Publications

morphological classification of retinal ganglion cells in adult xenopus laevis.	retrograde transport of horseradish peroxidase (hrp) was used to characterise the soma and dendritic arborization of retinal ganglion cells in adult xenopus laevis toad. hrp was administered to the cut end of the optic nerve and the morphological characteristics of hrp-filled ganglion cells were analysed in retinal wholemount preparations using computer assisted morphometry. ganglion cells were classified according to their soma size, dendritic branching pattern, dendritic field and the number o ...	1988	3394956
reversal of dorsoventral polarity in xenopus laevis embryos by 180 degrees rotation of the animal micromeres at the eight-cell stage.	the 180 degrees rotation of the animal cell quartet at the 8-cell stage of xenopus laevis embryos leads to a reversal of dorsoventral polarity in a majority of the embryos. dorsal micromeres appear to instruct the macromeres in contact with them to initiate later steps in dorsal development. this inductive process is most apparent in the second half of the third cell cycle and is largely lost by the beginning of the fourth cell cycle.	1988	3396766
homologous genes for mouse 4.5s hybrna are found in all eukaryotes and their low molecular weight rna transcripts intermolecularly hybridize with eukaryotic 18s ribosomal rnas.	previous work has reported the isolation and sequencing of a mouse low molecular weight rna species designated 4.5s hybridizing rna or hybrna because of its ability to intermolecularly hybridize with mouse mrna and 18s rrna sequences. using synthetic dna oligonucleotide probes we have examined the conservation of this gene sequence and its expression as a lmwrna transcript across evolution. southern blot analysis has shown that homologous genes of single or low copy number are found in all eukar ...	1988	3399384
transcription complexes that program xenopus 5s rna genes are stable in vivo.	the long-term stability of transcription complexes on 5s rna genes has been demonstrated in vivo. complexes on oocyte and somatic-type 5s rna genes injected into xenopus laevis oocyte nuclei are stable for at least 4 days. tissue culture cells and mature erythrocytes have equivalent numbers of somatic 5s rna genes programmed into transcription complexes, yet the former cell type has a greater than 50-fold higher cellular content of transcription factor iiia (tfiiia). functional transcription com ...	1988	3399503
comparison of a carboxypeptidase e-like enzyme in human, bovine, mouse, xenopus, shark and aplysia neural tissue.	several diverse species contain an enzyme with many properties in common with those of bovine carboxypeptidase e (cpe), a neuropeptide processing carboxypeptidase b-like enzyme. this enzyme has been designated ec 3.4.17.10, and is also known as enkephalin convertase and carboxypeptidase h. all tissues that are known to contain bioactive peptides also contain cpe-like enzymatic activity. in xenopus laevis, enzyme activity is highest in the brain and pituitary, lower in the skin, and undetectable ...	1988	3401766
calcium sensitivity of microtubules changes during the cell cycle of xenopus laevis tadpole endothelial cells.	endothelial cells derived from xenopus tadpole hearts (xth-2: schlage et al. 1981) have been permeabilized for calcium using the ionophore a 23187. a ca2+-concentration of 1 microm causes a graded disassembly of microtubules (mts): with increasing periods of incubation mts disintegrate and then depolymerize completely. the frequency of the different stages of depolymerization depends on the length of the ca2+ incubation period, even after 60 min incubation time some mts remain. the stage of depo ...	1988	3401933
accumulation and decay of dg42 gene products follow a gradient pattern during xenopus embryogenesis.	the dg42 gene is expressed during a short window during embryogenesis of xenopus laevis. the mrna for this gene can be first detected just after midblastula, peaks at late gastrula, and decays by the end of neurulation. the sequence of the dg42 cdna and genomic dna predicts a 70,000-da protein that is not related to any other known protein. antibodies prepared against portions of the dg42 open reading frame that had been expressed in bacteria detected a 70,000-da protein in the embryo with a tem ...	1988	3410156
in vitro proliferation and differentiation of myogenic cells from adult xenopus.	a technique is described for isolating amphibian myogenic cells from the muscle of adult xenopus laevis (dauchin). muscles were dissociated with 0.2% collagenase and 0.1% trypsin. the resulting cell suspensions were separated from the remaining myofibres by filtration through nylon grids. most of the cells remaining in the filtrate suspension were satellite cells or fibroblasts. when plated in petri dishes, satellite cells adhered to the substrate, became spindle-shaped and proliferated activity ...	1988	3408748
close juxtaposition between inducing chordamesoderm and reacting neuroectoderm is a prerequisite for neural induction in xenopus laevis.	the results of this study indicate that the induction of the central nervous system in xenopus laevis depends on the close juxtaposition of inducing chordamesoderm and reacting ectoderm, which is necessary for the short distance migration of neural inducing factors. the examination of the neuroectoderm-chordamesoderm interface at intervals of 1 h up to 5 h showed that the onset of neural induction is correlated to the degree of contact formation between ectodermal and mesodermal cells. in the ec ...	1988	3409323
a ventrally localized inhibitor of melanization in xenopus laevis skin.	melanophores normally differentiate in dorsal but not in ventral skin of xenopus laevis. we have sought factors which might regulate this differentiation pattern, and we have obtained a putative melanization inhibiting factor (mif) from ventral but not from dorsal skin. preliminary studies reveal that mif is destroyed by heat or trypsin treatment, indicating its protein composition, and has a molecular weight in the range of 300 kda. the effects of mif on the differentiation of neural crest deri ...	1988	3410161
corticosteroid receptors in liver cytosol of the clawed toad, xenopus laevis: daily and seasonal variations.	in postmetamorphic xenopus laevis liver cytosol the glucocorticoid binding capacity r0 and the dissociation constant kd were determined. the receptor assay included an incubation period of 24 hr at 0-4 degrees with sodium molybdate to stabilize the receptor. dexamethasone, triamcinolone acetonide, and corticosterone as tritiated ligands were compared regarding the r0 (67.6, 57.2, and 30.7 fmol/mg protein), the kd (3.54, 0.56, and 9.03 nm), and the rate of dissociation in young specimens of x. la ...	1988	3410292
monoclonal autoantibodies recognizing histone variants.	balb/c mice were immunized with affinity purified ro(ss-a) from human origin in order to allow the preparation of monoclonal anti-ro(ss-a) antibodies. after fusion of mouse myeloma cells (line sp2/0 a914) with spleen cells from one of these mice, anti-ro(ss-a) monoclonals were not obtained, but, instead, two igm producing hybridomas reactive with histone h1 and one with histone h2b. the specificity of the anti-h1 monoclonals was investigated by means of immunoblotting of very lysine-rich histone ...	1988	3410513
a membrane-associated dimer of acetylcholinesterase from xenopus skeletal muscle is solubilized by phosphatidylinositol-specific phospholipase c.	the susceptibility to phosphatidylinositol-specific phospholipase c of the membrane associated acetylcholinesterase (ache) forms of xenopus laevis skeletal muscle was examined. this treatment released almost all the detergent-soluble ache species from muscle homogenates. sucrose gradient analysis showed that the released acetylcholinesterase form corresponds to a hydrophilic g2 dimer, indicating that this dimer has a glycolipid anchoring domain which contains phosphatidylinositol.	1988	3412641
