Publications
| Title | Abstract | Year Filter | PMID(sorted descending) Filter |
|---|
| 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 |
| 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 |
| 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 |
| thyroid hormone induces competence for oestrogen-dependent vitellogenin synthesis in developing xenopus laevis liver. | 1979 | 763351 | |
| 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 ... | 1979 | 762287 |
| 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 ... | 1979 | 762270 |
| 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. ... | 1979 | 761968 |
| 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 ... | 1979 | 759451 |
| 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. | 1979 | 759450 |
| 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 ... | 1979 | 759449 |
| an investigation of de novo protein synthesis in the south african clawed frog, xenopus laevis. | 1978 | 751832 | |
| the effect of exposure to black background and to alpha-msh on black-white background preference in the amphibian xenopus laevis (daudin). | 1978 | 750347 | |
| [the influence of the eye on the regeneration of the lens in xenopus laevis larvae]. | 1978 | 747082 | |
| 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]. | 1978 | 744396 | |
| three different molecular weight forms of the vitellogenin peptide from xenopus laevis. | 1978 | 743270 | |
| 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 ... | 1978 | 739683 |
| patterns of synthesis and accumulation of heterogeneous rna in lampbrush stage oocytes of xenopus laevis (daudin). | 1978 | 738528 | |
| [sem analysis of mass isolated germinal vesicles of xenopus laevis oocytes]. | 1978 | 734349 | |
| 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 ... | 1978 | 729959 |
| 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. ... | 1978 | 724515 |
| 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 ... | 1978 | 722591 |
| 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 ... | 1978 | 722588 |
| 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 ... | 1978 | 722520 |
| amino acid and thyroid hormone transport systems in xenopus laevis. | 1978 | 720757 | |
| 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 ... | 1978 | 719747 |
| 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 ... | 1978 | 718864 |
| poly(adenosine diphosphate ribose) synthesis by isolated nuclei of xenopus laevis embryos: in vitro elongation of in vivo synthesized chains. | 1978 | 718695 | |
| 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 ... | 1978 | 717800 |
| thymocyte stem cell inflow in xenopus laevis, after grafting diploid thymic rudiments into triploid tadpoles. | 1978 | 710665 | |
| 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 ... | 1978 | 708388 |
| 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 ... | 1978 | 702033 |
| 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 ... | 1978 | 702027 |
| 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 ... | 1978 | 699054 |
| 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. | 1978 | 692721 |
| 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 ... | 1978 | 688390 |
| "delayed metamorphosis" (dm), a recessive subvital mutation affecting development and metamorphosis of xenopus laevis tadpoles. | 1978 | 685631 | |
| scanning electron microscopy of aggregates of cells from normal embryos and lithium-induced exogastrulae of xenopus laevis. | 1978 | 685629 | |
| rna metabolism in primary cultures of xenopus laevis kidney cells. iii. processing of rrna precursor in growing and resting cells. | 1978 | 679983 | |
| effects of 5-bromodeoxyuridine on development of mauthner's neuron and neural retina of xenopus laevis embryos. | bromodeoxyuridine (brudr) injected into xenopus embryos at stages before, during or after the last period of dna synthesis in mauthner's neurons had no serious effect on differentiation of mauthner's neurons. however, the brudr caused widespread cell degeneration in the central nervous system. the action of brudr on retinal neuronal differentiation depended on dose and stage of infection. at all doses (0.005-0.9 microgram per injection), and all stages (22-29), the main effect was retinal cell d ... | 1978 | 678990 |
| studies on the liver of xenopus laevis. iii. the ultrastructure and the glycogen content of the developing liver. | 1978 | 677479 | |
