Publications

TitleAbstractYear
Filter
PMID(sorted ascending)
Filter
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 ...1979385804
hypothalamic luteinizing hormone-releasing hormone content in relation to the seasonal reproductive cycle of xenopus laevis. 1979387514
[immunofluorescence evidence for prolactin and somatotropic cells in the hypophysis of xenpus tadpoles (xenopus laevis d.)]. 1979387515
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 ...1979388355
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 ...1979389428
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 ...1977402217
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 ...1977403009
[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.1977404053
[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 ...1977404062
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.1977406357
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 ...1977407058
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 ...1977409998
the onset of immunoglobulin synthesis during the development of xenopus laevis. 1977412718
synthesis and glycosylation of the mopc-46b immunoglobulin in kappa chain in xenopus laevis oocytes. 1977413546
the effect of karbatox 75, a carbaryl insecticide, upon the development of tadpoles of rana temporaria and xenopus laevis. 1977414939
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 ...1978417718
[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.1978418908
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 ...1979422678
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 ...1979424303
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 ...1979427216
transcription of a cloned ovalbumin ds-cdna in xenopus laevis oocytes. 1979435322
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 ...1979435978
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 s9.1979437035
absence of dorsal-ventral differences in energy metabolism in early embryos of xenopus laevis. 1979437316
purification of xenopus laevis embryo and liver nuclei using metrizamide. 1979437322
hybrids of xenopus laevis and xenopus borealis express proteins from both parents. 1979437325
synthesis and transport of various rna species in developing embryos of xenopus laevis. 1979437337
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.1979438715
an intermediate type of muscle fibre in xenopus laevis. 1979440437
poly(a)+ rna metabolism during oogenesis in xenopus laevis. 1979446893
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 ...1979447463
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 ...1979455441
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 ...1979455442
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 ...1979455459
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 ...1979456360
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 ...1979460182
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 ...1979461183
estrogen causes a rapid, large and prolonged rise in the level of nuclear estrogen receptor in xenopus laevis liver. 1979465076
chromatin structure of the 5s ribonucleic acid genes of xenopus laevis. 1979465464
toxicity and teratogenicity of aromatic amines to xenopus laevis. 1979465773
the carbohydrate content of isolated yolk platelets from early developmental stages of xenopus laevis. 1979466703
newly synthesized histones in chromatin of early embryos of xenopus laevis. 1979466704
the nucleolus organizers of plethodon and aneides located by in situ nucleic acid hybridization with xenopus 3h-ribosomal rna.the main clusters of ribosomal genes, or nucleolus organizers, have been located by in situ nucleic acid hybridization of xenopus laevis 3h labelled ribosomal rna to mitotic chromosomes in squash preparations of intestinal epithelium from 7 species of plethodon and 3 species of aneides. the species used were chosen on account of having well known karyotypes and genome sizes. the plethodon species covered a range of genome size of 20--69.4 pg. the locations of those nucleolus organizers that coul ...1979467168
biochemical research on oogenesis. transfer rna is fully charged in the 42-s storage particles of xenopus laevis oocytes.1. transfer rna makes up 30-40% of total rna in previtellogenic oocytes of xenopus laevis. the bulk of trna is associated with 5-s rna and two proteins in a high-molecular-weight complex sedimenting at 42s. 2. we show here that all kinds of trna are present in the 42-s particles and all of them sediment coincidently. particle trna is fully charged in vivo. during purification of the 42-s particles trna becomes partially uncharged. when purified particles are incubated in vitro with amino acids a ...1979467449
synthesis and glycosylation of rat prostatic binding protein in xenopus laevis oocytes. 1979467658
