| development of t lymphocytes in xenopus laevis: appearance of the antigen recognized by an anti-thymocyte mouse monoclonal antibody. | | 1986 | 3485547 |
| acetylcholine- and inositol 1,4,5-trisphosphate-induced calcium mobilization in xenopus laevis oocytes. | acetylcholine induces a complex electrical membrane response in xenopus laevis oocytes. this response is mimicked, and probably mediated by injected inositol 1,4,5-trisphosphate. oocytes prelabelled with 45ca released calcium in two phases, the second, slow phase exhibiting first order kinetics of release. brief exposure of prelabelled oocytes to acetylcholine resulted in a significant increase in the rate of calcium release that returned to control values 2-3 min following the removal of the ne ... | 1986 | 3486135 |
| translocation of murine interleukin 2 into microsomes during translation in a cell-free system. | interleukin 2 (il2) is a lymphokine which stimulates the growth of t lymphocytes. although il2 mrna is translated into biologically active il2 relatively efficiently in microinjected xenopus laevis oocytes, it has been difficult to establish reproducible cell-free translation systems for this lymphokine. such systems would be useful for the analysis of translational and post-translational events. in this paper, we show that a wheat germ extract will translate il2 mrna into biologically active mu ... | 1986 | 3486343 |
| high-frequency twinning of xenopus laevis embryos from eggs centrifuged before first cleavage. | in embryos of the frog xenopus laevis, the dorsal structures normally develop from regions of the egg opposite the side of sperm entry. gravity and centrifugal force, applied at an angle of 90 degrees to the animal-vegetal axis of the egg, can override this topographic relationship and can cause the dorsal structures to be positioned according to the force vector (s. black and j. gerhart, 1985, dev. biol. 108, 310-324). we report here that at time 0.40 (40% of the first cleavage interval), an av ... | 1986 | 3488238 |
| two cellular pathways regulate the response to tnp-ficoll in xenopus laevis. | the initiation of the anti-tnp response to tnp-ficoll in the amphibian xenopus laevis has been studied. although the response to this antigen is thymus independent in mammals, it is thymus dependent for the first three days following immunization in xenopus. this thymus regulation is not mhc restricted, since it can be substituted for by thymus xenografts, and by prior or co-injection of heterologous red blood cells or concanavalin a. the pathway which is activated by the con a to substitute for ... | 1986 | 3488928 |
| changes in dna topology during spermatogenesis. | dna topology in histone- and protamine-depleted nuclei (nucleoids) from somatic cells, sperm, and spermatogenic cells was studied to determine if the superhelical configuration of dna looped domains is altered during spermatogenesis. the expansion and contraction of nucleoid dna was measured with a fluorescence microscope following exposure of nucleoids to different concentrations of ethidium bromide (eb). nucleoids from xenopus laevis erythrocytes, primary spermatocytes, and round spermatids, a ... | 1986 | 3490360 |
| the development of the static vestibulo-ocular reflex in the southern clawed toad, xenopus laevis. ii. animals with acute vestibular lesions. | acute hemilabyrinthectomized tadpoles of the southern clawed toad (xenopus laevis), younger than stage 47 (about 6 days old), perform no static vestibulo-ocular reflex (fig. 1). older acute lesioned animals respond with compensatory movements of both eyes during static roll. their threshold roll angle, however, depends on the developmental stage. for lesioned stages 60 to 64, it is 75 degrees while stage 52 to 56 tadpoles respond even during a lateral roll of 15 degrees (figs. 1 and 2). selectiv ... | 1986 | 3492602 |
| intracellular signalling of initiation of dna synthesis: effect of cell-free extracts from anti-receptor-stimulated b lymphocytes on spleen cell nuclei. | to study the relatively late intracellular signals involved in the proliferative response of b lymphocytes to antibodies specific for surface membrane immunoglobulins, extracts from antibody activated cells were mixed with xenopus laevis splenic nuclei, and the incorporation of thymidine 5'-triphosphate into dna was assessed. the slight incorporation observed with either nuclei or extract alone was markedly enhanced upon mixing the two entities when the extract was derived from cells cultured wi ... | 1987 | 3493249 |
| androgen-binding levels in a sexually dimorphic muscle of xenopus laevis. | the larynx of adult south african clawed frogs, xenopus laevis, is larger in males than in females and hypertrophies in adult females and juveniles in response to androgen. sexual dimorphism and androgen sensitivity suggest that the larynx is a testosterone target tissue. saturation analysis of androgen (r1881) binding in laryngeal cytosol revealed an approximately threefold quantitative difference between male and female androgen-binding levels (36.4 vs 11.5 fm/mg protein). by contrast, as meas ... | 1987 | 3495467 |
| signals provided in vivo by human ril-2 and con a can switch hapten-specific tolerance from unresponsiveness to responsiveness in the south african clawed toad. | injection in vivo of trinitrobenzene sulphonic acid (tnbs) will conjugate trinitrophenyl (tnp) to the cells and proteins of rodents, and induce hapten-specific tolerance to this epitope. however, the induction of hapten-specific tolerance by this method in the south african clawed toad, xenopus laevis, is restricted to its subsequent presentation on ficoll or polyvinylpyrrolidone (pvp). this restricted tolerance depends on the stimulation of an n-methyl-n-nitrosourea (nmu)-insensitive, cyclophos ... | 1987 | 3496274 |
| corticosteroid regulation of il-1 production may be responsible for deficient immune suppressor function during the metamorphosis of xenopus laevis, the south african clawed toad. | thymus immune suppressor function is deficient during the metamorphosis of xenopus laevis, the south african clawed toad. thymuses of antigen-activated metamorphic larvae were tested for restoration of suppressor function by co-culture with matched fragments of spleens from immunized, antibody-producing young adults. the inhibition of unusually high endogenous corticosteroid levels in metamorphic larvae with metyrapone restores suppressor function. dexamethasone counteracts this effect. since co ... | 1987 | 3496321 |
| detection of receptors for murine b cell stimulatory factor 1 (bsf1): presence of functional receptors on cba/n splenic b cells. | the presence of receptors specific for murine b cell stimulatory factor 1 (bsf1) was demonstrated by utilizing an internally radiolabeled recombinant bsf1. radiolabeled bsf1 was efficiently produced in xenopus laevis oocytes injected with a cloned mrna for bsf1 and 35s-methionine. the labeled bsf1 specifically bound to splenic b cells. a scatchard analysis indicated the existence of one class of receptor sites. bsf1 receptors were found to be distributed on a wide range of hematopoietic lineage ... | 1987 | 3496389 |
| b cell growth modulating and differentiating activity of recombinant human 26-kd protein (bsf-2, huifn-beta 2, hpgf). | the human "26-kd protein' is a secreted glycoprotein expressed, for example, in (blood) leukocytes, in epithelial cells treated with various inducers, but most strongly in interleukin-1 (il-1)-treated fibroblasts. after finding it has antiviral and 2-5a synthetase-inducing activity, one group of authors called this protein ifn-beta 2. however, recently the full-length 26-kd cdna sequence was shown to be identical with that of a b-cell-differentiating lymphokine called bsf-2, and another report s ... | 1987 | 3497029 |
