Publications

the structure of the mitochondrial cloud of xenopus laevis oocytes.	the ultrastructure of the mitochondrial cloud (balbiani body) of the pre-vitellogenic oocytes of xenopus laevis has been examined using transmission and stereoscan electron microscopy. examination of conventional thin sections confirm previous observations which suggest that the cloud consists essentially of many thousands mitochondria and numerous small vesicles; larger clouds, in oocytes greater than 200 mum in diameter, contain relatively more vesicles. using a standard electron microscope at ...	1976	188969
biochemical data on subtotally hypophysectomized xenopus laevis (daudin) adult specimens treated or not with prolactin.	xenopus laevis (daudin) adult specimens were submitted to hypophysectomy. although the operation resulted subtotal, it served the purpose of removing the prolactin-producing cells, whereby the involvement of endogenous prolactin in osmoregulation phenomena was excluded. in the operated animals treated with ovine prolactin the following metabolic parameters, which are closely dependent upon interrenal activity, were estimated: 1) intestine alkaline phosphomonoesterase activity (e.c. 3.1.3.1); 2) ...	1976	218525
effect of xenopus laevis oocyte extract on supercoiled simian virus 40 dna: formation of complex dna.	a soluble cell-free extract derived from stage 6 xenopus laevis oocytes is described. from supercoiled simian virus 40 dna the extract produces nicked circles (having a single-strand scission), linear molecules of full unit size, shorter length fragments, and various forms of complex dna.	1976	174111
translation of oncogenic virus rna in xenopus laevis oocytes.		1976	175294
xenopus laevis 19s immunoglobulin. ultrastructure and j chain isolation.	electron microscopy examination of the 19s immunoglobulin of xenopus laevis revealed a hexameric structure with a central core. the molecules measured 360-430 a across the span of the arms and the average diameter of the central region was 140 a. a polypeptide, homologous to human j chain, was isolated by chromatography on deae-cellulose from the reduced and alkylated x. laevis hexameric macroglobulin. this polypeptide had a fast mobility in alkaline-urea gel electrophoresis, with distinct antig ...	1976	57921
diffusion of sodium in axoplasm of myelinated nerve fibre. potential clamp analysis.	the diffusion of sodium and lithium in the axoplasm of myelinated fibres of xenopus laevis was investigated. the sodium current associated with pulse steps was measured and the internal sodium concentration was calculated from these measurements with the constant field equation. the internal sodium concentration was increased either (i) by massive pulse trains or (ii) by applying a sodium containing solution to a cut end of the fibre. the time course of the concentration change was measured. equ ...	1976	61708
translation products of the alfalfa mosaic virus ribonuclei acids in wheat-germ cell-free system and in oocytes from xenopus laevis.		1976	64215
estimation of rdna content in xenopus laevis eggs during early development [proceedings].		1976	66019
mean velocity of optically detected intraaxonal particles measured by a cross-correlation method.	a method which uses by the cross correlation of optical signals is described for the determination of the mean velocity of somatopetally moving particles within nerve fibers. the method was validated by simulation experiments and by comparing the results with those obtained by averaging collections of velocities of individual particles. the significant contribution of the method is that it allows objective and rapid serial evaluation of mean particle velocity within individual nerve fibers with ...	1976	66091
surface immunoglobulins on xenopus laevis lymphocytes.		1976	3324
multiple forms of dna-dependent dna polymerase during early development and in somatic cells of xenopus laevis.	four distinct dna-dependent dna polymerase activities (dna polymerases i, ii, iii and iv according to the order of elution from a deae column) have been separated from extracts of unfertilized xenopus laevis eggs. the same activities, on the basis of their chromatographic properties, template specificities and sedimentation coefficients, have been found in embryos at least until the gastrula stage. on the other hand, xenopus kidney cells grown in culture, as well as full grown oocytes lack dna p ...	1976	9200
chemoreceptors of the lateral-line organs in intact, hypophysectomized, and prolactin-treated hypophysectomized xenopus laevis specimens.		1976	9241
translation of messenger rna specific for tyrosine aminotransferase in oocytes of xenopus laevis.		1976	10910
competition between motor nerves in the establishment of neuromuscular junctions in striated muscles of xenopus laevis.	after sectioning one of the two nerves of the pauci-innervated pectoralis muscle of xenopus laevis, a sprouting of the intact nerve is observed in the denervated zone. on subsequent reinnvervation by the original nerve, dually innervated end-plates are found in which the quantal content of the responses to foreign nerve stimulation does not change significantly while that from the original nerve increases during the course of reinnervation. on the other hand, functional innervation from both the ...	1976	19604861
