Publications

transcription of dnas of known sequence after injection into eggs and oocytes of xenopus laevis.	1. when the synthetic polynucleotide, poly[d(a-t) - d(a-t)] is injected into the eggs and oocytes of xenopus laevis, a stimulation of rna synthesis results. analysis of extracted rna by high-voltage electrophoresis, shows that this stimulation of rna synthesis is due to the production of poly[r(a-u)] transcripts. the rate of poly[r(a-u)] synthesis is calculated to be at least ten-fold greater in eggs than in oocytes. the amount of poly[r(a-u)] detectable in injected eggs has reached a maximum by ...	1975	1175643
[activity and isoenzymes of lactate dehydrogenase in tissues of amphibians (xenopus laevis, ambystoma mexicanum, triturus alpestris and vulgaris) and the response in the fat body of xenopus males to gonadotropin injection (author's transl)].	lactate-dehydrogenase activity was determined by the optical test method using pyruvate as substrate and the isoenzymes were separated by vertical starch gel electrophoresis. species-specific and organ-specific characteristics of the total activity and the isoenzyme patterns of the four amphibian species are compared with those of rat and mouse. application of gonadotropin increases the amount of soluble protein and the lactate-dehydrogenase activity in the fat body of xenopus and the isoenzyme ...	1975	1176091
autoradiographic localization of hormone-concentrating cells in the brain of an amphibian, xenopus laevis. i. testosterone.	autoradiographic methods were used to investigate locations of hormone concentrating cells in the cns of xenopus laevis. both male and female frog brains contained cells. four major hormone uptake sites were identified: the anterior preoptic area, the ventral infundibular nucleus, a dorsal tegmental area of the medulla and a presumptive motor nucleus of cranial nerves ix-x. the distribution of labelled cells was very similar for male and female brains. available information on these testosterone ...	1975	1176651
autoradiographic localization of hormone-concentrating cells in the brain of an amphibian, xenopus laevis. ii. estradiol.	autoradiographic techniques for light microscopic examination of sex steroid retention were applied to the brains of male and female xenopus laevis, and anuran amphibian, after 3h-estradiol administration. estrogen was concentrated by cells in three telencephalic areas (the ventral striatum, the ventral-lateral septum and the amygdala), the anterior preoptic area, the ventral thalamus, the ventral infundibular nucleus, and in the torus semicircularis. the anterior preoptic area and the ventral i ...	1975	1176652
[effect of selenium on the growth of carcinogenic fungi and the cytotoxic action of aflatoxin b-1 in cell of lymphocytes and on the embryonal development of xenopus laevis].		1975	1167689
the distribution of non-synaptic intercellular junctions during neurone differentiation in the developing spinal cord of the clawed toad.	the distribution of intercellular junctions, other than synapses and their precursors, has been described in the developing spinal cord of xenopus laevis between the neurula and free swimming tadpole stages. at the neurocoel, ventricular cells are joined in the apical contact zone by a sequence of junctions which usually has one or more intermediate junctions but also includes close appositions, gap junctions and desmosomes. this apical complex is more diverse than that reported in other vertebr ...	1975	1176854
the cement gland of xenopus laevis as an experimental model for embryonic differentiation. iii. histochemical and ultrastructural studies on cement glands differentiated in vitro.		1975	1211950
on the determination of the dorso-ventral polarity in xenopus laevis embryos.	when embryos, or dorsal or ventral half-embryos, of xenopus laevis are subjected to unilateral restriction of oxygen supply, the posterior end will always appear at the aerobic side, while the development of the anterior end, oriented towards the anaerobic side, will be partly suppressed. the shorter the time treatment lasts, the more normal the development will be. when the restriction of oxygen effects an inversion of the dorso-ventral polarity, development is retarded, otherwise not. measurem ...	1975	1176879
