Publications
| Title | Abstract | Year Filter | PMID(sorted descending) Filter |
|---|
| vital dye mapping of the gastrula and neurula of xenopus laevis. ii. prospective areas and morphogenetic movements of the deep layer. | 1976 | 950072 | |
| direct induction by estradiol on vitellogenin synthesis in organ cultures of male xenopus laevis liver. | organ cultures of liver from untreated male xenopus respond to 17 beta-estradiol in the culture medium by synthesizing and secreting the yolk protein precursor vitellogenin. vitellogenin synthesis, as a primary response, is first detectable on the fourth day of culture, and comprises up to 12% of the protein synthesized on the eighth day. estradiol is required during the lag period of 4 days. tissue from male xenopus injected with 1 mg of estradiol 30 days before the start of culture responds mo ... | 1976 | 949740 |
| processes for sodium permeability inactivation in the myelinated nerve fibre of the frog (xenopus laevis). | 1976 | 949010 | |
| measurement of potassium and chloride ion concentrations in the cupulae of the lateral lines of xenopus laevis. | 1. potential measurements were made with double barrel ion selective electrodes from the cupulae of lateral line organs in the aquatic toad xenopus laevis. 2. a positive endocupular potential (ecp) of 15-50 mv was recorded within the cupula, immediately above the hair cells. 3. increases in the cl- and k+ potentials were recorded when the ion selective electrodes touched the cupula. cupular cl- and k+ varied between 35 and 70 mm and 24 and 100 mm respectively. this variation existed between, rat ... | 1976 | 948058 |
| stage-sensitivity and dose-response curve of u.v. effect on germ cell formation in embryos of xenopus laevis. | ultraviolet light (u.v.) irradiation of the vegetal hemisphere of xenopus laevis eggs resulted in the elimination of primordial germ cells in tadpoles. quantitative studies were performed on this phenomenon. the stage sensitivity to u.v. inactivation of germ cell formation was obtained for the early developmental stages ranging from immediately after fertilization to small-cell blastula. it was found that u.v. irradiation at the stage immediately after fertilization was more injurious than irrad ... | 1976 | 947996 |
| melanoblast-tissue interactions and the development of pigment pattern in xenopus larvae. | the melanophores of larval xenopus laevis are disparately distributed on the hypomere in that the upper region (uht) is densely pigmented, the median region (mht) is moderately pigmented, and the lower region (lht) is unpigmented. the roles of the melanoblasts and their tissue environment in determining the melanophore pattern was investigated by heterotopic transplantation of hypomeric tissues, culture of neural crest explants in vesicles derived from hypomeric tissues and radioactive marking o ... | 1976 | 947992 |
| dna-dependent rna polymerase c from xenopus laevis ovaries. ability to transcribe intact double-stranded dna. | dna-dependent rna polymerase c, partially purified from xenopus laevis ovaries, has been resolved by deae-sephadex chromatography in two forms, eluting at 0.2 m and 0.3 m ammonium sulfate, respectively. both are sensitive to high concentrations of alpha-amanitin (200 mug/ml). their ionic strength dependence and divalent cation requirements are indistinguishable. quantitatively, rna polymerase c represents the major form of rna polymerase activity solubilized from the ovaries. both rna polymerase ... | 1976 | 947751 |
| subunit homologies of lactate dehydrogenase (ldh) isoenzymes between amphibians (xenopus laevis) and mammals (wistar rat). | 1976 | 947661 | |
| nuclear swelling and chromatin decondensation can occur without cortical granule explosion in eggs of xenopus laevis. | 1976 | 945774 | |
| control of 5s rna synthesis in xenopus laevis. | 1976 | 945465 | |
| cell-free translation of messenger rna from oocytes of xenopus laevis. | 1976 | 945202 | |
| the effect of thymectomy at different stages of larval development on the immune response of the clawed toad to sheep erythrocytes. | the role of the thymus during the first three weeks of larval life in the maturation of humoral immunity in the amphibian, xenopus laevis, is examined. thymectomy throughout this period dramatically affects the heterologous red cell response of young adults. sheep erythrocyte (srbc) administration elicited haemolytic antibody production in the blood and in the spleen (measured by the appearance of plaque forming cells) of control animals, but failed to do so in all thymectomized toadlets. moreov ... | 1976 | 944762 |
| the germinal vesicle nucleus of xenopus laevis oocytes as a selective storage receptacle for proteins. | the amorphous nucleoplasm of the germinal vesicle nucleus of xenopus laevis oocytes has been selectively extracted under conditions which leave the nuclear formed elements morphologically intact. the nucleoplasm contains about 97% of the total nuclear proteins and on sds-polyacrylamide gels some 68 polypeptides can be distinguished. on the basis of solubility differences, the nucleoplasmic proteins can be classified into two categories. the first consists of soluble or easily solubilized protein ... | 1976 | 944701 |
