rna metabolism in primary cultures of xenopus laevis kidney cells. iii. processing of rrna precursor in growing and resting cells. 1978679983
scanning electron microscopy of aggregates of cells from normal embryos and lithium-induced exogastrulae of xenopus laevis. 1978685629
"delayed metamorphosis" (dm), a recessive subvital mutation affecting development and metamorphosis of xenopus laevis tadpoles. 1978685631
sequence organization of a cloned tdna met fragment from xenopus laevis.3.18 kb fragments of x. laevis dna coding for trna 1 met have been inserted into a lambda vector via hind iii termini and cloned in e. coli. the organization of one cloned fragment has been analyzed by restriction endonuclease digestion and rna-dna hybridization. from the distribution of sites for three enzymes, this fragment appears to be typical of the majority of x. laevis tandem tdna 1 met repeat units. evidence is presented to suggest that it contains two genes coding for trna 1 met and at ...1978688390
nucleosomes are assembled by an acidic protein which binds histones and transfers them to dna.the nucleosome subunits of chromatin are assembled from histones and dna by an acidic protein which binds histones. the nucleosome assembly protein has been identified and purified from eggs of xenopus laevis.1978692721
effects of estradiol on early messenger rna in male xenopus laevis liver.cytoplasmic rna isolated from male xenopus liver between 1 and 6 h of hormone treatment was separated into distinct classes by sepharose 4b chromatography. assay of the mrna activity of these rna species in the wheat germ cell-free system demonstrated 2 populations of mrna activity (peak 2 and peak 3). the activity of 1 population of mrna (peak 2) was inducible by estradiol while the other (peak 3) remained unaltered for at least 6 h. mrnas obtained by sepharose 4b chromatography were also trans ...1978699054
electron microscopic studies on the structure of motile primordial germ cells of xenopus laevis in vitro.primordial germ cells (pgcs) of xenopus laevis have been isolated from early embryos and kept alive in vitro, in order to study the structural basis of their motility, using the transmission and scanning electron microscope. the culture conditions used mimicked as closely as possible the in vivo environment of migrating pgcs, in that isolated pgcs were seeded onto monolayers of amphibian mesentery cells. in these conditions we have demonstrated that: (a) no significant differences were found bet ...1978702027
biochemical changes in developmentally retarded xenopus laevis larvae. i. the lens crystallin transition.premetamorphic tadpoles of xenopus laevis reared in water containing 0.01% propylthiouracil are developmentally retarded and metamorphosis is prevented. when uncrowded, they continue to grow to a giant size. moderate crowding leads to a slower rate of growth. thus morphologically premetamorphic tadpoles were produced with lens diameters appropriate to either normal premetamorphic, climactic or post-metamorphic animals. the lens crystallins of such tadpoles have been separated by immunoelectropho ...1978702033
oestrogen-induced cholesterol and fatty acid biosynthesis in xenopus laevis liver during vitellogenic response.1. oestradiol-17beta induces livers of xenopus laevis (south african clawed toad) to synthesize and secrete into the serum large quantities of the egg-yolk-protein precursor, vitellogenin. the peak of this response occurs 9-16 days after hormone treatment [dolphin, ansari, lazier, munday & akhtar (1971) biochem. j.124, 751-758]. it is now shown that 6 days after hormone treatment a 120-160-fold stimulation of the synthesis of cholesterol and fatty acid compared with control values occurred. 2. a ...1978708388
thymocyte stem cell inflow in xenopus laevis, after grafting diploid thymic rudiments into triploid tadpoles. 1978710665
rod-shaped particles in the plasma membrane of the mitochondria-rich cell of amphibian epidermis.a freeze-fracture study has revealed rod-shaped intramembranous particles on the plasma membrane p-face (cytoplasmic leaflet) of the mitochondria-rich cell (or flask cell) of xenopus laevis and rana ridibunda epidermis. such particles have previously been found in all other mitochondria rich cells examined by this technique, namely, the mr-cell of toad bladder epithelium, the dark cell of rat kidney collecting tubule, and the flask cell of xenopus kidney collecting tubule. these particles are as ...1978717800
poly(adenosine diphosphate ribose) synthesis by isolated nuclei of xenopus laevis embryos: in vitro elongation of in vivo synthesized chains. 1978718695
