Publications
| Title | Abstract | Year Filter | PMID(sorted descending) Filter |
|---|
| estrogen causes a rapid, large and prolonged rise in the level of nuclear estrogen receptor in xenopus laevis liver. | 1979 | 465076 | |
| isolation and organization of calf ribosomal dna. | ribosomal dna (rdna) from calf was isolated by three density gradient centrifugations. the first centrifugation in cs2s04/bamd was used to obtain partially resolved dg+dc-rich fractions from total dna. the second and third centrifugations, in cs2s04/ag+, led to the isolation of an rdna fraction characterized by a symmetrical band in cscl, p = 1.724 g/cm3. this new procedure appears to be generally suitable for the isolation of rdna and other dg+dc-rich repeated genes. the organization of isolate ... | 1979 | 461183 |
| free cytoplasmic messenger ribonucleoprotein complexes from rabbit reticulocytes. | free cytoplasmic globin mrna containing mrnp-particles were isolated from rabbit reticulocytes by zonal sucrose gradient centrifugation and their properties were compared with mrnp particles isolated in the same way from edta-dissociated reticulocyte polyribosomes. the average poly(a)-length of 9s mrna from free cytoplasmic mrnp was 17-20 nucleotides being about two times shorter than the average poly(a)-length of polysomal 9s mrna. the protein composition of the free cytoplasmic mrnp particles ... | 1979 | 460182 |
| synthesis of albumin and malic enzyme in wheat-germ lysates and xenopus laevis oocytes programmed with chicken-liver messenger rna. | undegraded, biologically-active, polyadenylated rna was isolated from chicken liver by a rapid, simple procedure. liver cells were dispersed mechanically and then broken gently by controlled dounce homogenization in the absence of detergent or ribonuclease inhibitors. after removing lysosomes and mitochondria by centrifugation, rna was precipitated at ph 5.2. polyadenylated mrna was isolated directly from the detergent-solubilized precipitate by oligo(dt)-cellulose chromatography. the resulting ... | 1979 | 456360 |
| sequence organization of the spacer dna in a ribosomal gene unit of xenopus laevis. | a detailed restriction map was constructed for a cloned xenopus laevis rdna fragment containing the nontranscribed spacer (nts) and external transcribed spacer (ets) together with a portion of both the 18s and 28s rrna genes. the nts was found to contain at least three distinct repetitious areas. region 1 has a repeating unit of approximately 100 bp. the primary structure of this unit has been determined by dna sequencing. region 2 is very similar in organization to region 3, and both have an al ... | 1979 | 455459 |
| deletion mutants of xenopus laevis 5s ribosomal dna. | deletion mutants have been derived from a plasmid-cloned repeating unit of xenopus laevis oocyte 5s dna by introducing the transposable chloramphenicol-resistance element tn9 into the at-rich spacer sequence near the 5' terminus of the x. laevis 5s rrna gene in a recombinant plasmid and then selecting plasmids which had lost the transposable element. plasmids lacking the entire transposable element and various portions of the at-rich spacer sequence flanking the original site of tn9 integration ... | 1979 | 455442 |
| vitellogenin in xenopus laevis is encoded in a small family of genes. | vitellogenin, the yolk protein precursor, is produced in x. laevis liver from a 6.3 kilobase (kb) mrna. sequences of this mrna have been transcribed into cdna and cloned in e. coli. some properties of 21 of these cloned dnas, ranging in size from 1 to 3.7 kb, have been reported by wahli et al. (1978b). this paper reports restriction endonuclease mapping, cross hybridization, heteroduplex mapping in the electron microscope and heteroduplex melting experiments with these dnas. we conclude that the ... | 1979 | 455441 |
| light-triggered rod disc shedding in xenopus retina in vitro. | the present study was designed to determine whether light-induced rod outer segment disc shedding occurs when the eye is isolated from the rest of the organism. whole eye explants of xenopus laevis were maintained in vitro and either exposed to 5 min of light or kept in darkness. in both the in vitro eyes and in vivo controls exposed to the same conditions, a significant degree of disc shedding occurred within 1 hr of the light stimulus. the disc shedding response was larger in the explanted eye ... | 1979 | 447463 |
| poly(a)+ rna metabolism during oogenesis in xenopus laevis. | 1979 | 446893 | |
| an intermediate type of muscle fibre in xenopus laevis. | 1979 | 440437 | |
| tissue distribution of immunoreactive somatostatin in the south african clawed toad (xenopus laevis). | immunoreactive somatostatin is present in the brain, gut and pancreas of the south african clawed toad, but is absent from the skin, a rich source of many other brain-gut peptides. | 1979 | 438715 |
| synthesis and transport of various rna species in developing embryos of xenopus laevis. | 1979 | 437337 | |
| hybrids of xenopus laevis and xenopus borealis express proteins from both parents. | 1979 | 437325 | |
| purification of xenopus laevis embryo and liver nuclei using metrizamide. | 1979 | 437322 | |
| absence of dorsal-ventral differences in energy metabolism in early embryos of xenopus laevis. | 1979 | 437316 | |
