Publications

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
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 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
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
[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
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
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
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
crystalline lipoprotein-phosphoprotein complex in oocytes from xenopus laevis: determination of lattice parameters by x-ray crystallography and electron microscopy.		1975	1206699
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
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
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
[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
effects of 5-bromodeoxyuridine on the development of xenopus laevis. ii. stages of differentiation.		1975	1232721
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
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
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
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
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
inhibitor of ribosomal rna synthesis in xenopus laevis embryos. iv. the release of inhibitor from cultured cells.		1975	1239392
inhibitor of ribosomal rna synthesis in xenopus laevis embryos. v. inability of inhibitor to repress 5s rna synthesis.		1975	1239394
[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
immunoglobulin heavy chain mrna in mitogen-stimulated b cells.	this paper relates the synthesis of dna, immunoglobulin and heavy chain (h) mrna in murine spleen cells following activation of b cells with lipopolysaccharide from e. coli (lps). spleen cells (cba/h mice) were cultivated with 10% fcs and 10 mug lps/ml. 4 h pulses with [3h]thymidine showed that dna synthesis was stimulated within the first day following lps activation and exhibited a sharp peak at 24 h. the shape of the dna synthesis curve suggests that the cells susceptible to lps stimulation a ...	1975	824129
humoral antibodies to soluble antigens in larvae of xenopus laevis.		1975	804375
fine structure of the male genital tract and kidney in the anura xenopus laevis daudin, rana temporaria l. and bufo bufo l. under normal and experimental conditions.	the ultrastructure of the main cellular components of testicular interstitial spaces in three anuran species was studied during two short periods of the seasonal cycle and after treatment with 5- and 6-hydroxydopamine (5- and 6-ohda). in early december when seminiferous tubules are completely filled with resting spermatozoa in rana, leydig cells display a well developed smooth- and rough-surfaced er, numerous granular vesicles being untypical of mammalian leeydig cells, metochondria with tubular ...	1975	805666
the macromolecular composition of xenopus laevis egg jelly coat.	the three morphologically and functionally distinct jelly coat layers of xenopus laevis eggs, j1, j2, and j3, were separated by manual dissection, solubilized with dithiothreitol, and physicochemically analyzed. the chemical composition of the three jelly layers varied from 37 to 48% protein and 63 to 52% carbohydrate. the carbohydrate consisted of hexosamines, galactose, and fucose. some of the carbohydrate in each of the jelly layers was covalently linked to protein through o-glycosidic bonds ...	1975	807242
innervation of the male genital tract and kidney in the amphibia, xenopus laevis daudin, rana temporaria l., and bufo bufo l.	the innervation of the male genital tract and kidney in three anuran species was studied by the fluorescence histochemical method of falck-hillarp for the demonstration of monoamines whose identity was secured by thin-layer chromatography, and by electron microscopy including administration of 5- or 6- hydroxydopamine (5- and 6-odha). the genital tract comprises testis, intra- and extratesticular and intrarenal seminal efferent ducts, bidder's canal, renal dorsal transverse ducts, and ureter. in ...	1975	807332
adult amphibian epidermal proteins: biochemical characterization and developmental appearance.	the keratin-like proteins (klps) from the epidermis of adult frogs of the species xenopus laevis have been isolated and biochemically characterized by means of polyacrylamide gel electrophoresis, amino acid analysis, tryptic peptide mapping, amino-terminal end-group analysis and isoelectric focusing. one particular protein fraction of rather unusual amino acid composition found only in epidermal tissue was isolated in quantity by preparative gel electrophoresis and monospecific antibodies prepar ...	1975	810539
