| the enhancers and promoters of the xenopus laevis ribosomal spacer are associated with histones upon active transcription of the ribosomal genes. | the presence of histones on the enhancer-promoter region of the x.laevis ribosomal spacer has been studied in embryos at stage 40, where the ribosomal genes are actively transcribed. isolated tadpole nuclei were either fixed with formaldehyde or irradiated with uv laser to crosslink histones to dna. the purified protein-dna complexes were immunoprecipitated with antibodies to the histones h1, h2a and h4 and the dna fragments carrying the respective histones were analyzed for the presence of spac ... | 1990 | 2243781 |
| regeneration of optic fibres through the chiasma in xenopus laevis tadpoles. | the path through the chiasma followed by regenerating optic nerve fibres in xenopus tadpoles was studied at light- and electron-microscopic levels, and with horseradish peroxidase as a fibre label. over the period (5-10 days) in which regenerating fibres reach and cross the chiasma, they did not follow residual deep fibres through the chiasma, nor were they associated with the trail of degeneration in the chiasma which represented the remains of the deeper (older) parts of the original projectio ... | 1990 | 2244690 |
| mechanism of polyamine spermidine uptake by xenopus laevis oocytes. | in this study, the mechanisms of polyamine spermidine (spd) uptake were investigated in xenopus laevis oocytes. spd uptake followed a sigmoidal kinetics with [s]90/[s]10 = 3 microm and hill interaction coefficient (n) = 2. the order of magnitude of uptake and efflux was similar (t1/2 = 45 min). the equilibrium potential for spd, calculated by nenrst equation, was 90.78 mv. free energy change for the uptake (delta g) was found to be 2.31 kcal/mole of spd. during efflux, spd was not converted into ... | 1990 | 2241986 |
| serotonin-like immunoreactivity in the retina of the clawed frog xenopus laevis. | using an antiserum directed against serotonin, we have studied the morphology and distribution of serotonin-containing and serotonin-accumulating neurons in the retina of xenopus laevis. endogenous serotonin-like immunoreactivity was found in two classes of amacrine cell, one class of bipolar cell and a few centrifugal fibres. kainic acid-induced depletion of serotonin, under various conditions, enabled us to determine the distribution of stained bipolars, amacrine cells and centrifugal fibres w ... | 1990 | 2243244 |
| nucleotide sequence and 40 s subunit assembly of xenopus laevis ribosomal protein s22. | we have isolated and determined the nucleotide sequence of a cdna encoding xenopus laevis ribosomal protein s22. a synthetic s22 mrna derived from this cdna directs the synthesis of an in vitro translation product that is indistinguishable from s22 purified from xenopus ovarian ribosomes. in vitro translated s22 is assembled into 40 s subunits when microinjected into the cytoplasm of oocytes. analysis of the derived amino acid sequence indicates that xenopus s22 is homologous to escherichia coli ... | 1990 | 2246230 |
| xenopus y-box transcription factors: molecular cloning, functional analysis and developmental regulation. | we describe the cloning and characterization of two cdnas from xenopus laevis that encode sequence-specific dna binding proteins called frg y1 and frg y2 (frog y-box proteins 1 and 2). during oogenesis and embryogenesis, the genes encoding these proteins are differentially expressed. frg y1 mrna is present in oocytes, embryos, and all adult tissues examined, whereas frg y2 mrna is found only in testis and immature oocytes. the frg y1 and frg y2 proteins are shown to stimulate transcription from ... | 1990 | 2247479 |
| changes of egg retinoids during the development of xenopus laevis. | the changes of egg retinoids during the development of xenopus laevis were investigated by high-performance liquid chromatography (hplc). all-trans retinal and 3-dehydroretinal are endogenous in the egg and are distributed to both the eyes and the ventral portion of the larval body. these retinals are converted to all-trans retinyl palmitate and 3-dehydroretinyl palmitate during the development up to stage 46. 11-cis retinal and 3-dehydroretinal can be detected after stage 40 in the eyes but not ... | 1990 | 2247949 |
| structure of an invertebrate gene encoding cytoplasmic intermediate filament (if) proteins: implications for the origin and the diversification of if proteins. | the structure of the single gene encoding the cytoplasmic intermediate filament (if) proteins in non-neuronal cells of the gastropod helix aspersa is described. genomic and cdna sequences show that the gene is composed of 10 introns and 11 exons, spanning greater than 60 kb of dna. alternative rna processing accounts for two mrna families which encode two if proteins differing only in their c-terminal sequence. the intron/exon organization of the helix rod domain is identical to that of the vert ... | 1990 | 2249666 |
| gene structure of nuclear lamin liii of xenopus laevis; a model for the evolution of if proteins from a lamin-like ancestor. | the lamin liii gene of xenopus laevis has been characterized. the gene is duplicated in the xenopus genome. the transcribed region spreads over 22 kb of genomic dna encoding 12 exons. two alternatively spliced mrnas are observed which encode liii isoforms that differ only by the 12 c-terminal amino acids which, however, both contain the caax motif known to be the target of post-translational modifications. the intron pattern of the lamin liii gene is strikingly similar to that of an invertebrate ... | 1990 | 2249665 |
| identification of two types of neurophysins in xenopus laevis neurointermediate pituitary homologous to mammalian msel- and vldv-neurophysins. | xenopus laevis neurophysins have been purified from neurointermediate pituitaries through high-pressure reverse-phase liquid chromatography and their n-terminal amino acid sequences have been determined by microsequencing. two types of neurophysins, corresponding to mammalian msel- and vldv-neurophysins, have been distinguished. a strong homology exists between neurophysins of xenopus (pipidae), frog (ranidae) and toad (bufonidae). xenopus msel-neurophysin, as frog msel-neurophysin, has a high m ... | 1990 | 2250763 |
| argiotoxin-636 blocks effects of n-methyl-d-aspartate on lateral line of xenopus laevis at concentrations which do not alter spontaneous or evoked neural activity. | activity of primary afferent neurons in acousticolateralis organs can be modulated by excitatory amino acids (eaa) and their antagonists, and eaa are among the better candidates for the transmitter(s) between hair cells and afferent neurons. argiotoxin-636 (atx) is a spider venom toxin that is a selective antagonist of the n-methyl-d-aspartate (nmda) subtype of excitatory amino acid receptors in vertebrates. in the present study, the effects of nmda alone and in combination with atx on resting f ... | 1990 | 2250561 |
| direct effects of thymopentin (arg-lys-asp-val-tyr) on cholinergic agonist-induced slow inactivation of nicotinic acetylcholine receptor function. | the effects of thymopentin (tp-5) on the cholinergic agonist-induced inactivation of function (desensitization) of the nicotinic acetylcholine receptor (nachr) were explored using two systems, 1) torpedo californica electroplax nachr reconstituted into phospholipid vesicles and 2) t. californica nachr expressed, in xenopus laevis oocytes, from in vitro synthesized rna transcripts. the pentapeptide did not modify the equilibrium binding of 125i-alpha-bungarotoxin, but toxin rate binding assays in ... | 1990 | 2250665 |
