Publications

TitleAbstractYear(sorted ascending)
Filter
PMID
Filter
specificity in deoxyribonucleic acid uptake by transformable haemophilus influenzae.cells of haemophilus influenzae strain rd competent for genetic transformation irreversibly bound approximately five molecular fragments of h. influenzae deoxyribonucleic acid (dna) per cell; under identical conditions, dna derived from escherichia coli b was not taken up (<1 molecule per 50 cells). similarly, dna from xenopus laevis was not taken up by competent h. influenzae. of the heterologous dnas tested, only dna from h. parainfluenzae interfered with the uptake of h. influenzae dna, as ju ...19744597440
detection of haemoglobin in red cells of xenopus laevis by immunofluorescent double labelling. 19744597872
replication and transcription of eukaryotic dna in escherichia coli.fragments of amplified xenopus laevis dna, coding for 18s and 28s ribosomal rna and generated by ecori restriction endonuclease, have been linked in vitro to the bacterial plasmid psc101; and the recombinant molecular species have been introduced into e. coli by transformation. these recombinant plasmids, containing both eukaryotic and prokaryotic dna, replicate stably in e. coli. rna isolated from e. coli minicells harboring the plasmids hybridizes to amplified x. laevis rdna.19744600264
5'-ends of ribosomal and ribosomal precursor rnas form xenopus laevis. 19744600324
the lampbrush chromosomes of xenopus laevis (daudin). 19744609703
the response of xenopus laevis oocytes to injected somatic nuclei soon after germinal vesicle breakdown induced in vitro. 19744609785
ontogeny and localization of the lens crystallins in xenopus laevis lens regeneration. 19744618568
visual deprivation and intertectal neuronal connexions in xenopus laevis. 19751778
vital dye mapping of the gastrula and neurula of xenopus laevis. i. prospective areas and morphogenetic movements of the superficial layer. 197546836
structural studies of the xenopus 19s immunoglobulin and 7s immunoglobulin and two immunoglobulin-like proteins.xenopus laevis 19s and 7s immunoglobulins (ig) were extensively reduced and alkylated, their h and l chains spearated and their molecular weights determined. two kinds of l chains of molecular weight 25,000 and 27,000 were revealed by sds-polyacrylamide gel electrophoresis. in addition two ig-like proteins consisting of heavy chains only, of 19s h-type and with similar molecular weight, were detected in xenopus serum ans isolated. these proteins share common antigenic determinants with xenopus 1 ...197547834
chromosome banding pattern conservatism in birds and nonhomology of chromosome banding patterns between birds, turtles, snakes and amphibians.the g-banded karyotypes of 4 species of birds representing the orders galliformes, columbiformes and musophagiformes were compared. banding pattern homology between orders was limited t 5o 5 major chromosome arms and the z chromosome. even in these major chromosome arms pericentric and paracentric inversions produced alteration of the banding pattern sequences. addition of constitutive heterochromatin was responsible for changes in banding patterns in the z chromosome. the chromosome banding pat ...197548453
influence of antigen dose on antibody production of intact and splenectomised xenopus laevis.antigen persistence and serum antibody production in intact xenopus were monitored using human gamma globulin (hgg), in adjuvant, in various immunisation schedules. retention of hgg in spleen and serum was directly related to the quantity injected. however, antibody responses to a dose range between 1 mu-g-6 mg antigen were similar in intensity. these were detected in the serum two weeks after injection and at this stage were exclusively mercapto-ethanol (me) sensitive; me-resistant antibodies h ...197548536
utilization of yolk platelets and lipid bodies during the myogenesis of xenopus laevis (daudin).the premyoblast and differentiating mononuclear myoblasts of the metameric striated muscles of xenopus laevis were analysed for vitellolysis and lipid body utilization. in the course of myoblast differentiation the stainability of platelets stained with safranin and fast green shows essential variations. the platelets appear to lose their affinity for safranin and subsequently begin to stain with fast green. the yolk platelets were found to contain basic proteins, non-histone proteins, and phosp ...197550138
microfilaments in the external surface layer of the early amphibian embryo.a comparison was made by transmission electron microscopy of the microfilaments in the surface layers of the early embryos of triturus alpestris and xenopus laevis at stages of development up to neurulation. actin-like filaments which bound heavy meromyosin (hmm) were found in cell extracts of all stages, but were comparatively rare in the newly fertilized egg. ten nm microfilaments were present throughout development in xenopus, and from the mid-neurula stage in triturus. both kinds of microfil ...197550397
