| the germinal vesicle material required for sperm pronuclear formation is located in the soluble fraction of egg cytoplasm. | the chromatin of xenopus laevis sperm nuclei was induced to decondense, swell and form mitotic chromosomes following its injection into mature rana pipiens oocytes. in contrast, the sperm chromatin did not decondense or form mitotic chromosomes when injected into oocytes from which the germinal vesicle (gv) was removed prior to the initiation of maturation. injection into enucleated oocytes of the material extracted from manually-isolated gvs restored their ability to decondense sperm nuclei. th ... | 1983 | 6605256 |
| dual contribution of embryonic ventral blood island and dorsal lateral plate mesoderm during ontogeny of hemopoietic cells in xenopus laevis. | the early embryonic development of hemopoietic cells in xenopus laevis was examined. either dorsal lateral plate (dlp) or ventral blood island (vbi) mesoderm was reciprocally transplanted between cytogenetically distinct (2n or 3n) stage 14 to 19 (neural fold) embryos. f-dna content of circulating erythrocytes was assayed at stages 40, 41, 43, 45, and 49. the f-dna content of cells in the thymus and mesonephros was assayed at stage 49. f-dna values were used to distinguish between donor or host ... | 1983 | 6605382 |
| mechanical, electrical, and morphological characteristics of skeletal muscle fibers from xenopus and other species of frogs. | mechanical, electrical, and morphological properties of iliofibularis or semitendinosus of xenopus laevis, rana catesbeiana, and rana nigromaculata were investigated in an attempt to find out the differences between them which will give the basic knowledge for the study of excitation-contraction coupling. with application of electrical stimulation, a single muscle fiber from xenopus contracted at a faster rate of rise than did the other muscles tested. the maximum rate of rise (tmax) of tension ... | 1983 | 6606063 |
| is caerulein amphibian cck? | the amphibian skin decapeptide caerulein is structurally related to the mammalian peptides gastrin and cck, suggesting that the peptides might share a common evolutionary history. it has been suggested that caerulein is the amphibian counterpart of gastrin and cck, and that the amphibia do not possess authentic gastric and cck. high performance liquid chromatography (hplc) in conjunction with radioimmunoassay using a caerulein-specific antiserum and c-terminal cck antisera, was used to character ... | 1983 | 6606162 |
| cytoplasmic phases in the first cell cycle of the activated frog egg. | the first cell cycle of the activated frog egg is longer than subsequent cycles and several developmentally important events such as the determination of bilateral symmetry occur at this time. when eggs of rana pipiens or xenopus laevis are dissected at times after activation, differences in the consistency of the animal half cytoplasm can be detected visually, and the first cell cycle has been divided into four cytoplasmic phases on this basis. phase 1 includes the events of activation and last ... | 1983 | 6606589 |
| roles of cytosol and cytoplasmic particles in nuclear envelope assembly and sperm pronuclear formation in cell-free preparations from amphibian eggs. | a cell-free cytoplasmic preparation from activated rana pipiens eggs could induce in demembranated xenopus laevis sperm nuclei morphological changes similar to those seen during pronuclear formation in intact eggs. the condensed sperm chromatin underwent an initial rapid, but limited, dispersion. a nuclear envelope formed around the dispersed chromatin and the nuclei enlarged. the subcellular distribution of the components required for these changes was examined by separating the preparations in ... | 1984 | 6609160 |
| phorbol ester increases the level of interleukin 2 mrna in mitogen-stimulated human lymphocytes. | tpa alone did not induce the production of il 2 in human tonsillar lymphocytes but enhanced the pha-induced il 2 production by seven-fold. that the effect of tpa was due to an increase in il 2 mrna was demonstrated by examining the amount of il 2 mrna translatable in xenopus laevis oocytes, and by northern blotting analysis using il 2 cdna as a probe. in these ways, it was shown that tpa alone did not induce any significant il 2 mrna synthesis, but when added together with pha it increased the l ... | 1984 | 6609189 |
| control of biologically active interleukin 2 messenger rna formation in induced human lymphocytes. | the regulation of human interleukin 2 (il-2) mrna production in induced normal lymphocytes was studied by following the expression of isolated mrna in microinjected oocytes of xenopus laevis. mitogenic stimulation results in the appearance of greatly increased levels of il-2 mrna activity. this process requires de novo transcription. induction is followed promptly by a shutoff of active il-2 mrna formation. this shutoff requires the synthesis of a protein repressor and can be prevented by cycloh ... | 1984 | 6609365 |
| immunologic reactivity to tnp-ficoll during development and ageing in xenopus laevis, the south african clawed toad. | the immunological response of xenopus laevis to haptenated ficoll was examined throughout development. the capacity to respond to tnp-ficoll originated with the first appearance (at stage 48, 8 days post-fertilisation) of mature thymic lymphocytes, and preceded the ability to respond to heterologous erythrocytes. during premetamorphosis the response increased, while during prometamorphosis , particularly at stages 57-58, there was a marked reduction. the response recovered during the metamorphic ... | 1984 | 6609773 |
| isolation and functional property of mrnas coding for human interleukin 2. | interleukin 2 (il 2) is a lymphokine with specific growth promoting properties for activated t cells. the isolation and purification of specific mrnas coding for this protein is reported. the analysis of total poly a + containing rna from pha stimulated t lymphocytes on agarose gels reveals the existence of at least two different il-2 mrnas. isolated rnas have been microinjected separately into xenopus laevis oocytes for translation and consecutively the synthesized proteins were tested for acti ... | 1984 | 6609779 |
| isolation and partial characterization of messenger rna, from murine t cell hybrids, coding for suppressive immunoglobulin g-binding factor. | poly a rna has been isolated from a murine t cell hybridoma ( t2d4 ) that spontaneously secretes suppressive immunoglobulin g-binding factor ( iggbf ). translation products, obtained from a rabbit reticulocyte lysate translation system and after injection into xenopus laevis oocytes, contain material with the biologic activity, the affinity, and the m.w. of murine iggbf ; it suppresses secondary in vitro igg antibody production in a dose-dependent fashion. the suppressive factor binds to igg but ... | 1984 | 6609991 |
| during frog ontogeny, pha and con a responsiveness of splenocytes precedes that of thymocytes. | the in-vitro proliferation of splenocytes and thymocytes from xenopus laevis-gilli (hybrid clone lg-15) to the t cell mitogens, concanavalin a (con a) and phytohaemagglutinin-p (pha), were examined at specific stages of larval development (stages 51-66 of nieuwkoop & faber, 1967) and at 2 months post-metamorphosis. the responses of splenic lymphocytes to each mitogen were significant at all stages with stimulation indices ranging from 1.9 to 50.5 and 2.6 to 45.5 for pha and con a, respectively. ... | 1984 | 6611296 |