| comparison of exogenous energy sources for in vitro maintenance of follicle cell-free xenopus laevis oocytes. | the purpose of these experiments was to determine which exogenous energy sources are suitable for isolated follicle cell-free oocytes from the frog, xenopus laevis. in order to compare prospective energy sources, follicle cell-free oocytes from 0.4 to 1.3 mm in diameter were incubated in a 1 mm concentration of each of a variety of energy sources and scored daily for the maintenance of morphological characteristics. vitellogenic oocytes placed in succinate or fumarate deteriorated at the same ti ... | 1976 | 944165 |
| ribosomes from xenopus laevis eggs and embryos in a cell-free protein-synthesizing system: translational regulation. | three types of ribosomal preparations from xenopus laevis eggs and embryos were tested in a cell-free system to study possible translational regulation of protein synthesis as mediated by the ribosome during early amphibian development: type 1, a crude high-speed sediment, mainly containing monoribosomes completely dissociable by 0.5 m kc1; type ii, ribosomes washed with 0.5 m kc1; and type iii, ribosomes treated with puromycin - 0.5 m kc1. all three types showed an active response to the additi ... | 1976 | 944101 |
| an autoradiographic study of tritiated uridine incorporation into the larval ovary of xenopus laevis. | the in vitro incorporation of 3h-5-uridine into the germinal and somatic cells of the larval ovary of xenopus laevis has been studied using both light and electron microscope autoradiography. incubation for only one hour in the presence of precursor revealed that the follicle cells are highly active in rrna synthesis, whereas substantial oogonial nucleolar labeling was not detected for several hours. semi-quantitative analysis of high-resolution autoradiograms indicated that the density of silve ... | 1976 | 943967 |
| the effect of injected cytochalasin b on filament organization in the cleaving egg of xenopus laevis. | 1976 | 943569 | |
| morphological changes of the surface of the egg of xenopus laevis in the course of development. iii. scanning electron microscopy of gastrulation. | 1976 | 943347 | |
| nucleolar activity and rna metabolism in previtellogenic and vitellogenic oocytes of xenopus laevis. a biochemical and autoradiographical, light and em study. | 1976 | 943292 | |
| adult haemoglobin in developmentally retarded tadpoles of xenopus laevis. | tadpoles of xenopus laevis reared in water containing 0-01% propylthiouracil continue to grow but fail to develop or metamorphose. the haemoglobin of such tadpoles has been extracted in buffer, converted to a cyanmet form, and run on polyacrylamide gels. the developmentally retarded tadpoles are found to possess adult-type haemoglobin rather than the tadpole type which normally characterizes their developmental stage. | 1976 | 939939 |
| new membrane formation and intercellular communication in the early xenopus embryo. | the ionic permeability of the nonjunctional and newly formed junctional membranes was investigated in embryos of xenopus laevis up to the onset of the fifth cleavage. continuous measurements were made of the equivalent nonjunctional (r'o) and junctional resistances (r'i) in different pairs of adjacent cells separated by one of the four cleavage membranes formed in that period. the specific resistance of the nonjunctional membranes (ro) and of each cleavage membrane (ri) as a function of time wer ... | 1976 | 933155 |
| developmental changes in activity of choline acetyltransferase, acetyl-cholinesterase and glutamic acid decarboxylase in the central nervous system of the toad. xenopus laevis. | 1976 | 932736 | |
| a method for collecting naturally fertilized eggs of xenopus laevis immediately after laying. | 1977 | 926758 | |
| kinetics of estrogen induction of xenopus laevis vitellogenin messenger rna as measured by hybridization to complementary dna. | 1977 | 925003 | |
| isolation of globin messenger rna of xenopus laevis. | 1977 | 924017 | |
| toxicity of n-phenyl-alpha-naphthylamine and hydrazine to xenopus laevis embryos and larvae. | 1977 | 922193 | |
| retinal growth in double dorsal and double ventral eyes in xenopus. | the growth of normal and surgically produced compound dorsal and ventral retinae in xenopus laevis has been studied autoradiographically following injections of [3h] thymidine at stages 50 and 58. the animals were sacrificed 3 weeks after metamorphosis. the histogenetic pattern of the dorsal and ventral retinal halves was different at the three time points investigated, i.e. up to stage 50, between stages 50 and 58 and between stage 58 and 3 weeks after metamorphosis. asymmetrical dorsal retinal ... | 1977 | 915422 |
