Publications

the development of lampbrush chromosome-type transcription in the early diplotene oocytes of xenopus laevis: an electron-microscope analysis.	oocytes of xenopus laevis in pachytene and early diplotene of meiosis have been studied using the miller spreading technique. transcription first appears in germinal vesicles 25-40 micrometers in diameter, when the oocyte is in early diplotene. transcription at this stage consists of arrays of short rnp transcripts, irregularly distributed along the dnp axis. linear regression analysis has shown that many of these arrays are transcription units (type i) with the transcripts having a common point ...	1980	7440660
re-evaluation of the 'contralateral' effects of sodium and potassium on sodium transport through toad skin.	1. changes in the concentration of na in the outer bathing solution, [na]o, or of k in the inner bathing solution, [k]i, alter the electrical responses of the isolated toad skin to changes in ionic concentrations in the contralateral solutions. the mechanism(s) of these apparently contralateral effects remain(s) unknown. 2. the phenomenon has been investigated here in the isolated abdominal skin of xenopus laevis. each skin was exposed to multiple levels of [na]o and [k]i, of between 5 and 112 m ...	1980	7441564
rabies mrna translation in xenopus laevis oocytes.	two rabies virus-specific mrna species were identified by analysis of their encoded proteins after translation of the partially purified species in xenopus laevis oocytes. one of these coded for the virion surface glycoprotein (g protein), and the other coded for the major structural protein of the virion nucleocapsid (n protein). the g-mrna sedimented in a sucrose density gradient at about 18s, and the n-mrna had a sedimentation coefficient of approximately 16s. their respective translation pro ...	1980	7441819
lipid metabolism during embryonic and early postembryonic development of xenopus laevis.	xenopus laevis embryos were analyzed for their lipid content from fertilization to feeding stage. the amounts of the major lipids did not change until after hatching, but at the feeding stage the amounts of phosphatidylcholine (pc), phosphatidylethanolamine (pe), and sterol esters (se) increased approximately twofold. prior to hatching, [14c]acetate label was incorporated primarily into the fatty acyl chains of pe. after hatching, increasing amounts of label were found in other phospholipids, in ...	1980	7448620
nucleolar localization of 'template-bound' rna polymerase i in nuclei of xenopus laevis blastulae.		1980	7449853
effect of triiodo-l-thyronine on amino acid transport by xenopus laevis embryos.		1980	7450293
developmental and ploidy characteristics of "senescent" unfertilized eggs of xenopus laevis.	unfertilized eggs of xenopus laevis have been stored in a high salt physiological saline (de boer's solution) over a period of about 24 hours. during this time, aliquots have been subjected to lowered salinity and fertilized. the stored eggs undergo a defined series of morphological changes, which are initially reversible upon fertilization. length of storage may have little or no effect on the capacity of the eggs to undergo cleavage, but the normal developmental capacity declines with increasi ...	1980	7452193
lens formation from cornea in the presence of the old lens in larval xenopus laevis.	three different types of experiments were carried out to investigate the role of the lens in lens-forming transformations of the outer cornea of xenopus laevis tadpoles (at stage 51, as defined by nieuwkoop and faber, '56): 1) simple lentectomy; 2) incision of outer and inner cornea in the region opposite the dorsal iris without lens removal; and 3) incision of outer and inner cornea and perforation of dorsal iris without lens removal. the results indicate that the outer cornea of xenopus laevis ...	1980	7452196
[tumour induction by methylnitrosourea in clawed frogs (xenopus laevis) (author's transl)].	15 clawed frogs were bathed 12 to 17 times in solutions of 2 mg methylnitrosourea, dissolved in 1000 ml destilled water. 7 frogs developed tumours 8 to 22 months after starting the experiments. another frog died of polycystic kidneys. the tumours were adenocarcinomas of the kidneys, sarcomas and a benign papilloma of the pelvis of the left kidney. a sarcoma of the soft tissues of the head showed an excessive granular storage of acid mucopolysaccharides in the cytoplasma of many tumour cells. tum ...	1980	7458575
effects of alpha-amanitin and actinomycin d on xenopus laevis (daud.) heart in culture during cardiac differentiation (anuran amphibia).		1980	7459937
xenopus laevis histone genes: variant h1 genes are present in different clusters.	the xenopus laevis histone genes have been isolated from a bacteriophage lambda library using a cloned cdna probe to x. laevis h4 mrna (px1ch4). their structural organization has been determined by restriction mapping, blot hybridization and hybridization selection and translation of xenopus histone mrnas. they are clustered and probably tandemly arranged but, in contrast to invertebrate histone genes (kedes, 1979), there has been extensive sequence divergence in the spacer regions of the cluste ...	1980	7460012
accumulation of individual pa+ rnas during oogenesis of xenopus laevis.	rna metabolism during amphibian oogenesis has been investigated by the analysis of individual cdna cloned sequences. two cdna clone libraries were constructed from the pa+ rna of xenopus ovary and of tadpole. the accumulation of rnas complementary to individual clones was examined during oogenesis by isolating rna from oocytes of different stages. there are only two patterns of accumulation during oogenesis. mitochondrial mrna sequences accumulate throughout all the stages of oogenesis, whereas ...	1980	7460014
