| cell cycle dynamics of an m-phase-specific cytoplasmic factor in xenopus laevis oocytes and eggs. | we have examined the regulation of maturation-promoting factor (mpf) activity in the mitotic and meiotic cell cycles of xenopus laevis eggs and oocytes. to this end, we developed a method for the small scale extraction of eggs and oocytes and measured mpf activity in extracts by a dilution end point assay. we find that in oocytes, mpf activity appears before germinal vesicle breakdown and then disappears rapidly at the end of the first meiotic cycle. in the second meiotic cycle, mpf reappears be ... | 1984 | 6425302 |
| effects of ca2+ ions on the formation of metaphase chromosomes and sperm pronuclei in cell-free preparations from unactivated rana pipiens eggs. | nuclei transplanted into unactivated amphibian eggs are known to condense into metaphase chromosomes whereas those transplanted into activated eggs decondense and enlarge. we have made cell-free cytoplasmic preparations from rana pipiens eggs which can induce demembranated xenopus laevis sperm to undergo changes similar to those seen in intact eggs. sperm chromatin which is incubated for 3 hr in unactivated egg preparations made using a buffer containing 3 mm egta is induced to form metaphase ch ... | 1984 | 6427039 |
| beta 2-microglobulin induces intracellular transport of human class i transplantation antigen heavy chains in xenopus laevis oocytes. | human class i transplantation antigens are cell-surface-expressed molecules composed of one glycosylated, membrane-integrated heavy chain and one nonglycosylated, water-soluble subunit, beta 2-microglobulin (beta 2m). we have examined the intracellular transport of the two subunits by microinjecting mrna into xenopus laevis oocytes. beta 2m, translated in oocytes, was transported and secreted into the medium in the absence of heavy chains whereas heavy chains were retained in the endoplasmic ret ... | 1984 | 6429156 |
| calcium ultrastructural localization in xenopus laevis eggs following activation by pricking or by calcium ionophore a 23187. | in the egg of xenopus laevis a cortical network of smooth endoplasmic reticulum (ser) surrounds and interconnects each cortical granule (cg) (campanella and andreuccetti, '77). this network is a possible intracellular site of calcium storage to be called into action for cg exocytosis. in our experiments, xenopus eggs, unfertilized or activated by pricking or by calcium ionophore a 23187, have been fixed in osmium-pyroantimonate for calcium localization. our data show that deposits can be detecte ... | 1984 | 6429269 |
| fly and frog homoeo domains show homologies with yeast mating type regulatory proteins. | homoeotic genes in the bithorax and antennapedia complexes of drosophila melanogaster appear to specify the developmental fate of segments of the fly. some of these genes (ultrabithorax, antennapedia and fushi tarazu) share homology due to their conservation of a 'homoeo domain'1,2 consisting of 60 amino acids. cross-hybridization and cloning experiments show that the homoeo domain is conserved in a frog (xenopus laevis) gene expressed in early development and may also be present in earthworm, b ... | 1984 | 6429549 |
| increased rate of capping of concanavalin a receptors during early xenopus development is related to changes in protein and lipid mobility. | the mobility characteristics of plasma membrane constituents were studied in dissociated cells from embryos of xenopus laevis at various stages of development from early blastula until neurulation. an increased rate of fluorescein isothiocyanate-concanavalin a induced patching and capping of con a-binding proteins during this period of development was correlated with a threefold increase in the lateral mobility of the receptor molecules, as determined by the fluorescent photobleaching recovery ( ... | 1984 | 6430735 |
| the comparative distribution of xenopsin- and neurotensin-like immunoreactivity in xenopus laevis and rat tissues. | the regional distribution of xenopsin-like immunoreactivity (xpli) and of neurotensin-like immunoreactivity (ntli) was studied by radioimmunoassay in tissues of xenopus laevis and rat. in xenopus laevis, xpli showed a wide distribution throughout central and peripheral tissues with the highest concentration in the skin; ntli was found in both central and peripheral tissues with the exception of the skin. gel chromatography on sephadex g-25 was used in order to characterize the immunoreactive mat ... | 1984 | 6434152 |
| uncoupled synthesis of h1o-like histone h1s during late erythropoiesis in xenopus laevis. | this study investigated the synthesis of xenopus histones during erythropoiesis. although cessation of dna replication in the mid-stages of erythroid maturation is accompanied by arrested synthesis of histone h1 and core histones, synthesis of h1o (an h1o-like histone) was found to continue into late stages of erythropoiesis, as has been reported for avian erythrocyte histone h5. this was accompanied by a threefold increase in the relative amount of xenopus h1s, similar to the accumulation repor ... | 1984 | 6434311 |
| oocyte adenylyl cyclase contains ni, yet the guanine nucleotide-dependent inhibition by progesterone is not sensitive to pertussis toxin. | membranes were obtained from xenopus laevis oocytes after removal of follicular cells by collagenase treatment. [32p]adp-ribosylation with pertussis toxin showed them to contain a single mr = 40000 substrate for this toxin that co-migrates on sodium dodecylsufate-polyacrylamide gel electrophoresis with pure human erythrocyte ni, the inhibitory regulatory component of adenylyl cyclase. [32p]adp-ribosylation of oocyte membranes with cholera toxin also showed presence of a single substrate but of m ... | 1984 | 6434346 |
| distribution and utilization of 5 s-rna-binding proteins during the development of xenopus oocytes. | at early stages of oogenesis in xenopus laevis most of the ribosomal 5s rna is complexed with three proteins to form two types of cytoplasmic rnp storage particle. a particle sedimenting at 42s contains 5s rna and trna together with two proteins of mr 48000 (p48) and mr 43000 (p43) and a second particle sedimenting at 7s contains 5s rna plus a protein of mr 40000 (p40, also known as the transcription factor, tfiiia). in this report we use antibodies monospecific for each protein to follow the mo ... | 1984 | 6436024 |
| the structure of cytoplasm in directly frozen cultured cells. i. filamentous meshworks and the cytoplasmic ground substance. | cultured fibroblasts or epithelial cells derived from xenopus laevis embryos were directly frozen, freeze-substituted by an improved method, and then either critical-point-dried and viewed as whole mounts, or embedded and thin sectioned. in thin regions of these cells, where ice crystal artifacts are absent, the cytoplasm consisted of a dense, highly interconnected meshwork of filaments, embedded in a finely granular ground substance. the meshwork in directly frozen, intact cells was compared wi ... | 1984 | 6436253 |
| [potentiation of the effect of steroid hormones (progesterone and testosterone) inducing the reinitiation of meiosis in xenopus oocytes in vitro, by inhibitors of phosphatase activity]. | the induction of meiosis reinitiation by steroid hormones (progesterone and testosterone) in xenopus laevis oocytes was studied in vitro in presence of inhibitors of phosphatase activity such as beta-glycerophosphate, considered as a competitive inhibitor, and the two ions, zn++ and moo--4. kinetics of the germinal vesicle breakdown indicating the reinitiation of meiosis, have shown that while these phosphatase inhibitors were not active by themselves under the present experimental conditions, t ... | 1984 | 6437623 |