| nuclear transplantation from intestinal epithelial cells of early and late xenopus laevis tadpoles. | the aim of these experiments was to test whether the developmental potential of nuclei from intestinal epithelial cells of xenopus laevis tadpoles declined during the life of the functional larval gut. the results of transplantation of nuclei from three different stages of development were compared: stages 46-48, when feeding begins and while yolk is still present but before the formation of the typhlosole; stage 57, just prior to the onset of metamorphic reorganization; and stage 54, an interme ... | 1977 | 915421 |
| lipid and polypeptide components of the crystalline yolk system from xenopus laevis. | the polypeptide and lipid components of the crystallinelipoprotein-phosphoprotein from the yolk system of xenopus laevis are described. this lipoprotein complex contains 17% lipid of which 75% is phospholipid. the phospholipid fraction consists of mostly phosphatidylcholine and phosphatidylethanolamine. the neutral lipid fraction contains mainly triglyceride. the phosphoprotein, phosvitin, has been separated from the lipoprotein, lipovitellin, by classical methods. three polypeptide chains can b ... | 1977 | 914850 |
| purification of a dna-binding protein from xenopus laevis unfertilized eggs. | a dna-binding protein from xenopus laevis unfertilized eggs has been purified to apparent homogeneity. it is a heat stable, lysine-rich protein and has a molecular weight corresponding to 8,200 daltons, measured by sodium dodecyl sulphate gel electrophoresis. the protein, which is active in a monomeric form, stimulates dna polymerase alpha, and binds to single and double stranded dna. one egg contains about 4 x 10(12) molecules (minimum estimate) of the protein; since we calculate that 4 x 10(8) ... | 1977 | 909794 |
| the effect of tolbutamide on early embryos of xenopus laevis. | 1977 | 908419 | |
| treatment of skin-invading capillarid nematode in a colony of south african clawed frogs (xenopus laevis). | 1977 | 904298 | |
| slow mechanism for sodium permeability inactivation in myelinated nerve fibre of xenopus laevis. | 1. single myelinated nerve fibres were isolated and the nodal currents were recorded under potential clamp conditions. the effect of membrane potential on the na permeability (pna) mechanism was analysed. 2. the available pna increased slowly during negative polarization of the membrane. the time course of this change was about 10(3) times slower than the time course of the mechanism for the usual pna inactivation (h-system). the slow pna changes could be distinguished from changes in h because ... | 1977 | 903895 |
| development of the myotomal neuromuscular junction in xenopus laevis: an electrophysiological and fine-structural study. | 1977 | 902924 | |
| regeneration of the tail of x-irradiated xenopus tadpoles. | the effects of x-rays on the regeneration of the tail of xenopus laevis tadpoles have been studied. larvae of stage 52 were exposed in groups to irradiation either of the head or the body region with doses of 3,000 and 4,000 r. in both cases, the animals have regenerated the lost parts of their tails. | 1977 | 899691 |
| in vivo repair of the 3'terminus of transfer rna injected into amphibian oocytes. | yeast transfer rna specific for phenylalanine has been treated chemically to remove either one or two nucleotides of its 3' terminus and has been injected into xenopus laevis oocytes to test whether this rna can be repaired in vivo. the results obtained showed that oocytes could aminoacylate and thus repair trnaphe that has lost both its terminal adenosine and 3' phosphate. a similar result was obtained with trnaphe that had undergone two full cycles of 3' terminal nucleotide removal. the oocyte ... | 1977 | 896475 |
| biosynthesis, processing, and control of release of melanotropic peptides in the neurointermediate lobe of xenopus laevis. | the neurointermediate lobes of dark-adapted toads xenopus laevis were incubated for 30 min in [3h]arginine and then "chased" for various time periods. by use of this pulse-chase paradigm there were detected 10 trichloroacetic acid (tca)-precipitable peptides separated on acid-urea polyacrylamide gels and one tca-soluble peptide separated by high-voltage electrophoresis (ph 4.9) with melanotropic activity. each of these peptides had a different degree of melanocyte stimulating hormone (msh) activ ... | 1977 | 894250 |
| the sensitivity of xenopus laevis tadpole tail tissue to the action of thyroid hormones. | 1977 | 892410 | |
| transport of different rna species from the nucleus to the cytoplasm in xenopus laevis neurula cells. | 1977 | 892232 | |
| lens regeneration from cornea in tail ectopic eyes of xenopus laevis tadpoles. | 1977 | 891882 | |