properties of motor units in a small foot muscle of xenopus laevis.	1. extensor digitorum longus iv muscle (edl iv) of xenopus laevis was isolated together with its nerve and the 8th and 9th spinal roots. motor units were functionally isolated and their properties investigated. 2. the motor unit isometric twitch and tetanic tensions, contraction time and axon conduction time and distance were measured. axon conduction velocity and twitch:tetanus ratio were calculated. 3. the distributions of motor unit properties were continuous and showed no tendency to separat ...	1980	7463359
effects of some heavy metal ions on the ionic currents of myelinated fibres from xenopus laevis.	1. the effect of the heavy metal ions mn2+, co2+, ni2+, cu2+, zn2+, cd2+ and hg2+ on permeability parameters of the nerve membrane was investigated. the ions were applied externally to single myelinated fibres of xenopus laevis. the ionic currents, associated with potential steps were measured and analysed. 2. zn2+ reversibly slowed down the kinetics of the k system. the effect at large potential steps was described as an increase of tau n. 3.4 mm-zn2+ increased tau n about three times. 3. ni2+ ...	1980	7463361
polyneural innervation: mechanical properties of overlapping motor units in a small foot muscle of xenopus laevis.	1. extensor digitorum longus iv of xenopus laevis was isolated together with its nerve and the 8th and 9th spinal roots. motor units were functionally isolated, by splitting and stimulating ventral root filaments. 2. motor units were stimulated separately and in pairs. between many pairs, overlap of motor innervation was found (evidence of polyneuronal innervation of muscle fibres). evidence for overlap was a deficit in the tension developed when the two units were stimulated together compared w ...	1980	7463363
electrical responses of muscle fibres in a small foot muscle of xenopus laevis.	1. extensor digitorum longus iv (edl iv) of xenopus laevis was isolated together with its nerve and the 8th and 9th spinal roots. motor units were functionally isolated.2. glass micro-electrodes were used to penetrate the muscle fibres and to record their electrical responses to stimulation of single motor axons, or the total motor supply to the muscle.3. three types of electrical response were recorded from muscle fibres: an action potential in response to a single nerve stimulus (type 1), an a ...	1980	7463366
influence of the olfactory placode on the development of the brain in xenopus laevis (daudin). i. axonal growth and connections of the transplanted olfactory placode.		1980	7465050
nonsense suppression in eukaryotes: the use of the xenopus oocyte as an in vivo assay system.	amber, ochre, and opal nonsense suppressor trnas isolated from yeast were injected into xenopus laevis oocytes together with purified mrnas (globin mrna from rabbit, tobacco mosaic virus-rna). yeast opal suppressor trna is able to read the uga stop codon of the rabbit beta-globin mrna, thus producing a readthrough protein. a large readthrough product is also obtained upon coinjection of yeast amber or ochre suppressor trna with tmv-rna. the amount of readthrough product is dependent on the amoun ...	1980	7465411
changes in polyribosomes and poly(a)-containing polyribosomal rna in the uterus of the ovariectomized rat in response to oestradiol-17 beta treatment.	polyribosome formation and the characteristics of polyribosomal poly(a)-containing rna from uteri of ovariectomized rats responding to a single dose of oestradiol-17 beta was investigated. the mean proportion of polyribosomes in the atrophic uterus was 65%. in response to 10 micrograms of oestradiol-17 beta/100 g body mass, the amount of polyribosomes increased to 88% 24 h after stimulation. thereafter the proportion of polyribosomes decreased to a value of 48% at 72h. the pattern of amino acid ...	1980	7470028
the cellular basis of epiboly: an sem study of deep-cell rearrangement during gastrulation in xenopus laevis.	measurements of several indices of shape, contact, position and arrangement of deep cells in the late blastula and gastrula were made from scanning electron micrographs of carefully staged, fractured embryos in order to describe the cellular processes which account for the increased area of the deep region of the gastrula during extension of the dorsal marginal zone and epiboly of the animal region. at the onset of gastrulation, the deep cells of the dorsal marginal zone become elongated, extend ...	1980	7310269
paternal gene expression in developing hybrid embryos of xenopus laevis and xenopus borealis.	we have studied protein synthesis in the viable hybrid xenopus laevis (female) x xenopus borealis (male) using 2d gel electrophoresis. fourteen borealis-specific proteins were studied. two of these proteins appeared by the gastrula stage, five in the gastrula and the rest later. where homologous laevis proteins were tentatively identified, androgenetic haploid hybrids were used to study whether the protein was encoded by stored maternal mrna, and how long this mrna persisted. the two proteins ap ...	1980	7310276
ultrastructure of sites of cholinesterase activity on amphibian embryonic muscle cells cultured without nerve.	muscle cells, derived from 1-day-old embryos of xenopus laevis, were cultured in the absence of nerve and then examined histochemically for cholinesterase activity. virtually all of the cells exhibited one or more discrete patches of cholinesterase activity on their surface. the patches were located not only on the lower cell surface which was apposed to the floor of the culture dish but also on the lateral and upper surfaces which were not apposed to any solid substrate. at many of the cholines ...	1981	20737872