| fidelity of transcription of xenopus laevis globin genes injected into xenopus laevis oocytes and unfertilized eggs. | the xenopus laevis alpha 1- and beta 1-globin genes were injected into oocytes and unfertilized eggs of x. laevis. in oocytes, the injected globin genes were actively transcribed, but the majority of the transcripts were incorrectly initiated. in unfertilized eggs, the injected genes were transcribed at a low level but only from the correct start sites. in oocytes, the injected circular plasmid dna containing the cloned globin genes persisted but did not replicate. in contrast, dna injected into ... | 1984 | 6438494 |
| does the guanine nucleotide regulatory protein ni mediate progesterone inhibition of xenopus oocyte adenylate cyclase? | in xenopus laevis oocytes progesterone is able to inhibit directly the plasma membrane adenylate cyclase activity and induce reinitiation of meiotic maturation. to determine whether progesterone inhibition is mediated by the inhibitory guanine nucleotide-binding regulatory component of adenylate cyclase, ni, the effect of the bordetella pertussis toxin (iap) and limited proteolysis on progesterone action in oocytes was investigated. treatment of oocyte membranes with islet activating protein (ia ... | 1984 | 6439557 |
| evolution of the human sarcomeric-actin genes: evidence for units of selection within the 3' untranslated regions of the mrnas. | the complete 3' untranslated region (3'utr) sequence of the human skeletal-actin gene has been compared with the corresponding regions of the rat and chicken skeletal-actin genes. this comparison reveals that the skeletal-actin 3'utr is composed of conserved and nonconserved segments. by using genomic southern transfer blots and thermal stability (tm) measurements, we found that the cardiac-actin gene 3'utr also consists of conserved and nonconserved segments. comparison of human and xenopus lae ... | 1984 | 6439877 |
| isolation of two closely related vitellogenin genes, including their flanking regions, from a xenopus laevis gene library. | a gene library of xenopus laevis was constructed from embryonic dna partially digested with restriction endonucleases hae iii and alu i and joined to the phage lambda charon 4 cloning vector with ecori linkers. nucleotide sequences from three of the four related vitellogenin genes have been isolated. two of the genes (called a1 and a2) were isolated in their entirety together with long stretches of flanking sequences. these two closely related vitellogenin genes have lengths of about 21 and 16 k ... | 1980 | 6445556 |
| protein synthesis by hybrid ribosomes reconstructed from rabbit reticulocyte ribosomal core-particles and amphibian or fungal split-proteins. | it was shown that high-salt (2.75 m-nh4cl/69mm-mgcl2) shock treatment at 0 degrees c of the larger subparticles (l-subparticles) of rabbit, xenopus laevis and neurospora crassa cytoplasmic ribosomes yielded split-protein fractions that were not only functionally equivalent but also interchangeable. thus, although the remaining core-particles were inactive in both the puromycin reaction and in poly(u)-directed polyphenylalanine synthesis, activity was restored when they were combined with either ... | 1980 | 6446904 |
| maintenance of embryonically induced transplantation tolerance after short-term adult thymectomy in xenopus laevis. | | 1980 | 6447634 |
| cupular secretion by xenopus laevis line organs: autoradiographic evidence for incorporation of 3h-glucose and 35s-sulfate. | autoradiographic evidence for incorporation of 3h-glucose and 35s-sulfate into the cupulae of xenopus laevis (african clawed toad) lateral line organs was obtained after injection into the dorsal lymph sacs of adult animals. time intervals of 15 minutes to 4 hours after administration of these labeled metabolic precursors were used to examine the time course of the apparent mechanism of growth of the cupulae. our results suggest that the two layers of accessory cells (the sustentacular cells and ... | 1980 | 6447996 |
| monoclonal anti-igm can separate t cell from b cell proliferative responses in the frog, xenopus laevis. | the role of sigm+ lymphocytes in frog mitogen responses and mixed lymphocyte reactions was examined. a murine monoclonal antibody with specificity for xenopus laevis igm was produced. the anti-igm activity was not inhibited by glycoproteins other than xenopus igm, but could be inhibited with periodate-treated frog igm. fluorescent microsphere-coupled anti-igm was used to show that adult and larval thymocytes had few sigm+ lymphocytes, whereas spleens contained 19 to 34% sigm+ lymphocytes. the sp ... | 1981 | 6456307 |
| an in vivo study of the ontogeny of alloreactivity in the frog, xenopus laevis. | pre- and perimetamorphic larval and post-metamorphic juvenile frogs (xenopus laevis) from a single family were grafted with skin from either of their patents (who differed from the hosts by one major histocompatibility complex (mhc) haplotype and multiple minor h loci) or from an unrelated adult (to provide a greater immunogenetic disparity). the fate of such skin grafts transplanted to hosts of various developmental stages indicated that a net destructive alloimmunity in this amphibian species ... | 1982 | 6459993 |
| effect of skin allograft immunization on the mixed leukocyte reaction of the clawed frog, xenopus laevis. | one-way mixed leukocyte reactions (mlrs) of responder spleen cells from frogs (xenopus laevis) that had rejected skin grafts were examined. maximum and median stimulation indices (sis) of cultures that contained responder cells from the graft recipient and stimulator cells from the graft donor were significantly greater than the peak and median sis of cultures in which the responder splenocytes were from control, nonimmune animals. significant stimulation was also recorded earlier (day 2 of cult ... | 1981 | 6460353 |
| correlation between the cell cycle in the neurectoderm and differentiation during the early development of xenopus laevis. 2 inhibition of dna synthesis and mitosis during gastrulation. | the hypothesis that cell differentiation during primary induction may be coupled with a 'quantal' cell cycle in the presumptive neurectoderm is considered. embryos of xenopus laevis were incubated with fluorodeoxyuridine or mitomycin c during gastrulation or neurulation. embryos treated during the gastrula stage developed abnormalities of the brain but not of other tissues. this is seen as lending support to the idea that the wave of dna synthesis and mitosis in the presumptive neurectoderm duri ... | 1981 | 6460598 |
| membrane addition to rod photoreceptor outer segments: light stimulates membrane assembly in the absence of increased membrane biosynthesis. | the effect of light on the biosynthesis and the assembly of rod photoreceptor outer segment membranes was analyzed in vitro using retinas from xenopus laevis. the number of open discs at the base of the outer segment was used as a morphologic index to evaluate relative differences in rates of membrane assembly. assembly was stimulated in vitro by light, as evidenced by a greater number of open discs that accumulated in light-exposed retinas than that in retinas maintained under the same conditio ... | 1982 | 6460718 |