nucleosome structure of xenopus oocyte amplified ribosomal genes.the chromatin subunit or nucleosome structure of the amplified, extrachromosomal, ribosomal genes of oocytes of the amphibian xenopus laevis has been investigated during stages of growth when these genes are markedly changing their rates of transcriptional activity. nucleic acid hybridization studies involving micrococcal nuclease derived monomer nucleosome dna fragments and purified ribosomal rnas indicate that the apparent degree of accessibility of the ribosomal genes to short-term nuclease h ...1978718864
an estrogen receptor from xenopus laevis liver possibly connected with vitellogenin synthesis.this paper describes an estrogen receptor which is found in both the nucleus and cytoplasm of liver cells from male xenopus laevis, and which seems to be involved in the induction of vitellogenin synthesis. it has a high affinity for estradiol (kd = 0.5 x 10(-9) m), and the affinities of various steroids for the receptor correlate well with their ability to induce vitellogenin synthesis. it sediments at 3.5s at 0 degrees c in 0.5 m kci. the rate of sedimentation is unaffected by incubation at 20 ...1978719747
amino acid and thyroid hormone transport systems in xenopus laevis. 1978720757
latency-relaxation in single muscle fibres.1. latency relaxation and twitch tension were recorded simultaneously in single isolated muscle fibres of xenopus laevis. 2. during low frequency (0.6 or 1 pulse/sec) repetitive stimulation, three successive phases of twitch tension were observed: negative staricase (a slight drop in tension), positive staircase (about 15% increase in tension) and fatigue. at the same time the amplitude of latency relaxation decreased monotonically, and near the peak of positive staircase, the amplitude decrease ...1978722520
the force-velocity relation of isolated twitch and slow muscle fibres of xenopus laevis.1. a study has been made of the relation between force and speed of shortening, or lengthening, in isolated twitch and slow muscle fibres, dissected from the iliofibularis muscle of xenopus laevis. both after-loaded and quick-release contractions were studied. twitch fibres were stimulated electrically to give tetanic contractions (5-20 degrees c); slow fibres were activated by a rapid change to solutions with high k concentration (30-75 mm; experiments at 21-24 degrees c).2. the velocity of slo ...1978722588
action potentials of embryonic dorsal root ganglion neurones in xenopus tadpoles.1. several classes of action potentials can be distinguished in dorsal root ganglion cells, studied by intracellular recording techniques in xenopus laevis tadpoles 4.5--51 days old. the ionic basis of the action potential was investigated by changing the ionic environment of the cells and applying various blocking agents. 2. the ca2+-dependent action potential is a plateau of relatively long duration (mean 8.7 msec). it is unaffected by removal of na+ but blocked by mm quantities of co2+. it is ...1978722591
isolation of discrete repetitive sequence classes from xenopus dna by high temperature reassociation.sequences that did or did not reassociate at 75 dagrees c (stable and unstable, respectively) were isolated from total repetitive xenopus laevis dna. sequence complexities or frequencies were determined by self (minicot) or dna excess (slave minicot) reassociations at 60 degrees c. stable sequences were five times shorter and four times more frequent than unstable sequences. reassociations at 75 degrees c or at 50 degrees c were used to establish apparent sequence frequencies at these criteria. ...1978724515
induction of vitellogenin synthesis in xenopus laevis tadpoles.oestradiol induces vitellogenin synthesis in vitro in liver taken from xenopus laevis tadpoles that are in late metamorphosis. inducibility first appears at the end of prometamorphosis, and the response to oestradiol increases during the completion of metamorphosis. oestradiol continuously present during development does not influence the stage at which tadpole liver becomes inducible. it seems that the acquisition of inducibility is part of the normal development of the liver, and independent o ...1978729959
[sem analysis of mass isolated germinal vesicles of xenopus laevis oocytes]. 1978734349
patterns of synthesis and accumulation of heterogeneous rna in lampbrush stage oocytes of xenopus laevis (daudin). 1978738528
the chemical receptive mechanism in the lateral-line organ.stimulating effects of various mono- and divalent cations on the lateral-line organ were theoretically analysed by use of the site binding chemical adsorption model with the principle of "hard and soft acids and bases." a linear relation between the softness parameter and the logarithmic value of the intrinsic association constant was obtained for the cations of na, k, tl, ag, ca, mg, and cd. the order of effectiveness of these cations agreed with that of the intrinsic association constant. usin ...1978739683