classes of proteins synthesized in oocytes, eggs, embryos, and differentiated tissues of xenopus laevis.two-dimensional gel electrophoresis has been used to analyse protein synthesis in embryonic stages and in three differentiated tissues of xenopus laevis. the patterns found in oocyte, unfertilized eggs, embryos shortly after fertilization and at progressively later stages of development have been characterized and compared with the patterns found in the brain, heart and liver of tadpoles. the results suggest that at least four classes of proteins can be recognized among the proteins synthesized, ...1979467870
in vitro synthesis of rna by xenopus spermatogenic cells i. evidence for polyadenylated and non-polyadenylated rna synthesis in different cell populations.premeiotic and postmeiotic (haploid) gene expression during spermatogenesis in the anuran, xenopus laevis, was studied by analyzing the accumulation of radioactively labelled cytoplasmic polyadenylated [poly (a +)] and non-polyadenylated [poly (a -)] rnas. dissociated spermatogenic cells were labelled and maintained in an in vitro system capable of supporting cell differentiation. labelled cells were separated by density gradient centrifugation into subpopulations enriched for individual spermat ...1979469479
development of synaptic ultrastructure at neuromuscular contacts in an amphibian cell culture system.cultures of dissociated myotomal muscle and spinal cord derived from embryos of xenopus laevis were grown in the presence of curare in order to abolish neuromuscular activity and were examined by electron microscopy. in one-day-old cultures a few of the neuromuscular contacts already displayed several synaptic specializations including 500 a vesicles clustered against the axolemma, increased axolemmal densities, basal lamina in the cleft, an increased sarcolemmal density and subsarcolemmal filam ...1979469576
meiotic maturation in xenopus laevis oocytes initiated by insulin.insulin can induce meiotic division in xenopus laevis oocytes. this effect shows the specificity expected of a receptor-mediated mechanism. it is potentiated by ethynylestradiol, a steroid antagonist of pregesterone (the natural hormone that provokes meiosis). the xenopus laevis oocytes may serve as a model for the study of the poorly understood effect of insulin on cell division.1979472755
export of proteins from oocytes of xenopus laevis.when human lymphoblastoid mrna was microinjected into x. laevis oocytes, titers of interferon rapidly reached a maximum inside the oocyte while accumulation of interferon continued in the incubation medium for at least 45 hr. if interferon protein was injected into oocytes it was rapidly inactivated. significantly, newly synthesized interferon but not injected interferon was found to be membrane-associated. further experiments involving the co-injection of mrnas coding for secretory proteins (gu ...1979476830
synthesis of dictyostelium discoideum secretory proteins in xenopus laevis oocytes. 1979477987
a cell-free assay system for the analysis of changes in rna synthesis during the development of xenopus laevis. 1979478170
isolation from xenopus laevis embryonic cells of a factor which stimulates tibosomal rna synthesis by isolated nuclei. 1979478171
embryonic appearance of alpha, beta, and gamma crystallins in the periodic albinism (ap) mutant of xenopus laevis.the appearance of the crystallins during lens development in the periodic albinism (ap/ap) mutant of xenopus laevis has been studied. using antibodies specific for total crystallins, alpha + beta crystallins, and gamma crystallins in the immunofluorescence technique, the first positive reaction for all could be demonstrated in the nieuwkoop-faber stage 31 lens rudiment. the antibody to alpha + beta crystallins exhibited differences in intensity from cell to cell in the early rudiment, while the ...1979478209
the ultrastructure of the dorsal yolk-free cytoplasm and the immediately surrounding cytoplasm in the symmetrized egg of xenopus laevis.cytoplasmic segregation and subsequent dorsad displacement of the segregated cytoplasm lead to symmetrization of the egg of xenopus laevis. at 60 min post-fertilization (p.f.) the 'dorsal yolk-free cytoplasm' (dyfc) is located in the dorso-animal part of the egg. its ultrastructure and that of the immediately surrounding cytoplasm have been studied with transmission electron microscopy (tem). the endoplasmic reticulum (er) within the dyfc consists of single or paired cisternae and many small ves ...1979479742
cell number in relation to primary pattern formation in the embryo of xenopus laevis. i. the cell cycle during new pattern formation in response to implanted organizers.results are presented which offer strong evidence that extensive alteration of the fates of embryonic xenopus cells occurs independently of the schedule of cell division, after operations which lead to a doubling of the axial pattern of mesodermal differentiation in the gastrula. the experimental strategy was to make estimates of total mesodermal cell numbers and mitotic index in closely matched sets, each of three synchronous sibling embryos, fixed during the ten hours following the close of ga ...1979479743