biogenesis of plasmalemmal glycoproteins. intracellular site of synthesis of mouse liver plasmalemmal 5'-nucleotidase as determined by the sub-cellular location of messenger rna coding for 5'-nucleotidase.	1. free and membrane-bound mouse liver polyribosomes were separated by prolonged density-gradient centrifugation of the post-mitochondrial supernatant. rna was extracted from free and membrane-bound polyribosomes and mrna purified by oligo(dt)-cellulose column chromatography. 2. antisera against purified mouse liver plasma membrane 5'-nucleotidase and moust albumin were prepared and characterized. 3. microinjection of equivalent amounts of mrna from free and membrane-bound liver polyribosomes in ...	1975	810623
selenium effect on the growth of carcinogenic fungi and cytotoxic action of aflatoxin b1 on lymphocyte culture and on embryonal development of xenopus laevis.	the authors report the results of investigations on the protective effect of selenium against teratogenic and cytotoxic action of aflatoxin b1 and the inhibitory action of this element on the growth of fungi producing carcinogenic aflatoxins. sodium selenate inhibited the growth of cultures of such fungi belonging to the class fungi imperfecti as aspergillus flavus, aspergillus fumigatus, penicillium meleagrinum and penicillium rougolosum. added to cell cultures of lymphocytes sodium selenate in ...	1975	817275
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
induction of maturation (meiosis) in xenopus laevis oocytes by three organomercurials.	three organomercurials, p-hydroxymercuribenzoate, p-hydroxymercuriphenylsulfonate, and mersalyl, induce maturation (meiosis) in a large percentage (20-100 percent) of xenopus laevis oocytes. maturation takes place even when the follicle cells which surround the oocytes have been withdrawn. organomercurial- and progesterone-induced maturations have many features in common: they do not occur when the inducer is injected into the oocytes, they require the presence of ca++ in the medium, they are in ...	1975	1055428
cytoplasmic control of nuclear dna synthesis during early development of xenopus laevis: a cell-free assay.	nuclei isolated from nondividing cells were induced to synthesize dna by incubation with cytoplasm from early embryos of xenopus laevis. numerous replication eyes were formed in the nuclear dna molecules, and high levels of [3-h]dttp were incorporated. with this assay a protein(s) which appears to initiate dna synthesis was found at high levels in the cytoplasm of eggs, blastulae, or gastrulae, but only at low levels in the cytoplasm of oocytes, hatched embryos, or adult tissues.	1975	1056038
synthesis of vitellogenin in cultures of male and female frog liver regulated by estradiol treatment in vitro.	using the frog xenopus laevis, we show that the addition of physiological concentrations of estradiol to cultures of liver from untreated males rapidly induces the synthesis of large amounts of vitellogenin. sustained synthesis of vitellogenin requires continuous exposure to estradiol. a nonestrogenic steroid, dexamethasone, does not induce vitellogenin synthesis but does induce increased synthesis of a different protein in liver cultures.	1975	1059103
translation of hormone-induced messenger rna in amphibian oocytes: i. induction by estrogen of messenger rna encoded for vitellogenic protein in the liver of the male african clawed toad (xenopus laevis).	induction of the synthesis of the vitellogenic proteins, lipovitellin and phosvitin, in the liver of the male african clawed toad (xenopus laevis) was investigated as a function of time after treatment with estradiol-17beta [1,3,5(10)-estratriene-3,17beta-diol]. the appearance of mrnas encoded for lipovitellin and phosvitin in the cytoplasmic fraction of the liver was assayed by microinjections of hepatic mrna preparation [either polyribosomes or poly(a)-rich rna] into oocytes obtained from matu ...	1975	1060075
synthesis of mitochondrial rna by full-grown and maturing oocytes of rana pipiens and xenopus laevis.		1975	1081057
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
[meiosis: role of a histone kinase in the condensation of ovarian oocyte chromosomes of xenopus laevis and ambystoma mexicanum].	by injecting heterologous histone-kinase preparations into ovarian axolotl oocytes, it has been possible to speed up the progesterone-induced process of chromosome condensation. moreover, in some instances, this condensation and even complete maturation have been obtained after injection of protein kinase alone, thus in the absence of hormone stimulation. two different histone kinase preparations have been used: one was prepared from ascites cell chromatin and the other from in vitro ovulated xe ...	1975	177222