| expression of the native alpha and beta interferon genes in human cells. | we have investigated the expression of human interferon (ifn)-related transcripts in sendai virus-induced lymphoblastoid (namalwa) cells and in poly(i) x poly(c)-induced fibroblast (fs-4) cells by electrophoresis of rna through agarose-ch3hgoh gels followed by (a) blot hybridization of the rna using ifn-alpha 1 and ifn-beta 1 cdna probes, and (b) translation of the eluted rna into biologically active ifn using the xenopus laevis oocyte assay. in namalwa cells induced with or without prior treatm ... | 1983 | 6612995 |
| preliminary characterisation of inhibitors of dna polymerase isolated from xenopus laevis early embryos. | inhibitors of dna polymerase have been detected in xenopus laevis ovary and egg extracts. the characteristics of the inhibitors differ between the two extracts. in ovary preparations, the inhibitor is retained by dialysis tubing and is heat sensitive, whereas in egg extracts it is diffusable and heat stable. in both extracts, the activity co-elutes with dna polymerase after ion exchange chromatography. chromatography of ovary extracts renders the inhibitor diffusable and heat stable. preliminary ... | 1983 | 6615840 |
| effects of puromycin and cycloheximide on properties of cells from xenopus laevis early embryos. | the effects have been studied of puromycin and cycloheximide on the reaggregation of ectoderm cells dissociated from xenopus laevis blastulae. puromycin or cycloheximide can inhibit reaggregation, suggesting that cell reassociation is dependent upon protein synthesis. if the cells are allowed a 3 h 'recovery' period in culture medium following dissociation, before being exposed to either puromycin or cycloheximide, higher concentrations of the inhibitors are required to prevent cell aggregation, ... | 1983 | 6617261 |
| freeze-fracture electron microscopy of membrane changes in progesterone-induced maturing oocytes and eggs of xenopus laevis. | using freeze-fracture electron microscopy, compositional changes were analysed in the surface membrane of xenopus oocytes during maturation after in vitro progesterone treatment, as well as in eggs before and after fertilization. investigated stages were as follows: (1) defolliculated full-grown oocytes; (2) defolliculated oocytes after 5 min exposure to 5 micrograms/ml progesterone; (3) ditto at germinal vesicle breakdown (gvbd) after 5 h progesterone treatment; (4) unfertilized eggs at oviposi ... | 1983 | 6617673 |
| analysis of the base substitutions found in the xenopus laevis 5 s rna pseudogene. | a 5 s rna pseudogene is associated with the major oocyte 5 s rna gene of xenopus laevis. x. borealis has several oocyte specific 5 s rna genes. gene 1 is the dominant 5 s rna gene. gene 3 has sometimes been referred to as a pseudogene. we show that the base substitutions in the x. laevis 5 s pseudogene are non-random with respect to double and single-stranded regions of the 5 s rna using the chi 2 test of homogeneity with yates correction for continuity. in addition, conserved positions of eukar ... | 1983 | 6617857 |
| internal ph of xenopus oocytes: a study of the mechanism and role of ph changes during meiotic maturation. | the internal ph (phi) of xenopus laevis oocytes, as measured by the dmo method, covered a broad range of values from 7.06 +/- 0.01 to 7.93 +/- 0.01, with a mean value of 7.43 +/- 0.03. the phi measured by dmo and microelectrodes was nearly identical in control and maturing oocytes from the same batch. the oocytes from most females elevated their phi in response to progesterone, reaching a maximum elevation of 0.30 +/- 0.03 ph units above control values at 100% germinal vesicle breakdown (gvbd). ... | 1983 | 6617989 |
| globin gene expression in xenopus laevis: anemia induces precocious globin transition and appearance of adult erythroblasts during metamorphosis. | the expression of xenopus laevis larval and adult globin genes after phenylhydrazine-induced anemia has been investigated at the cellular and molecular levels by means of cloned cdna probes specific for the four main larval and the four main adult globin mrna species. in the circulating blood of anemic metamorphic larvae there are at least two distinct populations of erythroblasts containing either larval or adult globin mrna sequences. the cells expressing adult sequences replace those expressi ... | 1983 | 6618004 |
| the effects of aquatic oxygen concentration, body size and respiratory behaviour on the stamina of obligate aquatic (bufo americanus) and facultative air-breathing (xenopus laevis and rana berlandieri) anuran larvae. | larvae of the anurans rana berlandieri and xenopus laevis have lungs and can breathe air as well as irrigate buccal and pharyngeal surfaces for aquatic respiration. larvae of bufo americanus lack lungs until just before metamorphosis and are obligately aquatic. we examined the relationship between the locomotor stamina (time to fatigue), aquatic oxygen concentration, body size, and respiratory behaviour of swimming larvae of these species, with the following results: stamina is size-dependent in ... | 1983 | 6619726 |
| changes in polyamine content during limb regeneration in adult xenopus laevis. | polyamine contents in the regenerates were determined at various stages after amputation of the forelimbs of the adult female xenopus laevis. putrescine, spermidine, spermine, and sym-homospermidine were detected in all the specimens examined. cadaverine was detected only in a limited number of samples. at 5 days after amputation of forelimbs, well before the formation of regenerates, the putrescine content in the stump tissues increased, followed by the increase in spermidine content. the putre ... | 1983 | 6619761 |
| vasopressin and oxytocin precursors as model preprohormones. | using a combination of in vitro methodology, including cell-free translation, two-dimensional peptide mapping and recombinant dna techniques, the structure of the precursors of the hypothalamic nonapeptide hormones vasopressin and oxytocin has been elucidated. both hormone precursors are model cellular polyproteins in that they comprise several different entities within the same polypeptide molecule. in each precursor, the nonapeptide hormone follows immediately the signal peptide and is, in tur ... | 1983 | 6621804 |
| spacer sequences regulate transcription of ribosomal gene plasmids injected into xenopus embryos. | we have injected plasmids containing a repeating unit (spacer plus gene) of xenopus laevis ribosomal dna into fertilized eggs. transcription on these plasmids begins at the same time as transcription on the endogenous ribosomal genes (late blastula stage). previous work defined the ribosomal gene promoter as the region from -140 to +6 around the site of transcription initiation (reeder et al., 1982; moss, 1982; sollner-webb et al., submitted). we show here that the level of transcription of the ... | 1983 | 6627394 |
| changes of alanine-sodium co-transport during maturation of xenopus laevis oocytes. | maturation of full grown xenopus oocytes is associated with a decrease of their capacity to transport amino acids and nucleosides. nevertheless, the transport continues at a reduced rate until the time of metaphase arrest when the oocytes are ready for shedding. we have found that the l-alanine transport in unfertilized, shed oocytes is a saturable process which is na+-dependent. the stoichiometrical ratio between sodium and alanine is 2:1. comparison with the alanine uptake in full grown oocyte ... | 1983 | 6627406 |
