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inhibition of ras-induced germinal vesicle breakdown in xenopus oocytes by rap-1b.a cdna clone (krev-1) has recently been identified that possesses the ability to reverse the transformed phenotype when introduced into a k-ras-transformed nih/3t3 cell line. the krev-1 protein, also known as rap-1a, was found to share 50% homology with the ras proteins. the rap-1a protein has also been shown to block the interaction of ras with its gtpase activating protein in vitro, leading to speculation regarding its role in vivo. a closely related protein, rap-1b, has also been identified i ...19911899188
evidence for the involvement of a pertussis toxin-insensitive g-protein in egg activation of the frog, xenopus laevis.activation responses of the frog egg at fertilization include the release of calcium from intracellular stores and the opening of calcium-dependent chloride channels, which produce the fertilization potential. to investigate the presence of guanine nucleotide-binding proteins (g-proteins), and their role in initiation of these events in the egg of the frog xenopus laevis, we assayed for pertussis and cholera toxin substrates, and applied activators and inhibitors of g-proteins. pertussis toxin c ...19911899403
synthesis of sperm-specific basic nuclear proteins (sps) in cultured spermatids from xenopus laevis.the accumulation and synthesis of sperm-specific basic nuclear proteins (sps) in xenopus spermatids in vitro were studied by acid-urea-triton polyacrylamide gel electrophoresis and fluorography. in synchronous cultures of round spermatids, the amount of sp2 and sp3-5 accumulated almost linearly with time, while that of sp1 remained almost constant. fluorography showed that round spermatids incorporated [14c]arginine mostly into sp1 and sp3-5, very little into sp2, and none into histones. when [1 ...19911901796
purification of two thermostable components of messenger ribonucleoprotein particles (mrnps) from xenopus laevis oocytes, belonging to a novel class of rna-binding proteins.we have purified and partially sequenced two proteins from xenopus laevis previtellogenic oocytes, belonging to messenger ribonucleoprotein particles (mrnps). the purification procedure rests on the thermostability of these proteins, which remain soluble after heating the cell extracts at 80 degrees c. the thermostable proteins can be identified with two of the most abundant components (mrnp3 and mrnp4) of the mrnps, described by darnbrough and ford (1981) [eur. j. biochem. 118, 415-424]. mrnp3 ...19911902800
sequence of c region of l chains from xenopus laevis ig.a cdna expression library, prepared from xenopus laevis splenocytes, was screened with antibodies to xenopus ig. one clone, lambda xig23, reacted with antibodies to igy and to igm; the insert hybridized to approximately 1.3-kb rna from spleen, the approximate size expected for l chain mrna. an additional clone, lambda xig31, was identified by cross-hybridization. the inserts of lambda xig23 and lambda xig31 begin in the third framework region of the v region and extend through the c region to th ...19911903418
the genomic organization of immunoglobulin vh genes in xenopus laevis shows evidence for interspersion of families.the complete genomic sequences of xenopus laevis immunoglobulin heavy chain variable region (vh) genes comprising families iv-xi are reported. using vh family-specific probes, linkage relationships for xenopus vhi-vhxi have been determined. with the possible exceptions of vhiii and vhvii, xenopus vh genes appear to be interspersed. when from two to five vh segments are identified in individual clones, the elements are found to be in the same relative transcriptional orientation. although the rel ...19911905399
thyrotropin-releasing hormone facilitates display of reproductive behavior and locomotor behavior in an amphibian.in the amphibian brain, thyrotropin-releasing hormone (trh) is present in many regions outside the hypothalamus. the functions of this extrahypothalamic trh however are unknown. we sought to determine whether trh or its metabolites altered reproductive behaviors (amplectic clasping behavior) or locomotor behaviors of the male south african clawed frog, xenopus laevis. trh-injected (100 micrograms; dorsal lymph sac injection) male xenopus displayed significantly fewer amplectic clasp attempts and ...19911906046
a method for the demonstration of nadph-diaphorase activity in anuran species using unfixed retinal wholemounts.the presence of nadph-diaphorase enzyme has been previously revealed in fixed mammalian retinal tissue (sagar, 1986). fixed retinae of bufo marinus and xenopus laevis failed to yield selective staining when reacted for nadph-diaphorase. satisfactory staining of retinal neurons was attained when the histochemical reaction was carried out in unfixed retinal wholemounts. the applied method included the following steps: 1) dissection of the fresh retina and the separation of the neural retina from a ...19911908262
cell-surface receptor for ecotropic murine retroviruses is a basic amino-acid transporter.the complementary dna sequence encoding the cell-surface receptor for ecotropic host-range murine retroviruses (ecor) shows that it contains 622 amino acids and 14 hydrophobic potentially membrane-spanning sequences. because this receptor occurs on many or all murine cells and is probably essential for viability of cultured fibroblasts, its normal function might be to transport an essential metabolite. we expressed ecor in xenopus laevis oocytes by injecting rna transcribed from the cloned cdna. ...19911908564
[do the variations in water carbon dioxide pressure and ph have an effect on the nature of end products of protein catabolism, ammonia and urea, in the clawed frog xenopus laevis?].the effects of pco2 and ph changes in the ambient water on the nitrogen catabolism and the proportions of the excreted nitrogenous end products, ammonia and urea, were studied in the clawed frog, xenopus laevis, at 24 degrees c. in animals living in artificial fresh water, the exposure to a hypocapnic alkalosis (pco2 = 0.7 torr instead of 10 torr) did not entail any change in the nitrogen catabolism. in animals who lived in a water loaded with nacl and had therefore a higher oxygen consumption, ...19911913240
dna-dependent phosphorylation of histone h2a.x during nucleosome assembly in xenopus laevis oocytes: involvement of protein phosphorylation in nucleosome spacing.atp is required for physiological nucleosome alignment in chromatin reconstituted from high-speed nuclear supernatants of xenopus laevis oocytes. here we show that during in vitro nucleosome assembly the histone variant h2a.x becomes phosphorylated upon transfer onto dna, a process which is also observed in vivo. histone h2a.x phosphorylation increases in the early phase of the assembly reaction, reaching a steady state after approximately 16 min and is maintained with a half-life of the phospha ...19911915279
structural analysis of the entire proopiomelanocortin gene of xenopus laevis.in the pars intermedia of the pituitary the prohormone proopiomelanocortin (pomc) is tissue-specifically processed to, among other peptides, alpha-melanotropin (alpha msh). in the south african clawed toad xenopus laevis this hormone mediates the process of background adaptation: release of alpha-msh causes darkening of the animal, while inhibition of alpha-msh release results in a pale toad. elevated release of alpha-msh coincides with a higher rate of pomc gene transcription. the present study ...19911915355