| effects of ethanol on the primitive streak stage mouse embryo. | recent studies of mouse models have suggested that malformations associated with the fetal alcohol syndrome (fas) are caused by the effects of ethanol on early embryos during gastrulation and neurulation. a study of xenopus laevis embryos showed that exposure of gastrula stage amphibian embryos to ethanol inhibits migration of the mesodermal cells, causes formation of small neural plates, and subsequently causes hypoplastic craniofacial malformations in tadpoles. we now report effects of ethanol ... | 1984 | 6463902 |
| in vitro thymus suppression of hemagglutinin production in xenopus laevis: location, drug and temperature sensitivity. | suppression of splenic hemagglutinin (ha) production by allothymuses in vitro was further studied in xenopus laevis, the south african clawed toad. since thymic capacity to suppress splenic ha secretion into the culture medium is retained in animals previously exposed to n-methyl-n-nitrosourea (nmu), which destroys the thymus cortex in this species, suppressor function must be located in the thymus medulla. reciprocal thymus-spleen combinations showed that normal thymus can suppress immunised sp ... | 1984 | 6464095 |
| transport of amino acids and nucleosides in metaphase-arrested unfertilized oocytes of xenopus laevis. | metaphase-arrested, unfertilized shed oocytes of xenopus laevis obtained after hormonal stimulation of the female are able to take up nucleosides (u, t) and amino acids (ala, gly, glu, gln, tyr). for alanine, tyrosine, and glutamic acid the transport is uphill. the transport of the amino acids studied is activated by na+, whereas the uptake of the nucleosides is independent of the na+ concentration. ouabain does not inhibit the uptake of amino acids significantly. the uptake of alanine and thymi ... | 1984 | 6467381 |
| [evaluation of amputation techniques for the study of limb regeneration in the newt and toad]. | a comparison between forelimb amputations through the radius-ulna and the humerus was made in the adult newt, cynops pyrrhogaster pyrrhogaster and the young toad, xenopus laevis. newts regenerated their forelimbs after the amputations and the new parts resembled the old in structure and function. toads regenerated their forelimbs incompletely after the amputations. the new parts lacked joints and fingers showing a simply elongate pattern. the effect of re-amputation of exposed bone on the regene ... | 1984 | 6468505 |
| the thiol-disulfide balance during maturation of xenopus laevis oocytes. | we measured several of the components involved in the thiol-disulfide balance of immature and mature oocytes of xenopus laevis: total soluble native sulfhydryl, reduced and oxidized glutathione, native sulfhydryl content of soluble protein, and disulfide content of soluble protein. none of these values changed during maturation. both the immature and mature oocyte were characterized by a relatively high disulfide to sulfhydryl ratio. we also measured native sulfhydryl content of germinal vesicle ... | 1984 | 6470653 |
| effect of caffeine on induced damage in cells of xenopus laevis. | xenopus laevis cells were treated with mitomycin c and subsequently treated with caffeine during either the s- or g2-phase of the cell cycle. the frequency of induced chromatid exchanges was especially increased by caffeine posttreatment during the s-phase. this increase took place at the expense of the frequency of isochromatid breaks, which was reduced, both when the caffeine posttreatment was given during the s- and g2-phase. | 1984 | 6472303 |
| variations in transcriptional activity of rdna spacer promoters. | we have compared the dna sequences of several different examples of the duplicated polymerase i promoters that are found in rdna spacers of xenopus laevis. although different spacers exhibit different amounts of transcription in vivo, this does not seem to be due to dna sequence differences between spacer promoters. we have found that several different spacer promoters when subcloned and injected into oocytes exhibit similar promoter activities when transcription is assayed by primer extension a ... | 1984 | 6473101 |
| two populations of rod photoreceptors in the retina of xenopus laevis identified with 3h-fucose autoradiography. | the retina of xenopus laevis contains two populations of rod photoreceptors that differ in their utilization of l-fucose. following intraperitoneal injections with 3h-fucose, all rod and cone photoreceptors incorporate the label. one day after labeling, much of the radioactivity is associated with the photoreceptor outer segments. in rods, a band of radioactivity is initially located at the base of the outer segment. as the time interval between injection and recovery is extended, the band of ra ... | 1984 | 6474834 |
| assessment of mutagenic damage by monofunctional alkylating agents and gamma radiation in haploid and diploid frogs, xenopus laevis. | adult male south african clawed frogs, xenopus laevis, were mutagenized by 3-day immersion in aqueous solutions of ethyl methanesulfonate (ems), diethyl nitrosamine (den), or ethyl nitrosourea (enu), or by acute exposure to gamma radiation. they were then spawned repeatedly at 2-week intervals with untreated females, and embryonic survival of the progeny was used to assess genetic damage. recessive lethal effects were assessed from reduced survival of androgenetic haploid progeny. neither recess ... | 1984 | 6479115 |
| lineage segregation and developmental autonomy in expression of functional muscle acetylcholinesterase mrna in the ascidian embryo. | acetylcholinesterase is a histospecific marker of cell differentiation occurring only in the muscle and mesenchyme tissues of the ascidian embryo. the distribution of functional mrna coding for this enzyme has been investigated and it is shown here that only cells of muscle and mesenchyme lineages possess such a template. blastomeres of four cell lineage quadrants were separated microsurgically from eight-cell-stage embryos of ciona intestinalis and raised in isolation until muscle development w ... | 1984 | 6479447 |
| interneurones in the xenopus embryo spinal cord: sensory excitation and activity during swimming. | the dorsolateral spinal cord of embryonic xenopus laevis has previously been shown to contain two anatomical classes of interneurones with dendrites in the dorsal tract where they could be contacted by the central axons of rohon-beard cells (roberts & clarke, 1982). the activity of these neurones within the dorsolateral spinal cord has been examined using intracellular micro-electrodes. following electrical stimulation of rohon-beard neurites within the ipsilateral skin, dorsolateral neurones re ... | 1984 | 6481637 |
| [surface structure of the otolithic organs of the tadpole of the clawed toad xenopus laevis]. | beginning from the blastula and tail bud stages, 15 larvae of the clawed toad were kept in three emkon containers at temperature 15 degrees for 8-9 days. structure of the hair cells and otolith membrane of the larval otolithic organs was examined with a light microscope, tem and sem. in contrast to previous studies, it was found that at the stages mentioned larval otolithic organs are presented not by two, but by three maculae, i.e. the utricular, saccular and lagenar ones with two otoliths. sac ... | 1984 | 6485654 |