purification and characterization of a casein-kinase-ii-type enzyme from xenopus laevis ovary. biological effects on the meiotic cell division of full-grown oocyte.	a casein kinase of type ii has been highly purified from xenopus laevis ovary. a new experimental protocol has been developed for the purification, consisting in four chromatographic steps: hydrophobic on tyrosine-agarose, ion exchange on deae-sepharose, affinity on heparin-sepharose and fast protein liquid on mono q. the purification was greater than 20,000, taking into account an inhibitor present in the starting material which masked the activity in the crude fraction. the overall yield was g ...	1988	3422187
selective visualization of gene structure with ultraviolet light.	the ability of the ultraviolet (uv) "footprinting" technique to detect chromatin has been investigated in vitro. two basic types of chromatin, a phased nucleosome and a phased nucleosome containing a phased h1 protein, have been reconstituted onto a cloned 5s ribosomal rna gene from sea urchin. the histone-dna interactions in each complex have been probed with exonuclease iii, dnase i, dimethyl sulfate, and uv light. whereas dnase i and exonuclease iii readily detect interactions between histone ...	1988	3422448
cdna and deduced primary structure of rat protein b23, a nucleolar protein containing highly conserved sequences.	protein b23 (mr/pi = 38,000/5.1) is a major rna-associated nucleolar phosphoprotein which contains highly acidic segments and has a high affinity for silver ions. using synthetic oligonucleotides as probes cloned cdnas encoding protein b23 were isolated and characterized. one of the cdnas, obtained from a rat brain library, contained an insert of 1232 base pairs of dna encoding a polypeptide of 292 amino acid residues. segments of the protein sequence were confirmed by partial sequencing of cnbr ...	1988	3417636
the extracellular matrix of xenopus laevis eggs: a quick-freeze, deep-etch analysis of its modification at fertilization.	eggs of the amphibian, xenopus laevis, were quick-frozen, deep-etched, and rotary-shadowed. the structure of the extracellular matrix surrounding these eggs, including the perivitelline space and the vitelline envelope (ve), was visualized in platinum replicas by electron microscopy. the perivitelline space contains an elaborate filamentous glycocalyx which connects microvillar tips to the plasma membrane, to adjacent microvilli, and to the overlying ve. the ve is comprised of two layers, the in ...	1988	3417770
locations of methyl groups in 28 s rrna of xenopus laevis and man. clustering in the conserved core of molecule.	28 s ribosomal rna from several vertebrate species contains some 68 to 70 methyl groups. evidence described in this paper enables some 58 methyl groups to be located in the primary structure of 28 s ribosomal rna from xenopus laevis. most of the locations are unambiguous but a few are currently tentative. in human 28 s ribosomal rna the great majority of the same sites are methylated as in xenopus, but there are a few differences between the respective methyl group distributions. the main featur ...	1988	3418702
effect of denervation of carotid labyrinths on breathing in unrestrained xenopus laevis.	the effect of denervation of the carotid labyrinths on breathing responses to simultaneously applied aerial and aquatic normoxia, hypoxia, or hypercapnia has been studied in unrestrained xenopus laevis. denervation significantly reduced vi of normoxic toads compared with vi in intact and sham-operated toads, due to a significant reduction in the volume of each buccal pumping movement (vb) in denervates. breathing increased significantly in response to environmental hypoxia or hypercapnia in inta ...	1988	3420325
cell proliferation in ectodermal explants from xenopus embryos.	dissociated prospective ectoderm cells from xenopus laevis embryos divide autonomously up to the 17th division cycle of the embryo. to examine the requirements for the further proliferation of these cells, the continuation of cell division in compact ectodermal explants beyond the 17th division cycle has been studied. such explants develop into aggregates of epidermal cells, as can be shown immunohistochemically with an anti-serum against xenopus epidermal cytokeratin. cell division in these exp ...	1988	28305558
xenopus skin mucus induces oral dyskinesias that promote escape from snakes.	african clawed frogs fed to american water snakes induced yawning and gaping which slowed ingestion and facilitated the frogs' escape without inducing flavor aversion. the peptide and/or indolealkylamine contents of the frog's poison glands caused the effect because frogs with purged glands did not induce these behaviors and rarely escaped. poison gland mucus, applied orally, elicited similar oral movements. the frog's clear lubricating mucus was inactive. as several compounds in the poison glan ...	1988	3227042
crystallins during xenopus laevis free lens formation.	the ontogeny and localization of crystallins during free lens development (i.e. lens development without the optic vesicle) were investigated in xenopus laevis using the indirect immunofluorescence staining method with an antiserum raised against homologous total lens soluble proteins. since the developing free lenses pass through stages similar to those of the lenses regenerated from the inner cell layer of the outer cornea following lentectomy in the same species freeman's classification was u ...	1988	28305564
developmental pattern and molecular identification of globin chains in xenopus laevis.	high-resolution electrophoresis of larval and adult hemoglobins of xenopus laevis reveals stage-specific differences in the number and mobility of the globin chains. to establish the relationship between the globin chains and the previously described globin genes, the corresponding mrnas were hybrid-selected from total erythroblast rna by representative cdna clones, and translated in vitro. electrophoretic separation of the translation products allowed identification of a major and a minor α-glo ...	1988	28305747
protein kinases in amphibian ectoderm induced for neural differentiation.	ectoderm explants from early gastrula stages of xenopus laevis were induced with a neutralizing factor. the factor was isolated from xenopus gastrulae and partially purified by chromatography on deae cellulose. the ectoderm was cultured for different periods of time and then homogenized. protein kinase activity was determined in the homogenates from induced and control explants with histone h 1 or c-terminal peptide derived from histone h 1 as substrates. the c-terminal peptide is a more specifi ...	1988	28305429
import of peroxisomal hydroxypyruvate reductase into glyoxysomes.	a new procedure was used to purify the peroxisomal matrix enzyme hydroxypyruvate reductase (hpr) from green leaves of pumpkin (cucurbita pepo l.) and spinach (spinacia oleracea l.). monospecific antibodies were prepared against this enzyme in rabbits. immunoprecipitation of hpr from watermelon (citrullus vulgaris schrad.) yielded a single protein with a subunit molecular weight of 45 kda. immunohistochemical labeling of hpr was found exclusively in watermelon microbodies. isolated polyadenylated ...	1988	24220768
