Publications

photoreceptor outer segments: accelerated membrane renewal in rods after exposure to light.	the rate of rod outer segment renewal in rana pipiens tadpoles under constant light and under diurnal conditions of 12 or 2 hours light per day is significantly increased compared to that in animals in darkness. furthermore, during 24 hours in light after 6 days in darkness the rate of renewal is three to four times that in darkness. in xenopus laevis tadpoles the rate of renewal is more than five times greater during the first 8 hours of a normal diurnal cycle than during the following 16 hours ...	1977	300504
electron microscopic study on the early histogenesis of thymus in the toad, xenopus laevis.	sequential electron microscopic observations of thymic histogenesis in the toad, xenopus laevis, reveal that the thymus arises as epithelial buddings of the visceral pouches at nieuwkoop-faber stage 40, and acquires its basic histological features at stages 48-49. in the rudiments and the surrounding mesenchyme at stages 43-45, there are non-epithelial cells with pseudopodia, abundant ribosomes, and marginated heterochromatin. these cells, possible precursor cells of thymic lymphocytes, are freq ...	1977	300655
early steroid metabolism in xenopus laevis, rana temporaria and triturus vulgaris embryos.	embryos of xenopus laevis, rana temporaria and triturus vulgaris exposed to radioactive pregnenolone have been found to convert it to progesterone. incubations with radioactive progesterone showed that it was actively metabolized by oocytes and embryos. in xenopus incubations progesterone was converted to 5alpha-pregnane-3,20-dione, 17alpha-hydroxy-4-pregnen-3-one, 4-androstene-3,17-dione and 17alpha-20alpha-dihydroxy-4-pregne-3-one, indicating 5alpha-reductase, 17alpha-hydroxylase, 19-20-desmol ...	1977	303192
differences in pulmonary microvascular anatomy between bufo marinus and xenopus laevis.	1. histological and corrosion-casting techniques have been used to provide a comparison of lung structure between a terrestrial load (bufo marinus) and an aquatic one (xenopus laevis). the pulmonary microvascular anatomy is distinctly different in these two species and both differ from classical descriptions of other anuran lungs. 2. in x. laevis large peribronchial vessels form a number of direct connections between the pulmonary artery and vein at the base of the lung. as a result of their loc ...	1977	402217
evidence for a functional role of rna in centrioles.	basal bodies, purified from chlamydomonas and tetrahymena, were exposed to various enzymatic treatments and then assayed for their ability to nucleate aster formation upon injection into eggs of xenopus laevis. untreated basal bodies injected into frog eggs act as centrioles and induce the formation of asters. the aster-inducing activity of basal bodies was eliminated by treatment with proteolytic enzymes and ribonucleases. aster-inducing activity was not affected by dnase and a number of other ...	1977	403009
[cytoplasmic control of cell division in amphibians: changes in the timing of egg cleavage after injection of heterospecific cytoplasm].	cytoplasm of xenopus laevis virgin eggs is injected into fertilized eggs of pleurodeles waltlii, species characterized by an initial development slower than that of xenopus. the cytoplasm introduced into eggs at the 2 or 4 cell stages accelerates the division of cells in the site of injection, later on synchronism of cleavage for the different blastomers of operated eggs reappears. the effects of an heterologous cytoplasm on mitosis and endogenic rhythm of cleavage are discussed.	1977	404053
[inhibition of the reinitiation of meiosis in xenopus laevis oocytes by three natural antiproteases: antipain, chymostatin, and leupeptin].	oocytes incubated for 1 hr. in saline containing 1 mg/ml of antipain, leupeptin or chymostatin do not reinstate meiosis when progesterone or ionophore a 23187 are added. on the contrary such oocytes remain able to undergo meiosis when injected with cytoplasm of maturing oocytes (mpf), with rabbit phosphorylase kinase or with beef protein kinase. these results demonstrate that the loss of responsiveness to progesterone or ionophore is not due to toxic effects but rather to some interference with ...	1977	404062