| a projection from the mesencephalic tegmentum to the nucleus isthmi in the frogs, rana pipiens and acris crepitans. | the nucleus isthmi is a prominent part of the frog's visual system. each nucleus isthmi receives input from the ipsilateral tectum and sends output to both tecta. until now, no non-tectal inputs to the nucleus isthmi of amphibians have been demonstrated. anterograde and retrograde tracing with horseradish peroxidase in rana pipiens and acris crepitans now reveal that a diffuse group of cells in the mesencephalic tegmentum projects to the caudal region of the contralateral nucleus isthmi. these c ... | 1987 | 3497362 |
| fundulus heteroclitus gonadotropin(s). i. homologous bioassay using oocyte maturation and steroid production by isolated ovarian follicles. | isolated ovarian follicles from several species were cultured to develop an in vitro bioassay system for fundulus heteroclitus gonadotropin. an extract of f. heteroclitus pituitaries, when tested in heterologous systems using follicles from rana pipiens. xenopus laevis, and carassius auratus, was ineffective in provoking either germinal vesicle breakdown or steroid production. in a homologous system using f. heteroclitus follicles, f. heteroclitus pituitary extract was capable of inducing both g ... | 1987 | 3497837 |
| fibre organization and reorganization in the retinotectal projection of xenopus. | this study concerns the retinotopic organization of the ganglion cell fibres in the visual system of the frog xenopus laevis. hrp was used to trace the pathways taken by fibres from discrete retinal positions as they pass from the retina, along the optic nerve and into the chiasma. the ganglion cell fibres in the retina are arranged in fascicles which correspond with their circumferential positions of origin. within the fascicles the fibres show little age-related layering and do not have a stri ... | 1987 | 3498622 |
| a factor with interleukin-1-like activity is produced by peritoneal cells from the frog, xenopus laevis. | thymocytes from juevenile xenopus laevis did not proliferate in response to commercial preparations of lipopolysaccharide (lps), responded poorly when cultured with the t-cell mitogen, phytohaemagglutinin-p (pha), and were not co-stimulated by pha plus lps. however, supernatants (sns) from lps-treated cultures of adult xenopus macrophage-enriched resident peritoneal cells (pcs) enhanced the proliferative responses of thymocytes to a submitogenic dose of pha. these sns were incapable of supportin ... | 1987 | 3501401 |
| excretion and metabolism of phenol, 4-nitrophenol and 2-methylphenol by the frogs rana temporaria and xenopus laevis. | 1. rana and xenopus excrete 90-95% dose, and metabolize 50-65% dose of phenol, 4-nitrophenol and 2-methylphenol within 24 h, to about the same extent. 2. kinetic data for the excretion of phenols from both species fit a two-compartment model. the elimination constants of rana and xenopus are not significantly different. 3. metabolism is mostly conjugation by glucuronidation and sulphation of the original phenols. additionally, oxidations leading to dihydroxyphenols and benzoic acid from 2-methyl ... | 1987 | 3501639 |
| multinucleation during myogenesis of the myotome of xenopus laevis: a qualitative study. | ultrastructural studies of myogenesis in the myotome of xenopus laevis reveal that the myotubes developed by stage 33/34 have peripheral myofibrils but are still uninucleate with a single large nucleus. by stage 45, the cytoplasm of the muscle cells is filled with myofibrils and there are many small peripheral nuclei, resulting in multinucleate muscle fibres. with the electron microscope, we have examined myotomes from stages 33/34 to 59 of development and some stages were also investigated by a ... | 1987 | 3502996 |
| the organization of mesodermal pattern in xenopus laevis: experiments using a xenopus mesoderm-inducing factor. | in this paper, we study the mechanism by which a xenopus cell line-derived mesoderm-inducing factor (mif) might establish the spatial pattern of cellular differentiation in the mesoderm. the effects of the factor on competent animal pole tissue are consistent with it being identical to the natural mesoderm-inducing factor. the signal can only act on those membrane domains of the animal pole that face the blastocoel, but it can be stably recorded there, such that axial mesoderm is formed, after 1 ... | 1987 | 3503702 |
| cell behaviour during active cell rearrangement: evidence and speculations. | the cell behaviour and motility underlying cell rearrangement during gastrulation in amphibian and sea-urchin embryos are discussed. in particular, the cell behaviour of deep (non-epithelial) and epithelial cell populations that undergo cell rearrangement is compared and contrasted. deep cell rearrangement in xenopus laevis involves both convergence of cells towards the future dorsal midline and simultaneous axial extension of the mesodermal cell mass. time-lapse cinemicrography and scanning ele ... | 1987 | 3503894 |
| inhibition of progesterone-mediated maturation of oocytes of xenopus laevis by oocyte maturation inhibitor from pig follicular fluid: development of a routine assay for the inhibitor with xenopus oocytes. | we describe an assay for oocyte maturation inhibitor (omi) using the progesterone-mediated maturation of xenopus oocytes. the test fraction used was a partially purified fraction from pig follicular fluid, which gave consistent inhibition of maturation in the pig oocyte assay. in the toad assay, oocytes (30-50) from each toad were pretested to determine whether satisfactory maturation was achieved because widespread animal variation was observed. toads whose oocytes showed greater than 60% matur ... | 1987 | 3507352 |
| differentiation of neural crest cells of xenopus laevis in clonal culture. | clonal cultures were performed with the use of neural crest cells and their derivatives, chromatophores, from xenopus laevis in order to elucidate the state of commitment in early embryogenesis. neural crest cells that outgrew from neural tube explants were isolated and plated at clonal density. cloned neural crest cells differentiated and gave rise to colonies that consisted of 1) only melanophores, 2) only xanthophores, or 3) melanophores and xanthophores. xanthophores and iridophores, which d ... | 1987 | 3507660 |
| studies on cellular adhesion of xenopus laevis melanophores: modulation of cell-cell and cell-substratum adhesion in vitro by endogenous xenopus galactoside-binding lectin. | we have investigated cell-cell and cell-substratum adhesion of xenopus laevis neural crest cells at various stages of melanophore differentiation. single-cell suspensions were obtained by trypsinization and aggregated in a cell-cell adhesion assay. unpigmented cells did not adhere while the rate of adhesion of melanophores correlated with the degree of melanization. melanophore cell-cell adhesion decreased significantly in the presence of beta-galactosidase, which suggests that cell-surface gala ... | 1987 | 3508276 |