electrical membrane properties of the xenopus laevis oocyte during progesterone-induced meiotic maturation.	the membrane input resistance (r(m)), potential (e(m)), and capacitance (c(m)) of fully grown xenopus oocytes removed from their follicles have been measured. before hormonal maturation, r(m), e(m), and c(m) were found to be: 1.86 +/- 0.63 momega, -49 +/- 17 mv, and 11.9 +/- 4.8 microf/cm2 of apparent surface area. long-term recording from oocytes in the presence of 1 microm progesterone reveal that during early gvbd (germinal vesicle breakdown) the membrane potential depolarized to about -10 mv ...	1981	20737886
full-grown oocytes from xenopus laevis resume growth when placed in culture.	when most full-grown, follicle cell-invested oocytes from xenopus laevis are placed in an appropriate culture medium, they resume growth and remain physiologically healthy for at least 2-3 weeks. rates of growth by full-grown oocytes in vitro generally approximate and can even exceed the most rapid growth rate achieved by vitellogenic oocytes in vivo. resumption of oocyte growth can be correlated with the loss of investing follicle cells, which under normal conditions appear to interfere with vi ...	1981	16593019
cloning of cdna sequences derived from poly(a)+ nuclear rna ofxenopus laevis at different developmental stages: evidence for stage specific regulation.	nuclear poly(a)+ rna was isolated from gastrula and early tadpole stages ofxenopus laevis, transcribed into cdna and integrated as double stranded cdna by the g-c joining method into the pst cleavage site of plasmid pbr 322. after cloning ine. coli strain hb 101 the clone libraries were hybridized to32p labelled cdna derived from nuclear poly(a)+ rna of the two different developmental stages. about 20% of the clones gave a positive hybridization signal thus representing rna molecules of high and ...	1981	28305358
fiber type composition and postmetamorphic growth of anuran hindlimb muscles.	fiber type composition distinguished by the level of succinic dehydrogenase, mean fiber diameter, and fiber number were determined for the gracilis major and sartorius in ontogenetic series of the anurans rana pipiens, bufo americanus, and xenopus laevis to characterize muscle composition and mode of muscle growth. a correlation can be made between the respective locomotor mode of these anurans, their activity physiology, and the fiber type composition of the propulsive muscles. r. pipiens and x ...	1981	30119589
somitogenesis in the amphibian xenopus laevis: scanning electron microscopic analysis of intrasomitic cellular arrangements during somite rotation.	the intrasomitic changes in cell arrangement which accompany somite rotation during somitogenesis in xenopus laevis were analysed with the scanning electron microscope (sem). longitudinal, horizontal fractures of whole embryos were examined at various dorsoventral levels of stage-22 to -24 embryos. observations of the gross morphological features of somitogenesis, and the cellular changes which accompany somite segmentation and somite rotation were made. several of these observations lead to mod ...	1981	7310302
the formation of somites and early myotomal myogenesis in xenopus laevis, bombina variegata and pelobates fuscus.	myogenesis in xenopus laevis and in bombina variegata is similar despite differences in the structure of the nonsegmented mesoderm and in the formation of the myotomes. in x. laevis the nonsegmented mesoderm consists of two cell layers with the premyocoel between them. during somitogenesis the premyoblasts rotate covering subsequently the whole myotome length. in b. variegata the premyocoel is absent. the myotomal cells change their shape and elongate, attaining ultimately the whole myotome leng ...	1981	7310306
experimental evidence for autonomous action of the periodic albinism (ap) gene within developing retinal pigment cells and melanophores of xenopus laevis.	genes which affect pigment elaboration may do so by autonomous action within the developing pigment cells or by way of tissue interactions leading to pigment cell differentiation. the site of action of the periodic albinism (ap) gene was investigated by substituting presumptive neural ectoderm of gastrulae of one genotype with uncommitted ectoderm of different genotype. retinal pigment cells and melanophores arising from such grafts were found to differentiate according to their own genotype in ...	1981	7310308
the direction of growth of differentiating neurones and myoblasts from frog embryos in an applied electric field.	1. disaggregated single neurones and myoblasts obtained from the neural tube and somites of xenopus laevis embryos (stages 17-21) were cultured in the presence of steady small electric fields. 2. neurites grew preferentially towards the negative pole, or cathode, in field strengths of 7-190 mv/mm. many turned through considerable angles to do so. this effect disappeared below a threshold level of about 7 mv/mm. 3. greater numbers of neurones sprouted neurites in cultures exposed to an electric f ...	1981	7310685
adenylate cyclase activity in xenopus laevis ovarian follicles.		1981	7311973
two conserved sequence blocks within eukaryotic trna genes are major promoter elements.	the split promoter sequences of a trnaleucug gene of xenopus laevis have been mapped to nucleotides 13-20 and 51-64 of the trnaleu coding sequences. the sequences closely coincide with two conserved sequence blocks present in all eukaryotic trna genes. the two conserved sequence blocks were found to be exchangeable between trna genes as chimaeric trnamet--trnaleu genes proved transcriptionally active. furthermore, two prokaryotic trna genes exhibiting strong homologies with the two blocks yielde ...	1981	7312050
a microspectrophotometric study of normal and artificial visual pigments in the photoreceptors of xenopus laevis.		1981	7314464