| the effect of concanavalin-a on the reaggregation of cells dissociated from xenopus laevis early embryos. | the effects of concanavalin-a on the reaggregation and sorting of cells from xenopus laevis early embryos have been studied. the results suggest that at high concentrations, concanavalin-a can prevent reaggregation. | 1977 | 891827 |
| magnesium deficiency in embryos of xenopus laevis. | embryos of xenopus laevis reared in media with various low (less than or equal to 10(-5) m) magnesium ion concentrations will exhibit differing degrees of a potentially lethal magnesium starvation syndrome depending on the ion concentration and rearing temperature. the higher the rearing temperature or the lower the magnesium ion content of the medium the more severely the syndrome will be expressed. (normal development can be expected at temperatures 13-30 degrees c and magnesium ion concentrat ... | 1977 | 886266 |
| purification and characterization of xenopus laevis vitellogenin messenger rna. | 1977 | 885849 | |
| changes in protein phosphorylation accompanying maturation of xenopus laevis oocytes. | 1977 | 885290 | |
| changes in neuromast chemosensitivity in xenopus laevis kept under various environmental conditions. | 1977 | 874416 | |
| biochemical research on oogenesis: oocytes of xenopus laevis synthesize but do not accumulate 5s rna of somatic type. | 1977 | 873059 | |
| grafting analysis of the periodic albino mutant of xenopus laevis. | 1977 | 873057 | |
| differential accumulation of two size classes of poly(a) associated with messenger rna during oogenesis in xenopus laevis. | 1977 | 873054 | |
| very long-lived messenger rna in ovaries of xenopus laevis. | 1977 | 873053 | |
| sequential changes in the structure and function of hepatocytes in estrogen-treated xenopus laevis males. | 1977 | 872992 | |
| some morphogenetic features of the adenohypophysical primordium of early xenopus laevis tadpoles. | the adenohypophyses of xenopus laevis tadpoles at developmental stages 20 to 46 (nieuwkoop and faber, 1956) were studied. from its first appearance at about stage 20 to 21, the adenohypophysial primordium passes through four morphogenetic phases, each characterized by internal events. the first phase (stages 20 to about 33/34) is characterized by extensive proliferation of the primordium. during the second phase (stages 33/34 to about 37/38), the growth of the primordium is arrested. this arrest ... | 1977 | 872195 |
| an autoradiographic analysis of nucleic acid synthesis in the presumptive primordial germ cells of xenopus laevis. | microinjection of [3h]thymidine into xenopus laevis embryos between late blastula (stage 10) and early tadpole (stage 44) showed that the presumptive primordial germ cells synthesis dna between stages 10-33. the percentage of labelled cells was highest between stages 10 and 16, declined sharply between stages 22 and 26 and rose again between stages 26 and 33. the fluctuations in the labelling patterns together with increase in the number of presumptive primordial germ cells and direct observatio ... | 1977 | 870589 |
| lengths and patterns of transcriptional units in the amplified nucleoli of oocytes of xenopus laevis. | transcriptionally active chromatin from peripheral amplified nucleoli of lampbrush-chromosome stage oocytes of xenopus laevis was dispersed and spread in various solutions of low salt concentrations (including some with additions of detergents) and examined by electron microscopy. nucleolar material from oocytes of animals with normal (2-nu) and mutant (1-nu) genetical constitution of nucleolus organizers was compared. histograms showing the distributions of the length of matrix units, apparent ... | 1977 | 870292 |
| a stereological approach to the study of neural organogenesis in xenopus laevis. | stereological methods are applied to the study of structural changes undergone, during neurulation, by the neuroepithelium of early embryos of xenopus laevis. in light microscopy, we evaluate: the section area of the neuroepithelium, the nucleocytoplasmic ratio, the volume fraction of the intercellular spaces, of the nuclei and of the cytoplasm. in electron microscopy, the volumetric density and the surface ratio of mitochondria as well as the surface density of the endoplasmic reticulum are mea ... | 1977 | 869225 |
| histone mrna in xenopus laevis ovaries: identification of the h4 messenger. | rna extracted from ovaries of adult xenopus laevis and introduced into a wheat germ cell-free system, directs the synthesis of polypeptides co-electrophoresing with all five histones. by frationation of total ovary rna through sephadex g-200 and polyacrylamide gel, rna was isolated that is translated into histones 4 (h4) only. in addition, this rna labelled in vitro with [i125] hybridizes to a restriction fragment of cloned sea urchin dna known to contain the h4 gene. | 1977 | 866192 |
| persistence of oocyte amplified rdna during early development of xenopus laevis eggs. | 1977 | 863108 | |