| movements of supernumerary hindlimbs after innervation by single lumbar spinal nerves of xenopus laevis. | lumbar spinal nerves s8, s9, and s10, together innervating normal hindlimbs in xenopus laevis, were tested to cause coordinated movements in grafted hindlimbs. it could be shown that this ability is mainly restricted to lumbar nerve s9. | 1979 | 437035 |
| ultrastructural study of degeneration and regeneration in the amphibian tectum. | the processes of degeneration and reinnervation in the optic tectum of xenopus laevis have been detailed by quantitative ultrastructural analysis. the tecta were denervated either permanently, by removing the contralateral eye, or temporarily, by cutting the optic tract. after denervation the total number of synapses decreases rapidly within 4 days of a stable level of about 40% of the original number. vacated postsynaptic sites are subsequently removed by phagocytosis. when regenerating axons a ... | 1979 | 435978 |
| transcription of a cloned ovalbumin ds-cdna in xenopus laevis oocytes. | 1979 | 435322 | |
| histones of xenopus laevis erythrocytes. purification and characterization of the lysine-rich fractions. | lysine-rich histones have been isolated from the terminally differentiated erythrocytes of xenopus laevis. three major proteins have been separated by ion-exchange chromatography. these proteins have been characterized by electrophoresis, amino acid analysis and immunochemical techniques. it is concluded that two 'typical' lysine-rich subfractions are present in xenopus erythrocytes and, in addition, a serine-rich histone, that shares no common antigenic determinants with the other lysine-rich h ... | 1979 | 427216 |
| characterisation of bacterial clones containing dna sequences derived from xenopus laevis vitellogenin mrna. | a 1700 nucleotide dna sequence derived from xenopus vitellogenin mrna has been cloned in the bacterial plasmid pbr322. the identity of the cloned sequence was verified in two ways. firstly, the plasmid dna was shown to hybridise to an rna of the correct size (6,700 nucleotides). this was shown by in situ hybridisation to electrophoretically separated rna and also by the formation of "r-loops" with purified vitellogenin mrna. then, using a novel procedure in which plasmid dna covalently bound to ... | 1979 | 424303 |
| production and fate of erythroid cells in anaemic xenopus laevis. | adult xenopus laevis, rendered anaemic by phenylhydrazine injection, have been studied during the recovery from such anaemia. electron microscopy of liver and spleen sections indicates that both of these organs are active in the phagocytosis and destruction of the old damaged red blood cells. may-grunwald and giemsa staining of liver and spleen cells following anaemia has been used to show that erythropoiesis also occurs in both liver and spleen, and this has been confirmed by electron-microscop ... | 1979 | 422678 |
| [immunohistochemical localization by electron microscopy of gnrh in the median eminence of xenopus laevis daud]. | using antibodies against mammalian lhrh with the unlabeled antibody enzyme method immunoreactive nerve fibres were localized in the median eminence of xenopus laevis at the electron microscopic level. these fibres contain irregularly shaped neurosecretory granules with an average diameter of 890 a. | 1978 | 418908 |
| extensive homologies between the methylated nucleotide sequences in several vertebrate ribosomal ribonucleic acids. | the methylated nucleotide sequences in the rrna molecules of the following vertebrate cultured cells were compared: human (hela); hamster (bhk/c13); mouse (l); chick-embryo fibroblast; xenopus laevis kidney. in each species the combined 18s, 28s and 5.8s molecules possess approx. 110-115 methyl groups, and the methylated oligonucleotides released after complete digestion of the rrna by t1 ribonuclease encompass several hundred nucleotides. "fingerprints" of the three mammalian methyl-labelled 18 ... | 1978 | 417718 |
| the effect of karbatox 75, a carbaryl insecticide, upon the development of tadpoles of rana temporaria and xenopus laevis. | 1977 | 414939 | |
| synthesis and glycosylation of the mopc-46b immunoglobulin in kappa chain in xenopus laevis oocytes. | 1977 | 413546 | |
| the onset of immunoglobulin synthesis during the development of xenopus laevis. | 1977 | 412718 | |
| 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 |
| 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 |
| 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 |
| [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 |
| [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 |
| 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 |
| 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 |
| immunohistochemical localization of a gastrin-like peptide in the brain of an amphibian, xenopus laevis daud. | the indirect immunofluorescence technique was used to demonstrate a substance reacting with gastrin antisera in the brain of xenopus laevis. immunoreactive material was found in two sites: (1) in the caudal hypothalamus more precisely in the nucleus infundibularis ventralis, (niv) of the pars ventralis of the tuber cinereum, (pvtc). the fluorescent axons of the reactive parikarya of the niv give rise to two symmetrical tracts which run rostro-ventrally and join, in the infundibular floor, the pr ... | 1979 | 389428 |
