| the migration of presumptive primordial germ cells through the endodermal cell mass in xenopus laevis: a light and electron microscopic study. | presumptive primordial germ cells (ppgcs) were examined during migration from their deep endodermal position to the endodermal crest in xenopus laevis, using light and electron microscopy with epon sections, and several morphological characteristics of ppgcs, associated with their migration, were revealed. ppgcs displayed polymorphism, with smooth contours. the intercellular space around the pgcs was large and variable in width and cytoplasmic processes from ppgcs were occasionally observed in i ... | 1980 | 7217864 |
| 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 |
| [merkel cell differentiation in the developing tentacles of xenopus laevis (author's transl)]. | | 1980 | 7246046 |
| 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 |
| 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 |
| 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 |
| an autoradiographic study of the retinal projection in xenopus laevis with comparisons to rana. | the retinal projection to the brain in xenopus has been examined using autoradiographic techniques. the labelled moieties used were 3h-proline and 3h-fucose. there are three anterior thalamic optic terminal sites in xenopus. these are the nucleus of bellonci, the corpus geniculatum thalamicum and the rostral visual nucleus. the first two of these are similar to the homonymous nuclei in rana while the last, the rostral visual nucleus, appears to correspond to the rostral end of the posterior ento ... | 1980 | 7351442 |
| auditory and vocal nuclei in the frog brain concentrate sex hormones. | mate calling by south african clawed frogs, xenopus laevis, is under the control of androgens. autoradiographic studies demonstrate androgen-concentrating neurons in a motor nucleus that controls mate calling and a midbrain nucleus that is stimulated by sound. hormone concentration by laryngeal motor neurons suggests that steroids regulate the final common path for vocal behavior. modulation of auditory sensitivity by hormones could explain seasonal variations in behavioral responsiveness to con ... | 1980 | 7352269 |
| free calcium in xenopus embryos measured with ion-selective microelectrodes. | a regulatory role for intracellular free calcium has been suggested in cell division and intercellular communication via gap junctions. previous measurements of cytoplasmic free ca2+ during cell division and uncoupling have been made with the ca2+-sensitive photoprotein aequorin. we now report experiments using ca2+-sensitive microelectrodes to monitor free ca2+ in the cells and intercellular fluid of early embryos of the amphibian xenopus laevis. in addition to measuring basal levels, we have l ... | 1980 | 7354852 |
| nucleotide sequence of genes coding for trnaphe and trnatyr from a repeating unit of x. laevis dna. | a cloned 3.18 kb repeating unit of xenopus laevis dna, known to contain two trna1met genes, has been partially sequenced. the sequenced region could potentially code for two more trna species. one is a phenylalanine trna with the same primary sequence as that found in a variety of mammals. the other is a tyrosine trna with a 13 bp intervening sequence located immediately adjacent or very close to the 3' nucleotide of the anticodon. the two putative genes have opposite polarity and the sequences ... | 1980 | 7357612 |
| rohon-beard cells and other large neurons in xenopus embryos originate during gastrulation. | the time of origin (birthday) of rohon-beard cells in xenopus laevis was studied by 3h-thymidine autoradiography. rohon-beard cells were selected because they are a morphologically identifiable population of neurons in which the development of chemical and electrical excitability has been studied. a single injection of a radioactive dna precursor was given to animals in successive stages of development from blastula to late tail bud (nieuwkoop and faber stages 8--33/34). the label was available ... | 1980 | 7364967 |
| tadpole of the clawed frog, xenopus laevis, as an experimental intermediate host of angiostrongylus cantonensis. | frogs and toads, as paratenic hosts, are known to be sources of human angiostrongyliasis. the present investigation was carried out to examine the role of the tadpole as an experimental intermediate host. first-, second-, and third-stage larvae were found in tadpoles of xenopus laevis from the 1st, 14th, and 18th days, respectively, after exposure to the first-stage larva of angiostrongylus cantonensis. third-stage larvae collected from a frog which had metamorphosed from an exposed tadpole reac ... | 1980 | 7369450 |