three different molecular weight forms of the vitellogenin peptide from xenopus laevis. 1978743270
a novel recombinant of phage lambda and a conserved 3000-base-pair fragment of xenopus laevis ribosomal deoxyribonucleic acid produced by restriction with endonucleases hind iii/bami [proceedings]. 1978744396
[the influence of the eye on the regeneration of the lens in xenopus laevis larvae]. 1978747082
the effect of exposure to black background and to alpha-msh on black-white background preference in the amphibian xenopus laevis (daudin). 1978750347
an investigation of de novo protein synthesis in the south african clawed frog, xenopus laevis. 1978751832
patterns of cell proliferation in the retina of the clawed frog during development.quantitative assays of the spatial pattern of cell production in the developing retina of xenopus have been made using 3h-thymidine labelling and colcemid blockade of mitosis. reconstructions were made from serial sections showing the position of every mitotic figure in the retina. after stage 54 the number of mitotic figures decreases at the dorsal margin of the retina and increases at the ventral margin. the ventral:dorsal ratio of mitoses reaches 10:1 by metamorphosis. density of mitotic figu ...1979759449
influences of thyroxine on cell proliferation in the retina of the clawed frog at different ages.the change in spatial pattern of retinal cell production that occurs after midlarvae stages in xenopus is shown to occur because of a greater proliferative response to thyroxine in the ventral than in the dorsal margin of the retina. the asymmetry of retinal cell production is not caused by a dorsoventral difference in the duration of the mitotic cycle. it is concluded that the asymmetry is due to differences in the number of proliferative cells in different parts of the retinal margin.1979759450
patterns of cell proliferation in the developing retina of the clawed frog in relation to blood supply and position of the choroidal fissure.the pattern of retinal vasculative is described and the position at which cell proliferation at the ventral retinal margin is maximal was shown to be at the point of entry of the ventral blood vessels. to test whether there is a causal relation between retinal blood supply and retinal cell production, surgical inversion of the eye, transplantations and excisions of retina were done to change the pattern of retinal vasculature. the growth pattern of inverted eyes was normal with respect to the in ...1979759451
photoreceptor outer segment development: light and dark regulate the rate of membrane addition and loss.the rate of membrane addition during outer segment development and the onset of membrane loss through shedding was evaluated for xenopus laevis embryos reared at 23 degrees c in constant light (ll), constant darkness (dd), and cyclic light (12 hr l/12 hr d; ld). embryos were placed under these lighting conditions 1 day following fertilization at open neural plate stages and were sampled each day for 9 days. rod and cone outer segments were present in each treatment group on day 3 of development. ...1979761968
ultrastructural development of rohon-beard neurons: loss of intramitochondrial granules parallels loss of calcium action potentials.we have examined the ultrastructure of the cell body of a vertebrate spinal neuron, the rohon-beard cell of xenopus laevis, at four stages during its development (nieuwkoop and faber stages: 22, 29/30, 37/38 and 42). at this time it has attained its electrical excitability and the action potential mechanism in the cell body is maturing through a sequence of stages in which the inward current is carried by ca++ (stages 20-25), later by ca++ and na+ (stages 25-40), and finally by na+ (stages 40-51 ...1979762270
remodelling of optic nerve myelin sheaths and axons during metamorphosis in xenopus laevis.whole mounts and transverse sections of xenopus optic nerves were examined with the light and electron microscopes before, during, and after metamorphosis. in stage 52--58 tadpoles, almost all myelin sheaths were circular in transverse sections. early in metamorphosis (stages 60--61) large redundant myelin loops surrounded many large axons in central regions of the nerve. the loops subsequently were broken down into ovoids and lamellar segments that remained mostly within oligodendrocytes. these ...1979762287
thyroid hormone induces competence for oestrogen-dependent vitellogenin synthesis in developing xenopus laevis liver. 1979763351
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 ...1976765353