cytopathic effect and plaque formation by arboviruses in a continuous cell line (xtc-2) from the toad xenopus laevis.	forty-six arboviruses were tested for c.p.e. and/or plaque formation in an amphibian cell line. c.p.e. was observed with a high proportion of the viruses tested. comparative plaque assay, in the xtc-2 cells at 28 degrees c and vero cells at 37 degrees c, suggests that these systems are comparable in sensitivity and susceptibility to infection. practical uses of this cell line are discussed.	1977	406357
length and interspersion of repetitive and non repetitive dna sequences in four amphibian species with different genome sizes.	the interspersion period of repetitive and unique sequences was analyzed by two different methods, electron microscopy and agarose gel electrophoresis, for four amphibian species with different nuclear dna content, namely the anura xenopus laevis (3 pg dna per haploid genome) and bufo bufo (7 pg) and the urodela triturus cristatus (23 pg) and necturus maculosus (52 pg). within each of the two subclasses it has been found that interspecific differences, in dna content, due to variations in the am ...	1977	407058
nucleotide sequence relationships between vertebrate 5.8 s ribosomal rnas.	nucleotide sequences of the 5.8 s ribosomal rnas from hela cells, xenopus laevis and chick embryo fibroblasts were compared. xenopus laevis 5.8 s rna differs from that of hela cells in four internal positions and at the 3' end of the molecule. chick 5.8 s rna differs from that of hela cells in two positions. six out of the seven interspecies differences are due to base substitutions. the other difference is due to the presence of an extra nucleotide, internally located, within the xenopus 5.8 s ...	1977	409998
the onset of immunoglobulin synthesis during the development of xenopus laevis.		1977	412718
synthesis and glycosylation of the mopc-46b immunoglobulin in kappa chain in xenopus laevis oocytes.		1977	413546
the effect of karbatox 75, a carbaryl insecticide, upon the development of tadpoles of rana temporaria and xenopus laevis.		1977	414939
events in the germ cell lineage after entry of the primordial germ cells into the genital ridges in normal and u.v.-irradiated xenopus laevis.		1977	591877
variability among laboratories in the occurrence of functional modification in the intertectal visual projection of xenopus laevis [proceedings].		1977	592182
ultrastructural study on hepatic melanin in xenopus laevis.	the livers of xenopus laevis, grouped by chronological age (0.5, 2 and 3 yrs), were studied electron microscopically. ultrastructurally most of the melanin granules in the mature female liver showed an internal structure similar to the melanin granules of the oocytes. the hepatic melanin granules of immature females and of all males were pleomorphic and failed to show the characteristic internal structure similar to those of the oocytes. the oocyte is the probable source of most of the hepatic m ...	1977	597850
abnormalities in the visual system of xenopus after larval optic nerve section.	one optic nerve was cut in a series of larval xenopus laevis; in approximately half of these the corresponding eye was also rotated. the resultant primary visual projections were mapped in the adult. although in most cases the projections were retinotopically normal, some of them were not. these abnormal projections were consistently associated with a very thin optic nerve which reached the tectum via the oculomotor route. animals with rotated eyes which developed retinotopically organised prima ...	1977	598434
comparison of cell division and cell sizes in normal embryos and lithium-induced exogastrulae of xenopus laevis.		1977	605749
electron microscopic studies of the developing amphibian thymus.	electron-microscopic studies of larval xenopus laevis thymus at three different stages of development are presented. studies of thymus from 5 and 8 day old larvae (ages when early thymectomy is performed) reveal a relatively undifferentiated rudiment composed of epithelial cells and lymphoid cell precursors. these findings are in marked contrast to ultrastructural observations of 30 day old larval thymus, where there exists a well defined corticomedullary differentiation with an abundance of sma ...	1977	612468