| changes in nervous system glycolipids during metamorphosis of xenopus laevis. | qualitative and quantitative changes occurring in the myelin marker glycolipids, cerebrosides, sulfatides, and monogalactosyl diglyceride, in the nervous system (brain, spinal cord, and tail) of xenopus laevis during its metamorphic stages were analyzed by normal and reverse-phase high performance liquid chromatography. the concentration of these glycolipids increased rapidly in brain until the tadpole reached the middle of metamorphosis, fluctuated slightly, decreased until metamorphosis was co ... | 1983 | 6630186 |
| novel form of dna polymerase alpha associated with dna primase activity of vertebrates. detection with mouse stimulating factor. | with a specific stimulating factor of mouse dna replicase for its detection, a novel form of dna polymerase alpha (dna replicase) associated with dna primase activity was partially purified from several vertebrates, i.e. the cherry salmon oncorhyncus masou, the frog xenopus laevis, the chick, and human (hela cells). activity similar to dna replicase was also partially purified from embryos of the sea urchin anthocidaris crassispina. in all vertebrates examined, two forms of dna polymerase alpha ... | 1983 | 6630221 |
| size dependence during the development of the amphibian foot. colchicine-induced digital loss and reduction. | localized treatment of the limb buds of the frog, xenopus laevis, and the salamander, ambystoma mexicanum, with the mitotic inhibitor colchicine results in limbs that, when compared with the contralateral control, are smaller in size and have lost skeletal elements. there is a very well defined pattern in terms of what elements are most likely to be lost. for example, frogs that have lost a toe always lose the first toe, while salamanders always lose the fifth. these differences correspond to qu ... | 1983 | 6631320 |
| development of the lateral line system in xenopus laevis. ii. cell multiplication and organ formation in the supraorbital system. | cell multiplication was studied during development of the supraorbital lateral line system in xenopus laevis. the increase in cell number is biphasic. the first phase extends from the beginning of primordial elongation to the end of primary organ formation. cell number increases linearly during this interval. throughout this phase, a constant number of cells is in s phase of the cell cycle at a given time, despite a more than 10-fold increase in total cell number. after their formation, the numb ... | 1983 | 6631323 |
| development and differentiation of the brain ventricular system in tadpoles of xenopus laeris (daudin) (amphibia, anura). | the development and the differentiation of the ventricular system of the brain of tadpoles of the south african clawed toad, xenopus laevis (daudin), is studied by light microscopy (stages 45 to 66) and scanning and transmission electron microscopy (stages 50 to 66). special interest is paid to the ependymal structures of the foramen of monroe, the ventricles of the diencephalon, the mesencephalon, and the rhombencephalon, and to the ependymal of the central canal and the choroid plexus of the t ... | 1983 | 6636968 |
| calcium efflux from amphibian sciatic nerve. | eight xenopus laevis were injected intraperitoneally with 45cacl2 and 16-18 h later an unbranched section from each sciatic nerve was removed. efflux measurements of nerve from which the perineurial sheath had been removed could be described by three compartments of approximately equal size with half-lifes of 2.37 +/- 0.76 (sd), 30.3 +/- 17.3 and 196 +/- 61 min, the shortest lived compartment representing diffusion from the extracellular space with a coefficient of diffusion of 2.1 +/- 0.7 x 10( ... | 1983 | 6640431 |
| [nuclear behavior of the growing oocytes of the clawed frog in the cytoplasm of the maturing oocytes of the axolotl]. | | 1983 | 6641489 |
| partial purification of estradiol receptor from xenopus laevis liver and levels of receptor in relation to estradiol concentration. | we have used ammonium sulphate precipitation followed by affinity chromatography to partially purify the estrogen receptor from xenopus laevis liver which may control the genes for vitellogenin, the precursor of the egg yolk proteins. the rate at which receptor binds estradiol explains the kinetics of the induction of vitellogenin synthesis by estradiol, and the dissociation constant (0.5 x 10(-9) m) explains the concentration dependence of the response, which has a threshold of 10(-9) m estradi ... | 1983 | 6641722 |
| a new in vitro melanophore bioassay for msh using tail-fins of xenopus tadpoles. | a new in vitro melanophore system is described, which employs pieces from the ventral tail-fin of xenopus laevis tadpoles. tail-fin melanophores in vitro retain the ability to disperse their pigment in darkness and to reaggregate it upon illumination. in the light, alpha-msh, camp, dibutyryl-camp and theophylline induce a concentration-dependent pigment dispersion. the log dose-response curve obtained with alpha-msh is sigmoidal with a linear portion between 0.5 and 2.0 ng alpha-msh/ml. in this ... | 1983 | 6642076 |
| photoreceptor disc shedding in eye cups. inhibition by deletion of extracellular divalent cations. | to further define the medium requirements for in vitro rod disc shedding and phagocytosis in eye cups of xenopus laevis, the effect of deletion of divalent cations was examined. calcium-free medium completely eliminated both normal diurnal disc shedding (initiated by light onset) and dark-primed disc shedding (initiated by a period of darkness followed by additional darkness or light). the effect was reversible. furthermore, the events that occurred during the initial dark-priming period did not ... | 1983 | 6642925 |
| ion currents and membrane domains in the cleaving xenopus egg. | we used an extracellular vibrating probe to measure ion currents through the cleaving xenopus laevis egg. measurements indicate sharp membrane heterogeneities. current leaves the first cleavage furrow after new, unpigmented membrane is inserted. this outward current may be carried by k+ efflux. no direct involvement of the na+,k+-atpase in the generation of this outward current is detected at first cleavage. inward current enters the old, pigmented membrane; however, it does not enter uniformly. ... | 1983 | 6643577 |
| identification of multiple rnases in xenopus laevis oocytes and their possible role in trna processing. | a survey of rnases in xenopus laevis oocytes has been carried out to identify potential trna-processing enzymes in this system. using a variety of specific and nonspecific substrates, we have shown that oocytes contain multiple rnases with various specificities. three activities that could cleave the extraneous residues from the artificial trna precursor, trna-c-[14c]u-c, to generate a substrate for -c-c-a addition by trna nucleotidyltransferase were identified. one of these was a cytoplasmic ex ... | 1983 | 6646119 |