| fine structure of ribosomal rna. ii. distribution of methylated sequences within xenopus laevis rrna. | the distribution of methyl groups in rrna from xenopus laevis was analyzed by hybridization of rrna to subfragments of either of two cloned rdna fragments, x1r11 and x1r12, which together constitute a complete rdna repeat unit. using a mixture of 3h-methyl plus 32p-labelled rrna as probe, the molar yield of methyl groups per rrna region in hybrid could be calculated. for this calculation the length of the rrna coding region in each dna subfragment is needed, which was determined for x1r11 subfra ... | 1979 | 388355 |
| [immunofluorescence evidence for prolactin and somatotropic cells in the hypophysis of xenpus tadpoles (xenopus laevis d.)]. | 1979 | 387515 | |
| hypothalamic luteinizing hormone-releasing hormone content in relation to the seasonal reproductive cycle of xenopus laevis. | 1979 | 387514 | |
| the origin of yolk-dna in xenopus laevis. | xenopus laevis serum and plasma was found to contain an average of 25 microgram dna/ml. isolated x. laevis oocytes incubated in medium containing 25 microgram dna/ml labeled with either 125i, 32p or 14c and from three different sources (bovine, e. coli and x. laevis), incorporated the label at an average rate of 0.11 ng.mm-2.hr-1. sucrose gradient fractionation of oocytes revealed that 40-75% of the acid-precipitable label incorporated was associated with the yolk platelets. additional incubatio ... | 1979 | 385804 |
| structure of deletion derivatives of a recombinant plasmid containing the transposable element tn9 in the spacer sequence of xenopus laevis 5s dna. | 1979 | 385229 | |
| in vivo studies on the incorporation of microinjected acidic proteins of the large ribosomal subunit from escherichia coli and artermia salina into oocyte ribosomes from xenopus laevis. | tritium-labeled acidic proteins from the large ribosomal subunit of artermia salina or escherichia coli were microinjected into the cytoplasm of stage iv/v oocytes from xenopus laevis. el12 from the large ribosomal subunit of a. salina but not l7/l12 or l7/l12--l10 from e. coli is specifically incorporated into 60s ribosomal subunits of oocytes. this incorporation is not significantly inhibited by actinomycin d. incorporation of el12 into the 60s subunits occurs in enucleated oocytes, suggesting ... | 1979 | 385044 |
| cloning of nematode trna genes and their expression in the frog oocyte. | transfer rna genes of the nematode caenorhabditis elegans have been cloned in e. coli using the plasmid col e1 as vector. the trnas coded by 3 hybrid plasmids were purified by hybridisation of labelled nematode trna with the plasmid dnas. each plasmid appears to code for a single distinct trna species. the expression of the cloned dnas was analysed in vivo by injection into nuclei of xenopus laevis oocytes. evidence is presented which suggests that these nematode trna genes are accurately transc ... | 1978 | 370775 |
| a method for isolating uncontaminated nuclei from all stages of developing xenopus laevis embryos. | a method for isolating nuclei from xenopus laevis embryos has been developed. this procedure enables the isolation of nuclei, free from contamination with yolk and pigment granules, at all stages of embryoic development. using this method the nuclear yield is 60--70% of the estimated number of cells in the embryo. the dna, rna, histone and non-histone protein content of these nuclei during embryogenesis (from early cleavage to the swimming tadpole stage) has been measured. | 1978 | 370328 |
| lymphocyte surface immunoglobulin in xenopus laevis. light and electron microscopic demonstration by immunoperoxidase method. | 1978 | 355005 | |
| intracellular motility of mitochondria: role of the inner compartment in migration and shape changes of mitochondria in xth-cells. | mitochondrial movements have been followed by phase-contrast microscopy in living xth-cells (xenopus laevis tadpole-heart cells) in tissue culture. the same organelles have been viewed subsequently in electron micrographs. locomotion of mitochondria proceeds at velocities up to 100 micrometer/min. formation of branches of mitochondria and other shape changes may occur with the same speed. mitochondrial motility can be classified into 4 types: (i) alternating extension and contraction at the two ... | 1978 | 348713 |
| recombinant plasmids containing xenopus laevis globin structural genes derived from complementary dna. | details are presented of the in vitro synthesis of double-stranded dna complementary to purified xenopus globin messenger rna, using a combination of reverse transcriptase, fragment 'a' of e. coli dna polymerase 1 and s1 endonuclease. after selection of duplex dna molecules approaching the length of xenopus globin messenger rna by sedimentation of the dna through neutral sucrose gradients, the 3'-oh termini of the synthetic globin gene sequences were extended with short tracts of oligo dgmp usin ... | 1978 | 347404 |