particulate dna polymerase from the cytoplasm of xenopus laevis oocytes.	a dna polymerase has been partially purified and characterized from xenopus laevis stage 6 oocytes. the enzyme is present only in the cytoplasm and has been shown to be able to copy poly(a) x oligo(dt), to be sensitive to n-ethylmaleimide, and to sediment faster than 4 s in high salt glycerol gradient. the enzyme can be extracted from particulate material which has a density in sucrose gradient ranging from 1.200 to 1.225 g/cc. this particulate material is identified by its ability to use poly(a ...	1976	15625871
inducing activity of fractionated microsomal material from thexenopus laevis gastrula stage.	the postmitochondrial supernatant fromxenopus gastrulae has been fractionated on sucrose gradients. part of the microsomal material was treated with edta, which dissociates most of the polysomal and monosomal material into ribosomal subunits. in addition, a series of pooled fractions from the edta treated gradients has been applied to discontinuous gradients in more concentrated sucrose to separate membranous material from the remaining microsomal components.pooled fractions from all gradients h ...	1976	28305523
ontogeny of tyrosine aminotransferase in xenopus laevis.		1977	14857
histochemical and biochemical investigations on the changes of catecholamine content in the adrenal tissue of xenopus laevis--i. effect of salt-water stress.		1977	15773
histochemical and biochemical investigations on the changes of catecholamine content in the adrenal tissue of xenopus laevis--ii. effects of drug applications.		1977	15774
the time and duration of meiosis.	ever since meiosis was recognized as a process there has been a continuing interest in its temporal aspects. two main types of meiotic timing experiments have been conducted: first, experiments to estimate the duration of meiosis (and sometimes its stages); second, experiments to locate the sensitive stage(s) when exposure of meiocytes to various treatments can affect meiotic chromosome behaviour (e.g. pairing or recombination). such experiments have played an important role in increasing our un ...	1977	16285
alteration of structure and penetrability of the vitelline envelope after passage of eggs from coelom to oviduct in xenopus laevis.	the vitelline envelope (ve) that surrounds an egg released from the ovary into the coelom of xenopus laevis differs markedly, in structure and penetrability, from the ve surrounding an oviposited egg. in a coelomic egg, the filaments that form the ve are arranged in distinct fascicles or bundles. the exterior surface of the ve is irregular in contour and is permeated by channels. in an oviposited egg, the filaments are evenly dispersed and lack a fasciculated arrangement; the exterior surface is ...	1977	18549
effects of neurotransmitters upon the discharge of secretory product from the cutaneous glands of the red-spotted newt.	the effects of sympathetic and parasympathetic agonists and antagonists on discharge of secretory product by the granular and mucous glands were examined in the red-spotted newt, notopthalmus viridescens viridescens. observations were made also on the south african clawed toad. xenopus laevis, the grass frog, rana pipiens, and the crested newt, triturus cristatus. in contrast to the granular glands of the south african clawed toad and the grass frog, which were stimulated by alpha-adrenergic age ...	1977	21937
lectin-mediated agglutination of amphibian embryonic cells.	dissociated blastula cells of xenopus laevis are agglutinated with wheat germ agglutinin (wga), ricinus communis agglutinin (rca), concanavalin a (con a) and, to a lesser extent with soya bean agglutinin (sba). they are not agglutinated with fucose-binding protein. neuraminidase treatment of cells enhances their agglutinability with rca and sba, but has no effect on con a- and wga-mediated agglutinability. treatment of cells with procaine, or xylocaine, has no effect on the cells' agglutinabilit ...	1977	22553
in vitro studies on the effects on granular gland secretion in xenopus laevis skin of stimulation and blockade of alpha and beta adrenoceptors of myoepithelial cells.	secretion from the granular glands of xenopus laevis skin was stimulated by alpha-adrenergic agonists, an effect which was blocked by alpha-adrenergic antagonists and inhibited by beta-adrenergic agonists, db-camp and diazoxide. the inhibition by isoprenaline and salbutamol, but not that by diazoxide, was blocked by a beta-adrenergic antagonist. it is concluded that the myoepithelial cells surrounding the secretory compartment of the granular glands bear alpha and beta adrenoceptors, and that th ...	1977	24501
changes in the rate of histone synthesis during oocyte maturation and very early development of xenopus laevis.		1977	67977
inhibition of the rapid movement of optically detectable axonal particles colchicine and vinblastine.	the rapid saltatory motion of intra-axonal particles detected by dark-field microscopy in myelinated axons isolated from sciatic nerves of adult xenopus laevis was inhibited by colchicine or vinblastine at a concentration of larger than or equal to 0.1 mm. both the predominant somatopetal transport and the somatofugal transport of these round particles were inhibited. the reduction in numbers of moving particles was apparent first in the juxtanodal portions of the isolated axons within about 1 h ...	1977	68800
distribution of immunoglobulin determinants on the surface of xenopus laevis splenic lymphocytes.	the distribution of surface immunoglobulin (ig) determinants on xenopus laevis splenic lymphocytes after combination with divalent rabbit anti-ig coupled to ferritin was studied. the electron micrographs showed the presence of immune complexes in 67% of lymphocytes treated at 0 degrees c-4 degrees c. the complexes were located all around the membrane and uniformly distributed in a random fashion. the variation of ferritin grain counts on cell sections is such, that the existence of two major sub ...	1977	69676