| stimulated dna synthesis in frog nuclei by cytoplasmic extracts of temperature-sensitive mammalian cells. | cytoplasmic extracts of proliferating cells stimulate dna synthesis in isolated nuclei of xenopus laevis liver. when tested by the same assay, cytoplasmic extracts of resting cells are completely inactive. when cytoplasmic extracts are prepared from cell cycle-specific temperature-sensitive mutants arrestd in the g1 phase of the cell cycle by the nonpermissive temperature, they also fail to stimulate dna synthesis in frog nuclei. the results indicate that, to stimulate dna synthesis in isolated ... | 1978 | 675253 |
| the induction of triploidy by pressure in xenopus laevis. | 1978 | 675141 | |
| preparation and isolation of covalently closed circular rdna molecules from dna of xenopus laevis. | we describe a method leading to the formation of closed circles of rdna starting from total dna of xenopus laevis. linear dna molecules were digested with exonuclease 3 and self-annealed. open circles were enriched and covalently closed by the simultaneous use of polynucleotide kinase, dna polymerase and polynucleotide ligase. closed circles of rdna1 were shown to be alkali-resistant, to have higher density than linear molecules in cesium chloride density gradients containing ethydium bromide, a ... | 1978 | 673851 |
| freeze-fracture of xenopus laevis kidney: rod-shaped particles in the canalicular membrane of the collecting tubule flask cell. | 1978 | 671575 | |
| mapping of mitochondrial 4 s rna genes in xenopus laevis by electron microscopy. | 1978 | 671539 | |
| somite abnormalities caused by short heat shocks to pre-neurula stages of xenopus laevis. | this paper describes the small disturbances, in the regular pattern of the somites and the fissures between them, that are seen following short (around 300 s) heat shocks at 37.5 degrees c delivered to pre-neurula stages of xenopus laevis. affected groups of cells still finally differentiate as somite muscle, but the normally precise spatio-temporal sequence in which they move beforehand to give rise to the actual pattern of somite blocks, is disrupted. examination of the position and sizes of p ... | 1978 | 670864 |
| anatomical mapping of retino-tectal connections in developing and metamorphosed xenopus: evidence for changing connections. | neural connections between the eye and optic tectum in xenopus laevis were anatomically traced by observing the tectal location of wallerian degeneration after discrete retinal lesion. these retinotectal connections were mapped in postmetamorphic frogs and tadpoles at stage 51, the stage at which retinal axons have grown into about the rostral one-half of the tectum. the course of the experimental degeneration was the same in frogs and tadpoles, but degeneration proceeded faster in the younger a ... | 1978 | 670862 |
| the nucleotide sequences of 5.8-s ribosomal rna from xenopus laevis and xenopus borealis. | 1. the nucleotide sequence of 5.8-s rrna from xenopus laevis is given; it differs by a c in equilibrium u transition at position 140 from the 5.8-s rrna of xenopus borealis. 2. the sequence contains two completely modified and two partially modified residues. 3. three different 5' nucleotides are found: pu-c-g (0.4) pc-g (0.2) and pg (0.4). 4. the 3' terminus is c not u as in all other 5.8-s sequences so far determined. 5. the x. laevis sequence differs from the mammalian and turtle sequences by ... | 1978 | 668689 |
| lack of effect of blood-volume expansion on short-circuit current across an isolated toad skin incorporated in the circulation of a rat. | 1. evidence for the existence of 'natriuretic hormone' resides, in part, in the demonstration that blood volume expansion in the dog is followed by a transient fall in short-circuit current (scc) across a frog skin incorporated within its circulation. 2. we have attempted to confirm this effect in the rat, with a toad skin (xenopus laevis) incorporated within the circulation. the skins, bathed in whole rat blood, displayed low scc; skins bathed in 'mammalian' ringer solution displayed equally lo ... | 1978 | 668266 |
| characterization of globin mrna from xenopus laevis. | a 9s polyadenylated mrna was isolated from 'xenopus laevis reticulocytes and purified by sedimentation and oligo-dt-cellulose chromatography. the size of this rna estimated in denaturing agarose gels was 2.2 x 10(5) daltons. 9s polyadenylated mrna hydridized to total dna with a cot1/2 of 3.8 x 10(3). | 1978 | 667964 |
| the transcription map of mouse mitochondrial dna. | nine transcripts complementary to mouse l cell mitochondrial dna have been detected, sized and mapped to restriction fragments using the method of berk and sharp (1977). rna isolated from l cell mitochondria was hybridized to 32p-labeled, cloned l cell mitochondrial dna restriction fragments in 70% formamide under conditions 5 degrees c above the melting temperature of the dna-dna duplex, but approximately 15 degrees c below the melting temperature of the rna-dna duplex. the heteroduplexed mater ... | 1978 | 667930 |