| transplantation of nuclei from lymphocytes of adult frogs into enucleated eggs: special focus on technical parameters. | the technique of transplantation of nuclei from adult lymphocytes into enucleated eggs from xenopus laevis (south african clawed toad) is described. the splenic lymphocytes from the one-nucleolus mutant were bound via their immunoglobulin receptors to nylon fibers, derivatized with the antigen used for immunization. a technique for coupling other cell types with woodward reagent is also described. the cells were broken by aspiration into a micropipette and injected into enucleated eggs. the egg ... | 1977 | 340313 |
| injected amphibian oocytes: a living test tube for the study of eukaryotic gene transcription? | somatic-cell nuclei injected in xenopus laevis oocytes remain transcriptionally active for up to 4 weeks. the rate of rna synthesis increases as the somatic-cell nuclei enlarge. the message activity of the rna synthesized by the injected nuclei can be demonstrated, as new proteins are made a few days after injection of hela-cell nuclei. several lines of evidence demonstrate that these proteins are coded for by the hela-cell genome and that they result from rna synthesized within the oocytes in t ... | 1977 | 339919 |
| stimulation of cell division in ectopic liver tissue following partial removal of the lung. | autografts of liver were implanted into the left lung (xenopus laevis). subsequent removal of the right lung stimulated increased mitotic activity in the lung and in the liver graft. | 1977 | 336386 |
| ionic requirements for induction of maturation (meiosis) in full-grown and medium-sized xenopus laevis oocytes. | there is already good evidence that calcium ions are involved in the induction of maturation in full-grown amphibian oocytes; we show here that other cations (k+, mg2+) also play a role in this process. full-grown (1.3 mm in diameter) and medium-sized (0.8-1.0 mm in diameter) oocytes were compared in the present study. it was found that, provided the medium is k+-free, valinomycin induces maturation in full-grown, but not in medium-sized, oocytes. increasing the cacl2 (20 mm) or the mgso4 (40 mm ... | 1977 | 333439 |
| indirect immunofluorescent identification of 19s immunoglobulin-containing cells in the intestinal mucosa of xenopus laevis. | the lymphoid structures in the gastrointestinal tract of immunized and non-immunized adult xenopus laevis were studied by light and fluorescent microscopy. serial sections stained with may-grunnwald giemsa showed that lymphoid aggregations and scattered lymphoid cells are present along the whole digestive tract. the aggregations are few and rather small in the oesophagus and stomach, they are particularly voluminous in the duodenum. an indirect immunofluorescent technique using antisera against ... | 1977 | 328818 |
| free calcium in full grown xenopus laevis oocyte following treatment with ionophore a 23187 or progesterone. | free intracellular ca2+ was monitored in isolated xenopus laevis oocyte during induced maturation using the ca2+ -sensitive luminescent protein, aequorin. internal free ca2+ was not precisely measured but data suggest it was quite low (in the micromolar range). no change in internal free ca2+ was detected during maturation induced either by progesterone or by p-chloromercuribenzoate. by contrast, the ionophore a 23187 gave an increase in the free ca2+ level when there was a raised external ca2+ ... | 1977 | 328329 |
| stimulation of cell division in ectopic kidney grafts following unilateral removal of the lung. | small fragments of kidney tissue were grafted into the right lung (xenopus laevis) and the left lung was subsequently removed. this stimulated compensatory hyperplasia (increased mitotic rate) in alveolar tissue of the right lung and in the kidney graft. this suggests that the stimulus to compensatory hyperplasia is location-specific rather than tissue- or organ-specific. after implantation into the lung the kidney grafts are revascularized by the surrounding pulmonary supply. damage or functio ... | 1977 | 322542 |
| novel screening procedure for recombinant plasmids. | lysed bacterial colonies containing potential recombinant plasmids were mixed with molten agar and sealed into slots of an agarose gel. after electrophoresis overnight, the gel was stained with ethidium bromide, which clearly reveals recombinant plasmids. xenopus laevis ribosomal dna and histone dna of psammechinus miliaris were ligated into pcri plasmids and screened by this method. | 1977 | 318763 |
| histological changes in xenopus laevis daudin adult specimens kept under dry conditions, then moved back to their natural aquatic environment. ii. skin, kidney and interrenal tissue. | some cytological and histochemical characteristics of skin, the kidney and interrenal tissue were studied in xenopus laevis adult specimens (1) kept in their natural aquatic environment; (2) gradually exposed to dry conditions under which they were kept one week; and (3) returned from the dry environment to water for 24 hr or a week. in the skin, the most relevant changes are those exhibited by epidermal "flask" cells. these cells are generally rather lean, tall and pas-positive in "dry" animals ... | 1978 | 318018 |
| the effect of adult thymectomy upon helper function in xenopus laevis, the south african clawed toad. | carrier-primed helper activity enhancing anti-hapten (tnp-) responses in young adult xenopus laevis reached peak levels 2-4 days after a low dose challenge (0.005% rbc) of unconjugated carrier. it fell quickly to negligible levels by 10 days. adult thymectomized (atx) animals were consistently unable to generate substantial levels of hapten-specific antigen-binding spleen cell (abc) activity. since atx does not severely reduce splenic abc responses to the high dose (10% rbc) of carrier used for ... | 1979 | 315915 |