phosphorylation of ribosomal proteins during maturation of xenopus laevis oocytes.		1981	7318832
[abnormal thyroid gland occurred in a colony of xenopus laevis maintained at gumma university (author's transl)].	thyroid hypertrophy of unknown cause occurred in a colony of xenopus laevis maintained at the institute of endocrinology, gunma university, maebashi, japan. these animals were kept in small aquaria with well water and fed on minced pig liver. an etiologic investigation was made on the thyroid abnormality by assessing its occurrence and histopathologic features and rearing conditions of the animals in comparison with those of the colonies at tokyo and sendai. 1) the occurrence of abnormal thyroid ...	1981	7318945
measurement of 5 s rna accumulation in oocytes of xenopus laevis using a cdna probe.		1981	7327260
interferometric studies of endothelial cells in primary culture.	a population of endothelial cells grown from xenopus laevis tadpole hearts was investigated by microinterferometry. the resulting interferograms were evaluated by an automatic image analyzer. the mean values of dry mass were 778 +/- 340 pg (10(-15) g) for whole cells, 648 +/- 309 pg for cytoplasm, 116 +/- 45 pg for nuclei, and 19 +/- 10 pg for nucleoli. two subpopulations of cells were identified, an actively growing one and a less active one. the density (dry mass per microm2) of the nuclei and ...	1981	7327947
[ontogenesis of the acetylcholine system in the brain of the south african clawed toad (xenopus laevis daudin)].	1. during the development of the acetylcholine system of the xenopus brain a distinct increase in neurotransmitter content was found which is interpreted as an expression of increased activity of cholinergic neurons. the acetylcholine content in the whole brain increases markedly from hatching to metamorphosis. during this period regional differences of transmitter distribution can be observed. 2. the chat activity of the whole brain remains constant during total larval life, whereas the ache ac ...	1981	7328310
cell type-specific differences in protein composition of nuclear pore complex-lamina structures in oocytes and erythrocytes of xenopus laevis.		1981	7328650
cells of origin of descending pathways to the spinal cord in the clawed toad (xenopus laevis).		1981	7329548
factors involved in the development of ipsilateral retinothalamic projections in xenopus laevis.	the extent, and the development, of the ipsilateral retinothalamic projection in the frog xenopus laevis have been studied using terminal degeneration and autoradiographic techniques. this ipsilateral projection derives only from those retinal areas receiving visual information from the binocular portion of the visual field. in xenopus, the ipsilateral retinothalamic projection arises from a larger area of the retina than was found to be the case in earlier studies on rana. this correlates with ...	1981	7334300
selective in vitro transcription of one of the two alu family repeats present in the 5' flanking region of the human epsilon-globin gene.	the sequence of 2965 nucleotides 5' of the human epsilon-globin gene has been completed. it includes two alu family repeats present in an inverted configuration. only the one located farthest from the gene was active as template for rna polymerase iii in a transcription system prepared from nuclei of xenopus laevis oocytes. this selective transcription may be explained by the lack of homology of the first 45 nucleotides of the non transcribed repeat with other members of the alu family. in fact ...	1981	7335492
comparison of hemoglobins from the genus xenopus (amphibia salienta).	a survey of the electrophoretic mobility of hemoglobins of 14 species and subspecies of the genus xenopus was undertaken. it was found that the variation between the different taxons considered was quite important in the number and the degree of the hemoglobin bands on polyacrylamide slab gels. the profiles of the hemoglobin electrophoretic pattern in tube gels gave corresponding results, confirming the variation between the different xenopus species. the degree of resolution obtained on polyacr ...	1981	7338720
"degenerative cement gland" (dcg), a lethal recessive mutation in xenopus laevis.		1981	7340360
the invasion of cultured cell layers and intact epithelia.	this paper concerns the invasive behaviour of a migratory embryonic cell type, the primordial germ cell (pgc) of the anuran amphibian xenopus laevis. scanning electron microscopy of isolated pgcs shows that they invade layers of cells derived from adult xenopus mesentery, and the epithelium of the intact mesentery itself. this invasion is at least partly due to the stimulation by the pgcs of process formation in both cultured and intact epithelial cells. these broad lamellipodia move over the su ...	1981	7347430
germinal vesicle breakdown in the xenopus laevis oocyte: description of a transient microtubular structure.	during progesterone-induced meiotic maturation of xenopus oocytes in vitro, 7 morphological stages were defined. using cytological analysis, nuclear breakdown was divided into three stages. stage 1 corresponded to basal germinal vesicle breakdown. stage 2 was characterized by the advent and development of a fibrillar network formed by microtubules at the basal part of the nucleus. below, a lamellar microtubule organizing center (mtoc) was present. numerous vesicles of smooth endoplasmic reticulu ...	1981	7349521
synthesis in vitro of corticosteroid-binding globulin from rat liver messenger ribonucleic acid.	to show that corticosteroid-binding globulin (cbg), a plasma glycoprotein, is synthesized in the liver as well as to develop a tool with which to study the hormonal factors which control its synthesis, we undertook to translate rat cbg mrna in vitro. rat liver mrna was translated in the presence of [35s]methionine in both a rabbit reticulocyte lysate (cell-free) system and a xenopus laevis oocyte (whole cell) system. a monospecific antibody against highly purified rat cbg was used to precipitate ...	1981	7460843