| inhibitor of ribosomal rna synthesis in xenopus laevis embryos. vi. occurrence in mature oocytes and unfertilized eggs. | 1977 | 863107 | |
| progesterone-induced dna polymerase activity in full-grown oocytes of xenopus laevis (1). | dna polymerase activity increases in full-grown oocytes of xenopus laevis during in vitro progesterone-induced maturation. this increase is inhibited by cycloheximide. the presence of the oocyte's nucleus (germinal vesicle) seems essential for the induction of this increase: in previously enucleated oocytes, the level of dna polymerase activity does not change during progesterone treatment. furthermore, a new form of dna polymerase is detectable by deae chromatography in in vitro matured oocytes ... | 1977 | 859007 |
| effect of partial hepatectomy on the interrenal tissues of xenopus laevis (daudin). | partial hepatectomy was carried out on xenopus laevis to investigate its influence on the endocrine system. in addition to other endocrine effects, a marked hypertrophy and stimulation of the interrenal gland was observed. activated cells contain mitochondria with extended and irregularly coiled tubules embedded in a low electron dense matrix. hepatectomy induces two phases of proliferation [3 and 35 days postoperative (p.o.)]. after 106 days p.o. giant mitochondria possessing narrow and closely ... | 1977 | 858162 |
| lectin binding to dissociated cells from two species of xenopus embryos. | 1. fluorescein isothiocyanate-conjugated concanavalin a (f-cona) and soy bean agglutinin (f-sba) bind to the surface of edta-dissociated cells from blastula and gastrula stage xenopus laevis and x. mulleri embryos. 2. binding of these lectins is abolished by appropriate haptens (alpha-methyl-d-mannopyranoside for f-cona and 2-acetamido-2-deoxy-d-galactose for f-sba). 3. gastrula stage cells show a clustering or capping of lectin binding sites not shown by blastula stage cells. 4. at least for f- ... | 1977 | 856477 |
| rna synthesis in isolated nuclei of xenopus laevis emproyos. | nuclei were isolated from tailbud embryos of xenopus laevis and their rna synthetic activity was studied. the activity was sensitive to actinomycin d, and required the presence of all four ribonucleotide triphosphates and a divalent cation (mg2+ or mn2+). the effect of the divalent cation varied depending on the presence of 0.4 m kcl: in its absence more rna was synthesized with mg2+ than with mn2+, but in its presence the situation was reversed. about 50% of the rna synthesized was sensitive to ... | 1977 | 856273 |
| translation and distribution of rabbit globin mrna in separated cell types of xenopus laevis gastrulae. | 1977 | 849804 | |
| modifications by light of synaptic density in the inner plexiform layer of the toad, xenopus laevis. | 1977 | 849751 | |
| studies on the biosynthesis, assembly and secretion of vitellogenin, an oestrogen-induced multicomponent protein. | 1. the process by which the egg-yolk protein precursor vitellogenin is biosynthesized, assembled and secreted by xenopus laevis (south african clawed toad) liver was studied. it was previously shown in other laboratories that vitellogenin contains the two egg-yolk proteins lipovitellin (mol.wt. 140 000) and phosvitin (mol.wt. 35 000). 2. evidence is presented which shows that xenopus liver microsomal fractions synthesize precursors of vitellogenin. these precursors were solubilized from the memb ... | 1977 | 849274 |
| slow action of ca on myelinated nerve fibres of xenopus laevis. | single myelinated nerve fibres were isolated and the nodal currents were recorded with potential clamp technique. rapid solution changes were performed by use of a recording chamber so shaped that it had a minimal dead space. a volume ten times larger than the dead space flowed past the node within about 20 ms. the half-time of the change in na current (ina)amplitude associated with changes between solutions of different [na]:s was 100-150 ms, whereas the half-time of the change in ina associate ... | 1977 | 848308 |
| size of ribosomal dna repeating units in xenopus laevis: limited individual heterogeneity and extensive population polymorphism. | 1977 | 845941 | |
| transcription of specific genes in isolated nuclei by exogenous rna polymerases. | mouse plasmacytoma (mopc) 460 cells contain two chromatographic forms of rna polymerase iii (iiia and iiib) in addition to the major class i and ii rna polymerases. nuclei isolated from these cells actively synthesize rna. among the discrete transcription products observed are the 5s and 4.5s rnas and additional low molecular weight rna species (approximately 5.8s, 6.3s, and 6.6s in size). the 4.5s rnas appear to be trna precursors since they can be converted in vitro to 4s rnas. studies with al ... | 1977 | 844100 |