morphological and biochemical changes in the hepatic endoplasmic reticulum and golgi apparatus of male xenopus laevis after induction of egg-yolk protein synthesis by oestradiol-17 beta.	this report describes morphological and biochemical changes accompanying oestrogen induced synthesis of the egg-yolk protein precursor, vitellogenin, in male xenopus liver. extensive proliferation of the rough and smooth endoplasmic reticulum and the golgi apparatus occurs between 3 and 9 days after administration of oestradiol-17 beta. subcellular fractionation showed that microsomal fractions have an increased number of ribosomes available for protein synthesis, hormone treatment enhances the ...	1976	181282
the stimulatory effect of hypothalamic and mesencephalic tissue on the interrenal of tadpoles of xenopus laevis daudin.		1976	182611
[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
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
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
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
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
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
[oocyte maturation in xenopus laevis. arguments in favor of the role of calcium ions].	influx and efflux of 45ca++ ions in xenopus leavis isolated full-grown oocytes were measured. calcium influx was from 0.5 to 1 pmole/oocyte/h. progesterone, which induces maturation does not influence ca++ fluxes while pcmb caused a significant increase of ca++ influx during the course of pcmb (p-cl-hgbzo-) induced maturation. our results show that the presence of ca++ is not necessary in extracellular medium for germinal vesicle breakdown (gvbd) induced by progesterone. in contrast, the kinetic ...	1976	819172
[early changes in the electric properties of the oocyte plasma membrane of xenopus laevis during the reinitiation of meiosis induced by progesterone, para chloromercuribenzoate (pcmb) or the ionophore a 23187].	progesterone, pcmb and ionophore -mg++ triggers early and quite similar changes in the electrical properties of xenopus laevis plasma membrane which may play a key role in the process of meiosis reinitiation.	1976	819174
[in vitro maturation of the ovocyte of xenopus laevis under the effect of pharmacological agents related to propranolol].	the maturation of xenopus laevis ovocytes was performed after 15 hrs. exposure to progesterone (1 mug/ml). similar results were obtained following a treatment of ovocytes with pharmacological agents such as propranolol and related drugs, at 5 x 10(-4) to 10(-2) m concentrations. sotalol was totally ineffective at the same concentrations. the former drugs, and not sotalol, are supposed to interact within the membrane with some calcium sites, translocation of the ion inside being then produced. th ...	1976	821641
translation of ovalbumin mrna in xenopus laevis oocytes. characterization of the system and effects of estrogen on injected mrna populations.	ovalbumin messenger rna (mrnaov) purified from hen oviduct was injected into xenopus laevis oocytes. the oocytes were incubated in culture medium containing [3h]leucine. analysis of the oocyte cytosol on sephadex g-15o columns demonstrated a peak of radioactivity which cochromatographed with authentic ovalbumin. radioactive protein contained in this peak was precipitated by ovalbumin antiserum, coelectrophoresed with ovalbumin on sodium dodecyl sulfate (sds) and urea gels at ph 8.7, and eluted w ...	1976	765353
the formation of the gonadal ridge in xenopus laevis. iii. the behaviour of isolated primordial germ cells in vitro.	previous studies have described the morphology, including the ultrastructure, of primordial germ cells (pgcs), and the cells with which they associate to form the gonadal ridge, in xenopus laevis. in order to test their capacity for active movement we have studied single, isolated pgcs in vitro. time-lapse studies of these cells reveal that they are motile, using broad cytoplasmic processes. the fact that these cells are very large and easy to manipulate in vitro makes them an attractive subject ...	1976	775008
globin mrna species containing poly(a) segments of different lengths. their functional stability in xenopus oocytes.	rabbit globin mrna species containing poly(a) segments of different lengths were prepared by partial phosphorolysis of mrna with escherichia coli polynucleotide phosphorylase. by varying the salt concentration and the time of incubation of the phosphorolysis mixture, as well as performing oligo(dt)-cellulose chromatography at 22 degrees c and at 4 degrees c, globin mrna preparations containing poly(a) segments of approximately 122, 95, 68, 39, 32, 21, and 16 adenylate residues were obtained. it ...	1976	776610