antibody-dependent cellular cytotoxicity in poikilotherms.	51cr-chromate labelled chicken red blood cells, treated with rabbit (anti-chicken red blood cell) serum, are lysed in vitro, in the absence of complement, by spleen cells from xenopus laevis, ambystoma mexicanum or lacerta viridis. optimal conditions for lysis by xenopus spleen cells were determined. the phenomenon seems homologous with antibody-dependent cellular cytotoxicity (adcc) mediated by mammalian or avian k cells. the phylogenetic significance of the finding is discussed.	1977	612470
researches on the development of xenopus laevis larvae fed on tubifex tubifex. i. presence of liposoluble vitamins in the lipid extract from tubifex worms.	vitamin e acetate (alpha-tocopheryl acetate) and related tocopherols, vitamin a acetate (dehydroretinyl acetate), vitamin a alcohol (retinol), and cholesterol were identified by thin-layer chromatography in the lipid extract from tubifex tubifex worms. compounds (perhaps vitamin d precursors, or seroidal substances) absorbing short wave uv light and/or reacting with antimony trichloride were also present but not identified. the results are discussed in relation to the growth, metamorphosis and p ...	1977	576033
differentiated protein synthesis with polysomes from petunia ovaries before fertilization.	polysomes from cross-, self- and unpollinated ovaries have been injected in xenopus laevis eggcells. the synthesised proteins have been identified by means of gel-electrophoresis. it appeared that few hours after pollination the protein pattern of the pollinated ovary has changed in comparison with that of unpollinated ones. however, in this early stage, there is only little difference found in the protein pattern of selfed and crossed ovaries. from 12 h after pollination and onwards, the differ ...	1977	24425225
inducing activity of fractionated microsomal material from thexenopus laevis gastrula stage.	the postmitochondrial supernatant fromxenopus gastrulae has been fractionated on sucrose gradients. part of the microsomal material was treated with edta, which dissociates most of the polysomal and monosomal material into ribosomal subunits. in addition, a series of pooled fractions from the edta treated gradients has been applied to discontinuous gradients in more concentrated sucrose to separate membranous material from the remaining microsomal components.pooled fractions from all gradients h ...	1976	28305523
competition between motor nerves in the establishment of neuromuscular junctions in striated muscles of xenopus laevis.	after sectioning one of the two nerves of the pauci-innervated pectoralis muscle of xenopus laevis, a sprouting of the intact nerve is observed in the denervated zone. on subsequent reinnvervation by the original nerve, dually innervated end-plates are found in which the quantal content of the responses to foreign nerve stimulation does not change significantly while that from the original nerve increases during the course of reinnervation. on the other hand, functional innervation from both the ...	1976	19604861
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
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
[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
nature of progesterone action on amino acid uptake by isolated full-grown oocyte of xenopus laevis.	l-leucine uptake into full-grown oocytes of xenopus laevis is a saturable process which is na+ dependent and presumably coupled to na+ gradient. our results indicate that progesterone (10(-6) m) blocks abruptly, around the germinal vesicle breakdown, the saturable transport of l-leucine. p-chloromercuribenzoate (10(-4) m) induces maturation and after a short lag of time strongly inhibits l-leucine uptake. cycloheximide prevents progesterone-induced maturation and permeability changes.	1976	1247560
in situ hybridization of "nick-translated" 3h-ribosomal dna to chromosomes from salamanders.	a technique is described for preparation of 3h-labelled dna by nick-translation employing deoxyribonuclease i and dna polymerase i. the labelled dna can be obtained in high yield with specific activities of 10(6) cpm/mug or more. ribosomal dna, isolated from ovaries of young xenopus laevis, and whole dna from plethodon cinereus were labelled in this way. the rdna was used for in situ hybridization to meiotic chromosomes from p. cinereus, p. vehiculum and p. dunni. autoradiographs of in situ hybr ...	1976	1248332