| segregation of fate during cleavage of frog (xenopus laevis) blastomeres. | a detailed fate map of all the progeny derived from each of the blastomeres of the 4- and 8-cell stage south african clawed frog (xenopus laevis) embryo is presented. each "identified" blastomere that results from stereotypic cleavages has a characteristic set of progeny that distinguishes it from the other blastomeres of the embryo. the 4-cell dorsal (d) blastomere is the major progenitor of the stomodeum, cement gland, retina, notochord, head somite, pharynx and liver. the 4-cell ventral (v) b ... | 1990 | 2252221 |
| regulation of nicotinic acetylcholine receptor function by adenine nucleotides. | 1. nicotinic acetylcholine receptors (nachr)4 from bc3h1 cells (which express a skeletal muscle-type receptor) and from torpedo californica electric organ were expressed in xenopus laevis oocytes and studied with a voltage-clamp technique. 2. we found that bath application of atp in the micromolar to millimolar range increased the ach-elicited current in both muscle and electrocyte receptors. the effect of atp increased with successive applications. this "use-dependent" increase in potentiation ... | 1990 | 2253264 |
| physical and immunological characterization of human transcription factor iiia. | human transcription factor iiia (htfiiia), specifically required for transcription of the gene for 5s ribosomal rna has been characterized with respect to some of its physical, immunological and functional properties. tfiiia from hela cells, which selectively binds 5s rna, is a monomer of approximately 35 kda with a stokes' radius of approximately 2.65 nm and a sedimentation coefficient of approximately 2.8 s. these values indicate that the human protein is of rather globular shape and hence div ... | 1990 | 2253613 |
| the incorporation of myo-inositol into phosphatidylinositol derivatives is stimulated during hormone-induced meiotic maturation of amphibian oocytes. | the incorporation of myo-[3h]inositol into phosphatidylinositol and its phosphorylated derivatives was studied by microinjection of the radioactive precursor into xenopus laevis oocytes. induction of meiotic maturation of the oocytes by treatment with either progesterone one or insulin resulted in a significant increase in the incorporation of myo-[3h]inositol into the phospholipid fraction. this increase occurred 3-6 h after hormonal treatment, a time coincident with the start of the breakdown ... | 1990 | 2257883 |
| cell migration in the formation of the pronephric duct in xenopus laevis. | to determine if cell migration is involved in the formation of the pronephric duct in xenopus, we used morphometry, ablation, and videomicroscopy of vitally stained cells to study duct formation. in st 23-24 (nieuwkoop and faber, 1956) embryos, a ridge of cells forms caudal to the pronephric rudiment. the ridge lengthens at approximately the same rate as the embryonic trunk from st 23 to st 31. ablation experiments demonstrated that the ridge constitutes the pronephric duct rudiment (pdr); when ... | 1990 | 2257968 |
| spatial distribution of the capacity to initiate a secondary embryo in the 32-cell embryo of xenopus laevis. | to examine the spatial distribution of dorsal determinants in the early embryos of xenopus laevis, individual cells from the 32-cell embryo were transplanted into the same tier of the ventral side of a synchronous recipient. their abilities to initiate a secondary embryo were measured by the incidence of secondary embryos and by the length of the secondary axis relative to the primary embryo. the ability was found to be localized in all cells (a1, b1, c1, and d1) of the dorsal most column and in ... | 1990 | 2257976 |
| extracts from eggs and oocytes of xenopus laevis differ in their capacities for nuclear assembly and dna replication. | we describe a cell-free extract derived from the oocytes of xenopus laevis. the oocyte extract is capable of decondensing sperm chromatin and of replicating single-stranded dna in a semiconservative, aphidicolin-sensitive manner. in addition, oocyte extract supports the elongation phase of dna synthesis in nuclei that have been preinitiated for replication. all of these properties are shared by previously described egg extracts. however, oocyte extracts differ from egg extracts in two important ... | 1990 | 2258387 |
| metamorphosis alters the response to spinal cord transection in xenopus laevis frogs. | a series of studies has examined the response of the spinal cord to lesions made at various stages prior to and after metamorphic climax in the clawed frog xenopus laevis. complete transections made between nieuwkoop and faber (1956) stages 50 and 62 were followed by gradual recovery of righting and coordinated swimming as animals metamorphosed into juveniles (stage 66). examination of descending axonal projections using horseradish peroxidase (hrp) showed fibers crossing the lesion site and dis ... | 1990 | 2258724 |
| atlantic salmon (salmo salar) serum albumin: cdna sequence, evolution, and tissue expression. | atlantic salmon serum albumin is one of the most abundant proteins in salmon liver, representing 1.6% of all clones in a cdna library made from salmon liver rna. the dna from a number of clones was sequenced to reveal an open reading frame of 1,827 bases encoding a 608-amino-acid protein. the sequenced 5' untranslated region is 69 bases long and the 3' untranslated region contains two putative polyadenylation signals and poly(a) tail. sequence analysis of different clones indicates the presence ... | 1990 | 2261082 |
| expression of ca2+ mobilizing receptors in xenopus oocytes: a tool for receptor characterization. | in order to investigate the molecular characteristics of gastrointestinal hormone receptors, we have expressed their mrnas in xenopus laevis oocytes. xenopus oocytes possess intrinsic muscarinic cholinergic receptors which couple to intracellular ca2+ release. release of intracellular ca2+ was detected by an increase in 45ca2+ release from preloaded oocytes or by using the ca2+-sensitive fluorescent dye fura-2. similarly, cholecystokinin (cck) receptors expressed on the surface of oocytes which ... | 1990 | 2262046 |
| the characterization of the tfiiia synthesized in somatic cells of xenopus laevis. | in somatic cells of xenopus, transcription of the tfiiia gene initiates greater than 200 bp upstream from the start site used in oocytes. the resultant mrna encodes a protein, s-tfiiia, that is 22 amino acids longer at its amino terminus than the abundant form of tfiiia in oocytes (o-tfiiia). s-tfiiia binds the 5s rna gene and 5s rna, and both o- and s-tfiiia promote the formation of stable transcription complexes on oocyte-type 5s rna genes in an oocyte nuclear extract. we have not found any fu ... | 1990 | 2253880 |
| mesoderm induction in xenopus laevis distinguishes between the various tgf-beta isoforms. | induction of mesoderm in ectodermal explants of xenopus laevis blastula embryos had previously been shown to respond selectively to tgf-beta 2, with tgf-beta s 1 and 5 having no activity in this assay. as tgf-beta s 1, 2, and 3 are frequently coexpressed in tissues, we wished to examine the activity of tgf-beta 3 relative to that of tgf-beta s 1 and 2 in this assay as well as in other in vitro assays. we report here that when the activity of recombinant tgf-beta 3 is normalized to that of tgf-be ... | 1990 | 2257149 |