| transcription in oocytes of highly methylated rdna from xenopus laevis sperm. | the genes for ribosomal rna exist as multiple copies in the genome. each repeated unit comprises a region that codes for the 40s rrna precursor, and a spacer region of uncertain function (fig. 1a). in xenopus laevis there are about 1,000 copies of the dinucleotide sequence c-g in each repeat unit, and of these about 250 can be tested for the presence of 5-methylcytosine using restriction endonucleases. most of the detectable c-gs are heavily methylated, but in somatic cells unmethylated c-gs occ ... | 1983 | 6646203 |
| scattering of repetitive dna sequences in the albumin and vitellogenin gene loci of xenopus laevis. | we have analyzed middle repetitive dna in the albumin and vitellogenin gene families of xenopus laevis. mapping specific repetitive dna sequences derived from introns of the a1 vitellogenin gene reveals that these sequences are scattered within and around the four vitellogenin genes (a1, a2, b1 and b2) and the two albumin genes (74 kd and 68 kd). three repetitive dna elements present in the a1 vitellogenin transcriptional unit are also located in introns of the 74 kd albumin gene. this apparentl ... | 1983 | 6647035 |
| craniofacial malformation in xenopus laevis tadpoles caused by the exposure of early embryos to ethanol. | the principal features of fetal alcohol syndrome (fas) include microcephaly, reduced body size, and characteristic facial malformation, most of which are associated with hypoplasticity of structures around the mouth. a recent study using pregnant mice suggested that the malformations in fas are caused by the effects of ethanol on early embryos during gastrulation and neurulation. exposure of xenopus laevis early embryos to 1-2% ethanol until they developed to the late neurula stage produced cran ... | 1983 | 6648833 |
| [essential and substituted amino acids as chemical stimuli in the clawed frog xenopus laevis]. | studies have been made of the effect of all 20 natural amino acids on motor activity of the clawed toad xenopus laevis. it was demonstrated that essential amino acids act as more effective chemical stimuli than replaceable ones. | 1983 | 6650035 |
| spacer regulation of xenopus ribosomal gene transcription: competition in oocytes. | xenopus laevis ribosomal gene plasmids bearing different length spacers were injected into oocyte nuclei in competition with each other. the spacer has two basic effects on transcription from the gene promoter. first, if the competing pair have unequal spacer lengths, the gene promoter attached to the longer spacer is always dominant in transcription (the competition effect). second, as the total amount of spacer in the reaction increases, the total amount of transcription decreases (the sink ef ... | 1983 | 6652676 |
| fertilization and artificial activation of chlorpromazine-treated eggs in xenopus laevis. | | 1983 | 6653839 |
| two-dimensional gel analysis of the fate of oocyte nuclear proteins in the development of xenopus laevis. | the amphibian oocyte nucleus is thought to provide a maternal store of protein required in embryogenesis. the fate of germinal vesicle proteins has been studied by comparing polypeptide patterns of oocytes, embryos, and several adult organs of xenopus laevis on two-dimensional gels. a combination of silver staining and fluorography of radiolabeled protein on gels was used to analyze maternal and newly synthesized polypeptides in embryogenesis. comparison of protein patterns was facilitated and c ... | 1983 | 6653879 |
| determination of locust vitellogenin by radioimmunoassay with [3h]propionyl-vitellogenin. | a simple procedure for radiolabeling of locust vitellogenin is described. this procedure involves coupling of [3h]propionyl succinimidate to purified vitellogenin with high yield and specific activity. using this radiolabeled analog, a specific and sensitive radioimmunoassay was developed for determining locust vitellogenin content, with a lower detection limit of 1 ng. [3h]propionyl-vitellogenin binds completely to rabbit anti-vitellogenin (locust) and can be completely competed out by locust v ... | 1983 | 6654032 |
| the positional coding system in the early eye rudiment of xenopus laevis, and its modification after grafting operations. | in a series of xenopus embryos, 60-90 degrees sectors at various positions distributed around the eye rudiment were replaced with sectors grafted from the opposite position in the rudiment on the same side of the head of a donor. the majority of the operations were carried out before stage 28 (nieuwkoop & faber, 1956), and many before stage 26. the patterns of retinotectal connectivity which then developed were assayed electrophysiologically soon after metamorphosis. the visuotectal maps were fr ... | 1983 | 6655437 |
| the distribution of small ions during the early development of xenopus laevis and ambystoma mexicanum embryos. | the free ion concentrations of na+, k+ and cl- have been measured in the cells and intercellular spaces of developing amphibian embryos using ion-sensitive microelectrodes. ca2+, h+ and buffering capacity have also been measured in the intercellular spaces. the free intracellular na+ and k+ concentrations in the early cleavage stages remain approximately constant at 21 mm and 90 mm respectively. the free intracellular cl- concentration, approximately 60 mm during the egg to 4-cell stage, falls d ... | 1983 | 6655587 |
| organization of the noncontiguous promoter components of adenovirus vai rna gene is strikingly similar to that of eucaryotic trna genes. | the intragenic transcriptional control region (internal promoter) of the adenovirus type 2 vai rna gene was mutated by deletion, insertion, and substitution of dna sequences at the plasmid level. the mutant plasmids were assayed for in vitro transcriptional activity by using hela cell extracts. the mutant clones with substitution or insertion of dna sequences or both between nucleotides +18 and +53 of the vai rna gene were all transcriptionally active, although to various extents. substitution o ... | 1983 | 6656762 |
| toxic and teratogenic effects of chemical class fractions of a coal-gasification electrostatic precipitator tar. | dimethyl sulfoxide slurries of a coal gasifier electrostatic precipitator tar and its chemical class fractions were assayed for their toxicity and teratogenicity using early embryos of the frog xenopus laevis. of the 5 tar fractions the ether-soluble base and polyaromatic were found to be the most teratogenic and the ether-soluble acid and ether-soluble base were the most toxic. the teratogenic effects of the raw tar suggest synergism. the toxic effects to newly metamorphosed froglets is 1-2 ord ... | 1983 | 6658803 |
| androgen and gonadotropin effects on male mate calls in south african clawed frogs, xenopus laevis. | mate calling is a prominent reproductive behavior of male south african clawed frogs. calls consist of alternating slow- and fast-amplitude-modulated trills. each trill is made up of a series of clicks. the effects of administration of exogenous gonadotropin and androgen on mate calling were studied in male xenopus laevis. males were paired with unreceptive female frogs to elicit maximal calling. the amount of time each animal spent calling during the testing period, the peak fundamental frequen ... | 1983 | 6662518 |
| the interval of the cytoplasmic cycle observed in non-nucleate egg fragments is longer than that of the cleavage cycle in normal eggs of xenopus laevis. | non-nucleate fragments of animal eggs are known to show a cyclic change in rigidity similar to the change observed in the cleavage of normal eggs. the interval of cyclic change was compared with that of the cleavage cycle in xenopus eggs. procedures employed by both hara and co-workers and sakai & kubota to obtain non-nucleate fragments were carefully repeated. non-nucleate fragments produced by either of those procedures had a longer duration of cycle than the normal cleavage cycle (about 30%). ... | 1983 | 6662856 |