effects of innervation on the distribution of acetylcholine receptors on cultured muscle cells.	1. myotomal muscle cells from embryos of xenopus laevis were cultured as a monolayer either alone or together with neural tube cells from the same embryos. 2. spontaneous twitching and contractions evoked by electrical stimulation of neural perikarya were observed only in nerve-contacted muscle cells, and could be abolished by curare or alpha-bungarotoxin. 3. within 2 days in culture muscle cells not contacted by nerve developed one or more discrete patches of acetylcholine (ach) receptors as re ...	1977	69706
nerve-induced and spontaneous redistribution of acetylcholine receptors on cultured muscle cells.	1. theree-day-old cultures of myotomal muscle, obtained from embryos of xenopus laevis, were stained with fluorescent conjugates of alpha-bungarotoxin and maintained in native toxin in order to ensure that ach receptors subsequently inserted into the sarcolemma would not be stained. neural tube cells were then added to the cultures. 2. when cultures were exmained 1-3 days later fluorescent stain was found to be associated with sites of nerve-muscle contact. in some cases the stain along the path ...	1977	69707
retrograde axonal transport of horseradish peroxidase for determining motor projection patterns to the developing limb in xenopus.	horseradish peroxidase (hrp) injected into developing limb buds of xenopus laevis tadpoles is carried by retrograde axonal transport to the somata of motoneurones in the ventral horn. small injection of 10% hrp were found to remain well localised to specified sites in the limb bud. two types of labelled cells were found: diffusely labelled and granular labelled. diffusely labelled cells result from axonal damage in the presence of hrp. granular labelled cells result only from uptake of hrp from ...	1977	70260
cytotoxic effect of a reverse transcriptase inhibitor, af/abdp cis, on ovaries of young xenopus laevis--ultrastructural and autoradiographic study.	observations with the light and electron microscopes showed that a reverse transcriptase inhibitor, af/abdp cis which is a rifampicin derivative, had a toxic effect on ovaries of young xenopus laevis. it induced mitochondrial damage in all observed cells and marked alteration of the ultrastructure of nucleus of the pachytene oocyte. light autoradiography showed that af/abdp cis caused wide variation in nuclear labelling with [3h] thymidine from one pachytene oocyte to another. somatic cells were ...	1977	70278
variations in differentiation in the regenerating lens of xenopus laevis.		1977	70371
inhibition of the progesterone-dependent induction of meiosis by gammexane in xenopus laevis oocytes.		1977	71148
progesterone-induced meiotic reinitation in vitro in xenopus laevis oocytes: a role for the displacement of membrane-bound calcium.		1977	73488
synthesis of interferon in heterologous cells, cell-free extracts, and xenopus laevis oocytes.		1977	80829
stimulation of poly(adenosine diphosphate ribose) synthase activity of xenopus germinal vesicle by progesterone.	a practical procedure for the isolation of massive numbers of gv from oocytes of xenopus laevis at various stages of oogenesis was developed. the method is simple, rapid, and easy to perform. the isolated gv possess high activity of poly(adp-ribose) synthase. incubation of class-a oocytes (stages v and vi) with progesterone resulted in a stimulation of the poly(adp-ribose) synthase activity in the gv. the stimulation of enzymatic activity occurred prior to gvbd. this stimulatory effect of proges ...	1977	214004
discussion paper: induction by progesterone and a "maturation-promoting factor" of soluble proteins in xenopus laevis oocytes in vitro.	in vitro incubation of isolated x. laevis oocytes with progesterone induces the specific labeling of proteins during maturation. they are detected as several discrete peaks with a double-labeling technique that involves the injection of [3h] leucine into hormone-treated and [14c] leucine into control cells. the peaks are separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. identical proteins are obtained with two other steroids that provoke maturation and with p-chloromercurib ...	1977	214005
turnover of rod photoreceptor outer segments. ii. membrane addition and loss in relationship to light.	the rate of disk addition to rod outer segments (ros) varies widely in xenopus laevis tadpoles kept in cyclic light (12l:12d). when measured as radioactive band (3h-band) displacement during the 2nd day after injection of [3h]leucine, 75% of the daily increment of displacement occurred during the first 8 h of light. during the same interval, the number of open disks at the ros base increased more than threefold. during the last 8 h of darkness, 3h-band displacement was undetectable and the numbe ...	1977	264121
selective and accurate transcription of the xenopus laevis 5s rna genes in isolated chromatin by purified rna polymerase iii.	chromatin isolated from immature oocytes was found to contain an endogenous rna polymerase activity (rna nucleotidyltransferase; nucleoside triphosphate:rna nucleotidyltransferase, ec 2.7.7.6) that synthesizes predominately 5s rna. however, the levels of total rna synthesis and 5s rna synthesis in chromatin were each stimulated 10- to 50-fold by an exogenous rna polymerase iii purified from x. laevis oocytes. the 5s genes in chromatin were transcribed by the exogenous enzyme in a highly selectiv ...	1977	264693