the mucosubstance coating the pneumonocytes in the lungs of xenopus laevis and lacerta viridis.the layer of mucosubstance that is associated with the free surface membranes of the pneumonocytes in the lungs of the toad xenopus laevis and the lizard lacerta viridis was demonstrated by electron microscopy using iron oxide stain. the form and staining reactions of the mucosubstance layer were similar in both animals. in electron micrographs the mucosubstance was represented by a band of densely stained material (25-50 nm thick) which coated the entire free surface of the pneumonocytes. it ap ...1975165163
response of large oocytes of xenopus laevis to progesterone in vitro in relation to oocyte size and time after previous hcg-induced ovulation. 1975166003
in vitro progesterone binding to xenopus laevis oocytes. 1975166010
studies on the liver of xenopus laevis. i. the ultrastructure of the parenchymal cell.the liver of xenopus laevis was examined with electron microscopy. its structure was found to be markedly different from that of mammals, particularly regarding the morphology of the hepatocytes to be classified as typical. it was established that the main function of such a cell is the storage of glycogen, and further that it possesses only scant organelles and other inclusions. since this type of cell was found most frequently in the liver of untreated animals, it was designated as normal cell ...1975167614
template specificity of the cytoplasmic dna polymerase in xenopus laevis oocytes. 1975167780
molecular weights of estrogen and androgen binding proteins in the liver of xenopus laevis.[3-h]estradiol-17beta and [3-h]dihydrotestosterone binding proteins in the cytosol fraction of liver from both male and female xenopus laevis were characterized by electrophoresis on polyacrylamide gels. these binding proteins, which were indistinguishable based upon their mobilities on gels of different acrylamide concentrations, migrated as single components with a molecular weight of 2.0 x 10-4. separation of native or sodium dodecyl sulfate denatured specific estrogen-binding components on d ...1975167818
[the effects of cortisol and progesterone injected directly into the oocytes of xenopus laevis]. 1975167990
synthesis and secretion of a large glycoprotein in the pars intermedia.the biosynthesis, intracellular transport and release of [3-h]-leucine-containing secretory product has been followed in the pars intermedia of xenopus laevis and, in particular, the synthesis and secretion of a large molecular weight glycoprotein secretory product was demonstrated. however, if xenopus adrenocorticotrophin does contain a leucine residue the results obtained provided no support for the view that it serves as a precursor for melanocytestimulating hormone in this species.1975168285
inhibitor induced alterations of chromatoid bodies in male germ line cells of xenopus laevis.the action of inhibitors of protein synthesis on the structure of cytoplasmic inclusions found in the male germ cell line of the anuran, xenopus laevis, has been studied by light and electron microscopy. results indicate that one such inclusion, the chromatoid body, is sensitive to treatment with either chloramphenicol or puromycin. these drugs administered in vivo or in vitro cause up to a thirty-fold increase in the volume of the chromatoid body in all stages where it is normally present. maxi ...1975169993
mechanism of action of progesterone on amphibian oocytes. uptake and metabolism of progesterone by isolated oocytes of pleurodeles waltlii and xenopus laevis. 1975170033
light-induced formation of dense-core vesicles in rod photoreceptors in retina of xenopus laevis. 1975170537
ultrastructural and pharmacological studies on the afferent synapse of lateral-line sensory cells of the african clawed toad, xenopus laevis.lateral-line sensory cells of xenopus show considerable similarity to central nervous system synapses in their responses to the zinc iodide-osmium tetroxide, and bismuth-iodide cytochemical staining techniques. both reserpine and fla-63 cause a reduction in the diameter and electron density of the synaptic bars, and a dramatic loss of synaptic vesicles surrounding the bars. aminooxy acetic acid and 3-mercaptopropionic acid cause no significant changes in the sensory-cell afferent synaptic appara ...1975171077
changes in the content of cyclic amp and cyclic gmp during the development of xenopus laevis. 1975172338