tubulin:tyrosine ligase in oocytes and embryos of xenopus laevis.		1981	7461286
influence of diet on the susceptibility of xenopus laevis tadpoles to thiopentone and a membrane probe.	xenopus laevis tadpoles were produced from wild-caught, laboratory-reared toads. separate sets were fed on diets of (1) liver powder; (2) nettle powder; (3) aminosol and intralipid. the tadpoles were reared for 3 weeks at 22 degrees c and then three groups of experiments performed. group i experiments showed a significant difference in the response to thiopentone between tadpoles fed on liver powder and those fed on nettle powder. group ii experiments showed a difference in response to thiopento ...	1981	7248121
h1 histone variants in xenopus laevis.		1981	7250503
locations of androgen-concentrating cells in the brain of xenopus laevis: autoradiography with 3h-dihydrotestosterone.	the distribution of hormone-concentrating cells in the brains of south african clawed frogs, xenopus laevis, was examined autoradiographically after the administration of 3h-dihydrotestosterone. hormone-accumulating cells were found in cranial nerve nucleus ix-x and adjacent smaller cells, a presumed medullary vestibular nucleus, a presumed sensory nucleus of cranial nerve v, dorsal tegmental area of the medulla, laminar nucleus of the torus semicircularis, ventral thalamus, and anterior pituita ...	1981	7251941
toxic and teratogenic effects of selected aromatic amines on embryos of the amphibian xenopus laevis.	evaluations of the toxic and teratogenic effects of four aromatic amines, acridine, aniline, pyridine, and quinoline, have been made on amphibian (xenopus laevis) embryos. for toxicity testing, the embryos were divided into three groups according to stage of development: group i were mid-blastulae, group ii were tailbud embryos, and group iii were swimming larvae. of the amines tested, acridine and quinoline were the most toxic, followed by aniline and pyridine. ninety six hr lc50 values for acr ...	1981	7259304
the structure of vitellogenin. multiple vitellogenins in xenopus laevis give rise to multiple forms of the yolk proteins.		1981	7263674
isolation of a xenopus laevis alpha-globin gene.		1981	7265209
aeromonas hydrophila infection in xenopus laevis.	aeromonas hydrophila caused severe disease in a group of xenopus laevis within 3 weeks of receipt. the primary clinical signs were marked pallor of the skin, petechiation, lethargy, anorexia, and edema. the duration of the outbreak was approximately 45 days during which time 21 frogs became sick and 18 died, despite tetracycline therapy. pale skin, subcutaneous edema and hemorrhages, ascites, and pale livers were seen at necropsy. aeromonas hydrophila was isolated from skin, and the same organis ...	1981	7265911
oestrogen receptor levels and vitellogenin synthesis during development of xenopus laevis.		1981	7266654
a simple apparatus for injection of nanoliter quantities into xenopus laevis oocytes.		1981	7270884
a giant cell with dendritic cell properties in spleens of the anuran amphibian xenopus laevis.		1981	7274523
development of axosomatic synapses of the xenopus spinal cord with special reference to subsurface cisterns and c-type synapses.	the relationships of highly flattened subsurface cisterns (sccs) were investigated electron microscopically in the spinal cord at various developmental stages of tadpoles and adult toads, xenopus laevis. in medial ventral motor cells (mvcs) of the adult, more than 90% of 156 sscs examined were situated postsynaptically. similarly, more than 90% of 540 sscs in lateral motor column cells (lmcs) were postsynaptic. by contrast, in early developmental stages, the sscs were initially formed by regiona ...	1981	7276242
development of sodium permeability inactivation in nodal membranes.	1. the time course of inactivation of the sodium permeability was studied in myelinated nerve fibres of xenopus laevis using the voltage-clamp technique of nonner (1969). the potassium currents were blocked by 10 mm-tetraethylammonium chloride (tea). the remaining currents were corrected for leakage and capacity currents. 2. the decay of the sodium current was double-exponential confirming chiu's (1977) findings the slower time constant was observed in tea-free solutions by clamping to vk in hig ...	1981	7277227
dna methylase during xenopus laevis development.	the dna methylase activity present in embryos and cultured cells of xenopus laevis resembles dna methylase from mammalian tissues. little or no activity is found in mature germinal vesicles, though nuclear activity rises rapidly after fertilization. this rise may result in part from a relocation of cytoplasmic enzyme.	1981	7284389
isolation and characterization of xenopus laevis albumin mrna.	the messenger rna for albumin was isolated from the liver of male frogs. purification was achieved using oligo(dt)-cellulose chromatography and sucrose gradient centrifugation under denaturing conditions. as judged by translational activity in a cell-free protein-synthesizing system derived from rabbit reticulocytes, albumin mrna was enriched 259-fold as compared to the total ribonucleic acid of the liver cells. purified albumin mrna migrated after sucrose gradient centrifugation as a single sym ...	1981	7285921
the movement of the prospective eye vesicles from the neural plate into the neural fold in ambystoma mexicanum and xenopus laevis.		1981	7286445