the development of animals homozygous for a mutation causing periodic albinism (ap) in xenopus laevis.	this paper describes the development of a mutant strain associated with periodic albinism (ap) in the clawed toad xenopus laevis. the most outstanding feature of this mutation is the instability of the albino state. in the course of the development there is a succession of three periods of pigment expression: (1) complete absence of melanin pigment, (2) appearance of melanin in the pigmented epithelium of the eyes and in small quantities in skin melanophores, (3) disappearance of most pigment gr ...	1975	1185102
effects of ionic concentration on sodium permeability properties of myelinated nerve fibres of xenopus laevis.	1. the nodal currents of single myelinated nerve fibres were recorded under potential clamp conditions, and the effect of [ca], [na] and [k] in the external solution on some of the na permeability properties were analysed. 2. [ca], [na] and [k] all affected the position of the steady-state na inactivation (h) curve on the potential axis. the curve was displaced in positive direction by high ionic concentration. 3. the shift associated to different [ca] was largest in low [na] and [k]. similarly ...	1975	1177104
in vivo synthesis and turnover of cytoplasmic ribosomal rna by stage 6 oocytes of xenopus laevis.		1975	1181216
location of genes coding for 18s and 28s ribosomal rna within the genome of mus musculus.	cytological detection of cistrons coding for 18s and 28s ribosomal rna (rrna) within the genome of mus musculus inbred strain sec/1rej was accomplished using the technique of in situ hybridization. metaphase chromosome spreads prepared from cultured fetal mouse cells were stained with quinacrine-hcl and photographed. after destaining, they were hybridized to xenopus laevis tritiated 18s and 28s rrna, specific activity 7.5 x 10(6) dpm/mug. silver grains clustered over specific chromosomes were re ...	1975	1183299
mitotic activity of germ cells during normal development of xenopus laevis tadpoles.	data on the spatio-temporal pattern of germ cell proliferation in xenopus laevis tadpoles were obtained, tracing the germ cells from the cloacal position forward. this spatial pattern in germ cell distribution and its change during normal development clearly coincided with histological observations of germ gland development. by application of regression lines to the analysis of this complex pattern, an interesting conclusion about the mitotic activity of germ cells was suggested. while the mitot ...	1975	1214114
development of intertectal neuronal connections in xenopus: the effects of contralateral transposition of the eye and of eye removal.	the development of intertectal neruonal connections has been investigated in xenopus laevis. contralateral eye grafts and enucleations were performed in embryos and the resultant visual projections to the optic tecta were mapped electrophysiologically after metamorphosis. in enucleated animals the ipsilateral projections were found to be normally organised retinotopically but consisted of visual units with abnormally large multi-unit receptive fields. in 10 animals with contralaterally grafted e ...	1975	1204691
factors determining decussation at the optic chiasma by developing retinotectal fibres in xenopus.	in amphibia all primary retinotectal nerve fibres cross at the chiasma. to investigate why this decussation takes place, a series of embryological operations were performed in which one host eye was replaced by an eye from the opposite side of a donor in xenopus laevis. the visual projections to the optic tecta were mapped electrophysiologically in these animals when adult to reveal to which side of the brain the nerve fibres had become connected. in the majority of cases the contralaterally gra ...	1975	1204693
oocyte maturation in vitro: contribution of the oviduct to total maturation in xenopus laevis.	contact of progesterone matured oocytes of xenopus laevis with the oviduct reduces the time necessary to attain cleavage capacity from 24 h to 3 h. full maturity has been demonstrated by normal development of the matured eggs after fertilization.	1975	1204772
hormonal effects on rna synthesis by stage 6 oocytes of xenopus laevis.		1975	1204941
the erythroid cells of anaemic xenopus laevis. i. studies on cellular morphology and protein and nucleic acid synthesis during differentiation.	phenylhydrazine has been used to induce anaemia in xenopus laevis. the dosage used causes the complete destruction of all mature erythrocytes within twelve days. the anaemia results in the initiation of a wave of erythropoiesis and large numbers of immature erythroid cells are released into the circulation. the morphological and biosynthetic changes which these cells undergo as they differentiate in circulation are described. the origin of the circulating erythroid cells is also discussed.	1975	1206046
