microinjection of trna into amphibian oocytes.the microinjection technique affords us the possibility to introduce purified components into living cells and to answer the question of what effects the change introduced has on cellular metabolism. this technique can therefore be used to test the hypothesis that transfer rna plays a regulatory role in cellular protein synthesis. prior to these experiments it is important, however, to test whether transfer rna microinjected into amphibian oocytes is stable and functional inside this cells. thes ...19761036012
evidence that the fertilization envelope blocks sperm entry in eggs of xenopus laevis: interaction of sperm with isolated envelopes. 19761036730
distinct molecular structures of nuclear class i, ii, and iii dna-dependent rna polymerases.class iii rna polymerases purified from the murine plasmacytoma mopc 315 and from xenopus laevis ovaries were compared. the subunit structures of the chromatographically distinct murine enzymes iiia and iiib were indistinguishable and were remarkably similar to that of the amphibian enzyme iii. the plasmacytoma class iii rna polymerases were also compared with purified plasmacytoma rna polymerases i and ii. sedimentation studies indicated that rna polymerase iii si significantly larger than rna ...19751054509
induction of maturation (meiosis) in xenopus laevis oocytes by three organomercurials.three organomercurials, p-hydroxymercuribenzoate, p-hydroxymercuriphenylsulfonate, and mersalyl, induce maturation (meiosis) in a large percentage (20-100 percent) of xenopus laevis oocytes. maturation takes place even when the follicle cells which surround the oocytes have been withdrawn. organomercurial- and progesterone-induced maturations have many features in common: they do not occur when the inducer is injected into the oocytes, they require the presence of ca++ in the medium, they are in ...19751055428
cytoplasmic control of nuclear dna synthesis during early development of xenopus laevis: a cell-free assay.nuclei isolated from nondividing cells were induced to synthesize dna by incubation with cytoplasm from early embryos of xenopus laevis. numerous replication eyes were formed in the nuclear dna molecules, and high levels of [3-h]dttp were incorporated. with this assay a protein(s) which appears to initiate dna synthesis was found at high levels in the cytoplasm of eggs, blastulae, or gastrulae, but only at low levels in the cytoplasm of oocytes, hatched embryos, or adult tissues.19751056038
synthesis of vitellogenin in cultures of male and female frog liver regulated by estradiol treatment in vitro.using the frog xenopus laevis, we show that the addition of physiological concentrations of estradiol to cultures of liver from untreated males rapidly induces the synthesis of large amounts of vitellogenin. sustained synthesis of vitellogenin requires continuous exposure to estradiol. a nonestrogenic steroid, dexamethasone, does not induce vitellogenin synthesis but does induce increased synthesis of a different protein in liver cultures.19751059103
translation of hormone-induced messenger rna in amphibian oocytes: i. induction by estrogen of messenger rna encoded for vitellogenic protein in the liver of the male african clawed toad (xenopus laevis).induction of the synthesis of the vitellogenic proteins, lipovitellin and phosvitin, in the liver of the male african clawed toad (xenopus laevis) was investigated as a function of time after treatment with estradiol-17beta [1,3,5(10)-estratriene-3,17beta-diol]. the appearance of mrnas encoded for lipovitellin and phosvitin in the cytoplasmic fraction of the liver was assayed by microinjections of hepatic mrna preparation [either polyribosomes or poly(a)-rich rna] into oocytes obtained from matu ...19751060075
localization by situ hybridization of amplified ribosomal dna during xenopus laevis oocyte maturation (a light and electron microscopy study).the presence of ribosomal dna has been demonstrated, by light and electron microscopy study of in situ hybridization with 125i-labeled ribosomal rna, in the feulgen-positive bodies which appear during maturation in the cytoplasm of xenopus laevis oocytes. the ultrastructure of these bodies is described.19761062796
the development of the action potential mechanism of amphibian neurons isolated in culture.nerve and muscle cells differentiated morphologically, in cultures of dissociated cells prepared from amphibian neural plate and underlying mesoderm (xenopus laevis, nieuwkoop and faber stage 15). cultures were grown in a defined medium containing sterile steinberg's salt solution and 0.1% bovine serum albumin, and maintained for periods up to 5 days.19761064036