identification of rauscher murine leukemia virus-specific mrnas for the synthesis of gag- and env-gene products.	polyadenylylated mrna isolated from cells infected with rauscher murine leukemia virus was fractionated by centrifugation in in a denaturing sucrose gradient into different sizes. each rna fraction was injected into oocytes of xenopus laevis and the virus-specific products were analyzed by immunoprecipitation with polyvalent and monospecific antisera against polypeptides of rauscher murine leukemia virus, and then by gel electrophoresis and scintillation autoradiography. it was shown that a 35s ...	1977	266707
regulation by estrogen of the vitellogenin gene.	the vitellogenin gene is inactive in the liver of male xenopus laevis, unless exogenous estrogen is administered. we have previously shown that conventional doses of estradiol-17beta result in the appearance of new hepatic messenger rnas, some of which are encoded for vitellogenin. we now report that much higher doses of the hormone (2 mg/frog per day for 4 days) are required to elicit maximal responses. the relative levels of membrane-bound polysomes and vitellogenin mrna were determined as a f ...	1977	267932
gene activation in somatic nuclei after injection into amphibian oocytes.	genes that are unexpressed in somatic cells have been activated by injecting cultured cell nuclei of the frog xenopus laevis into oocytes of the newt pleurodeles waltlii. the genes that were activated are normally expressed in oocytes but not in cultured cells. conversely, genes that are normally expressed in cultured cells but not in oocytes became inactive when cultured cell nuclei were injected into oocytes. these changes in gene activity were detected by two-dimensional gel electrophoresis o ...	1977	267940
synthesis of human interferon by xenopus laevis oocytes: two structural genes for interferons in human cells.	human fibroblasts and leukocytes produce interferons which may be distinguished by their antigenic and species specificity as well as by their molecular weight distributions. to elucidate the basis for these differences, we isolated mrna from induced human fibroblasts and lymphoblastoid (namalva) cells and studied the products of translation in xenopus laevis oocytes. the mrna from the respective cells yielded translation products, in oocytes, that were characteristic of the cells from which the ...	1977	269391
interferon messenger rna content of human fibroblasts during induction, shutoff, and superinduction of interferon production.	translation of injected mrna in oocytes of xenopus laevis has been used as a highly sensitive and quantitative assay for interferon mrna. injection into oocytes of polyadenylylated rna extracted from poly(i).poly(c)-induced human diploid fibroblasts (fs-4) leads to the synthesis of biologically active human fibroblast interferon over a period of 24-32 hr. there is a linear relationship between the amount of mrna injected and the interferon yield obtained over a range of 1-20 ng of injected rna. ...	1977	269400
prescence of tadpole and adult globin rna sequences in oocytes of xenopus laevis.	complementary dna transcribed from adult xenopus laevis globin mrna was used to assay ovary rna from xenopus for the presence of globin sequences by rna.cdna hybridization. these sequences are present at approximately the same concentration as the majority of poly(a)-containing ovary sequences. the sequences are also found at approximately 200,000 copies per cell in poly(a)-containing rna extracted from mature oocytes. to rule out contamination of the oocytes with somatic cells, two additional e ...	1977	269434
induction and decay of human fibroblast interferon mrna.	polyadenylylated interferon mrna, obtained from induced human fibroblasts, was quantitatively assayed by synthesis of biologically active human interferon in xenopus laevis oocytes. the assay for interferon mrna was used to distinguish between various hypotheses relating to interferon induction and biosynthesis. the data demonstrate that on induction with poly(i-poly(c) human fibroblasts accumulate interferon mrna for 1-1.5 hr, after which time the mrna is rapidly degraded with a half-life (t 1/ ...	1977	270686
sites of transcription initiation in vivo on xenopus laevis ribosomal dna.	we report the results of a novel method for locating sites of transcription initiation using a complex of capping enzymes from vaccinia virions that catalyze the reaction pppg + s-adenosylmethionine + (p)ppxpypzp..... -->(7m)gpppxpypzp..... [ensinger, m. j., martin, s. a., paoletti, e. and moss, b. (1975) proc. natl. acad. sci. usa 72, 2525-2529]. this enzyme complex will cap di- or triphosphate termini but will not cap monophosphate or hydroxyl termini. xenopus laevis 40s precursor rrna from oo ...	1977	271962
assembly of sv40 chromatin in a cell-free system from xenopus eggs.	a cell-free system is described which assembles chromatin from purified dna in 1 hr under physiological incubation conditions. it consists of a 145,000 x g (maximum) supernatant fraction from eggs of xenopus laevis. it converts sv40 dna to a nucleoprotein which co-sediments with naturally occurring sv40 chromatin and which can be cleaved by micrococcal nuclease to a highly ordered pattern of dna fragments resembling those from digestion of liver chromatin. it inserts superhelical turns into rela ...	1977	189936
