| b-lymphocyte differentiation in xenopus laevis larvae. | | 1982 | 7042416 |
| localization of mitotic factors on metaphase chromosomes. | the objective of this study was to determine whether the mitotic factors of hela cells, which induce meiotic maturation, i.e. germinal vesicle breakdown (gvbd) and chromosome condensation, when injected into fully grown xenopus laevis oocytes, were localized in the cytoplasm or associated with the metaphase chromosomes. cytoplasmic extracts were prepared by lysing mitotic hela cells in low-salt hypotonic buffer and separating the chromosomes by centrifugation. th mitotic factors bound to chromos ... | 1982 | 7042719 |
| skin autografts as markers in the toad (xenopus laevis). | | 1982 | 7043079 |
| dynamics of the cytoskeleton of epidermal cells in situ and in culture. | the cytoskeleton of primary tissue-culture cells from the epidermis of xenopus laevis tadpoles was investigated by phase-contrast, immunofluorescence, and electron microscopy. the connection between the arrangement of different types of filaments and the mechanical properties of the epidermis is discussed. the bilayered epidermis attains stability from thick bundles of tonofilaments interconnecting the basal desmosomes. twisting of tonofilaments around each other can explain the occurrence of el ... | 1982 | 7044557 |
| increased phosphorylation of ribosomal protein s6 during meiotic maturation of xenopus oocytes. | a single ribosomal protein (mr, 32,000) becomes phosphorylated during progesterone-induced in vitro maturation of xenopus laevis oocytes. the protein is identified as 40s ribosomal protein s6. phosphorylation of s6 is monitored by incorporation of 32pi and by two-dimensional polyacrylamide gel electrophoresis. s6 is minimally phosphorylated in unstimulated oocytes. after progesterone treatment, phosphorylation of s6 precedes germinal vesicle breakdown (gvbd) and is maximal at the time when 50% o ... | 1982 | 7045876 |
| nucleotide sequence of the 5'- and 3'- domains for rabbit 18s ribosomal rna. | by direct rna sequence analysis we have determined the primary structures of both the 5' and 3' domains for rabbit 18s ribosomal rna. purified 18s rrna was labeled in vitro at either its 5' or 3' terminus with 32p, base-specifically fragmented enzymatically and chemically, and the resulting fragments electrophoretically fractionated by size in adjacent lanes of 140 cm long polyacrylamide sequencing gels run in 90% formamide. a phylogenetic comparison of both the mammalian 5' proximal 400 residue ... | 1982 | 7048256 |
| nucleotide sequences of cloned cdna fragments specific for six xenopus laevis ribosomal proteins. | we have previously constructed and selected six recombinant plasmids containing cdna sequences specific for different ribosomal proteins of xenopus laevis (bozzoni et al., 1981). dna cloned in these plasmids have been isolated and sequenced. amino acid sequences of the corresponding portions of the proteins have been derived from dna sequences; they are arginine- and lysine-rich as expected for ribosomal proteins. one of the cdna sequences has an open reading frame also on the strand complementa ... | 1982 | 7049839 |
| intracellular glycosylation of vitellogenin in the liver of estrogen-stimulated xenopus laevis. | pulse-chase experiments measuring the rates of incorporation of radiolabeled glucosamine and galactose into intracellular vitellogenin show that glycosylation of this multicomponent protein occurs in a golgi-enriched fraction isolated from homogenized liver slices. no apparent role of the rough endoplasmic reticulum in this process was demonstrable. kinetics of the intracellular translocation of glycosylated vitellogenin indicate that the galactosylated intermediate is secreted more rapidly than ... | 1982 | 7053388 |
| the steroid ligands of estrogen binding proteins in xenopus laevis liver cytosol are primarily metabolites 17beta-estradiol. | the interactions in vitro between [3h]estradiol and liver proteins from xenopus laevis have been examined to determine if the binding reaction meets criteria of steroid-receptors which may function in the induction of vitellogenesis. estrogenic hormones associated with proteins is serum and liver cytosol from xenopus laevis. however, the interactions between soluble liver proteins and estrogens apparently do not result from serum contamination of liver as specific binding was distinguishable by ... | 1982 | 7055614 |
| an electrical block is required to prevent polyspermy in eggs fertilized by natural mating of xenopus laevis. | | 1982 | 7056442 |
| testosterone 5 alpha-reductase in spinal cord of xenopus laevis. | testosterone 5 alpha-reductase, the enzyme that converts testosterone to 5 alpha-dihydrotestosterone, is present in the spinal cord of xenopus laevis. in adult males the enzymatic activity is optimal at ph 7.4 and 27 degrees c; the apparent km is 2.0 x 10(-5) m and the vmax is 10.0 pmol/mg protein/h. enzymatic activity was assayed in segments of the spinal cord in each of four groups: control untreated males, females, castrated males, and sexually active clasping males. striking differences in b ... | 1982 | 7057185 |
| structure of the active nucleolar chromatin of xenopus laevis oocytes. | active nucleolar chromatin of xenopus laevis oocytes was prepared for electron microscopy by a step gradient method, which separates the chromatin from proteins and other constituents that might nonspecifically bind at low ionic strength. between putative rna polymerases and within the nontranscribed spacer region, the chromatin appears as smooth, thin filaments. for the first time, it is shown here that these filaments are indistinguishable from pure dna absorbed to the same specimen, even when ... | 1982 | 7060131 |