nuclear pore complex glycoprotein p62 of xenopus laevis and mouse: cdna cloning and identification of its glycosylated region.cdna clones for nuclear pore complex glycoprotein p62 of two distantly related species, mouse and xenopus laevis, were isolated. antibodies raised against recombinant murine p62 react on protein blots with p62 of both species and decorate pore complexes. analysis of the predicted protein sequence indicates that vertebrate p62 is organized into two structurally different regions. the entire carboxy-terminal half (86.7% identical amino acids) and the amino-terminal 56 amino acids (62.5% identity) ...19911915419
furrow-related contractions are inhibited but furrow-unrelated contractions are not affected in af mutant eggs of xenopus laevis.in embryos from af mutant females of xenopus laevis, the cleavage furrows stayed on the surface and cytoplasmic divisions did not take place at all, while nuclear divisions continued (kubota et al., 1991). to gain insights into the roles of the normal product of af on early development, contractile events which have been observed in the period from fertilization until first cleavage in wild-type eggs were examined in af mutant eggs. activation waves, activation contraction, and surface contracti ...19911916014
tunicamycin-inducible polypeptide synthesis during xenopus laevis embryogenesis.tunicamycin treatment of xenopus laevis embryos enhanced the synthesis of a specific set of polypeptides with molecular masses of 98, 78, 59 and 58 kda. the 78-kda polypeptide was tentatively identified as glucose-regulated protein (grp) 78 on the basis of molecular mass, pl (5.2), and tunicamycin inducibility, which took place upon treating embryos after the midblastula transition (mbt). the synthesis of a polypeptide with this electrophoretic mobility was detected but was not tunicamycin-induc ...19911916065
internal deletions in human interleukin-6: structure-function analysis.by cdna mutagenesis, we have constructed internal and c-terminal deletions (delta 21-51, delta 52-97, delta 97-104, delta 127-174, delta 97-184 and delta 134-184) in human interleukin-6 (hil-6). all those deletion-carrying hil-6 (delta hil-6) proteins were then produced in xenopus laevis oocytes and examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (sds-page). the results show that, at least in frog oocytes, the first potential n-glycosylation site (asn45) is utilized exclusi ...19911916293
expression of two nonallelic type ii procollagen genes during xenopus laevis embryogenesis is characterized by stage-specific production of alternatively spliced transcripts.the pattern of type ii collagen expression during xenopus laevis embryogenesis has been established after isolating specific cdna and genomic clones. evidence is presented suggesting that in x. laevis there are two transcriptionally active copies of the type ii procollagen gene. both genes are activated at the beginning of neurula stage and steady-state mrna levels progressively increase thereafter. initially, the transcripts are localized to notochord, somites, and the dorsal region of the late ...19911918153
novel applications of acrylamide for cryosectioning of isolated cells, tissues, and arthropods.cross-linked and uncross-linked acrylamide polymers were used to alleviate technical difficulties in cryosectioning and autoradiographic processing of marine arthropods (pycnogonum litorale), larval insect tissues (sarcophaga bullata), and amphibian (xenopus laevis) oocytes. rapidly polymerized cross-linked acrylamide was used to prepare sections from an animal with a hard thick cuticle, p. litorale. fragmentation and compression artifacts caused by tissue density differences were avoided and in ...19911918945
subdivisions of the terminal nerve in xenopus laevis.the majority of recent studies on the terminal nerve (nt) in various vertebrates either involved tracer injections into the nasal cavity or made use of the lhrh-/fmrfamide-like immunoreactivity (ir) of a portion of its fibers. the present investigation was designed to determine the extent of overlap between data rendered by the two methods in xenopus. the findings reveal no overlap of nt projections visualized by the two experimental techniques. this result sheds doubt on the validity of current ...19911919462
identification and functional analysis of the nuclear localization signals of ribosomal protein l25 from saccharomyces cerevisiae.the regions of the large subunit ribosomal protein l25 from saccharomyces cerevisiae responsible for nuclear localization of the protein were identified by constructing fusion genes encoding various segments of l25 linked to the amino terminus of beta-galactosidase. indirect immunofluorescence of yeast cells expressing the fusions demonstrated that amino acid residues 1 to 17 as well as 18 to 41 of l25 promote import of the reporter protein into the nucleus. both nuclear localization signal (nls ...19911920406
coordinate estrogen-regulated instability of serum protein-coding messenger rnas in xenopus laevis.estrogen causes the cytoplasmic destabilization of albumin and gamma-fibrinogen mrna in xenopus laevis liver. the purpose of the present study was to determine whether mrna destabilization is a generalized phenomenon in response to estrogen, or whether this process is restricted to a particular class of mrnas. to address this, we have expanded our bank of serum protein-coding cdna clones to include transferrin, the second protein of inter-alpha-trypsin inhibitor and clone 12b, for which there is ...19911922078
in vitro binding of the purified hormone-binding subunit of the estrogen receptor to oligonucleotides containing natural or modified sequences of an estrogen-responsive element.estrogen receptor (er) was purified from calf uterus by immunoaffinity chromatography in the absence of the ligand. the purified er consists of a mixture of monomer and homodimer forms of 67-kda hormone-binding subunit (no 90-kda heat shock protein is present). the purified er was incubated with a 32p-labeled 61-basepair oligonucleotide containing the sequence of the estrogen response element (ere) of the xenopus laevis a2 vitellogenin gene. dna mobility shift assays showed formation of specific ...19911922088
coordinate regulation of fibrinogen subunit messenger rna levels by glucocorticoids in primary cultures of xenopus liver parenchymal cells.fibrinogen synthesis is specifically induced by a synthetic glucocorticoid, dexamethasone, in primary liver parenchymal cell cultures of the frog xenopus laevis. here we demonstrate that this increase in the level of fibrinogen protein production is accompanied by an induction in the three mrnas coding for the fibrinogen subunits, designated a alpha, b beta, and gamma. the stimulation of fibrinogen mrna levels appears to be mediated by the glucocorticoid receptor, because 1) the dose-response re ...19911922091
germ cell-specific expression of a gene encoding eukaryotic translation elongation factor 1 alpha (eef-1 alpha) and generation of eef-1 alpha retropseudogenes in xenopus laevis.we have studied by in situ hybridization the expression of the genes encoding the somatic form and the oocyte form of xenopus laevis eef-1 alpha. the somatic form of eef-1 alpha (eef-1 alpha s) mrna is virtually undetectable in male and female germ cells of the adult gonad but is very abundant in embryonic cells after the neurula stage. in contrast, another form of eef-1 alpha (eef-1 alpha o) mrna is highly concentrated in oogonia and in previtellogenic oocytes but is undetectable in eggs and em ...19911924391