| dorsalization and neural induction: properties of the organizer in xenopus laevis. | we have studied the action of the organizer in xenopus laevis using grafts labelled with horseradish peroxidase (hrp). orthotropic grafts of the dorsal marginal zone (the organizer) from an hrp-labelled embryo into an unlabelled host showed that this region contributes to the anterior archenteron wall, to the entire craniocaudal extent of the notochord and to a few cells in the somites. little or no contribution was made to the neural tube. orthotopic grafts of the ventral marginal zone (the tis ... | 1983 | 6663230 |
| acetylcholinesterase activity of xenopus laevis oocytes. | the cholinesterase activity of xenopus laevis oocytes was assessed using [3h]acetylcholine in a simple radiometric procedure. the cholinesterase activity of mature (stage v-vl) oocytes was very sensitive to inhibition by the specific acetylcholinesterase inhibitor, bw284-c5l, and relatively insensitive to an inhibitor of non-specific, or butyrylcholinesterase. the km and vmax of the acetylcholinesterase measured in homogenates of oocytes were 312 microm and 4.6 nmol-oocyte 1-h 1, respectively. t ... | 1983 | 6664498 |
| axon number in oculomotor nerves in xenopus: removal of one eye primordium affects both sides. | unilateral removal of one eye primordium from xenopus laevis embryos affects the number of axons in both oculomotor nerves: on the side of the operation, we observed a substantial decrease, and on the contralateral side an increase of over 30%. mechanisms that may be invoked to explain this striking increase are: sprouting, rerouting of axons, decreased death of the motoneurones involved, and abnormal survival of ephemeral axon collaterals. | 1983 | 6664614 |
| the 22 s cylinder particles of xenopus laevis. i. biochemical and electron microscopic characterization. | supernatant fractions obtained after high speed centrifugation (1 h at 100 000 x g) of homogenates from whole ovaries, oocytes as well as from separated nuclei and ooplasms of xenopus laevis contain distinct 22 s particles which have been purified and characterized by sucrose gradient centrifugation, ion exchange chromatography on deae-sephacel and fast protein liquid chromatography (fplc). the purity of the particle fraction has been assessed by electron microscopy as well as one- and two-dimen ... | 1983 | 6667691 |
| the 22 s cylinder particles of xenopus laevis. ii. immunological characterization and localization of their proteins in tissues and cultured cells. | cylinder-shaped particles of 10 nm diameter were isolated from nuclei of xenopus laevis oocytes and purified by sucrose gradient centrifugation and deae-sephacel chromatography. antibodies to protein constituents of these isolated particles were elicited in guinea pigs and examined by immunoblotting and immunoprecipitation techniques as well as by immunofluorescence microscopy. the antibodies reacted with only two out of the 12 constituent polypeptides characteristic for these particles when exa ... | 1983 | 6667692 |
| motility and fertilization capability of mouse and toad (xenopus laevis) chlorpromazine-treated spermatozoa. | | 1983 | 6667751 |
| changes in the ultrastructure of neural tube cells and the notochordal sheath of ultraviolet irradiated xenopus laevis embryos. | | 1983 | 6670436 |
| radioiodination studies of the envelopes from xenopus laevis eggs. | to investigate the molecular basis of the observed morphological and biological characteristics of coelomic egg envelopes (ce), vitelline envelopes (ve), and fertilization envelopes (fe) of xenopus laevis eggs, envelopes were radioiodinated under a variety of conditions: in situ, isolated and intact, or solubilized. the distribution of 125i in envelope components was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. each envelope type displayed unique profiles when iodinated ... | 1983 | 6671992 |
| the external transcribed spacer and preceding region of xenopus borealis rdna: comparison with the corresponding region of xenopus laevis rdna. | we report sequence data from a cloned rdna unit from xenopus borealis, extending leftwards from the 18s gene to overlap a region previously sequenced by r. bach, b. allet and m. crippa (nucleic acids research 9, 5311-5330). comparison with data from other species of xenopus leads to the inference that the transcription initiation site in x.borealis is in the newly sequenced region and not, as was previously thought, in the region sequenced earlier. the x.borealis external transcribed spacer thus ... | 1983 | 6672764 |
| scanning electron microscopical investigation of the larval development and the morphological differentiation of the paraventricular organ (pvo) of the south african clawed toad xenopus laevis daudin. | the development and the differentiation of the surface of the paraventricular organ (pvo) in tadpoles of the south african clawed toad xenopus laevis daudin from stages 46 to 66 and one adult animal was studied by means of light microscopy, scanning and transmission electron microscopy. at the light microscopical level, the pvo is visible from stage 46 on. from stage 48 on the organ is divided into two parts, a narrow rostral one and a more flattened and broad caudal one. from stage 58 on the ro ... | 1983 | 6673388 |
| evidence for structuring of water in growing oocytes: an x-ray microanalysis and nuclear magnetic resonance study. | energy dispersive x-ray microanalysis measured the na, k, cl, p, mg, s and ca contents (mm/kg dry weight) in the nucleus and yolk-free cytoplasm of growing xenopus laevis oocytes quick frozen in the ovary. nuclear magnetic resonance measurements of t2, the transverse relaxation time of water protons, were obtained on small immature oocytes and on large, fully grown oocytes. changes in the nucleus and cytoplasmic content were observed for all elements except for ca. nuclear/cytoplasmic macroscopi ... | 1983 | 6675023 |
| amphibian oocytes respond to heat shock after the induction of meiotic maturation by hormones. | exposure of xenopus laevis oocytes to temperatures above 31 degrees causes a drastic decrease in protein synthesis and a relative increase of a heat shock protein (hsp) of approximate molecular weight of 68,000. a significant increase in the synthesis of hsp is observed after only 5 minutes incubation of oocytes at 35 degrees. oocytes that have suffered heat shock immediately prior to treatment with human chorionic gonadotropin or progesterone can respond by undergoing meiotic maturation almost ... | 1983 | 6679722 |
| nad turnover during early development of xenopus laevis. | the nad pools of xenopus laevis oocytes and early embryos can be radioactively labelled by microinjection of [adenine-3h]nad. this technique is used to study the metabolism of nad in oocytes and during early development. the rate at which nad is degraded in vivo has been monitored by determining the rate of transfer of adenine residues from the nad pool into other nucleotides and polynucleotides. in oocytes, nad turnover is extremely slow, with a half-life of about 400 h. nad turnover increases ... | 1983 | 6681987 |