| ribosomal protein s6 from xenopus laevis ovaries. isolation, phosphorylation in vivo and cross-reaction with heterologous anti-s6 antibodies. | ribosomal protein s6 from xenopus laevis ovaries was prepared by ion-exchange chromatography on phosphocellulose and gel filtration on sephadex g-75. the protein was identified as s6 from its position on two-dimensional polyacrylamide gels and from its immunological cross-reaction with monoclonal antibody raised against chicken liver s6, and from the fact that it is the major phosphorylated protein of the small subunit. when oocytes were incubated with [32p]orthophosphate in the presence of prog ... | 1982 | 7060584 |
| anomalous axonal outgrowth at the retina caused by injury to the optic nerve or tectal ablation in adult xenopus. | the retina and optic nerve head have been examined by light and electron microscopy in adult xenopus laevis after injury to optic nerve fibres. intraorbital resection, transection or crush of the optic nerve all resulted in the appearance at the retina of a mass of actively growing axons which formed a ring around the intraretinal and adjacent choroidal portions of the optic nerve head. formation of this heterotopic axon population was first noted at two weeks after nerve injury and fibres persi ... | 1982 | 7069447 |
| subcellular transport and ribosomal incorporation of microinjected protein s6 in oocytes from xenopus laevis. | protein s6 was isolated from 40s ribosomal subunits of xenopus laevis oocytes, labeled with sodium boro[3h]hydride, and microinjected back into oocytes. in the first 4 h of incubation, the uptake of s6 into the nucleus increased to a maximum, with, however, no detectable incorporation into 40s ribosomal subunits. after this lag period, s6 was progressively integrated into the small ribosomal subunit. when rrna transcription was inhibited by actinomycin d, the uptake of s6 into the nucleus and it ... | 1982 | 7074038 |
| inhibition of lens regeneration in larval xenopus laevis. | the present research aims at showing the role played by the lens in inhibiting lens-forming transformations of the outer cornea of xenopus laevis tadpoles. two types of experiment were carried out: 1) lentectomy and insertion of a millipore filter disk at the side of the lens, and 2) lentectomy and insertion of a millipore disk with a central hole. results indicate that when the lens is replaced by a mechanical obstacle capable of preventing direct communication between vitreous and anterior cha ... | 1982 | 7077262 |
| in vitro induction of germinal vesicle breakdown in xenopus laevis oocytes by melittin. | the bee venom, melittin, is an amphipathic polypeptide comprising 26 amino acids with known sequence. it consists of a hydrophobic and a basic hydrophilic segment, possesses lipolytic activity, and stimulates na+-k+ pump activity. at 1.5 microm melittin induces 98% germinal vesicle breakdown (gvbd) in stage vi (dumont) oocytes and 96% in stage iv oocytes. progesterone (30 microm) induced 100% gvbd in stage vi oocytes and none in stage iv oocytes. gvbd occurs earlier with melittin than with proge ... | 1982 | 7084570 |
| endocytosis of yolk proteins by xenopus laevis oócytes: kinetics of uptake of estrogen and gonadotropin-induced vitellogenins. | | 1982 | 7084664 |
| lectin from embryos and oocytes of xenopus laevis. purification and properties. | soluble extracts of xenopus laevis blastula stage embryos, oocytes, and adult liver contain lectin activities detected by agglutination of trypsinized, glutaraldehyde-fixed rabbit erythrocytes. lectin from the embryos and oocytes was purified by affinity chromatography on a column derivatized with melibiose. trace contaminants were removed either by preparative isoelectric focusing or by gel filtration. based on its behavior on sepharose 6b the purified oocyte lectin has an apparent molecular we ... | 1982 | 7085636 |
| high sensitivity of xenopus gustatory receptors to amino acids and bitter substances. | the gustatory nerve responses of the aquatic toad xenopus laevis to salts, acids, amino acids, and bitter substances were recorded. 1) the gustatory receptors were sensitive to amino acids and bitter substances. the thresholds were 10(-7) m for arg, 3 x 10(-9) m for strychnine, and 3 x 10(-8) m for quinine, 200-20,000 times lower than the thresholds for the respective stimuli in the bullfrog. 2) the basic and the neutral amino acids were effective whereas the acidic ones were not. relations betw ... | 1982 | 7091394 |
| observations on the development of descending pathways from the brain stem to the spinal cord in the clawed toad xenopus laevis. | anurans such as the clawed toad xenopus laevis offer a unique opportunity to study the ontogeny of descending pathways to the spinal cord. their transition from aquatic limbless tadpole to juvenile toad occurs over a protracted period time during which the animal is accessible for experimental studies. in xenopus laevis tadpoles the development of descending pathways has been studied from early limb-bud stage on (stage 50) with the aid of hrp slow-release gels. in stage 50, cells of origin of de ... | 1982 | 7091712 |
| an improved method for the isolation of leucocytes from xenopus laevis blood. | | 1982 | 7095237 |
| effects of cholera toxin and actinomycin on synthesis of [35s]methionine-labeled proteins during progesterone-induced maturation of xenopus laevis oocytes. | | 1982 | 7095262 |
| urea cycle enzymes and glutamate dehydrogenase in xenopus laevis and bufo viridis adapted to high salinity. | xenopus laevis was adapted stepwise to 600 m osmolar sodium chloride. after adaptation, the level of argininosuccinate lyase was raised 9-fold, carbamoylphosphate synthetase 6-fold, and ornithine carbamoyltransferase and arginase 3-fold. liver glutamate dehydrogenase was also raised 5-fold; kidney glutamate dehydrogenase was unchanged. in bufo viridis similarly adapted, there was a 5-fold increase in argininosuccinate lyase. when xenopus laevis was adapted to 600 m osmolar sucrose, there was onl ... | 1982 | 7097181 |