morphological and immunological changes in the spleen of xenopus laevis during metamorphosis. 19911925006
biological structures imaged in a hybrid scanning transmission electron microscope and scanning tunneling microscope.a hybrid scanning transmission electron microscope (stem) and scanning tunneling microscope (stm) is described which allows simultaneous imaging of biological structures adsorbed to electron-transparent specimen supports in both modes of scanning microscopy, as demonstrated on uncoated phage t4 polyheads. we further discuss the reproducibility and validity of height data obtained from stm topographs of biomacromolecules and present raw data from topographs of freeze-dried, metal-coated nuclear e ...19911926633
microglia in tadpoles of xenopus laevis: normal distribution and the response to optic nerve injury.we have studied the distribution of microglia in normal xenopus tadpoles and after an optic nerve lesion, using a monoclonal antibody (5f4) raised against xenopus retinas of which the optic nerves had been cut 10 days previously. the antibody 5f4 selectively recognizes macrophages and microglia in xenopus. in normal animals microglia are sparsely but widely distributed throughout the retina, optic nerve, diencephalon and mesencephalon (other regions were not examined). after crush or cut of an o ...19911928746
glycoconjugate histochemistry of xenopus laevis fundic gland with special reference to mucous neck cells during development.mucous neck cells (mncs) of the fundic gland are phylogenetically thought to have first appeared in amphibians. we studied the origin and differentiation of mncs in fundic glands of xenopus laevis. by means of lectin histochemical methods using griffonia simplicifolia agglutinin-ii (gsa-ii), mncs were detected specifically in fundic glands of adult x. laevis. mucous granules of mncs were labeled by gsa-ii-colloidal gold (cg) staining. other cells such as surface mucous cells (smcs), oxynticopept ...19911928755
mapping the polarity profiles of general anesthetic target sites using n-alkane-(alpha, omega)-diols.the effects of the homologous series of n-alkane-(alpha, omega)-diols have been studied on the inhibition of the purified firefly luciferase enzyme from photinus pyralis, the inhibition of the purified bacterial luciferase enzyme from vibrio harveyi, and the induction of general anesthesia in xenopus laevis tadpoles. all but one of the diols tested were found to be reversible general anesthetics. the diols inhibited firefly luciferase by competing with its normal substrate firefly luciferin, and ...19911931978
the switch from larval to adult globin gene expression in xenopus laevis is mediated by erythroid cells from distinct compartments.the transition of hemoglobins during metamorphosis of xenopus laevis involves replacement of the larval erythrocytes by adult ones, suggesting that the developmental control of this event depends upon the growth characteristics of the precursor cells. to identify the erythroid precursor cells and to investigate their developmental fate, we analyzed the distribution of stage-specific globin mrnas by northern blotting in dorsal and ventral fragments of stage 32 embryos after in vitro culture as we ...19911935695
purification and cdna cloning of xenopus laevis skin peptidylhydroxyglycine n-c lyase, catalyzing the second reaction of c-terminal alpha-amidation.the alpha-amidation of glycine-extended peptides is a two-step reaction catalyzed by peptidylglycine alpha-hydroxylating monooxygenase (phm) and peptidylhydroxyglycine n-c lyase (phl). phl was purified to homogeneity from xenopus laevis skin and its partial amino acid sequence (including the n-terminal 35 residues) was determined. it was found that the cdna codes for a 935-residue precursor protein (ae-iii protein), containing the phm and phl sequences at its n terminus and c terminus, respectiv ...19911935950
mechanisms of the tetrahydroaminoacridine effect on action potential and ion currents in myelinated axons.9-amino-1,2,3,4-tetrahydroacridine (tha) in the range of 10-300 microm was shown to prolong the action potential in myelinated nerve fibres of xenopus laevis. voltage-clamp experiments showed that tha, besides reducing the na+ and the k+ current, modified the na+ current inactivation and the k+ current activation. the effects were frequency dependent. quantitative models were developed and used in computer simulations of the tha effect on the action potential. the computations showed that the ob ...19911936128
posttranscriptional regulation of c-myc rna during early development of xenopus laevis.the remarkable stability of c-myc during oogenesis contrasts with its degradation during the early developmental period in xenopus laevis. three evolutionary conserved motifs found in the 3'-untranslated region of xenopus c-myc rnas have been analyzed for a possible role in c-myc rna degradation. no specific degradation was observed when these sequences were cloned downstream of a reporter gene and the corresponding rnas were injected into fertilized eggs. the relation between polyadenylation an ...19911936260
cellular mechanism of metformin action.activation of the insulin receptor tyrosine kinase and tyrosine phosphorylation of intracellular substrates are important steps in insulin signalling. in order to elucidate the cellular mechanism of action of metformin (nn'dimethylbiguanide) we have focused towards the effects of metformin on the insulin receptor kinase, the phosphorylation cascade and the biological effect of insulin. since annexins (lipocortins) have been recently recognized as substrates of several tyrosine kinases we have in ...19911936468
the cloning and characterization of a maternally expressed novel zinc finger nuclear phosphoprotein (xnf7) in xenopus laevis.we report the cloning of a cdna (xnf7) coding for a maternally expressed xenopus protein that becomes highly enriched in nuclei of the central nervous system during later development and in nuclei of adult brain. the protein also shows stage-specific nuclear/cytoplasmic partitioning and phosphorylation that may be related to its function. in addition, it binds to double-stranded dna in vitro. the conceptual protein produced by the xnf7 clone contains several acidic domains, a novel zinc finger d ...19911936552
characterization of the ooplasmic factor inducing decondensation of and protamine removal from toad sperm nuclei: involvement of nucleoplasmin.immunohistochemical studies with antiserum against the protamines of the toad, bufo japonicus, revealed that the sperm nucleus loses protamines within 5 min after entry into the egg. likewise, lysolecithin-permeabilized sperm incubated with the egg extract lose the protamines within 1 min, accompanied by nuclear decondensation. the activities that induce both protamine removal and decondensation in sperm nuclei were found in extracts from growing and mature oocytes and pregastrula embryos, but n ...19911936566
a xenopus laevis creatine kinase isozyme (ck-iii/iii) expressed preferentially in larval striated muscle: cdna sequence, developmental expression and subcellular immunolocalization.a cdna containing the nearly complete coding sequence of ck-iii subunit of x. laevis was isolated, sequenced and further identified by comparing the tissue distribution of ck-iii/iii isozyme with that of its messenger. comparison of ck-iii deduced amino acid sequence with other ck sequences published reveals its close homology to m-ck subunits. results using both cdna probes and monoclonal antibodies specific for ck-iii subunits indicate that the appearance and the accumulation of ck-iii occur i ...19911936981