31p nuclear-magnetic-resonance studies on the developing embryos of xenopus laevis.	the concentrations of nucleoside triphosphate, inorganic phosphate and the yolk proteins, phosvitin and lipovitellin, have been monitored in living embryos of xenopus laevis by 31p nuclear magnetic resonance (nmr) spectroscopy. the nucleoside triphosphate levels remain relatively constant at about 3.5-4.5 nmol/embryo at least until the 'spontaneous movement' stage of development. by the swimming tadpole stage an inorganic phosphate resonance representing about 30 nmol/embryo becomes evident in t ...	1976	1248465
characterization of polysomes from xenopus liver synthesizing vitellogenin and translation of vitellogenin and albumin messenger rna's in vitro.	1. conditions are described for the isolation of polysomes from the liver of xenopus laevis. the method involves homogenization of liver in 0.2 m tris-hcl ph 8.5, treatment with 2% triton x-100 and subsequent sucrose density gradient fractionation of polysomes from a 10000 x g supernatant. 2. vitellogenin synthesis was induced in male xenopus liver by oestradiol treatment. polysomes were isolated and vitellogenin-synthesizing polysomes characterized by their association with monospecific 125 i- ...	1976	1248478
incorporation of (5-3h) uridine into ribonucleotide pools and rna during thyroxine-induced metamorphosis of xenopus laevis tadpoles.	incorporation of [3h] uridine into the ribonucleoside triphosphates utp and ctp, total rna, and nuclear and cytoplasmic rna was followed in xenopus laevis tadpole liver during thyroxine (t4)-induced metamorphosis. pool sizes of utp and ctp were found to remain unchanged, although turnover the ribonucleoside triphosphates was found to be greatly stimulated after 4 days of hormone treatment. the time course of labeling of the 40-s pre-rrna was very similar to that of utp in both thyreostatic and t ...	1976	1248666
progesterone biosynthesis and metabolism by ovarian follicles and isolated oocytes xenopus laevis.		1976	1252564
histogenesis of retina in the clawed frog with implications for the pattern of development of retinotectal connections.		1976	1252942
electron microscope analysis of amplifying ribosomal dna from xenopus laevis.		1976	1253845
in vivo and in vitro hormonal effects on the metabolism of immature oocytes of xenopus laevis.		1976	1254084
the ionic basis of the resting potential and a slow depolarizing response in rohon-beard neurones of xenopus tadpoles.	1. rohon-beard cells in the spinal cord of xenopus laevis tadpoles have been studied in animals 4-days to 2-weeks-old (nieuwkoop & faber, 1956, stages 45-49). these neurones have an unusually large resting membrane potential of -88 mv, in ringer solution containing 3-0 mm k+. 2. their resting potential (r..) depends on the concentration gradient of k+ across the cell membrane. these cells follow the prediction of the nernst equation for a k+-selective electrode, down to external k+ concentration ...	1976	1255512
low resistance junctions between mesoderm cells during development of trunk muscles.	1. electrical connexions between mesoderm cells have been examined during the formation of somites in xenopus laevis, bombina orientalis and ambystoma mexicanum. 2. in xenopus the resting potentials of presumptive myotome cells (-65 + 2 mv, s.e. of mean) and somite muscle cells (-65 +/- 0-6 mv s.e. of mean) were 40 mv, greater than dermatome cells (-25 +/- 0-6 mv, s.e. of mean). similar differences were found in bombina and ambystoma. 3. in all three species cells of the dermatome layer of the m ...	1976	1255515
iodination of xenopus laevis histone f2a1 in chromatin.	the reaction of calf thymus and xenopus laevis histones with radioactive iodine has been studied under various conditions that affect chromatin structure. all histones from both species contain at least one tyrosine residue and, in a denaturing solvent, all the the histones react with iodine. histone f2a1 has been studied in detail. calf thymus f2a1 is known to contain four tyrosyls and all four react with iodine. in high voltage paper electrophoresis, the tyrosine-containing peptides from calf ...	1976	1259948