| isolation and translation in vitro of four related vitellogenin mrnas of estrogen-stimulated xenopus laevis. | cloning of vitellogenin cdna of xenopus laevis revealed that vitellogenin is encoded in a small family of genes representing two distantly related main groups a and b, each comprising two more closely related subgroups a1, a2, and b1, b2 respectively. to characterize the proteins derived from these genes we have isolated the corresponding mrnas by hybridizing, under stringent conditions, cytoplasmic poly(a)-containing rna from the liver of estrogen-stimulated xenopus to filter-bound cdna clones ... | 1980 | 7371639 |
| specification of retinotectal connexions during development of the toad xenopus laevis. | the specification of central connexions of retinal ganglion cells was studied in xenopus laevis. in one series of experiments, the right eye primordium was rotated 180 degrees at embryonic stages 24-32. in the other series, the left eye was transplanted into the right orbit, and vice versa, with either 0 degrees or 180 degrees rotation. after metamorphosis the visual projections from the operated eye to the contralateral optic tectum were mapped electrophysiologically and compared with the norma ... | 1980 | 7373205 |
| trochlear nerve regeneration in xenopus laevis larvae. | the trochlear nerve of xenopus laevis larvae was sectioned in the orbit, and the nerve distal to the section was removed, so that it could not serve to guide the return of the regenerating nerve to the superior oblique muscle (som). in a second series, in addition to removing the distal nerve segment, the som was removed or damaged. the regeneration pattern of the trochlear nerve fibers was recorded in situ at 1 to 5-day intervals with the aid of methylene blue staining. the early growth or rege ... | 1980 | 7373272 |
| the effect of divalent and trivalent cations on the sodium permeability of myelinated nerve fibres of xenopus laevis. | the effect of external ca, mg, sr, ba and la concentration was studied in potential clamp experiments on single myelinated nerve fibres of the frog (xenopus laevis). an increase in cationic concentration caused a positive shift of the na permeability (pna) curve along the potential axis, a decrease in max. pna and a decrease in the slope of the pna curve. the effectiveness of mg, sr and ba was similar and about 0.6 compared to that of ca, whereas la was about 80 times more effective than ca. | 1980 | 7376904 |
| the use of xenopus laevis for studies of osmotic regulation. | | 1980 | 7379538 |
| scanning electron microscopy of cells from hydroxyurea-arrested blastulae of xenopus laevis. | cells from xenopus embryos blocked at the blastula stage by treatment with hydroxyurea have been isolated and cultured in vitro. the morphology of these cells has been compared with that of cells from normal embryos using scanning electron microscopy. cells from such hydroxyurea-blocked embryos do not show the features, or changes in features, in culture shown by cells from normal embryos. | 1980 | 7379924 |
| ontogeny of the retina and optic nerve of xenopus laevis. iv. ultrastructural evidence of early ganglion cell differentiation. | | 1980 | 7380095 |
| ontogeny of the retina and optic nerve in xenopus laevis. i. stages in the early development of the retina. | a staging series for retinal histogenesis is described for xenopus laevis. it is based on scanning em studies of intact eyes and serial section analysis of silver-stained preparations. retinal development is arbitrarily divided into twelve stages (i--xii) based on distinct morphological and histological changes. in general, four different phases of retinal development can be identified: an embryonic phase of rapid histogenesis (nieuwkoop-faber stages 21--39) and onset of visual function; a secon ... | 1980 | 7381043 |
| ontogeny of the retina and optic nerve in xenopus laevis. ii. ontogeny of the optic fiber pattern in the retina. | the ontogeny of optic fiber patterns within the xenopus laevis retina has been studied in silver-stained serial sections and whole mounts. ganglion cell axons ("pioneers") appear much earlier than previously recognized, at nieuwkoop-faber ('56) stage 28. fibers fasciculate into bundles as they arise in the retina and reach the chiasma by nf stage 32. because the retina grows in rings at its margins, ganglion cell axons differentiate at the periphery and join the nearest fiber bundles (fascicles) ... | 1980 | 7381045 |