| the pseudouridine contents of the ribosomal ribonucleic acids of three vertebrate species. numerical correspondence between pseudouridine residues and 2'-o-methyl groups is not always conserved. | the pseudouridine contents of the rrna species of hela cells, mouse l-cells and xenopus laevis cultured kidney cells were examined. pseudouridine, like 2'-o-methylation, was found to occur relatively frequently in each of the high-molecular-weight rrna species. however, the numerical data do not support the idea that there is a general one-to-one relationship between pseudoridine residues and 2'-o-methyl groups in vertebrate rrna. | 1978 | 666737 |
| induced formation of asters and cleavage furrows in oocytes of xenopus laevis during in vitro maturation. | we have previously reported that injection of purified basal bodies or sperm into unfertilized eggs of xenopus laevis induced the formation of asters and irregular cleavage furrows. fully grown oocytes were found to be unable to form asters or cleavage furrows. in this paper we show that the oocyte acquires the ability to form asters upon basal body injection at the time of germinal vesicle breakdown during in vitro maturation. our evidence indicates that aster formation requires progesterone-st ... | 1978 | 660144 |
| rapid accumulation of vitellogenin messenger rna during secondary estrogen stimulation of xenopus laevis. | accurate quantitation of low concentrations of vitellogenin mrna by hybridization to vitellogenin cdna allows analysis of the accumulation of new vitellogenin mrna sequences throughout secondary estrogen stimulation. administration of a secondary injection of estradiol-17 beta to male xenopus laevis which have been withdrawn from estrogen for 60 days results in synthesis of complete vitellogenin mrna molecules in as little as 1 h after restimulation. vitellogenin mrna accumulates at a rate of 13 ... | 1978 | 659432 |
| relative amounts of newly synthesized poly(a)+ and poly(a)- messenger rna during development of xenopus laevis. | 1978 | 658590 | |
| large scale isolation of nuclei and nucleoli from vitellogenic oocytes of xenopus laevis. | a new method is described which allows the purification of large quantities of nuclei (germinal vesicles) from xenopus laevis vitellogenic oocytes of different developmental stages. from the isolated nuclei, purified nucleoli were obtained. the isolated germinal vesicles are transcriptionally active showing endogenous rna polymerase activity as well as a high level of activity with an exogenously added template. | 1978 | 657930 |
| an autoradiographic analysis of the retinal projection in the frog xenopus laevis: new observations in an anuran visual projection. | 1978 | 656924 | |
| effect of the nonionic detergent triton x-100 on sodium permeability of the myelinated nerve fibre of xenopus laevis. | the effect of the nonionic detergent triton x-100 (tx-100) on the na permeability (pna) properties of the nodal membrane in myelinated nerve fibres of xenopus laevis was analysed with potential clamp technique. application of tx-100 caused a rapid initial decrease in pna that was reversible at wash out as well as a slow irreversible block. both effects dependend on [tx-100] and duration of exposure. the reversible reduction of pna at the steady state was 50% at 40--60 micrometer tx-100. the slop ... | 1978 | 654934 |
| [transfer of behavior patterns through transplantation of systems of neuroanatomic structures in amphibian larvae. ii. xenoplastic transplantation of hind brain systems between xenopus laevis (daud.) as well as hymenochirus boettgeri (torn.) and triturus vulgaris]. | by replacing parts of the neural plate (prospective medulla oblongata) of triturus vulgaris by neural ectoderm of xenopus laevis larval chimaeras were obtained, which showed donorlike rhythmical movements of distinct parts of the visceral musculature according to the place of implantation. especially the branchial region with its external gills showed rhythmical movements and is the special object of this investigation. | 1978 | 654606 |
| differently sized rdna repeating units of xenopus laevis are arranged as internally homogeneous clusters along the nucleolar organizer. | the organization of differently sized genes coding for rrna in xenophus laevis has been investigated by partial ecori or hindiii digestion. the electrophoretic patterns obtained revealed that most adjacent repeating units are equally sized. this conclusion is in agreement with a previous suggestion that the nucleolar organizer is made up of internally homogeneous blocks of rrna genes. | 1978 | 652524 |