mesoderm induction in the future tail region of xenopus.	we have used interspecific grafts between xenopus borealis and xenopus laevis to study the signalling system that produces tail mesoderm. early gastrula ectoderm grafted into the posterior neural plate region of neurulae responds to a mesodermal inducing signal in this region and forms mainly tail somites; this signal persists until at least the early tail bud stage. ventral ectoderm grafted into the posterior neural plate loses its competence to respond to this signal after stage 10 1/2. we hav ...	1988	28305752
the response of structure and function of the gravireceptor in a vertebrate to near weightlessness.	the paper sums up results of a 7-day space flight experiment (d-l-mission-bw-sta 00-statex) using growing frog embryos and larvae (xenopus laevis) as a model system. evaluation of photographs taken from the surface of sectioned deep-frozen objects, and micrographs using tem and sem show no aberrations in the shape, size, position, or respective electron density of the otolith membranes in larvae developed for 154 h under near-zero g. the further evaluation of the "weightless larvae" revealed a p ...	1988	11542431
a step in embryonic axis specification in xenopus laevis is simulated by cytoplasmic displacements elicited by gravity and centrifugal force.	determination of the body pattern in xenopus embryos is known to involve at least six steps. one of these steps can be experimentally simulated by inclining the fertilized egg with respect to gravity or centrifugal force (10-30 g x 4 min, directed 90 degrees to the animal-vegetal axis). in these eggs, the dorsal structures of the body axis form from the side of the egg that was uppermost in the gravitational or centrifugal field. this topography is seen even if the sperm entry point side (the ...	1989	11537329
the amphibian egg as a model system for analyzing gravity effects.	amphibian eggs provide several advantageous features as a model system for analyzing the effects of gravity on single cells. those features include large size, readily tracked intracellular inclusions, and ease of experimental manipulation. employing novel gravity orientation as a tool, a substantial data base is being developed. that information is being used to construct a 3-d model of the frog (xenopus laevis) egg. internal cytoplasmic organization (rather than surface features) are being ...	1989	11537330
subcellular components of the amphibian egg: insights provided by gravitational studies.	most cytoplasmic regions of fertilized amphibian eggs move with respect to the gravity vector in experimentally gravity oriented eggs. the pattern and extent of this movement varies among different batches of eggs. this variation in apparent cytoplasmic viscosity (or, conversely, cytoplasmic mobility) can be correlated with variations in subsequent morphogenesis of experimental, gravitationally manipulated eggs. therefore, the proper interpretation of gravity experiments with amphibian eggs r ...	1989	11537331
fertilization of frog eggs on a sounding rocket in space.	during the texus-17 flight (april/may 1988) eggs of a higher organism, the anuran amphibian xenopus laevis, have for the first time been successfully fertilized under microgravity on a sounding rocket. this result also implies that life sciences experiments of short duration can be carried out on sounding rockets. the latter can therefore function as additional carriers for such experiments. histological sections of the experimental material demonstrated the penetration of sperm into eggs, wh ...	1989	11537332
is the capacity for optic nerve regeneration related to continued retinal ganglion cell production in the frog?	in the central nervous system of fish and frogs, some, but not all, axons can regenerate. retinal ganglion cells are among those that can. the retinae of fish and frogs produce new retinal neurons, including ganglion cells, for months or years after hatching. we have evaluated the hypothesis that retinal axonal regeneration is obligatorily linked to continued production of new ganglion cells. we used bromodeoxyuridine immunocytochemistry to assess retinal neurogenesis in juvenile, yearling, and ...	1989	12106120
modulation of neuropeptide-lnduced membrane currents by protein kinase c in xenopus oocytes injected with gh pituitary cell poly(a) rna.	abstract protein kinase c was activated in xenopus laevis oocytes by phorbol ester treatment and its effects on the inositol trisphosphate/ca(2+) transmembrane signalling pathway analysed. induction of the pathway was achieved by ligand stimulation of trh receptors translated from gh(3) pituitary cell mrna. in voltage-clamped oocytes bath application of peptide, injection of guanosine 5'-(3-o-thio) triphosphate (gtpgammas), inositol trisphosphate or ca(2+) all elicited inward membrane currents. ...	1989	19210484
a mesoderm-inducing factor from a xenopus laevis cell line : chemical properties and relation to the vegetalizing factor from chicken embryos.	we have compared the chemical properties and biological activities of the mesoderm-inducing factor that is secreted by the xenopus xtc cell line with the vegetalizing factor from chicken embryos. the inducing activity of the factors was tested in different concentrations on totipotent ectoderm either by implantation into early gastrulae of triturm alpestris or by application of solutions to isolated ectoderm of early gastrulae of xenopus laevis. both factors have similar properties. they are not ...	1989	28305777
gaba and the regulation of serotonin n-acetyltransferase activity in amphibian retina-i. effects of gaba agonists and antagonists.	retinal melatonin biosynthesis is regulated in part by changes in the activity of serotonin n-acetyltransferase (nat), which increases at night in dark-adapted retinas, but not in light-exposed retinas. using an in vitro preparation of xenopus laevis (african clawed frog) eye cups, we have obtained evidence supporting the involvement of gamma-aminobutyric acid (gaba) in the regulation of nat activity. gaba, the gaba-a receptor agonists muscimol and isoguvacine, and the gaba-b receptor agonist (? ...	1989	20504530
gaba and the regulation of serotonin n-acetyltransferase activity in amphibian retina-ii. the role of dopamine.	retinal melatonin biosynthesis is regulated in part by the activity of serotonin n-acetyltransferase (nat), which increases in dark-adapted, but not light-exposed, retinas at night. using an in vitro eye cup preparation from the african clawed frog (xenopus laevis), we have obtained evidence indicating that dopamine and gamma-aminobutyric acid (gaba) interact in the regulation of the nocturnal rise in nat activity. increases of nat activity induced by the gaba agonist muscimol were suppressed by ...	1989	20504531
the metamorphic switch in hemoglobin phenotype ofxenopus laevis involves erythroid cell replacement.	to elucidate the cellular basis of hemoglobin transition inxenopus laevis the distribution of larval and adult hemoglobins was analyzed by indirect immunofluorescence in the circulating erythrocytes during metamorphosis. in addition, the morphological characteristics as well as the capacity for synthesis of dna and hemoglobin in the erythrocytes were followed during the same developmental period. our quantitative analysis on the distribution of larval and adult hemoglobins suggests that they are ...	1989	28305873
development of the ethmoidal structures of the endocranium in the anuran pipa pipa.	investigation of eight developmental stages by means of serial sections and subsequent graphic or wax model reconstructions, as well as by means of cleared-and-stained and dissected material, revealed that the ethmoidal endocranium in pipa pipa consists in early states of a single horizontal ethmoid plate lacking labial cartilages. later in the course of development, structures comparable with those in other anurans appear, though modified and of reduced size. these adult structures arise from t ...	1989	29865644