| requirement of ets-2 expression for xenopus oocyte maturation. | a molecular clone of the xenopus laevis ets-2 gene was isolated from an oocyte complementary dna library. the amount of messenger rna (mrna) in each oocyte or embryo was almost constant during oogenesis and was maintained until the blastula stage of embryonic development, indicating that the observed 3.2-kilobase transcript is a maternal message. the only normal adult tissue in which ets-2 mrna was detected was the ovary. injection of antisense oligonucleotides homologous to the ets-2 sequence i ... | 1990 | 2255913 |
| complete assignment of the 1h nmr spectrum and secondary structure of the dna binding domain of gal4. | complete 1h nmr resonance assignments are presented for the cysteine rich region of the dna binding domain of the yeast transcriptional activator gal4. the protein contains short helical regions between asp-12 and leu-19 and between lys-30 and trp-36. it is clearly distinct from the c2h2 class of zinc finger protein typified by the xenopus laevis transcription factor (tf)iiia. we also find that the first sp(x)(x) sequence, a recently proposed dna binding motif (residues 41 to 44), appears to be ... | 1990 | 2265711 |
| the cu,zn superoxide dismutase isoenzymes of xenopus laevis: purification, identification of a heterodimer and differential heat sensitivity. | the three cu,zn superoxide dismutase electromorphs of the amphibian xenopus laevis were purified by an original procedure. n-terminal sequence analysis demonstrated that they are two different homodimers (aa and bb) and a hybrid heterodimer (ab), arising from the co-expression of duplicated genes. the three forms have the same pi, same enzyme activity and epr spectra, but different heat-sensitivity, form bb being more resistant than form aa, with form ab showing intermediate sensitivity. thermos ... | 1990 | 2268321 |
| the primary structure of rat ribosomal protein s3. | the amino acid sequence of rat ribosomal protein s3, which has been reported to form part of the binding site for initiation factors, was deduced from the sequence of nucleotides in a recombinant cdna. ribosomal protein s3 contains 243 amino acids and has a molecular weight of 26,643. rat s3 and xenopus laevis ribosomal protein s1 are homologous: there are 62 identities in 63 consecutive residues in the carboxyl-terminal amino acid acid sequence of rat s3 and in a partial sequence of xenopus s1. ... | 1990 | 2275563 |
| sensory neglect in a frog: evidence for early evolution of attentional processes in vertebrates. | mammalian-like 'sensory neglect' phenomena were elicited in xenopus laevis by unilateral telencephalic lesion: after damage of the caudal striatum response rate to contralateral water waves was significantly lower than to ipsilateral ones. response accuracy, however, was not affected. within 6-8 weeks, animals recovered from neglect of unilateral stimuli; but simultaneous bilateral stimulation revealed an enduring neglect of contralateral stimuli. latencies during acute neglect were significantl ... | 1990 | 2271937 |
| patterns of protein synthesis during xenopus oocyte maturation differ according to the type of stimulation. | we examined the qualitative patterns of protein synthesis in fully grown prophase-blocked oocytes of xenopus laevis and after meiosis reinitiation accompanying maturation of the oocytes. newly synthesized proteins labelled with [35s]methionine were run on isoelectric focusing gels and further separated in the second dimension on sds-polyacrylamide slab gels. three types of maturation inducer were compared: progesterone, considered as the natural inducer of xenopus oocyte maturation, hcg (human c ... | 1990 | 2271996 |
| a correlation of thyroid hormone receptor gene expression with amphibian metamorphosis. | the expression of the thyroid hormone (th) receptor genes alpha (tr alpha) and beta (tr beta) in xenopus laevis begins after the embryo hatches. the tr alpha mrna increases throughout the premetamorphosis stage of tadpole development, is maximal by prometamorphosis, and falls after climax of metamorphosis to a lower level in frogs. the tr beta mrna is barely detectable during premetamorphosis. in synchrony with the onset of endogenous th synthesis by the thyroid gland (prometamorphosis), the lev ... | 1990 | 2276625 |
| thyroid hormone regulates type i deiodinase messenger rna in rat liver. | conversion of the prohormone t4 to the active hormone t3 is catalyzed by 5'-deiodinases, enzymes that have not been purified. previous studies have shown that modulating thyroid status results in changes in type i deiodinase activity in the rat liver. we have quantitated type i deiodinase mrna in liver by an expression assay using xenopus laevis oocytes. we report here that changes in enzyme activity correlate closely with changes in levels of the mrna for this enzyme, indicating that thyroid ho ... | 1990 | 2274056 |
| bifurcation of the amphibian embryo's axis: analysis of variation in response to egg centrifugation. | xenopus embryos have been reported to vary widely in their developmental response to centrifugation. variation in response to centrifugation, as measured by embryo survival and twinning of axial structures, was monitored different spawnings of xenopus laevis eggs. a convenient method for quantifying the egg cytoplasm's potential for displacement in a centrifugal field was employed. it involved testing small batches of eggs from each spawn under carefully controlled conditions for displacement of ... | 1990 | 2288862 |
| effects of relaxation of mechanical tensions upon the early morphogenesis of xenopus laevis embryos. | in xenopus laevis embryos at the early gastrula stage, circumferential tensions of embryonic ectoderm were relaxed by making sagittal or transversal slits in the ventral parts of embryos and inserting into surgical cuts the sectors of homologous tissue from same-stage embryos. changes in tensile patterns were controlled by measuring cell surface angles. immediate decreases in surface cell wall tension as related to transversal wall tension were registered. within minutes of the operation, the lo ... | 1990 | 2288863 |
| 28s ribosomal rna in xenopus borealis: gene sequence and differences from xenopus laevis sequence. | | 1990 | 2276499 |
| transcription of endogenous and injected cytoskeletal actin genes during early embryonic development in xenopus laevis. | the transcriptional regulation of a cytoskeletal actin gene during xenopus laevis embryonic development has been investigated. new transcripts of this gene begin to accumulate at approximately the mid-gastrula stage, between 12 and 16 hours after fertilization, replenishing maternal supplies of this transcript. to study the molecular processes which act to determine the timing of transcriptional activation of this gene, a gene-injection assay was devised, utilizing a cloned copy of the gene whic ... | 1990 | 2283001 |