| application of antimony microelectrodes to intracellular ph monitoring. | some novel studies of the properties of the antimony microelectrode used for intracellular ph measurements are described. first, it is shown that currents in the picoampere range, such as those encountered as leakage in some electrometers, induce important changes in ph sensitivity. the response time of the electrode has also been measured and indicates that the electrode exhibits a rapid time course which would be very useful for dynamic cytoplasmic ph investigations. an example of internal ph ... | 1983 | 6681988 |
| membrane junctions in xenopus eggs: their distribution suggests a role in calcium regulation. | we have observed the presence of membrane junctions formed between the plasma membrane and cortical endoplasmic reticulum of mature, unactivated eggs of xenopus laevis. the parallel, paired membranes of the junction are separated by a 10-mn gap within which electron-dense material is present. this material occurs in patches with an average center-to-center distance of approximately 30 nm. these junctions are rare in immature (but fully grown) oocytes (approximately 2 percent of the plasma membra ... | 1983 | 6682118 |
| pattern formation in amphibian embryos prevented from undergoing the classical "rotation response" to egg activation. | fertile xenopus laevis eggs were immobilized so that they were prevented from undergoing the "rotation response" to activation. many of those unrotated eggs developed through organogenesis, indicating that egg rotation is not a prerequisite for normal early embryogenesis. various aspects of the regulation of pattern formation were analyzed in unrotated eggs: it was discovered that a substantial rearrangement of yolk platelets occurred without affecting subsequent pattern formation. the germ plas ... | 1983 | 6682386 |
| reactions in vitro of the dna polymerase-primase from xenopus laevis eggs. a role for atp in chain elongation. | a form of dna polymerase alpha was purified several thousandfold from a protein extract of xenopus laevis eggs. the enzyme effectively converts, in the presence of ribonucleoside triphosphates, a circular single-stranded phage fd dna template into a double-stranded dna form and, therefore, must be associated with a dna primase. we first show by gel electrophoresis in the presence of sodium dodecyl sulfate that both enzymatic activities, dna polymerase and primase, most probably reside on a great ... | 1983 | 6684549 |
| changes in nucleotide-binding proteins during oocyte maturation in xenopus laevis. | photoaffinity nucleotide analogs of atp and gtp have been used to investigate the purine nucleotide-binding proteins of xenopus laevis oocytes. these analogs label xenopus oocyte supernatant proteins in a highly specific manner. the pattern of proteins labeled with these analogs was determined by polyacrylamide gel electrophoresis. a number of changes in this pattern were observed during the time course of progesterone-stimulated maturation in vitro. if one alters the dynamic balance of phosphat ... | 1983 | 6684605 |
| axis determination in eggs of xenopus laevis: a critical period before first cleavage, identified by the common effects of cold, pressure and ultraviolet irradiation. | exposure of eggs of xenopus laevis to a temperature of 1.0 degree c for 4 min or a pressure of 8000 psi for 5 min in a critical period before first cleavage results in embryos exhibiting a reduction and loss of structures of the body axis. the deficiencies occur in a craniocaudal progression which is dose dependent. in the extreme, totally axis-deficient embryos with radial symmetry are formed. maximum sensitivity to cold and pressure occurs at 0.6 of the time from fertilization to first cleavag ... | 1983 | 6684607 |
| experimental evidence for the accumulation of egg pigment in the brain cavities of xenopus tadpoles. | the origin and fate of darkly pigmented clusters of cells that float freely in the brain cavities of the tadpoles of xenopus laevis have been experimentally investigated. the results point to the conclusion that the clusters are the sites of egg pigment accumulation, which remain within the brain cavities or at its walls until metamorphosis. | 1983 | 6684673 |
| nested control regions promote xenopus ribosomal rna synthesis by rna polymerase i. | the dna regions required for accurate initiation by rna polymerase 1 on the ribosomal rna genes of xenopus laevis consist of at least two domains within a 150 bp segment adjoining the initiation site. a region of only 13 nucleotides (from -7 to +6) appears sufficient to specify accurate and efficient initiation when various 5' and 3' deletion mutants are injected into oocyte nuclei. in contrast, a 10-fold larger region (from -142 to +6) is required for maximal synthesis when deletion mutants are ... | 1983 | 6684995 |
| histone gene expression in early development of xenopus laevis. analysis of histone mrna in oocytes and embryos by blot-hybridization and cell-free translation. | this study comprises the hybridization analysis of electrophoretically separated histone mrnas from oocytes and embryos of xenopus laevis, and analysis of in vitro translation products of these mrnas on polyacrylamide gels containing sodium dodecyl sulfate (sds) or triton x-100. in oocytes and embryos up to the tailbud stage, four types of mrnas complementary to histone h2b dna and two complementary to histone h4 dna can be discriminated by their different electrophoretic mobilities on polyacryl ... | 1983 | 6685077 |
| further analysis of the effect of ultra-violet irradiation on the formation of the germ line in xenopus laevis. | ultra-violet (u.v.) irradiation of the vegetal pole of newly fertilized eggs has three documented effects: reduction of primordial germ cells (pgcs), cytological damage to the vegetal hemisphere and disruption of the normal mechanism by which the vegetal yolk mass induces the formation of the dorsal axis of the embryo. in this study, we find that 90 degrees rotation of the egg for various periods after irradiation rescues the dorsal axial structures but does not restore the number of pgcs found ... | 1983 | 6685167 |
| neural tube (canal) morphogenesis in notochordless amphibian (xenopus laevis) embryos. | neural tube (canal) morphogenesis was examined in embryos which exhibited notochord defects. embryos which displayed a range of notochord defects were produced by either ultraviolet irradiation or cold shock treatments. both treatments produced similar results. the neural canal appeared normal in morphology and internal ciliation in many of the embryos which contained severe notochord defects. | 1983 | 6686677 |
| replication, methylation, and expression of x laevis globin genes injected into fertilized xenopus eggs. | in the south african clawed toad, xenopus laevis, the tadpole alpha-globin gene (alpha t1) and the major adult alpha- and beta-globin genes (alpha 1 and beta 1) are linked in the genome in the order alpha t1-alpha 1-beta 1. we show that cloned dna fragments containing the xenopus globin genes are replicated after injection into newly fertilized xenopus eggs, reaching a maximal copy number at gastrulation. the dna initially replicates as supercoils, but later it is found in a high-molecular-weigh ... | 1983 | 6686679 |