| influence of ca2+ on the voltage dependent mechanosensitivity of the hair cells in the lateral line organs of xenopus laevis. | the influence of the transepithelial voltage (vt) on the degree of synchronization (dos) of afferent spikes from lateral line organs to mechanical stimulation has been examined in the isolated voltage clamped skin of xenopus laevis. with 1 mm cacl2, 5 mm mops-koh (ph = 7.1) in the apical solution and ringer's solution on the serosal side of the skin, changes in vt from -60 mv to 65 mv (inside relative to outside) lead to a nonlinear reduction in dos to a minimum value, where the afferent spikes ... | 1984 | 6485827 |
| in vitro inhibition of tubulin assembly by a ribonucleoprotein complex associated with the free ribosome fraction isolated from xenopus laevis oocytes: effect at the level of microtubule-associated proteins. | the 100 000 x g supernatant prepared from defolliculated xenopus laevis oocytes inhibits, in a dose-dependent manner, the in vitro polymerization of rat brain neurotubulin. the oocyte inhibitory factor is thermolabile, totally inactivated by rnase and partially by trypsin. a preliminary purification of the inhibitor showed that it is associated with the free oocyte ribosomes (80 s). the saturable binding of microtubule-associated proteins, essentially map2, to this 80 s ribonucleoprotein fractio ... | 1984 | 6488322 |
| variations in aldosterone and corticosterone plasma levels during metamorphosis in xenopus laevis tadpoles. | aldosterone and corticosterone plasma levels have been determined by radioimmunoassay at various stages (st) of metamorphosis in xenopus laevis tadpoles. the aldo level first showed a significant peak at the beginning of the climax (st 58), and again at the middle of the climax (st 61-62); b level increased slightly but significantly at st 59, then showed an important peak at st 62-63. the high levels of these hormones at these stages seem to be associated with the concomitant surge of interrena ... | 1984 | 6489739 |
| effects of radius--ulna removal on forelimb regeneration in xenopus laevis froglets. | regeneration of boneless amputated forearms of adult newts was found to progress at a rate and to a degree comparable to amputated control limbs in which stump bones were not removed. in contrast, regeneration of boneless amputated xenopus froglet forearms was significantly delayed and did not occur until two to three weeks following amputation. this is in comparison with the initiation of distal cartilage formation observed one week postamputation in control forelimbs of xenopus froglets. the r ... | 1984 | 6491587 |
| effect of estrogen on xenopus laevis albumin mrna levels. | accurate quantitation of concentrations of albumin mrna by hybridization to albumin cdna allows analysis of the estrogen effect on the xenopus laevis albumin mrna levels in the liver cytoplasm during the primary stimulation. administration of estradiol-17 beta to male xenopus laevis increases the amount of both total cellular rna and poly(a)-rna but has no effect on the albumin mrna level and the amount of albumin mrna per cell is constant. | 1984 | 6493219 |
| identification and treatment of a lethal nematode (capillaria xenopodis) infestation in the south african frog, xenopus laevis. | | 1984 | 6500144 |
| inhibition of na-alanine cotransport in oocytes of xenopus laevis during meiotic maturation is voltage-regulated. | during progesterone-induced maturation of oocytes of xenopus laevis the fast decrease of the rate of na+-alanine cotransport is accompanied by a depolarization of the membrane potential and an increase in the intracellular na+ activity. it is demonstrated that the decrease of the na+-dependent alanine uptake is the result of the depolarization while the simultaneous increase in intracellular na+ activity has no significant effect. | 1984 | 6504692 |
| evolution of vitellogenin genes: comparative analysis of the nucleotide sequences downstream of the transcription initiation site of four xenopus laevis and one chicken gene. | electron microscopic analysis of heteroduplexes between the most distantly related xenopus vitellogenin genes (a genes x b genes) has revealed the distribution of homologous regions that have been preferentially conserved after the duplication events that gave rise to the multigene family in xenopus laevis. dna sequence analysis was limited to the region downstream of the transcription initiation site of the xenopus genes a1, b1 and b2 and a comparison with the xenopus a2 and the major chicken v ... | 1984 | 6504704 |
| sequence homologies in the region preceding the transcription initiation site of the liver estrogen-responsive vitellogenin and apo-vldlii genes. | in the liver of oviparous vertebrates vitellogenin gene expression is controlled by estrogen. the nucleotide sequence of the 5' flanking region of the xenopus laevis vitellogenin genes a1, a2, b1 and b2 has been determined. these sequences have been compared to each other and to the equivalent region of the chicken vitellogenin ii and apo-vldlii genes which are also expressed in the liver in response to estrogen. the homology between the 5' flanking region of the xenopus genes b1 and b2 is highe ... | 1984 | 6504705 |
| interaction between rat brain microtubule associated proteins (maps) and free ribosomes from xenopus oocyte: a possible mechanism for the in ovo distribution of maps. | the binding of microtubule associated proteins (maps) to free 80 s ribosomes isolated from xenopus laevis oocytes inhibits in vitro tubulin assembly (jessus et al., 1984). the inhibition of tubulin polymerisation was shown to be dependent upon gtp. the dose of gtp needed to induce 50% of the maximal effect was 0.5 mm. furthermore, the inhibition is enhanced by pretreatment of the ribosomes with atp-gamma-s, and partially abolished after phosphatase treatment, which strongly suggests that protein ... | 1984 | 6509556 |
| interrenal function during amphibian metamorphosis: in vitro biosynthesis of radioactive corticosteroids from (4(14)c)-progesterone by interrenal in xenopus laevis tadpoles. | whole kidneys of xenopus laevis tadpoles (containing interrenal cells) or the outer postero-dorsal part of adult kidney (containing a few or no interrenal cells) were incubated with (4(14)c)-progesterone. methylene chloride extractable radioactivity of tissue homogenates in their incubation medium were purified by sequential paper chromatography and identification of some isolated fractions was attempted. a significant conversion of progesterone was only observed when interrenals were present in ... | 1984 | 6509915 |
| regulation by estrogen receptor of vitellogenin gene transcription in xenopus hepatocyte cultures. | we have used primary cell cultures of hepatocytes from male or female xenopus laevis to study the mechanisms by which estrogen induces vitellogenin gene transcription and how primary exposure to estrogen renders cells more responsive to secondary stimulation. we have characterized the estrogen receptor in hormonally naïve cells and in hepatocytes treated with estrogen under a variety of conditions. under all conditions the receptor has a kd congruent to 4 x 10(-10) m. hormonally naïve male cells ... | 1984 | 6510549 |
| [glomus cell in controlling vascular tone of the carotid labyrinth (xenopus laevis)]. | to clarify the physiological significance of g-s connection (intimate apposition of the glomus cell to the smooth muscle), vascular responses of the carotid labyrinth to both catecholamines and chemoreceptor stimulants were investigated using xenopus laevis. the results obtained were as follows. density of dense-cored vesicles in the glomus cell was significantly varied in three different parts of the cytoplasm (n, m, p). in the part of the cytoplasm containing the nucleus (n) the density was lo ... | 1984 | 6520799 |