changes in trna nucleotidyl transferase activity during embryonic development of xenopus laevis.		1976	776635
adjacent repeating units of xenopus laevis 5s dna can be heterogeneous in length.	the distribution of length heterogeneity in adjacent repeating units of x. laevis 5s dna has been examined by "cloning" 5s dna in bacteria. fragments of 5s dna produced by partial digestion with hind iii and containing 1, 4, and 5 repeating units have been inserted at the single hind iii site of the tetracycline-resistance plasmid, psc101, and the hybrid plasmids cloned in e. coli. adjacent 5s dna repeats in the cloned multi-repeat fragments can differ in length. this finding rules out some mech ...	1976	782719
the molecular basis for length heterogeneity in ribosomal dna from xenopus laevis.		1976	787539
lhrh-like system in the brain of xenopus laevis daud: immunohistochemical idenfication.	rabbit antiserum to synthetic lhrh was used with the immunofluorescence technique to identify the lhrh-secreting neurons and their axonal pathways in the brain of xenopus laevis. three groups of immunoreactive neurons were identified: the first, in the telencephalon, is a paired group of cells scattered near the two telencephalic ventricles; the second group lies near the preoptic recess; the third group occurs in the ventral wall of the infundibulum. two principal neuronal pathways were observe ...	1976	791498
acitivity of yeast extracts in cell-free stimulation of dna replication.	extracts of the cytoplasm of disrupted spheroplasts of saccharomyces cerevisiae (bakers' yeast) stimulated dna synthesis in a cell-free system consisting of nuclei from spleen cells of the frog xenopus laevis, the stimulation required mg++8 atp, and the deoxynucleoside triphosphates, was saturated by an excess of nuclei or extract, and had kinetics resembling those obtained previously with extracts from mammalian and avian cells. after addition of the yeast extract, replication "eyes" were forme ...	1976	792878
restoration of immune responsiveness in early thymectomized xenopus by implantation of histocompatible adult thymus.	larvae of the south african clawed toad, xenopus laevis, were thymectomized at nieuwkoop and faber stages 45-46 (4-5 days after fertilization). the 1-1.5-year-old thymusless toads thus obtained were implanted with histocompatible thymus from 1-year-old toads, and 4 weeks later were given skin allografts or rabbit red blood cells (rrbc) to determine their immune response. in contrast with the perfectly tolerant thymusless controls, the thymus-implanted toads rejected skin allografts after longer ...	1976	797285
[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
[ulstrastructure of xenopus heart primordia, differentiated in culture in the presence of actinomycin d].	the cellular differentiation of xenopus laevis cardiac primordia, developed in vitro with actinomycin d, was studied in fine structure. the ultrastructural changes appeared in mitochondria, and in nucleus, which showed a nucleolar characteristic segregation.	1976	825283
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
developmental changes in activity of choline acetyltransferase, acetyl-cholinesterase and glutamic acid decarboxylase in the central nervous system of the toad. xenopus laevis.		1976	932736
new membrane formation and intercellular communication in the early xenopus embryo.	the ionic permeability of the nonjunctional and newly formed junctional membranes was investigated in embryos of xenopus laevis up to the onset of the fifth cleavage. continuous measurements were made of the equivalent nonjunctional (r'o) and junctional resistances (r'i) in different pairs of adjacent cells separated by one of the four cleavage membranes formed in that period. the specific resistance of the nonjunctional membranes (ro) and of each cleavage membrane (ri) as a function of time wer ...	1976	933155
adult haemoglobin in developmentally retarded tadpoles of xenopus laevis.	tadpoles of xenopus laevis reared in water containing 0-01% propylthiouracil continue to grow but fail to develop or metamorphose. the haemoglobin of such tadpoles has been extracted in buffer, converted to a cyanmet form, and run on polyacrylamide gels. the developmentally retarded tadpoles are found to possess adult-type haemoglobin rather than the tadpole type which normally characterizes their developmental stage.	1976	939939