circular ribosomal dna and ribosomal dna: replication in somatic amphibian cells.	pulse labelled rdna from cultured somatic cells of xenopus laevis was examined by electron microscope autoradiography. the pattern of replication closely resembles that of bulk chromosomal dna and differs considerably from rdna synthesis during amplification in the oocyte. - about 0.15% of the rdna molecules in the purified preparations were circular. the presence of interlocked circles of equal size indicates that the circles are not in vitro cyclization artefacts, but may represent free rrna g ...	1975	1238239
the erythroid cells of anaemic xenopus laevis. ii. studies on nuclear non-histone proteins.	the mass ratio of nuclear non-histone protein: dna in the immature circulating erythroid cells of phenylhydrazine-induced anaemic xenopus is approximately threefold higher than in mature erythrocytes. this is largely due to the presence of increased amounts of low and intermediate molecular weight proteins in the nuclei of the immature cells. there are a few qualitative differences in the components of this class of proteins between the mature and immature cells, the most notable of which is the ...	1975	1206047
xenopus laevis cement gland as an experimental model for embryonic differentiation. ii. the competence of embryonic cells.	explants of the blastocoelic roof of xenopus laevis embryos were incubated for 6 h in holtfreter solution containing 10 mm ammonium chloride and 10 mm sodium bicarbonate. after this incubation they were transferred for 5 days to barth's physiological salt solution. under these conditions the explants underwent differentiation into cement gland tissue. the ability to produce cement gland was highest when explants were dissected from young gastrulae (stage 10). explants from younger and older embr ...	1975	1176883
initiation of meiotic maturation in xenopus laevis oocytes by the combination of divalent cations and ionophore a23187.	meiotic maturation was induced in xenopus laevis oocytes when the external ca++ or mg++ ion concentration was raised above 5 mm in the presence of the ionophore. ionophore-divalent cation-induced maturation appears to be due to the stimulation of the oocyte itself. cytoplasm of responding oocytes induced maturation when microinjected into ovarian oocytes. cycloheximid, an inhibitor of progesterone-induced maturation, inhibited the maturational response induced by the ionophore and divalent catio ...	1975	1176910
effects of 5-bromodeoxyuridine on the development of xenopus laevis. ii. stages of differentiation.		1975	1232721
oogenesis in xenopus laevis (daudin). iv. effects of gonadotropin, estrogen and starvation on endocytosis in developing oocytes.	this study was designed to explore the relationship of estrogen, human chorionic gonadotropin (hcg), and food availability to endocytosis in developing oocytes. when estrogen alone is administered to an animal, large amounts of vitellogenin are synthesized by the liver and secreted into the circulatory system, where it accumulates. under these conditions there is no evidence of endocytosis at the surface of the oocytes. other studies have shown that following hcg injection into estrogen-treated ...	1975	1181038
biochemical research on oogenesis. comparison between transfer rnas from somatic cells and from oocytes in xenopus laevis.	the properties of trna from oocytes of xenopus laevis were compared with those of trna from somatic cells of the same species. both types of trnas were found to have the same average length and to contain an equal variety of modified nucleotides. however, trna from small oocytes differed from somatic trna by its chromatographic behavior on methylated-albumin kieselguhr columns. the elution profiles from reversed-phase chromatography 5 columns of several aminoacyl trnas were compared after chargi ...	1975	1183439
the effect of stretch on potassium contracture tension in twitch and slow muscle fibres of xenopus laevis.		1975	1189943
lymphocytes of the toad xenopus laevis have the gene set for promoting tadpole development.	nuclear transplantation experiments show that differentiated cells, such as lymphocytes, from the adult frog can express the genes necessary for tadpole development. the transplanted cells were proven to be lymphocytes by immunological methods. the origin of the tadpoles that developed after lymphocyte nuclei injections was ascertained by a karyotypic marker.	1975	1198115