| cholinesterase localization at sites of nerve contact on embryonic amphibian muscle cells in culture. | cholinesterase (che), detected histochemically, was found to be localized at many sites of nerve-muscle contact in cultures of spinal cord and muscle cells derived from xenopus laevis embryos. such contacts were often characterized by a corresponding localization of acetylcholine receptors and by synaptic ultrastructure, including aggregates of clear vesicles in the nerve fibre and an 80-100 nm wide intercellular cleft. the che reaction product was localized in the cleft. when cultures were grow ... | 1982 | 7097313 |
| [cellular proliferative potentials of the pigment and ciliated epithelium of the eye in clawed toads normally and during regeneration]. | it was shown by means of 3h-thymidine autoradiography that the cells of almost all layers of intact eyes had proliferative potencies both in albino and normal strains of xenopus laevis, as it is the case in the urodela. the removal of retina and lens in x. laevis, unlike in the urodela, did not result in the intensification of proliferation of the pigment epithelium cells. the cells of ciliary region represent the source of retina regeneration of x. laevis. the regenerating retina is incomplete ... | 1982 | 7099515 |
| [ratio of the depressive effect of macromolecular synthetic inhibitors in the mitochondria to the concentration of gonadotropic hormones in the in vitro maturation of xenopus oocytes]. | the inhibitory action of ethidium bromide (ethbr) and chloramphenicol (cm) on in vitro oocyte maturation in xenopus laevis induced by different gonadotropic hormone concentrations was studied. two concentrations of hormone were used (hypophysial suspension of hcg): one yielding high but not maximal incidence of maturation and another exceeding 4 to 8 times the former. under the higher hormone concentration the inhibitory action of cm decreased and that of ethbr increased. | 1982 | 7099517 |
| the influence of voltage conditioning on chloride currents in amphibian muscle membrane: the sigmoid conductance-voltage relation extended into the outward current region. | sartorius muscle fibres of xenopus laevis were depolarized in solutions of high k+ content and then voltage clamped in solutions in which k+ was replaced by rb+ and(or) tetraethylammonium ion (tea+) at ph 9. a three-microelectrode clamp system was used in which the bath was held at virtual ground using an operational amplifier in a current meter configuration. the holding potential was set at zero membrane current potential (resting potential), close to -25 mv. a two-pulse paradigm was used to t ... | 1982 | 7104847 |
| the glomus cell of the carotid labyrinth of xenopus laevis. | the ultrastructure of the glomus cells of the carotid labyrinth was investigated in the anuran, xenopus laevis. these cells show many catecholamine containing granules. about 50 cells in groups of 3-5 are located near the sinusoids. morphologically, their organelles are similar to those previously reported in bufo vulgaris. striking features are (1) intimate appostion of the glomus cell to smooth muscle (g-s connection), (2) gap junctions between adjacent glomus cells, (3) exocytotic figures. ba ... | 1982 | 7105145 |
| gap junctions and impulse propagation in embryonic epithelium of amphibia. a freeze-etching study. | epithelium of amphibian embryos (cynops orientalis, xenopus laevis) was found in preceding experiments to generate and conduct impulses during a limited stage (26-37) of development . in order to elucidate the structural basis of impulse propagation, epithelial cells of four stages were examined by the freeze-etching method: (i) before and (ii) during acquisition of conductivity; (iii) when propagation was fully established, and (iv) when it was no longer present. only few gap junctions (gj) of ... | 1982 | 7105147 |
| expression and organization of the globin genes in xenopus laevis. | | 1982 | 7111273 |
| differential inhibition by progesterone of the adenylate cyclase of oocytes and follicle cells of xenopus laevis. | | 1982 | 7117515 |
| primary structure of the histone h2a and h2b genes and their flanking sequences in a minor histone gene cluster of xenopus laevis. | | 1982 | 7117538 |
| subcellular localization of the trna processing enzyme, trna nucleotidyltransferase, in xenopus laevis oocytes and in somatic cells. | earlier studies of the trna processing enzyme, trna nucleotidyltransferase, in rat liver cells suggested that the enzyme was absent from nuclei, whereas more recent studies with trna transcription-processing systems from xenopus laevis oocytes indicated that the enzyme was present in germinal vesicles of these cells. in order to resolve this apparent discrepancy, the subcellular localization of trna nucleotidyltransferase in oocytes was directly determined, and its distribution in somatic cells ... | 1982 | 7122242 |
| biosynthesis of two structurally different pro-opiomelanocortins in the pars intermedia of the amphibian pituitary gland. | this study reports the biosynthesis of two forms of pro-opiomelanocortin in the pars intermedia of the pituitary gland of the african clawed toad xenopus laevis. the two forms could be resolved by dodecyl sulphate gel electrophoresis on a 9-16% acrylamide gradient and their molecular weights were 38200 and 37300. incubation of neurointermediate lobes with [3h]glucosamine followed by tryptic digestion of the newly synthesized glycoproteins, revealed that both prohormones have only one glycosylate ... | 1982 | 7128582 |
| biosynthesis of a gamma 3-melanotropin-like peptide in the pars intermedia of the amphibian pituitary gland. | this study reveals the biosynthesis of a gamma 3-melanotropin-like peptide in the pars intermedia of the pituitary gland of the aquatic toad xenopus laevis. pulse-chase experiments in vitro showed that this product is synthesized through processing of a prohormone, pro-opiomelanocortin, and that it is released into the incubation medium. the peptide immunoprecipitated with antiserum to gamma 3-melanotropin, appeared to be a glycopeptide and displayed melanotropic activity. this last observation ... | 1982 | 7128584 |