| cytotoxic effects of sodium selenite on tadpoles (xenopus laevis). | the cytotoxic effects of sodium selenite on developing tadpoles (xenopus laevis) were examined by scanning, light, and electron microscopy. selenium exposure resulted in disorganization, vacuolization, and swelling of the outer layer of epithelial cells in the tadpole epidermis. examination of muscle cells in the somites revealed myofibril disorganization and cell degeneration. mitochondria in both epithelial and muscle cells were swollen and showed loss of cristae. it is likely that sublethal e ... | 1980 | 7387186 |
| construction of a cloned library of expressed embryonic gene sequences from xenopus laevis. | | 1980 | 7390012 |
| use of a cloned library for the study of abundant poly(a)+rna during xenopus laevis development. | | 1980 | 7390013 |
| messenger rna for ribosomal proteins in xenopus laevis oocytes. | xenopus laevis oocytes (stage ii--iii) incorporate [35s]methionine into ribosomal proteins identifiable by two-dimensional electrophoresis. poly(a)-rich rna prepared form this source has been translated in a wheat germ cell-free system. among the products synthesized in vitro 30 are clearly identifiable as ribosomal proteins. some are not individually resolved, whereas a few of them may lack methionine or may not be correctly processed after the synthesis in vitro. an enrichment of our mrna prep ... | 1980 | 7398629 |
| the persistence in xenopus laevis dna of o6-methylguanine produced by exposure to n-methyl-n-nitrosourea. | | 1980 | 7398719 |
| chromatin organization within nuclear blebs in leukocytes of xenopus laevis. | the nuclei from leukocytes of peripheral blood, liver and spleen of an individual anaemic xenopus laevis have been found to possess numerous nuclear blebs or projections. there structures were found to be very variable in size and shape as viewed in electron micrographs, but commonly included an enclosed mass of cytoplasm bound on one side by a very thin section of nuclear material. such sections are membrane bounded on each side and frequently display an interesting ordered array of chromatin. | 1980 | 7398859 |
| ultrastructural analysis of ribosomal gene transcription in vitro. | xenopus laevis oocyte nuclei were manually isolated and incubated in vitro to synthesize rna. aliquots were removed before and during the reaction and prepared for electron microscopy, in order to observe the amplified ribosomal rna (rrna) genes. before in vitro incubation the rrna transcription units are covered with close-packed rna polymerase molecules and attached rrnp fibers, which are interpreted to have initiated in vivo. with incubation, these close-packed transcription complexes move do ... | 1980 | 7400153 |
| an interaction between dorsal and ventral regions of the marginal zone in early amphibian embryos. | when small explants from early gastrulae of xenopus laevis are allowed to develop in a buffered salt solution there is a considerable difference between the patterns of differentiation obtained from different dorsoventral levels of the marginal zone. these patterns of differentiation correspond to the fates of the different regions in the course of normal development. they are not altered if several explants of the same type are fused before culture. if a ventral marginal zone explant from xenop ... | 1980 | 7400747 |
| neutral carrier ion-selective microelectrodes for measurement of intracellular free calcium. | this paper describes the making and testing of calcium-selective microelectrodes for measurement of intracellular [free ca2+] levels. pipettes of tip outer diameter down to 0.4 micron were siliconized by a novel and easy method of vapor treatment. the tips were filled with a sensor mixture using the neutral ligand and solvent of oehme et al. (oehme, m., kessler, m. and simon, w. (1976) chimia (aarau) 30, 204-206) but with very hydrophobic cations replacing na+ in the salt component. this change ... | 1980 | 7407109 |