protein incorporation by isolated amphibian oocytes. v. specificity for vitellogenin incorporation.	macromolecules of vitellogenin were sequestered by xenopus laevis oocytes 20-50 times (on a molar basis) more rapidly than other proteins tested. selectivity for vitellogenin did not appear to involve molecular size or charge. the km for vitellogenin incorporation was at least several orders of magnitude less than that for bovine serum albumin (bsa). at concentrations less than 10 mg-ml-1, bsa did not measurably compete with vitellogenin; a slight, apparent competition observed above a bsa conce ...	1976	1262394
morphology and kinetics of spermatogenesis in xenopus laevis.	the light microscopic characteristics of spermatogenic stages of the germ cell line in the anuran, xenopus laevis, have been described as they appear in both nuclear squash preparations and plastic embedded thick sections of intact testes. tritiated thymidine autoradiography was employed to unequivocally identify stages. using this methodology, it was determined that the premeiotic dna synthetic period occurs in a cell which is morphologically indistinguishable from a late secondary spermatogoni ...	1976	1262821
nucleotide sequences within the ribosomal ribonucleic acids of hela cells, xenopus laevis and chick embryo fibroblasts.		1976	1263259
oogenesis in xenopus laevis (daudin). iii. localization of negative charges on the surface of developing oocytes.		1976	1263301
genomic transcriptional activity and the structure of chromatin.	nucleic acid hybridisation has shown that micrococcal nuclease-derived chromatin subunits from the cells of xenopus laevis contain fragments of ribosomal 28s, 18s and 5s rnas within the population of 200 base-pair pieces of dna. subunits from cultured embryonic cells actively transcribing ribosomal rna contain only 70-74% of the cistrons present in undigested wild-type dna, while subunits from adult erythrocytes not active in rna transcription contain close to 90% of the ribosomal cistrons in na ...	1976	1264202
utrastructure of the cement gland of xenopus laevis.	to establish a morphological baseline for experimental studies of differentiation using the cement gland as a model, the following observations are added to those on record. the elongated cells of xenopus laevis cement glands have an internal organization displaying five distinct zones differing in structure and specialized function. the apical zone contains packed secretion vesicles apparently belonging to two different types. the transit zone appears to be devoid of major biosynthetic activity ...	1976	1267966
analysis of moving supernumerary limbs of xenopus laevis.		1976	1269564
polyadenylic acid-containing rna and its polyadenylic acid sequences newly synthesized in isolated embryonic cells of xenopus laevis.		1976	1269831
stereological analysis of the effects of 6-hydroxydopamine on the ultrastructure of the melanocyte-stimulating hormone cell of the pars intermedia of the pituitary of xenopus laevis.		1976	1269902
in vitro translation and estradiol-17beta induction of xenopus laevis vitellogenin messenger rna.	administration of estradiol-17beta to male xenopus laevis induces synthesis and secretion by the liver of the egg yolk precursor protein vitellogenin. rna extracted from livers of estradiol-17beta-treated xenopus laevis directs the synthesis of the entire 200,000-dalton vitellogenin monomer in a cell-free protein synthesizing system derived from rabbit reticulocytes. vitellogenin synthesized in vitro was isolated and quantitated by indirect immunoprecipitation and identified by comparison to aut ...	1976	1270438
the formation of the gonadal ridge in xenopus laevis. i. a light and transmission electron microscope study.	in xenopus laevis tadpoles, between stages 44 and 49 (nieuwkoop & faber, 1956), the primordial germ cells (pgcs) migrate from the dorsal mesentery of the gut to the site of the presumptive gd gonadal ridge. this paper describes the process at the light- and electronmicroscope levels. the pgcs in the mesentery, which at first are very large and yolk-laden, seem to lie entirely within the cellular matrix of the mesentery, although this is not obvious in light micrographs. where the pgcs bulge out ...	1976	1270975
the formation of the gonadal ridge in xenopus laevis. ii. a scanning electron microscope study.	this paper studies the surface morphology of the developing gonadal ridge in x. laevis between stages 44 and 49 (nieuwkoop & faber, 1956). during this period the primordial germ cells (pgcs) move laterally from the dorsal mesentery of the gut to the position of the presumptive gonadal ridge. as they do so the coelomic lining cells lateral to the mesentery differentiate into a specialized, longitudinally orientated band, stretching nearly the full length of the dorsal mesentery on each side. the ...	1976	1270976