| mapping of the xenopus laevis 5.8s rdna by restriction and dna sequencing. | the location of the 5.88 rdna within the internal transcribed spacer has been found by restriction and sequence analysis. these analyses indicate the deletion of a dinucleotide from the known rrna sequence. regions to the 5' and 3' of the gene contain both uncommon sequences and palindromic structures which might provide potential control points. a secondary structure model is suggested for the 5.8s rrna incorporating the flanking sequences. | 1978 | 652517 |
| estradiol-binding protein in the nucleus of male xenopus laevis liver. | 1978 | 651871 | |
| neural transduction in xenopus laevis lateral line system. | 1. the process of neural excitation in hair cell systems was studied in an in vitro preparation of the xenopus laevis (african clawed toad) lateral line organ. a specially designed stimulus chamber was used to apply accurately controlled pressure, water movement, or electrical stimuli, and to record the neural responses of the two afferent fibers innervating each organ or stitch. the objective of the study was to determine the characteristics of the neural responses to these stimuli, and thus ga ... | 1978 | 650276 |
| nuclear surface complex as observed with the high resolution scanning electron microscope. visualization of the membrane surfaces of the neclear envelope and the nuclear cortex from xenopus laevis oocytes. | the nuclear envelope and associated structures from xenopus laevis oocytes (stage vi) have been examined with the high resolution scanning electron microscope (sem). the features of the inner and outer surfaces of the nuclear surface complex were revealed by manual isolation , whereas the membranes facing the perinuclear space (the space between the inner and outer nuclear membranes) were observed by fracturing the nuclear envelope in this plane and splaying the corresponding regions apart. pore ... | 1978 | 649659 |
| cell specialization in the epithelium of the small intestine of feeding xenopus laevis tadpoles. | the intestinal epithelium of feeding xenopus laevis tadpoles was studied using light microscope, electron microscope and autoradiographic techniques. the wall of the small intestine differs from that of most other vertebrates studied in that it lacks villous-like folds. a single prominent longitudinal fold, the typhlosole, forms about stage 49, and a series of shallow longitudinal epithelial pleats is also present in some animals. the morphology of the epithelial cells indicates that there are n ... | 1978 | 649494 |
| fenestrae in the rough endoplasmic reticulum of xenopus laevis hepatocytes. | the rough endoplasmic reticulum (rer) of xenopus laevis hepatocytes was examined by freeze-fracture and by conventional thin section electron microscopy. much of the rer was present as stacks of cisternae at the cell periphery but, in addition, large whorls of cisternae were seen in the cytoplasm in most sections. freeze-fracture replicas revealed fenestrae in both stacked and whorled cisternae, although the fenestrae were more numerous in the whorls. the role of these fenestrae is unknown, but ... | 1978 | 646133 |
| oogenesis in xenopus laevis (daudin). vi. the route of injected tracer transport in the follicle and developing oocyte. | in xenopus laevis, vitellogenin (the yolk precursor) is synthesized in the liver and transported via the circulatory system to the ovary. in order to reach developing oocytes where it is sequestered, it must exit the circulatory system and traverse several follicular tissue layers including the theca, the follicle cell layer, and the vitelline envelope. this study demonstrates this pathway by means of electron-opaque tracers, and follows the fate of heterologous macromolecules after their incorp ... | 1978 | 641487 |
| an ultrastructural study of the thyroid gland in the pre-metamorphic xenopus laevis (daudin) tadpole. | a simple method for obtaining the thyroid tissue of anuran tadpoles for ultrastructural study has been described. follicle and colloid formation in the thyroid gland have been observed in xenopus laevis tadpoles at an early stage. the activity of the thyroid gland of pre-metamorphic tadpoles does not seem to depend on the activity of the hypophysis cerebri and the hypothalamus. both 'light' and 'parafollicular' cells are present in the thyroid gland of premetamorphic xenopus laevis tadpoles. | 1978 | 640959 |
| xenopus laevis as a model for the study of immunology. | 1978 | 640116 | |
| histone h2b variants from the erythrocytes of an amphibian, a reptile and a bird. | histones h2b have been isolated from the terminally differentiated diploid erythrocytes of three different classes, amphibia (xenopus laevis), reptilia (crocodilus niloticus) and aves (gallus domesticus). partial amino acid sequences revealed three regions of sequence variation, each variant involving a single amino acid substitution. | 1978 | 638193 |