| two different mrnas coding for identical elongation factor 1 alpha (ef-1 alpha) polypeptides in xenopus laevis embryos. | two related but clearly different cdna clones corresponding to elongation factor 1 alpha (ef-1 alpha) mrnas were isolated from a xenopus laevis gastrula-stage library. whereas the nucleotide sequences of these two cdnas differ within the coding region at 49 out of 1386 positions (3.5%), the derived amino acid sequences are completely identical, thereby indicating a substantial evolutionary constraint on this translation factor. southern-blot analysis of genomic dna suggests that, besides the two ... | 1990 | 2283000 |
| intercellular communication is cell cycle modulated during early xenopus laevis development. | we investigated intercellular communication during the seventh and tenth cell cycles of xenopus laevis development using microinjection of lucifer yellow and fitc-dextran as well as freeze-fracture electron microscopy. we found that gap junction-mediated dye coupling visualized using lucifer yellow was strongly cell cycle modulated in the tenth cell cycle. cytoplasmic bridge-mediated dye coupling visualized via fitc-dextran was also, of course, cell cycle modulated. the basis of cell cycle-modul ... | 1990 | 2295681 |
| isolation and characterization of cdna clones for the gamma subunit of xenopus fibrinogen, the product of a coordinately regulated gene family. | fibrinogen, the major structural protein involved in blood coagulation, is synthesized and secreted by the liver. in the frog xenopus laevis, fibrinogen production is dramatically induced by glucocorticoids. the hormonal stimulation requires synthesis of three separate subunits, designated a alpha, b beta, and gamma. for investigation of the molecular mechanisms underlying this coordinate induction, we have isolated cdna clones for the subunits of xenopus fibrinogen. in this communication we des ... | 1990 | 2289632 |
| identification of a novel transforming growth factor-beta (tgf-beta 5) mrna in xenopus laevis. | a novel transforming growth factor-beta (tgf-beta) mrna of about 3.0 kilobases, which encodes a putative protein of 382 amino acids, has been identified in amphibians by cdna cloning. this mrna, which we designate as tgf-beta 5, is developmentally regulated and highly expressed beginning at early neurula (stage 14) and in many adult tissues in xenopus laevis. following the first methionine, the putative precursor protein has a hydrophobic region, approximately 22 amino acids long, which probably ... | 1990 | 2295601 |
| retinal detachment prevents normal assembly of disk membranes in vitro. | the effects of retinal detachment upon disk membrane assembly in rod outer segments were assessed in xenopus laevis retinas that had been maintained in eyecup cultures for up to 4 days. in these cultures, assembly of disk membranes occurred at a normal rate in regions of the retina that remained attached to the retinal pigment epithelium. in regions of the retina that were detached from the pigment epithelium, the assembly of new disk membranes either was abnormal or was inhibited. this result c ... | 1990 | 2298531 |
| how is the flagellar length of mature sperm determined? ii. comparison of tubulin synthesis in spermatids between newt and xenopus in vitro. | in order to elucidate mechanisms that control flagellar length of mature sperm, we studied in synchronous cell suspension cultures flagellar growth, tubulin pool, and tubulin synthesis in round spermatids of xenopus laevis and the newt cynops pyrrhogaster. the average final length of flagella in xenopus round spermatids was 35 mum, almost the same length as that in mature sperm, whereas in the newt round spermatids, the length was 210 mum, almost half that of mature sperm. kinetics of flagellar ... | 1990 | 2298244 |
| dermal glands of xenopus laevis contain a polypeptide with a highly repetitive amino acid sequence. | mature dermal glands of xenopus laevis contain storage granules with a characteristic ellipsoid shape. these granules contain, as a minor component, a heat-stable, acidic polypeptide with an apparent molecular mass of 75 kda. using antibodies against this protein, positive clones were isolated from a cdna expression library prepared from skin of x. laevis. one of the cloned cdnas encodes a pre-protein with a typical signal sequence and a mature part of 396 amino acids. the protein contains 33 co ... | 1990 | 2298293 |
| experimental reorganization in the alar plate of the clawed toad, xenopus laevis. i. quantitative and qualitative effects of embryonic otocyst extirpation. | the area octavolateralis and the lateral line projections were examined in larval and postmetamorphic clawed toads, which had one otic vesicle removed at embryonic stage 38 (ref. 20). premetamorphic tadpoles show a smaller octavolateral area on the operated side as compared to the contralateral control side. this area is in postmetamorphic toadlets significantly reduced as compared to the control side. the largest cells of the magnocellular vestibular nucleus show no significant difference in si ... | 1990 | 2297887 |
| circadian regulation of melatonin in the retina of xenopus laevis: limitation by serotonin availability. | treatments expected to increase retinal serotonin levels were found to stimulate melatonin production by cultured eyecups from xenopus laevis. the monoamine oxidase inhibitor pargyline (100 microm) caused a sixfold increase in melatonin release, and the serotonin precursor 5-hydroxy-l-tryptophan (100 microm) caused a 70-fold increase. both acted synergistically with eserine, an inhibitor of melatonin deacetylation in the retina. the effect of 5-hydroxytryptophan was dose dependent, with effects ... | 1990 | 2299362 |
| evidence that xenopus laevis contains two different nonallelic insulin-like growth factor-i genes. | using the polymerase chain reaction (pcr), we have amplified and characterized partial nucleotide sequences of two distinct insulin-like growth factor-i genes (designated igf-i' and igf-i") from the amphibian, xenopus laevis. the amplified fragments encoded much of the coding region of the mature peptide (exon iii in mammalian igf-i genes), and exhibited 93% similarity to each other, and 68-82% similarity to mammalian igf-i amino acid sequences. southern blot analysis using genomic dna from a ho ... | 1990 | 2302204 |
| regulation of carbon flux from amino acids into sugar phosphates in xenopus embryos. | xenopus laevis oocytes and embryos are glycogenic cells, metabolizing sugar phosphates into glycogen. these cells have very low pyruvate kinase activity in vivo and, consequently, make little pyruvate and lactate through glycolysis. nevertheless, oocytes and embryos do contain significant pyruvate and lactate levels. to determine the source of carbon for sugar phosphates and pyruvate, 14c-labeled intermediary metabolites were injected into fertilized eggs and their metabolism examined by thin-la ... | 1990 | 2307283 |
| gonadal hormones inhibit the induction of metamorphosis by thyroid hormones in xenopus laevis tadpoles in vivo, but not in vitro. | although the major hormones controlling amphibian metamorphosis are those of the thyroid, other hormones, notably prolactin and the adrenal steroids, modulate the effects of thyroid hormones (th). some authors report that the gonadal steroids stimulate the metamorphic actions of th whereas others report inhibition. the aims of the present study were to determine the effects of gonadal steroids on th-induced metamorphosis in xenopus laevis and to determine the site of action of these steroids. in ... | 1990 | 2307343 |