conservatism of the h-y/h-w receptor.	soluble h-y antigen is taken up by cells of the homogametic gonad of cattle, dog, chicken and south african clawed frog. after in vitro exposure to mouse testis supernatant or male fetal calf serum, xx ovary cells or zz testis cells, which are normally h-y-, acquire the h-y+ (h-w+) phenotype and absorb mouse h-y antibody in standard serological assays. in addition, h-y antigens of the different species can compete for attachment to target cells of a single species. in a new competitive binding r ...	1981	7286993
regional effects of sodium aspartate and sodium glutamate on protein synthesis in the retina.	isolated retinas from xenopus laevis tadpoles or juvenile frogs were incubated in ringer's bicarbonate-glucose medium in which sodium chloride was replaced with equimolar amounts of either sodium aspartate (naasp) or sodium glutamate (naglu). at all concentrations tested (0.1 to 50 mm), both acidic amino acids caused a dramatic decrease in the incorporation of 3h-leucine into proteins in the inner retina. higher concentrations of these acids (50 mm) caused an increase in the incorporation of the ...	1981	7287345
an experimental analysis of the role of bottle cells and the deep marginal zone in gastrulation of xenopus laevis.	earlier work suggested that the change in shape or the active migration of the bottle cells in the amphibian blastoporal region results in an invagination that comprises a major part of gastrulation. in the present study of gastrulation in xenopus laevis, microsurgical extirpation and rearrangement experiments, analyzed with time-lapse cinemicrography and scanning electron microscopy, show that the bottle cells have a lesser role in gastrulation. gastrulation is not a process of invagination but ...	1981	7288390
development of xenopus laevis embryos in a static magnetic field.		1981	7295366
light stimulates the incorporation of inositol into phosphatidylinositol in the retina.	the incorporation of [3h]inositol into phosphatidylinositol in retinas of xenopus laevis tadpoles or young adults in short-term organ culture is stimulated by light, compared to retinas maintained under identical conditions in darkness. over 95% of the label incorporated into lipid was in phosphatidylinositol, and none was incorporated into retinal proteins. the stimulation of incorporation was localized by autoradiography to the outer plexiform layer, a neurophil composed primarily of horizonta ...	1981	7295756
replication of ribosomal dna in xenopus laevis.	the study of the localization of the replication origins of rdna in xenopus laevis has been approached by two different methods. 1. the dna of x. laevis larvae was fractionated by cscl gradient centrifugation in bulk and ribosomal dna and examined in the electron microscope. in bulk dna, clusters of microbubbles, which are related with the origins of replication, appear to be spaced along the dna molecules at intervals comparable with the size of the 'average' replicon of x. laevis. in ribosomal ...	1981	7297565
effect of 5'-methylthioadenosine on nucleolar morphology and rna metabolism in cultured xenopus laevis cells.		1981	7308302
a middle-affinity estrogen-specific binding protein in livers of vitellogenic and nonvitellogenic xenopus laevis.		1981	7308579
neural plate morphogenesis and axial stretching in "notochord-defective" xenopus laevis embryos.		1981	7308580
patterns of transcriptional activity of nucleolar genes during progesterone-induced maturation of oocytes of xenopus laevis.	maturation has been induced in full grown oocytes of xenopus laevis by incubation in progesterone, and the ultrastructure of their nucleoli has been examined by electron microscopy using the chromatin spreading technique. we show that in this species numerous extrachromosomal nucleoli maintain high levels of transcription of rdna for up to 200 min after the application of the hormone, i.e., shortly before germinal vesicle breakdown. transcription has been identified as normal arrays of matrix un ...	1981	7308608
target dependency of developing motoneurons in xenopus laevis.	the effect of complete and partial limb bud removal on motoneuron survival was studied in xenopus laevis tadpoles. amputation of both hind limb buds at stage 49 before limb innervation begins caused the subsequent death of all motoneurons. this result confirms that there are no exceptions to the rule that developing motoneurons must contact the limb to survive. partial removals of the limb at early stages of innervation caused the subsequent death of motoneurons that normally project to the dele ...	1981	7309919
axon regeneration by developing limb motoneurones in xenopus laevis.	newly generated motoneurones invading the limb bud were labelled with horseradish peroxidase to identify them later in development. they were then axotomized by amputating the limb bud. the limb bud was replaced immediately in some animals. after the period of normal motoneurone death, which falls a few days after the operation, many horseradish peroxidase labelled motoneurones were still alive provided the limb bud had been replaced. without a limb bud, labelled motoneurones were few or non-exi ...	1981	7225797
pineal complex of the clawed toad, xenopus laevis daud.: structure and function.	the morphological and physiological properties of the pineal complex of xenopus laevis were investigated in larval, juvenile and adult animals. in a representative majority of adult x. laevis, the frontal organ does not display signs of degeneration. fully differentiated frontal organs contain photoreceptors typical of the pineal complex of lower vertebrates. by means of the acetylcholinesterase (ache)-reaction approximately 30 neurons of two different types were demonstrated in the frontal orga ...	1981	7226202