| melanophore differentiation in the periodic albino mutant of xenopus laevis. | that embryonic ventral truck tissue might play a role in expression of the periodic albino mutant phenotype (ap/ap) in xenopus laevis was suggested from the experiments of macmillan (1980). in contrast, the present experiments, involving the culture of isolated regions of xenopus embryos, have demonstrated that both mutant and wild-type melanoblasts differentiate independently of a ventral trunk factor. a similar conclusion, that mutant melanoblasts differentiate independently of a ventral trunk ... | 1987 | 3508277 |
| secretion of a cytoplasmic lectin from xenopus laevis skin. | the skin of xenopus laevis contains a soluble beta-galactoside-binding lectin with a approximately 16,000-mol-wt subunit. it resembles similar lectins purified from a variety of tissues from other vertebrates, and differs from two other soluble x. laevis lectins from oocytes and serum that bind alpha-galactosides. the skin lectin is concentrated in the cytoplasm of granular gland and mucous gland cells, as demonstrated by immunohistochemistry with the electron microscope. upon injection with epi ... | 1986 | 3511073 |
| synthesis and maturation of recombinant human tumor necrosis factor in eukaryotic systems. | the biosynthesis of human tumor necrosis factor (htnf) was studied. the amino-terminal extension of the htnf precursor (26 kda polypeptide) was not cleaved off in a cell-free system supplemented with dog pancreas microsomes. correct maturation of pre-htnf was nevertheless not restricted to the macrophage system: in the medium of a tnf-producing, transformed cho cell line, a (weak) approximately 20 kda, an approximately 18.5 kda (doublet) and a 17 kda tnf polypeptide, the latter corresponding to ... | 1986 | 3512310 |
| extraction and preliminary characterization of maturation-promoting factor from starfish oocytes. | cytoplasm of maturing starfish oocytes possesses a factor which induces maturation upon injection into immature oocytes. such maturation-promoting factor (mpf) was extracted from maturing oocytes of asterina pectinifera and characterized preliminarily. after 1-methyladenine (1-meade) treatment, maturing oocytes were packed in a centrifuge tube to remove jelly and excess medium, and then crushed by centrifugation. the turbid supernatant was homogenized with a buffer containing naf, na-beta-glycer ... | 1986 | 3514247 |
| cosegregation of the polymorphic c4 with the mhc in the frog, xenopus laevis. | employing isoeletric focusing combined with enzyme-linked immunoelectrotransfer blot analysis, the fourth component of complement (c4) was analyzed in the two highly histocompatible, major histocompatibility complex homozygous groups (j and k) of xenopus laevis. each group had a characteristic c4 isoelectric focusing pattern, i.e., an isoelectric point range of 8.0-8.5 for j (c4jc4j) and 7.6-8.1 for k (c4kc4k). in (j x k)f1 frogs, c4 proteins were expressed in a codominant fashion (c4jc4k). in t ... | 1986 | 3514445 |
| sequence homology of the yeast regulatory protein adr1 with xenopus transcription factor tfiiia. | classical yeast genetics coupled with the cloning of regulatory genes by complementation of function is a powerful means of identifying and isolating trans-acting regulatory elements. one such regulatory gene is adr1 which encodes a protein required for transcriptional activation of the glucose-repressible alcohol dehydrogenase (adh2) gene. we now report the nucleotide sequence of adr1; it encodes a polypeptide chain of 1,323 amino acids, of which the amino-terminal 302 amino acids are sufficien ... | 1986 | 3515197 |
| organisation of lateral line and auditory areas in the midbrain of xenopus laevis. | lateral line areas in the midbrain of xenopus laevis were identified by recording evoked potentials and neural activity elicited by stimulating anterior and posterior lateral line nerves. spike activity was found in the lateral half of the optic tectum, ventrolateral tectum, and torus semicircularis. contra- and ipsilateral lateral line pathways to these regions were identified. spike discharge was associated with an evoked potential (ep) consisting of a large negative-positive wave sometimes pr ... | 1986 | 3517085 |
| control of the development of the ipsilateral retinothalamic projection in xenopus laevis by thyroxine: results and speculation. | the ipsilateral retinothalamic projection of the frog xenopus laevis is formed by the axons of a subset of retinal ganglion cells which are found throughout peripheral and non-nasodorsal retina. unlike the crossed retinotectal and retinothalamic projections, which begin to form during early embryonic stages, the ipsilateral projection does not begin to develop until late in tadpole life, at stages when thyroxine first becomes detectable in the circulation. blocking the production of thyroid horm ... | 1986 | 3519864 |
| neuroeffectors for vocalization in xenopus laevis: hormonal regulation of sexual dimorphism. | south african clawed frogs use sex-specific vocalizations during courtship. in the male, vocalizations are under the control of gonadal androgen. though females have moderate levels of circulating androgen, they do not give male-typical mate calls. both muscles of the vocal organ and neurons of the central nervous system (cns) vocal pathway are sexually dimorphic and androgen-sensitive. recent studies suggest that the failure of androgen to masculinize adult females results from a male-specific, ... | 1986 | 3519865 |
| xenopus nucleoplasmin: egg vs. oocyte. | nucleoplasmin has been purified from either oocytes or unfertilized eggs of the frog, xenopus laevis. we find that the pentameric form of egg nucleoplasmin exhibits an apparent molecular mass approximately 15 000 daltons larger than its oocyte counterpart upon sodium dodecyl sulfate (sds)-acrylamide gel electrophoresis. egg nucleoplasmin monomers are more heterogeneous, substantially more acidic, and overall larger in apparent molecular weight than oocyte nucleoplasmin monomers when analyzed by ... | 1986 | 3521726 |
| enzymatic 2'-o-methylation of the wobble nucleoside of eukaryotic trnaphe: specificity depends on structural elements outside the anticodon loop. | we have investigated the specificity of the enzyme trna (wobble guanosine 2'-o-)methyltransferase which catalyses the maturation of guanosine-34 of eukaryotic trnaphe to the 2'-o-methyl derivative gm-34. this study was done by micro-injection into xenopus laevis oocytes of restructured yeast trnaphe in which the anticodon gmaa and the 3' adjacent nucleotide 'y' were substituted by various tetranucleotides. the results indicate that the enzyme is cytoplasmic; the chemical nature of the bases of t ... | 1986 | 3522221 |
| androgen-induced alterations in vocalizations of female xenopus laevis: modifiability and constraints. | we examined effects of exogenous androgen (testosterone and dihydrotestosterone) on vocalizations of ovariectomized, adult female south african clawed frogs, xenopus laevis. when paired with sexually active males, all ovariectomized females exhibited ticking, the unreceptive or 'release' call. ticking consists of low amplitude, regularly spaced clicks with a mean interclick interval of 154 ms. when androgen-treated and paired with sexually active males, these ovariectomized females also exhibite ... | 1986 | 3522887 |
| [appearance of a factor stimulating oocyte maturation in the karyoplasm of the oocytes of the green toad, the clawed toad and the starred sturgeon]. | the karyoplasm (the contents of germinal vesicle) of the bufo viridis, xenopus laevis, and acipenser stellatus oocytes maturing under the influence of progesterone acquires the ability to induce the maturation (germinal vesicle breakdown) of the full grown oocytes, when injected into them. this ability arises in the karyoplasm earlier than in the cytoplasm and is preserved until the germinal vesicle breakdown. | 1986 | 3523350 |