synthesis of human placental lactogen in xenopus oocytes.	oocytes from xenopus laevis were injected with polysomes from normal human term placenta. synthesis of the protein hormone human placental lactogen (hpl) in the oocytes was demonstrated by specific immunoprecipitation with anti-hpl serum. analysis of the immunoprecipitates on sds-polyacrylamide gel revealed one peak, with a migration distance corresponding exactly to that of [14c]-radioacetylated hpl added as a marker. two days after injection the mrna was still able to direct the synthesis of h ...	1976	1272264
the effects of neuraminidase and protamine chloride on potential clamp parameters of the node of ranvier (xenopus laevis).	the effects of neuraminidase and protamine chloride on the ionic currents associated with step changes in membrane potential were studied. neuraminidase (a hydrolase which cleaves glycosidically bound sialic acid) had negligible effects on the permeability properties. the polycation protamine chloride decreased the sodium as well as the potassium currents. the sodium equilibrium potential decreased during the experiments which indicates a gain in internal sodium concentration. the analysis showe ...	1976	1274627
lipid composition of developing xenopus laevis embryos.	the total lipid content, amount of phospholipid, proportions of major polar and neutral lipid classes, and the overall fatty acid composition were examined in xenopus laevis embryos. no obvious differences were observed in any of the parameters between fertilization and hatching or between eggs produced by different females. the average lipid content per egg was 113 mug, 31.6 mug of which was phospholipid. the major phospholipids were phosphatidylcholine and sphingomyelin. the major fatty acids ...	1976	1276984
biochemical data on subtotally hypophysectomized xenopus laevis (daudin) adult specimens treated or not with prolactin.	xenopus laevis (daudin) adult specimens were submitted to hypophysectomy. although the operation resulted subtotal, it served the purpose of removing the prolactin-producing cells, whereby the involvement of endogenous prolactin in osmoregulation phenomena was excluded. in the operated animals treated with ovine prolactin the following metabolic parameters, which are closely dependent upon interrenal activity, were estimated: 1) intestine alkaline phosphomonoesterase activity (e.c. 3.1.3.1); 2) ...	1976	218525
[the tail of the tadpole of alytes obstetricans in organ culture with or without the addition of thyroxine. ultrastructural controls].	the tail of the alytes obstetricans tadpole, isolated at different stages (end of proclimax and climax), was studied in organ culture. the addition of thyroxine at a concentration of 5.10(-7) induces an involution slower than in vivo. besides, this regression is comparatively slower in similar conditions, than in xenopus laevis. this delay could be explained by the important volume and the very developed musculature of this anuran tail. ultrastructural controls reveal the form of the muscles, th ...	1976	139991
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
effect of xenopus laevis oocyte extract on supercoiled simian virus 40 dna: formation of complex dna.	a soluble cell-free extract derived from stage 6 xenopus laevis oocytes is described. from supercoiled simian virus 40 dna the extract produces nicked circles (having a single-strand scission), linear molecules of full unit size, shorter length fragments, and various forms of complex dna.	1976	174111
translation of oncogenic virus rna in xenopus laevis oocytes.		1976	175294
synthesis of the mitochondrial inner membrane in cultured xenopus laevis oocytes.	the purpose of this study was to investigate the contribution of mitochondrial and cytoplasmic protein synthesis to the biogenesis of cytochrome oxidase (ferrocytochrome c:oxygen oxidoreductase ec 1.9.3.1) and rutamycin-sensitive adenosine triphosphatase (atp phosphohydrolase ec 3.6.1.3) in cultured oocytes of the toad, xenopus laevis. x. laevis cytochrome oxidase was purified over 23-fold with respect to specific activity and over 29-fold with respect to specific heme a content from oocyte subm ...	1976	184093