nucleolar activity and rna metabolism in previtellogenic and vitellogenic oocytes of xenopus laevis. a biochemical and autoradiographical, light and em study.		1976	943292
morphological changes of the surface of the egg of xenopus laevis in the course of development. iii. scanning electron microscopy of gastrulation.		1976	943347
the effect of injected cytochalasin b on filament organization in the cleaving egg of xenopus laevis.		1976	943569
an autoradiographic study of tritiated uridine incorporation into the larval ovary of xenopus laevis.	the in vitro incorporation of 3h-5-uridine into the germinal and somatic cells of the larval ovary of xenopus laevis has been studied using both light and electron microscope autoradiography. incubation for only one hour in the presence of precursor revealed that the follicle cells are highly active in rrna synthesis, whereas substantial oogonial nucleolar labeling was not detected for several hours. semi-quantitative analysis of high-resolution autoradiograms indicated that the density of silve ...	1976	943967
ribosomes from xenopus laevis eggs and embryos in a cell-free protein-synthesizing system: translational regulation.	three types of ribosomal preparations from xenopus laevis eggs and embryos were tested in a cell-free system to study possible translational regulation of protein synthesis as mediated by the ribosome during early amphibian development: type 1, a crude high-speed sediment, mainly containing monoribosomes completely dissociable by 0.5 m kc1; type ii, ribosomes washed with 0.5 m kc1; and type iii, ribosomes treated with puromycin - 0.5 m kc1. all three types showed an active response to the additi ...	1976	944101
comparison of exogenous energy sources for in vitro maintenance of follicle cell-free xenopus laevis oocytes.	the purpose of these experiments was to determine which exogenous energy sources are suitable for isolated follicle cell-free oocytes from the frog, xenopus laevis. in order to compare prospective energy sources, follicle cell-free oocytes from 0.4 to 1.3 mm in diameter were incubated in a 1 mm concentration of each of a variety of energy sources and scored daily for the maintenance of morphological characteristics. vitellogenic oocytes placed in succinate or fumarate deteriorated at the same ti ...	1976	944165
the germinal vesicle nucleus of xenopus laevis oocytes as a selective storage receptacle for proteins.	the amorphous nucleoplasm of the germinal vesicle nucleus of xenopus laevis oocytes has been selectively extracted under conditions which leave the nuclear formed elements morphologically intact. the nucleoplasm contains about 97% of the total nuclear proteins and on sds-polyacrylamide gels some 68 polypeptides can be distinguished. on the basis of solubility differences, the nucleoplasmic proteins can be classified into two categories. the first consists of soluble or easily solubilized protein ...	1976	944701
the effect of thymectomy at different stages of larval development on the immune response of the clawed toad to sheep erythrocytes.	the role of the thymus during the first three weeks of larval life in the maturation of humoral immunity in the amphibian, xenopus laevis, is examined. thymectomy throughout this period dramatically affects the heterologous red cell response of young adults. sheep erythrocyte (srbc) administration elicited haemolytic antibody production in the blood and in the spleen (measured by the appearance of plaque forming cells) of control animals, but failed to do so in all thymectomized toadlets. moreov ...	1976	944762
cell-free translation of messenger rna from oocytes of xenopus laevis.		1976	945202
control of 5s rna synthesis in xenopus laevis.		1976	945465
nuclear swelling and chromatin decondensation can occur without cortical granule explosion in eggs of xenopus laevis.		1976	945774
subunit homologies of lactate dehydrogenase (ldh) isoenzymes between amphibians (xenopus laevis) and mammals (wistar rat).		1976	947661
dna-dependent rna polymerase c from xenopus laevis ovaries. ability to transcribe intact double-stranded dna.	dna-dependent rna polymerase c, partially purified from xenopus laevis ovaries, has been resolved by deae-sephadex chromatography in two forms, eluting at 0.2 m and 0.3 m ammonium sulfate, respectively. both are sensitive to high concentrations of alpha-amanitin (200 mug/ml). their ionic strength dependence and divalent cation requirements are indistinguishable. quantitatively, rna polymerase c represents the major form of rna polymerase activity solubilized from the ovaries. both rna polymerase ...	1976	947751