| differential chromosomal distribution of ribonucleoprotein antigens in nuclei of drosophila spermatocytes. | the ribonucleoprotein (rnp) composition of the active y chromosomal structures in spermatocyte nuclei of drosophila hydei has been investigated using the anti-rnp antibodies dm 28k2 and pp60 as a probe. antibody dm 28k2 was raised against an rnp protein of cytoplasmic rnp particles in d. melanogaster cells, while antibody pp60 was raised against a pre-messenger rnp fraction from oocytes of xenopus laevis. both antibodies detect nuclear rnp (nrnp) antigens of d. hydei. this is shown by cscl densi ... | 1986 | 3536959 |
| major histocompatibility complex-encoded class i molecules are absent in immunologically competent xenopus before metamorphosis. | the expression of class i and class ii major histocompatibility complex (mhc)-encoded antigens has been examined at various stages of the development of the clawed frog, xenopus. by immunoprecipitation with alloantisera or xenoantisera from radio-labeled spleen and thymus lysates, and by mixed lymphocyte reaction analysis, it was determined that the same class ii molecules are expressed throughout ontogeny. in contrast, by fluorescence on frozen sections of tadpoles and by immunoprecipitation, t ... | 1986 | 3537126 |
| antibodies to the ras gene product inhibit adenylate cyclase and accelerate progesterone-induced cell division in xenopus laevis oocytes. | microinjection of monoclonal antibodies (lines 238, 172, and 259) directed against the ras gene product, p21, into xenopus laevis oocytes accelerated progesterone-induced germinal vesicle breakdown. antibody 238 had the greatest effect on the acceleration of progesterone-induced oocyte maturation, and this effect was correlated with in vitro inhibition of adenylate cyclase (ec 4.6.1.1) activity in a concentration-dependent manner. inhibition of adenylate cyclase by antibody 238 was also measured ... | 1986 | 3537692 |
| partial purification of the maturation-promoting factor mpf from unfertilized eggs of xenopus laevis. | a 200-fold purification of the maturation-promoting factor or mpf from unfertilized eggs of xenopus laevis is reported for the first time. purification was achieved by three successive column chromatographies on hydroxyapatite, trisacryl blue and l-arginine-agarose. the presence of mpf was assessed by the usual maturation criteria after injections of test material into immature stage vi unstimulated x. laevis oocytes: the precocious appearance of the maturation spot (within 45-120 min), the germ ... | 1986 | 3539598 |
| expression of the c-myc proto-oncogene during development of xenopus laevis. | we isolated and characterized xenopus laevis c-myc cdnas from an oocyte-specific library. these cdna clones encompass 2.35 kilobases of the x. laevis c-myc rna and contain the entire coding domain of 1,257 nucleotides of the 419-amino acid-long x. laevis c-myc protein. the 2.7-kilobase x. laevis c-myc mrna is expressed in the oocyte, maintained in the egg, and is present throughout the early cleavage stages of embryogenesis. at the time of transcriptional activation in the embryo the c-myc rna l ... | 1986 | 3540613 |
| identification of his5,trp7,tyr8-gnrh (chicken gnrh ii) in amphibian brain. | gnrh immunoreactive and bioactive peptides in xenopus laevis brain extract were investigated by high performance liquid chromatography (hplc), radioimmunoassay with region-specific antisera raised against gnrh (mammalian), his5,trp7,tyr8-gnrh (chicken ii) and tyr3,leu5,glu6,trp7,lys8-gnrh (lamprey), and by assessment of biological activity. two immunoreactive peptides eluted in the same positions as gnrh and his5,trp7,tyr8-gnrh respectively in hplc systems which were specifically designed to sep ... | 1986 | 3540909 |
| alkaline phosphatase activity in the membrane of xenopus laevis oocytes: effects of steroids, insulin, and inhibitors during meiosis reinitiation. | the mechanism of steroid hormone-induced reinitiation of meiosis in xenopus laevis oocytes in vitro involves interaction of the hormone with an ooplasma membrane receptor and early changes of enzymatic activities (adenylate cyclase, p48 protein kinase). in full-grown (stage 6) oocytes, we have observed cytochemically, at the ultrastructural level, alkaline phosphatase activity in the ooplasma membrane of microvilli, its decrease by 2 hr of progesterone action, and its complete disappearance at t ... | 1987 | 3542638 |
| immunofluorescent detection and localization of thyroxine in blood of adult amphibians. | indirect immunofluorescent staining was used to detect and localize thyroxine (t4) in blood smears from different species of adult amphibians, namely, rana pipiens, rana catesbeiana, bufo marinus, xenopus laevis, and notopthalmus viridescens. fluorescence, indicative of t4, was observed in both plasma and erythrocytes (rbc) from all individuals of the five species studied. it was weak and diffuse in the plasma and in the cytoplasm of the rbc but was intense in the nuclei (especially the nuclear ... | 1986 | 3542699 |
| molecular cloning and expression of a human b-cell growth factor gene in escherichia coli. | a human b-cell growth factor (bcgf) (12 kilodaltons) supports the clonal proliferation of b lymphocytes. a clone was isolated that contained the proper structural sequence to encode biologically active, 12-kilodalton bcgf in escherichia coli and to hybridize to a specific messenger rna, identified by in vitro translation in xenopus laevis oocytes. a relatively hydrophobic region of 18 amino acids was found at the amino terminal of the 124-amino acid-long polypeptide. the carboxyl terminal is com ... | 1987 | 3547651 |
| the action of acrosin on the zona pellucida. | the presence of hydrolytic enzymes in and associated with the sperm head has long argued for their functioning in fertilization. several observations led investigators to propose that the acrosomal trypsin-like enzyme, acrosin in mammals, functioned in fertilization in aiding the sperm to penetrate the zona pellucida. while many have raised significant objections to this role, the action of acrosin on its presumed physiological substrate has not been characterized in a biochemical fashion. the i ... | 1986 | 3548237 |
| biochemical studies of the envelope transformations in xenopus laevis eggs. | the envelopes that enclose the eggs of the amphibian xenopus laevis were isolated and examined for biochemical correlates of the ultrastructural and sperm penetrability differences among the coelomic egg envelope (ce), the vitelline envelope (ve), and the fertilization envelope (fe). by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (sds-page), the 43,000 molecular weight glycoproteins of ces were found to be converted to components with molecular weights of 41,000 in ves; also, a pro ... | 1986 | 3548238 |
| molecular characterization of a karyophilic, histone-binding protein: cdna cloning, amino acid sequence and expression of nuclear protein n1/n2 of xenopus laevis. | in the amphibian oocyte, most of the non-chromatin-bound histones are not free but form complexes with specific karyophilic proteins, the most prominent being nucleoplasmin and 'protein n1/n2'. using antibodies against polypeptide n1 and n2 (mr approximately 105,000 and approximately 110,000) we have isolated, from a xenopus laevis ovary lambda gt11 expression library, several full length cdna clones encoding one of the two closely related polypeptides n1 and n2 (these could not be distinguished ... | 1986 | 3549279 |