transplantation of insect giant chromosome nuclei into amphibian oocytes.	polytene salivary gland nuclei of chironomus pallidivittatus were transplanted into oocytes of xenopus laevis which were then cultured in vitro for 18 h. the giant chromosomes and nucleoli as well as the entire nuclei enlarged considerably in volume during this time. the polyteny and specific chromomere pattern of the chromosomes were maintained, and the puffing of the salivary gland-specific balbiani rings was not noticeably changed. - polytene nuclei from differentiated insect cells transplant ...	1981	7227037
patterns of protein synthesis in livers of xenopus laevis during metamorphosis: effects of estrogen in normal and thyrostatic animals.		1981	7227631
patterns of motor innervation in the pectoral muscle of adult xenopus laevis: evidence for possible synaptic remodelling.	1. an anatomical and electrophysiological study was performed on the pectoral muscle of xenopus laevis. 2. silver-impregnated preparations revealed immature endings, collateral and terminal sprouting and signs of synaptic regression. 3. twenty percent of the fibres received a dual innervation from two different nerves. the synapses of 25% of these fibres are formed in close vicinity. 4. some of the singly innervated and most of the dually innervated end-plates generated only subthreshold electri ...	1981	7230035
modifications in oocyte protein synthesis induced by progesterone in xenopus laevis.		1981	7238884
a method for the enhancement of bi- and trispermic fertilization in eggs of xenopus laevis.		1981	7238954
characterization of a new cell line, xl2, obtained from xenopus laevis and determination of optimal culture conditions.	a new amphibian permanent cell line is described. it is called xl2 and was initiated from stage 35 tadpoles of xenopus laevis. the cell line has an epithelioid morphology and most cells can be classified into two populations with respective chromosome modal numbers 36 and 74. contact inhibition is low. its growth is vigorous in l15 or mem medium supplemented with fetal bovine serum. the mean doubling time is 39 hr and the saturation density is 700,000 cells/cm2 at 25 degrees c. the absolute plat ...	1981	7239540
experimental analysis of the lens-forming competence of the cornea, iris, and retina in xenopus laevis tadpoles.	the present research was carried out using xenopus laevis tadpoles at stage 50-51 to ascertain whether eye territories other than the outer cornea and the pericorneal epidermis have lens-forming competence, particularly the iris and/or retina. five experiments were performed: simple lentectomy; removal of lens, outer cornea, and pericorneal integument; removal of lens, outer cornea, and pericorneal integument, and simultaneous incision of retina; removal of lens, outer cornea and pericorneal int ...	1981	7241066
[replication of heterologous and recombinant dna in xenopus laevis oocytes].		1981	7245876
synthesis of androgen-dependent secretory proteins by rat seminal vesicles.	androgenic steroids control the synthesis and secretion of several proteins by the seminal vesicles of the male rat. prominent among them are 2 basic proteins, s and f, previously used as markers of androgen action. these proteins are not found among translation products of a wheat-germ protein-synthesising system supplied with mrna from seminal vesicles of normal rats. instead, higher molecular weight forms, s' and f', are formed which are nonetheless related antigenically to s and f respective ...	1981	7215704
identification and properties of terminal deoxynucleotidyltransferase from xenopus embryos prior to the development of the thymus.	the appearance of terminal deoxynucleotidyltransferase (tdt), a marker for early lymphoid cells, has been measured during the development of the south african clawed frog, xenopus laevis. the enzyme can first be detected in 2-day-old embryos, at approximately the same time as the first detectable embryonic immunoglobulin and well before the appearance of the thymus. xenopus tdt has been partially purified and some of its properties have been investigated. the partially purified enzyme is 68,000 ...	1981	7217050
intracellular phosphorylation of vitellogenin in the liver of estrogen-stimulated xenopus laevis.	a procedure was developed for the preparation of rough and smooth microsomes from small quantities of liver obtained from estrogen-stimulated xenopus laevis females. the separation involves th centrifugation of a postmitochondrial supernatant over a cscl-containing, discontinuous sucrose gradient. morphological, biochemical, and enzymatic characterization of these fractions indicates that excellent separation of rough microsomes from smooth microsomes is achieved. in addition, pulse-chase experi ...	1981	7217071
vitellogenesis and the vitellogenin gene family.	vitellogenin is synthesized under estrogen control in the liver, extensively modified, transported to the ovary, and there processed to the yolk proteins lipovitellin and phosvitin. in the frog xenopus laevis there are at least four distinct but related vitellogenin genes. the two genes a1 and a2 have a 95 percent sequence homology in their messenger rna coding regions, and contain 33 introns that interrupt the coding region (exons) at homologous positions. sequences and lengths of analogous int ...	1981	7209528
some observations on the behaviour of chloride current--voltage relations in xenopus muscle membrane in acid solutions.	chloride current--voltage relations in xenopus laevis muscle membrane have been investigated in phosphate-buffered solution (ph 5.2--5.4) using a three-microelectrode voltage clamp. resting chloride conductance in these conditions is about 10(-4) s/cm2, approximately 1/10th that at ph 8.8. when the membrane potential is stepped from the holding (resting) potential to a more negative voltage the current rises from the initial to the steady state. the instantaneous current--voltage relation is lin ...	1981	7214211
