| characterization of a xenopus laevis mitochondrial protein with a high affinity for supercoiled dna. | a dna binding protein of 31 kd -mtdbpc- has been isolated from x. laevis oocyte mitochondria. it is present in large amounts in the organelle and does not show any enzymatic activity. its binding to the superhelical form of a dna is higher than for any other form, or for rna. no sequence specificity could be found for any mtdna fragments tested, including both origins of replication. it is able to introduce superhelical turns into relaxed circular dna in the presence of a topoisomerase i activit ... | 1986 | 3748802 |
| analysis of the rna structural elements involved in the binding of the transcription factor iii a from xenopus laevis. | xenopus laevis 5s rrna isolated from 7s particles or transcribed in vitro is found to adopt two alternative conformations. these two conformers contain different structural elements within the major tf iii a binding domain, which, when isolated as rna fragments, still interact with the transcription factor. chemical modification of easily accessible adenines in their n-1 position does not have any measurable effect on the binding of 5s rrna to tf iii a. these observations are in support of the i ... | 1986 | 3748810 |
| changes in the utilization of cell surface carbohydrates are implicated in the adhesion of xenopus laevis melanophores in vitro. | | 1986 | 3749182 |
| nucleotide sequence of cloned cdna specific for rat ribosomal protein l35a. | a cdna clone specific for rat ribosomal protein l35a, which is known to be a trna-binding protein, was isolated by hybrid-selected translation from a cdna library made for 8-9-s poly(a)-rich rna from regenerating rat liver. the nucleotide sequence of the cdna was determined. it consists of one base pair from the 5' leading sequence, the entire coding sequence of 333 base pairs and 14 base pairs from the 3' trailing sequence. the primary structure of protein l35a was deduced from the nucleotide s ... | 1986 | 3753935 |
| sequence of preprocaerulein cdnas cloned from skin of xenopus laevis. a small family of precursors containing one, three, or four copies of the final product. | from skin of xenopus laevis, cdna libraries were constructed and clones coding for the precursors of caerulein were isolated and sequenced. using restriction endonuclease digestions, three different types of preprocaerulein cdnas could be discerned. these were termed types i, iii, and iv in accordance with the number of caerulein copies present in the sequence, the type iii being the most abundant one. an incomplete copy of a fourth variant, termed type i', was also found. besides deletions/inse ... | 1986 | 3753978 |
| expression of two proopiomelanocortin genes in the pituitary gland of xenopus laevis: complete structures of the two preprohormones. | a number of cdna clones corresponding to xenopus pomc mrna was isolated from a cdna library constructed from xenopus pituitary polyadenylated rna. characterization of the cdna inserts revealed two groups of structurally different proopiomelanocortin mrnas, indicating that two proopiomelanocortin genes are expressed to virtually the same level in xenopus pituitary glands. from the mrna structures the complete amino acid sequences of the two xenopus preproopiomelanocortins could be deduced. compar ... | 1986 | 3754961 |
| the developmental expression of the gene for tfiiia in xenopus laevis. | the sequence of the trans-acting positive transcription factor tfiiia has been deduced by sequencing cdna and genomic dna clones. using dna from a homozygous diploid animal we show that there is one gene for tfiiia per haploid genome of x. laevis. protein sequencing of proteolytic fragments of tfiiia orients the protein in its interaction with the internal control region (icr) of the 5s rna gene. the protein lies along the dna with its carboxyl terminus at the 5' end of the icr and its amino ter ... | 1986 | 3755818 |
| the retinotectal projection of quarter eyes in xenopus laevis. | following extirpation of three quarters of the eye anlage of xenopus laevis in stage 33/34, the remaining quadrants developed into small eyes of normal shape. irrespective of the different portions of the eye anlage the quarter eyes originated from, the retinotectal projection was always confined to the rostrolateral part of the tectum, forming an orderly map, and its dimensions corresponded to the size of the contralateral eye. therefore, it was suggested that during development both size and l ... | 1986 | 3756530 |
| influence of cytochalasin b on oocyte maturation in xenopus laevis. | cytochalasin b (cb) exerts an inhibiting effect on the formation, migration and anchoring in the cortex of the meiotic spindle in maturing xenopus laevis oocytes. regional sensitivity to cb (cb-sensitive zones) has been found in the oocytes which varies with reference to the stage of oocyte maturation at which cb is applied. light and electron microscopy has shown that in these cb-sensitive zones the yolk and pigment granules, unlike the cortical ones, are displaced into the cytoplasm centripeta ... | 1986 | 3757040 |
| the phylogeny of macrophage function: antigen uptake and degradation by peritoneal exudate cells of two amphibian species and caf1 mice. | equal numbers of thioglycollate mobilized peritoneal exudate cells (pec) of the newt, notophthalmus viridescens, the south african clawed toad, xenopus laevis, and caf1 mice were compared with respect to their capacity to take up and degrade soluble 14c-ovalbumin (ova). pec of the newt failed to take up the labeled antigen, while those of the toad incorporated only one-half as much as those of the mice. moreover, the toad pec degraded only 42% of the immunogen which was taken up, while pec of th ... | 1986 | 3757044 |