induction of maturation (meiosis) in small xenopus laevis oocytes by injection of maturation promoting factor.treatment of small-(stage iii) or medium-sized (stage iv) xenopus laevis oocytes with progesterone, human chorionic gonadotropin, or para-hydroxymercuriphenylsulfonate does not induce maturation. only the full-grown oocytes (stage vi) undergo maturation when treated with either one of these three substances. in contrast, injection of maturation promoting factor into oocytes of stages iii-vi invariably leads to chromosome condensation and germinal vesicle breakdown. no maturation spindle is found ...19761064873
integration of eukaryotic genes for 5s rna and histone proteins into a phage lambda receptor.highly purified hindiii restriction fragments of xenopus laevis 5s dna and of psammechinus miliaris histone dna have been covalently inserted into a derivative of phage lambda. this phage, genetically constructed by murray et al. (1), contains only a single target for hindiii in the ci gene. viable hybrid molecules were detected as clear plaque-forming phage after transfection of e. coli, the vast majority of which were shown by hybridization to be recombinants of the desired type. the lambdasam ...19761069257
a plasmid cloning vehicle allowing regulated expression of eukaryotic dna in bacteria.we have constructed a plasmid cloning vehicle in which transcription of inserted heterologous dna fragments can be regulated by a defined bacterial operator and promoter. the lambda plac 5 ecoridna fragment containing the operator, promoter, and beta-galactosidase gene of the lactose operon was linked to the cole1 derivative plasmid psf2124, creating a plasmid designated pbgp100, pbgp100 contains one ecori site at the lac dna/psf2124 dna junction and another at the lambda dan/psf2124 dna junctio ...19761069275
synthesis of mitochondrial rna by full-grown and maturing oocytes of rana pipiens and xenopus laevis. 19751081057
aspects of tail muscle ultrastructure and its degeneration in rana temporaria.1. tail muscles of larval rana temporaria and to a lesser extent xenopus laevis, at prometamorphosis, were investigated by light and electron microscopy. in the case of rana their degeneration is described at metamorphic climax. 2. the non-degenerate tail muscles of both genera are generally similar in their ultrastructure and likewise similar to those striated muscles of other adult vertebrates including amphibians. 3. at climax tail muscles of rana degenerate by autolysis. it seems likely that ...19751081119
[the development of the vestibular apparatus under conditions of weightlessness].the spawn of the aquarium fish brachydanio rerio was developing during 5--6 days under conditions of weightlessness (first on board the spaceship "sojuz-16", then in the space station "salut-4") in special aquariums "emkon", in thermostable installations. electron microscopically the embryos were found to have a well developed labyrinth in early developmental histologically and cytologically differentiated receptory structures of the macula utriculi and macula saccili. in contrast to controls, t ...19761082742
a cytoplasmic factor promoting oocyte maturation: its extraction and preliminary characterization.cytoplasm of maturing amphibian oocytes possesses a factor that induces germinal vesicle breakdown. this factor was extracted from rana pipiens eggs and assayed by microinjection in xenopus laevis oocytes. the activity of this factor is mg-dependent, ca-sensitive, and associated with heat-labile protein. centrifugation on a sucrose density gradient revealed that the factor exists in three different molecular sizes.19761083070
aluminium localization in amphibian skin with the electron microprobe and ion microanalyzer.emp and ima studies show the presence of a1 in the epidermis of larvae and young adults of discoglossus pictus and rana esculenta, which disappears during later stages of development. a1 is practically absent in the epidermis of xenopus laevis and pleurodeles waltlii. the localization of a1 with emp and ima supports the biochemical results. the function of a1 in the epidermis is not known at present.19761083571
architecture of the marrow vasculature in three amphibian species and its significance in hematopoietic development.architecture of the bone marrow vasculature, particularly that of the femur, was analyzed in three amphibian species in relation to the early phylogeny of marrow hematopoiesis. a dye-injection method and histological techniques, including both serial sectioning and reconstruction methods, were used for this purpose. from these observations the following conclusions may be drawn. (1) marrow hematopoiesis is absent from the femur of the urodelan (triturus pyrrhogaster) and appears first in the fem ...19761083670