| insulin induction of xenopus laevis oocyte maturation is inhibited by monoclonal antibody against p21 ras proteins. | microinjection of transforming p21 ras protein induces maturation of xenopus laevis oocytes, and the induction is blocked by coinjection of monoclonal antibody (y13-259) against p21 ras proteins. similar to other inducing agents, the effect of p21 ras protein is mediated via the appearance of maturation or meiosis-promoting factor activity. in addition, the neutralizing antibody markedly reduces oocyte maturation after insulin induction, whereas it fails to inhibit progesterone induction. our re ... | 1987 | 3550436 |
| induction of maturation in small xenopus laevis oocytes. | the competence of xenopus laevis oocytes in various stages of growth to respond to progesterone treatment was investigated. full-grown (stage 6) oocytes undergo nuclear membrane dissolution and resume meiosis in response to progesterone exposure, while smaller oocytes (stages 3-5; less than 1100 micron in diameter) do not. the defect which prevents 750- to 1050-micron oocytes from responding to progesterone can be overcome by microinjecting cytoplasm withdrawn from a stage 6 oocyte. germinal ves ... | 1987 | 3552785 |
| alterations in cloned xenopus ribosomal spacers generated by high-frequency plasmid recombination. | in an attempt to understand the mechanisms that have led to the complex intraspecific heterogeneity in spacer organisation found in xenopus r.dna, we have transformed escherichia coli strains that exhibit high levels of plasmid recombination with xenopus laevis r.dna sequences inserted in pbr322. we have found that in these recbc sbca strains, plasmid recombination results in the generation of many types of altered r.dna spacer at a high frequency. the altered spacers result from two types of de ... | 1986 | 3552890 |
| translocation of globin fusion proteins across the endoplasmic reticulum membrane in xenopus laevis oocytes. | we have studied the translocation of a normally cytoplasmic protein domain across the membrane of the endoplasmic reticulum in cell-free systems and in xenopus laevis oocytes. coding regions for the normally cytoplasmic protein globin were engineered in frame either 3' or 5' to the coding region for the signal sequence of either escherichia coli b-lactamase or bovine preprolactin, respectively, in sp6 expression plasmids. rna transcribed from these plasmids was microinjected into oocytes as well ... | 1987 | 3553206 |
| enzymatic conversion of guanosine 3' adjacent to the anticodon of yeast trnaphe to n1-methylguanosine and the wye nucleoside: dependence on the anticodon sequence. | n1-methylguanosine (m1g) or wye nucleoside (y) are found 3' adjacent to the anticodon (position 37) of eukaryotic trnaphe. the biosynthesis of these two modified nucleosides has been investigated. the importance of the type of nucleosides in the anticodon of yeast trnaphe on the potentiality of this trna to be a substrate for the corresponding maturation enzyme has also been studied. this involved microinjection into xenopus laevis oocytes and incubation in a yeast extract of restructured yeast ... | 1987 | 3556165 |
| ribosomal protein, histone and calmodulin mrnas are differently regulated at the translational level during oogenesis of xenopus laevis. | the localization of r-protein mrna in subcellular compartments has been analysed. it was observed that the mrna for a representative r-protein (l1) is diffuse in the cytoplasm, as shown by in situ hybridization experiments and that the distribution of rp-mrna between polysomes and light mrnps changes during oogenesis. in early oogenesis this mrna is found mostly in subpolysomal fractions, whereas at the beginning of vitellogenesis (stage ii) it becomes associated with polysomes where it remains ... | 1987 | 3556426 |
| replication of injected dna templates in xenopus embryos. | we have analysed the replication of both exogenous frog dnas and heterologous dnas during development from the first cleavage through the blastula stage, by their microinjection into fertilized eggs of xenopus laevis. the data show that various plasmids increase to different extents and that the differences cannot be attributed to size alone. plasmids containing the xenopus ribosomal gene repeat unit do not replicate efficiently, and they also inhibit the replication of co-injected dna templates ... | 1987 | 3556428 |
| estrogen induction of a 45 kda secreted protein coordinately with vitellogenin in xenopus liver. | in the frog xenopus laevis, vitellogenin is the major estrogen-induced protein in the liver. we have characterized an additional secreted protein, of 45,000 da and designated ep45, which is also responsive to estrogen treatment. like vitellogenin, ep45 is not normally found in the plasma nor synthesized by the liver of the male frog. its synthesis increases 6-fold between days 2 and 8 following a single 2 mg injection of estradiol-17 beta. for comparison, we have also studied a third estrogen-re ... | 1987 | 3556750 |
| regulation of melanotropin release from the pars intermedia of the amphibian xenopus laevis: evaluation of the involvement of serotonergic, cholinergic, or adrenergic receptor mechanisms. | melanophore-stimulating hormone (msh) release from the pars intermedia of the pituitary gland is probably regulated by multiple factors of hypothalamic origin. we have examined a number of potential regulatory factors for their effects on msh release from the amphibian xenopus laevis. serotonin and acetylcholine have no effect on msh release. both adrenaline and noradrenaline inhibit release of msh in a dose-dependent manner. studies with specific receptor agonists and antagonists reveal that th ... | 1986 | 3557070 |
| microenvironments of photoreceptor and interphotoreceptor matrix glycoconjugates. | enzyme-linked lectin cytochemical and biochemical analyses have been used to identify microdomains of retinal outer segments and interphotoreceptor matrix glycoconjugates. we have devised a highly reproducible trypsin digestion procedure to identify protease-resistant wheat germ agglutinin (wga) domains on the distal tips of some photoreceptor outer segments, and on shed outer segment membrane in xenopus laevis retina. wga binding sites in the frog interphotoreceptor matrix were completely susce ... | 1986 | 3558000 |
| estrogen induces transcription of the xenopus laevis serum retinol-binding protein gene. | we have isolated and sequenced a full-length cdna cloned tentatively identified as encoding xenopus laevis serum retinol-binding protein (rbp) mrna. the derived amino acid sequence of the xenopus protein is 63% homologous to the sequence of the human rbp. 17 of 19 amino acids identified as critical in the retinol-binding pocket of human rbp are identical or conservative replacements in the xenopus protein. the rbp cdna clone has been used as a hybridization probe to demonstrate that administrati ... | 1987 | 3558378 |
| expression of the ca2+-binding protein, parvalbumin, during embryonic development of the frog, xenopus laevis. | a cdna segment encoding the ca2+-binding protein, parvalbumin, was isolated with the use of antibodies, from a lambda gtll expression library of xenopus laevis tadpole poly(a)+ rnas. the bacterially expressed beta-galactosidase-parvalbumin fusion protein of one lambda recombinant shows high affinity 45ca2+ binding. the sequence of the tadpole parvalbumin is highly similar to previously characterized beta-parvalbumins of other organisms. data from protein and rna blotting experiments demonstrate ... | 1987 | 3558484 |