dna-relaxing activity and endonuclease activity in xenopus laevis oocytes.	complex simian virus 40 dna produced by a soluble cell-free extract derived from stage 6 oocytes of xenopus laevis consists of fully relaxed circles (i.e., with no superhelical turns). an endonuclease and a dna-relaxing protein, either or both of which could be responsible for the relaxation of the complex dna, have been purified from the extract. the endonuclease(s) produces nicked circles (having a single-strand scission) and linear full-size molecules. the dna-relaxing protein is in the nucle ...	1976	188045
the structure of the mitochondrial cloud of xenopus laevis oocytes.	the ultrastructure of the mitochondrial cloud (balbiani body) of the pre-vitellogenic oocytes of xenopus laevis has been examined using transmission and stereoscan electron microscopy. examination of conventional thin sections confirm previous observations which suggest that the cloud consists essentially of many thousands mitochondria and numerous small vesicles; larger clouds, in oocytes greater than 200 mum in diameter, contain relatively more vesicles. using a standard electron microscope at ...	1976	188969
xenopus laevis 19s immunoglobulin. ultrastructure and j chain isolation.	electron microscopy examination of the 19s immunoglobulin of xenopus laevis revealed a hexameric structure with a central core. the molecules measured 360-430 a across the span of the arms and the average diameter of the central region was 140 a. a polypeptide, homologous to human j chain, was isolated by chromatography on deae-cellulose from the reduced and alkylated x. laevis hexameric macroglobulin. this polypeptide had a fast mobility in alkaline-urea gel electrophoresis, with distinct antig ...	1976	57921
diffusion of sodium in axoplasm of myelinated nerve fibre. potential clamp analysis.	the diffusion of sodium and lithium in the axoplasm of myelinated fibres of xenopus laevis was investigated. the sodium current associated with pulse steps was measured and the internal sodium concentration was calculated from these measurements with the constant field equation. the internal sodium concentration was increased either (i) by massive pulse trains or (ii) by applying a sodium containing solution to a cut end of the fibre. the time course of the concentration change was measured. equ ...	1976	61708
translation products of the alfalfa mosaic virus ribonuclei acids in wheat-germ cell-free system and in oocytes from xenopus laevis.		1976	64215
estimation of rdna content in xenopus laevis eggs during early development [proceedings].		1976	66019
mean velocity of optically detected intraaxonal particles measured by a cross-correlation method.	a method which uses by the cross correlation of optical signals is described for the determination of the mean velocity of somatopetally moving particles within nerve fibers. the method was validated by simulation experiments and by comparing the results with those obtained by averaging collections of velocities of individual particles. the significant contribution of the method is that it allows objective and rapid serial evaluation of mean particle velocity within individual nerve fibers with ...	1976	66091
surface immunoglobulins on xenopus laevis lymphocytes.		1976	3324
multiple forms of dna-dependent dna polymerase during early development and in somatic cells of xenopus laevis.	four distinct dna-dependent dna polymerase activities (dna polymerases i, ii, iii and iv according to the order of elution from a deae column) have been separated from extracts of unfertilized xenopus laevis eggs. the same activities, on the basis of their chromatographic properties, template specificities and sedimentation coefficients, have been found in embryos at least until the gastrula stage. on the other hand, xenopus kidney cells grown in culture, as well as full grown oocytes lack dna p ...	1976	9200
chemoreceptors of the lateral-line organs in intact, hypophysectomized, and prolactin-treated hypophysectomized xenopus laevis specimens.		1976	9241
translation of messenger rna specific for tyrosine aminotransferase in oocytes of xenopus laevis.		1976	10910
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