| [dynamics of the redistribution of pigment granules in the dermal melanophores of anuran amphibians. 1. dispersion]. | the dispersion of melanosomes in the dermal melanophores of the xenopus laevis larvae has been studied by time--lapse cinematography. the process began with the appearance of distally directed melanosome flows in the cell cytoplasm. during the subsequent migration of pigment granules, the flows branched forming branches of the 2nd and higher orders. the whole cytoplasm became filled with a layer of melanosomes. during the dispersion, the movement of melanosomes in a flow is replaced by their dis ... | 1984 | 6521976 |
| shedding is correlated with disk membrane axial position rather than disk age in xenopus laevis rod outer segments. | disk membrane synthesis and displacement rates in xenopus laevis retinal rod outer segments, as measured by light-dark dependent birefringence band periods, are proportional to incubation temperature. outer segment length, however, is approximately the same for frogs raised at different temperatures. therefore the age of disks shed from outer segment distal tips is a function of temperature. unless the rate of disk synthesis coincidentally has the same temperature dependence as putative disk mem ... | 1984 | 6523739 |
| transient paralysis by heat shock of hormonal regulation of gene expression. | we have investigated the effect of heat shock on primary cultures of male and female xenopus laevis hepatocytes as a function of estrogen-induced vitellogenin gene expression. coincident with the induction of heat-shock protein (hsp) synthesis, thermal stress abolishes the estrogen activated transcription and accumulation of vitellogenin mrna, at the same time causing the destabilization of vitellogenin mrna accumulated by prior treatment with the hormone. exposure of the cells to estrogen befor ... | 1984 | 6526005 |
| an unusual repetitive structure of caerulein mrna from the skin of xenopus laevis. | the nucleotide sequence of a 784-bp segment of cloned caerulein mrna obtained from the skin of xenopus laevis was determined. it codes for five heterogeneous procaerulein peptides interspersed with three 147-bp intercaerulein segments (ics). the icss contain six inverted repeats and five eukaryotic enhancer-like sequences. evidence for the presence of multiple forms of caerulein mrna is presented. | 1984 | 6526274 |
| protein synthesis in dorsal, ventral, animal and vegetal half-embryos of xenopus laevis isolated at the 8-cell stage. | dorsal, ventral, animal and vegetal half-embryos of xenopus laevis were isolated at the 8-cell stage, and their synthesis of protein examined during 12 h of culture. the kinetics of the uptake and incorporation of [35s]-methionine did not differ greatly among the four kinds of half-embryos. two-dimensional gel electrophoreses showed that there were no detectable differences in the pattern of protein synthesis for the four types of half-embryos, at least during the first 6 h of culture which cove ... | 1984 | 6529755 |
| effects of alterations of cell size and number on the structure and function of the xenopus laevis nervous system. | | 1984 | 6532155 |
| common mechanisms in vertebrate axonal navigation: retinal transplants between distantly related amphibia. | embryonic eye primordia were transplanted from the anuran, xenopus laevis, to the urodele, ambystoma mexicanum, in order to assess whether retinal axons of one species could grow to appropriate central targets in a distantly related species. to trace the early retinal projections, xenopus primordia were removed, incubated for 20 min in a solution containing [3h]proline, washed, and then transplanted to host axolotl embryos. genetically eyeless hosts were used in some of the experiments so that t ... | 1984 | 6536722 |
| dna binding protein from ovaries of the frog, xenopus laevis which promotes concatenation of linear dna. | a soluble extract of xenopus laevis ovaries catalyzed atp-dependent concatenation of linear duplex dna molecules. dna ligase and a unique x. laevis dna binding protein were required for the formation of concatemers. a linear dna concatenation system was reconstituted using t4 dna ligase and homogeneous x. laevis dna binding protein. this system catalyzed intermolecular ligation of dna molecules into linear concatemers of up to ten or more times monomer length. | 1984 | 6537981 |
| studies on the mechanism of inhibition of amphibian oocyte adenylate cyclase by progesterone. | progesterone treatment induces the meiotic maturation of xenopus laevis oocytes. previous evidence indicates that this hormonal effect may be due to inhibition of oocyte adenylate cyclase. the present work studies several aspects of the mechanism of adenylate cyclase inhibition by this hormone. forskolin greatly stimulates oocyte adenylate cyclase in the absence of guanine nucleotides and this activity is not sensitive to progesterone inhibition. in addition the forskolin-activated enzyme is not ... | 1984 | 6538078 |
| detection of human beta-2 interferon using a radioimmunoassay. | does the human "beta 2 interferon" (huifn-beta 2) mrna of length 1.3 kb obtained from poly(i) x poly(c) and cycloheximide-induced human diploid fibroblasts (fs-4) code for an interferon per se, or for a protein which, in turn, induces ifn-beta in the cell culture assay that is usually used to detect the antiviral activity of the translation product (obtained from xenopus laevis oocytes) of this mrna? this question has been resolved by demonstrating that the ifn derived from the 1.3 kb mrna can b ... | 1984 | 6538894 |
| acetylcholine promotes progesterone-induced maturation of xenopus oocytes. | progesterone-induced maturation of follicle-enclosed and denuded xenopus laevis oocytes was significantly shortened by a concomitant exposure to acetylcholine. the promotion of maturation by acetylcholine was blocked by the specific muscarinic antagonist atropine. the action of acetylcholine was dose dependent, and the neurotransmitter was effective at very low concentrations. progesterone progressively reduced the electrophysiological responses of x. laevis oocytes to acetylcholine, which compl ... | 1984 | 6539359 |
| karyophobic proteins. a category of abundant soluble proteins which accumulate in the cytoplasm. | the cytoplasm of oocytes of xenopus laevis is enriched in several soluble proteins which are either absent from the nucleus or are present there at very low concentrations. these molecules, collectively referred to as karyophobic (from the greek verbs and which are meant here in the sense of "to be afraid of" or "to avoid") proteins represent more than 20% of the total soluble cytoplasmic proteins and include some of the most abundant soluble cellular components. they may be recovered from high- ... | 1984 | 6539709 |
| identification and localization of a novel nucleolar protein of high molecular weight by a monoclonal antibody. | a monoclonal murine antibody (no-114) is described which reacts specifically with a polypeptide of molecular weight (mr) 180 000 present in low-speed nuclear pellets from oocytes and somatic cells of xenopus laevis and x. borealis and in isolated amplified nucleoli. two-dimensional gel electrophoresis has revealed the acidic nature of this polypeptide (isoelectric at ph of ca 4.2 in the presence of 9.5 m urea). a relatively large proportion of the protein is extracted at elevated ionic strength ... | 1984 | 6539710 |