| resolution of parameters in the equivalent electrical circuit of the sodium transport mechanism across toad skin. | in amphibian epithelia, amiloride reduces net sodium transport by hindering the entry of sodium to the active transport mechanism, that is, by increasing the series resistance (rser). theoretically, therefore, analysis of amiloride-induced changes in potential differences and short-circuit current should yield numerical estimates of all the parameters in the equivalent electrical circuit of the sodium transport mechanism. the concept has been explored by analysis of such changes in toad skins (x ... | 1977 | 839526 |
| changes in the cell coat at the onset of gastrulation in xenopus laevis embryos. | four developmental stages of xenopus laevis embryos were fixed in standard electron microscopic fixatives with 1% lanthanum nitrate added. this treatment reveals a lanthanum staining material (lsm) on the cell surface and in extracellular spaces. morula and blastula stage cells have a small amount of lsm; in blastulae, 3 +/- 3 sd % of the cell surface is coated with lsm. in early gastrulae, 29 +/- 6 sd % of the cell periphery is covered with lsm. in late gastrulae, 82 +/- 13 sd % of the cell per ... | 1977 | 839183 |
| ribosomal rna synthesis in the eastern north-american newt, notophthalmus viridescens. | ribosomal rna (rrna) synthesis, the initiation of which is an early major event during the transformation of iris into lens in the newt, was characterized in the tvi cell-line derived from the eastern north-american newt notophthalmus viridescens. employing the technique of polyacrylamide gel electrophoresis, molecular-weight measurements were made on newt rrnas using xenopus laevis and e. coli rrnas as standards. the molecular weights of n. viridescens 28s and 18s rrna were found to be 1.4 x 10 ... | 1977 | 838209 |
| accumulation of mitochondrial dna during oogenesis in xenopus laevis. | 1977 | 838132 | |
| ultrastructural observations on cortical endoplasmic reticulum and on residual cortical granules in the egg of xenopus laevis. | 1977 | 838127 | |
| evidence for polarizing zone in the limb buds of xenopus laevis. | 1977 | 838122 | |
| the visual pigment and vitamin a of xenopus laevis embryos, larvae and adults. | 1977 | 838004 | |
| in situ effects of s1 endonuclease (neurospora crassa) on pachytene chromatin of xenopus laevis females at metamorphosis. | 1977 | 837986 | |
| the effects of biogenic amines on carbohydrate metabolism in xenopus laevis daudin. | 1977 | 832822 | |
| existence of ultraviolet-labile germ cell determinant in unfertilized eggs of xenopus laevis and its sensitivity. | 1977 | 832771 | |
| correlation between the cell cycle in the neurectoderm and differentiation during the early development of xenopus laevis. 1. budr sensitivity during gastrulation. | an hypothesis has been proposed by holtzer and co-workers (1963, 1970, 1973) that the process of cell differentiation may be coupled in an obligatory manner with 'quantal' cell cycle(s) which precede it. we have demonstrated that a 'wave' of dna synthesis occurs in the neurectoderm of xenopus laevis gastrula. this event of the cell cycle appears to be associated with the primary embryonic induction by the subjacent mesodermal tissue. the peak of dna synthesis was observed in that area of the neu ... | 1976 | 829417 |
| high tyrosinase activity in albino xenopus laevis oocytes. | tyrosinase was measured in oocytes of the recently described albino mutant (apap) of xenopus laevis. although these oocytes show no pigmentation and the eggs are known to contain no melanosomes, tyrosinase - which is probably the only enzyme necessary for melanin synthesis from tyrosine - was increased more than twofold relative to the wild type. tyrosinase recovered from albino and wild type oocytes showed the same km with respect to tyrosine, and this was not altered by previous gonadotrophin ... | 1976 | 827598 |
| [ perfecting a simple method of organotypic thyroid gland culture in xenopus laevis (amphibia, anoura)]. | the larval thyroid of xenopus cultured in an adequate medium, keeps its morphological differentiations at an ultrastructural scale and reacts against tsh added to the culture medium, through the development of apical microvilli, which is a sign of an active pinocytosis of the colloid, and also of ergastoplasmic lamellar and vesicular structures suggesting an active protein synthesis. | 1976 | 827362 |
| dna reassociation kinetics in relation to genome size in four amphibian species. | dna reassociation kinetics were studied, by means of the hydroxyapatite chromatography method, for four species of amphibians with different nuclear dna content: xenopus laevis (3 pg dna per haploid genome) and bufo bufo (7 pg) of the anura subclass and triturus cristatus (23 pg) and necturus maculosus (52 pg) of the urodela subclass. within each subclass the two species studied were found to have about the same absolute amount of unique dna. the differences of total nuclear dna can be accounted ... | 1976 | 826380 |