translation of messenger ribonucleic acid from isolated pancreatic islets and human insulinomas.rna preparations from isolated rat pancreatic islets and from human insulinomas were injected into oocytes of xenopus laevis which were then incubated with [3h]leucine. acid-ethanol extracts of the oocytes were immunoprecipitated with anti-insulin serum using the double antibody technique. sodium dodecyl sulfate disc gel electrophoresis of the immunoprecipitates showed the presence of an insulin-displaceable immunoreactive material with a molecular weight of about 18,000 in extracts from oocytes ...1975174093
[enzymatic aspects of the mitochondria of xenopus laevis oocytes]. 1975183438
[extra- and intra-mitochondrial distribution of respiratory enzymes in oocytes of xenopus laevis]. 1975183439
'immobile' (im), a recessive lethal mutation of xenopus laevis tadpoles.'immobile' (im) is a recessive lethal mutation discovered in the f3 of a xenopus (xenopus laevis laevis) originating from a mesodermal nucleus of a neurula transplanted into an enucleated egg. the im embryos do not contract after mechanical stimulation nor do they present any spontaneous contraction from the neurula stage onwards. development proceeds normally during the first days after which deformation of the lower jaw and tail are observed. the im tadpoles die when normal controls are at the ...1975127824
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 ...1975237058
the time course of experience-dependent synaptic switching of visual connections in xenopus laevis. 1975237285
osmotic and ionic regulation in xenopus laevis daud. during adaptation to different osmotic environments--v. quantitative alterations of the acid glycosaminoglycans in the kidney. 1975237733
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 ...1975238247
template preferences of dna polymerase and nuclease activities appearing during early development of xenopus laevis. 1975238871
changes in the activity and isozymes of acetyl and butyrylcholinesterase during xenopus laevis development. 1975240618
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 ...1975240903
tissue typing by skin grafting during metamorphosis of the toad xenopus laevis (daudin). 19751089553
replication of amplifying ribosomal deoxyribonucleic acid in rolling circles in xenopus laevis oocytes. 19751095648
in situ hybridization of ribosomal dna labelled with 125iodine to metaphase and lampbrush chromosomes from newts.methods are described for in situ hybridization of ribosomal dna from xenopus laevis, labelled in vitro with 125iodine, to mitotic and lampbrush chromosomes from triturus cristatus carnifex. the hybridization reaction was carried out in a mixture containing 50% formamide, 4 x ssc, 0.1 m ki, at 37 degrees c, or in 2 x ssc, 0.1 m ki at 65 degrees c. autoradiographs of mitotic metaphases from 2 males showed labelling over the middle of the short arm of one chromosome ix in each metaphase. in some c ...19751097214
aminoacylation of transfer rna microinjected into xenopus laevis oocytes. 19751097945
types and distribution of lamellar bodies in first cleavage xenopus embryos.lamellar bodies in first cleavage xenopus laevis embryos have been examined with the electron microscope. based on the arrangement and relative thickness of the lamellae, three types of lamellar bodies have been identified. in the first type, a band of two to ten lamellae (spacing about 3.5 nm) was interwined at random. this type of lamellar body was seen closely associated with the concave or the forming face of the golgi body and may have been derived from this organelle. the frequent associat ...19751102108
replication and expression of constructed plasmid chimeras in transformed escherichia coli--a review.ecori restriction-endonuclease-generated fragments of bacterial plasmids isolated from staphylococcus aureus or escherichia coli, or of amplified dna coding for the 18s and 28s ribosomal rna of xenopus laevis, have been linked to the psc101 plasmid replicon and introduced into e. coli by transformation. the constructed plasmid chimeras can be cloned as stable replicons in e. coli, where they synthesize rna and/or protein products specified by their component genes.19751103843
distribution of 18+28s ribosomal genes in mammalian genomes.in situ hybridization with 3h 18s and 28s ribosomal rna from xenopus laevis has been used to study the distribution of dna sequences coding for these rnas (the nucleolus organizing regions) in the genomes of six mammals. several patterns of distribution have been found: 1) a single major site (rat kangaroo, seba's fruit bat), 2) two major sites (indian muntjac), 3) multiple sites in centromeric heterochromatin (field vole), 4) multiple sites in heterochromatic short arms (peromyscus eremicus), 5 ...19751104290