| mapping of mitochondrial dna in xenopus laevis and x. borealis: the positions of ribosomal genes and d-loops. | 1978 | 633366 | |
| a low molecular weight dna polymerase from ovaries of the frog xenopus laevis. dna polymerase-beta (ovarian). | 1978 | 632291 | |
| translation and characterization of the fatty acid synthetase messenger rna. | fatty acid synthetase messenger rna was obtained from rat liver polysomal rna and then injected into xenopus laevis oocytes. the radioactive fatty acid synthetase protein synthesized in the oocytes was identified by immunoprecipitation with anti-fatty acid synthetase antibody and the immunoprecipitate was then characterized by electrophoresis on sodium dodecyl sulfate-polyacrylamide gel. co-migration of authentic fatty acid synthetase and the labeled product synthesized in oocytes was observed. ... | 1978 | 632268 |
| cell specialization in the small intestinal epithelium of adult xenopus laevis: structural aspects. | the structure, cellular composition and organization of the small intestinal epithelium of adult xenopus laevis are described. the mucosa is thrown into a system of longitudinal folds and is composed mainly of columnar cells and goblet cells. leucocytes comprise about 28% of the mucosal cells. the degree of structural specialization of columnar cells varies according to their position in the folds. cells at the crest of the folds display the greastest degree of specialization, evidenced by the d ... | 1978 | 632211 |
| steroid biosynthesis by ovarian follicles of xenopus laevis in vitro during oogenesis. | 1978 | 631550 | |
| use of restriction enzymes to study eukaryotic dna methylation: i. the methylation pattern in ribosomal dna from xenopus laevis. | 1978 | 625056 | |
| the permeability of the skin of the aquatic anuran xenopus laevis (pipidae). | the undirectional transcutaneous fluxes of na, cl, water and urea were measured, in vitro, in the pipoid anuran xenopus laevis. an active uptake (outside to inside) of na was observed but cl movements appeared to be passive. the effluxes of na and cl were low compared to those measured in other species of amphibians. the active na transport was less than that of more terrestrial species and, although it could be stimulated by vasotocin, aldosterone was ineffective. the permeability of the skin t ... | 1978 | 624899 |
| cell specialization in the small intestinal epithelium of adult xenopus laevis: functional aspects. | the functional activity of the epithelial cells of the intestinal folds of xenopus was analysed histochemically. there is a gradient of increasing absorptive, digestive and secretory activity from the trough regions to the crests of the longitudinal folds. the differences in functional activity correspond to differences in structural complexity, and confirm the existence of a more specialized population of cells at the fold crests and a less specialized population at the fold troughs, analogous ... | 1978 | 624675 |
| oogenesis in xenopus laevis (daudin). v. relationships between developing oocytes and their investing follicular tissues. | 1978 | 619165 | |
| 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 |
| 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 |
| comparison of cell division and cell sizes in normal embryos and lithium-induced exogastrulae of xenopus laevis. | 1977 | 605749 | |
| 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 |
| 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 |
| variability among laboratories in the occurrence of functional modification in the intertectal visual projection of xenopus laevis [proceedings]. | 1977 | 592182 | |
| 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 | |
| a natural heterohaemagglutinin in xenopus laevis serum. | in most adult xenopus laevis the serum contains a 'natural' factor capable of lysing the erythrocytes from a wide variety of amniote species. the factor has no effect on the erythrocytes of another amphibian, ambystoma mexicanum, nor will serum from one animal lyse red cells from another xenopus individual. no lysing factor was present in the serum of larval (tadpole) xenopus. heating of xenopus serum to 56 degrees for 30 min, absorption of the serum with zymosan or inulin, or removal of calcium ... | 1978 | 580428 |
| 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 |