| cortex and plasma membrane proteins of xenopus laevis oocytes. | the disposition of proteins in the plasma membrane and cortex of metaphase-arrested, shed oocytes of xenopus laevis has been studied. extraction at low ionic strengths or high ph reduces the number of identifiable bands seen on sds-polyacrylamide gel electropherograms. after exposure to high ph the number of bands decreases approximately one half from about 25. bands iii (mw 115ooo) and vii2 (mw 27ooo) are most pronounced amongst the surviving bands. band vii2 can be labeled by the non-penetrati ... | 1983 | 6686805 |
| the nucleotide sequence of the mrna encoding a tadpole beta-globin polypeptide of xenopus laevis. | we have determined the nucleotide sequence of a cloned cdna derived from the mrna encoding an abundant xenopus laevis tadpole beta-globin polypeptide. the cloned sequence contains the entire coding region of the mrna as well as most of its 5'- and 3' -noncoding regions. the complete amino acid sequence of the protein has been deduced. comparison of this sequence with that of the major adult beta-globin polypeptide of x. laevis shows that the two gene products are highly diverged from each other, ... | 1983 | 6688076 |
| synthesis and characterization of a dna complementary to xenopus laevis albumin mrna. | albumin complementary dna (cdna) was transcribed from purified albumin mrna from the liver of xenopus laevis. the resultant cdna was an almost full length copy as defined by denaturing gel electrophoresis; was hybridized specifically to albumin mrna with pseudo-first-order reaction kinetics and the mrna . cdna hybrid exhibited a sharp melting profile with a tm of 83 degrees c. the identity of the cdna was confirmed by gel electrophoresis following hybridization-arrested translation. | 1983 | 6688290 |
| differential gene expression in the gastrula of xenopus laevis. | a modified cloning method designed to produce differential complementary dna libraries permits the isolation of sequences that are present in the rna population of any developmental stage or tissue, but are not present or are much less abundant in another stage or tissue. selective complementary dna cloning is especially useful when the differentially expressed rna's are of low to moderate abundance in the cells in which they occur. a class of cytoplasmic polyadenylated rna's differentially expr ... | 1983 | 6688681 |
| cyclic cytoplasmic activity of non-nucleate egg fragments of xenopus controls the morphology of injected sperms. | triton x-100-treated sperms were injected into non-nucleate egg fragments of xenopus laevis to determine whether the structure of the injected sperm nucleus is affected by the cyclic activity of the cytoplasm. swollen vesicular nuclei were very frequently observed when the sperms were injected and incubated during the 'rounding-up' phase of the recipient fragment, whereas no such structures were found when they were incubated during the 'relaxing' phase. | 1983 | 6688810 |
| a novel peptide designated pyla and its precursor as predicted from cloned mrna of xenopus laevis skin. | a variety of peptides closely related to mammalian hormones and neurotransmitters are secreted from amphibian skin. using cdna clones of mrna isolated from skin of xenopus laevis, we have been searching for precursors of some of these constituents. here we present the sequences of parts of cloned mrnas which code for precursors of a novel peptide. in the predicted polypeptides, pairs of basic residues flank a sequence of 25 amino acids terminating with glycine, the signal for the formation of a ... | 1983 | 6688991 |
| evidence for a functional role of the cytoskeleton in determination of the dorsoventral axis in xenopus laevis eggs. | a normal table of events of the first cleavage period in the fertilized egg (cf. gerhart, 1980) has been completed (cf. table i) by studying external and internal features. through a cytological study of eggs fixed after video time-lapse observation such features can directly be correlated and it has been shown that the first postfertilization wave (pfw) reflects spermaster growth, which causes rearrangements of animal yolk material. this may, in conjunction with the interaction of the spermaste ... | 1983 | 6689175 |
| effects of polyamines on the first division cycle of xenopus laevis eggs. | the involvement of polyamines in cytokinesis has been examined in eggs of the amphibian x. laevis. microinjection of spermine or spermidine into unfertilized eggs induced a shortening of the first division cycle and early formation of cleavage-like constrictions. eggs were activated by injection and developed furrows about 45 min later, whereas the first division normally occurred around 120 min after activation. in terms of concentration, spermine was slightly more effective than spermidine, bu ... | 1984 | 6692860 |
| pattern regulation in defect embryos of xenopus laevis. | defect embryos of 24 series were prepared by removing increasing numbers of blastomeres from an 8-cell embryo of xenopus laevis. they were cultured and their development was examined macroscopically when controls reached a tailbud stage or later. results show that most of defect embryos of 12 series develop normally, and some of them become normal frogs. each of these defect embryos contain at least two animal blastomeres, one dorsal, and one ventral blastomere of the vegetal hemisphere. this su ... | 1984 | 6692985 |
| biochemical and histochemical aspects of acetylcholinesterase development in the larval cns of xenopus laevis. | | 1984 | 6697348 |
| comparison by electrophoresis of proteins characteristic of the lateral line and skin of xenopus laevis. | in experiments aimed at determining acousticolateralis marker proteins, fractions of lateral-line organs and skin of xenopus laevis were analyzed by one- and two-dimensional polyacrylamide-gel electrophoresis. a protein fraction of approximately 44k mol. wt (k = 1000 daltons) and isoelectric ph 6.3, consisting of at least two components, was enhanced in lateral-line neuromast tissue (containing hair cells) and was decreased in tactile organs and skin (lacking hair cells). this "neuromast-marker- ... | 1984 | 6697690 |
| isolated clusters of paired tandemly repeated sequences in the xenopus laevis genome. | there exist in the xenopus laevis genome clusters of tandemly repeated dna sequences, consisting of two types of 393-base-pair repeating unit. each such cluster contains several units of one of these paired tandem repeats (ptr-1), followed by several units of the other repeat (ptr-2). the number of repeats of each type is variable from cluster to cluster and averages about seven of each type per cluster. every cluster has ca. 1,000 base pairs of common left flanking sequence (adjacent to the ptr ... | 1984 | 6700590 |
| induction of the ipsilateral retinothalamic projection in xenopus laevis by thyroxine. | hormones are important in the development of behaviour and there is now abundant evidence that they also affect the morphological development of the nervous system. in principle, hormones could act by inducing new patterns of connectivity between widely separated structures in the nervous system or by influencing local connectivity. most available work documents effects of the latter sort. we present here evidence for the former. our results indicate that thyroxine, the hormone which causes meta ... | 1984 | 6700701 |