| replication, integration and expression of exogenous dna injected into fertilized eggs of xenopus laevis. | we have analyzed the fate of circular and linear dna molecules following microinjection into the cytoplasm of fertilized eggs of xenopus laevis. recombinant plasmids containing sea urchin histone genes (psp 102), drosophila adh genes (sac-1), and sv40 (sv2 cat) replicate during the development of the injected frog embryo. in contrast, pbr322 either as monomers or multimers does not appear to replicate as efficiently. generally, injected circular dnas were not detectable by the gastrula stage of ... | 1984 | 6539719 |
| progesterone receptor characterized by photoaffinity labelling in the plasma membrane of xenopus laevis oocytes. | r 5020 (17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione) is a synthetic analogue of progesterone, which is the physiological hormone that reinitiates germinal vesicle breakdown in xenopus laevis oocytes. u.v.-driven photoaffinity labelling experiments were conducted with [3h]r 5020 in oocyte subcellular fractions, and covalently bound radioactivity was analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. in p-10000 (the pellet sedimenting between 1000 and 10000 g and which co ... | 1984 | 6540084 |
| the transcriptional regulation of xenopus 5s rna genes in chromatin: the roles of active stable transcription complexes and histone h1. | the properties of active and repressed 5s rna genes in somatic cell chromatin from xenopus laevis cultured cells were studied by transcription in vitro. the somatic 5s rna genes, which are active in vivo, are packaged in chromatin as active stable transcription complexes lacking only rna polymerase iii for transcription activity. the oocyte 5s rna genes, which are inactive in somatic tissues, do not have transcription factors bound to them in purified chromatin and are prevented from binding the ... | 1984 | 6540147 |
| structural basis of the activation wave in the egg of xenopus laevis. | a series of changes in the surface of activated xenopus eggs was observed. within a few seconds of prick activation a light area appears near the pricking point and expands as a circular light zone (light wave). some 60 s later this is followed by a dark area expanding as a circular dark zone (dark wave). both waves travel at a rate of about 9 micron/s at 21 degrees c. in the light zone, cortical granules are breaking down, microvilli are elongating, and the egg surface is expanded. on the other ... | 1984 | 6540794 |
| tumor promoter pma stimulates the synthesis and secretion of mouse pro-urokinase in msv-transformed 3t3 cells: this is mediated by an increase in urokinase mrna content. | in mouse msv-3t3 cells the synthesis of the urokinase form of plasminogen activator was increased 10-fold after addition of the tumor promoter phorbol-12-myristate-13-acetate (pma). pma also stimulated the secretion of the protein into the culture medium, mostly in the form of enzymatically inactive pro-urokinase. when assayed by injecting rna into xenopus laevis oocytes, the concentration of functional urokinase mrna was found to be 6- to 10-fold higher in the pma-treated cells; a similar incre ... | 1984 | 6541126 |
| control of cell shape and locomotion by external calcium. | dependence of locomotion of xenopus laevis epidermal cells on calcium influx from the external medium was investigated. inhibition of ca2+ influx by 2 mm la3+ or 4 mm tb3+ in the culture medium causes an immediate stop to locomotion and a loss of motion at the outer margin of the lamella; microcolliculi disappear and the entire lamella becomes flat and very thin. the cell body region enlarges by spreading into the lamella to an extent approximately coincident with the distribution of myosin. the ... | 1984 | 6541148 |
| the mitochondrial cloud of xenopus oocytes: the source of germinal granule material. | the mitochondrial cloud is a prominent mass in the cytoplasm of previtellogenic oocytes of xenopus laevis. it is shown here that the cloud contains both mitochondria and electron-dense granulofibrillar material (gfm). using a combination of light microscopical, fluorescence, time-lapse filming, and electron microscopical techniques, the ontogeny of these components is reported and their fate is studied. it was found that the cloud is stationary in previtellogenic stages and fragments into island ... | 1984 | 6541166 |
| reactivity of lectin from xenopus laevis eggs towards tumor cells and human erythrocytes. | | 1984 | 6541530 |
| progesterone inhibition of xenopus oocyte adenylate cyclase is not mediated via the bordetella pertussis toxin substrate. | preincubation of intact xenopus laevis oocytes with islet-activating protein (iap) stimulates plasma membrane adenylate cyclase activity measured in the presence of either gtp or 5'-guanylyl imidodiphosphate. the toxin appears to act by catalyzing the adp-ribosylation of a 41,000-d protein in the oocyte plasma membrane that is distinct from the 45,000- and 52,000-d proteins labeled by cholera toxin. preincubation of intact oocytes with iap for 2.5 hr inhibits 80% of the adp-ribosylation of oocyt ... | 1984 | 6541752 |
| chromosomal location of a major trna gene cluster of xenopus laevis. | in xenopus laevis, genes encoding trnaphe, trnatyr, trnamet1, trnaasn, trnaala, trnaleu, and trnalys are clustered within a 3.18-kb (kilobase) fragment of dna. this fragment is tandemly repeated some 150 times in the haploid genome and its components are found outside the repeat only to a limited extent. the fragment hybridizes in situ to a single site very near the telomere on the long arm of one of the acrocentric chromosomes of the group comprising chromosomes 13-18. all the chromosomes of th ... | 1984 | 6542486 |
| segregation of mutant ovalbumins and ovalbumin-globin fusion proteins in xenopus oocytes. identification of an ovalbumin signal sequence. | the intramolecular signals for chicken ovalbumin secretion were examined by producing mutant proteins in xenopus oocytes. an ovalbumin complementary dna clone was manipulated in vitro, and constructs containing altered protein-coding sequences and either the simian virus 40 (sv40) early promoter or herpes simplex thymidine kinase promoter, were microinjected into xenopus laevis oocytes. the removal of the eight extreme n-terminal amino acids of ovalbumin had no effect on the segregation of ovalb ... | 1984 | 6543229 |
| effect of intercalating agents on rna polymerase i promoter selection in xenopus laevis. | we have analyzed the effect of dna intercalating agents on the transcription signals from two different xenopus laevis rna polymerase i promoters. the transcription signal from the promoter for the 7.5-kilobase rrna precursor (the gene promoter) is unaffected over a large range of intercalating agent concentrations regardless of whether the template is injected plasmid dna in oocytes, the amplified endogenous nucleoli of oocytes, or the endogenous chromosomes of cultured xenopus kidney cells. th ... | 1984 | 6543244 |
| unequal activation by estrogen of individual xenopus vitellogenin genes during development. | using a technique of filter hybridization under very stringent conditions to hindiii fragments of complementary dna cloned in plasmids, we have measured the accumulation in hepatocytes of mrna specified by each of the four vitellogenin genes (a1, a2, b1, b2) at different stages of development of xenopus laevis. the ontogenic competence of embryonic liver to respond to the first exposure to estradiol-17 beta, in terms of activation of transcription of this multigene family, is acquired late in me ... | 1984 | 6546552 |