purified dnas are transcribed after microinjection into xenopus oocytes.	the possibility of using dna-injected xenopus laevis oocytes and eggs for studying the control of transcription in eukaryotes has been investigated. when purified dna of simian virus 40 (sv40) is injected into xenopus laevis oocytes, tritiated rna precursors are incorporated into dnase-i-resistant, rnase-a- and alkali-sensitive material that hybridizes specifically to sv40 dna. this viral transcription continues for at least 5 days and occurs only when the injected dna is directed to the nucleus ...	1977	193103
cyclic gmp accumulation causes degeneration of photoreceptor cells: simulation of an inherited disease.	guanosine 3',5'-monophosphate (cyclic gmp) metabolism in developing eye rudiments of xenopus laevis embryos in culture is disrupted by the phosphodiesterase inhibitor isobutylmethylxanthine. at low concentrations of inhibitor the rudiments develop normally, but at higher concentrations of the inhibitor, cyclic gmp accumulates in the rudiments and the retinal photoreceptor cells degenerate selectively. the isobutylmethylxanthine-induced photoreceptor degeneration is associated with an accumulatio ...	1977	193183
developmental immunohistology of melanotrophs in xenopus laevis tadpoles.	the adenohypophysial primordium of xenopus laevis tadpoles at stages 33/34 to 46 (nieuwkoop and faber, 1956) were examined immunohistologically for alpha-msh, beta-msh and acth. beta-msh was demonstrated from stage 37/38 onwards, and alpha-msh from stage 39. no signs of acth production were detected. alpha-msh and beta-msh occurred in the same cells. no differences were found in the intensity of immunofluorescence between tadpoles which were kept on a black and a white background. the present st ...	1977	194700
kynureninase-type enzymes and the evolution of the aerobic tryptophan-to-nicotinamide adenine dinucleotide pathway.	kynureninase-type (l-kynurenine hydrolase, ec 3.7.1.3) activity has been found to be present in the livers of fish, amphibia, reptiles, and birds. in addition to past information concerning this enzyme activity in mammalian liver, it is now clear that all the major classes of vertebrates carry a highly specialized kynureninase-type enzyme, which we have termed a hydroxykynureninase. to compare the reactivities of these enzymes with l-kynurenine and l-3-hydroxykynurenine, ratios of tau values (km ...	1977	195620
coupled transcription-translation of dna injected into xenopus oocytes.	a previous report from this laboratory showed that purified dnas are transcribed after injection into the nucleus of xenopus laevis oocytes (mertz and gurdon, 1977). here we demonstrate that at least some of the rna synthesized is translated within these injected cells to produce the correct protein products. injection of simian virus 40 dna into oocytes induces the synthesis of at least two proteins not normally synthesized in these cells. using two-dimensional polyacrylamide gel electrophoresi ...	1977	198138
the activity of poly(adenosine diphosphate ribose) polymerase during the embryonic development of the south african clawed toad xenopus laevis [proceedings].		1977	198268
frog oocytes synthesize and completely process the precursor polypeptide to virion structural proteins after microinjection of avian myeloblastosis virus rna.	after microinjection of xenopus laevis oocytes with rna from avian myeloblastosis virus, viral structural proteins p27, p19, p15, and p12 are formed by a sequence of posttranslational cleavages of a high-molecular-weight precursor polypeptide. the 60-70s rna aggregate or its 30-40s rna subunits obtained by heat or formamide treatment possess the same ability to serve as template in x. laevis oocytes. the processing pattern of virus-specific precursor polypeptides is the same in x. laevis oocytes ...	1977	198776
formation of branched dna structures by xenopus laevis oocyte extract.		1977	201869
the activity of some intracellular oxidative enzymes in the thyroid follicular epithelium of xenopus laevis daud. in experimental long-term hypokinesia.	histoenzymological methods were applied to examine the activities of previously little studied intracellular oxidative enzymes in the cells of the thyroid follicular epithelium of xenopus laevis daud. specimens kept in aquarium. succinate, lactate, alpha-glycerophosphate, glucose-6-phosphate and reduced nad and nadp dehydrogenases and cytochrome oxidase were studied. in comparison with other chordate species a very strong activity was revealed particularly by lactate dehydrogenase. the data obta ...	1977	202546
[effects of alpha-amanitin on the development of xenopus (xenopus laevis daud.) heart in vitro].	the differentiation of xenopus heart is studied in vitro, in the presence of alpha-amanitin. the results obtained depend on the concentration of the inhibitor, the length of treatment and the stage of primordium. the mrna pool assures the differentiation of explants, removed from young stages, for 12 hours. this time is half for the primordia removed from stages greater than 3,5 mm.	1977	143992
control of msh synthesis and release in the aquatic toad, xenopus laevis.		1977	207601
aminoacyl transfer from phenylalanyl-trna microinjected into xenopus laevis oocytes.		1977	244308