| [ulstrastructure of xenopus heart primordia, differentiated in culture in the presence of actinomycin d]. | the cellular differentiation of xenopus laevis cardiac primordia, developed in vitro with actinomycin d, was studied in fine structure. the ultrastructural changes appeared in mitochondria, and in nucleus, which showed a nucleolar characteristic segregation. | 1976 | 825283 |
| [oocyte maturation in xenopus laevis. the entry of progesterone is necessary for maturation]. | in vitro progesterone-induced maturation of xenope ovocyte was studied as a function of progesterone uptake and extracellular progesterone concentration. maturation depends on the initial total amount of progesterone in incubation medium and does not depend on the extracellular hormonal concentration. this result strongly argues for an intracellular receptor site for progesterone. | 1976 | 825259 |
| immunoglobulin heavy chain mrna in mitogen-stimulated b cells. | this paper relates the synthesis of dna, immunoglobulin and heavy chain (h) mrna in murine spleen cells following activation of b cells with lipopolysaccharide from e. coli (lps). spleen cells (cba/h mice) were cultivated with 10% fcs and 10 mug lps/ml. 4 h pulses with [3h]thymidine showed that dna synthesis was stimulated within the first day following lps activation and exhibited a sharp peak at 24 h. the shape of the dna synthesis curve suggests that the cells susceptible to lps stimulation a ... | 1975 | 824129 |
| [in vitro maturation of the ovocyte of xenopus laevis under the effect of pharmacological agents related to propranolol]. | the maturation of xenopus laevis ovocytes was performed after 15 hrs. exposure to progesterone (1 mug/ml). similar results were obtained following a treatment of ovocytes with pharmacological agents such as propranolol and related drugs, at 5 x 10(-4) to 10(-2) m concentrations. sotalol was totally ineffective at the same concentrations. the former drugs, and not sotalol, are supposed to interact within the membrane with some calcium sites, translocation of the ion inside being then produced. th ... | 1976 | 821641 |
| [early changes in the electric properties of the oocyte plasma membrane of xenopus laevis during the reinitiation of meiosis induced by progesterone, para chloromercuribenzoate (pcmb) or the ionophore a 23187]. | progesterone, pcmb and ionophore -mg++ triggers early and quite similar changes in the electrical properties of xenopus laevis plasma membrane which may play a key role in the process of meiosis reinitiation. | 1976 | 819174 |
| [oocyte maturation in xenopus laevis. arguments in favor of the role of calcium ions]. | influx and efflux of 45ca++ ions in xenopus leavis isolated full-grown oocytes were measured. calcium influx was from 0.5 to 1 pmole/oocyte/h. progesterone, which induces maturation does not influence ca++ fluxes while pcmb caused a significant increase of ca++ influx during the course of pcmb (p-cl-hgbzo-) induced maturation. our results show that the presence of ca++ is not necessary in extracellular medium for germinal vesicle breakdown (gvbd) induced by progesterone. in contrast, the kinetic ... | 1976 | 819172 |
| selenium effect on the growth of carcinogenic fungi and cytotoxic action of aflatoxin b1 on lymphocyte culture and on embryonal development of xenopus laevis. | the authors report the results of investigations on the protective effect of selenium against teratogenic and cytotoxic action of aflatoxin b1 and the inhibitory action of this element on the growth of fungi producing carcinogenic aflatoxins. sodium selenate inhibited the growth of cultures of such fungi belonging to the class fungi imperfecti as aspergillus flavus, aspergillus fumigatus, penicillium meleagrinum and penicillium rougolosum. added to cell cultures of lymphocytes sodium selenate in ... | 1975 | 817275 |
| biogenesis of plasmalemmal glycoproteins. intracellular site of synthesis of mouse liver plasmalemmal 5'-nucleotidase as determined by the sub-cellular location of messenger rna coding for 5'-nucleotidase. | 1. free and membrane-bound mouse liver polyribosomes were separated by prolonged density-gradient centrifugation of the post-mitochondrial supernatant. rna was extracted from free and membrane-bound polyribosomes and mrna purified by oligo(dt)-cellulose column chromatography. 2. antisera against purified mouse liver plasma membrane 5'-nucleotidase and moust albumin were prepared and characterized. 3. microinjection of equivalent amounts of mrna from free and membrane-bound liver polyribosomes in ... | 1975 | 810623 |
| adult amphibian epidermal proteins: biochemical characterization and developmental appearance. | the keratin-like proteins (klps) from the epidermis of adult frogs of the species xenopus laevis have been isolated and biochemically characterized by means of polyacrylamide gel electrophoresis, amino acid analysis, tryptic peptide mapping, amino-terminal end-group analysis and isoelectric focusing. one particular protein fraction of rather unusual amino acid composition found only in epidermal tissue was isolated in quantity by preparative gel electrophoresis and monospecific antibodies prepar ... | 1975 | 810539 |