the activity of cholinesterases during the development of xenopus laevis.the activity of cholinesterases during the early development of xenopus laevis has been examined, and the activity of acetylcholinesterase in particular has been distinguished from other cholinesterases. in contrast to some earlier findings, the activity of acetylcholinesterase is low at early stages and gradually increases during development. possible reasons for the differences between the earlier results and those reported here are discussed.1979479745
structural changes in single muscle fibers after stimulation at a low frequency.direct stimulation of single muscle fibers from xenopus laevis at a frequency of 1 hz results in a decline of the peak isometric twitch tension after about 200 twitches. fibers were chemically fixed in glutaraldehyde after a varying number of twitches and at several fatigue levels, and the ultrastructural appearance was compared with that of resting fibers treated by identical fixation methods. no gross structural abnormalities were observed but subtle changes occurred. the mitochondria of stimu ...1979479818
[cell proliferation and migration in the roof of the mesencephalon (tectum) in xenopus laevis tadpoles and adult frogs normally and in brain injury. ii. cell proliferation and differentiation of the tectum in frogs].the proliferation and directions of cell differentiation in tectum opticum were studied in the young frogs under the conditions of normal development and upon brain trauma by means of 3h-thymidine autoradiography. the same types of cells were shown to be able of proliferation in both the cases: cells of the ventricle zone and glioblasts (gliocytes) in all other tectum layers. a study of directions of the tectum proliferating cells' differentiation in the frogs has shown that the proliferating ce ...1979481850
contrasting denaturation maps of xenopus laevis and xenopus borealis mitochondrial dnas.denaturation maps of mitochondrial dnas of xenopus laevis and xenopus borealis are radically different from each other. this is in striking contrast to the invariant denaturation patterns previously recognized among mtdnas of various drosophila species, particularly, since the two toads may be even more closely related to each other than the drosophila species.1979486484
quantitative determination of amplified rdna and its distribution during oogenesis in xenopus laevis.the number of extra-chromosomal nucleoli and their rdna content were determined during oogenesis in xenopus laevis. the highly variable number of nucleoli (500 to 2,500) in oocytes of the same stage and from the same female or of different stages or from different females is not a measure of the extent of amplification. in all oocytes examined, a inversely proportional relation was found between the number of nucleoli in an oocyte and their mean rdna content. these results indicate that there is ...1979487908
enrichment and characterization of the dna coding for vitellogenin in xenopus laevis.purified vitellogenin mrna of xenopus laevis was incubated with mechanically sheared dna in high concentrations of formamide and the resulting r-loops (i.e. rna . dna hybrid fragments) separated from the bulk dna by caesium chloride buoyant density centrifugation. hybridization with 125i-labeled vitellogenin mrna revealed a 15--30-fold enrichment of the dna coding for vitellogenin. restriction analysis of the r-loop-enriched dna demonstrated that all known endonuclease hindiii fragments coding f ...1979488117
alpha-melanotropin-like substances in the pituitary and plasma of xenopus laevis in relation to colour change responses. 1979488671
trochlear-oculomotor nerve interactions in xenopus laevis tadpoles: a temporal study.when the trochlear nerve (niv), which innervates the superior oblique muscle (som), is crushed or cut at stages 48-49 in xenopus tadpoles, fibers from the oculomotor nerve (niii) sprout and invade the som. the maximal percentage of specimens having at least one oculomotor nerve fiber on the som on a given day increased from 9.1% following a single crushing of niv to 84.2% following three successive severings of niv and the average number of silver-impregnated niii fibers per specimen increased f ...1979490132
x-ray effect on the development of xenopus laevis embryos--with special reference to primordial germ cells. 1979490458