| multiple factors involved in the transcription of class iii genes in xenopus laevis. | cell-free extracts from xenopus laevis oocytes (ovarian tissue), unfertilized eggs, embryos, and cultured kidney cells direct accurate transcription of cloned 5 s rna and trna genes. fractionation of these extracts by conventional ion exchange chromatography shows that multiple components are essential for the transcription of each of these genes by rna polymerase iii. two chromatographically distinct fractions from ovary, egg, embryo, and kidney cell extracts are necessary and sufficient, in th ... | 1982 | 7130190 |
| the neuromuscular basis of swimming movements in embryos of the amphibian xenopus laevis. | when removed from their egg membranes, xenopus embryos can swim. high-speed cinematography shows that, in swimming, lateral undulations pass rostro-caudally down the body. the swimming rhythm period is 40-100 ms. in swimming, electrical activity in myotomal muscles alternates on opposite sides of a segment and sweeps rostro-caudally in ipsilateral myotomes. myotome muscle physiology was examined. muscle fibres are electrically coupled to each other, and the fibres are able to spike. the possible ... | 1982 | 7130896 |
| the central nervous origin of the swimming motor pattern in embryos of xenopus laevis. | rhythmic motor nerve activity was recorded in stage 37/38 xenopus embryos paralysed with curare. the activity was similar to the swimming motor pattern in the following ways: cycle period (40-125 ms), alternation of activity on either side of a segment, rostro-caudal phase lag. episodes of rhythmic motor activity could be evoked by stimuli that evoke swimming and inhibited by stimuli that normally inhibit swimming. on this basis we conclude that the swimming motor pattern is generated by a centr ... | 1982 | 7130897 |
| the neuromuscular basis of rhythmic struggling movements in embryos of xenopus laevis. | xenopus embryos struggle when restrained. struggling involves rhythmic movements of large amplitude, in which waves of bending propagate from the tail to the head. underlying this, electrical activity in myotomal muscles occurs in rhythmic bursts that alternate on either side of a segment. bursts in ipsilateral segments occur in a caudo-rostral sequence. curarized embryos can generate motor nerve activity in a struggling pattern in the absence of rhythmic sensory stimulation; the pattern is ther ... | 1982 | 7130898 |
| purification and physical properties of arginase from xenopus laevis. | arginase from the liver of xenopus laevis has been purified to homogeneity by heat treatment, acetone fractionation, and isoelectric focussing. the main component had an isoelectric point (i.e.p.) of 7.3; there is a minor component of i.e.p. 7.8. the molecular weight of the enzyme, as determined by gel filtration on sephadex g200, is 76,000 daltons, substantially less than that of rat liver arginase studied concurrently. the molecular weight of the subunits, as determined by electrophoresis in s ... | 1982 | 7130924 |
| characterization of spermatid/sperm basic chromosomal proteins in the genus xenopus (anura, pipidae). | spermatid/sperm basic chromosomal proteins from 17 species and subspecies of the genus xenopus (anura, pipidae) were compared. electrophoresis on acetic acid/urea/triton x-100 polyacrylamide gels revealed that each xenopus species with a diploid chromosome number of 36, 72, or 108 showed multiple, diverse spermatid/sperm-specific basic chromatin proteins with mobilities greater than the somatic histones. the numbers and mobilities of these proteins were characteristic of each xenopus species and ... | 1982 | 7130928 |
| schooling behavior of tadpoles: a potential indicator of ototoxicity. | fish and tadpoles in schools use hair cells of their lateral line system to assess their position in relation to neighbors. this suggests that pharmaceutical agents that damage hair cells in the mammalian inner ear may also alter geometry in fish and tadpole schools. we used a computer-based image analysis system to examine the effect of the ototoxic aminoglycoside antibiotic, streptomycin, on school geometry for tadpoles of the african clawed frog xenopus laevis. tadpoles exposed to streptomyci ... | 1982 | 7134246 |
| contractile properties of two varieties of twitch muscle fibres in xenopus laevis. | the contractile properties of twitch muscle fibres in the iliofibularis muscle of xenopus laevis with characteristic differences in light-microscopical appearance have been studied under isometric and isotonic conditions. type 1 fibres (large, pale) have a short contraction time (tc), a shoulder in the relaxation phase, and a high twitch-tetanus ratio. in type 2 fibres (medium-to-large with abundant mitochondria and lipid droplets) tc is longer, half-relaxation time equals tc, and the twitch-tet ... | 1982 | 7136781 |
| on the development of the spinal cord of the clawed frog, xenopus laevis. i. morphogenesis and histogenesis. | the morphogenesis and histogenesis of the spinal cord of xenopus were examined. the study encompasses the developmental period between stage 41 and stage 66 (stages according to nieuwkoop and faber 1967). this period can roughly be divided into three phases. from stage 50 up to stage 53 strong proliferation and rapid growth are the most striking features. this developmental phase is preceded and followed by less dynamic periods. from stage 41 up to stage 50 the rate of proliferation is relativel ... | 1982 | 7137589 |
| on the development of the spinal cord of the clawed frog, xenopus laevis. ii. experimental analysis of differentiation and migration. | in order to determine the time and site of origin and the final location of various cell groups in the spinal cord, tadpoles of xenopus laevis, ranging from stage 48 to stage 56 were treated with tritiated thymidine and sacrificed at various stages from 49 to 66 (stages according to nieuwkoop and faber (1967). from the poorly developed matrix at stage 48-49 not only ventral horn cells, but also neuroblasts of the intermediate zone and the dorsal horn arise. both the matrix and the ventricle expa ... | 1982 | 7137590 |