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 ...1976775008
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 ...1976776610
changes in trna nucleotidyl transferase activity during embryonic development of xenopus laevis. 1976776635
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 ...1976782719
the molecular basis for length heterogeneity in ribosomal dna from xenopus laevis. 1976787539
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 ...1976791498
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 ...1976792878
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 ...1976797285
humoral antibodies to soluble antigens in larvae of xenopus laevis. 1975804375
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 ...1975805666
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 ...1975807242
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 ...1975807332
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 ...1975810539
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 ...1975810623
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 ...1975817275
[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 ...1976819172
[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.1976819174
[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 ...1976821641
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 ...1975824129
[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.1976825259
[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.1976825283
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 ...1976826380
[ 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.1976827362
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 ...1976827598
correlation between the cell cycle in the neurectoderm and differentiation during the early development of xenopus laevis. 1. budr sensitivity during 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 ...1976829417
existence of ultraviolet-labile germ cell determinant in unfertilized eggs of xenopus laevis and its sensitivity. 1977832771
the effects of biogenic amines on carbohydrate metabolism in xenopus laevis daudin. 1977832822
in situ effects of s1 endonuclease (neurospora crassa) on pachytene chromatin of xenopus laevis females at metamorphosis. 1977837986
the visual pigment and vitamin a of xenopus laevis embryos, larvae and adults. 1977838004
evidence for polarizing zone in the limb buds of xenopus laevis. 1977838122
ultrastructural observations on cortical endoplasmic reticulum and on residual cortical granules in the egg of xenopus laevis. 1977838127
accumulation of mitochondrial dna during oogenesis in xenopus laevis. 1977838132
ribosomal rna synthesis in the eastern north-american newt, notophthalmus viridescens.ribosomal rna (rrna) synthesis, the initiation of which is an early major event during the transformation of iris into lens in the newt, was characterized in the tvi cell-line derived from the eastern north-american newt notophthalmus viridescens. employing the technique of polyacrylamide gel electrophoresis, molecular-weight measurements were made on newt rrnas using xenopus laevis and e. coli rrnas as standards. the molecular weights of n. viridescens 28s and 18s rrna were found to be 1.4 x 10 ...1977838209
changes in the cell coat at the onset of gastrulation in xenopus laevis embryos.four developmental stages of xenopus laevis embryos were fixed in standard electron microscopic fixatives with 1% lanthanum nitrate added. this treatment reveals a lanthanum staining material (lsm) on the cell surface and in extracellular spaces. morula and blastula stage cells have a small amount of lsm; in blastulae, 3 +/- 3 sd % of the cell surface is coated with lsm. in early gastrulae, 29 +/- 6 sd % of the cell periphery is covered with lsm. in late gastrulae, 82 +/- 13 sd % of the cell per ...1977839183
resolution of parameters in the equivalent electrical circuit of the sodium transport mechanism across toad amphibian epithelia, amiloride reduces net sodium transport by hindering the entry of sodium to the active transport mechanism, that is, by increasing the series resistance (rser). theoretically, therefore, analysis of amiloride-induced changes in potential differences and short-circuit current should yield numerical estimates of all the parameters in the equivalent electrical circuit of the sodium transport mechanism. the concept has been explored by analysis of such changes in toad skins (x ...1977839526