toxicity of selenium to developing xenopus laevis embryos.se in the form of sodium selenite is toxic to xenopus laevis embryos and tadpoles continuously exposed to concentrations above 1 ppm. concentrations of 2 ppm and above result in severe developmental abnormalities and increased mortality. uptake and loss of radioactive se from water are rapid, but depuration is not complete indicating that some se can remain bound by the organism. the facts that se is toxic at low levels to xenopus embryos and tadpoles, can cause developmental abnormalities, and ...1979490681
the putative promoter of a xenopus laevis ribosomal gene is reduplicated.with the aid of a novel poly-da tailing-partial restriction technique and s1-protection mapping, the 5' terminal coding sequence for the 40s precursor ribosomal rna of xenopus laevis has been exactly identified. since the promoter sequence for the 40s rna should lie close to its 5' terminal coding sequence, we are able to conclude that the "bam-island" sequence reduplication (1) almost certainly represents a promoter reduplication.1979493120
expression of the mitochondrial genome in xenopus laevis: a map of transcripts.the twelve most abundant transcripts in x. laevis mitochondria were characterized, and their coding regions were mapped on the mitochondrial dna (mtdna) by r loop mapping in the electron microscope and by rna gel transfer hybridization. the transcripts map in nonoverlapping positions with one exception, and they account for about 80% of the coding capacity of mtdna. ten of the twelve rna molecules contain poly(a): the two poly(a)-lacking transcripts are the rrnas. analysis withe single-strand-sp ...1979498281
turnover and processing of poly(a) in full-grown oocytes and during progesterone-induced oocyte maturation in xenopus laevis. 1979499663
the time scale of tooth development and replacement in xenopus laevis (daudin).one hundred and seventy two larval specimens of xenopus laevis were reared in such a way that their rates of development (as measured by external criteria) were similar, and so the course of dental development could be examined histologically in a cross sectional study. in this way the events of tooth development were observed, and a time scale constructed for these events. the teeth took an average time of 26 days to develop, erupt and become ankylosed to the bony pedestal, after which each too ...1979500489
transcription initiation of xenopus 5s ribosomal rna genes in vitro.we have studied initiation of transcription of 5s rna genes in extracts of xenopus laevis oocyte nuclei. to aid in this study we developed a general assay for specificity of transcription initiation that does not require accurate termination of transcription. following in vitro transcription with gamma-32p-labeled nucleoside triphosphages, the rna is digested with pancreatic rnaase and fingerprinted by two dimensional chromatography. a 5s rna gene with a variant sequence, in which the g residue ...1979503853
[determination of the decrease in the regenerative power of the optic tectum of xenopus laevis (daudin) during the tadpole stage]. 1979506629
unusual particle trajectories and structural arrangements in myelinated nerve fibers.others have reported that axonally transported particles, which usually travel in a direction roughly parallel to the axis of the nerve fiber, may suddenly shift sideways as though changing tracks. examples of this rare type of movement are shown for particles undergoing transport in myelinated axons of xenopus laevis. an examination of the structure of axons from xenopus showed that some microtubules, neurofilaments, and elements of endoplasmic reticulum may also exhibit marked deviations from ...1979509371
utilization of stored mrna in xenopus embryos and its replacement by newly synthesized transcripts: histone h1 synthesis using interspecies hybrids.we studied h1 gene expression in hybrids of xenopus laevis (female) x xenopus borealis (male) and saw paternal h1 synthesis in mid-blastulae, which indicates that the h1 genes are active by this stage. the behavior of the maternal store of h1 histone mrna was studied in androgenetic haploids. in which all stored mrna is of the laevis type and all new transcripts are borealis. this showed that the initial activation of h1 synthesis occurs entirely by mobilizing maternal transcripts and that these ...1979509520
phylogeny of immunocompetent cells: iii. mitogen response characteristics of lymphocyte subpopulations from normal and thymectomized frogs (xenopus laevis). 1979509538
the activity and properties of poly(adenosine diphosphate ribose) polymerase in vitro during the embryonic development of the south african clawed toad xenopus laevis. 1979510788
analysis of xenopus laevis globins during development and erythroid cell maturation and the construction of recombinant plasmids containing sequences derived from adult globin mrna. 1979510792