| mapping the auditory central nervous system of xenopus laevis with 2-deoxyglucose autoradiography. | | 1982 | 7139290 |
| transcription of cloned xenopus laevis ribosomal dna microinjected into xenopus oocytes, and the identification of an rna polymerase i promoter. | transcription of a cloned xenopus laevis ribosomal dna (rdna) fragment, microinjected into xenopus oocytes, is initiated at the in vivo 40s pre-ribosomal rna (pre-rrna) site (+/- 2 bp) by rna polymerase i. an x. laevis rna polymerase i promoter has been mapped by studying the transcription of in vitro rdna mutants in the oocyte system. the active promoter lies within the dna segment beginning 145 bp upstream, and most probably ending 16 bp downstream, from the 40s pre-rrna initiation site (-145 ... | 1982 | 7139716 |
| changes in the activities of mitochondrial carriers during the development of xenopus laevis. | | 1982 | 7140847 |
| the influence of miedzian 50, a cupric pesticide, on the internal organs of adult xenopus laevis. i. liver and intestine. | | 1982 | 7141044 |
| transcription of xenopus borealis rrna genes in nuclei of xenopus laevis oocytes. | | 1982 | 7141111 |
| transcription of xenopus ribosomal rna genes by rna polymerase i in vitro. | we have developed an in vitro system in which rna polymerase i accurately transcribes xenopus ribosomal rna (rrna) genes. cloned xenopus laevis ribosomal dna (rdna) is incubated in a homogenate of manually isolated xenopus borealis oocyte nuclei. the resultant rna is analyzed by an s1 nuclease mapping procedure specific for the initiation region of x. laevis rrna. we show that transcription initiates in vitro on the cloned x. laevis rdna at the in vivo initiation site. in addition, the dinucleot ... | 1982 | 7142215 |
| the development of the peripheral trigeminal innervation in xenopus embryos. | the development of the ophthalmic, maxillary and mandibular nerves has been followed in xenopus laevis embryos from the first emergence of growth cones from the trigeminal ganglia until the establishment of functional innervation of the skin or cement gland. the course of each main nerve is highly predictable and follows pre-existing openings between blocks of other tissues. the development of the mandibulary nerve was observed most easily. like that of the other trigeminal nerves it falls into ... | 1982 | 7142898 |
| regeneration and functional reconnection of an identified vertebrate central neuron. | i have examined the axonal regeneration of a pair of identified central neurons, the mauthner (m) neurons, in xenopus laevis tadpoles. lucifer yellow injections reveal regenerative sprouts arising from the proximal stumps of the m axons within a few days after axotomy; some of these can cross the lesion within 1 week. many specimens examined at later times (up to 21 weeks) have processes that extend more than 2 mm (equivalent to 5 to 10 spinal segments) beyond the lesion. m axons which have rege ... | 1982 | 7143053 |
| [translation of the genomic and subgenomic rnas of cucumber virus 3 in a cell free system from wheat embryos and in xenopus laevis oocytes]. | the purified preparation of cucumber virus 3 (cv3) (one of the member of tobamovirus group) contains, besides full-length (2.0 x 10(6)) genomic rna, a short (0.24 x 10(6)) subgenomic rna coding for coat protein in xenopus laevis oocytes as well as in the cell-free protein synthesizing system from wheat embryos. the similarity of the polypeptide coded by short cv3 rna in vitro to natural cv3 coat protein is proved by the similarity of their molecular weights, antigenic specificity and by the simi ... | 1982 | 7144749 |
| dorsal root projections in the clawed toad (xenopus laevis) as demonstrated by anterograde labeling with horseradish peroxidase. | horseradish peroxidase was applied to the proximal stumps of severed cervical, thoracic and lumbar dorsal roots in the clawed toad, xenopus laevis, in order to study the course, distribution and site of termination of dorsal root fibers in the spinal cord and brain stem. the anterograde transport of horseradish peroxidase as applied in the present study proved to be a useful and reliable technique. results show that on entering the spinal cord, dorsal root fibers segregate into a medially placed ... | 1982 | 7145089 |
| circular single stranded phage m13-dna as a template for dna synthesis in protein extracts from xenopus laevis eggs: evidence for a eukaryotic dna priming activity. | unfractionated protein extracts from activated xenopus laevis eggs contain all functions required for the chain elongation reactions in replicative dna synthesis (a.richter, b. otto and r.knippers, 1981, nucl.ac.res. 9, 3793-3807). in order to further explore the dna synthesizing capacity of this in vitro system and to obtain information on the dna priming activity in these extracts single stranded phage m13-dna was used as template for in vitro dna synthesis. the main results of this investigat ... | 1982 | 7145711 |
| oocyte growth in the sheepshead minnow: uptake of exogenous proteins by vitellogenic oocytes. | the structure of the vitellogenic follicles of the sheepshead minnow, cyprinodon variegatus, is described. follicles enlarge primarily by protein yolk accumulation (vitellogenesis) and subsequently increase in size by hydration. this study uses the electron-dense tracer, horseradish peroxidase, and a larger heterologous protein, xenopus laevis [3h]vitellogenin, to follow the fate of exogenous proteins from the maternal circulation to yolk spheres of the growing oocyte. materials appear to leave ... | 1982 | 7147228 |
| formation of gap junctions by stem cells in the developing retina of the clawed frog (xenopus laevis). | to ascertain whether gap junctions are preferentially formed by proliferated retinal stem cells, an analysis by electron microscopic autoradiography was made on the retina of the xenopus embryo at stages 26, 29 and 31, after pulse labelling with 3h-thymidine. when the administration of the isotope was carried out for 0.5 or 3 h, retinal cells in s phase or s to m phase in the cell cycle were marked with the isotope, respectively. in these specimens, most gap junctions were found on the isotope-l ... | 1982 | 7149274 |