| intracellular and surface acetylcholine receptors during the normal development of a frog skeletal muscle. | 125i-alpha-bungarotoxin (125i-alpha bt) was used to measure the pool sizes of surface and intracellular acetylcholine receptors (achrs) in the myotomal muscle of xenopus laevis over a developmental period (stages 23-48; 1.03-7.5 d) which ranged from initial to mature stages of neuromuscular synaptogenesis. the surface pool increased progressively throughout development. the intracellular pool increased more slowly and also underwent a transient decrease. linear regression indicated that achrs be ... | 1990 | 2303855 |
| enzymatic and envelope-converting activities of pars recta oviductal fluid from xenopus laevis. | conversion of the coelomic egg envelope to the vitelline envelope of the xenopus laevis egg is known to take place in the pars recta (pr) region of the oviduct. a method for collecting fluid generated from pr cultured in vitro was devised which enhanced the recovery of envelope-converting factors. by the criteria of melting temperature analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, 125i labeling, ferritin binding, and in vitro fertilization assays, the secretions collected ... | 1990 | 2307282 |
| high resolution mapping of xenopus laevis 5s and ribosomal rna genes by em in situ hybridization. | we have developed a modification of in situ hybridization at the electron microscope level that permits simultaneous detection of at least two sequences. probes are labelled with either biotin or aaf and detected with two distinct sizes of colloidal gold. this protocol has been applied to map the positions of xenopus laevis oocyte-type 5s genes relative to ribosomal precursor genes in several independently derived cell lines. the results for the line trxo, which expresses some oocyte 5s rna, ind ... | 1990 | 2307055 |
| point mutation analysis of the xenopus laevis rna polymerase i core promoter. | the core region of the xenopus laevis pre-ribosomal rna promoter was subjected to point mutation analysis. a total of 27 point mutants within a 78 base pair region from -64 to +14, (relative to the start of transcription at +1), were assayed by oocyte microinjection. the results locate the 3' boundary of the core promoter at +4 and the 5' boundary at between -33 and -39 and suggest that this region of the xenopus promoter is generally similar in organisation to mammalian core promoters. in parti ... | 1990 | 2308816 |
| organization of the mitochondrial genome of atlantic cod, gadus morhua. | the mitochondrial dna (mtdna) from the atlantic cod, gadus morhua, was mapped using 11 different restriction enzymes and cloned into plasmid vectors. sequence data obtained from more than 10 kilobases of cod mtdna show that the genome organization, genetic code, and the overall codon usage have been conserved throughout the evolution of vertebrates. comparison of the derived amino acid sequences of proteins encoded by cod mtdna to the ones encoded by xenopus laevis mtdna revealed that the amino ... | 1990 | 2308841 |
| variation and symmetry in the lumbar and thoracic dorsal root ganglion cell populations of newly metamorphosed xenopus laevis. | the sizes of the lumbar and thoracic dorsal root ganglion cell populations in normally developing newly metamorphosed xenopus laevis were measured in order to determine whether these neuron populations have the same characteristics as the hindlimb motoneuron population (i.e., large individual as well as sibling group differences, striking bilateral symmetry, and a rough correspondence between neuron number and body size that suggests some peripheral control of cell number during normal developme ... | 1990 | 2312786 |
| nucleotide sequence and estrogen induction of xenopus laevis 3-hydroxy-3-methylglutaryl-coenzyme a reductase. | we have isolated and sequenced overlapping cdna clones encompassing the entire protein coding region of xenopus laevis 3-hydroxy-3-methylglutaryl-coenzyme a reductase (hmg-coa reductase). this 3-kilobase cdna codes for an 883-amino acid protein, which exhibits extensive amino acid sequence homology to mammalian hmg-coa reductases. the highly conserved 341-amino acid membrane spanning domain exhibits 89% amino acid sequence identity with hamster hmg-coa reductase. in contrast to the high degree o ... | 1990 | 2307680 |
| interactions of light and gravity reception with magnetic fields in xenopus laevis. | tadpoles of xenopus laevis are shown to respond to magnetic fields using a gravity-related test paradigm. they exhibit a directional selectivity with respect to angular variations of the inclination of low-intensity magnetic fields. this response is abolished when the optic nerves of the tadpole are transected, indicating that the peripheral optical system is involved in the detection of magnetic fields. | 1990 | 2307926 |
| effects of cell heterogeneity on production of polypeptide growth factors and mesoderm-inducing activity by xenopus laevis xtc cells. | the xenopus laevis xtc cell line has been analyzed for the production of polypeptide growth factors and mesoderm-inducing activity. by the use of specific biological assays, it is shown that xtc cells produce a growth factor functionally related to the platelet-derived growth factor (pdgf) and two transforming growth factor (tgf) beta-like activities. mesoderm-inducing activity, as measured on x. laevis ectodermal explants from stage 10 embryos, was found to coelute on a bio-gel p-100 column wit ... | 1990 | 2318264 |
| expression of the hepatocyte na+/bile acid cotransporter in xenopus laevis oocytes. | the expression of the basolateral na+/bile acid (taurocholate) cotransport system of rat hepatocytes has been studied in xenopus laevis oocytes. injection of rat liver poly(a)+ rna into the oocytes resulted in the functional expression of na+ gradient stimulated taurocholate uptake within 3-5 days. this na(+)-dependent portion of taurocholate uptake exhibited saturation kinetics (apparent km approximately 91 microm) and could be inhibited by 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene. fur ... | 1990 | 2318817 |
| biochemical study of prolactin binding sites in xenopus laevis brain and choroid plexus. | the occurrence of prolactin binding sites in some brain structures (telencephalon, ventral hypothalamus, myelencephalon, hypophysis, and choroid plexus) from xenopus laevis (anuran amphibian) was studied by the in vitro biochemical technique. the higher binding values were obtained at the level of the choroid plexus and above all of the hypothalamus. on the bases of hormonal specificity and high affinity, these binding sites are very similar to those of prolactin receptors of classical target ti ... | 1990 | 2319226 |
| ocular dominance stripe formation by regenerated isogenic double temporal retina in xenopus laevis. | in lower vertebrates such as frogs and fish, long ocular dominance stripes with anterior-posterior (a-p) orientation can be produced by causing both eyes to innervate one optic tectum during the course of development. similar experiments on adult animals usually produce patches rather than stripes. during development, new retinal fibers from the nasal retina segregate into appropriate stripes at the growing edge of the posterior (p) tectum while new temporal fibers segregate at the non-growing a ... | 1990 | 2307975 |