| single-unit study of lateral line cells in the optic tectum of xenopus laevis: evidence for bimodal lateral line/optic units. | responses of single units in the xenopus tectum to stimulation of the contralateral anterior lateral line nerve (calln) and optic nerve were studied. cells responded to calln stimulation with a phasic burst of spikes that was repeatable between trials; latencies ranged from 4 to 23 msec. the most excitable cells were located in layer 6 of the ventrolateral tectum. cells responding to stimulation of the ipsilateral alln were far less numerous and robust, and showed latencies 3-10 msec greater tha ... | 1987 | 3558896 |
| effect of ouabain on the meiotic maturation of stage iv-v xenopus laevis oocytes. | full-grown stage vi xenopus laevis oocytes (1,200 to 1,300 micron) respond to progesterone stimulation by undergoing a series of physiological and morphological changes that are referred to as meiotic maturation. oocytes in earlier stages of oogenesis (i through v) do not undergo these changes and remain in prophase arrest when exposed to this steroid. we have found that oocytes ranging from 850 micron (stage iv) to 1,000 micron (stage v) are capable of responding to progesterone under the appro ... | 1987 | 3559500 |
| physiologically-induced changes in proopiomelanocortin mrna levels in the pituitary gland of the amphibian xenopus laevis. | in the pars intermedia of the pituitary gland of the amphibian xenopus laevis the level of mrna encoding proopiomelanocortin (pomc), the precursor protein for alpha-melanophore-stimulating hormone (alpha-msh), is shown to be dependent on physiological parameters. pomc mrna levels in the pars intermedia of black-background-adapted xenopus are much higher than those of white-adapted animals. these physiological changes in pomc mrna levels are tissue-specific because they were not found in the pars ... | 1987 | 3566743 |
| dnaase i sensitivities in chromatin of the xenopus laevis somatic and oocyte 5 s dnas. | the dnaase i sensitivities of the somatic-type 5 s dna and oocyte-type 5 s dna have been compared in nuclei from adult somatic tissues of xenopus laevis. neither of these type iii genes is expressed in mature erythrocytes and only somatic-type 5 s dna is expressed in liver. we find that somatic-type 5 s dna is dnaase-i-sensitive in liver nuclei and less sensitive in erythrocyte nuclei, while oocyte-type 5 s dna is insensitive in both tissues. the dnaase i sensitivity appears to be uniform across ... | 1987 | 3567198 |
| melatonin and rhythmic photoreceptor metabolism: melatonin-induced cone elongation is blocked at high light intensity. | we have proposed a model for circadian regulation of cone position in xenopus laevis that involves interaction of melatonin and dopamine as signals for darkness and light respectively. one problem, however, is that the effects of melatonin have not been detected in eye cups prepared from animals maintained on a cyclic light schedule. since melatonin's effect would be expected to occur in low light intensity at night, we have investigated the relationship among melatonin, light intensity, and con ... | 1987 | 3567617 |
| transcription termination and processing of transcripts from trna-related xenopus satellite dna sequences. | nucleotide sequence homologies have been found between the transcriptional unit of a xenopus laevis satellite dna containing 1037-bp monomeric repeats and trna-coding genes. since the trna-homologous region forms only part of the transcriptional unit, we have analyzed the size of transcripts being made after injection of cloned dna into xenopus oocyte nuclei. incubation for 6 h mainly results in three rna species comprising 130, 180 and 196 nucleotides, which originate at the same initiation sit ... | 1987 | 3569263 |
| interaction of protein synthesis initiation factor 2 from xenopus laevis oocytes with gdp and gtp analogs. | the structural specificity of the purified protein synthesis initiation factor 2 (eif-2) from x. laevis ovary towards analogs of gtp and gdp was studied. the relative affinity of the structural analogs was measured by their capacity to inhibit the formation of the [3h]gdp x eif-2 binary complex. the results obtained demonstrate that modifications in the ribose moiety are well tolerated by eif-2 which binds dgtp, 2',3'-dialdehyde gtp (ogtp) and 2',3'-dialdehyde gdp (ogdp) and even the dinucleotid ... | 1987 | 3569534 |
| do calcium and calmodulin trigger maturation in amphibian oocytes? | in contrast to earlier reports (j. l. maller and e. g. krebs, 1980, curr. top. cell. regul. 16, 271-311; m. moreau, j. p. vilian, and p. guerrier, 1980, dev. biol. 78, 201-214; w. j. wasserman and l. d. smith, 1981, j. cell biol. 89, 389-394; d. huchon, r. ozon, e. h. fischer, and j. g. demaille, 1981, mol. cell. endocrinol. 22, 211-222) calmodulin preparations isolated from xenopus laevis ovaries or obtained commercially rarely induced maturation upon microinjection into individual oocytes. cal ... | 1987 | 3569665 |
| complementarity of conserved sequence elements present in 28s ribosomal rna and in ribosomal protein genes of xenopus laevis and xenopus tropicalis. | the sequence analysis of the l1 ribosomal protein (r-protein) gene of xenopus laevis has revealed a strong homology in four out of the nine introns of the gene; this homology region spans 60 nucleotides (nt) with 80% homology [loreni et al., embo j. 4 (1985) 3483-3488]. we have extended our analysis to x. tropicalis, a species which is closely related to x. laevis. partial sequencing of the isolated l1 gene has revealed that these 60-nt homology regions are also present in at least two introns o ... | 1986 | 3569921 |
| transcriptional behavior of silkmoth chorion genes in vivo and in injected xenopus laevis oocytes. | a cloned fragment of bombyx mori genomic dna containing a pair of chorion genes was injected into xenopus laevis oocytes. the rna transcribed from the injected template was examined by primer extension analysis for the presence of transcripts initiated correctly from the two chorion genes. using as primers a number of fragments derived from various parts of the injected dna, we have found that transcription initiation around the cap sites of the chorion genes was considerably more frequent than ... | 1987 | 3571273 |
| pertussis toxin blocks melatonin-induced pigment aggregation in xenopus dermal melanophores. | the molecular mechanism of action for the pineal hormone melatonin was explored by testing melatonin interaction with the components of the hormone-sensitive adenylate cyclase complex in a xenopus dermal melanophore bioassay. forskolin was employed to stimulate melanosome dispersion. the ability of melatonin to reverse forskolin-stimulated pigment dispersion was assessed, as was the effect of pertussis toxin on the ability of melatonin to aggregate dispersed pigment. forskolin elicited dispersal ... | 1987 | 3571570 |
| unresponsive, a behavioral mutant in xenopus laevis: electrophysiological studies of the neuromuscular system. | normal xenopus laevis embryos begin movements at 1 day after fertilization. embryos homozygous for the unresponsive mutation fail to move until 4 days after fertilization (just prior to feeding), after which they recover slowly. electrophysiological studies were undertaken to determine the focus of this mutation. formamide treatment of normal embryos was used to produce a phenocopy of the unresponsive condition, permitting direct comparisons between mutant and normal embryos. intracellular recor ... | 1987 | 3572392 |