transcription of specific genes in isolated nuclei by exogenous rna polymerases.mouse plasmacytoma (mopc) 460 cells contain two chromatographic forms of rna polymerase iii (iiia and iiib) in addition to the major class i and ii rna polymerases. nuclei isolated from these cells actively synthesize rna. among the discrete transcription products observed are the 5s and 4.5s rnas and additional low molecular weight rna species (approximately 5.8s, 6.3s, and 6.6s in size). the 4.5s rnas appear to be trna precursors since they can be converted in vitro to 4s rnas. studies with al ...1977844100
size of ribosomal dna repeating units in xenopus laevis: limited individual heterogeneity and extensive population polymorphism. 1977845941
slow action of ca on myelinated nerve fibres of xenopus laevis.single myelinated nerve fibres were isolated and the nodal currents were recorded with potential clamp technique. rapid solution changes were performed by use of a recording chamber so shaped that it had a minimal dead space. a volume ten times larger than the dead space flowed past the node within about 20 ms. the half-time of the change in na current (ina)amplitude associated with changes between solutions of different [na]:s was 100-150 ms, whereas the half-time of the change in ina associate ...1977848308
studies on the biosynthesis, assembly and secretion of vitellogenin, an oestrogen-induced multicomponent protein.1. the process by which the egg-yolk protein precursor vitellogenin is biosynthesized, assembled and secreted by xenopus laevis (south african clawed toad) liver was studied. it was previously shown in other laboratories that vitellogenin contains the two egg-yolk proteins lipovitellin (mol.wt. 140 000) and phosvitin (mol.wt. 35 000). 2. evidence is presented which shows that xenopus liver microsomal fractions synthesize precursors of vitellogenin. these precursors were solubilized from the memb ...1977849274
modifications by light of synaptic density in the inner plexiform layer of the toad, xenopus laevis. 1977849751
translation and distribution of rabbit globin mrna in separated cell types of xenopus laevis gastrulae. 1977849804
rna synthesis in isolated nuclei of xenopus laevis emproyos.nuclei were isolated from tailbud embryos of xenopus laevis and their rna synthetic activity was studied. the activity was sensitive to actinomycin d, and required the presence of all four ribonucleotide triphosphates and a divalent cation (mg2+ or mn2+). the effect of the divalent cation varied depending on the presence of 0.4 m kcl: in its absence more rna was synthesized with mg2+ than with mn2+, but in its presence the situation was reversed. about 50% of the rna synthesized was sensitive to ...1977856273
lectin binding to dissociated cells from two species of xenopus embryos.1. fluorescein isothiocyanate-conjugated concanavalin a (f-cona) and soy bean agglutinin (f-sba) bind to the surface of edta-dissociated cells from blastula and gastrula stage xenopus laevis and x. mulleri embryos. 2. binding of these lectins is abolished by appropriate haptens (alpha-methyl-d-mannopyranoside for f-cona and 2-acetamido-2-deoxy-d-galactose for f-sba). 3. gastrula stage cells show a clustering or capping of lectin binding sites not shown by blastula stage cells. 4. at least for f- ...1977856477
effect of partial hepatectomy on the interrenal tissues of xenopus laevis (daudin).partial hepatectomy was carried out on xenopus laevis to investigate its influence on the endocrine system. in addition to other endocrine effects, a marked hypertrophy and stimulation of the interrenal gland was observed. activated cells contain mitochondria with extended and irregularly coiled tubules embedded in a low electron dense matrix. hepatectomy induces two phases of proliferation [3 and 35 days postoperative (p.o.)]. after 106 days p.o. giant mitochondria possessing narrow and closely ...1977858162
progesterone-induced dna polymerase activity in full-grown oocytes of xenopus laevis (1).dna polymerase activity increases in full-grown oocytes of xenopus laevis during in vitro progesterone-induced maturation. this increase is inhibited by cycloheximide. the presence of the oocyte's nucleus (germinal vesicle) seems essential for the induction of this increase: in previously enucleated oocytes, the level of dna polymerase activity does not change during progesterone treatment. furthermore, a new form of dna polymerase is detectable by deae chromatography in in vitro matured oocytes ...1977859007
inhibitor of ribosomal rna synthesis in xenopus laevis embryos. vi. occurrence in mature oocytes and unfertilized eggs. 1977863107
persistence of oocyte amplified rdna during early development of xenopus laevis eggs. 1977863108