photoreceptor outer segments: accelerated membrane renewal in rods after exposure to light.	the rate of rod outer segment renewal in rana pipiens tadpoles under constant light and under diurnal conditions of 12 or 2 hours light per day is significantly increased compared to that in animals in darkness. furthermore, during 24 hours in light after 6 days in darkness the rate of renewal is three to four times that in darkness. in xenopus laevis tadpoles the rate of renewal is more than five times greater during the first 8 hours of a normal diurnal cycle than during the following 16 hours ...	1977	300504
electron microscopic study on the early histogenesis of thymus in the toad, xenopus laevis.	sequential electron microscopic observations of thymic histogenesis in the toad, xenopus laevis, reveal that the thymus arises as epithelial buddings of the visceral pouches at nieuwkoop-faber stage 40, and acquires its basic histological features at stages 48-49. in the rudiments and the surrounding mesenchyme at stages 43-45, there are non-epithelial cells with pseudopodia, abundant ribosomes, and marginated heterochromatin. these cells, possible precursor cells of thymic lymphocytes, are freq ...	1977	300655
early steroid metabolism in xenopus laevis, rana temporaria and triturus vulgaris embryos.	embryos of xenopus laevis, rana temporaria and triturus vulgaris exposed to radioactive pregnenolone have been found to convert it to progesterone. incubations with radioactive progesterone showed that it was actively metabolized by oocytes and embryos. in xenopus incubations progesterone was converted to 5alpha-pregnane-3,20-dione, 17alpha-hydroxy-4-pregnen-3-one, 4-androstene-3,17-dione and 17alpha-20alpha-dihydroxy-4-pregne-3-one, indicating 5alpha-reductase, 17alpha-hydroxylase, 19-20-desmol ...	1977	303192
novel screening procedure for recombinant plasmids.	lysed bacterial colonies containing potential recombinant plasmids were mixed with molten agar and sealed into slots of an agarose gel. after electrophoresis overnight, the gel was stained with ethidium bromide, which clearly reveals recombinant plasmids. xenopus laevis ribosomal dna and histone dna of psammechinus miliaris were ligated into pcri plasmids and screened by this method.	1977	318763
stimulation of cell division in ectopic kidney grafts following unilateral removal of the lung.	small fragments of kidney tissue were grafted into the right lung (xenopus laevis) and the left lung was subsequently removed. this stimulated compensatory hyperplasia (increased mitotic rate) in alveolar tissue of the right lung and in the kidney graft. this suggests that the stimulus to compensatory hyperplasia is location-specific rather than tissue- or organ-specific. after implantation into the lung the kidney grafts are revascularized by the surrounding pulmonary supply. damage or functio ...	1977	322542
free calcium in full grown xenopus laevis oocyte following treatment with ionophore a 23187 or progesterone.	free intracellular ca2+ was monitored in isolated xenopus laevis oocyte during induced maturation using the ca2+ -sensitive luminescent protein, aequorin. internal free ca2+ was not precisely measured but data suggest it was quite low (in the micromolar range). no change in internal free ca2+ was detected during maturation induced either by progesterone or by p-chloromercuribenzoate. by contrast, the ionophore a 23187 gave an increase in the free ca2+ level when there was a raised external ca2+ ...	1977	328329
indirect immunofluorescent identification of 19s immunoglobulin-containing cells in the intestinal mucosa of xenopus laevis.	the lymphoid structures in the gastrointestinal tract of immunized and non-immunized adult xenopus laevis were studied by light and fluorescent microscopy. serial sections stained with may-grunnwald giemsa showed that lymphoid aggregations and scattered lymphoid cells are present along the whole digestive tract. the aggregations are few and rather small in the oesophagus and stomach, they are particularly voluminous in the duodenum. an indirect immunofluorescent technique using antisera against ...	1977	328818
ionic requirements for induction of maturation (meiosis) in full-grown and medium-sized xenopus laevis oocytes.	there is already good evidence that calcium ions are involved in the induction of maturation in full-grown amphibian oocytes; we show here that other cations (k+, mg2+) also play a role in this process. full-grown (1.3 mm in diameter) and medium-sized (0.8-1.0 mm in diameter) oocytes were compared in the present study. it was found that, provided the medium is k+-free, valinomycin induces maturation in full-grown, but not in medium-sized, oocytes. increasing the cacl2 (20 mm) or the mgso4 (40 mm ...	1977	333439
stimulation of cell division in ectopic liver tissue following partial removal of the lung.	autografts of liver were implanted into the left lung (xenopus laevis). subsequent removal of the right lung stimulated increased mitotic activity in the lung and in the liver graft.	1977	336386
injected amphibian oocytes: a living test tube for the study of eukaryotic gene transcription?	somatic-cell nuclei injected in xenopus laevis oocytes remain transcriptionally active for up to 4 weeks. the rate of rna synthesis increases as the somatic-cell nuclei enlarge. the message activity of the rna synthesized by the injected nuclei can be demonstrated, as new proteins are made a few days after injection of hela-cell nuclei. several lines of evidence demonstrate that these proteins are coded for by the hela-cell genome and that they result from rna synthesized within the oocytes in t ...	1977	339919