evidence for corticotropin releasing factor (crf) synthesis in the preoptic nucleus of xenopus laevis tadpoles: a preliminary report based on lesion experiments.for the study of the hypothalamo-hypophysial system of xenopus laevis tadpoles, hypothalamic lesions were made by means of the electrocoagulation technique. lesioning of the ventral region of the preoptic nucleus resulted in a decrease of the number of acth cells in the pars distalis of the pituitary gland and in a diminution of the pas-positive reaction of these cells. in addition, regeneration of the neurosecretory cells of the ventral region of the preoptic nucleus observed 6 weeks after lesi ...19761084220
species specificity in the response of an in vitro amphibian (xenopus laevis) ovulation assay to mammalian luteinizing hormones. 19761085276
[regeneration of the crystalline lens in anuran amphibia in the postembryonal stage. experimental excision of the crystalline lens in rana esculenta and xenopus laevis larvae]. 19761088056
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 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 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 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 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 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
in vivo synthesis and turnover of cytoplasmic ribosomal rna by stage 6 oocytes of xenopus laevis. 19751181216
location of genes coding for 18s and 28s ribosomal rna within the genome of mus musculus.cytological detection of cistrons coding for 18s and 28s ribosomal rna (rrna) within the genome of mus musculus inbred strain sec/1rej was accomplished using the technique of in situ hybridization. metaphase chromosome spreads prepared from cultured fetal mouse cells were stained with quinacrine-hcl and photographed. after destaining, they were hybridized to xenopus laevis tritiated 18s and 28s rrna, specific activity 7.5 x 10(6) dpm/mug. silver grains clustered over specific chromosomes were re ...19751183299
biochemical research on oogenesis. comparison between transfer rnas from somatic cells and from oocytes in xenopus laevis.the properties of trna from oocytes of xenopus laevis were compared with those of trna from somatic cells of the same species. both types of trnas were found to have the same average length and to contain an equal variety of modified nucleotides. however, trna from small oocytes differed from somatic trna by its chromatographic behavior on methylated-albumin kieselguhr columns. the elution profiles from reversed-phase chromatography 5 columns of several aminoacyl trnas were compared after chargi ...19751183439
the development of animals homozygous for a mutation causing periodic albinism (ap) in xenopus laevis.this paper describes the development of a mutant strain associated with periodic albinism (ap) in the clawed toad xenopus laevis. the most outstanding feature of this mutation is the instability of the albino state. in the course of the development there is a succession of three periods of pigment expression: (1) complete absence of melanin pigment, (2) appearance of melanin in the pigmented epithelium of the eyes and in small quantities in skin melanophores, (3) disappearance of most pigment gr ...19751185102
the effect of stretch on potassium contracture tension in twitch and slow muscle fibres of xenopus laevis. 19751189943
lymphocytes of the toad xenopus laevis have the gene set for promoting tadpole development.nuclear transplantation experiments show that differentiated cells, such as lymphocytes, from the adult frog can express the genes necessary for tadpole development. the transplanted cells were proven to be lymphocytes by immunological methods. the origin of the tadpoles that developed after lymphocyte nuclei injections was ascertained by a karyotypic marker.19751198115
[ontogenesis of the endocardial cushions in the vertebrate heart. an experimental- and comparative embryological study (author's transl)].by means of comparative ontogenetical findings and organ cultured whole hearts of tadpoles (xenopus laevis) there has been evidence that the localization of the endocardial cushions in the embryonic heart tube of landliving vertebrates is phylogenetically caused. on the contrary ontogenetically the shape of these cushions are dependent on the varying hemodynamic conditions in heart development. by this the anlage of endocardial cushions are the presupposition of the phylogeny and ontogeny in the ...19751200397