| properties of a cytostatic factor from xenopus laevis eggs. | 1979 | 315899 | |
| fine structural distribution of the surface-connected canalicular system in frog thrombocytes. | the existence of the surface-connected canalicular system (sccs) has been demonstrated in semithick sections of the frog thrombocytes by the use of a high voltage electron microscope. the sccs of the thrombocytes in rana catesbeiana and rana nigromaculata consists of numerous canaliculi and vesicles with a diameter of 250 nm, which join with one another to make a complex network throughout the cytoplasm. although the sccs of xenopus laevis fits well into the pattern described in rana catebeiana, ... | 1979 | 315820 |
| somitogenesis in amphibian embryos. i. experimental evidence for an interaction between two temporal factors in the specification of somite pattern. | somitogenesis is described in two species of anuran amphibians, xenopus laevis and rana temporaria, in which the cellular mechanics of somite formation are distinctly different. heat shocks are employed to demonstrate a wave of cellular change which precedes somite formation down the body axis. this prior wave is shown to be kinematic. it is not a propagated wave. it is a consequence of the temporal activities of the cells laid out in space, but there is no evidence that these activities depend ... | 1979 | 314486 |
| lens regeneration from cornea of larval xenopus laevis in the presence of the lens. | in xenopus laevis tadpoles, wounding of the outer cornea failed to initiate lens regeneration. if both the outer and inner corneas were wounded or if the lens was dislocated, lens regeneration was initiated but failed to continue beyond stage iii. however, lensectomy followed by re-implantation of the lens resulted in the regeneration of a fully differentiated lens in several cases, despite the presence of the re-implanted lens. although some of the regenerates in these eyes were also arrested a ... | 1978 | 311375 |
| the effects of exogenous melatonin upon the gut of larval xenopus laevis. | 1978 | 310409 | |
| amphibian cells in culture. ii. isolation of drug-resistant variants and an asparagine-independent variant. | with l-15 as the base medium, drug-resistant variants were isolated from two amphibian tissue culture strains: the xenopus laevis a8 diploid cell line and the icr 2a cell line of rana pipiens. four different classes of variants were obtained: (1) a8 cells resistant to chloramphenicol, an inhibitor of mitochondrial protein synthesis; (2) a8 cells resistant to ouabain, an inhibitor of the na+/k+-activated atpase of the plasma membrane;(3) icr 2a cells resistant to low (20 microgram/ml) and high (3 ... | 1978 | 307557 |
| 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 |
| 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 |
| 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 |
| structures of gustatory organs of xenopus laevis during metamorphosis. | 1979 | 297731 | |
| mitotic factors from mammalian cells induce germinal vesicle breakdown and chromosome condensation in amphibian oocytes. | cytoplasmic extracts of hela cells synchronized in various phases of the cell cycle were injected into fully grown xenopus laevis oocytes to monitor the presence of factors that can induce meiotic maturation: i.e., germinal vesicle breakdown and chromosome condensation. extracts from gi and s phase cells had no activity. the maturation-inducing activity, which was found to be low during early and mid g2 phases, increased rapidly during late g2 and reached a peak in mitosis. the results of this s ... | 1979 | 288067 |
| delimitation of a promoter for rna polymerase iii by means of a functional test. | a xenopus laevis dna segment containing the structural gene for trna1met and 22 base pairs at the 5' side of the gene is active in trna production. the dna segment was ligated to sea urchin histone dna and was also inserted into plasmid pcr1. both recombinant dnas were shown to produce mature trna1met at a high rate when injected into centrifuged xenopus oocytes. | 1979 | 288049 |
| electrical currents through full-grown and maturing xenopus oocytes. | an extracellular vibrating electrode was used to map the current pattern around xenopus laevis oocytes. current was found to enter the animal hemisphere and leave the vegetal hemisphere; in fully grown oocytes from which the follicle cells had been removed, the maximal current density was about 1 microamperemeter/cm2. this current decreased to nearly zero in response to progesterone and several other maturation-producing agents. in the case of progesterone, the decline began within a few minutes ... | 1979 | 284407 |
| isolation of a 7s particle from xenopus laevis oocytes: a 5s rna-protein complex. | previtellogenic oocytes of xenopus laevis contain a free 5s rna-protein complex sedimentating at 7 s. this particle consists of one molecule of 5s rna and one 45,000-dalton protein. the protein of the 7s particle and the protein that is released in association with 5s rna when the ribosome is treated with edta are unrelated. because the 5s rna accumulated by small oocytes in storage particles is incorporated into the ribosome later in oogenesis, we conclude that 5s rna is succesively associated ... | 1979 | 284338 |