post-translational modification of rat immunoglobulins synthesized in the xenopus oocyte translation system.the post-translational modification of rat immunoglobulin synthesised in xenopus laevis oocytes was studied. the major products of translation of rat spleen poly-(a) containing mrna were found to be assembled 7s immunoglobulin molecules indicating extensive modification of primary translation products. the possibility that these immunoglobulin molecules might include antibodies of defined specificity was investigated using spleen mrna from rats hyperimmunized with ferritin and keyhole limpet hae ...1979511214
relationships between eye factors and lens-forming transformations in the cornea and pericorneal epidermis of larval xenopus laevis.larval xenopus laevis at stage 56 (nieuwkoop and faber, '56) were subjected to various types of lentectomy: (1) simple lentectomy, from the pupillary space after incision of outer and inner cornea; (2) lentectomy from the dorsal region of the eye; (3) lentectomy from the dorsal region of the eye and simultaneous incision of the outer cornea; (4) lentectomy from the dorsal region of the eye and simultaneous incision of the outer and inner cornea. the results obtained show that the outer cornea un ...1979512595
[elongated mitotic cells in the neuroepithelium of xenopus laevis and notophtalmus viridescens].most neuroepithelial cells in the embryos of xenopus laevis and notophtalmus viridescens become round upon entering into mitosis. however, many maintain their elongated form, or show long cytoplasmic processes, during mitosis. it therefore seems possible that, in these species, two groups of microtubules are present during mitosis: cytoplasmic microtubules and mitotic microtubules.1979515478
aerobic and anaerobic contributions to sustained activity in xenopus laevis.in conditions of declining water po2, xenopus obtains the majority of resting oxygen needs from lung breathing at 15 degrees and 25 degrees c. the critical oxygen tension was 120 +/- 9 mm hg at 15 degrees c, and 90 +/- 10 mm hg at 25 degrees c. during 30 min stimulation of activity to complete exhaustion at 15 degrees c, frogs exhibited an aerobic capacity of 1.7 microliter o2.g-1.h-1 and accumulated 2.22 mg lactate . g-1. following activity these animals exhibited an oxygen debt of 49.2 microli ...1979515565
sequestration and turnover of guinea-pig milk proteins and chicken ovalbumin in xenopus oocytes.the stability and distribution of proteins within the living cell can be studied using xenopus laevis oocytes. microinjection of messenger rnas and secretory proteins, followed by cell fractionation, shows that transfer of ovalbumin and milk proteins across intracellular membranes of the oocyte only occurs during their synthesis. thus milk protein primary translation products, made in the wheat germ cell-free system, when injected into oocytes remain in the cytosol and are not recovered within m ...1979520309
influence of ci-628 (cn-55, 945-27) on estrogen-induced vitellogenin synthesis and on the ultrastructure of hepatocytes in male xenopus laevis. 1979520332
elimination and metabolism of dimethylnitrosamine (dmn) by xenopus laevis and other amphibians.the elimination of (14c)-dmn after i.p. injection into xenopus was measured, as was the metabolism in vitro of (14c)-dmn by liver from xenopus and 9 other amphibian species. in view of its rapid elimination from the body and low rate of metabolism by xenopus liver in vitro, dmn is unlikely to be toxic or carcinogenic in xenopus.1979520492
the localisation of lead in the skin of light- and dark-adapted xenopus laevis.toads pretreated for 2 months on either a dark or a light background were then exposed to lead nitrate at 50 ppm lead for 21 days, the illumination regimes being maintained. metal analysis of dorsal skin showed significantly higher lead levels (p less than 0.01) in dark-adapted toads. no precipitated lead deposits were observed at the ultrastructural level, necessitating x-ray microanalysis of sections containing melanophores, gland cells and general (non-melanophore) cytoplasm. analysis showed ...1979521319
the emergence, localization and maturation of neurotransmitter systems during development of the retina in xenopus laevis. i. gamma aminobutyric acid.the high-affinity uptake, biosynthesis and release of gaba have been studied in the retina of xenopus laevis. in the mature retina, [3h]-gaba is accumulated predominantly by horizontal cells. a second population of cells located in the inner nuclear layer (possibly a type of amacrine cell) also showed a specific gaba uptake. in addition, this retina contains significant activities of l-glutamic acid decarboxylase and also releases [3h]-gaba in response to increasing k+ concentrations in the medi ...1979521507
the use of radioiodinated protein substrates for the assay of trypsin and the hatching enzyme from the amphibian xenopus laevis. 1979525784