| retinal axons in xenopus laevis recognise differences between tectal and diencephalic glial cells in vitro. | explants of retina from xenopus laevis were cultured on monolayers of tectal and diencephalic glial cells in order to determine whether the glia, normally encountered by optic nerve fibres as they grow to the optic tectum, can influence the growth of these neurons in any way. explants of nasal retina produced prolific radial outgrowth patterns on both tectal and diencephalic monolayers. explants of temporal retina produced similar outgrowth patterns on diencephalic glia, but on tectal glia the o ... | 1990 | 2317846 |
| reaction parameters of tfiiia-induced supercoiling catalyzed by a xenopus laevis cell-free extract. | in addition to its fundamental role of nucleating the formation of stable transcription complexes, the xenopus laevis 5s rna specific transcription factor, tfiiia, promotes a variety of dna-associated metabolic reactions. we report that tfiiia can induce a dna supercoiling catalyzed by the xenopus laevis s-150 cell-free extract on plasmids containing a single copy of the xenopus 5s rna gene (somatic-type). stimulated supercoiling occurs in the presence of high concentrations of atp (4 mm) and at ... | 1990 | 2315014 |
| nucleosome assembly in vitro: separate histone transfer and synergistic interaction of native histone complexes purified from nuclei of xenopus laevis oocytes. | high speed supernatants of xenopus laevis oocyte nuclei efficiently assemble dna into nucleosomes in vitro under physiological salt conditions. the assembly activity cofractionates with two histone complexes composed of the acidic protein n1/n2 in complex with histones h3 and h4, and nucleoplasmin in complex with histones h2b and h2a. both histone complexes have been purified and their nucleosome assembly activities have been analysed separately and in combination. while the histones from the n1 ... | 1990 | 2323341 |
| plasticity in the ipsilateral visuotectal projection persists after lesions of one nucleus isthmi in xenopus. | visual input has a profound effect on the development of binocular maps in the tectum of the frog xenopus laevis. input from the ipsilateral eye, which is relayed to the tectum via the opposite nucleus isthmi, is normally in register with the retinotectal map from the contralateral eye. however, if one eye is rotated during larval stages while the other eye is left in normal orientation, then the resulting mismatched visual input induces the crossed isthmotectal axons to change their trajectorie ... | 1990 | 2323380 |
| synaptic potentials in afferent fibers innervating hair cells of the lateral line organ in xenopus laevis. | spontaneous synaptic activity in afferent fibers innervating hair cells of the lateral line organ was monitored with micropipettes at visually identified locations near the peripheral terminations of the fibers. spontaneous action potentials as well as spontaneous excitatory post-synaptic potentials (epsps) were observed. some action potentials were preceded by epsps. most epsps did not reach threshold to generate action potentials. the frequency of occurrence of spontaneous epsps was related to ... | 1990 | 2324020 |
| inositol 1,4,5-trisphosphate-induced calcium release in the organelle layers of the stratified, intact egg of xenopus laevis. | using double-barreled, ca2(+)-sensitive microelectrodes, we have examined the characteristics of the ca2+ release by inositol 1,4,5-trisphosphate (ins(1,4,5)p3) in the various layers of xenopus laevis eggs in which the organelles had been stratified by centrifugation. centrifugation of living eggs stratifies the organelles yet retains them in the normal cytoplasmic milieu. the local increase in intracellular free ca2+ in each layer was directly measured under physiological conditions using theta ... | 1990 | 2324195 |
| correlation between structure and mass distribution of the nuclear pore complex and of distinct pore complex components. | nuclear pore complexes (npcs) prepared from xenopus laevis oocyte nuclear envelopes were studied in "intact" form (i.e., unexposed to detergent) and after detergent treatment by a combination of conventional transmission electron microscopy (ctem) and quantitative scanning transmission electron microscopy (stem). in correlation-averaged ctem pictures of negatively stained intact npcs and of distinct npc components (i.e., "rings," "spoke" complexes, and "plug-spoke" complexes), several fine struc ... | 1990 | 2324201 |
| development of the abducens nuclei in the xenopus laevis. | the development of the main (nvi) and the accessory abducens (nvia) nuclei was studied with the horseradish peroxidase and cobaltic-lysine labeling techniques in xenopus laevis tadpoles. in earliest labeling was obtained at stage 39, and neuroblasts of both nuclei formed two separate groups according to their definitive positions in relation to other rhombencephalic structures in this young age of development. conspicuous morphological differences were observed between the two nuclei: the access ... | 1990 | 2323026 |
| expression of the brown fat mitochondria uncoupling protein in xenopus oocytes and important into mitochondrial membrane. | non shivering thermogenesis of brown adipose tissue is due to the uncoupling protein (ucp), located in the inner mitochondrial membrane, which functions as a proton translocator and can thus uncouple mitochondrial respiration. we describe here the expression of ucp in xenopus laevis oocytes after injection of ucp mrna, which was transcribed in vitro. ucp seems to be correctly transported into mitochondria and integrated into the membrane, but we were not able to establish definitely the function ... | 1990 | 2322252 |
| the effects of n-cadherin misexpression on morphogenesis in xenopus embryos. | n-cadherin is a calcium-dependent, cell adhesion molecule that has been proposed to play a role in morphogenesis in vertebrate embryos. throughout early neural development, n-cadherin is expressed during the morphogenetic changes that occur when ectoderm, in response to neural induction, forms a neural plate and tube. to study the role of n-cadherin in these processes, cdna clones encoding xenopus laevis n-cadherin were isolated and used to study the expression of n-cadherin in frog embryos. the ... | 1990 | 2322458 |
| evolution of insulin-like growth factor i (igf-i): structure and expression of an igf-i precursor from xenopus laevis. | by means of a cloning strategy employing the polymerase chain reaction, we have isolated and characterized cdnas for xenopus laevis insulin-like growth factor i (igf-i). these cdnas encode a primary igf-i translation product of 153 residues that demonstrates considerable amino acid sequence similarity with igf-ia peptides from other species. fifty-seven of 70 residues of the mature protein are identical among human, rat, chicken, and xenopus igf-i, while less amino acid conservation is found at ... | 1990 | 2330002 |
| atp inhibition competes with activating cations in modulating the nad(p)(+)-malic enzyme activity in the mitochondrial matrix of xenopus laevis oocytes. | 1. atp inhibits nad(p)(+)-dependent malic enzyme activity by competing with the essential activators mn2+ and mg2+. 2. the kinetics fit an equation of co-operative kind with ki of 26 microm and ka of 11.3 microm for atp/mn2+ competition; with ki of 1.1 mm and ka of 0.96 mm for atp/mg2+ competition. 3. in the absence of the inhibitor, the co-operativity index increases from 1.77 to greater than 4 in the presence of atp, in the case of atp/mn2+ competition, while it increases from 1.88 to greater ... | 1990 | 2332098 |