| transcription of cloned xenopus 5s rna genes by x. laevis rna polymerase iii in reconstituted systems. | when incubated with a soluble extract from large oocytes of xenopus laevis, recombinant dna plasmids containing either x. laevis oocyte 5s dna or x. borealis oocyte 5s dna direct the synthesis of discrete 5s rnas, which by size and sequence analysis are similar or identical to the corresponding 5s rnas synthesized in vivo. synthesis of the 5s rnas is mediated by a soluble endogenous rna polymerase iii (nucleosidetriphosphate:rna nucleotidyltransferase, ec 2.7.7.6), which presumably recognizes sp ... | 1979 | 284325 |
| does 3'-terminal poly(a) stabilize human fibroblast interferon mrna in oocytes of xenopus laevis? | polynucleotide phosphorylase (polyribonucleotide:orthophosphate nucleotidyltransferase, ec 2.7.7.8) purified from escherichia coli was used enzymatically to deadenylate polyadenylated human fibroblast interferon mrna preparations obtained from human diploid fibroblasts (fs-4 strain) induced by poly(i)-poly(c) (20 microgram/ml) in the presence of cycloheximide (50 microgram/ml, 4 hr). both the polyadenylated and the deadenylated interferon mrna preparations were translated into biologically activ ... | 1978 | 283411 |
| the nucleotide sequence of the repeating unit in the oocyte 5s ribosomal dna of xenopus laevis. | 1978 | 277309 | |
| induction of maturation in xenopus laevis oocytes by a steroid linked to a polymer. | a progesterone analog has been covalently linked via an amide bond to polyethylene oxide (molecular weight, 20,000). this macromolecular steroid molecule displays the biological activity of progesterone in inducing meiotic maturation when incubated with xenopus laevis oocytes (stage vi) in vitro. its efficiency (half-maximum effective concentration, 30 mum) is approximately 10 times lower than that of its low molecular weight homolog (3 mum). control experiments with polyethylene oxide and an es ... | 1978 | 276879 |
| cloned single repeating units of 5s dna direct accurate transcription of 5s rna when injected into xenopus oocytes. | single and multiple repeating units of three types of xenopus 5s dna recombined with the plasmid pmb9 serve as templates for the accurate synthesis of 5s rna after their injection into xenopus laevis oocyte nuclei. all 15 cloned single repeating units of x. laevis oocyte 5s dna that were tested supported 5s rna synthesis. three cloned fragments of x. borealis oocyte 5s dna and one cloned single repeating unit of x. borealis somatic 5s dna were templates for 5s rna synthesis. we conclude that the ... | 1978 | 275856 |
| transcription of cloned trna gene fragments and subfragments injected into the oocyte nucleus of xenopus laevis. | cloned 3.18 kilobase fragments of xenopus laevis dna containing genes for trnamet1 and for at least one other 4s rna species are transcribed rapidly after their injection into the nucleus of x. laevis oocytes. the newly synthesized rna can be resolved by gel electrophoresis into a few predominant 4s rna species and a series of slower migrating components. one of the 4s rna species appears to be identical, by fingerprint analysis, to the trnamet1 isolated by hybridization of somatic cell rna to t ... | 1978 | 274710 |
| displacement-loop replication initiation sequence in animal mitochondrial dna exists as a family of discrete lengths. | the single-stranded mitochondrial dna (mtdna) displacement-loop initiation sequence (7s mtdna) is hydrogen-bonded at the origin of replication in animal cell mtdna. analysis of 7s mtdna from several cell sources indicates that this initiation sequence exists as a family of fragments of relatively discrete lengths. mtdna from both mouse l cells and mouse liver has four major sizes of 7s mtdna fragments, ranging from 500 to 580 nucleotides in length. the 5'-end region of each of these species is t ... | 1978 | 273230 |
| sites of transcription initiation in vivo on xenopus laevis ribosomal dna. | we report the results of a novel method for locating sites of transcription initiation using a complex of capping enzymes from vaccinia virions that catalyze the reaction pppg + s-adenosylmethionine + (p)ppxpypzp..... -->(7m)gpppxpypzp..... [ensinger, m. j., martin, s. a., paoletti, e. and moss, b. (1975) proc. natl. acad. sci. usa 72, 2525-2529]. this enzyme complex will cap di- or triphosphate termini but will not cap monophosphate or hydroxyl termini. xenopus laevis 40s precursor rrna from oo ... | 1977 | 271962 |
| induction and decay of human fibroblast interferon mrna. | polyadenylylated interferon mrna, obtained from induced human fibroblasts, was quantitatively assayed by synthesis of biologically active human interferon in xenopus laevis oocytes. the assay for interferon mrna was used to distinguish between various hypotheses relating to interferon induction and biosynthesis. the data demonstrate that on induction with poly(i-poly(c) human fibroblasts accumulate interferon mrna for 1-1.5 hr, after which time the mrna is rapidly degraded with a half-life (t 1/ ... | 1977 | 270686 |