| chromatin structure of xenopus rdna transcription termination sites. evidence for a two-step process of transcription termination. | the ultrastructure of xenopus laevis (x.l.) 40s pre-rrna transcription termination sites was investigated by electron microscopy. amplified nucleolar chromatin was rapidly dispersed and processed for chromatin spread preparations. this type of preparation revealed that many rdna termination sites appeared as 50 nm long segments of chromatin axis covered by a complex of three closely spaced rna polymerase particles. particle (ptl) was characterized by the association with the terminal full-length ... | 1982 | 7151544 |
| visuotectal projections following temporary transplantation of embryonic eyes to the body in xenopus laevis. | eye anlagen of xenopus laevis at stages 22-26 were transplanted, 180 degrees rotated, into the flank of similarly staged embryos and 24-36 h later were placed into the orbits of final hosts at stages 32-36. after metamorphosis visuotectal projections were mapped electrophysiologically. in one series, eyes were normally oriented in the final host and visuotectal projections were found to be normal. a second series, in which eyes were placed in a rotated orientation in the final host, had develope ... | 1982 | 7153700 |
| trifluoperazine-induced meiotic maturation in xenopus laevis. | xenopus oocytes were exposed to trifluoperazine, a drug that binds to the calcium-regulating protein, calmodulin. the drug induced meiotic maturation even in the absence of progesterone. when trifluoperazine was microinjected directly into oocytes the maturation of the cells was partially inhibited in that the white spot, indicative of germinal vesicle breakdown, did not appear even though the germinal itself was absent in dissected oocytes. | 1982 | 7153737 |
| the development of connections between the isthmic nucleus and the tectum in xenopus and limnodynastes tadpoles. | in adult anura reciprocal connections exist between the isthmic nucleus and ipsilateral tectum. these pathways, with a projection from the isthmic nucleus to the opposite tectum, constitute the binocular visual connections. isthmic nuclei were examined histologically after injection of horseradish peroxidase into the tectum of xenopus laevis and limnodynastes dorsalis from midlarval stages to the completion of metamorphosis and in adults. the isthmic nuclei were present throughout, their cell nu ... | 1982 | 7155452 |
| [development of the structure and stability of mauthner's neurons in xenopus laevis tadpoles on the implantation of additional auditory vesicles]. | the ultrastructure and functional changes of the mauthner cells were studied in the x. laevis tadpoles under the conditions of the experimentally doubled source of their afferentation, an additional pair of ear vesicles. additional afferent fibers grow from the receptors to the brain and form additional synapses on the soma of the mauthner cells, indistinguishable by their morphology from the terminals of their own acoustic nerves. the altered interneuronal interactions lead, on one hand, to the ... | 1982 | 7155508 |
| spontaneous and experimental infections of xenopus laevis with chlamydia psittaci. | chlamydial infection was suspected when widespread pyogranulomatous inflammation and large basophilic intracytoplasmic inclusion bodies were evident histopathologically in african clawed frogs (xenopus laevis) dying of a spontaneous disease of high morbidity and mortality. organism morphology was determined by electron microscopy of infected hepatic sinusoidal lining cells, and it was characteristic of the unique developmental cycle of a chlamydial agent. isolation and speciation of the organism ... | 1982 | 7162133 |
| activation of vitellogenin gene transcription is a direct response to estrogen in xenopus laevis liver. | estrogen induces the synthesis of vitellogenin mrna by activating transcription of the vitellogenin genes. quantitative inhibition of liver protein synthesis by cycloheximide does not prevent activation of vitellogenin gene transcription. the relative transcription rate of the vitellogenin genes in estrogen stimulated liver is similar in control and cycloheximide treated animals (800-1000 ppm). selective estrogen activation of vitellogenin gene transcription therefore represents a direct effect ... | 1982 | 7162991 |
| difference in the mechanism of the action of caffeine and thymol on the calcium sequestering property of sarcoplasmic reticulum of frog skinned muscle fibers. | the effects of caffeine and thymol on the release of calcium from sarcoplasmic reticulum (sr) of mechanically skinned fibers isolated from semitendinosus muscle of frog, xenopus laevis, are studied. calcium release caused by caffeine is composed of two processes, a fast and a slow ones. the fast process is observable only when the amount of calcium stored in sr is above a "threshold" value while the slow one detectable only below the threshold value. the rate of these two processes does not depe ... | 1982 | 7166721 |
| the role of neural retina in lens regeneration from cornea in larval xenopus laevis. | | 1982 | 7170907 |
| use of xenopus laevis larvae in 96-hour, flow-through toxicity tests with naphthalene. | | 1982 | 7171848 |
| cell locomotion in vitro by xenopus laevis gastrula mesodermal cells. | prospective mesodermal cells of xenopus laevis gastrulae showed substantial locomotion in vitro, averaging 4.3 microns/min, when dissociated and cultured on a glass surface coated with collagen and fetal bovine serum. the cells translocate by making lamellipodia and filopodia whereas the main cell body remains rounded. when two mesodermal cells made contact with each other, they showed contact paralysis of lamellipodial activity. in contrast, when mesodermal cells contact ectodermal cells, conta ... | 1982 | 7172219 |