| xenopus laevis cu,zn superoxide dismutase b cdna sequence. | | 1990 | 2326205 |
| glucose transporters serve as water channels. | water traverses the plasma membranes of some eukaryotic cells faster than can be explained by the water permeability of their lipid bilayers. this has led to a search for a water channel. our previous work identified glucose transporters as candidates for such a channel. we report here that xenopus laevis oocytes injected with mrna encoding the brain/hep g2, adult skeletal muscle/adipocyte, or liver forms of the glucose transporter exhibit an osmotic water permeability of their plasma membranes ... | 1990 | 2326282 |
| nucleotide sequence of xenopus laevis oct-1 cdna. | | 1990 | 2326173 |
| the primary structure of rat ribosomal protein s24. | the amino acid sequence of rat ribosomal protein s24 was deduced from the sequence of nucleotides in a recombinant cdna. s24 contains 133 amino acids and has a molecular mass of 15,413. hybridization of the cdna to digests of nuclear dna suggests that there are 12-16 copies of the s24 gene. the mrna for the protein is about 600 nucleotides in length. rat s24 is homologous to xenopus laevis s19 and related to halobacterium morismortui ribosomal protein s15. | 1990 | 2335205 |
| structure-activity relationships for osteolathyrism. iii. substituted thiosemicarbazides. | eight substituted thiosemicarbazides were assayed for their toxicity and teratogenicity using early embryos of xenopus laevis. results of the 96-h static tests on seven 4-position alkyl substituents were used for quantitative structure-activity relationship (qsar) analyses, with thiosemicarbazide as the parent compound. the compounds induced malformations via the connective tissue defect osteolathyrism. teratogenicity (log ec50) was negatively correlated with molar refractivity, suggesting that ... | 1990 | 2335712 |
| spatial gradients of intracellular calcium in skeletal muscle during fatigue. | we have measured the distribution of intracellular calcium concentration in isolated single muscle fibres from xenopus laevis using the fluorescent calcium indicator fura-2 with digital imaging fluorescence microscopy. under control conditions, resting and tetanic calcium were uniform throughout a fibre. when fatigue was produced using a prolonged, high-frequency tetanus, the distribution of calcium within muscle fibres became non-uniform, with greater levels near the outer parts of a fibre than ... | 1990 | 2336350 |
| estrogen regulation of xenopus laevis gamma-fibrinogen gene expression. | albumin gene expression in xenopus is regulated by estrogen through changes in the stability of its mrna. the goal of the present study was to determine whether a similar pathway regulates gamma-fibrinogen. degenerate oligonucleotides directed to conserved regions of the carboxyl-terminal half (domain d) of human and lamprey gamma-fibrinogen were used to isolate a full-length cdna clone for xenopus gamma-fibrinogen. analysis of codon utilization from the dna sequence of this clone revealed that ... | 1990 | 2334684 |
| an nf1-related vitellogenin activator element mediates transcription from the estrogen-regulated xenopus laevis vitellogenin promoter. | we have used a homologous transfection system employing cell lines derived from xenopus hepatocytes and fibroblasts and cloned xenopus estrogen receptor to identify a dna sequence essential for efficient transcription of the powerful estrogen-regulated xenopus laevis vitellogenin b1 promoter. although deletion of the caat box, the conserved nematode box, and several other sequences had little effect on vitellogenin promoter activity, deletion or mutation of a short sequence related to the nf1 tr ... | 1990 | 2335521 |
| a cadherin-like protein in eggs and cleaving embryos of xenopus laevis is expressed in oocytes in response to progesterone. | a new cadherin-like protein (clp) was identified in oocytes, eggs, and cleavage stage embryos of xenopus laevis. as a probe for detecting new cadherin proteins, an antiserum was raised to a 17 amino acid peptide derived from a highly conserved region in the cytoplasmic domain of all cadherins which have been sequenced to date. this antipeptide antibody recognized xenopus e-cadherin and a polypeptide in xenopus brain extracts similar to n-cadherin, which were independently identified by specific ... | 1990 | 2335564 |
| sequence of xenopus laevis ferritin mrna. | | 1990 | 2336402 |
| the sequence of tgf-beta 2 from xenopus laevis. | | 1990 | 2336403 |
| stepwise transformation of the vitelline envelope of xenopus eggs at activation: a quick-freeze, deep-etch analysis. | the extracellular matrix of xenopus laevis eggs was analyzed at fixed intervals after prick-activation using quick-freeze, deep-etch, rotary-shadow electron microscopy. this technique revealed that the modifications of the matrix seen at fertilization do not occur simultaneously, but that instead there is an orderly progression of alterations at activation. the first modification, conversion of the vitelline envelope (ve) to the altered vitelline envelope (ve), occurs within 2 to 3 min after act ... | 1990 | 2338169 |
| physicochemical characterization of progressive changes in the xenopus laevis egg envelope following oviductal transport and fertilization. | previous studies have shown that the xenopus laevis egg envelope exists in three forms with differing ultrastructural, macromolecular, and sperm penetrability properties. the coelomic envelope (ce) is derived from eggs released from the ovary into the body cavity of the female, the vitelline envelope (ve) from eggs which have passed through the oviduct, and the fertilization envelope (fe) from fertilized eggs. in the present study, the physicochemical characteristics of these three envelope type ... | 1990 | 2337586 |
| b-lymphocyte populations in xenopus laevis. | two-color immunofluorescence technique was used to show the development and distribution of surface mu- cytoplasmic mu+ (s mu- c mu+) pre-b, s mu+ b- and s mu+ cig+ plasma cells in metamorphic, postmetamorphic, and adult xenopus. generation of pre-b cells was evident in hematopoietic liver and spleen, but not in bone marrow, thymus, and duodenal mucosa. surface immunoglobulin positive small lymphocytes were the most abundant in the spleen while plasma cells were detected in the thymus, duodenal ... | 1990 | 2338158 |
| comparative studies on the vascular organization of carotid labyrinths of anurans and caudates. | the three-dimensional structures of the carotid labyrinth in five species of anurans representing four families (rana nigromaculata, rana catesbeiana, bufo japonicus, hyla arborea, and xenopus laevis), and three species of caudates representing three families (cynops pyrrhogaster, hynobius nebulosus, ambystoma mexicanum) were compared using vascular corrosion castings and scanning electron microscopy (sem). anuran carotid labyrinths are spherical in shape and are classified into two groups accor ... | 1990 | 2338718 |