ultrastructural changes in the connective tissue of the gastric region during the metamorphosis of xenopus laevis.	development of the gastric connective tissue of xenopus laevis during metamorphosis was investigated by electron microscopy. throughout the larval period to stage 60, the layer of connective tissue underlying the gastric epithelium consists of immature fibroblasts surrounded by a sparse extracellular matrix. at the beginning of the transition from the larval to the adult epithelial form, at about stage 60, extensive changes occur in the connective tissue. the number of cells suddenly increses an ...	1989	29865622
b----a transitions within a 5 s ribosomal rna gene are highly sequence-specific.	the uv footprinting technique has been used to detect and map, at single nucleotide resolution, the formation of a conformations within a sea urchin 5s ribosomal rna gene. increasing amounts of the dehydrating agent, trifluorethanol, were used to induce the b----a transition. our measurements argue that the b----a transition is highly sequence-specific. fourteen different sequences within a fragment of dna bearing the 5 s gene were found to undergo the b----a transition independently of one anot ...	1989	2917994
bouton ultrastructure and synaptic growth in a frog autonomic ganglion.	postmetamorphic growth in the frog, xenopus laevis, is accompanied by an increase both in the size of autonomic neurons in the heart and in the number of synaptic boutons that contact their surface. to determine whether the properties of individual boutons change as their number increases, serial-section electron microscopy was used to examine bouton ultrastructure at the end of metamorphosis and in the adult. the area of bouton contact, number of active zones per bouton, active zone size, perce ...	1989	2925900
a morphometric study of bone and tooth volumes in the pipid frog xenopus laevis (daudin), with comments on the importance of tooth resorption during normal tooth replacement.	volumetric estimations of teeth and bone on serial sections using a semiautomatic image analyzer indicate that, in the polyphyodont dentition of the pipid anuran xenopus laevis (daudin), the mean volume of the dentine composing the teeth is about 23.5% of the volume of the supporting maxillae and premaxillae. during tooth replacement, osteoclasts resorb up to 98% of the dentine. teeth may be resorbed rather than shed in order to conserve tooth constituents because, if shedding of complete teeth ...	1989	2926364
gradual appearance of a regulated retinotectal projection pattern in xenopus laevis.	the topographic projection pattern formed by the retinal ganglion cell axons in the tectum of the lower vertebrate appears to require positional cues that guide the optic nerve fibers to their appropriate targets. one approach to understanding these positional cues or "positional information" has been to investigate changes in the pattern of the retinotectal projection after surgical manipulation of the embryonic eyebud. analysis of these apparent changes in the patterns of positional informatio ...	1989	2917695
the effects of forced and voluntary diving on plasma catecholamines and erythrocyte ph in the aquatic anuran, xenopus laevis.	the lactacidosis and hypoxaemia associated with enforced diving in xenopus leads to a marked increase in circulating catecholamines, a phenomenon not observed during periods of voluntary diving. the magnitude of the catecholamine surge (predominantly noradrenaline) during an enforced dive appears to be matched to the severity of the hypoxaemia and/or acid-base disturbance. indeed, a strong linear correlation was found between the decrease in arterial ph and the rise in plasma catecholamines that ...	1989	2920814
melatonin analogues induce pigment granule condensation in isolated xenopus laevis melanophores in tissue culture.	2-iodomelatonin, a ligand which has recently been used to identify melatonin-binding sites in the brain, produced condensation of pigment granules when added to isolated xenopus laevis melanophores in culture. melatonin (ec50 = 5.7 x 10(-13) mol/l), 2-iodomelatonin (ec50 = 3.4 x 10(-12) mol/l) and also 2-chloromelatonin (ec50 = 2.9 x 10(-13) mol/l) were all potent agonists in this test. melatonin analogues in which the side-chain was conformationally restricted by linkage to the 2-position of th ...	1989	2918260
conservation of structural and functional domains in complement component c3 of xenopus and mammals.	the cdna sequence and the deduced amino acid sequence of the mr 34,000 c-terminal fragment of xenopus laevis complement component c3 are presented. the sequence of xenopus c3 has 57% nucleotide identity to the corresponding sequence of human c3 and approximately 49% amino acid identity to c3 from human, mouse, and rabbit. the xenopus c3 sequence shows clusters of high and of low similarity to the mammalian c3 sequences. one of these regions of high similarity represents the domain of mammalian c ...	1989	2919181
the coelomic envelope of xenopus laevis eggs: a quick-freeze, deep-etch analysis.	the extracellular matrix of xenopus laevis oocytes was analyzed before and after meiotic maturation using quick-freeze, deep-etch, rotary-shadow electron microscopy. the perivitelline space (ps) of the meiotically immature oocyte contains a filamentous network which connects microvilli (mv) and follicle cell macrovilli to the folded oocyte surface below. the envelope overlying the ps is composed of bundles of large fibers which course between the tips of the mv. spaces between these bundles cont ...	1989	2909400
loss of material from the retrograde axonal transport system in frog sciatic nerve.	rapid axonal transport was studied in sciatic nerve preparations of the amphibian xenopus laevis maintained in vitro at 23.0 +/- 0.2 degrees c. a pulse of [35s]methionine-labeled material was allowed to move in the anterograde direction until encountering a lesion, at which a portion of the pulse reversed directions and moved in the retrograde direction. by constricting the nerve during the course of the experiment, it was possible to prevent continuous return of label from the lesion, thus crea ...	1989	2466951
the role of the various human peripheral blood mononuclear cells in the production of sendai virus-induced interferon: ifn mrna studies.	we have studied the relative contribution made to the production of interferon (ifn) in vitro in response to sendai virus by the cells of different types present in human peripheral blood, with particular emphasis on the amounts of poly(a) plus rna extractable from each subpopulation and its content of ifn mrna. peripheral blood cells were fractionated by conventional techniques, and the amounts of ifn made after induction with sendai virus were measured. the proportion of ifn-producing cells in ...	1989	2473143
gene-specific labeling of chromatin for electron microscopy.	in restriction enzyme digested xenopus laevis erythrocyte chromatin, the 5s oocyte genes were specifically labeled with colloidal gold so they could be identified in an electron microscopic study. nuclei were digested first with hindiii restriction endonuclease followed by t7 exonuclease to leave single-stranded 3' tails on the fragments. a biotinylated 15-mer oligonucleotide complementary to the tail on the 3' end of the 5s gene was annealed to the chromatin, and streptavidin complexed colloida ...	1989	2474479