| in vivo uptake of mitochondrial malate dehydrogenase from watermelon by mitochondria of xenopus laevis oocytes. | the heterologous in vivo translation system of xenopus laevis oocytes was used to translate messenger rna isolated from water-melon cotyledons. immunocytochemistry was used to localize the translation products in situ within the oocyte. in addition, the translation products were immunoprecipitated from homogenized oocytes, separated on sds-polyacrylamide electrophoresis and visualized by fluorography. a variety of watermelon proteins encoded in the injected mrna were translated within the oocyte ... | 1986 | 3758084 |
| tumorigenic xenopus cells express several maternal and early embryonic mrnas. | recombinant cdna libraries were constructed from poly(a)+ rna isolated from different stages of oogenesis and embryogenesis from the clawed toad xenopus laevis. hybridization analyses were used to describe the accumulation of specific rnas represented by these cdna clones in oocytes, embryos, adult liver, a cell line derived from xenopus borealis embryos (xb693), and a tumorigenic substrain of that cell line (xb693t). it was found that from 550 cdna clones analysed, six sequences accumulate to h ... | 1986 | 3758199 |
| replacement of posterior by anterior endoderm reduces sterility in embryos from inverted eggs of xenopus laevis. | the genital ridges of xenopus laevis tadpoles reared from eggs kept in an inverted position contain less than 40% of the number of primordial germ cells (pgcs) of controls (cleine & dixon, 1985). it has been suggested that this reduction is caused by the germ cells' ectopic position in the anterior endoderm of larvae from inverted eggs, from where they may be unable to migrate into the genital ridges (cleine & dixon, 1985). this hypothesis is tested here by interchanging anterior and posterior e ... | 1986 | 3760765 |
| massive phosphorylation distinguishes xenopus laevis nucleoplasmin isolated from oocytes or unfertilized eggs. | nucleoplasmin isolated from unfertilized xenopus laevis eggs possesses an in vitro chromatin assembly activity which is superior to nucleoplasmin isolated from oocytes. it is demonstrated here that the two forms of the protein differ in the amount of attached phosphate, with the egg protein possessing nearly 20 phosphate groups per protein monomer and the oocyte protein possessing less than 10 phosphate groups per monomer. a kinase preparation from unfertilized eggs is shown to be capable of mod ... | 1986 | 3768332 |
| isolation of a dipeptidyl aminopeptidase, a putative processing enzyme, from skin secretion of xenopus laevis. | a dipeptidyl aminopeptidase has been purified to apparent homogeneity from skin secretion of xenopus laevis. this enzyme is a glycoprotein with a molecular mass of about 98 kda. it hydrolyzes a variety of dipeptidyl-p-nitroanilides and oligopeptides containing proline, alanine or glycine as the second amino acid and is inhibited by diisopropylfluorophosphate. the ph optimum was found to be around 8, while at ph 6, substrates were cleaved at about one-third of the maximal rate. this dipeptidyl am ... | 1986 | 3769921 |
| the distribution of interrenal stimulating activity in the brain of xenopus laevis. | the stimulation of corticosteroid release by the interrenal tissue of xenopus laevis was investigated using an in vitro preparation of the interrenals and a radioimmunoassay for determinations of corticosterone and aldosterone in the perifusate. the stimulatory activity of four different areas was tested, the pars distalis, the post- and preoptic hypothalamus, and the cerebrum. it was found that besides the pars distalis, the post- and preoptic hypothalamus exhibit stimulatory activity on the in ... | 1986 | 3770444 |
| tunicamycin-induced dysgenesis of retinal rod outer segment membranes. ii. quantitative freeze-fracture analysis. | tunicamycin (tm), a selective inhibitor of dolichylphosphate-dependent oligosaccharide biosynthesis, effectively blocks glycosylation, but not synthesis, of opsin, the rod visual pigment apoglycoprotein. in parallel with this inhibition, vesicular membrane material accumulates in the compartment between rod inner and outer segments (the intersegmental space) in tm-treated retinas (fliesler et al, j cell biol 100:574-587, 1985). freeze-fracture analysis was applied to isolated xenopus laevis reti ... | 1986 | 3771140 |
| intrinsic control of regenerative loss in xenopus laevis limbs. | the regenerative capability of xenopus laevis hindlimbs was studied at different developmental stages. three types of surgical deletion of the autopod were performed: simple amputations, 3-digit wedge-shaped deletions and 1-digit wedge-shaped deletions. the frequency of regenerative response and the digital patterns of the regenerates were analyzed. regenerative capacity declines with developmental stage for all three types of deletions. for simple amputations this decline occurs in an orderly m ... | 1986 | 3772329 |