identification in xenopus laevis of a class of oocyte-specific proteins bound to messenger rna.	proteins associated with poly(a)-rich rna in xenopus laevis oocytes have been identified in immature ovary homogenates using sucrose gradient centrifugation, oligo(dt)-cellulose fractionation and analysis by sodium dodecyl sulphate/polyacrylamide gel electrophoresis and two-dimensional acid/urea/sodium dodecyl sulphate gel electrophoresis. at least eight proteins are associated with ribonucleoprotein complexes and have the following properties. 1. four major proteins, mrnp1-4, cosediment with po ...	1981	7215334
monoclonal anti-igm can separate t cell from b cell proliferative responses in the frog, xenopus laevis.	the role of sigm+ lymphocytes in frog mitogen responses and mixed lymphocyte reactions was examined. a murine monoclonal antibody with specificity for xenopus laevis igm was produced. the anti-igm activity was not inhibited by glycoproteins other than xenopus igm, but could be inhibited with periodate-treated frog igm. fluorescent microsphere-coupled anti-igm was used to show that adult and larval thymocytes had few sigm+ lymphocytes, whereas spleens contained 19 to 34% sigm+ lymphocytes. the sp ...	1981	6456307
effect of skin allograft immunization on the mixed leukocyte reaction of the clawed frog, xenopus laevis.	one-way mixed leukocyte reactions (mlrs) of responder spleen cells from frogs (xenopus laevis) that had rejected skin grafts were examined. maximum and median stimulation indices (sis) of cultures that contained responder cells from the graft recipient and stimulator cells from the graft donor were significantly greater than the peak and median sis of cultures in which the responder splenocytes were from control, nonimmune animals. significant stimulation was also recorded earlier (day 2 of cult ...	1981	6460353
correlation between the cell cycle in the neurectoderm and differentiation during the early development of xenopus laevis. 2 inhibition of dna synthesis and mitosis during gastrulation.	the hypothesis that cell differentiation during primary induction may be coupled with a 'quantal' cell cycle in the presumptive neurectoderm is considered. embryos of xenopus laevis were incubated with fluorodeoxyuridine or mitomycin c during gastrulation or neurulation. embryos treated during the gastrula stage developed abnormalities of the brain but not of other tissues. this is seen as lending support to the idea that the wave of dna synthesis and mitosis in the presumptive neurectoderm duri ...	1981	6460598
messenger rnas of mouse hepatitis virus a59: isolation and characterization, translation in xenopus laevis oocytes of rnas 3, 6 and 7, uv target sizes of the transcription templates.		1981	6278883
equilibrium properties of a voltage-dependent junctional conductance.	the conductance of junctions between amphibian blastomeres is strongly voltage dependent. isolated pairs of blastomeres from embryos of ambystoma mexicanum, xenopus laevis, and rana pipiens were voltage clamped, and junctional current was measured during transjunctional voltage steps. the steady-state junctional conductance decreases as a steep function of transjunctional voltage of either polarity. a voltage-insensitive conductance less than 5% of the maximum remains at large transjunctional vo ...	1981	6259274
hormone effects on transport in cultured epithelia with high electrical resistance.	three continuous lines of amphibian epithelial cells form epithelia with a high transepithelial resistance (greater than 4,000 omega . cm2) in culture. the cell lines are tb-m and tb-6c, derived from the urinary bladder of bufo marinus, and a6, derived from the kidney of xenopus laevis. short-circuit current is equivalent to net mucosa-to-serosa sodium transport in two cell lines and slightly exceeds sodium transport in epithelia formed by tb-6c cells. none of the cell lines has an adenylate cyc ...	1981	6259946
purification and characterization of xenopus laevis type i topoisomerase.	a topoisomerase activity was purified from mature ovaries and from nuclei of stage 6 oocytes of xenopus laevis. from both preparations we obtained a single polypeptide chain having an estimated molecular weight of 67,000. the enzyme purified from ovaries is active in the presence of 150 mm monovalent cation, but its activity is more than 1 order of magnitude higher in the presence of 6 mm mg2+; the enzyme purified from nuclei requires mg2+ through all the steps of purification. enucleated oocyte ...	1981	6260773
in vitro transcription of a cloned mouse ribosomal rna gene.	an in vitro transcription system which utilizes cloned mouse ribosomal rna gene (rdna) fragments and a mouse cell extract has been developed. rna polymerases i is apparently responsible for this transcription as evidenced by the complete resistance to a high concentration (200 micrograms/ml) of alpha-amanitin. run-off products obtained with three different truncated rdna fragments indicated that rna was transcribed from a unique site of rdna. the s1 nuclease protection mapping of the in vitro pr ...	1981	6278446
the rise and fall of electrical excitability in the oocyte of xenopus laevis.	1. an electrically excited (gated) sodium selective channel has been found in the xenopus laevis oocyte, a cell membrane previously considered non-excitable. 2. the channel is produced by prolonged depolarization of the membrane and is removed by prolonged repolarization. both processes are very dependent on temperature and potential. 3. once produced, the channel can be opened and closed electrically, but does not show inactivation as is found in other sodium selective channels. 4. the sodium s ...	1981	6286961
replication of heterologous dna in xenopus laevis oocytes.		1981	6262120