xubf contains a novel dimerization domain essential for rna polymerase i transcription.xenopus laevis upstream binding factor (xubf) is an rna polymerase i transcription factor that is required for formation of the stable initiation complex. the 701-amino-acid protein contains three regions of homology to the chromosomal protein hmg1 (the hmg boxes), which act in comparative independence to cause dna binding. dna binding is augmented by a 102-residue amino-terminal domain that causes xubf to form dimers. the dimerization domain is bipartite in structure, consisting of two regions ...19911936987
xp1 and xp4. p-domain peptides expressed in xenopus laevis stomach mucosa.two different precursors for secretory polypeptides from the stomach of xenopus laevis have been characterized by cdna cloning. both mature polypeptides are potential candidates for gastrointestinal growth factors. one, xp1, is the x. laevis homologue of the ps2 gene product consisting only of a single p-domain, whereas the second, xp4, is a novel polypeptide formed by four p-domains arranged in tandem. northern analysis detected both transcripts in the stomach but not in the skin or the brain. ...19911939167
the astacin family of metalloendopeptidases.molecular cloning of a human intestinal brush border metalloendopeptidase (n-benzoyl-l-tyrosyl-p-aminobenzoic acid hydrolase, pph) and a mouse kidney brush border metalloendopeptidase (meprin a) has revealed 82% identity in the nh2-terminal amino acid sequences (198 residues) of the mature enzymes. furthermore, searching of protein sequence data bases with the inferred peptide sequences as probes revealed strong similarities to astacin, a crayfish digestive protease, and an nh2-terminal domain o ...19911939172
the influence of denervation on grafted hindlimb regeneration of larval xenopus laevis.the aim of the present research is to ascertain whether in larval xenopus laevis nerve-independence for the regeneration of early stage limbs and nerve-dependence of late stage limbs observed in a previous work (filoni and paglialunga, '90) is related to extrinsic (systemic) factors or to intrinsic changes taking place in the limb cells themselves during development. in this paper the regenerative capacity of early and late stage hindlimbs under the same extrinsic conditions, insofar as both are ...19911940823
lens formation from the cornea following implantation into hindlimbs of larval xenopus laevis: the influence of limb innervation and extent of differentiation.corneal fragments of larval xenopus laevis at stage 48 (according to nieuwkoop and faber, '56), were implanted into sham denervated unamputated hindlimbs, denervated unamputated hindlimbs, amputated and sham denervated hindlimbs, and amputated and denervated hindlimbs of larvae at stages 52 and 57. the results show that unamputated limbs at stage 52, either innervated or denervated, manifest a weak capacity to promote the first lens-forming transformations of the outer cornea. this capacity is a ...19911940824
an epizootic of cutaneous zygomycosis in cultured dwarf african clawed frogs (hymenochirus curtipes) due to basidiobolus ranarum.morbidity and mortality approaching 100% occurred in dwarf african clawed frogs (hymenochirus curtipes) from a culture facility in central california. moribund frogs exhibited preference for a terrestrial environment rather than their normal aquatic environment. affected animals had a slight pallor of the integument but were otherwise grossly unremarkable. microscopic examination revealed a fungal infection of the integument primarily characterized by the presence of surface and intra-epidermal ...19911941429
developmentally regulated alternative splicing in the xenopus laevis c-myc gene creates an intron-1 containing c-myc rna present only in post-midblastula embryos.two distinct c-myc rna classes have been identified in xenopus laevis, presumably expressed from the duplicated c-myc locus (1, 6). the major xenopus c-myc transcripts arise from sites termed p1 and p2 similarly to those of the mammalian c-myc genes. i have used a cloned xenopus c-myc gene to examine the regulated pattern of expression from this gene during early xenopus embryogenesis. analysis of the pattern of transcript processing indicates that not only are p1 and p2 differentially active du ...19911945855
acetylaminofluorene and aminofluorene adducts inhibit in vitro transcription of a xenopus 5s rna gene only when located on the coding strand.unique n-acetyl-2-aminofluorene (aaf) or 2-aminofluorene (af) adducts were introduced into the xenopus borealis somatic 5s rna gene between the intragenic control region and the transcription termination site. the effects of these bulky adducts on transcription were studied in a cell-free extract derived from xenopus laevis oocytes. aaf and af adducts inhibit transcription only when they are on the template strand, whereas transcription passes through these adducts when they are placed on the no ...19911946373
cloning and expression of cdna for a na/pi cotransport system of kidney cortex.a cdna library from rabbit kidney cortex was screened for expression of na-dependent transport of phosphate (pi) using xenopus laevis oocytes as an expression system. a single clone was eventually isolated (designated napi-1) that stimulated expression of na/pi cotransport approximately 700-fold compared to total mrna. the predicted sequence of the na/pi cotransporter consists of 465 amino acids (relative molecular mass, 51,797); hydropathy profile predictions suggest six (possibly eight) membra ...19911946375
lumbar lateral motor columns and hindlimbs of two xenopus laevis chromosome mosaics.two chromosome mosaic xenopus laevis, one tadpole and one metamorphic animal, both with different sizes of neurons on the left and right sides of their brains and spinal cords, have left and right lumbar lateral motor columns (l-lmcs) of equal lengths but composed of strikingly different numbers of motoneurons (40% fewer motoneurons on the side composed of larger cells). one portion of the lumbar cord in the metamorphic animal is bilaterally symmetrical; the cells on both sides are small and the ...19911951137
primary structure of the two variants of xenopus laevis mtssb, a mitochondrial dna binding protein.the primary structure of the single-stranded dna binding protein from xenopus laevis oocyte mitochondria (mtssb) has been determined by edman degradation of the intact molecule and peptides derived from partial alpha-chymotrypsin proteolysis and enzymatic cleavage with trypsin and endoproteinase glu-c. the native mtssb is composed of two related polypeptide chains, mtssbs and mtssbr. the sequence of mtssbs consists of 129 amino acids with a calculated molecular mass of 14,627 da. comparison of t ...19911952953
teratogenesis, toxicity, and bioconcentration in frogs exposed to dieldrin.teratogenesis, acute and chronic toxicity, growth and bioconcentration were investigated in various life stages (embryos, tadpoles, juveniles, adults) of the frogs xenopus laevis (african clawed frog), rana catesbeiana (bullfrog) and rana pipiens (leopard frog) exposed to aqueous dieldrin in static-renewal and flow-through systems in a study on the development of wildlife-based water quality criteria. r. catesbeiana was the most sensitive tadpole in acute tests; x. laevis was the most sensitive ...19911953024