transplantation of nuclei from lymphocytes of adult frogs into enucleated eggs: special focus on technical parameters.	the technique of transplantation of nuclei from adult lymphocytes into enucleated eggs from xenopus laevis (south african clawed toad) is described. the splenic lymphocytes from the one-nucleolus mutant were bound via their immunoglobulin receptors to nylon fibers, derivatized with the antigen used for immunization. a technique for coupling other cell types with woodward reagent is also described. the cells were broken by aspiration into a micropipette and injected into enucleated eggs. the egg ...	1977	340313
mitochondrial dna synthesis in large and mature oocytes of xenopus laevis.		1977	556708
concanavalin a binding to oocytes and eggs of xenopus laevis.		1977	556994
5'-terminal structure and mrna stability.	reovirus mrnas with 5'terminal m7gpppgm or gpppg are more stable than mrna containing unblocked ppg 5'-ends when injected into xenopus laevis oocytes or incubated in cell-free protein synthesising extracts of wheat germ and mouse l cells. the greater stability of mrna with blocked 5' termini is not dependent upon translation but seems to result from protection against 5'-exonucleolytic degradation.	1977	557727
a method for enucleating oocytes of xenopus laevis.	a method is described for the enucleation and complete healing of xenopus oocytes so that the enucleated oocytes withstand multiple injections and culture for several days. the oocytes are defolliculated and enucleated manually and allowed to heal in a potassium phosphate buffer. oocytes enucleated in this way support rna synthesis by injected hela-cell nuclei 3 days later. this method is valuable in providing a low-background system in which transcription of injected nuclei can be studied.	1977	558275
[molecular mechanisms for establishing the block to polyspermy at fertilization of xenopus laevis egg (author's transl)].		1977	558632
the synthesis and storage of histones during the oogenesis of xenopus laevis.		1977	558925
transcriptional organization of the 5.8s ribosomal rna cistron in xenopus laevis ribosomal dna.	hybridization of purified, 32p-labeled 5.8s ribosomal rna from xenopus laevis to fragments generated from x. laevis rdna by the restriction endonuclease, ecori, demonstrates that the 5.8s rrna cistron lies within the transcribed region that links the 18s and 28s rrna cistrons.	1977	559301
citrus exocortis viroid: survey of protein synthesis in xenopus laevis oocytes following addition of viroid rna.		1977	560084
restriction analysis of the nontranscribed spacers of xenopus laevis ribosomal dna.		1977	560255
synthesis of heterogeneous nuclear rna in full-grown oocytes of xenopus laevis (daudin).	at various times following injection of either 3h-gtp or 32po4 into full-grown (stage 6) xenopus laevis oocytes, rna has been extracted and fractionated on polyacrylamide gels. based on size, base composition and incorporation data, we have defined the kinetics of synthesis and accumulation of ribosomal rna (40s, 28s, 18s), heterogeneous rna of high molecular weight (greater than 40s) and heterogeneous rna migrating with molecular weights of from 4s to 40s. nuclear isolations have been performe ...	1977	560257
protein synthesis in oocytes of xenopus laevis is not regulated by the supply of messenger rna.		1977	560911
a pseudogene structure in 5s dna of xenopus laevis.	the 5s dna of xenopus laevis, coding for oocyte-type 5s rna, consists of many copies of a tandemly repeated unit of about 700 base pairs. each unit contains a "pseudogene" in addition to the gene. the pseudogene has been partly sequenced and appears to be an almost perfect repeat of 101 residues of the gene. the order of components in the repeat unit is (5') long spacer--gene--linker--pseudogene (3') in the "+" strand (or h strand) of the dna. the possible function of the pseudogene is discussed ...	1977	561661
recombinant dna formation in a cell-free system from xenopus laevis eggs.	a cell-free system is described which formed very high levels of recombinant dna structures in 4 hr at 26 degrees c. it consisted of a single fraction of a high speed supernatant prepared from an extract of unfertilized eggs of the frog xenopus laevis. this fraction eluted at 0.16-0.18 m tris homogenization buffer from a deae-cellulose column. when two partially homologous supercoiled dna molecules of different contour lengths were incubated simultaneously in this system, high levels of heterolo ...	1977	561663
cellular localization of dna polymerase activities in full-grown oocytes and embryos of xenopus laevis.		1977	562269
calcium, potassium, and sodium exchange by full-grown and maturing xenopus laevis oocytes.		1977	562807
comparison of in vivo and in vitro ribosomal rna synthesis in nucleolar mutants of xenopus laevis.	cells of embryos carrying a lethal nucleolar mutation have been maintained in vitro for extended periods of time. normally these mutants live only 9 to 12 days after fertilization but their cells in culture will survive for more than 3 months. the extent of ribosomal rna (rrna) synthesis was determined in primary cultures prepared from normal embryos and nucleolar mutants having different numbers of ribosomal rna genes. we found that the accumulation of radioactivity into rrna for normal and mut ...	1977	562840
the isolation and characterization of a second oocyte 5s dna from xenopus laevis.	a second and minor dna component containing 5s rna genes has been purified from the genomic dna of xenopus laevis (xit 5s dna). some of its physical and chemical characteristics are described. it contains a 5s rna gene sequence which has some oocyte and some somatic-specific residues, as well as nucleotides which differ from both types of 5s rna. there are about 2000 of these 5s rna genes per haploid complement of dna compared to about 24,000 of the principal oocyte 5s rna genes. the multiple re ...	1977	563770