messenger activity of ribonucleic acid form yeast mitochondria.total yeast mitochondrial rna was shown to possess messenger rna activity when injected into oocytes of the frog xenopus laevis. the specific polypeptides formed were precipitated by mitochondrial antisera. a comparison was made of the molecular weights of the proteins obtained form this system with those made by mitochondria in vivo in the presence of cycloheximide. no rna containing poly(a) sequences was detected in yeast mitochondria.19751106402
readenylation of polyadenylate-free globin messenger rna restores its stability in vivo.using an atp:rna adenyltransferase from escherichia coli, a polyadenylic sequence was resynthesized onto rabbit globin mrna from which the poly (a) segment had been previously removed. conditions for obtaining a homogenous reconstituted globin mrna preparation containing 30 adenylic residues per message molecule were determined. the reconstituted globin mrna was microinjected into xenopus laevis oocytes. its stability was very similar to that of native mrna.19751107033
ribosomal protein synthesis in xenopus laevis oocytes. 19751112442
synthesis of soluble protein in oocytes of xenopus laevis.oocytes of five stages of development were isolated from ovaries of xenopus laevis and allowed to take up radioactive amino acids. after six hours of labeling the amount of label incorporated into perchloric acid precipitable material from the soluble oocyte fraction and the specific activity of the label free pool was determined. from these figures an estimate of the rate of protein synthesis was calculated. labeled soluble protein from each oocyte stage was analyzed by electrophoresis on sds p ...19751113071
initiation factor distribution in xenopus laevis eggs.the distribution of activity similar to that of one of the initiation factors (if2) was determined as a function of developmental stage in xenopus laeviseggs and embryos. in vivo exposure of mature oocytes to hormone increases the total amount of detectable factor activity and facilitates the binding of if2-like factor to ribosomes. the quality of factor bound is not correlated with polysome content.19751113074
control of somite number during morphogenesis of a vertebrate, xenopus laevis.during xenopus embryogenesis and early growth, somite number stays close to a species-typical value for each morphological stage. this remains true even after operations on blastulae which lead to the development of abnormally small but otherwise complete early embryos, involving reduction in number of cells assigned to each somite. evidence presented suggests that a body-position gradient may be involved, but in rather different ways at different stages, in controlling total somite number.19751113883
biochemical research on oogenesis. comparison between the proteins of the ribosomes and the proteins of the 42 s particles from small oocytes of xenopus laevis. 19751116647
sequential changes in the protein synthetic activity of male xenopus laevis liver following induction of egg-yolk proteins by estradiol-17 beta.administration of a single injection of estradiol-17 beta to adult male xenopus laevis induces the synthesis and secretion by the liver of the egg-yolk protein complex vitellogenin. explants taken from livers of hormone-treated animals and maintained in organ culture continue to produce this protein at a rate which is dependent on the length of time between estrogen injection of the donor and preparation of the explants. organ culture, therefore, can be used to quantitate the vitellogenic respon ...19751117004
morphological changes of the surface of the egg of xenopus laevis in the course of development. i. fertilization and early cleavage. 19751117474
[time dependence of the reaction rate constant of potassium permeability of ranvier's node membrane].to describe the kinetics of potassium permeability (conductance) changes in the squid giant axon membrane the hodgkin--huxley formulation uses a single first-order in time variable n with forward and backward rate constants, respectively alpha-n and beta-n, potential-dependent but time-independent. it has been shown by frankenhaeuser that in the potassium-carrying system of the myelinated nerve fiber membrane of xenopus laevis the rate constant beta-n is dependent on the duration of previous de ...19751118903
[rhythmical changes in the reaction to various olfactory stimulants in the frog (xenopus laevis)]. 19751120515
the effect of porphyrin precursors on monosynaptic reflex activity in the isolated hemisected frog spinal cord.the porphyrin precursors beta-aminolevulinic acid (beta-ala) and porphobilinogen (pbg) which accumulate, and are excreted in the urine in increased amounts during acute attacks of porphyria, were tested for their effects on reflex activity in the isolated hemisected spinal cords of xenopus laevis. the two compounds were found to exert an inhibitory effect on monosynaptic ventral root responses, as well as on dorsal root responses (drr) and dorsal root potentials (drp). the latent period for inhi ...19751120952