high yield purification of active transcription factor iiia expressed in e. coli.transcription factor iiia (tfiiia), a sequence-specific dna-binding protein from xenopus laevis, is a zinc finger protein required for transcription of 5s rrna genes by rna polymerase iii. we describe the purification and characterization of recombinant tfiiia (rectfiiia) expressed in e. coli. rectfiiia was purified to greater than 95% homogeneity at a yield of 2-3 milligrams per liter of bacterial culture. this purified protein protects the internal control region of a 5s rrna gene from dnase i ...19911956778
interaction of xenopus lamins a and lii with chromatin in vitro mediated by a sequence element in the carboxyterminal domain.morphological data suggest an interaction of the nuclear lamina with chromatin which markedly changes during the cell cycle. to study the molecular basis of this interaction we developed a novel lamin/chromatin binding assay that quantitated the binding of soluble, radiolabeled lamins to minichromosomes assembled in xenopus laevis oocyte nuclear extracts. lamins were derived from couple in vitro transcription and translation of the corresponding cdnas. chromatin binding was detected by monitorin ...19911959562
substitute anions and the chloride conductance of frog muscle: effects of chlorate and bromate on steady-state values and kinetics.voltage-clamp experiments have been used to study the effects of external nitrate, chlorate and bromate on the chloride conductance of sarcolemma of xenopus laevis. nitrate reduces inward current (chloride efflux), but less potently than does thiocyanate [vaughan (1987) pflügers arch 410:153-158] and does not affect conductance kinetics. as its concentration is increased the blocking effect of nitrate saturates; at a nitrate mole fraction of 0.6 the anion conductance is reduced to about 50% and ...19911961685
functional expression cloning and characterization of the hepatocyte na+/bile acid cotransport system.liver parenchymal cells continuously extract high amounts of bile acids from portal blood plasma. this uptake process is mediated by a na+/bile acid cotransport system. a cdna encoding the rat liver bile acid uptake system has been isolated by expression cloning in xenopus laevis oocytes. the cloned transporter is strictly sodium-dependent and can be inhibited by various non-bile-acid organic compounds. sequence analysis of the cdna revealed an open reading frame of 1086 nucleotides coding for a ...19911961729
expression of gata-binding proteins during embryonic development in xenopus laevis.proteins that recognize the core sequence gata are important regulators of hematopoietic-specific gene transcription. we have characterized cdnas encoding the xenopus laevis homologues of three related transcription factors, designated gata-1, -2, and -3. comparative sequence analysis reveals strong conservation of the zinc-finger dna-binding domain among all vertebrate gata-binding proteins. gata-2 and gata-3 polypeptides are homologous throughout their entire sequences, whereas gata-1 sequence ...19911961730
homologous recombination catalyzed by a nuclear extract from xenopus oocytes.xenopus laevis oocytes efficiently recombine linear dna injected into their nuclei (germinal vesicles). this process requires homologous sequences at or near the molecular ends. here we report that a cell-free extract made from germinal vesicles is capable of accomplishing the complete recombination reaction in vitro. like the in vivo process, the extract converts the overlapping ends of linear substrate molecules into covalently closed products. establishment of this cell-free system has allowe ...19911961753
a homolog of the armadillo protein in drosophila (plakoglobin) associated with e-cadherin.three cytoplasmic proteins, called catenins, bind to the cytoplasmic tail of the epithelial cell-cell adhesion molecule e-cadherin. the complementary dna sequence was determined for the 92-kilodalton beta catenin of xenopus laevis. the sequence is homologous to mammalian plakoglobin, a protein of desmosomal and zonula adherens cell junctions, and to the plakoglobin homolog in drosophila melanogaster, the product of the segment polarity gene armadillo. a monoclonal antibody to bovine plakoglobin ...19911962194
regulation of c-erba-alpha messenger rna species in tadpole erythrocytes by thyroid hormone.putative thyroid hormone (th) nuclear receptors have been detected in several tissues of rana catesbeiana tadpoles. t3 receptor number (sites per nucleus) in red blood cells (rbcs) and tail increases substantially just before metamorphic climax or in response to exogenous th; in contrast, receptor number in liver remains relatively constant. th receptors in mammals and birds are thought to be encoded by a c-erba gene. in the present study, two c-erba cdnas, one prepared from xenopus laevis oocyt ...19911645454
differential mechanisms for the n-acetylation of alpha-melanocyte-stimulating hormone and beta-endorphin in the intermediate pituitary of the frog, xenopus laevis.immunohistochemical analysis of the pituitary of xenopus laevis revealed the colocalization of alpha-melanocyte-stimulating-hormone (msh)-related immunoreactivity and n-acetyl-beta-endorphin-related immunoreactivity in the cells of the intermediate pituitary. in order to determine whether the immunoreactive n-acetylated beta-endorphin is released in parallel with the immunoreactive alpha-msh, intermediate pituitaries were incubated in l-15 medium for 24 h. the medium and an acid extract of the i ...19911646412
in vitro translation and expression of renal intrinsic factor-cobalamin receptor.the primary translation product of intrinsic factor (if)-cobalamin receptor (ifcr) mrna from rat kidney is a single polypeptide chain of mr = 215,000. when expressed in xenopus laevis oocytes the ifcr binding activity is expressed with mrna of a size between 5 to 7 kb. these results suggest that ifcr mrna transcripts are present in the renal tissue and encode a single chain, large molecular weight precursor. furthermore, xenopus oocytes can be used as a screening system in the expression cloning ...19911646608
release of acetylcholine by xenopus oocytes injected with mrnas from cholinergic neurons.xenopus laevis oocytes were injected with poly(a)+ mrnas extracted from the electric lobes of torpedo marmorata. the electric lobes contain the perikarya of approximately 120,000 cholinergic neurons that innervate the electric organs and are homologous to motor neurons. the injected oocytes accumulated acetylcholine and were able to synthesize [14c]acetylcholine from 1-[14c]acetate. with kcl depolarization and upon treatment with a ca2+ ionophore, they released their endogenous as well as the ra ...19911646712
hormone-regulated k+ channels in follicle-enclosed oocytes are activated by vasorelaxing k+ channel openers and blocked by antidiabetic sulfonylureas.follicular oocytes from xenopus laevis contain k+ channels activated by members of the recently recognized class of vasorelaxants that include cromakalim and pinacidil and blocked by antidiabetic sulfonylureas, such as glibenclamide. these channels are situated on the adherent follicular cells and are not present in denuded oocytes. cromakalim-activated k+ channels are also activated by increases in intracellular camp, and camp-activated k+ channels are blocked by glibenclamide. although cromaka ...19911647032
a perichromosomal region contains proteins phosphorylated during mitosis in xenopus laevis cells.an antibody that recognizes the phosphorylated form of nucleoplasmin has identified another nuclear protein whose antigenic form is regulated in a mitosis-specific manner, with a dramatic increase in binding occurring in all mitotic cells. the protein is localised around the periphery of condensed chromosomes during mitosis in a manner analogous to another nucleoplasmin-related polypeptide no38. mitosis-specific expression of the antigenic site is dependent on phosphorylation of the polypeptide; ...19911647398