| polymorphism and absence of leu-enkephalin sequences in proenkephalin genes in xenopus laevis. | the structures of the genes coding for the opioid peptide precursors proopiomelanocortin, proenkephalin (proenkephalin a) and prodynorphin (proenkephalin b), are known for some mammalian species. to gain insight into the evolutionary history of these precursors, we have examined the proenkephalin gene in the south african clawed toad, xenopus laevis, which diverged from the principal line of vertebrate evolution some 350 myr ago. the human proenkephalin gene consists of four exons, of which the ... | 1984 | 6547769 |
| partial characterization of lectin binding sites of retinal photoreceptor outer segments and interphotoreceptor matrix. | we have used cytochemistry together with exoglycosidase digestion and polyacrylamide gel electrophoresis to partially characterize lectin binding sites of the interphotoreceptor matrix and of photoreceptor outer segments. in order to obtain uniform access of reagents to all regions of the preparation, we have used a procedure in which plastic sections are etched with sodium ethoxide prior to cytochemical analysis. neuraminidase pretreatment of plastic-embedded sections of xenopus laevis eyecups ... | 1984 | 6548230 |
| the accumulation of prominent tadpole mrnas occurs at the beginning of neurulation in xenopus laevis embryos. | cloned cdna probes have been used to measure the sizes and titers of transcripts in total rna preparations during early development in xenopus laevis. of more than 20 different sequences derived from abundant and moderately abundant rna which were present in full-grown oocytes and persisted during early development, the transcript sizes of all but 3 of these sequences were invariant. two transcripts were of a higher molecular weight in oocytes than in embryos, but their titers in oocytes were le ... | 1984 | 6548717 |
| identification of xenopus laevis mrnas with homology to repetitive sequences. | hybrid selection translation experiments have been carried out with genomic and cdna relatives of two repetitive sequence families. on the basis of the in vitro translation products detected, it was found that transcripts complementary to these repeats are linked to several different mature mrnas in stage 40 embryos of xenopus laevis. one repeat hybridizes to mrnas that direct the synthesis of 17 proteins. the second is present on mrnas coding for 3 proteins. by estimating the abundance of these ... | 1984 | 6549063 |
| the oocyte as a secretory cell. | xenopus laevis oocytes secrete a large variety of foreign secretory proteins after the microinjection of mrna or dna. two classes of such proteins are discussed in detail. these are the chick oviduct proteins ovalbumin and lysozyme, and the mouse mopc 21 immunoglobulin. the injection of mrnas for mouse immunoglobulin heavy or light chain leads to the synthesis, segregation, but not secretion of the encoded proteins unless the two mrnas are simultaneously or sequentially injected into the same oo ... | 1983 | 6557008 |
| the nucleotide sequence of mannosyl-q-containing trnaasp from xenopus laevis oocytes. | the nucleotide sequence of trnaasp from x. laevis oocytes was determined as being: (sequence in text) the trna is 75 nucleotides long. this sequence is very similar (75% to 97% identity) to all other eukaryotic trnaasp sequenced so far, except for the bovine liver trnaasp (32% identity). the relation between the presence of a mannosyl group on queuosine (q) at position 34 and the nucleotide sequence of the anticodon loop is discussed. | 1984 | 6570443 |
| cooperative model for the binding of xenopus transcription factor a to the 5s rna gene. | 7s particles containing 5s rna and the transcription regulatory protein factor a have been purified to near homogeneity from xenopus laevis oocytes. the binding of the transcription factor to the xenopus borealis somatic 5s rna gene has been monitored by quantitating the dnase i protection patterns of the protein-dna interaction. under stoichiometric binding conditions--i.e., when all added dna binds to the factor--two protein molecules are required to saturate the 5s rna gene. under equilibrium ... | 1983 | 6572967 |
| transcription of repetitive sequences on xenopus lampbrush chromosomes. | we reinvestigated the lampbrush chromosomes of xenopus laevis and found them well suited for the study or transcription by in situ hybridization to nascent rna transcripts. using this technique, we analyzed the transcription of three repetitive sequences that do not show any sequence homology and that differ in their degree of interspersion. we found that they are located on different parts of the chromosomes: two are clustered, one is interspersed. all three of these sequences are transcribed a ... | 1983 | 6574489 |
| development of translationally active mrna for larval muscle acetylcholinesterase during ascidian embryogenesis. | relative quantities of translationally active acetylcholinesterase (acetylcholine acetylhydrolase, ec 3.1.1.7) mrna present at various developmental stages were compared in embryos of the ascidian ciona intestinalis. purified rna was tested for its translational capacity by microinjection into xenopus laevis oocytes; the acetylcholinesterase produced was immunoprecipitated with antibody to ciona acetylcholinesterase and enzyme activity was assayed radiometrically. with this protocol, enzyme synt ... | 1983 | 6576358 |
| replication and expression of xenopus laevis globin genes injected into fertilized xenopus eggs. | cloned xenopus adult alpha 1- and beta 1-globin genes were injected into fertilized xenopus eggs, and the eggs were allowed to develop into swimming tadpoles. the injected dna replicated during early xenopus development but did not become methylated de novo. when dna was modified with hpa ii methylase before injection, methylation was maintained during replication. although the xenopus adult globin genes are not normally expressed until metamorphosis, both the unmethylated and in vitro methylate ... | 1983 | 6578503 |
| trna transport from the nucleus in a eukaryotic cell: carrier-mediated translocation process. | the mechanism by which a trna molecule is delivered from the nucleus of a cell to the cytoplasm has been studied in the xenopus laevis oocyte utilizing nuclear microinjection and manual microdissection techniques. trna nuclear transport in this cell resembles a carrier-mediated translocation process rather than diffusion through a simple pore or channel. trna transport is saturable by trna, with a maximal rate measured to be about 190 x 10(7) molecules per min per nucleus (21 degrees c) in the m ... | 1983 | 6579529 |
| transcription in cloned spacers of xenopus laevis ribosomal dna. | rare individuals of xenopus laevis exhibit frequent initiation of transcription in the spacers of oocyte ribosomal dna (rdna). using electron microscopy we have characterized spacer transcription in such an individual and have confirmed that the sites of transcription initiation correspond to the imperfectly duplicated promoters ("bam islands") present in the x. laevis rdna spacer. we have cloned a repeat unit containing a gene and a spacer from this individual and have injected the recombinant ... | 1983 | 6579535 |