effects of cycloheximide on the "autocatalytic" nature of the maturation promoting factor (mpf) in oocytes of xenopus laevis.it is shown that a factor arising during the course of maturation in amphibian oocytes is by itself capable of inducing maturation when injected into recipient oocytes even after a series of 10 transfers. the mechanism of action of this phenomenon is shown to be under translational control. experiments using cycloheximide suggest that mpf does not need protein synthesis for germinal vesicle breakdown (gvbd), but does require a translational step when serially transferred in order to sustain its ...19751122557
characterization of the two major dna polymerase activities in oocytes and eggs of xenopus laevis. 19751123043
decreased uptake of (3h)leucine during progesterone induced maturation of xenopus laevis oocytes. 19751123045
a dissociation factor from embryos of xenopus laevis.a dissociating factor has been extracted from the ribosomal kcl wash and from the cytosol of developing embryos of xenopus laevis. no dissociating activity could be detected in the kcl wash of ribosomes from full grown oocytes and unfertilized eggs. as in bacteria, the acitivity of the dissociation factor seems to be correlated with the rate of protein synthesis suggesting a physiological role of the dissociation factor. the possibility that the dissociation factor might be one of the components ...19751125315
effects of protease inhibitiors on early stages of meiosis in xenopus laevis oocytes. 19751126395
effects of protease inhibitors on early stages of meiosis in xenopus laevis oocytes. 19751126396
autoradiographic study of [3h] glucosamine incorporation by the developing retina of the clawed toad, xenopus laevis. 19751126404
dna synthesis during lens regeneration in larval xenopus laevis.larvae of xenopus laevis at stages 50-53 were lentectomized and then injected with tritiated thymidine at various times after lentectomy. in series i, the animals were injected 1,2,3,4,6,8,10,12,15, or 17 days after lens removal and fixed three hours after injection. autoradiograpns of serial cross sections through the eyes were prepared. increased incorporation of thymidine in the cells of the regenerating lens was first observed two days (stage 2) after lentectomy. all of the cells of the lens ...19751127410
parthenogenic development after chemical treatment of xenopus laevis spermatozoa.eggs of xenopus laevis were fertilized in vitro by spermatozoa pre-treated with various concentrations of aziridinyl urea (ethyleneurea) for between 30 and 120 minutes. at 2 and 4 mg/ml for 30 minutes there was a high incidence of abnormal embryos, few of which developed into tadpoles; after 6 and 8 mg/ml no tadpoles were produced. however, the highest concentration 10 mg/ml, yielded 66% of tadpoles, only 7% of which were obviously abnormal. with increasing time the same pattern of events was ob ...19751127411
permeability of xenopus laevis embryos: specific incorporation of precursors into eukaryotic proteins and nucleic acids. 19751132584
proceedings: effect of hypothalamic lesions on colour change in tadpoles of xenopus laevis. 19751133553
effect of uv on cleavage of xenopus laevis.uv irradiation of the vegetal pole of stage 2 x. laevis embryos with doses of 6000-18000 ergs/mm-2 delayed or inhibited cytokinesis in the vegetal hemisphere. nuclear division continued so that a syncytium was formed, the size and persistence of which depended on the dose. embryos which received a low uv dose were subsequently able to recover whereas embryos receiving a high dose were unable to gastrulate successfully. the implications for investigations into the role of cytoplasmic determinants ...19751133572
mitosis in presumptive primordial germ cells in post-blastula embryos of xenopus laevis.in x. laevis embryos injected with (3-h) thymidine between early gastrula and late neurula, the presumptive primordial germ cell nuclei were labelled and some were observed in mitosis, confirming that division occurs throughout this developmental period. in all labelled and mitotic cells, the germ plasm adjoined the nucleus, an observation which invalidates the hypothesis that germ plasm inhibits mitosis in presumptive primordial germ cells after gastrula. in embryos which had been irradiated wi ...19751133573
isolation of a dna fraction highly enriched in transfer rna genes from xenopus laevis.a dna fraction highly enriched in trna genes can be isolated from the xenopus laevis genome by the use of ag+/cs2so4 density gradients. ag+ shows a low affinity for some trna cistrons, allowing their separation from bulk dna upon equilibrium centrifugation in a cs2so4 density gradient. contaminating dna in the resulting tdna fraction is further removed by two additional cscl density gradient centrifugations. the final dna fraction is 60-fold enriched in trna genes, compared to the starting dna m ...19751138936