| lactate dehydrogenase of xenopus laevis laevis and xenopus borealis depends on a multiple gene system. | lactate dehydrogenase isozymes have been reinvestigated in xenopus laevis laevis and xenopus borealis. high resolution zymograms of various organs demonstrate that in both species the ldh isozymes are governed basically by a three-gene system: ldh-a coding for positively charged polypeptide, and ldh-b and ldh-c for negatively charged polypeptides (at ph 8.9). these three ldh subunits when assembled in tetramers show differential sensitivity to heat inactivation; the c4 homotetramer is the most l ... | 1982 | 7175448 |
| the regional distribution of poly (a) and total rna concentrations during early xenopus development. | xenopus laevis embryos were oriented and sectioned into six regions along one of three axes: animal-vegetal, dorsal-ventral, or right-left. total rna (predominantly ribosomal rna) and poly riboadenylate [poly (a)] were measured for each region during early embryogenesis. the concentrations of both total rna and poly(a) are nonuniformly distributed during early development. total rna is approximately four-fold more concentrated in the more animal portions than the more vegetal portions of the emb ... | 1982 | 7175452 |
| voltage- and stage-dependent uncoupling of rohon-beard neurones during embryonic development of xenopus tadpoles. | 1. electrical coupling of rohon-beard neurones in the spinal cord of xenopus laevis has been studied from the time of closure of the neural tube (stage 20, 22h after fertilization of the egg) to the free swimming tadpole (stage 49, 12d old). pairs of cells were examined by impaling both simultaneously with single micro-electrodes having current-passing and voltage-recording capabilities.2. at the earliest time studied (stage 20), before ca(2+) action potentials are detected, cells are electrical ... | 1982 | 7175739 |
| [modeling a persistent infection by tick-borne encephalitis virus strains in a cell culture of the clawed toad]. | differences in the ability of 12 tick-borne encephalitis virus strains to induce persistent infection in the culture of clawed frog cells incubated at 26-32 degrees c were shown. in 8 strains the process of persistence was accompanied by the stable preservation of the infectious virus in the culture medium during 10 passages, while in 4 strains the virus disappeared already in passages 3-8. | 1982 | 7180255 |
| comparative study of ultrastructures of the lateral-line organs and the palatal taste organs in the african clawed toad, xenopus laevis. | the fine structure of the lateral-line organ and the palatal taste organ in the african clawed toad, xenopus laevis, was examined by means of electron microscopy. the lateral-line organ consisted of hair and accessory cells. the apical surface of a hair cell was studded with one kinocilium and 20 to 40 stereocilia. synaptic bodies and subsynaptic cisternae were found in the cytoplasm of a hair cell adjacent to the synaptic contacts with the afferent and the efferent nerve endings, respectively. ... | 1982 | 7181143 |
| development of the optic nerve in xenopus laevis. i. early development and organization. | development of the xenopus laevis optic nerve was studied by light and electron microscopy from embryonic stage 26, before the retina has formed, to juveniles, 8 months postmetamorphic. low-power em photographs of sections through the retinal optic nerve (ron), middle optic nerve (mon) and chiasmatic optic nerve (con) were prepared at different stages and the areas containing large axons (0.5 micron) were traced in optic nerve reconstructions. ordering of fibre size along a dorsoventral axis was ... | 1982 | 7183741 |
| development of the optic nerve in xenopus laevis. ii. gliogenesis, myelination and metamorphic remodelling. | we studied the time of origin, development and location of glial elements in the developing optic nerve of xenopus with light and electron microscopy. the first cells acting as a primitive glia are ependymal cells lying dorsal to the chiasmatic optic nerve (con) at nieuwkoop & faber (1956) nf stage 39. later (stage 47/48), immature astrocyte cell bodies migrate from the periphery of the middle optic nerve (mon) into the central fibre mass along cytoplasmic processes extending from the outer glia ... | 1982 | 7183742 |
| increased adhesiveness at sites of high acetylcholine receptor density on embryonic amphibian muscle cells cultured without nerve. | in culture, myotomal muscle cells from xenopus laevis embryos develop discrete patches of high acetylcholine receptor (achr) density. to examine the relative adhesiveness of these sites, muscle cells having achr patches on their lower surface (apposed to the culture dish) were identified and were then treated with dibucaine or potassium-ringer in order to cause the cells to round up. more than 90% of these cells remained attached at an achr patch after rounding up, and this was the case even whe ... | 1982 | 7183745 |
| the functional stability of sea urchin histone mrna injected into oocytes of xenopus laevis. | | 1980 | 7189490 |
| the stability and translation of sea urchin histone messenger rna molecules injected into xenopus laevis eggs and developing embryos. | | 1980 | 7189491 |
| does h-y antigen induce the heterogametic ovary? | to determine whether phylogenetically conservative h-y antigen plays any part in gonadal differentiation among the nonmammalian vertebrates, we studied expression and binding of h-y in the frog, xenopus laevis. soluble h-y obtained from mouse testis and soluble h-w from chicken ovary bound specifically to cells of the zz testis from normal xenopus males. in addition, h-y (h-w) appeared selectively in the ovaries of zz genetic males that had been induced to become functional females by exposure t ... | 1980 | 7191350 |