diffusible and bound actin nuclei of xenopus laevis oocytes.	several criteria have been used to identify actin in hand-isolated nuclei of xenopus laevis oocytes; these include co-migration with actin on sds-polyacrylamide gels, immunological cross-reactivity with antiserum against actin, binding to dnaase i and peptide mapping on sds gels. the use of hand-isolated nuclei precludes the possibility of contamination from cytoplasmic actin or the leakage of significant amounts of actin from nuclei during isolation. actin constitutes roughly 6% of the total nu ...	1977	563771
differences in pulmonary microvascular anatomy between bufo marinus and xenopus laevis.	1. histological and corrosion-casting techniques have been used to provide a comparison of lung structure between a terrestrial load (bufo marinus) and an aquatic one (xenopus laevis). the pulmonary microvascular anatomy is distinctly different in these two species and both differ from classical descriptions of other anuran lungs. 2. in x. laevis large peribronchial vessels form a number of direct connections between the pulmonary artery and vein at the base of the lung. as a result of their loc ...	1977	402217
evidence for a functional role of rna in centrioles.	basal bodies, purified from chlamydomonas and tetrahymena, were exposed to various enzymatic treatments and then assayed for their ability to nucleate aster formation upon injection into eggs of xenopus laevis. untreated basal bodies injected into frog eggs act as centrioles and induce the formation of asters. the aster-inducing activity of basal bodies was eliminated by treatment with proteolytic enzymes and ribonucleases. aster-inducing activity was not affected by dnase and a number of other ...	1977	403009
[cytoplasmic control of cell division in amphibians: changes in the timing of egg cleavage after injection of heterospecific cytoplasm].	cytoplasm of xenopus laevis virgin eggs is injected into fertilized eggs of pleurodeles waltlii, species characterized by an initial development slower than that of xenopus. the cytoplasm introduced into eggs at the 2 or 4 cell stages accelerates the division of cells in the site of injection, later on synchronism of cleavage for the different blastomers of operated eggs reappears. the effects of an heterologous cytoplasm on mitosis and endogenic rhythm of cleavage are discussed.	1977	404053
[inhibition of the reinitiation of meiosis in xenopus laevis oocytes by three natural antiproteases: antipain, chymostatin, and leupeptin].	oocytes incubated for 1 hr. in saline containing 1 mg/ml of antipain, leupeptin or chymostatin do not reinstate meiosis when progesterone or ionophore a 23187 are added. on the contrary such oocytes remain able to undergo meiosis when injected with cytoplasm of maturing oocytes (mpf), with rabbit phosphorylase kinase or with beef protein kinase. these results demonstrate that the loss of responsiveness to progesterone or ionophore is not due to toxic effects but rather to some interference with ...	1977	404062
cytopathic effect and plaque formation by arboviruses in a continuous cell line (xtc-2) from the toad xenopus laevis.	forty-six arboviruses were tested for c.p.e. and/or plaque formation in an amphibian cell line. c.p.e. was observed with a high proportion of the viruses tested. comparative plaque assay, in the xtc-2 cells at 28 degrees c and vero cells at 37 degrees c, suggests that these systems are comparable in sensitivity and susceptibility to infection. practical uses of this cell line are discussed.	1977	406357
length and interspersion of repetitive and non repetitive dna sequences in four amphibian species with different genome sizes.	the interspersion period of repetitive and unique sequences was analyzed by two different methods, electron microscopy and agarose gel electrophoresis, for four amphibian species with different nuclear dna content, namely the anura xenopus laevis (3 pg dna per haploid genome) and bufo bufo (7 pg) and the urodela triturus cristatus (23 pg) and necturus maculosus (52 pg). within each of the two subclasses it has been found that interspecific differences, in dna content, due to variations in the am ...	1977	407058
nucleotide sequence relationships between vertebrate 5.8 s ribosomal rnas.	nucleotide sequences of the 5.8 s ribosomal rnas from hela cells, xenopus laevis and chick embryo fibroblasts were compared. xenopus laevis 5.8 s rna differs from that of hela cells in four internal positions and at the 3' end of the molecule. chick 5.8 s rna differs from that of hela cells in two positions. six out of the seven interspecies differences are due to base substitutions. the other difference is due to the presence of an extra nucleotide, internally located, within the xenopus 5.8 s ...	1977	409998
the onset of immunoglobulin synthesis during the development of xenopus laevis.		1977	412718
synthesis and glycosylation of the mopc-46b immunoglobulin in kappa chain in xenopus laevis oocytes.		1977	413546
the effect of karbatox 75, a carbaryl insecticide, upon the development of tadpoles of rana temporaria and xenopus laevis.		1977	414939
events in the germ cell lineage after entry of the primordial germ cells into the genital ridges in normal and u.v.-irradiated xenopus laevis.		1977	591877