rna synthesis in nuclei isolated from early embryos of xenopus laevis.1. rates of rna synthesis in isolated xenopus embryo nuclei decrease from blastula through gastrula and neurula stages to hatching tadpoles. 2. in blastula and gastrula nuclei, net synthesis of rna continues for over 30 min, both in the presence of kcl at 0.4 m and in its absence. in nuclei from later stages, net synthesis continues for only about 10 min in the absence of kcl. 3. at low ionic strength, rna synthesis in all nuclei is greater with optimum mg-2+ (6 mm) than with optimum mn-2+ (1 mm ...19751138937
regeneration of the tail bud in xenopus embryos.in an attempt to solve some aspect of the long-standing controversy about the regenerative ability of appendages in vertebrate embryos, the tail bud of xenopus laevis embryos has beenamputated at stage sranging from st. 26 to st. 32 and its ability to regenerate duringa culture period of 2-3 days has been studied. at amputation stages 26-28,the tail bud consisted only undifferentialted mesoderm and ectoderm, but at stage 32 it had afully differentiated neural tube, a vaculotaed notochord and ...19751141840
membrane properties during myotome formation in tadpoles of xenopus laevis and bombina bombina. 19751142280
a comparison of the structural organization of amplified ribosomal dna from xenopus mulleri and xenopus laevis. 19751142438
studies on the liver of xenopus laevis. ii. the ultrastructure of the peritoneal cover and the perihepatic layer.the peritoneal cover and the subcapsular region of the liver of xenopus laevis were examined with electron microscopy. in the subcapsular region a prominent perihepatic layer two to ten cells wide was found. this perihepatic layer is mainly composed of granulocytopoietic tissue. other cell types found in the perihepatic layer were lymphocytes, pigment cells and fat storing cells. the presence of a perihepatic granulocytopoietic layer in the liver of xenopus laevis is in contrast to current opini ...19751147287
caerulein secretion by dermal glands in xenopus laevis.since gastrin and its related peptides are secreted by a minority population of widely dispersed cells in mamamalian tissues it has, in the past, been difficult to study the subcellular aspects of their secretion. from published reports (1, 2) it seemed possible that a satisfactory system for such studies might be provided by the skin of certain amphibians such as xenopus laevis since in these tissues high concentrations of peptides such as caerulein exist, and there is some indication (3) that ...19751150750
area specific reflexes from normal and supernumerary hindlimbs of xenopus laevis.two area specific reflexes elicited by natural stimulation of different regions of the hindlimbs of xenopus laevis have been identified. light or intense mechanical stimulation of the foot evokes reflex activity in the ipsilateral knee flexor nerve; moderate pressure applied to the calf evokes reflex activity predominantly in the ipsilateral knee extensor nerve. the reflex responses have been recorded electrophysiologically to overcome the limitations of behavioral observations for determining t ...19751150919
local autonomy of gastrulation movements after dorsal lip removal in two anuran amphibians.the time-course of the remaining gastrulation movements has been investigated after removal of the dorsal lip, the presumptive foregut endoderm and the anterior mid-dorsal mesoderm as a plug-shaped mass of cells from beginning gastrulae of xenopus laevis and bombina orientalis. this embryonic region has been previously studied in its role as an organizer, when grafted into a host gastrula marginal zone. there is usually no effect of the removal of these cells, the first morphogenetically active ...19751151264
quantitative studies of germ plasm and germ cells during early embryogenesis of xenopus laevis.the germ plasm in the egg is paritioned between the first four blastomeres by the first two cleavage planes. although the blastomeres divide 10-11 times through the rest of cleavage, as shown by reduction in their size, the number of presumptive primordial germ cells (p.p. germ cells) does not increase significantly. during and as a result of the formation of the first two cleavage planes, the germ plasm aggregates together and moves towards and along the cleavage furrows. at subsequent mitoses, ...19751151270
properties of surface and junctional membranes of embryonic cells isolated from blastula stages of xenopus laevis.1. some membrane properties of endoderm and mesoderm cells isolated from late blastula stages of xenopus laevis have been examined using electrophysiological techniques. 2. cells were isolated by treatment of whole embryos with ca-free edta containing media, or mechanically by micro-dissection, and cultured in ca-containing holtfreter solution (60 mm-nacl) or ringer solution (120 mm-nacl). 3. membrane potentials lay between -6 and -84 mv; specific membrane resistances ranged from 500 to 29,000 o ...19751151835