morphological changes of the surface of the egg of xenopus laevis in the course of development. i. fertilization and early cleavage.		1975	1117474
aspects of tail muscle ultrastructure and its degeneration in rana temporaria.	1. tail muscles of larval rana temporaria and to a lesser extent xenopus laevis, at prometamorphosis, were investigated by light and electron microscopy. in the case of rana their degeneration is described at metamorphic climax. 2. the non-degenerate tail muscles of both genera are generally similar in their ultrastructure and likewise similar to those striated muscles of other adult vertebrates including amphibians. 3. at climax tail muscles of rana degenerate by autolysis. it seems likely that ...	1975	1081119
[time dependence of the reaction rate constant of potassium permeability of ranvier's node membrane].	to describe the kinetics of potassium permeability (conductance) changes in the squid giant axon membrane the hodgkin--huxley formulation uses a single first-order in time variable n with forward and backward rate constants, respectively alpha-n and beta-n, potential-dependent but time-independent. it has been shown by frankenhaeuser that in the potassium-carrying system of the myelinated nerve fiber membrane of xenopus laevis the rate constant beta-n is dependent on the duration of previous de ...	1975	1118903
[ontogenesis of the endocardial cushions in the vertebrate heart. an experimental- and comparative embryological study (author's transl)].	by means of comparative ontogenetical findings and organ cultured whole hearts of tadpoles (xenopus laevis) there has been evidence that the localization of the endocardial cushions in the embryonic heart tube of landliving vertebrates is phylogenetically caused. on the contrary ontogenetically the shape of these cushions are dependent on the varying hemodynamic conditions in heart development. by this the anlage of endocardial cushions are the presupposition of the phylogeny and ontogeny in the ...	1975	1200397
identification of the lampbrush chromosome loops which transcribe 5s ribosomal rna in notophthalmus (triturus) viridescens.	the loops which transcribe 5s ribosomal rna in lampbrush chromosomes of the newt, notophthalmus (triturus) viridescens, were identified by hybridizing purified 5s dna to nascent 5s rna in situ. the genes which code for 5s rna were found near the centromeres of chromosomes 1, 2, 6, and 7 by hybridizing iodinated 5s rna to denatured lampbrush and mitotic chromosomes in situ. these genes and their intervening spacer dna were isolated from xenopus laevis using sequential silver-cesium sulfate equili ...	1975	1201684
ovarian progesterone levels during in vitro oocyte maturation and ovulation in xenopus laevis.		1975	1203411
control of cell division and cell differentiation by deoxynucleotides in the early embryo of xenopus laevis.	it is proposed that the deoxyriboside triphosphates present in the egg of xenopus laevis support the synchronous cell divisions occurring during the earliest phase of embryonic development and that, as long as synchrony prevails, the cells are prevented from undergoing differentiation. this hypothesis has been tested by injecting deoxyribonucleotides into fertilized eggs. the following effects were observed: 1) the duration of synchrony is prolonged, 2) the morphological development is suppresse ...	1975	1203982
crystalline lipoprotein-phosphoprotein complex in oocytes from xenopus laevis: determination of lattice parameters by x-ray crystallography and electron microscopy.		1975	1206699
biochemical research on oogenesis. nucleotide sequence of initiator trna from oocytes and from somatic cells of xenopus laevis.	the nucleotide sequence of initiator trna, trnafmet, from vitellogenic oocytes of xenopus laevis was determined. the sequence was deduced from analysis of all t1 and pancreatic oligonucleotides and comparison with the sequence of initiator trna from other animal species. at least 80% of all initiator trna molecules from oocytes have the same nucleotide sequence. this means that most and probably all initiator trna genes which are active in oocytes are identical to one another. no structural diff ...	1975	1204643