use of different carriers to demonstrate thymic-dependent and thymic-independent anti-trinitrophenyl reactivity in the ambhibian xenopus laevis. 1979527747
structure and formation of ankylosis in xenopus laevis.the structure of ankylotic teeth in xenopus laevis was studied by light, transmission, and scanning electron microscopy as well as by microradiography in decalcified and undecalcified specimens. the mature teeth of xenopus laevis are calcified from the crown to the base, fused to the jaw bone, and have no uncalcified area, such as a fibrous ring separating the tooth into the crown and pedicle. microradiography shows that the mature tooth and jaw bone appear as an x-ray opaque area, except for th ...1979529293
metabolic state dependent preservation of cells by fixatives for electron microscopy.the preservation of mitochondria, cytoplasmic vacuoles and cytoplasm by various fixatives after various pretreatments of ethothelial heart cells from xenopus laevis tadpoles in tissue culture was investigated. the study was based on phase contrast cinemicrographic recordings and on qualitative and quantitative observations with the electron microscope. three fixatives were used: 3% glutaraldehyde in phosphate buffer, followed by 1% osmium tetroxide postfixation, fixation only with 1% osmium tetr ...1979530094
neurite complexes with merkel cells in larval tentacles of xenopus laevis. 1979535028
a quantitative electron-microscope analysis of chromatin from xenopus laevis lampbrush chromosomes.the morphology of the dnp axis and rnp transcripts from xenopus laevis lampbrush chromosomes has been analysed using a modified miller spreading technique. two basictypes of chromatin have been distinguished. (1) discrete portions of dnp exhibiting high levels of transcriptive activity, with clear initiation and termination points (transcription units). interspersed with the units are sequences with little or no transcriptive activity (spacer dnp). the combination of transcription unit plus spac ...1979536383
cell number in relation to primary pattern formation in the embryo of xenopus laevis. ii. sequential cell recruitment, and control of the cell cycle, during mesoderm formation.morphological evidence is presented that definitive mesoderm formation in xenopus is best understood as extending to the end of the neurula phase of development. a process of recruitment of cells from the deep neurectoderm layers into mesodermal position and behaviour, strictly comparable with that already agreed to occur around the internal blastoporal 'lip' during gastrula stage 20 (earliest tail bud). spatial patterns of incidence of mitosis are described for the fifteen hours of development ...1979536690
calcium-induced dehiscence of cortical granules in xenopus laevis oocytes.microinjection of 0.1 microgram of ca++ into xenopus laevis oocytes induces breakdown of the cortical granules. the cortical granules disappeared in both full grown (stage vi) and small growing (stage iv) oocytes. microinjection of mg++, k+, or na+ had no effect on cortical granules in either stage iv or stage vi oocytes. small quantities (0.03 microgram) of ca++ induced dehiscence of the cortical granules only in proximity to the injection site.1979536708
expression of sea urchin histone genes in the oocyte of xenopus laevis. 1979537089
a trna gene of xenopus laevis contains at least two sites promoting transcription.a small cloned dna segment previously shown to contain all genetic information for the expression of the trna1met gene of xenopus laevis was cleaved into an anterior and posterior portion by hae iii restriction. both restriction fragments were cloned in pcr1 using ecori linkers. starting from these tdna subclones, a series of new recombinants were constructed. the transcriptional activity of the cloned dna's was tested both in an in vitro transcriptional system and by means of the oocyte injecti ...1979537910
a new method for local artificial insemination of xenopus laevis eggs. 1979545168
expression of regenerative capacity of caudal spinal cord during the larval development of xenopus laevis. 1979547620
indirect identification of prolactin-producing cells in the pituitary gland of xenopus laevis daudin. 1979550867
axonal-ependymal associations during early regeneration of the transected spinal cord in xenopus laevis tadpoles.the nature and organization of the cellular substrate supporting axonal outgrowth during early regeneration of the spinal cord following transection and/or segment removal were examined in xenopus tadpoles. longitudinal axonal compartments, formed by radial ependymal processes in unoperated spinal cords, were maintained within the rostral and caudal stumps throughout the early post-operative period. the first neuritic sprouts to appear near the cut ends of the cord were frequently associated wit ...1979553146
Displaying items 201 - 300 of 16237