| innervation of the male genital tract and kidney in the amphibia, xenopus laevis daudin, rana temporaria l., and bufo bufo l. | the innervation of the male genital tract and kidney in three anuran species was studied by the fluorescence histochemical method of falck-hillarp for the demonstration of monoamines whose identity was secured by thin-layer chromatography, and by electron microscopy including administration of 5- or 6- hydroxydopamine (5- and 6-odha). the genital tract comprises testis, intra- and extratesticular and intrarenal seminal efferent ducts, bidder's canal, renal dorsal transverse ducts, and ureter. in ... | 1975 | 807332 |
| the macromolecular composition of xenopus laevis egg jelly coat. | the three morphologically and functionally distinct jelly coat layers of xenopus laevis eggs, j1, j2, and j3, were separated by manual dissection, solubilized with dithiothreitol, and physicochemically analyzed. the chemical composition of the three jelly layers varied from 37 to 48% protein and 63 to 52% carbohydrate. the carbohydrate consisted of hexosamines, galactose, and fucose. some of the carbohydrate in each of the jelly layers was covalently linked to protein through o-glycosidic bonds ... | 1975 | 807242 |
| fine structure of the male genital tract and kidney in the anura xenopus laevis daudin, rana temporaria l. and bufo bufo l. under normal and experimental conditions. | the ultrastructure of the main cellular components of testicular interstitial spaces in three anuran species was studied during two short periods of the seasonal cycle and after treatment with 5- and 6-hydroxydopamine (5- and 6-ohda). in early december when seminiferous tubules are completely filled with resting spermatozoa in rana, leydig cells display a well developed smooth- and rough-surfaced er, numerous granular vesicles being untypical of mammalian leeydig cells, metochondria with tubular ... | 1975 | 805666 |
| humoral antibodies to soluble antigens in larvae of xenopus laevis. | 1975 | 804375 | |
| restoration of immune responsiveness in early thymectomized xenopus by implantation of histocompatible adult thymus. | larvae of the south african clawed toad, xenopus laevis, were thymectomized at nieuwkoop and faber stages 45-46 (4-5 days after fertilization). the 1-1.5-year-old thymusless toads thus obtained were implanted with histocompatible thymus from 1-year-old toads, and 4 weeks later were given skin allografts or rabbit red blood cells (rrbc) to determine their immune response. in contrast with the perfectly tolerant thymusless controls, the thymus-implanted toads rejected skin allografts after longer ... | 1976 | 797285 |
| acitivity of yeast extracts in cell-free stimulation of dna replication. | extracts of the cytoplasm of disrupted spheroplasts of saccharomyces cerevisiae (bakers' yeast) stimulated dna synthesis in a cell-free system consisting of nuclei from spleen cells of the frog xenopus laevis, the stimulation required mg++8 atp, and the deoxynucleoside triphosphates, was saturated by an excess of nuclei or extract, and had kinetics resembling those obtained previously with extracts from mammalian and avian cells. after addition of the yeast extract, replication "eyes" were forme ... | 1976 | 792878 |
| lhrh-like system in the brain of xenopus laevis daud: immunohistochemical idenfication. | rabbit antiserum to synthetic lhrh was used with the immunofluorescence technique to identify the lhrh-secreting neurons and their axonal pathways in the brain of xenopus laevis. three groups of immunoreactive neurons were identified: the first, in the telencephalon, is a paired group of cells scattered near the two telencephalic ventricles; the second group lies near the preoptic recess; the third group occurs in the ventral wall of the infundibulum. two principal neuronal pathways were observe ... | 1976 | 791498 |
| the molecular basis for length heterogeneity in ribosomal dna from xenopus laevis. | 1976 | 787539 | |
| adjacent repeating units of xenopus laevis 5s dna can be heterogeneous in length. | the distribution of length heterogeneity in adjacent repeating units of x. laevis 5s dna has been examined by "cloning" 5s dna in bacteria. fragments of 5s dna produced by partial digestion with hind iii and containing 1, 4, and 5 repeating units have been inserted at the single hind iii site of the tetracycline-resistance plasmid, psc101, and the hybrid plasmids cloned in e. coli. adjacent 5s dna repeats in the cloned multi-repeat fragments can differ in length. this finding rules out some mech ... | 1976 | 782719 |
| changes in trna nucleotidyl transferase activity during embryonic development of xenopus laevis. | 1976 | 776635 |