translation in xenopus laevis oocytes of hybrid selected lew rat rt1.b alpha- and beta-chain transcripts results in serologically discrete class ii polypeptide chain complexes.	using the non-crossreactive mab mrc-ox3 and mrc-ox6, two serologically distinct rt1.b-specific (i-a equivalent) alpha, beta heterodimers have previously been described by us as residing at the cell surface of lew rat spleen cells. the two-chain elements were suggested to represent stable conformation isomers, diverged by dissociation of the mature gamma-chain from a mab mrc-ox6 reactive biosynthetic intermediate, composed of terminally glycosylated alpha-, beta- and gamma-chains. in this study w ...	1989	2465490
a specific quisqualate agonist inhibits kainate responses induced in xenopus oocytes injected with rat brain rna.	electrophysiological recording was used to study non-n-methyl-d-aspartate (nmda) excitatory amino acid (eaa) receptors after injection of rat brain ribonucleic acid (rna) in xenopus laevis oocytes. quisqualate (qa) induced two types of responses, a smooth one and an oscillatory one. these responses are probably mediated by the ionotropic (qai, a cationic channel) and the metabotropic (qap, a newly discovered receptor coupled to phospholipase c) qa receptors respectively. alpha-amino-3-hydroxy-5- ...	1989	2471121
effects of tha on ionic currents in myelinated axons of xenopus laevis.	in voltage-clamp experiments with the myelinated nerve fibre of xenopus laevis, 9-amino-1,2,3,4-tetrahydroacridine (tha) decreased both na+ and k+ currents and shifted the steady state inactivation potential curve in a negative direction. the effects may be described as (a) a decrease of the permeability constant pna, (b) a modified potential dependence of the inactivating system and (c) a decrease of pk. the na+ system was affected more than the k+ system.	1989	2475350
inhibition of in vivo and in vitro transcription by monoclonal antibodies prepared against wheat germ rna polymerase ii that react with the heptapeptide repeat of eukaryotic rna polymerase ii.	wheat germ rna polymerase ii was used to raise monoclonal antibodies (mabs) that cross-react with the largest subunit of calf thymus rna polymerase ii. most of these mabs were of the igm isotype and were shown to react with a synthetic peptide containing the consensus sequence for the c-terminal heptapeptide repeat that has been found on the largest subunit of rna polymerase ii from a variety of eukaryotic organisms. a representative mab (3wg2) was tested for its effect on transcription in both ...	1989	2472398
a major single-stranded dna binding protein from ovaries of the frog, xenopus laevis, is lactate dehydrogenase.	the most abundant single-stranded dna binding protein (ssb) found in ovaries of the frog, xenopus laevis, was purified to electrophoretic homogeneity. under physiological conditions, the purified ssb lowered the tm of poly[d(a-t)] and stimulated dna synthesis by the homologous dna polymerase dna primase alpha complex on single-stranded dna templates. these properties are characteristic of a bona fide single-stranded dna binding protein. the stokes radius of native ssb was calculated to be 45 a, ...	1989	2470407
5 alpha-dihydrotestosterone has nonspecific effects on membrane channels and possible genomic effects on ach-activated channels.	1. myotubes cultured from adult male xenopus laevis laryngeal muscle have been found to express androgen receptors. 2. using patch-clamp techniques, it was found that 5 alpha-dihydrotestosterone (5 alpha-dht) can act directly at membranes of these myotubes to alter the kinetic properties of acetylcholine- (ach) activated single channels. 3. when the culture medium contains 5 alpha-dht for greater than 6 days, the androgen acts through its receptors to markedly increase ach-activated, single-chan ...	1989	2470867
protein kinase c modulates neurotransmitter responses in xenopus oocytes injected with rat brain rna.	oocytes of the frog xenopus laevis express various exogenous neurotransmitter receptors and ion channels when injected with rna from excitable tissues. the oocytes serve as a convenient model system in which modulation of neurotransmitter responses can be studied. we examined the effects of activators and an inhibitor of protein kinase c (pkc) on responses to serotonin (5-ht), acetylcholine (ach), kainate, and gamma-aminobutyric acid (gaba) in oocytes injected with rna from rat brain. the pkc ac ...	1989	2471032
changes in the patterns of rna synthesis in early embryogenesis of xenopus laevis.	we analyzed the accumulation of newly-synthesized heterogeneous mrna-like rna, 4 s rna, 5 s rna, snrnas and rrna before and after the midblastula transition (mbt) in xenopus laevis embryogenesis. based on the kinetics of the labeling, we concluded that the pattern of rna synthesis in xenopus embryogenesis changes following at least three characteristically different phases. the first phase is the pre-mbt stage, which is characterized by the synthesis of heterogeneous mrna-like rna, accompanied b ...	1989	2478271
mediolateral cell intercalation in the dorsal, axial mesoderm of xenopus laevis.	the pattern of mediolateral cell intercalation in mesodermal tissues during gastrulation and neurulation of xenopus laevis was determined by tracing cells labeled with fluorescein dextran amine (fda). patches of the involuting marginal zone (imz) of early gastrula stage embryos, labeled by injection of fda at the one-cell stage, were grafted to the corresponding regions of unlabeled host embryos. the host embryos were fixed at several stages, serially sectioned, and examined with fluorescence mi ...	1989	2463948
expression of type i iodothyronine 5'-deiodinase in xenopus laevis oocytes.	the enzymes mediating the conversion of thyroxine to 3,5,3'-triiodothyronine have proved difficult to purify and characterize biochemically. in this report we describe the successful expression in xenopus laevis oocytes of type i iodothyronine 5'-deiodinase. oocytes injected with rat liver mrna and then incubated for 5 days demonstrated a progressive increase in 5'-deiodinase activity. this activity: (a) manifested a km for 3,3',5'-triiodothyronine of 0.24 microm, (b) was sensitive to inhibition ...	1989	2464594
the genes for the frog skin peptides gla, xenopsin, levitide and caerulein contain a homologous export exon encoding a signal sequence and part of an amphiphilic peptide.	from genomic libraries of xenopus laevis, parts of the genes coding for the precursors of the skin peptides gla (peptide with amino-terminal glycine and carboxy-terminal leucinamide), xenopsin and levitide have been isolated and sequenced. the gene for prepropeptide gla comprises four exons, separated by relatively small introns. the gene for preproxenopsin is composed of five exons, of which all but the last one have been analyzed. this is a large gene encompassing at least 25,000 base pairs. i ...	1989	2465151
weak bases mimic the fertilization-associated chloride conductance increase and induce morphological changes in the cortex of xenopus laevis eggs.	ammonia and other weak bases (methylamine, trimethylamine) including certain local anesthetics (benzocaine, procaine, lidocaine) depolarized the plasma membrane of unactivated xenopus eggs. exposure to different [cl-]o or to the other halides (f-, br-, i-) revealed a similar anion dependency of the weak base-induced conductance change to that found for the normal fertilization potential. although transient, the induced depolarization was slower and of longer duration than the fertilization poten ...	1989	2469526
primary structure and developmental expression of a large cytoplasmic domain form of xenopus laevis neural cell adhesion molecule (ncam).	the neural cell adhesion molecule, (ncam), is involved in cell-cell interactions during development of the vertebrate nervous system. ncam exists in multiple protein forms and these are selectively expressed in different cells and at different times during development. here we report the complete amino acid sequence of the large cytoplasmic form of xenopus laevis ncam, derived from a full-length cdna clone. using specific probes the expression of different ncam transcripts during xenopus embryog ...	1989	2481269