translation of plant messengers in egg cells of xenopus laevis. 19751153004
mitochondrial pleiomorphism in sustentacular cells of xenopus laevis.the mitochondrial population of sustentacular cells in the testis of the amphibian, xenopus laevis, has been examined by electron microscopy. three distinct types of mitochondria have been observed. the first and most common mitochondrial type is a "typical" organelle with a rod-like profile containing tubular to plate-like cristae. the second mitochondrial form is characterized externally by irregular bulbous protrusions and internally by increased numbers of tubular cristae. the third mitochon ...19751155790
microtubule protein synthesis during oogenesis and early embryogenesis in xenopus laevis.a method is described which permits the preparation of descrete classes of oocytes of different sizes from all stages of oogenesis in xenopus laevis. this technique is used in the determination of the content of microtubule protein in oocytes during the course of oogenesis. these experiments show that microtubule protein is present in oocytes of all sizes assayed and that the amount is simply related to the volume of the oocyte. in the largest oocytes microtubule protein constitutes 1% of the so ...19751156371
dna synthesis during larval development and compensatory growth in the mesonephros of xenopus laevis. 19751158024
mitochondrial ribosomal proteins in xenopus laevis/x. mulleri interspecific hybrids. 19751159786
dna sequence organization in the mollusc aplysia californica.the sequence organization of the dna of the mollusc aplysia californica has been examined by a combination of techniques. close-spaced interspersion of repetitive and single copy sequences occurs throughout the majority of the genome. detailed examination of the dna of this protostome reveals great similarities to the pattern observed in the two deuterostome organisms previously examined in detail in this laboratory, xenopus laevis and strongylocentrotus purpuratus. labeled and unlabeled aplysia ...19751164733
[effect of selenium on the growth of carcinogenic fungi and the cytotoxic action of aflatoxin b-1 in cell of lymphocytes and on the embryonal development of xenopus laevis]. 19751167689
dna synthesis in ocytes and eggs of xenopus laevis injected with dna. 19751171034
transcription of dnas of known sequence after injection into eggs and oocytes of xenopus laevis.1. when the synthetic polynucleotide, poly[d(a-t) - d(a-t)] is injected into the eggs and oocytes of xenopus laevis, a stimulation of rna synthesis results. analysis of extracted rna by high-voltage electrophoresis, shows that this stimulation of rna synthesis is due to the production of poly[r(a-u)] transcripts. the rate of poly[r(a-u)] synthesis is calculated to be at least ten-fold greater in eggs than in oocytes. the amount of poly[r(a-u)] detectable in injected eggs has reached a maximum by ...19751175643
[activity and isoenzymes of lactate dehydrogenase in tissues of amphibians (xenopus laevis, ambystoma mexicanum, triturus alpestris and vulgaris) and the response in the fat body of xenopus males to gonadotropin injection (author's transl)].lactate-dehydrogenase activity was determined by the optical test method using pyruvate as substrate and the isoenzymes were separated by vertical starch gel electrophoresis. species-specific and organ-specific characteristics of the total activity and the isoenzyme patterns of the four amphibian species are compared with those of rat and mouse. application of gonadotropin increases the amount of soluble protein and the lactate-dehydrogenase activity in the fat body of xenopus and the isoenzyme ...19751176091
autoradiographic localization of hormone-concentrating cells in the brain of an amphibian, xenopus laevis. i. testosterone.autoradiographic methods were used to investigate locations of hormone concentrating cells in the cns of xenopus laevis. both male and female frog brains contained cells. four major hormone uptake sites were identified: the anterior preoptic area, the ventral infundibular nucleus, a dorsal tegmental area of the medulla and a presumptive motor nucleus of cranial nerves ix-x. the distribution of labelled cells was very similar for male and female brains. available information on these testosterone ...19751176651