| prescence of tadpole and adult globin rna sequences in oocytes of xenopus laevis. | complementary dna transcribed from adult xenopus laevis globin mrna was used to assay ovary rna from xenopus for the presence of globin sequences by rna.cdna hybridization. these sequences are present at approximately the same concentration as the majority of poly(a)-containing ovary sequences. the sequences are also found at approximately 200,000 copies per cell in poly(a)-containing rna extracted from mature oocytes. to rule out contamination of the oocytes with somatic cells, two additional e ... | 1977 | 269434 |
| interferon messenger rna content of human fibroblasts during induction, shutoff, and superinduction of interferon production. | translation of injected mrna in oocytes of xenopus laevis has been used as a highly sensitive and quantitative assay for interferon mrna. injection into oocytes of polyadenylylated rna extracted from poly(i).poly(c)-induced human diploid fibroblasts (fs-4) leads to the synthesis of biologically active human fibroblast interferon over a period of 24-32 hr. there is a linear relationship between the amount of mrna injected and the interferon yield obtained over a range of 1-20 ng of injected rna. ... | 1977 | 269400 |
| synthesis of human interferon by xenopus laevis oocytes: two structural genes for interferons in human cells. | human fibroblasts and leukocytes produce interferons which may be distinguished by their antigenic and species specificity as well as by their molecular weight distributions. to elucidate the basis for these differences, we isolated mrna from induced human fibroblasts and lymphoblastoid (namalva) cells and studied the products of translation in xenopus laevis oocytes. the mrna from the respective cells yielded translation products, in oocytes, that were characteristic of the cells from which the ... | 1977 | 269391 |
| gene activation in somatic nuclei after injection into amphibian oocytes. | genes that are unexpressed in somatic cells have been activated by injecting cultured cell nuclei of the frog xenopus laevis into oocytes of the newt pleurodeles waltlii. the genes that were activated are normally expressed in oocytes but not in cultured cells. conversely, genes that are normally expressed in cultured cells but not in oocytes became inactive when cultured cell nuclei were injected into oocytes. these changes in gene activity were detected by two-dimensional gel electrophoresis o ... | 1977 | 267940 |
| regulation by estrogen of the vitellogenin gene. | the vitellogenin gene is inactive in the liver of male xenopus laevis, unless exogenous estrogen is administered. we have previously shown that conventional doses of estradiol-17beta result in the appearance of new hepatic messenger rnas, some of which are encoded for vitellogenin. we now report that much higher doses of the hormone (2 mg/frog per day for 4 days) are required to elicit maximal responses. the relative levels of membrane-bound polysomes and vitellogenin mrna were determined as a f ... | 1977 | 267932 |
| identification of rauscher murine leukemia virus-specific mrnas for the synthesis of gag- and env-gene products. | polyadenylylated mrna isolated from cells infected with rauscher murine leukemia virus was fractionated by centrifugation in in a denaturing sucrose gradient into different sizes. each rna fraction was injected into oocytes of xenopus laevis and the virus-specific products were analyzed by immunoprecipitation with polyvalent and monospecific antisera against polypeptides of rauscher murine leukemia virus, and then by gel electrophoresis and scintillation autoradiography. it was shown that a 35s ... | 1977 | 266707 |
| selective and accurate transcription of the xenopus laevis 5s rna genes in isolated chromatin by purified rna polymerase iii. | chromatin isolated from immature oocytes was found to contain an endogenous rna polymerase activity (rna nucleotidyltransferase; nucleoside triphosphate:rna nucleotidyltransferase, ec 2.7.7.6) that synthesizes predominately 5s rna. however, the levels of total rna synthesis and 5s rna synthesis in chromatin were each stimulated 10- to 50-fold by an exogenous rna polymerase iii purified from x. laevis oocytes. the 5s genes in chromatin were transcribed by the exogenous enzyme in a highly selectiv ... | 1977 | 264693 |
| turnover of rod photoreceptor outer segments. ii. membrane addition and loss in relationship to light. | the rate of disk addition to rod outer segments (ros) varies widely in xenopus laevis tadpoles kept in cyclic light (12l:12d). when measured as radioactive band (3h-band) displacement during the 2nd day after injection of [3h]leucine, 75% of the daily increment of displacement occurred during the first 8 h of light. during the same interval, the number of open disks at the ros base increased more than threefold. during the last 8 h of darkness, 3h-band displacement was undetectable and the numbe ... | 1977 | 264121 |
| studies on aminoacyl trna synthetases and transfer rna in living xenopus laevis oocytes. | the microinjection of transfer rna into amphibian oocytes permits one to study under in vivo conditions the reactions that affect this important macromolecule. a comparative study has been carried out between the in vivo and in vitro specificity of the aminoacylation reacton. the results obtained show that modifications of the trna structure affect aminoacyl-trna synthetase recognition in the same fashion in both conditions. the in vivo aminoacylation was not affected by the presence of puromyci ... | 1979 | 261727 |