| xanthine dehydrogenase activity in the clawed frog, xenopus laevis. | xanthine dehydrogenase (xdh; ec 1.2.1.37) activity in the clawed frog, xenopus laevis, was detected in kidney tissue homogenates, but not in skin, liver, ovaries or gut tissues. the enzyme migrated as a single band of activity on both polyacrylamide and starch gel electropherograms, exhibited substrate inhibition, and did not appear developmentally until feeding larval stages. the tissue specificity, post-fertilization stage of appearance and single isozymic form make this a useful enzyme marker ... | 1983 | 6580098 |
| perpendicular orientation and directional migration of amphibian neural crest cells in dc electrical fields. | the behavior of cultured neural crest cells of ambystoma mexicanum and xenopus laevis in dc electrical fields was studied. in fields of 1-5 v/cm, isolated or confluent cells retract both their anode- and cathode-facing margins. subsequently, the cells elongate, with protrusive activity confined to their narrow ends. in larger fields (greater than or equal to 5 v/cm), protrusions form on the cathode-facing sides of the perpendicularly oriented cells. the cells then begin migrating laterally, perp ... | 1984 | 6582473 |
| xenopsin: the neurotensin-like octapeptide from xenopus skin at the carboxyl terminus of its precursor. | we have synthesized two oligodeoxyribonucleotide mixtures that contain sequences complementary to different parts of the hypothetical mrna sequence of xenopsin, a biologically active octapeptide found in skin extracts from xenopus laevis. the two primer pools were independently used to initiate reverse transcription on skin poly(a)+ rna and the resulting cdnas were then used to screen in parallel a cdna library prepared from skin poly(a)+ rna. one of the clones that hybridized with both probes w ... | 1984 | 6582494 |
| 3' editing of mrnas: sequence requirements and involvement of a 60-nucleotide rna in maturation of histone mrna precursors. | in vitro-synthesized transcripts of the sea urchin histone h2a gene with 3' extensions are efficiently and rapidly processed to h2a mrna with faithful 3' ends in xenopus laevis oocyte nuclei. processing requires the presence of a histone-specific dyad symmetry element and of h2a-proximal spacer sequences in the precursor rna. in dna injection experiments with a processing-deficient h2a mutant, the transcription products appear to terminate heterogeneously in the first 100-200 base pairs of the p ... | 1984 | 6583695 |
| alteration of the retinotectal map in xenopus by antibodies to neural cell adhesion molecules. | the neural cell adhesion molecule (n-cam) mediates neuron-neuron adhesion, is ubiquitous in the nervous system of developing and mature vertebrates, and undergoes major alterations in both amount and distribution during development. perturbation of homophilic (n-cam to n-cam) binding by univalent fragments of specific anti-n-cam antibodies has previously been found to alter neural tissue patterns in vitro. to show that significant alterations can also occur in vivo, antibodies to xenopus n-cam w ... | 1984 | 6588385 |
| [effects of calcium ions on the inner side of the skin in the lateral line organs of xenopus laevis]. | | 1983 | 6588666 |
| lactoferrin biosynthesis during granulocytopoiesis. | we examined the synthesis of lactoferrin, an iron binding protein that, among hematopoietic cells, is restricted to secondary granules of polymorphonuclear leukocytes. lactoferrin biosynthesis was absent from leukemic myeloblasts and promyelocytes but abundant in normal bone marrow and both the bone marrow and peripheral blood of patients with chronic myelogenous leukemia (cgl) if the samples contained substantial numbers of myelocytes and metamyelocytes. lactoferrin was present in the steady st ... | 1984 | 6593100 |
| diploid gynogenesis in xenopus laevis and the localization with respect to the centromere of the gene for periodic albinism ap. | diploid gynogenetic xenopus laevis were obtained by inseminating the eggs with u.v. irradiated spermatozoa, and treating them with hydrostatic pressure to inhibit the expulsion of the second polar body. a u.v. dose of 3000 ergs/mm2 genetically inactivates the spermatozoa without loss of their ability to activate egg development. the use of a genetic marker on very large samples of eggs made it possible to verify the efficiency of the methods employed. the comparison of the development of diploid ... | 1984 | 6594425 |
| formation in vitro of sperm pronuclei and mitotic chromosomes induced by amphibian ooplasmic components. | a cell-free preparation of the cytoplasm from activated eggs of rana pipiens induces, in demembranated sperm nuclei of xenopus laevis, formation of a nuclear envelope, chromatin decondensation, initiation of dna synthesis, and chromosome condensation. both soluble and particulate cytoplasmic constituents are required to initiate these processes in vitro. the observed changes resemble processes occurring during fertilization and the mitotic cycle in early amphibian embryos. therefore, this cell-f ... | 1983 | 6601299 |
| comparative study of extracellular fibrils on the ectodermal layer in gastrulae of five amphibian species. | previous studies have shown the presence of a network of extracellular fibrils on the inner surface of the ectodermal layer of the ambystoma maculatum gastrulae. the alignment of the network along the blastopore-animal pole axis has suggested that the network of fibrils guides the migrating mesodermal cells in gastrulae by contact guidance. we have also shown that these fibrils can be deposited on substrata by explanted embryonic fragments and that substrata conditioned in this manner support di ... | 1983 | 6602807 |
| lipovitellin-phosvitin crystals with orthorhombic features: thin-section electron microscopy, gel electrophoresis, and microanalysis in teleost and amphibian yolk platelets and a comparison with other vertebrates. | yolk-platelet crystals in the teleosts pelvicachromis pulcher and noemacheilus barbatulus and the amphibians xenopus laevis, rana temporaria, r. esculenta, and triturus sp. have been studied by electron diffraction and imaging using a standardized processing (glutaraldehyde-osmium tetroxide fixation, glutaraldehyde-urea embedding, thin-section staining), by x-ray microanalysis, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of their constituents. the crystal lattice is orthorhombi ... | 1983 | 6602894 |
| translation of human interleukin 2 mrna in xenopus laevis oocytes. | poly(a)-positive mrna extracted from tonsillar mononuclear cells stimulated with phytohemagglutinin-m and 12-o-tetradecanoyl phorbol 13-acetate was successfully translated into biologically active interleukin 2 (il-2) in xenopus laevis oocytes, and secreted into the incubation medium. in control experiments, the extract of oocytes injected with either poly(a)-negative rna or buffer did not show any il-2 activity. by sucrose density gradient centrifugation analysis, il-2 mrna was found as a singl ... | 1983 | 6602934 |
| cold- and heat-shock induction of new gene expression in cultured amphibian cells. | exposing primary epidermal cell cultures from the american bullfrog rana catesbeiana to elevated (greater than or equal to 32 degrees c; heat shock) or depressed (less than or equal to 5 degrees c; cold shock) temperatures for a short time results in the new and (or) enhanced synthesis of a 65 000 dalton (isoelectric point (pi) 6.7-6.9) polypeptide. with increasing temperature, a marked decrease in the synthesis of polypeptides observed at the control temperature (22 degrees c) and the new and ( ... | 1983 | 6603891 |