autoradiographic localization of hormone-concentrating cells in the brain of an amphibian, xenopus laevis. ii. estradiol.autoradiographic techniques for light microscopic examination of sex steroid retention were applied to the brains of male and female xenopus laevis, and anuran amphibian, after 3h-estradiol administration. estrogen was concentrated by cells in three telencephalic areas (the ventral striatum, the ventral-lateral septum and the amygdala), the anterior preoptic area, the ventral thalamus, the ventral infundibular nucleus, and in the torus semicircularis. the anterior preoptic area and the ventral i ...19751176652
the distribution of non-synaptic intercellular junctions during neurone differentiation in the developing spinal cord of the clawed toad.the distribution of intercellular junctions, other than synapses and their precursors, has been described in the developing spinal cord of xenopus laevis between the neurula and free swimming tadpole stages. at the neurocoel, ventricular cells are joined in the apical contact zone by a sequence of junctions which usually has one or more intermediate junctions but also includes close appositions, gap junctions and desmosomes. this apical complex is more diverse than that reported in other vertebr ...19751176854
myogenesis in the trunk and leg during development of the tadpole of xenopus laevis (daudin 1802).xenopus embryos pass through five behavioural stages between the end of neurulation (stage 20) and the accomplishment of free swimming (stage 33). these are (i) non-motile (stage 20-22) when the myotome muscle begins to differentiate; (ii) pre-motile (stage 22-24) when the first striated fibrils are visible and contractions are possible; (iii) early flexure (stage 24-27) when reflex responses are given and peripheral nerves are present; (iv) early swimming (stage 28-33); and (v) free swimming (s ...19751176869
on the determination of the dorso-ventral polarity in xenopus laevis embryos.when embryos, or dorsal or ventral half-embryos, of xenopus laevis are subjected to unilateral restriction of oxygen supply, the posterior end will always appear at the aerobic side, while the development of the anterior end, oriented towards the anaerobic side, will be partly suppressed. the shorter the time treatment lasts, the more normal the development will be. when the restriction of oxygen effects an inversion of the dorso-ventral polarity, development is retarded, otherwise not. measurem ...19751176879
xenopus laevis cement gland as an experimental model for embryonic differentiation. ii. the competence of embryonic cells.explants of the blastocoelic roof of xenopus laevis embryos were incubated for 6 h in holtfreter solution containing 10 mm ammonium chloride and 10 mm sodium bicarbonate. after this incubation they were transferred for 5 days to barth's physiological salt solution. under these conditions the explants underwent differentiation into cement gland tissue. the ability to produce cement gland was highest when explants were dissected from young gastrulae (stage 10). explants from younger and older embr ...19751176883
initiation of meiotic maturation in xenopus laevis oocytes by the combination of divalent cations and ionophore a23187.meiotic maturation was induced in xenopus laevis oocytes when the external ca++ or mg++ ion concentration was raised above 5 mm in the presence of the ionophore. ionophore-divalent cation-induced maturation appears to be due to the stimulation of the oocyte itself. cytoplasm of responding oocytes induced maturation when microinjected into ovarian oocytes. cycloheximid, an inhibitor of progesterone-induced maturation, inhibited the maturational response induced by the ionophore and divalent catio ...19751176910
effects of ionic concentration on sodium permeability properties of myelinated nerve fibres of xenopus laevis.1. the nodal currents of single myelinated nerve fibres were recorded under potential clamp conditions, and the effect of [ca], [na] and [k] in the external solution on some of the na permeability properties were analysed. 2. [ca], [na] and [k] all affected the position of the steady-state na inactivation (h) curve on the potential axis. the curve was displaced in positive direction by high ionic concentration. 3. the shift associated to different [ca] was largest in low [na] and [k]. similarly ...19751177104
oogenesis in xenopus laevis (daudin). iv. effects of gonadotropin, estrogen and starvation on endocytosis in developing oocytes.this study was designed to explore the relationship of estrogen, human chorionic gonadotropin (hcg), and food availability to endocytosis in developing oocytes. when estrogen alone is administered to an animal, large amounts of vitellogenin are synthesized by the liver and secreted into the circulatory system, where it accumulates. under these conditions there is no evidence of endocytosis at the surface of the oocytes. other studies have shown that following hcg injection into estrogen-treated ...19751181038
Displaying items 901 - 1000 of 17138