| synthesis of very high molecular weight thyroglobulin in three heterologous systems. | calf thyroid rna has been translated in the wheat germ and messenger-dependent reticulocyte lysate cell free systems and in xenopus laevis oocytes. peptides immunologically related to and comigrating with 330 000 molecular weight thyroglobulin as well as both larger and smaller immunopeptides have been synthesized. the smaller molecular weight peptides were due at least in part to degradation during incubation despite the presence of protease inhibitors. the larger molecular weight peptides coul ... | 1980 | 7407682 |
| lipoprotein crystals in the yolk platelet of a teleost, pelvicachromis pulcher (cichlidae). | yolk-platelt crystals in the oocytes of the teleost pelvicachromis pulcher (cichlidae) were shown, using electron diffraction and tilting of thin-sectioned specimens, to possess an orthorhombic lattice with unit-cells sides a = 8.3 nm, b = 16.6 nm and c = 18.0 nm. they thus closely resemble the crystals known for a newt (triturus sp.) and a frog (xenopus laevis). | 1980 | 7407843 |
| assembly of nucleosomes: the reaction involving x. laevis nucleoplasmin. | we analyze the nucleosome core assembly reaction which is mediated in vitro by a protein previously purified from xenopus laevis eggs, now named nucleoplasmin in reference to its occurrence in the soluble phase of the nucleus of a wide range of vertebrate cell types. nucleoplasmin is present in solution as a pentamer. we use nuclease digestion analysis to show that the protein assembles bona fide nucleosome cores in vitro from purified histones and dna. nucleoplasmin itself binds neither to dna ... | 1980 | 7407918 |
| biochemical research on oogenesis. composition of the 42-s storage particles of xenopus laevix oocytes. | previtellogenic oocytes of xenopus laevis contain far more 5-s rna and trna than 28-s + 18-s rna. trna and 5-s rna are storage products that will be used in later oogenesis for protein synthesis and ribosome assembly. stored trna and 5-s rna are not free in the cell sap but belong to nucleoprotein particles of various sizes. there are two prominent kinds of storage particles in previtellogenic oocytes of x. laevis. the smaller ones (7-s) contain about half of the cell's 5-s rna. the larger ones ... | 1980 | 7408887 |
| kinetics of synthesis and processing of precursor polypeptides of murine leukemia virus in frog oocytes following microinjection of viral rna. | microinjection of rauscher murine leukemia viral rna into living oocytes from xenopus laevis, in contrast to cell-free systems, allowed detailed studies on the processing of newly synthesized viral precursor polypeptides. the viral messenger appeared to be stable for at least 5 days. maximal rate of translation of 70-s virion rna was observed 10 h after injection. the predominant translation products after a 1-h labeling period were three precursor polypeptides of mr 77000, 75000 and 65000. foll ... | 1980 | 7408891 |
| effects of the carcinogens n-methyl-n-nitrosourea and n-dimethylnitrosamine on spleen cell antigen binding in xenopus laevis. | | 1980 | 7409292 |
| determination of the dorsal-ventral axis in eggs of xenopus laevis: complete rescue of uv-impaired eggs by oblique orientation before first cleavage. | | 1980 | 7409319 |
| xenopus laevis oocyte calmodulin in the process of meiotic maturation. | calcium ions are postulated to be involved in the process of meiotic maturation of amphibian oocytes. since several of the calcium effects in eukaryotic cells are mediated by calmodulin, the present study was undertaken to assess the presence and level of calmodulin in xenopus laevis oocytes before and after progesterone treatment. calmodulin was shown to be present at a concentration of approximately microm in control oocytes cytosol. this level remained stable for 2 h when the maturation promo ... | 1980 | 7410431 |
| electrical excitability of outgrowing neurites of embryonic neurones in cultures of dissociated neural plate of xenopus laevis. | 1. i have studied the electrical excitability of outgrowing processes of individual neurones in cultures made from dissociated neural plates of embryos of xenopus laevis prior to the time of neurite outgrowth in vivo. 2. the electrical excitability of neurites was tested by stimulating them extracellularly and recording responses with an intracellular electrode in their cell bodies; neurites were excitable at all times examined. 3. the ionic basis of the excitability of neurites was tested by re ... | 1980 | 7411426 |