| appearance and distribution of laminin during development of xenopus laevis. | a cloned cdna fragment, homologous to domain ii of the mouse laminin b1 chain, was obtained from a xenopus neurula cdna library. using this probe northern-blot analysis over the course of embryogenesis revealed a first signal of a laminin transcript at midgastrula (stage 11). affinity-purified polyclonal antibodies directed against xenopus laminin were obtained via a lacz fusion protein. immunohistology demonstrated the appearance of the antigen at about one developmental stage after the detecti ... | 1990 | 2340971 |
| mitotic activity in the blastema and stump tissues of regenerating hind limbs of xenopus laevis larvae after amputation at ankle level. an autoradiographic study. | mitotic activity, as indicated by dna synthesis, was studied by autoradiographic analysis along the proximodistal axis of regenerating limbs in the early and later larval stages 53 and 57 of xenopus laevis. wound-healing, dedifferentiation, blastema formation and growth phases were studied. most of the various stump tissues, as well as the cell mass of the regeneration blastema, were involved. the study showed an increase in dna synthesis in the stump tissues during their dedifferentiation as we ... | 1990 | 2341072 |
| comparative neuroanatomy of the histaminergic system in the brain of the frog xenopus laevis. | the distribution of the histaminergic neuronal system in the brain of the clawed frog xenopus laevis was mapped with an antiserum against carbodiimide-fixed histamine and compared to that in mammals. the histamine-immunoreactive cell bodies were located in a small area of the posterolateral hypothalamus, close to the dorsal infundibular nucleus, which contains catecholaminergic and serotonergic neurons. this area may be homologous to the tuberomammillary nucleus in mammals. a thick process exten ... | 1990 | 2341609 |
| a dna-binding protein is required for termination of transcription by rna polymerase i in xenopus laevis. | we describe a partially fractionated in vitro transcription system from xenopus laevis for the assay of transcription termination by rna polymerase i. termination in vitro was found to require a specific terminator sequence in the dna and a dna-binding protein fraction that produces a footprint over the terminator sequence. | 1990 | 2342463 |
| underwater hearing in the clawed frog, xenopus laevis. tympanic motion studied with laser vibrometry. | | 1990 | 2342580 |
| support of xenopus laevis spermatogenesis in vitro by different energy substrates. | the support of xenopus laevis spermatogenesis in vitro by different energy-yielding substrates has been investigated. isolated spermatogenic cells maintained their levels of adenosine-triphosphate for 24 h in serum-free medium containing only amino acids as energy substrates. dl-aminocarnitine, an inhibitor of carnitine palmitoyltransferase, reduced cell viability 87% during a 15-h culture in the same medium, indicating that beta oxidation of endogenous fatty acids is a significant source of ene ... | 1990 | 2340334 |
| distal invaginations and the renewal of cone outer segments in anuran and monkey retinas. | although it is now clear that the outer segments of mature vertebrate cones are regularly renewed, it is not known how a cone outer segment can maintain a tapered shape if its narrower tip is periodically lost by shedding. this problem was addressed by morphological examination of photoreceptors in retinas of anurans (xenopus laevis) and monkeys (macaca fascicularis). light microscopy revealed a marked daily change in the shape of cone outer segments in x. laevis: at light offset they were long ... | 1990 | 2340582 |
| the role of the dorsal lip in the induction of heart mesoderm in xenopus laevis. | we have examined the tissue interactions responsible for the expression of heart-forming potency during gastrulation. by comparing the specification of different regions of the marginal zone, we show that heart-forming potency is expressed only in explants containing both the dorsal lip of the blastopore and deep mesoderm between 30 degrees and 45 degrees lateral to the dorsal midline. embryos from which both of these 30 degrees-45 degrees dorsolateral regions have been removed undergo heart for ... | 1990 | 2340810 |
| sequence analysis of the upstream regions of xenopus laevis beta-globin genes and arrangement of repetitive elements within the globin gene clusters. | the globin gene clusters of xenopus laevis are interspersed by various different repetitive dna elements. a specific repeat, the jh12 element, has been mapped by southern analysis and some of its locations have been subsequently confirmed by nucleotide sequencing. jh12 family members seem to represent mobile genetic elements and display a high degree of divergence. the nucleotide sequences upstream to the adult beta i-globin gene and to the two coordinately expressed larval beta i- and beta ii-g ... | 1990 | 2345547 |
| heteromultimeric channels formed by rat brain potassium-channel proteins. | an important step towards understanding the molecular basis of the functional diversity of voltage-gated k+ channels in the mammalian brain has been the discovery of a family of genes encoding rat brain k+ channel-forming (rck) proteins. all species of these rck proteins form homomultimeric voltage-gated k+ channels with distinct functional characteristics in xenopus laevis oocytes following injection of the respective crnas. rck-specific mrnas are coexpressed in several regions of the brain, su ... | 1990 | 2348860 |
| identification of a tfiiia binding site on the 5' flanking region of the tfiiia gene. | xenopus transcription factor iiia (tfiiia) regulates 5s ribosomal rna gene transcription in a positive manner by binding to the internal control region (icr) of the 5s rna gene. the present study reports the identification of a tfiiia binding site on the 5' flanking region of the xenopus laevis gene that codes for the synthesis of this transcription factor. this tfiiia binding site (deduced from tfiiia-dependent alterations in dnase i protection patterns) extends on the 5' flanking region from a ... | 1990 | 2349091 |
| oogenesis in fundulus heteroclitus. vi. establishment and verification of conditions for vitellogenin incorporation by oocytes in vitro. | a procedure was developed for studying vitellogenin (vtg) incorporation by vitellogenic oocytes of fundulus heteroclitus in vitro. since homologous vtg can be obtained from this animal only with great difficulty, the use of [32p]vtg from xenopus laevis was explored as an alternative. vitellogenic as well as maturational-stage oocytes were found to sequester x. laevis [32p]vtg from the medium, and incorporation was found to be linear with time for at least up to 12 hr. once incorporated into the ... | 1990 | 2345348 |
| the induction of an anomalous ipsilateral retinotectal projection in xenopus laevis. | the conditions necessary for extensive regeneration of fibres from one optic nerve to both tecta in xenopus have been investigated. the effects of various types and positions of nerve lesion on the distribution of regenerated projections were examined by labelling the regenerated projections with either horseradish peroxidase or tritiated proline. the only types of nerve lesion which consistently gave rise to extensive regeneration to both the contralateral and the ipsilateral tectum were those ... | 1990 | 2346232 |