high initiation rates at the ribosomal gene promoter do not depend upon spacer transcription.	we report experiments that test the model that in xenopus laevis, rna polymerase i is "handed over" in a conservative fashion from the t3 terminator to the adjacent gene promoter. we have introduced transcription-terminating lesions into the ribosomal dna repeat by irradiating cultured cells with ultraviolet light. we used isolated nuclei to measure the effect of such lesions on transcription. uv damage sufficient to prevent all elongating rna polymerase from reaching t3 from upstream had no adv ...	1989	2470092
receptor number determines latency and amplitude of the thyrotropin-releasing hormone response in xenopus oocytes injected with pituitary rna.	trh evokes depolarizing membrane electrical responses in xenopus laevis oocytes injected with rna from pituitary cells. we have shown previously that the amplitude of this response is directly proportional to the dose of trh and the amount of rna injected. herein we show that the number of trh receptors expressed on oocytes after injection of rat pituitary (gh3) cell rna or mouse thyrotropic (ttt) tumor rna determines the latency as well as the amplitude of the response. in oocytes injected with ...	1989	2472551
long-term cultures of neurons from adult frog brain express gaba and glutamate-activated channels.	cells from adult xenopus laevis brainstem and spinal cord were dissociated with mild enzymatic treatment and grown in long-term cell culture. these cells had specific attachment/substrate and medium/serum requirements. cells with bipolar and multipolar morphology were positively identified as neurons using immunohistochemistry with monoclonal antibodies to rat and bovine neurofilament proteins which we show here cross-react with similar amphibian proteins. patch clamp recordings demonstrated tha ...	1989	2474056
genetic mapping in xenopus laevis: eight linkage groups established.	inheritance of alleles at 29 electrophoretically detected protein loci and one pigment locus (albinism) was analyzed in xenopus laevis by backcrossing multiply heterozygous individuals generated by intersubspecies hybridization. pairwise linkage tests revealed eight classical linkage groups. these groups have been provisionally numbered from 1 to 8 in an arbitrarily chosen order. linkage group 1 includes alb-2 (albumin), adh-1 (alcohol dehydrogenase), np (nucleoside phosphorylase), and ap (perio ...	1989	2583481
development of early swimming in xenopus laevis embryos: myotomal musculature, its innervation and activation.	the development of the axial musculature, its innervation and early locomotion in xenopus laevis embryos are described. between stages 17 and 40 some 45 myotomes are formed on each side of the body. during this period the animals develop from non-motile to free swimming embryos. using fluorescein-conjugated bungarotoxin the acquisition of acetylcholine receptor-sites was studied. at stage 25 (early flexure stage) bound bungarotoxin was confined to the first seven intermyotomal clefts, in free sw ...	1989	2586744
quick-freeze, deep-etch, rotary-shadow views of the extracellular matrix and cortical cytoskeleton of xenopus laevis eggs.	the quick-freeze, deep-etch, rotary-shadow technique provides a powerful tool to study the structural dynamics of extracellular matrices. using this technique, we show that the extracellular investments of the xenopus laevis egg are multilayered and securely anchored to the egg surface. the cortical cytoskeleton within the egg contains embedded cortical granules with surrounding endoplasmic reticulum and is capped by a thin reticular sheet that contacts the inner surface of the plasma membrane. ...	1989	2585120
dna polymerase gamma from xenopus laevis. i. the identification of a high molecular weight catalytic subunit by a novel dna polymerase photolabeling procedure.	dna polymerase gamma has been purified over 10,000-fold from mitochondria of xenopus laevis ovaries. we have developed a novel technique which specifically photolabels dna polymerases. this procedure, the dna polymerase trap, was used to identify a catalytic subunit of 140,000 da from x. laevis dna polymerase gamma. additional catalytically active polypeptides of 100,000 and 55,000 da were identified in the highly purified enzyme. these appear to be products of degradation of the 140,000-da subu ...	1989	2600077
degradation of linear dna by a strand-specific exonuclease activity in xenopus laevis oocytes.	linear dna injected into xenopus laevis oocyte nuclei recombines with high efficiency if homologous sequences are present at overlapping molecular ends. we found that injected linear dna was degraded by a 5'----3' strand-specific exonuclease activity during incubation in the oocyte nucleus to leave a heterogeneous population of 3'-tailed molecules. decreasing the concentration of dna injected increased the heterogeneity and the average rate of degradation. the 3' tails created were relatively st ...	1989	2601699
trans activation of rat phosphoenolpyruvate carboxykinase (gtp) gene expression by micro-coinjection of rat liver mrna in xenopus laevis oocytes.	to study the liver-specific trans activation of the rat phosphoenolpyruvate carboxykinase (pepck) gene, the pepck promoter was linked to a reporter gene and was microinjected into xenopus laevis oocytes alone or in conjunction with rat liver poly(a)+ rna. the rat liver mrna markedly enhanced the expression of the pepck-chimeric construct. this effect appeared to be sequence specific, as it was dependent on the presence of the intact promoter. moreover, the rna effect was limited to mrna preparat ...	1989	2601721
presence of high molecular weight glycans on the surface of germ and embryonic cells of xenopus laevis.	xenopus laevis male germ cells, fertilized eggs and gastrula cells were labelled with 3h labelled sodium borohydride reduction after galactose oxidase treatment. after pronase digestion, the bulk of the label is carried by high molecular weight glycans (greater than or equal to 6,000 d). the high molecular weight of these labelled glycans and their susceptibility to degradation by endo-beta-galactosidase suggest that they may be related to the polylactosaminoglycans.	1989	2605647
a transcription factor, tfis, interacts with both the promoter and enhancer of the xenopus rrna genes.	an activity that binds sequence specifically to the enhancer of the xenopus laevis rrna genes has been highly purified. this activity stimulates transcription of coinjected rrna templates in xenopus oocytes and has been named tfis, as it binds to the enhancer sequences within the intergenic spacer. in addition to its enhancer binding activity, tfis binds to the promoter of the xenopus rrna genes, as predicted by models for enhancer action. dnase i footprinting on promoter mutants suggests that t ...	1989	2606346
the xenopus ribosomal gene enhancers bind an essential polymerase i transcription factor, xubf.	we purified xubf on the basis of its ability to specifically bind the enhancer elements of the xenopus laevis rrna genes. xubf also binds to both upstream and downstream regions of the x. laevis ribosomal gene promoter and is essential for polymerase i transcription. unexpectedly, xubf binds to both upstream and downstream regions of the human ribosomal gene promoter, producing footprints that are indistinguishable from the footprints produced by hubf, a previously described polymerase i transcr ...	1989	2606347