the cell cycle dependence of protein synthesis during xenopus laevis development.the regulation of early embryonic development in the amphibian xenopus laevis depends largely upon translational and post-translational regulatory mechanisms to direct the complex cytodifferentiations that take place during early cleavage and blastula formation. the cell cycle dependence of protein synthesis was examined in developing xenopus embryos as well as in cycling cell-free lysates from xenopus eggs. in both cases m-phase and the activation of the m-phase kinase were found to be correlat ...19911647990
the 165-kda dna topoisomerase i from xenopus laevis oocytes is a tissue-specific variant.two forms of topoisomerase i can be purified from xenopus laevis. a protein with a molecular mass of 165 kda has been identified as topoisomerase i in ovaries (richard and bogenhagen, 1989. j. biol. chem. 264, 4704-4709). when a similar purification is performed using liver tissue, topoisomerase i is purified as a 110-kda protein. separate rabbit antisera were raised against oocyte and liver topoisomerase i polypeptides. each antiserum reacts in immunoblotting or immunoprecipitation procedures o ...19911647991
melatonin receptor mrna expression in xenopus oocytes: inhibition of g-protein-activated response.melatonin is the major endocrine product of the pineal gland in the mammalian brain and plays a variety of roles in photoperiodic functions. in order to investigate melatonin receptors, poly(a)+ rna was extracted from pars tuberalis of the ovine pituitary and injected into oocytes of xenopus laevis. after 3-5 days of incubation, functional melatonin receptors were expressed. receptors were revealed by their inhibitory effect upon oscillatory currents resulting from alf4-induced activation of g-p ...19911648693
genes encoding receptors for insulin and insulin-like growth factor i are expressed in xenopus oocytes and embryos.insulin and insulin-like growth factor i (igf-i) initiate their metabolic, growth, and differentiation effects through binding to the insulin receptor and the igf-i receptor, two members of the tyrosine kinase family of receptors. to study the role of these peptides and receptors in early development, we used the polymerase chain reaction and embryo-derived rna to generate partial cdna sequences of the insulin receptor and igf-i receptor from the amphibian xenopus laevis. three unique tyrosine k ...19911648732
characterization of the defect in the na(+)-phosphate transporter in vitamin d-resistant hypophosphatemic mice.hypophosphatemic vitamin d-resistant rickets is the most common form of vitamin d-resistant rickets in man. the hypophosphatemic mouse model (hyp) is phenotypically and biochemically similar to the human disease. biochemically, hypophosphatemia is the hallmark of this disorder. the cause of the hypophosphatemia is thought to be secondary to a defect in the renal and/or intestinal na(+)-phosphate transporter. the current studies were designed to investigate and characterize the localization of th ...19911649826
segregation of nmda and non-nmda receptors at separate synaptic contacts: evidence from spontaneous epsps in xenopus embryo spinal neurons.many excitatory amino acid (eaa)-mediated synaptic potentials are dual-component as a result of the simultaneous activation of n-methyl-d-aspartate (nmda) and non-nmda receptor subtypes, the two major classes of eaa receptor in vertebrates. this raises the question of whether the two receptor types are located separately or together at individual synaptic contacts. support for the segregation of nmda and non-nmda receptors in discrete anatomical patches arises from the observation that the fast ...19911650276
study of frog (rana esculenta) proopiomelanocortin processing in the intermediate pituitary. identification of alpha-melanotropin, beta-melanotropin, lys-gamma-melanotropin, and corticotropin-like intermediate lobe peptide.the proteolytic processing of frog (rana esculenta) proopiomelanocortin in melanotropic cells of the intermediate pituitary gland has been examined through purification of the mature fragments by reverse-phase high-pressure liquid chromatography and microsequencing of isolated peptides. alpha-melanotropin, beta-melanotropin, lys-gamma-melanotropin, corticotropin-like intermediate lobe peptide, and hinge peptide have been isolated and chemically characterized. the results show a high preservation ...19911651291
effects of calcitonin gene-related peptide and efferent nerve stimulation on afferent transmission in the lateral line organ.1. calcitonin gene-related peptide (cgrp) is a 37-amino acid peptide immunolocalized in efferent fibers innervating hair-cell organs, including the lateral line organ of xenopus laevis. cgrp, applied in nanomolar concentrations, increased the spontaneous discharge rate in afferent fibers innervating hair cells of the lateral line organ. 2. the increase in spontaneous discharge rate with application of cgrp was associated with an increase in the rate of occurrence of spontaneous excitatory postsy ...19911651373
simple luminometric assay to detect phosphoinositol-linked receptor expression in xenopus oocytes.a simple and sensitive method to measure the expression of phosphoinositol-linked receptors in xenopus laevis oocytes is described. oocytes are co-injected with the calcium photoprotein aequorin and rna, encoding the receptor of interest. the binding of ligand to the expressed receptor increases intracellular calcium that induces the aequorin to luminesce. with an autosampler-equipped luminometer, this provides a fully automated assay of receptor expression of oocytes. this method was applied to ...19911652262
coordinated expression of 7b2 and alpha msh in the melanotrope cells of xenopus laevis. an immunocytochemical and in situ hybridization study.7b2 is a highly conserved protein present in many secretory cells. using in situ hybridization techniques and immunocytochemistry, parameters concerning the biosynthesis and storage of the 7b2 protein were studied in the pituitary gland and median eminence of the clawed toad xenopus laevis, in relation to the physiological process of background adaptation. 7b2-like immunoreactivity was present in the median eminence, in the neural and anterior pituitary lobes and, particularly, in the melanotrop ...19911652364
conditions for a backward-running na+/k+ pump in xenopus oocytes.current generated by the electrogenic na+/k+ pump protein was determined in oocytes of xenopus laevis as strophantidine-sensitive current measured under voltage clamp. under conditions of reduced intracellular [na+] and [atp], both to values below 1 mm, and in extracellularly k(+)-free medium, the na+/k+ pump seems to operate in a reversed mode pumping na+ into the cell and k+ out of the cell. this is demonstrated by strophantidine-induced hyperpolarization of the membrane and inward-directed cu ...19911654105
role of gtpase activating protein in mitogenic signalling through phosphatidylcholine-hydrolysing phospholipase c.recent evidence has accumulated showing that activation of plc-catalysed hydrolysis of phosphatidylcholine (pc-plc) is a critical step in mitogenic signal transduction both in fibroblasts and in oocytes from xenopus laevis. the products of ras genes activate pc-plc, bind guanine nucleotides, have intrinsic gtpase activity, and are regulated by a gtpase-activating protein (gap). it has been suggested that, in addition to its regulatory properties, gap may also be necessary for ras function as a d ...19911655413