| the 5'-leader sequence of tobacco mosaic virus rna enhances the expression of foreign gene transcripts in vitro and in vivo. | a 67-nucleotide portion of the non-coding, 5'-leader sequence of tobacco mosaic virus rna [defined as omega' (gr. omega prime)] has been shown to enhance the translation of contiguous foreign gene transcripts both in vitro and in vivo. chemically-synthesized omega', containing convenient linker sequences, was inserted into derivatives of an in vitro transcription plasmid (psp64) between the bacteriophage-sp6 promoter and sequences coding for either chloramphenicol acetyltransferase (cat) or neom ... | 1987 | 3575095 |
| change of motor innervation pattern in musculus longissimus dorsi of xenopus laevis at metamorphosis. | | 1986 | 3577333 |
| [production of androgenetic diploid adults of xenopus laevis]. | | 1986 | 3577552 |
| improved method for purification of xenopus laevis vitellogenin and demonstration of cross-reactivity among wide-range species by radioimmunoassay. | this study was performed to improve the purification of xenopus vitellogenin and establish the radioimmunoassay. the procedure of purification consisted of ammonium precipitation, deae-sephadex chromatography and sephadex g-200 gel chromatography. using this procedure, 934 mg vitellogenin was purified from 49 ml of estradiol treated female xenopus plasma (about 19 mg/ml). vitellogenins purified from male and female plasma after a single injection of estradiol showed good correspondence in electr ... | 1986 | 3582267 |
| xenopus transcription factor iiia binds primarily at junctions between double helical stems and internal loops in oocyte 5s rna. | rnases and chemical probes were used to study the accessibility of each nucleotide of 5s rna in the native and reconstituted 7s particle from xenopus laevis oocytes. rnase or chemically treated 5s rna from intact 7s particles was isolated and analysed using an oligodeoxynucleotide primer and reverse transcriptase. the results were superimposed on a cylindrical projection of an rna double helix and the protection effects were shown to cluster at two regions on the molecular surface. a three-dimen ... | 1987 | 3582366 |
| xenopus cytoskeletal actin and human c-fos gene promoters share a conserved protein-binding site. | xenopus laevis cytoskeletal actin gene promoters contain a 20-bp sequence homologous to the serum response element (sre) required for transient human c-fos gene transcription in response to serum factors. both sequences bind the same factor in hela cell extracts, as shown by binding competition, dnase i and dimethylsulphate (dms) protection and dms interference assays. a similar protein is present in xenopus laevis oocytes. sequences containing the sre homology are essential for constitutive act ... | 1987 | 3582369 |
| aerial respiration facilitates growth in suspension-feeding anuran larvae (xenopus laevis). | xenopus laevis tadpoles are midwater suspension-feeders that use buccopharyngeal surfaces for both food capture and aquatic respiration, but also have functioning lungs well before metamorphosis. to examine the effect of aerial respiration on premetamorphic growth and development in this species, tadpoles were raised in normoxic water for from one to three weeks at three different concentrations of food (yeast cells in suspension). at each food concentration the larvae were either allowed or den ... | 1987 | 3582584 |
| the effects of various nutritional supplements on the growth, migration and differentiation of xenopus laevis neural crest cells in vitro. | this study investigates the nutritional requirements of xenopus laevis neural crest cells and melanophores developing in vitro. a comparison is made between the growth and differentiation of cells in serum-containing medium and a chemically defined, serum-free medium that we have designed. our chemically defined medium is more efficient than serum-supplemented medium in promoting proliferation of these cells. several supplements are required to enhance culture development. these include insulin, ... | 1987 | 3583983 |
| effect of tetraploidy on dendritic branching in neurons and glial cells of the frog, xenopus laevis. | morphological aspects of four different groups of golgi impregnated brain cells from a tetraploid strain of xenopus laevis frogs were compared to analogous cells in comparably sized diploid frogs. the cells examined included neurons from the telencephalon, caudal hypothalamus, and optic tectum, and radial glial cells from the optic tectum. the brains of tetraploid frogs appeared grossly normal and were the same size and contained similar cell types as diploid brains. as observed in previous stud ... | 1987 | 3584543 |
| suppressive rod-cone interaction in distal vertebrate retina: intracellular records from xenopus and necturus. | the influence of dim diffuse adapting fields upon the sensitivity to focal photic stimulation was studied by means of intracellular recording in retinal neurons of the south african clawed frog, xenopus and the mudpuppy, necturus. in cones and in most horizontal and bipolar cells lacking color opponency, dim diffuse backgrounds have little influence upon the response to diffuse flicker of low (less than 2 hz) temporal frequencies; however, with small diameter test probes of higher temporal frequ ... | 1987 | 3585472 |
| in vitro maintenance of spermatogenesis in xenopus laevis testis explants cultured in serum-free media. | spermatogenesis has been maintained for extended periods in xenopus laevis testis explants cultured in serum-free media supplemented with bovine serum albumin, insulin, transferrin, follicle-stimulating hormone, dihydrotestosterone, testosterone, retinol, ascorbate, and tocopherol. the organization of the testis fragments was maintained for 28 days, and all stages of development were present throughout the culture period. 3h-thymidine-labeled secondary (type b) spermatogonia developed in 28 days ... | 1987 | 3593863 |
| sequestration of iontophoretically injected calcium by living endothelial cells. | sequestration of iontophoretically injected ca2+ by monolayer culture cells (primary xenopus laevis tadpole heart cells, xth p, and an established cell line, xth 2) is investigated. injections are made at different velocities by changing the influx current. on ca2+ injection the entire er desintegrates, and near to the tip of the injecting pipette microtubules depolymerize. the time required to attain cell death is taken as the parameter indicating an overload of cellular ca2+ sequestration capa ... | 1987 | 3594554 |
| ribosomal precursor 3' end formation requires a conserved element upstream of the promoter. | in xenopus laevis the 3' end of the longest intact ribosomal rna precursor is formed by a processing event at site t2, which is located 7860 bp downstream of the site of transcription initiation. processing at t2 is eliminated by mutations within the t2 box, a 7 nucleotide conserved element, gacttgc, located 15 bp downstream of the 3' ends. the same conserved box is also present at t3, a site 60 bp upstream of the gene promoter and that is part of a termination site. surprisingly, mutations with ... | 1987 | 3594564 |