| changes in protein synthesis during the development of xenopus laevis. | patterns of protein synthesis during the development of xenopus were studied by two-dimensional gel electrophoresis. up to the end of the blastula stage we find no newly synthesized proteins which are not already made in the oocyte. the first new proteins are seen during gastrulation, and they increase in number during neurulation. some of these are restricted to the 'ectodermal' region, and some to the 'endodermal' region of embryos divided into two parts. these new, region-specific proteins in ... | 1979 | 573306 |
| an ultrastructural study of the effects of wheat germ agglutinin (wga) on cell cortex organization during the first cleavage of xenopus laevis eggs. ii. cortical wound healing. | uncleaved fertilized eggs of xenopus laevis treated with wheat germ agglutinin (wga) have been pricked at the animal pole both inside and outside the regressed furrow region. the wounded cortex of both regions has been studied with the electron microscope and compared with the same region of wounded, untreated eggs. in all 3 cases, filaments are organized in an annular zone in the damaged cortex. when the surface is pricked outside the regressed furrow of wga-treated embryos, bundles of microfil ... | 1979 | 573275 |
| an ultrastructural study of the effects of wheat germ agglutinin (wga) on cell cortex organization during the first cleavage of xenopus laevis eggs. i. inhibition of furrow formation. | xenopus laevis fertilized eggs have been treated with wheat germ agglutinin (wga) before the onset of the first cleavage, at the stripe stage and during groove deepening. the ultrastructure of the animal cortex of the arrested embryos has been compared with that of the same region of control embryos at different stages of first furrow formation and of cytochalasin b-treated embryos. the outer side of the plasma membrane of wga-treated embryos is covered with a coat which is different from the di ... | 1979 | 573274 |
| modulations of histone messenger rna during the early development of xenopus laevis. | 1979 | 572787 | |
| ultraviolet effects on presumptive primordial germ cells (ppgcs) in xenopus laevis after the cleavage stage. | 1979 | 571826 | |
| the modification of stored histones h3 and h4 during the oogenesis and early development of xenopus laevis. | 1979 | 571369 | |
| effects of injected inhibitors of microfilament and microtubule function on the gastrulation movement in xenopus laevis. | 1979 | 571368 | |
| mitochondria dna synthesis in oocytes of xenopus laevis. | 1979 | 570931 | |
| effects of estradiol-17beta in the male xenopus laevis: isolation and translation of cytoplasmic messenger rna populations. | total xenopus liver cytoplasmic rna isolated following long-term estrogen administration (14 days) was fractioned using sepharose 4b chromatography. one of the sepharose 4b peaks was shown to contain rna with a molecular weight reported for vitellogenin mrna (approximately 34s). the presence of estrogen-induced vitellogenin mrna in the peak 5 rna was determined by translation of the rna in the oocyte and analysis of the oocyte translational products by immunoprecipitation with anti-vitellogenin. ... | 1978 | 569762 |
| a nuclear extract of xenopus laevis oocytes that accurately transcribes 5s rna genes. | xenopus 5s rna genes in recombinant form with the plasmid pmb9 are transcribed accurately when added to a supernatant fraction obtained from disrupted nuclei of xenopus laevis oocytes. after an initial 30 min lag period, the rate of synthesis of 5s rna is constant for at least an hour and synthesis is still detected after 18 hr. as much as 40% of the total rna synthesized from the recombinant dna used in these experiments can be 5s rna. the coding strand of the 5s rna genes is transcribed at a r ... | 1978 | 569551 |
| surface changes during development and involution of the cement gland of xenopus laevis. | the cement gland was studied from stage 17, when the anlage is established, to stage 49, shortly before its disappearance. at early stages, the apical membrane is covered by small microvilli that are more abundant than in the surrounding epiblast cells. vesicular protrusions along the cell boundaries are also more numerous in the gland cells. when the gland reaches maturity, the apical membranes of gland cells differentiate into two regions. in the cranial, kidney-shaped region, the membranes ar ... | 1978 | 569548 |
| oocyte-follicle cell gap junctions in xenopus laevis and the effects of gonadotropin on their permeability. | junctions between xenopus laevis oocytes and follicle cells have been identified as gap junctions by the passage of microinjected fluorescent dye from oocytes to follicle cells. the opening or assembly of these junctions, or both, appears to be regulated by gonadotropins. | 1979 | 569364 |