functional expression of n-terminal truncated alpha-subunits of na,k-atpase in xenopus laevis oocytes.n-terminal deletion mutants of na,k-atpase alpha 1 isoforms initiating translation at met34 (alpha 1t1) or at met43 (alpha 1t2) were expressed in x. laevis oocytes. compared to beta 3 crna injected controls, the co-expression of alpha 1wt, alpha 1t1, alpha 1t2 with beta 3 subunits results in a 2- to 3-fold increase of ouabain binding sites, parallelled by a concomitant increase in na,k-pump current. the apparent k1/2 for potassium activation of the alpha 1t2/beta 3 na,k-pumps is significantly hi ...19911655538
the receptor for yolk lipoprotein deposition in the chicken oocyte.the final rapid growth phase of the chicken oocyte is characterized by massive uptake of hepatically synthesized yolk precursor proteins from the plasma. the two major yolk-forming components, very low density lipoprotein (vldl) and vitellogenin (vtg), have been shown to interact with a 95-kda protein present in detergent extracts of ovarian membranes; this protein is absent in hens of a mutant nonlaying chicken strain (nimpf, j., radosavljevic, m., and schneider, w. j. (1989) j. biol. chem. 264 ...19911655760
the thyroid hormone receptor gene (c-erba alpha) is expressed in advance of thyroid gland maturation during the early embryonic development of xenopus laevis.the c-erba proto-oncogene encodes the thyroid hormone receptor, a ligand-dependent transcription factor which plays an important role in vertebrate growth and development. to define the role of the thyroid hormone receptor in developmental processes, we have begun studying c-erba gene expression during the ontogeny of xenopus laevis, an organism in which thyroid hormone has well-documented effects on morphogenesis. using polymerase chain reactions (pcr) as a sensitive assay of specific gene expr ...19911656222
inhibition of chromatin assembly in xenopus oocytes correlates with derepression of the mouse mammary tumor virus promoter.the mouse mammary tumor virus (mmtv) promoter is positively regulated by glucocorticoid hormone via binding of glucocorticoid receptor to a specific response element. upon addition of hormone, a nucleosome containing the glucocorticoid response element is removed or structurally altered, suggesting that the nucleosome interferes with transcription. accordingly, inhibition of chromatin assembly should relieve the repression and result in an increased constitutive activity. we have tested this hyp ...19911656227
indirect action of elevated potassium and neuropeptide y on alpha msh secretion from the pars intermedia of xenopus laevis: a biochemical and morphological study.a number of neurochemical messengers have been shown to act directly on the melanotrope cells of the pars intermedia of xenopus laevis to regulate alpha msh secretion. in the present study the possibility that the melanotropes are also indirectly controlled has been examined. for this purpose, the characteristics of alpha msh release from superfused intact lobes, cultured lobe and isolated melanotropes were compared after treatment with elevated potassium. isolated melanotropes responded with an ...19911656300
adrenocorticotropin receptors: functional expression from rat adrenal mrna in xenopus laevis oocytes.the adrenocorticotropin (acth) receptor, which binds corticotropin and stimulates adenylate cyclase and steroidogenesis in adrenocortical cells, was expressed in xenopus laevis oocytes microinjected with rat adrenal poly(a)+ rna. expression of the acth receptor in individual stage 5 and 6 oocytes was monitored by radioimmunoassay of ligand-stimulated camp production. injection of 5-40 ng of adrenal mrna caused dose-dependent increases in acth-responsive camp production. these were detected at 48 ...19911656448
immunolocalization of n-acetylgalactosaminylphosphotransferase in the adult retina and subretinal space.the cell surface n-acetylgalactosaminylphosphotransferase (galnacptase) modulates n-cadherin-mediated adhesion among embryonic chick retinal cells (balsamo et al., 1990). we are investigating the potential role of this transferase in modulating adhesive interactions in the adult retina. using a previously characterized monoclonal anti-galnacptase, we have used immunohistochemical and immunoblot techniques to localize and characterize the transferase in the retinas of the post metamorphic frog (x ...19911657627
native yeast telomeres are sufficient to stabilize linear dna in xenopus laevis oocytes.we have constructed a linear plasmid in yeast containing the entire bovine papillomavirus genome and tested its physical stability following microinjection into stage vi oocytes of xenopus laevis. our results show that unmodified telomeres, in contrast to the yeast-passaged telomeres, drastically affect the stability of the injected linear plasmid. plasmids carrying unmodified tetrahymena thermophila telomeric sequences are rapidly degraded in oocytes. when these plasmids are passed through yeas ...19911657721
molecular cloning and expression of platelet-activating factor receptor from human leukocytes.the cdna for a platelet-activating factor (paf) receptor was cloned from a human leukocyte cdna library using a 0.8-kilobase pair fragment of the guinea pig lung paf receptor cdna (honda, z., nakamura, m., miki, i., minami, m., watanabe, t., seyama, y., okado, h., toh, h., ito, k., miyamoto, t., and shimizu, t. (1991) nature 349, 342-346). the cdna (1.8-kilobase pairs) had an open reading frame encoding 342 amino acid residues with a calculated mr of 39,203. the clone was shown to code for a paf ...19911657923
characterization of an endogenous na+/h+ antiporter in xenopus laevis oocytes.the amiloride-sensitive na+/h+ antiporter in defolliculated oocytes of xenopus laevis was characterized by measurements of 22na+ influx and apparent h+ efflux. uptake of 22na+ was linear over a 90-min incubation period and was inhibited approximately 80% with 5 x 10(-4) mol l-1 amiloride. amiloride-sensitive sodium uptake was reduced following collagenase treatment or oocyte aging. k0.5 for amiloride inhibition was 4.13 x 10(-6) +/- 1.33 x 10(-6)mol l-1 and the km for na+ was 4.25 x 10(-3) mol l ...19911658182
sodium dependence of the epithelial sodium conductance expressed in xenopus laevis oocytes.the epithelial na+ conductance was expressed in xenopus laevis oocytes by injection of size-fractionated mrna of bovine tracheal epithelium. fractionation was achieved by sucrose density gradient centrifugation. successful expression was analysed by recording current/voltage (i/v) curves in the presence and absence of amiloride (10 mumol/l). the newly expressed conductance was half-maximally inhibited by 44 nmol/l amiloride and exhibited a selectivity for na+ over k+ of 140:1. i/v curves obtaine ...19911658728
[from ovocyte to biochemistry of the cell cycle].the cell division cycle in eukaryotes contains up to three major transition points; the conversion of quiescent cells to a stage of active proliferation, the initiation of dna synthesis (s phase) and the induction of mitosis in cells with newly replicated genome (m phase). within the past years two strategies, have converged to identify, genetically and biochemically a key protein kinase p34 cdc2 that governs the entry into mitosis. in the fission yeast schizosaccharomyces pombe a number of muta ...19911659057