histone mrna in xenopus laevis ovaries: identification of the h4 messenger.rna extracted from ovaries of adult xenopus laevis and introduced into a wheat germ cell-free system, directs the synthesis of polypeptides co-electrophoresing with all five histones. by frationation of total ovary rna through sephadex g-200 and polyacrylamide gel, rna was isolated that is translated into histones 4 (h4) only. in addition, this rna labelled in vitro with [i125] hybridizes to a restriction fragment of cloned sea urchin dna known to contain the h4 gene.1977866192
a stereological approach to the study of neural organogenesis in xenopus laevis.stereological methods are applied to the study of structural changes undergone, during neurulation, by the neuroepithelium of early embryos of xenopus laevis. in light microscopy, we evaluate: the section area of the neuroepithelium, the nucleocytoplasmic ratio, the volume fraction of the intercellular spaces, of the nuclei and of the cytoplasm. in electron microscopy, the volumetric density and the surface ratio of mitochondria as well as the surface density of the endoplasmic reticulum are mea ...1977869225
lengths and patterns of transcriptional units in the amplified nucleoli of oocytes of xenopus laevis.transcriptionally active chromatin from peripheral amplified nucleoli of lampbrush-chromosome stage oocytes of xenopus laevis was dispersed and spread in various solutions of low salt concentrations (including some with additions of detergents) and examined by electron microscopy. nucleolar material from oocytes of animals with normal (2-nu) and mutant (1-nu) genetical constitution of nucleolus organizers was compared. histograms showing the distributions of the length of matrix units, apparent ...1977870292
an autoradiographic analysis of nucleic acid synthesis in the presumptive primordial germ cells of xenopus laevis.microinjection of [3h]thymidine into xenopus laevis embryos between late blastula (stage 10) and early tadpole (stage 44) showed that the presumptive primordial germ cells synthesis dna between stages 10-33. the percentage of labelled cells was highest between stages 10 and 16, declined sharply between stages 22 and 26 and rose again between stages 26 and 33. the fluctuations in the labelling patterns together with increase in the number of presumptive primordial germ cells and direct observatio ...1977870589
some morphogenetic features of the adenohypophysical primordium of early xenopus laevis tadpoles.the adenohypophyses of xenopus laevis tadpoles at developmental stages 20 to 46 (nieuwkoop and faber, 1956) were studied. from its first appearance at about stage 20 to 21, the adenohypophysial primordium passes through four morphogenetic phases, each characterized by internal events. the first phase (stages 20 to about 33/34) is characterized by extensive proliferation of the primordium. during the second phase (stages 33/34 to about 37/38), the growth of the primordium is arrested. this arrest ...1977872195
sequential changes in the structure and function of hepatocytes in estrogen-treated xenopus laevis males. 1977872992
very long-lived messenger rna in ovaries of xenopus laevis. 1977873053
differential accumulation of two size classes of poly(a) associated with messenger rna during oogenesis in xenopus laevis. 1977873054
grafting analysis of the periodic albino mutant of xenopus laevis. 1977873057
biochemical research on oogenesis: oocytes of xenopus laevis synthesize but do not accumulate 5s rna of somatic type. 1977873059
changes in neuromast chemosensitivity in xenopus laevis kept under various environmental conditions. 1977874416
changes in protein phosphorylation accompanying maturation of xenopus laevis oocytes. 1977885290
purification and characterization of xenopus laevis vitellogenin messenger rna. 1977885849
magnesium deficiency in embryos of xenopus laevis.embryos of xenopus laevis reared in media with various low (less than or equal to 10(-5) m) magnesium ion concentrations will exhibit differing degrees of a potentially lethal magnesium starvation syndrome depending on the ion concentration and rearing temperature. the higher the rearing temperature or the lower the magnesium ion content of the medium the more severely the syndrome will be expressed. (normal development can be expected at temperatures 13-30 degrees c and magnesium ion concentrat ...1977886266
the effect of concanavalin-a on the reaggregation of cells dissociated from xenopus laevis early embryos.the effects of concanavalin-a on the reaggregation and sorting of cells from xenopus laevis early embryos have been studied. the results suggest that at high concentrations, concanavalin-a can prevent reaggregation.1977891827
lens regeneration from cornea in tail ectopic eyes of xenopus laevis tadpoles. 1977891882
transport of different rna species from the nucleus to the cytoplasm in xenopus laevis neurula cells. 1977892232
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