| structural organization of the proopiomelanocortin gene in xenopus laevis. 5'-end homologies within the toad and mammalian genes. | this study reports the isolation and characterization of the entire proopiomelanocortin (pomc) gene of the amphibian xenopus laevis. the xenopus pomc gene consists of three exons of which the main exon 3 codes for all of the bioactive domains of the precursor protein. intron a (2.6 kb) separates the segments encoding the 5'-untranslated mrna region and intron b (2.5 kb) interrupts the protein-coding sequence near the signal peptide coding region. in that this structural organization of the xenop ... | 1987 | 3595598 |
| differentiation of the animal-vegetal axis in xenopus laevis oocytes. i. polarized intracellular translocation of platelets establishes the yolk gradient. | the animal-vegetal axis of the oocyte of xenopus laevis is recognizable not only by the pattern of surface pigmentation, but also by the distribution of yolk platelets, with the largest platelets (congruent to 14 microns in diameter) and 70% of the total yolk protein localized in the vegetal hemisphere. we have used fluorescent and radioactive vitellogenins (yolk protein precursors) to study the spatial and temporal patterns of yolk deposition along this axis. we find that the rate of uptake of ... | 1987 | 3596006 |
| fates of the blastomeres of the 32-cell-stage xenopus embryo. | a detailed fate map of all of the progeny derived from each of the blastomeres of the 32-cell-stage south african clawed frog embryo (xenopus laevis), which were selected for stereotypic cleavages, is presented. individual blastomeres were injected with horseradish peroxidase and all of their descendants in the late tailbud embryo (stages 32 to 34) were identified after histochemical processing of serial tissue sections and whole-mount preparations. the progeny of each blastomere were distribute ... | 1987 | 3596014 |
| scanning acoustic microscopy visualizes cytomechanical responses to cytochalasin d. | the reactions of xth-2 cells (line derived from xenopus laevis tadpole hearts) to cytochalasin d (cd) were followed using scanning acoustic microscopy (sam) at 0.9 ghz, fluorescence and electron microscopy. the first reaction to cd which can be detected by sam is a loss of image contrast, indicating a decrease in acoustic impedance of about 30%. based on structural changes revealed by staining of actin with tritc-phalloidin, and taking theoretical considerations into account, a relationship betw ... | 1987 | 3599068 |
| xenopus laevis lectins. | | 1987 | 3600344 |
| dna sequence-directed nucleosome reconstitution on 5s rna genes of xenopus laevis. | nucleosomes were reconstituted in vitro with several singly end-labeled restriction fragments derived from a cloned somatic-type 5s rna gene of xenopus laevis and purified nucleosome core particles from xenopus cultured cells or chicken erythrocytes. nucleosome locations were determined by digestion of the reconstitutes with exonuclease iii and dnase i and were the same for all fragments investigated, extending from 20 base pairs (bp) within the 5s gene to 80 bp beyond the 3' end of the gene. bo ... | 1987 | 3600640 |
| a 12-base-pair sequence is an essential element of the ribosomal gene terminator in xenopus laevis. | rrna transcription in xenopus laevis terminates near a 7-base-pair (bp) conserved sequence (t3 box) located 200 bp upstream of the site of transcription initiation for the adjacent gene promoter. we present evidence here that a 12-bp element containing the t3 box is an essential part of the terminator. using an oocyte injection assay, we found that the 12-bp element (but not the t3 box alone) severely reduced the amount of rna detectable at sites downstream from itself and that the t3 box within ... | 1987 | 3600650 |
| translocation of a localized maternal mrna to the vegetal pole of xenopus oocytes. | a prominent hypothesis in embryology is that localized maternal factors are important in specifying cell fate. there are, however, only a few examples of maternal molecules that have been shown to be localized and very little is known about how such factors are physically localized within an egg (for review see ref. 1). previously, cdna clones were obtained for a class of localized maternal mrnas from xenopus laevis. these mrnas are unusual in that they are concentrated at either the animal or v ... | 1987 | 3600777 |
| effects of weak magnetic fields on background adaptation in xenopus laevis. | | 1987 | 3600814 |
| precursor-product relationship between vitellogenin and the yolk proteins as derived from the complete sequence of a xenopus vitellogenin gene. | in xenopus laevis four estrogen-responsive genes are expressed simultaneously to produce vitellogenin, the precursor of the yolk proteins. one of these four genes, the gene a2, was sequenced completely, as well as cdnas representing 75% of the coding region of the gene. from this data the exon-intron structure of the gene was established, revealing 35 exons that give a transcript of 5,619 bp without the poly a-tail. this a2 transcript encodes a vitellogenin of 1,807 amino acids, whose structure ... | 1987 | 3601655 |
| coadministration of methylxanthines and inhibitor compounds potentiates teratogenicity in xenopus embryos. | inhibitors of dna synthesis (hydroxyurea and cytosine arabinoside), protein synthesis (cycloheximide and emetine), and nucleic acid synthesis (5-fluorouracil) were administered with each of three methylxanthines (caffeine, theophylline, and theobromine) to determine if teratogenic effects could be potentiated in xenopus laevis embryos. the animals were exposed for 96 hours to methylxanthine and inhibitor concentrations that, alone, produced low percentages of malformations. coadministration of c ... | 1987 | 3603405 |
| biosynthesis and degradation of peptides derived from xenopus laevis prohormones. | peptides present in the skin secretion of the south african frog, xenopus laevis, have been analysed by fast atom bombardment mass spectrometry and h.p.l.c. in the mass range 500-3200 da. we have investigated the effects of successive glandular secretions induced by noradrenaline injections on these peptide levels and have found that the replenishment of the whole range of peptides is complete within 2-6 days. intact secretory vesicles free of cellular contaminants contain a relatively large num ... | 1987 | 3606567 |
| heat and sodium arsenite act synergistically on the induction of heat shock gene expression in xenopus laevis a6 cells. | heat shock protein (hsp) synthesis was studied in the xenopus epithelial cell line a6 in response to heat and sodium arsenite, either singly or together. temperatures of 33-35 degrees c consistently brought about the synthesis of hsps at 87, 73, 70, 54, 31, and 30 kilodaltons (kda), whereas sodium arsenite at 25-100 microm induced the synthesis of hsps at 73 and 70 kda. in cultures exposed to 10 microm sodium arsenite at 30 degrees c, hsp synthesis in the 68- to 73-kda and 29- to 31-kda regions ... | 1987 | 3606855 |
| regional differences of proteins in isolated cells of early embryos of xenopus laevis. | regional differences of proteins were studied by two-dimensional gel electrophoresis in early embryos of xenopus laevis. pairs of blastomeres on the dorso-ventral axis were isolated from 16- and 32-cell embryos. some dorso-ventral differences have been detected at 32-cell embryos. the proteins which were clearly detectable in the vegetal cells of the ventral marginal zone were only faintly detectable or undetectable in those of the dorsal marginal zone, and a regionally specific spot was detecte ... | 1987 | 3607883 |