| aminoacyl transfer from phenylalanyl-trna microinjected into xenopus laevis oocytes. | 1977 | 244308 | |
| xenopus laevis cement gland as an experimental model for embryonic differentiation. i. in vitro stimulation of differentiation by ammonium chloride. | ectoblastic cells explanted from the animal pole of young xenopus laevis gastrulae have been cultured in vitro. when these cells were cultured for five days in standard salt solutions they formed atypical epidermis. when they were first submitted for 6 h to holtfreter solution containing ammonium chloride and then transferred for five days in standard barth's solution they underwent differentiation into typical cement gland tissue. the optimum concentration of ammonium chloride was 10 mm. below ... | 1975 | 240903 |
| changes in the activity and isozymes of acetyl and butyrylcholinesterase during xenopus laevis development. | 1975 | 240618 | |
| template preferences of dna polymerase and nuclease activities appearing during early development of xenopus laevis. | 1975 | 238871 | |
| steady state current rectification in potential clamped nodes of ranvier (xenopus laevis). | the membrane potential in single nodes of ranvier was changed in rectangular pulse steps while the membrane currents, associated with the potential steps, were measured. changes were made in the ionic composition of the external and the internal medium. the latter changes were obtained by free diffusion through a cut internode. the steady state currents, described on the basis of potassium and leak permeability, were affected by the solution composition in a characteristic way. increased inside ... | 1975 | 238247 |
| osmotic and ionic regulation in xenopus laevis daud. during adaptation to different osmotic environments--v. quantitative alterations of the acid glycosaminoglycans in the kidney. | 1975 | 237733 | |
| the time course of experience-dependent synaptic switching of visual connections in xenopus laevis. | 1975 | 237285 | |
| alkaline phosphatase isozymes of xenopus laevis embryos and tissues. | alkaline phosphatase was obtained by treating embryos of xenopus laevis with n-butanol at different developmental stages from gastrula to tadpole; the enzyme was also obtained from adult kidney, liver, and intestinal mucosa. purification was carried out by gel filtration and polyacrylamide gel electrophoresis. the enzyme activity is chromatographically spearated into two peaks, with molecular weights of approximately 200,000 and 400,000. alternatively, two groups may be characterized on the basi ... | 1975 | 237058 |
| na+/k+-dependent adenosinetriphosphatase activity in the skin, kidney and muscle in xenopus laevis (daud.) adult specimens under different experimental conditions. | xenopus laevis adult specimens were exposed to environmental changes simulating those undergone by these animals in their natural "habitat". after keeping groups of animals under dry conditions, some of them were returned to water. in both cases some parameters were compared with those of control animals kept in water. a lower activity in the na+/k+-dependent atpase of the epidermis and striated muscle was detected in "dry" animals with respect to the control ones or those rehydrated whereas the ... | 1978 | 233463 |
| biochemical characterization of lysosomes in unfertilized eggs of xenopus laevis. | relations between lysosomes and yolk platelets of amphibian eggs have been suggested. this work demonstrates the presence of acid hydrolases in oocytes induced to ovulate in vitro. about 40% of the acid hydrolases are found in a sedimentable fraction, and, in accordance with the lysosomal concept, they display structural latency. biochemical data did not indicate any association between lysosomal enzymes and yolk platelets. the mechanism of yolk resorption is discussed and it is suggested that t ... | 1979 | 228752 |
| onset of neural function in the lateral line. | the development of the nervous system includes the formation of specific neuronal connections. some insight into the mechanisms by which these connections are made may be obtained by determining the order in which the elements of a developing system begin to function and examining any changes that may occur in the system shortly after it begins functioning. i have investigated the lateral line of the south african clawed frog, xenopus laevis and i have classified the afferent system into three e ... | 1979 | 228196 |
| characterization of interferon messenger rna from human lymphoblastoid cells. | after treatment with sendai virus, namalwa cells form large amounts of interferon. rna extracted from treated whole cells or from their polysomes was injected into xenopus laevis oocytes and the interferon formed was titrated. the results show that the amount of interferon mrna was maximal by 9 h after treatment of the cells with sendai virus and then declined. sucrose gradient centrifugation of the mrna gave substantial purification and showed that its size was 12 s. | 1979 | 227993 |
| roles of cyclic amp and calcium in maturation of xenopus laevis oocytes. | 1979 | 226799 |