myogenesis in the trunk and leg during development of the tadpole of xenopus laevis (daudin 1802).	xenopus embryos pass through five behavioural stages between the end of neurulation (stage 20) and the accomplishment of free swimming (stage 33). these are (i) non-motile (stage 20-22) when the myotome muscle begins to differentiate; (ii) pre-motile (stage 22-24) when the first striated fibrils are visible and contractions are possible; (iii) early flexure (stage 24-27) when reflex responses are given and peripheral nerves are present; (iv) early swimming (stage 28-33); and (v) free swimming (s ...	1975	1176869
isolation and structure of a new active peptide xenopsin on rat stomach strip and some biogenic amines in the skin of xenopus laevis.		1975	1218451
effects of 5-bromodeoxyuridine on the development of xenopus laevis eggs. i. early stages of development.		1975	1233854
excitatory and depressant effects of dieldrin and aldrin-transdiol in the spinal cord of the toad (xenopus laevis).	an investigation was made into the action of the insecticide dieldrin and one of its metabolites, aldrin-transdio, on the isolated spinal cord of the toad, xenopus laevis. conventional electrophysiological techniques were used for stimulating and recording of dorsal and ventral spinal roots. an augmentation of polysynaptic reflex activity along with a marked reduction of orthodromic postsynaptic inhibition could be demonstrated in preparations isolated from dieldrin-poisoned animals. however, ap ...	1975	1234759
[metaplastic transformation of the tissue of the eye in tadpoles and adult xenopus laevis frogs].	the pigment epithelium of the tadpoles and adults x. laevis, as well as of other anurans and cyprinids, is not capable of transformation into the retina without the special influences of agents produced by the retina. when implanting a layer of pigmented epithelium of tadpoles with the bruch's membrane into the cavity of lensless eye of a tadpole, the transformation of pigment epithelium into retina proceeded in 40% of cases and when implanting the pigment epithelium of adults without the bruch' ...	1975	1230674
melatonin content of cat cerebrospinal fluid and blood following intravenous injection of melatonin as measured by xenopus laevis skin melanophore test.	melatonin content of the cerebrospinal fluid (csf), serum and choroid plexus was measured in untreated and melatonin-injected cats using the xenopus laevis melanophore-contracting bioassay. csf and choroid plexus had a considerable melanophore contracting activity in the untreated animals. intravenously injected melatonin considerably enhanced the melanophore-contracting activity of the csf and choroid plexus. two hours later, melatonin was still present at high concentrations in these tissues, ...	1975	1235454
effect of uv on cleavage of xenopus laevis.	uv irradiation of the vegetal pole of stage 2 x. laevis embryos with doses of 6000-18000 ergs/mm-2 delayed or inhibited cytokinesis in the vegetal hemisphere. nuclear division continued so that a syncytium was formed, the size and persistence of which depended on the dose. embryos which received a low uv dose were subsequently able to recover whereas embryos receiving a high dose were unable to gastrulate successfully. the implications for investigations into the role of cytoplasmic determinants ...	1975	1133572
mitosis in presumptive primordial germ cells in post-blastula embryos of xenopus laevis.	in x. laevis embryos injected with (3-h) thymidine between early gastrula and late neurula, the presumptive primordial germ cell nuclei were labelled and some were observed in mitosis, confirming that division occurs throughout this developmental period. in all labelled and mitotic cells, the germ plasm adjoined the nucleus, an observation which invalidates the hypothesis that germ plasm inhibits mitosis in presumptive primordial germ cells after gastrula. in embryos which had been irradiated wi ...	1975	1133573
distinct molecular structures of nuclear class i, ii, and iii dna-dependent rna polymerases.	class iii rna polymerases purified from the murine plasmacytoma mopc 315 and from xenopus laevis ovaries were compared. the subunit structures of the chromatographically distinct murine enzymes iiia and iiib were indistinguishable and were remarkably similar to that of the amphibian enzyme iii. the plasmacytoma class iii rna polymerases were also compared with purified plasmacytoma rna polymerases i and ii. sedimentation studies indicated that rna polymerase iii si significantly larger than rna ...	1975	1054509