the bovine mannose 6-phosphate/insulin-like growth factor ii receptor. localization of mannose 6-phosphate binding sites to domains 1-3 and 7-11 of the extracytoplasmic region.the extracytoplasmic region of the 270-kda mannose 6-phosphate/igf-ii receptor is composed of 15 repeating domains and is capable of binding 2 mol of mannose 6-phosphate (man-6-p). to localize the man-6-p binding domains, bovine receptor was subjected to partial proteolysis with subtilisin followed by affinity chromatography on pentamannosyl phosphate-agarose. eleven proteolytic fragments ranging in apparent molecular mass from 53 to 206 kda were isolated. sequence analysis of six of the fragmen ...19911660469
presence of vi-transposon-like elements in the proopiomelanocortin gene a of xenopus laevis does not affect gene activity.restriction mapping of the two proopiomelanocortin (pomc) genes of the south african clawed toad xenopus laevis revealed that pomc gene a is much larger than pomc gene b. here we report that this size difference is mainly due to the presence of four vitellogenin (vi)-transposon-like elements in pomc gene a, while vi elements are absent from pomc gene b. alignment of these elements with other vi elements revealed a consensus sequence of 463 bp, which is bounded by a 16 bp inverted repeat and flan ...19911662768
regulation of beta-adrenergic response in xenopus laevis oocytes. 19911663058
systems for the study of nuclear assembly, dna replication, and nuclear breakdown in xenopus laevis egg extracts. 19911664032
the hydrolysis of phosphatidylinositol 4-phosphate in membranes of xenopus laevis oocytes: characteristics of a phosphomonoesterase.1. phosphatidylinositol 4-phosphate (ptdins4p) is degraded by isolated membranes from xenopus laevis oocytes. 2. incubation of [4-32p]ptdins4p with membranes yields only radioactive inorganic phosphate, indicating the presence of a phosphomonoesterase. 3. membranes hydrolyze ptd[2-3h]ins4p to produce mainly ptd[2-3h]ins in the lipid phase. in this incubation [3h]inositol and inositol monophosphate appear in the water phase. 4. membrane incubations of ptd[2-3h]ins4p carried out in the presence of ...19911664308
type iii phosphodiesterase plays a necessary role in the growth-promoting actions of insulin, insulin-like growth factor-i, and ha p21ras in xenopus laevis oocytes.three phosphodiesterase (pde) type iii inhibitors were tested and found to inhibit xenopus oocyte maturation induced by insulin with apparent ic50 values of 2.2 +/- 0.2 microm cl-930, 25 +/- 3 microm imazodan (cl-914), and 786 +/- 237 microm piroximone (mdl 19,205). the same rank order of potencies was observed for inhibition of insulin-like growth factor-i (igf-i)-induced oocyte maturation, with ic50 values of 5.5 +/- 0.9 microm cl-930, 54 +/- 4 microm imazodan, and 1190 +/- 395 microm piroximo ...19911665204
[two types of nondepolarizing-activated calcium channels on the spinal cholinergic neurons from embryonic xenopus laevis].single calcium channel current was studied on the identified spinal cholinergic neurons from embryonic xenopus laevis with patch clamp method. the results indicate that some calcium channels show opening activity at resting membrane potential. according to the characteristics of conductance and kinetics of such channels, they could be divided into two types: a stretch sensitive type-ns with a slope conductance of 7.5 ps (mean open time 0.58 ms at resting membrane potential) and a type-nl with a ...19911665590
aggregation of pigment granules in single cultured xenopus laevis melanophores by melatonin analogues.1. isolated melanophores were differentiated from aggregates of neural crest obtained from neurula stage xenopus laevis embryos after 2 days in culture. 2. condensation of pigment granules in these cells by melatonin (5-methoxy n-acetyltryptamine, amt) and various novel analogues was monitored with an image analysis system to quantitate the area occupied by pigment in individual cells. 3. melanophores exposed to vehicle (a maximum of 0.1% meoh) showed little (less than 5%) change in pigment area ...19911667293
nephroblastoma in the clawed frog xenopus laevis.one 2.5-3 year old female clawed frog (xenopus laevis), out of a consignment of 4,000 frogs, was found to have an abnormal abdominal growth, weighing 7.9 g. the growth was examined histologically and on the basis of the abundant stroma and serially-arranged tubules nephroblastoma was diagnosed. the growth is not considered to be transmissible.19911667587
oscillatory muscarinic acetylcholine responses of xenopus oocytes are desensitized by protein kinase c and sensitized by protein phosphatase 2b.the oscillatory current response to acetylcholine (ach) in xenopus laevis oocytes, mediated by endogenous muscarinic ach receptors, is known to be mildly desensitized by repetitive ach applications. pretreatment of oocytes with staurosporine (an inhibitor of protein kinases) was found not only to abolish this desensitization but also to positively and progressively potentiate oscillatory ach responses. this sensitization by staurosporine was suppressed by 12-o-tetradecanoylphorbol 13-acetate (an ...19911667757
pathways of degradation and mechanism of action of antisense oligonucleotides in xenopus laevis embryos.recently, we described a new class of antisense oligonucleotides that can be used to direct the cleavage of mrnas in xenopus laevis embryos by rnase h (dagle et al., nucleic acids res. 18, 4751-4757). in this study, we have examined several factors that determine the activity of these derivatives. in embryos, oligodeoxyribonucleotides were found to be rapidly degraded by a 3' exonuclease. modification of 3'-terminal phosphodiester linkages as phosphoramidates blocks this activity. the predominan ...19911668307
different forms of soluble cytoplasmic mrna binding proteins and particles in xenopus laevis oocytes and embryos.to gain insight into the mechanisms involved in the formation of maternally stored mrnps during xenopus laevis development, we searched for soluble cytoplasmic proteins of the oocyte that are able to selectively bind mrnas, using as substrate radiolabeled mrna. in vitro mrnp assembly in solution was followed by uv-cross-linking and rnase digestion, resulting in covalent tagging of polypeptides by nucleotide transfer. five polypeptides of approximately 54, 56 60, 70, and 100 kd (p54, p56, p60, p7 ...19911670777
distinct, developmentally regulated brain mrnas direct the synthesis of neurotransmitter transporters.the xenopus laevis oocyte expression system was utilized to define developmental and structural properties of neurotransmitter transporter mrnas and the pharmacological characteristics of encoded carriers independent of the complexities of brain tissue preparations. poly(a)+ rna from dissected brain regions of neonatal and adult rats was microinjected into xenopus oocytes and the expression of na(+)-dependent neurotransmitter transporters determined 48 h later. transport studies conducted with o ...19911671586
functional expression of the intestinal peptide-proton co-transporter in xenopus laevis oocytes.the expression of the intestinal peptide-proton cotransporter was examined in xenopus laevis oocytes by microinjection of poly(a)+ mrna prepared from rabbit intestinal mucosal cells. the concomitant expression of the glucose-sodium co-transporter was used as the control for the effectiveness of the expression technique. there was significant endogenous activity of gly-sar uptake in water-injected oocytes, but the uptake activity increased nearly 3-fold in poly(a)+ mrna-injected oocytes. the expr ...19911672128
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