identification of the lampbrush chromosome loops which transcribe 5s ribosomal rna in notophthalmus (triturus) viridescens.the loops which transcribe 5s ribosomal rna in lampbrush chromosomes of the newt, notophthalmus (triturus) viridescens, were identified by hybridizing purified 5s dna to nascent 5s rna in situ. the genes which code for 5s rna were found near the centromeres of chromosomes 1, 2, 6, and 7 by hybridizing iodinated 5s rna to denatured lampbrush and mitotic chromosomes in situ. these genes and their intervening spacer dna were isolated from xenopus laevis using sequential silver-cesium sulfate equili ...19751201684
ovarian progesterone levels during in vitro oocyte maturation and ovulation in xenopus laevis. 19751203411
control of cell division and cell differentiation by deoxynucleotides in the early embryo of xenopus is proposed that the deoxyriboside triphosphates present in the egg of xenopus laevis support the synchronous cell divisions occurring during the earliest phase of embryonic development and that, as long as synchrony prevails, the cells are prevented from undergoing differentiation. this hypothesis has been tested by injecting deoxyribonucleotides into fertilized eggs. the following effects were observed: 1) the duration of synchrony is prolonged, 2) the morphological development is suppresse ...19751203982
biochemical research on oogenesis. nucleotide sequence of initiator trna from oocytes and from somatic cells of xenopus laevis.the nucleotide sequence of initiator trna, trnafmet, from vitellogenic oocytes of xenopus laevis was determined. the sequence was deduced from analysis of all t1 and pancreatic oligonucleotides and comparison with the sequence of initiator trna from other animal species. at least 80% of all initiator trna molecules from oocytes have the same nucleotide sequence. this means that most and probably all initiator trna genes which are active in oocytes are identical to one another. no structural diff ...19751204643
development of intertectal neuronal connections in xenopus: the effects of contralateral transposition of the eye and of eye removal.the development of intertectal neruonal connections has been investigated in xenopus laevis. contralateral eye grafts and enucleations were performed in embryos and the resultant visual projections to the optic tecta were mapped electrophysiologically after metamorphosis. in enucleated animals the ipsilateral projections were found to be normally organised retinotopically but consisted of visual units with abnormally large multi-unit receptive fields. in 10 animals with contralaterally grafted e ...19751204691
factors determining decussation at the optic chiasma by developing retinotectal fibres in amphibia all primary retinotectal nerve fibres cross at the chiasma. to investigate why this decussation takes place, a series of embryological operations were performed in which one host eye was replaced by an eye from the opposite side of a donor in xenopus laevis. the visual projections to the optic tecta were mapped electrophysiologically in these animals when adult to reveal to which side of the brain the nerve fibres had become connected. in the majority of cases the contralaterally gra ...19751204693
oocyte maturation in vitro: contribution of the oviduct to total maturation in xenopus of progesterone matured oocytes of xenopus laevis with the oviduct reduces the time necessary to attain cleavage capacity from 24 h to 3 h. full maturity has been demonstrated by normal development of the matured eggs after fertilization.19751204772
hormonal effects on rna synthesis by stage 6 oocytes of xenopus laevis. 19751204941
the erythroid cells of anaemic xenopus laevis. i. studies on cellular morphology and protein and nucleic acid synthesis during differentiation.phenylhydrazine has been used to induce anaemia in xenopus laevis. the dosage used causes the complete destruction of all mature erythrocytes within twelve days. the anaemia results in the initiation of a wave of erythropoiesis and large numbers of immature erythroid cells are released into the circulation. the morphological and biosynthetic changes which these cells undergo as they differentiate in circulation are described. the origin of the circulating erythroid cells is also discussed.19751206046
the erythroid cells of anaemic xenopus laevis. ii. studies on nuclear non-histone proteins.the mass ratio of nuclear non-histone protein: dna in the immature circulating erythroid cells of phenylhydrazine-induced anaemic xenopus is approximately threefold higher than in mature erythrocytes. this is largely due to the presence of increased amounts of low and intermediate molecular weight proteins in the nuclei of the immature cells. there are a few qualitative differences in the components of this class of proteins between the mature and immature cells, the most notable of which is the ...19751206047
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