| genetic limits of thymic immunosuppression of anti-hapten antibody production in xenopus laevis laevis, the south african clawed toad. | thymic immunosuppression in adult xenopus laevis laevis, the south african clawed toad, is antigen-dependent and antigen-specific, but it is not genetically restricted. in this report, we show that combination in vitro with a thymus from an immunized xenopus laevis laevis can suppress antibody production to a hapten from spleen fragments, if the spleen fragments are derived from a subspecies of xenopus laevis or a species of xenopus which shares the same diploid chromosome number (2n = 36). some ... | 1984 | 6707484 |
| sodium-alanine cotransport in oocytes of xenopus laevis: correlation of alanine and sodium fluxes with potential and current changes. | the sodium-dependent l-alanine transport across the plasma membrane of oocytes of xenopus laevis was studied by means of [14c]-l-alanine, 22na+ and electrophysiological measurements. at fixed sodium concentrations, the dependence of alanine transport on alanine concentration follows michaelis-menten kinetics; at fixed alanine concentrations, the transport varies with sodium concentration with a hill coefficient of 2. in the presence of sodium the uptake of alanine is accompanied by a depolarizat ... | 1984 | 6708092 |
| compact structure of ribosomal chromatin in xenopus laevis. | micrococcal nuclease digestion was used as a tool to study the organization of the ribosomal chromatin in liver, blood and embryo cells of x. laevis. it was found that in liver and blood cells, ribosomal dna is efficiently protected from nuclease attack in comparison to bulk chromatin. although ribosomal chromatin is fragmented in a typical nucleosomal pattern, a considerable portion of ribosomal dna retains a high molecular weight even after extensive digestion. a greater accessibility of the c ... | 1984 | 6709502 |
| pathology of naturally occurring chlamydiosis in african clawed frogs (xenopus laevis). | chlamydiosis was diagnosed in six african clawed frogs (xenopus laevis) from a tank of laboratory-bred frogs experiencing sudden deaths. gross findings were hepatomegaly, distention of the gall bladder, and splenomegaly. hepatic lesions were present in each frog and were characterized by mononuclear cell infiltrates, necrosis of hepatocytes, kupffer's cell proliferation, and sinusoidal fibrin thrombi. cholestasis, hemosiderin-laden kupffer's cells, parenchymal infarction, and multinucleated hepa ... | 1984 | 6710808 |
| the ultrastructural organization of gap junctions between follicle cells and the oocyte in xenopus laevis. | the cellular contact sites between the full-grown oocyte of xenopus laevis and the surface extensions of surrounding follicles cells were analysed by electron microscopy of ultrathin sections, freeze-fracture replicas and critical point-dried specimens. evidence is given for the presence of clusters of intramembranous particles (imps) at the p-face which represent gap junctions in diverse forms. most common are maculae (phi 0.2-0.5 micron) of densely packed imps (phi 12 +/- 2 nm) which represent ... | 1984 | 6714245 |
| nerve disperses preexisting acetylcholine receptor clusters prior to induction of receptor accumulation in xenopus muscle cultures. | we have investigated the sequential changes of acetylcholine receptor (achr) distribution on identified xenopus laevis muscle cells in culture before and after innervation. achrs on muscle cells were stained with tetramethylrhodamine-conjugated alpha-bungarotoxin and the distribution of achr clusters was examined on a fluorescence microscope using an image intensifier. large receptor clusters were identified on muscle cells and their fate was followed afterward. in muscle cells cultured without ... | 1984 | 6714520 |
| in vivo development of cholinesterase at a neuromuscular junction in the absence of motor activity in xenopus laevis. | embryos of xenopus laevis were selected prior to the onset of innervation and were raised for 2 days in the anaesthetic tricaine methanesulphonate (200 micrograms/ml). the gross development of these tricaine-reared animals appeared normal despite the absence of spontaneous motor activity and the lack of motor responses to prodding with a pin. motor activity quickly appeared when the anaesthetic was withdrawn. intracellular recording from the myotomes of intact, tricaine-maintained animals failed ... | 1984 | 6716295 |
| differential expression of the xenopus laevis tadpole and adult beta-globin genes when injected into fertilized xenopus laevis eggs. | xenopus laevis tadpole and adult beta-globin genes were injected into fertilized x. laevis eggs. both injected genes replicated and were retained in the developing embryos with equal efficiency. transcripts of the injected adult gene were detectable at gastrulation and reached a maximum level shortly thereafter. in contrast, transcripts of the injected tadpole gene were not detected until much later stages of development. the level of expression of both the injected genes was low compared with t ... | 1984 | 6717434 |
| enhancer-like properties of the 60/81 bp elements in the ribosomal gene spacer of xenopus laevis. | the spacer region of the xenopus laevis ribosomal gene contains blocks of repetitive sequence elements that are 60 or 81 bp long. these 60/81 bp elements function as enhancer elements for the rna polymerase i promoter at the 5' end of the gene. an rna polymerase i promoter adjacent to a block of 60/81 bp elements is always dominant over a promoter on a second plasmid when both are coinjected into oocyte nuclei. if two promoters are placed on the same plasmid containing enhancers, both promoters ... | 1984 | 6722873 |
| inhibitor of ribosomal rna synthesis in xenopus laevis embryos. vii. inhibition of 40s pre-rrna synthesis in xenopus neurula cells. | a fraction containing acid-soluble materials (pca-extract) from xenopus early blastulae preferentially inhibits the incorporation of [3h]uridine into 18s and 28s rrna in xenopus neurula cells. pulse- laneling experiments revealed that whereas tubercidin, a known inhibitor of rrna processing, produced a marked accumulation of the label in 40s pre-rrna, xenopus inhibitor suppressed labeling of the pre-rrna. when tubercidin was added to cells whose activity for rrna synthesis had been lowered by th ... | 1984 | 6722909 |
| protein synthesis in dorsal and ventral regions of xenopus laevis embryos in relation to dorsal and ventral differentiation. | two-dimensional gel electrophoresis has been used to analyze protein synthesis in dorsal and ventral regions in embryonic stages of xenopus laevis. proteins specific either to dorsal or to ventral regions are synthesized for the first time at gastrulation, concomitant with morphological differentiation. the reliability of these proteins as markers of dorsal and ventral differentiation was tested by examining their synthesis in uv-irradiated embryos, which have severely reduced capacity for dorsa ... | 1984 | 6724133 |
| stimulation of dna synthesis by microinjection of diadenosine 5',5''-p1, p4-tetraphosphate (ap4a) into xenopus laevis oocytes. | ap4a stimulated dna synthesis when injected into oocytes. the stimulation was dramatically increased when an exogenous template was microinjected. aphidicolin inhibited the effect of ap4a, supporting a role of dna polymerase alpha in this process. no stimulation by ap4a was observed in microinjected eggs, nor atp was able to mimic the in vivo effect of ap4a. besides microinjected activated dna, the stimulation by ap4a of dna synthesis was also observed with poly dt and poly dt-poly da as templat ... | 1984 | 6724135 |