| modification of mitochondria-rich cells in different ionic conditions: changes in cell morphology and cell number in the skin of xenopus laevis. | xenopus laevis were kept in salt water (1.25% nacl), distilled water, or tapwater for a month. compared to the animals kept in tap water, the number of mitochondria-rich (mr) cells in the nacl-adapted animals was significantly reduced, while it was increased in those maintained in distilled water. in addition, the mr-cells of nacl-adapted animals lost their slender flask shape and developed large deposits of glycogen. the alteration of this cell type in conditions of high or low salinity may ref ... | 1980 | 7416509 |
| the morphology of cultured melanophores from tadpoles of xenopus laevis: scanning electron microscopical observations. | tail-fin melanophores of tadpoles of xenopus laevis (daudin) in primary culture were examined scanning electron microscopically in the aggregated and in the dispersed state. after isolation, the melanophores are spherical, but within 24 h they develop thin filopodia for attachment to the substratum. subsequently, cylinder-like as well as flat sheet-like processes are formed, which adhere to the substratum with terminal pseudopodia and filopodia. the processes of adjacent melanophores contact eac ... | 1980 | 7417982 |
| location of motoneurons supplying individual muscles in normal and grafted supernumerary limbs of xenopus laevis. | the purpose of this study was to investigate innervation of transplanted supernumerary hindlimbs in the frog (xenopus laevis). motoneurons innervating identified muscles in normal and supernumerary limbs were located by the method of retrograde transport of hrp after intramuscular injection. in the lumbar spinal cord of normal xenopus, motoneurons supplying medial hindlimb muscles, which are derived from the ventral muscle mass during development, are located at the medial end of the motor colum ... | 1980 | 7419750 |
| differential postendocytotic compartmentation in xenopus oocytes is mediated by a specifically bound ligand. | xenopus laevis oocytes were used as a model system to study the intracellular fate of proteins incorporated by endocytosis. we found that the intracellular stability and compartmentation of proteins incorporated by receptor-mediated endocytosis differed substantially from that of proteins incorporated by nonspecific endocytosis. after its uptake, the specifically sequestered yolk precursor protein vitellogenin was converted to the yolk proteins lipovitellin and phosvitin which were stable with t ... | 1980 | 7428040 |
| the effect of actinomycin d on the nucleolus and on pigment synthesis in pigment cells of xenopus laevis: an ultrastructural study. | the effect of amd on the nucleolus and on melanogenesis in differentiating pigment cells of xenopus laevis was investigated in cultured neural crest cells. cultures were treated with either 2 or 10 microgram/ml amd for 41/2 hours. following treatment the antibiotic was removed. observations of the cells were made with both scanning and transmission electron microscopes. actinomycin d almost entirely stopped pigment formation in neural crest cultures during treatment. the morphological sequence i ... | 1980 | 7429969 |
| membrane assembly in retinal photoreceptors i. freeze-fracture analysis of cytoplasmic vesicles in relationship to disc assembly. | to study precursor-product relationships between cytoplasmic membranes of the inner segment of photoreceptors and the continually renewed outer disc membrane, we have compared the density and size distribution of intramembrane particles (imp) in various membrane compartments of freeze-fractured photoreceptor inner and outer segments. both rod and cone outer segments of xenopus laevis are characterized by a relatively uniform distribution of approximately 4,400-4,700 imp/micron2 in p-face (pf) le ... | 1980 | 7430251 |
| disruption of optic fibre growth following eye rotation in xenopus laevis embryos. | eye rotation is an experimental paradigm used to study axial specification of the amphibian retina and its connections to the tectum. jacobson reported that the naso-temporal and dorso-ventral axes are determined sequentially and independently between nieuwkoop-faber (nf) stages 28 and 32 in xenopus. others claim however, that both retinal axes are determined much earlier and not independently in xenopus and rana. we now find that in xenopus this operation can disturb the exit of optic fibres fr ... | 1980 | 7432498 |