| progesterone inhibits membrane-bound adenylate cyclase in xenopus laevis oocytes. | recent experimental evidence indicates that progesterone acts at the cell surface to trigger protein synthesis and to reinitiate the first meiotic division in xenopus laevis oocytes. the steroid hormone is physiologically released by follicle cells surrounding oocytes in the ovaries, and this naturally occurring event can be reproduced in vitro by adding progesterone to the incubation medium. recently, cyclic amp has been implicated in the mechanism of progesterone action in oocytes; there was a ... | 1981 | 7195984 |
| a reinvestigation of the role of the grey crescent in axis formation in xenopus laevis. | gravitationally induced displacements of the contents of the frog egg can predictably determine the orientation of the subsequent dorsal-ventral axis of the embryo, regardless of the original position of sperm entry or of the grey crescent. in certain conditions, these displacements in the egg can also lead to the formation of a second axis, that is, to twinning. the previously reported ability of grafts of grey crescent cortex to induce secondary axes in recipient eggs is interpreted here as an ... | 1981 | 7195987 |
| stability of non-polyadenylated viral mrnas injected into frog oocytes. | the naturally non-polyadenylated mrnas of reovirus were shown to have a half-life in excess of 3 days when injected into xenopus laevis oocytes. hybridization analysis and gel electrophoresis showed that all 10 mrna species had a similar high stability, despite being translated at widely differing rates. we have confirmed previous findings indicating a role for the 5'-terminal cap structure in determining reovirus mrna stability [furuichi et al. (1977) nature (lond.) 266, 235-239]. the significa ... | 1981 | 7196332 |
| the secretion of proteins in vitro from xenopus oocytes and their accessory cells: a biochemical and morphological study. | protein secretion by xenopus laevis oocytes and their surrounding follicular cells in vitro has been investigated using two-dimensional gel electrophoresis. viable oocytes, devoid of follicle layers, were prepared by treatment with collagenase; they retain in full their capacity to synthesize, sequester and export secretory proteins following microinjection with heterologous messenger rna. both rna-injected and normal cells export a large number of endogenous oocyte proteins and, as with heterol ... | 1981 | 7196433 |
| mitochondrial dna synthesis in xenopus laevis enucleated eggs. | | 1981 | 7197198 |
| the primary structure of oocyte and somatic 5s rrnas from the loach misgurnus fossilis. | somatic and oocyte 5s rrnas from the liver and unfertilized eggs of the loach (misgurnus fossilis have been sequenced and found to differ in six nucleotides. all the substitutions are confined to the 5'-half of the molecules; 4 of them are pyrimidine-pyrimidine substitutions, and 2 are purine-pyrimidine ones. considerable differences, both in the position and the character of substitutions, have been established when these 5s rrnas were compared with somatic and oocyte 5s rrnas from xenopus bore ... | 1981 | 7197777 |
| observations on intracellular ph during cleavage of eggs of xenopus laevis. | direct measurements of intracellular ph was made with recessed-tip ph microelectrodes in fertilized eggs of the frog, xenopus laevis, from approximately 1 h after fertilization to mid-blastula. the intracellular ph just before first cleavage was 7.65 +/- 0.04 (sd; n = 9). by stage 5 to the middle of stage 6, average intracellular ph was 7.70 +/- 0.06 (sd; n = 16). a statistically significant alkalization of 0.18 +/- 0.03 ph unit (sd; n = 5) was observed beginning in early blastula. a cycle of le ... | 1981 | 7198125 |
| in vivo distribution of proteins within a single cell. | using the oocyte of xenopus laevis, we present an experimental system, involving two-dimensional gel electrophoresis, for measuring unambiguously the nucleocytoplasmic distribution of proteins within a living cell. | 1982 | 7200407 |
| assembly of transcriptionally active 5s rna gene chromatin in vitro. | we have studied the requirements for the in vitro assembly of transcriptionally active 5s rna gene chromatin from cloned xenopus laevis 5s plasmid dna. both plasmid dna and dna assembled into chromatin with xenopus oocyte extracts are transcribed efficiently in vitro. chromatin prepared by nacl reconstitution with purified histones in the absence of any cellular factors, however, is transcriptionally inert. a transcriptionally active template is formed if plasmid dna is incubated in an ovary ext ... | 1982 | 7201351 |
| fate of amplified nucleoli in xenopus laevis embryos. | | 1982 | 7201429 |
| structure of the active nucleolar chromatin of xenopus laevis oocytes. | active nucleolar chromatin of xenopus laevis oocytes was prepared for electron microscopy by a step gradient method, which separates the chromatin from proteins and other constituents which might unspecifically bind at low ionic strength. between putative rna polymerases and within the non-transcribed spacer region, the chromatin appears as smooth, thin filaments, indistinguishable from pure dna adsorbed to the same specimen. these filaments are found under all conditions tested, even in the pre ... | 1982 | 7202203 |
| effects of temperature on sister chromatid exchanges. | the influence of temperature on sister chromatid exchanges was investigated, and the results are discussed in connection with factors possible involved in temperature-induced sce-formation. whereas the sce frequency increased with increasing growth temperature in a cell line of xenopus laevis (eax), which permits the examination of great temperature differences, a chinese hamster cell line (v-79) revealed a u-shaped temperature-response curve. in addition, it was found that cold treatment at 4 d ... | 1980 | 7203467 |
| 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 |
| the effect of a pesticide, gesagard 50, on regeneration of the endbrain of xenopus laevis (daud.) tadpoles. | | 1980 | 7215599 |
| 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 |