aster formation in eggs of xenopus laevis. induction by isolated basal bodies.	we have assayed various materials for their ability to induce aster formation by microinjection into unfertilized eggs of xenopus laevis. we have found that purified basal bodies from chlamydomonas reinhardtii and tetrahymena pyriformis induce the formation of asters and irregular cleavage furrows within 1 h after injection. other microtubule structures such as flagella, flagellar axonemes, cilia, and brain microtubules are completely ineffective at inducing asters or cleavage furrows in unferti ...	1975	1236852
studies on maturation in xenopus laevis oocytes. iii. energy production and requirements for protein synthesis.	the following results were obtained: 1) the oxygen comsumption of progesterone-stimulated x. laevis oocytes increases at the time of germinal vesicle (gv) breakdown. 2) continous treatment with 1 mm kcn, 1 mm and 0.1 mm dnp completely inhibits gv breakdown. 3) pretreatment experiments with kcn, dnp and cycloheximide show that binding of progesterone to the plasma membrane and the specific hormone receptor requires neither energy, nor protein synthesis. 4) 1 h pulses of dnp (1mm) or cycloheximide ...	1975	1237439
the effect of u.v. irradiation of the vegetal pole of xenopus laevis eggs on the presumptive primordial germ cells.	the initial effect of u.v. irradiation of the vegetal pole was to inhibit cleavage in the vegetal hemisphere although karyokinesis was not substantially affected. in this way a syncytium formed in the vegetal hemisphere which broke down into individual cells some time between morula and late blastula. the movement of the germ plasm from the peripheral cortical regions into the interior of the egg was not appreciably delayed although aggregation of the germ plasm did not take place until the indi ...	1975	1237530
in vitro differentiation of a homogeneous cell population--the epidermis of xenopus laevis.	a simple culture technique is described for obtaining homogeneous populations of differentiating epidermal cells from adult amphibian skin. this population of cells continues its normal differentiation, namely keratinization, in vitro. by the third day of culture more than 99-9% of the cells in the population contain immunoreactive keratin. during the next 5-7 days of culture these cells synthesize increasing amounts of a tissue-specific keratin-like protein until this protein constitutes more t ...	1975	1237533
effects of differences in mitotic activity, stage of cell cycle, and degree of specialization of donor cells on nuclear transplantation in xenopus laevis.		1975	1238302
intermolecular renaturation of hairpin loops leads to stable and specific aggregates of 28-s rrna and precursor rrnas from xenopus laevis.	under certain extraction conditions, 28-s rrna of xenopus laevis can form specific dimers by intermolecular renaturation of a particular hairpin loop near the b end of the molecules. this was demonstrated by electron microscopy of isolated aggregates under conditions where rrna shows a reproducible pattern of secondary structure. in 50% formamide, 15 mm sodium chloride, 1.5 mm trisodium citrate, ph 7.0, the aggregates dissociate into their monomers at a temperature (61 degrees c) at which the mo ...	1975	1239380
[heat production and respiration of the oocyte of xenopus laevis l. in various stages of oogenesis].	the data are given on the respiration and heat production intensity in the x. laevis oocytes by which the value and patterns of change of psiu-function (function of bound dissipation) during oogenesis are calculated. all 3 values were shown to decrease rapidly from the stage of previtellogenesis till the stage of mature oocyte what agrees with the thermodynamic theory of development.	1975	1241800
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
nucleotide sequences within the ribosomal ribonucleic acids of hela cells, xenopus laevis and chick embryo fibroblasts.		1976	1263259
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
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
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
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
integration of eukaryotic genes for 5s rna and histone proteins into a phage lambda receptor.	highly purified hindiii restriction fragments of xenopus laevis 5s dna and of psammechinus miliaris histone dna have been covalently inserted into a derivative of phage lambda. this phage, genetically constructed by murray et al. (1), contains only a single target for hindiii in the ci gene. viable hybrid molecules were detected as clear plaque-forming phage after transfection of e. coli, the vast majority of which were shown by hybridization to be recombinants of the desired type. the lambdasam ...	1976	1069257
