenopus laevis consists of fully relaxed circles (i.e., with no superhelical turns). an endonuclease and a dna-relaxing protein, either or both of which could be responsible for the relaxation of the complex dna, have been purified from the extract. the endonuclease(s) produces nicked circles (having a single-strand scission) and linear full-size molecules. the dna-relaxing protein is in the nucle ...	1976	188045