characterization of neutral and cationic amino acid transport in xenopus oocytes.	amino acid transport was characterized in stage 6 xenopus laevis oocytes. most amino acids were taken up by the oocytes by way of both na+-dependent and saturable na+-independent processes. na+-dependent transport of 2-aminoisobutyric acid (aib) was insensitive to cis- or trans-inhibition by the system a-defining substrate 2-(methylamino)-isobutyric acid (meaib), although threonine, leucine, and histidine were found to be effective inhibitors, eliminating greater than 80% of na+-dependent aib up ...	1989	2592432
observation on the basal lamina of duodenal mesothelial cells during metamorphosis of xenopus laevis.	morphologic changes in the basal lamina of duodenal mesothelial cells during metamorphosis of xenopus laevis were observed. in the prometamorphosis stage (stage 56-59), the basal lamina was almost completely flat; the lamina densa of the basal lamina was a 50 nm layer of high electron density. in the early stages of metamorphic climax (stage 60-62), the basal lamina showed occasional slight folding (stage 60), with the lapse of time, the folding became continuous and deeper. the development of a ...	1989	2608259
genes encoding neuronal nicotinic acetylcholine receptors.	four genes (alpha 2, alpha 3, alpha 4, and beta 2), which encode proteins homologous to the torpedo electric organ and vertebrate muscle nicotinic acetylcholine receptors, have been identified by cloning rat brain cdnas. injection of transcripts derived from these cdnas into xenopus laevis oocytes results in the formation of three nicotinic acetylcholine receptors. two of these receptors, alpha 3/beta 2 and alpha 4/beta 2, have the characteristics of ganglionic nicotinic receptors. the third (al ...	1989	2655998
nucleolin from xenopus laevis: cdna cloning and expression during development.	nucleolin is a key nucleolar protein in higher eukaryotic cells and is involved directly in ribosome biogenesis. using an antiserum raised against hamster nucleolin, the homologous protein was detected in nucleoli of xenopus laevis hepatocytes as well as in the amplified nucleoli of oocytes. a cdna encoding xenopus nucleolin has been isolated and sequenced. the deduced protein sequence reveals similar domains in xenopus and in mammals, but they have undergone separate evolutions. in particular, ...	1989	2656405
the anatomical substrate for telencephalic function.	the basic thesis for this study was that the telencephalon is needed to make decisions in new situations. subsidiary hypotheses were that the telencephalon consists of: (a) a sensorimotor system which generates motor activity from sensory input and (b) a selection system which makes choices from possible motor programs. it was postulated that the selection system should fulfil the following requirements: be accessible for past and present events, have the capacity to process this information in ...	1989	2618850
involvement of endogenous galactoside-binding lectin of xenopus laevis in pattern formation of xenopus neurites in vitro.	galactoside-binding lectin has been purified from xenopus laevis embryos at the stage of neural crest migration. addition of this lectin to neurite cultures correlates with the appearance of fascicles of greater diameter and shorter length compared with controls. lectin-treated neurites are also more spread out on the substratum than their controls. the potent hapten inhibitor of the endogenous lectin, thiodigalactoside (tdg), was also added to these cultures. tdg-treated neurites are less well ...	1989	2620261
neural differentiation of xenopus laevis ectoderm takes place after disaggregation and delayed reaggregation without inducer.	when xenopus blastula or early gastrula ectoderm is disaggregated and cells are kept dispersed for up to 5 h prior to reaggregation, the resulting spheres will differentiate into large neural structures. in contrast, dissociated and immediately reaggregated ectoderm will only differentiate into ciliated epidermis (so-called 'atypical epidermis'). ectoderm treated with mesoderm-inducing xtc-conditioned medium during the period of reaggregation immediately after disaggregation will only form one- ...	1989	2620262
evaluation of the developmental toxicity of five compounds with the frog embryo teratogenesis assay: xenopus (fetax) and a metabolic activation system.	the potential teratogenic hazard of five compounds was evaluated using the frog embryo teratogenesis assay--xenopus (fetax) and a metabolic activation system. embryos of the south african clawed frog, xenopus laevis, were exposed to (i) three compounds suspected to be proteratogenic in mammalian test systems--[2-acetylaminofluorene (2-aaf), rifampicin (ra) and benzo[a]pyrene (bp)] for 96 h; (ii) one compound unaffected by mixed-functional oxidase (mfo) metabolism--znso4; (iii) one compound thoug ...	1989	2613998
neuroleptic modulation of oral dyskinesias induced in snakes by xenopus skin mucus.	the skin mucus of the african clawed frog xenopus laevis promotes escape from the american water snake nerodia sipedon by inducing oral dyskinesias. as xenopus mucus contains peptides and indoleamines with known neuroleptic properties, and because neuroleptics are the chief cause of drug-induced orofacial dyskinesias in humans, the hypothesis was tested that the neuroleptic haloperidol (hal) would induce oral dyskinesias when given alone and would potentiate dyskinesias in nerodia if injected pr ...	1989	2626458
evidence for a pertussis toxin-sensitive g protein involved in the control of meiotic reinitiation of xenopus laevis oocytes.	meiotic reinitiation of xenopus laevis oocytes is induced in vitro by progesterone or insulin. the hormonal effect is inhibited in a dose-dependent manner by the injection of the a protomer of pertussis toxin (islet-activating protein, iap) into the oocytes. this inhibition occurs only before the appearance of a maturation-promoting activity in the cytoplasm. furthermore, injection of the toxin a protomer into recipient oocytes does not inhibit the induction of maturation obtained through inject ...	1989	2661247
dynamics of background adaptation in xenopus laevis: role of catecholamines and melanophore-stimulating hormone.	the pars intermedia of the pituitary gland in xenopus laevis secretes alpha-melanophore-stimulating hormone (alpha-msh), which causes dispersion of pigment in dermal melanophores in animals on a black background. in the present study we have determined plasma levels of alpha-msh in animals undergoing adaptation to white and black backgrounds. plasma values of black-adapted animals were high and decreased rapidly after transfer to a white background, as did the degree of pigment dispersion in der ...	1989	2599346
analysis of 3'-untranslated regions of seven c-myc genes reveals conserved elements prevalent in post-transcriptionally regulated genes.	we have characterized the complete sequence of two c-myc cdnas from the amphibian xenopus laevis, and could thus compare the 3'-non-coding sequences of 7 myc cdnas from 6 species spread over 350 million years of evolution. although the size of these sequences is heterogeneous, we identified three completely conserved sequences of 10, 11 and 12 contiguous nucleotides. we observed that two of these elements may be contained in conserved stem-loop structures previously implicated in mrna turnover. ...	1989	2666167
mitochondrial rna polymerase: dual role in transcription and replication.	mitochondrial rna polymerases from humans, xenopus laevis and saccharomyces cerevisiae are very similar in protein composition and function. they consist of a nonspecific core rna polymerase and a protein factor that confers promoter selectivity on the core component, and they participate in transcription as well as in dna replication. amino acid sequence comparisons indicate that the yeast mitochondrial core component is related to bacteriophage t3 and t7 rna polymerases; mitochondrial and phag ...	1989	2667219