species specificity in the response of an in vitro amphibian (xenopus laevis) ovulation assay to mammalian luteinizing hormones.		1976	1085276
[regeneration of the crystalline lens in anuran amphibia in the postembryonal stage. experimental excision of the crystalline lens in rana esculenta and xenopus laevis larvae].		1976	1088056
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
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
[the development of the vestibular apparatus under conditions of weightlessness].	the spawn of the aquarium fish brachydanio rerio was developing during 5--6 days under conditions of weightlessness (first on board the spaceship "sojuz-16", then in the space station "salut-4") in special aquariums "emkon", in thermostable installations. electron microscopically the embryos were found to have a well developed labyrinth in early developmental histologically and cytologically differentiated receptory structures of the macula utriculi and macula saccili. in contrast to controls, t ...	1976	1082742
a cytoplasmic factor promoting oocyte maturation: its extraction and preliminary characterization.	cytoplasm of maturing amphibian oocytes possesses a factor that induces germinal vesicle breakdown. this factor was extracted from rana pipiens eggs and assayed by microinjection in xenopus laevis oocytes. the activity of this factor is mg-dependent, ca-sensitive, and associated with heat-labile protein. centrifugation on a sucrose density gradient revealed that the factor exists in three different molecular sizes.	1976	1083070
aluminium localization in amphibian skin with the electron microprobe and ion microanalyzer.	emp and ima studies show the presence of a1 in the epidermis of larvae and young adults of discoglossus pictus and rana esculenta, which disappears during later stages of development. a1 is practically absent in the epidermis of xenopus laevis and pleurodeles waltlii. the localization of a1 with emp and ima supports the biochemical results. the function of a1 in the epidermis is not known at present.	1976	1083571
architecture of the marrow vasculature in three amphibian species and its significance in hematopoietic development.	architecture of the bone marrow vasculature, particularly that of the femur, was analyzed in three amphibian species in relation to the early phylogeny of marrow hematopoiesis. a dye-injection method and histological techniques, including both serial sectioning and reconstruction methods, were used for this purpose. from these observations the following conclusions may be drawn. (1) marrow hematopoiesis is absent from the femur of the urodelan (triturus pyrrhogaster) and appears first in the fem ...	1976	1083670
evidence for corticotropin releasing factor (crf) synthesis in the preoptic nucleus of xenopus laevis tadpoles: a preliminary report based on lesion experiments.	for the study of the hypothalamo-hypophysial system of xenopus laevis tadpoles, hypothalamic lesions were made by means of the electrocoagulation technique. lesioning of the ventral region of the preoptic nucleus resulted in a decrease of the number of acth cells in the pars distalis of the pituitary gland and in a diminution of the pas-positive reaction of these cells. in addition, regeneration of the neurosecretory cells of the ventral region of the preoptic nucleus observed 6 weeks after lesi ...	1976	1084220
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
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
electron microscope analysis of amplifying ribosomal dna from xenopus laevis.		1976	1253845
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
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
oogenesis in xenopus laevis (daudin). iii. localization of negative charges on the surface of developing oocytes.		1976	1263301
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
a plasmid cloning vehicle allowing regulated expression of eukaryotic dna in bacteria.	we have constructed a plasmid cloning vehicle in which transcription of inserted heterologous dna fragments can be regulated by a defined bacterial operator and promoter. the lambda plac 5 ecoridna fragment containing the operator, promoter, and beta-galactosidase gene of the lactose operon was linked to the cole1 derivative plasmid psf2124, creating a plasmid designated pbgp100, pbgp100 contains one ecori site at the lac dna/psf2124 dna junction and another at the lambda dan/psf2124 dna junctio ...	1976	1069275
localization by situ hybridization of amplified ribosomal dna during xenopus laevis oocyte maturation (a light and electron microscopy study).	the presence of ribosomal dna has been demonstrated, by light and electron microscopy study of in situ hybridization with 125i-labeled ribosomal rna, in the feulgen-positive bodies which appear during maturation in the cytoplasm of xenopus laevis oocytes. the ultrastructure of these bodies is described.	1976	1062796
the development of the action potential mechanism of amphibian neurons isolated in culture.	nerve and muscle cells differentiated morphologically, in cultures of dissociated cells prepared from amphibian neural plate and underlying mesoderm (xenopus laevis, nieuwkoop and faber stage 15). cultures were grown in a defined medium containing sterile steinberg's salt solution and 0.1% bovine serum albumin, and maintained for periods up to 5 days.	1976	1064036
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
[oocyte maturation in xenopus laevis. the entry of progesterone is necessary for maturation].	in vitro progesterone-induced maturation of xenope ovocyte was studied as a function of progesterone uptake and extracellular progesterone concentration. maturation depends on the initial total amount of progesterone in incubation medium and does not depend on the extracellular hormonal concentration. this result strongly argues for an intracellular receptor site for progesterone.	1976	825259
dna reassociation kinetics in relation to genome size in four amphibian species.	dna reassociation kinetics were studied, by means of the hydroxyapatite chromatography method, for four species of amphibians with different nuclear dna content: xenopus laevis (3 pg dna per haploid genome) and bufo bufo (7 pg) of the anura subclass and triturus cristatus (23 pg) and necturus maculosus (52 pg) of the urodela subclass. within each subclass the two species studied were found to have about the same absolute amount of unique dna. the differences of total nuclear dna can be accounted ...	1976	826380
[ perfecting a simple method of organotypic thyroid gland culture in xenopus laevis (amphibia, anoura)].	the larval thyroid of xenopus cultured in an adequate medium, keeps its morphological differentiations at an ultrastructural scale and reacts against tsh added to the culture medium, through the development of apical microvilli, which is a sign of an active pinocytosis of the colloid, and also of ergastoplasmic lamellar and vesicular structures suggesting an active protein synthesis.	1976	827362
high tyrosinase activity in albino xenopus laevis oocytes.	tyrosinase was measured in oocytes of the recently described albino mutant (apap) of xenopus laevis. although these oocytes show no pigmentation and the eggs are known to contain no melanosomes, tyrosinase - which is probably the only enzyme necessary for melanin synthesis from tyrosine - was increased more than twofold relative to the wild type. tyrosinase recovered from albino and wild type oocytes showed the same km with respect to tyrosine, and this was not altered by previous gonadotrophin ...	1976	827598
correlation between the cell cycle in the neurectoderm and differentiation during the early development of xenopus laevis. 1. budr sensitivity during gastrulation.	an hypothesis has been proposed by holtzer and co-workers (1963, 1970, 1973) that the process of cell differentiation may be coupled in an obligatory manner with 'quantal' cell cycle(s) which precede it. we have demonstrated that a 'wave' of dna synthesis occurs in the neurectoderm of xenopus laevis gastrula. this event of the cell cycle appears to be associated with the primary embryonic induction by the subjacent mesodermal tissue. the peak of dna synthesis was observed in that area of the neu ...	1976	829417
induction of maturation (meiosis) in small xenopus laevis oocytes by injection of maturation promoting factor.	treatment of small-(stage iii) or medium-sized (stage iv) xenopus laevis oocytes with progesterone, human chorionic gonadotropin, or para-hydroxymercuriphenylsulfonate does not induce maturation. only the full-grown oocytes (stage vi) undergo maturation when treated with either one of these three substances. in contrast, injection of maturation promoting factor into oocytes of stages iii-vi invariably leads to chromosome condensation and germinal vesicle breakdown. no maturation spindle is found ...	1976	1064873
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
a recessive semi-lethal mutation, "distended lungs" (dl) affecting the tadpoles of xenopus laevis.		1976	1020625