preparation and characterization of cell-free protein synthesis systems from oocytes and eggs of xenopus laevis.	during the maturation of the oocytes of the frog xenopus laevis, the rate of protein synthesis shows a twofold increase. studies of the mechanisms involved in this stimulation have been seriously limited by the lack of an active cell-free translation system. we have now prepared such systems from oocytes, progesterone-matured oocytes and eggs of xenopus laevis by induction of lysis by centrifugation of whole cells. the extracts are highly active in incorporation of labelled amino acids and, in t ...	1989	2627883
evolutionary conservation of the biochemical properties of p53: specific interaction of xenopus laevis p53 with simian virus 40 large t antigen and mammalian heat shock proteins 70.	we have investigated the biochemical properties of xenopus laevis p53. with an in vitro binding assay, we can detect a specific association between x. laevis p53 and simian virus 40 large t antigen. furthermore, x. laevis p53 expressed in monkey cos cells is stably associated with this viral antigen. like mammalian p53, x. laevis p53 in complex with simian virus 40 large t antigen exhibits a 20-fold increase of its half-life. on the other hand, x. laevis p53 is unable to associate either in vivo ...	1989	2668561
nucleocytoplasmic transport of ribosomes in a eukaryotic system: is there a facilitated transport process?	we have examined the kinetics of the process by which ribosomes are exported from the nucleus to the cytoplasm using xenopus laevis oocytes microinjected into the germinal vesicle with radiolabeled ribosomes or ribosomal subunits from x. laevis, tetrahymena thermophila, or escherichia coli. microinjected eukaryotic mature ribosomes are redistributed into the oocyte cytoplasm by an apparent carrier-mediated transport process that exhibits saturation kinetics as increasing amounts of ribosomes are ...	1989	2648382
expression of human and murine interleukin-5 in eukaryotic systems.	a cdna coding for murine interleukin-5 (il-5) was isolated from the el4.exc5 cell line. with the exception of a single amino acid substitution at position 79 (arg----his), it is identical to a published sequence. the coding sequence for human il-5 was synthesized chemically, allowing the introduction of strategically located restriction enzyme cleavage sites. both cdnas were expressed in various eukaryotic systems. deletion of the 3' untranslated region of the murine il-5 gene led to a 5- to 10- ...	1989	2670497
temporal and tissue-specific expression of the proto-oncogene c-fos during development in xenopus laevis.	we describe the isolation and complete sequence of the xenopus c-fos proto-oncogene. c-fos expression throughout xenopus development was analysed using a homologous probe derived from the cloned gene. c-fos rna is accumulated during oogenesis to reach a plateau of 2 x 10(5) transcripts per stage vi oocyte, suggesting an unusual stability of the c-fos message. the amount of rna per embryo decreases substantially after fertilisation to reach a level corresponding to less than 0.1 molecule per cell ...	1989	2632235
signals from the dorsal blastopore lip region during gastrulation bias the ectoderm toward a nonepidermal pathway of differentiation in xenopus laevis.	epi 1, a monoclonal antibody, was generated against an epidermal specific epithelial antigen; it does not stain neural epithelium. we have used epi 1 as a marker to determine when the spatial patterns delineating neural from nonneural epithelium become established. we used ventral ectoderm in a sandwich assay to show that signals from the central blastopore lip region, passing through the plane of the ectoderm sheet, define the pattern and boundary characteristics of epi 1 expression. the dorsal ...	1989	2651180
expression of the four subunits of the torpedo californica nicotinic acetylcholine receptor in saccharomyces cerevisiae.	yeast expression vectors were constructed containing complementary dna encoding the alpha-, beta-, gamma-, and delta-subunits of the torpedo californica nicotinic acetylcholine receptor under the control of the saccharomyces cerevisiae alcohol dehydrogenase promoter. all four plasmids were integrated into the yeast genome of a single yeast cell. the resulting yeast strain synthesized polypeptides novel to yeast that had the molecular weights and antigenic properties similar to the authentic t. c ...	1989	2670931
magainins and the disruption of membrane-linked free-energy transduction.	magainins, a family of positively charged peptides, are partly if not wholly responsible for antimicrobial activity in skin extracts of xenopus laevis. we report here that members of the magainin family--i.e., the 21-amino acid peptide pgla and the 23-amino acid peptide magainin 2 amide (pgsa)--dissipate the electric potential across various energy-transducing membranes and thus uncouple respiration from other free-energy-requiring processes. we propose that this is a likely mechanism for the an ...	1989	2671997
synthesis of a thymosin beta 4-like peptide, deacetyl-thymosin beta xen4, and its restorative effect on depressed lymphocyte blastogenic response to phytohemagglutinin (pha) in uremic patients.	an analog of thymosin beta xen4 isolated from oocytes of xenopus laevis, deacetyl-thymosin beta xen4, was synthesized by assembling 6 peptide fragments, followed by deprotection with 1 m trifluoromethanesulfonic acid-thioanisole (molar ratio, 1:1) in trifluoroacetic acid in the presence of dimethylselenium. finally, the deprotected peptide was incubated with dithiothreitol to reduce sulfoxide on the methionine side chain. the synthetic tritetracontapeptide was found to have a restoring effect on ...	1989	2605693
cholinoceptive properties of human primordial, preantral, and antral oocytes: in situ hybridization and biochemical evidence for expression of cholinesterase genes.	in addition to their well-known involvement in neuromuscular junctions and in brain cholinergic synapses, cholinergic mechanisms have been implicated in the growth and maturation of oocytes in various species. functional acetylcholine receptors were electrophysiologically demonstrated in amphibian and mammalian oocyte membranes, and activity of the acetylcholine-hydrolyzing enzyme, acetylcholinesterase (ache), was biochemically measured in the exceptionally big oocytes of the frog xenopus laevis ...	1989	2641279
the micronucleus test in xenopus: a new and simple 'in vivo' technique for detection of mutagens in fresh water.	the aim of this study was to extend the micronucleus test to xenopus laevis to screen water for potential mutagens. up to now, the most commonly used methods for screening fresh water are the bacterial tests (ames tests). ames tests are well validated, but are merely in vitro bacterial assays which can only detect point mutations whereas the micronucleus test is an in vivo assay using a vertebrate species, and thus is able to detect both chromosome and genome mutations. this study was designed t ...	1989	2654547
the development of the xenopus retinofugal pathway: optic fibers join a pre-existing tract.	the developing optic nerve and tract have received considerable attention in recent years, but the cellular and subcellular microenvironment of the growing axons has not been described. in the belief that such a description is essential (though certainly not sufficient) for an understanding of pathway formation, we have examined the normal development of the retinofugal projection of xenopus laevis. optic fibers were labeled anterogradely at the retina with horseradish peroxidase (hrp) or the ca ...	1989	2612377