| corticosteroid binding in plasma of xenopus laevis. modifications during metamorphosis and growth. | the binding of corticosteroids has been studied by equilibrium dialysis at 4 degrees c and electrophoresis on polyacrylamide gel. aldosterone was not bound specifically. large amounts of corticosterone (b) were bound. a high affinity (ka = 2.8 x 10(8) m-1) low capacity (70.1 nm) component was found in tadpoles. its affinity and its electrophoretic mobility were not significantly modified during metamorphosis and growth until adult. it differs from mammalian cbg with respect to affinity, electrop ... | 1986 | 3773513 |
| multiple activation currents can be evoked in xenopus laevis eggs when cortical granule exocytosis is inhibited by weak bases. | the fertilization potential in xenopus eggs under normal circumstances is considered to be a unique event. it is associated with a concomitantly occurring cortical granule exocytosis. if eggs were exposed to weak bases, exocytosis was inhibited but the fertilization potential could still be evoked. after recovery from this first transient increase in membrane conductance, a second could be elicited by a further stimulus. a fertilization potential could be triggered either before or after the egg ... | 1986 | 3774504 |
| sequences coding for the ribosomal protein l14 in xenopus laevis and xenopus tropicalis; homologies in the 5' untranslated region are shared with other r-protein mrnas. | in the haploid genome of xenopus laevis there are two genes coding for the r-protein l14. it is not known if they are located on the same chromosome. cdna clones deriving from the transcripts of the two genes have been isolated from an oocyte messenger cdna bank showing that they are both expressed. we have studied the structure of one of the l14 genes by electron microscopy, restriction mapping and sequencing. an allelic form of the l14 gene was also isolated. it contains a large deletion cover ... | 1986 | 3774540 |
| developmental changes in p-face and e-face particle densities of xenopus cardiac muscle plasma membrane. | p- and e-face particle densities (ppd and epd) were measured in electron micrographs of freeze-fractured cardiac sarcolemma from eight developmental stages of xenopus laevis (stages 33/34 (33 post-otic somite embryos) to 66 (fully metamorphosed juvenile toad], using stereo-imaged replicas. we found striking progressive increases in ppd and epd, most rapid between stages 33/34 and 37/38; that ppd was significantly greater than epd at all stages; that both ppd and epd of stereo-imaged replicas wer ... | 1986 | 3775759 |
| a termination site for xenopus rna polymerase i also acts as an element of an adjacent promoter. | on the xenopus laevis ribosomal genes, rna polymerase traverses the entire repeating unit of gene plus spacer and terminates just upstream of the next gene promoter. a conserved 7 bp element located at about -200 is an essential part of this terminator. in this paper we show that, in addition to its termination function, this same sequence motif acts as an upstream element of the adjacent promoter and appears to contribute to the long-term stability of the transcription complex. | 1986 | 3779846 |
| detection of inhibitors of protein and nucleic acid synthesis using oocytes of xenopus laevis microinjected with the herpes thymidine kinase gene. | we have developed an assay that measures the inhibition of protein synthesis and can be used in conjunction with a whole embryo bioassay that detects the ability of a chemical to cause fetotoxicity, malformation and abnormal growth. the assay involves microinjecting the herpes thymidine kinase gene into stage 6 oocytes of xenopus laevis then exposing the oocytes to a test compound for 18-24 h. the inhibition of thymidine kinase (tk) expression caused by an inhibitor is then measured by simple en ... | 1986 | 3779882 |
| synthesis, processing, and secretion of rat immunoglobulin e made in xenopus oocytes. | rat immunoglobulin e (ige) synthesized in xenopus laevis oocytes, injected with rat plasmacytoma mrna, was analysed by specific immunoprecipitation and sds-polyacrylamide gel electrophoresis under reducing as well as non-reducing conditions. the results indicate that the oocytes will translate and correctly process the rat ige heavy and light chains, resulting in secretion of a correctly assembled, normal immunoglobulin molecule. the normal, extensive glycosylation of the ige heavy chain (e-chai ... | 1986 | 3780973 |
| lack of correlation between extensive accumulation of bisnucleoside polyphosphates and the heat-shock response in eukaryotic cells. | the accumulation in large amounts of bisnucleoside polyphosphates (ap4x) after heat shock in xenopus laevis oocytes or cultured hepatoma cells (htc cells) is observed after exposure to temperatures of 45 degrees c or higher. the accumulation is a transient phenomenon, with the collapse in cellular atp concentration severely affecting the rate of synthesis of ap4x, allowing degrading activities to empty the pool of these compounds under prolonged heat shock. this accumulation of ap4x to high leve ... | 1986 | 3782130 |
| skin peptides in xenopus laevis: morphological requirements for precursor processing in developing and regenerating granular skin glands. | the biosynthesis of the peptides caerulein and pgla in granular skin glands of xenopus laevis proceeds through a pathway that involves discrete morphological rearrangements of the entire secretory compartment. immunocytochemical localization of these peptides during gland development indicates that biosynthetic precursors are synthesized in intact secretory cells, whereas posttranslational processing requires morphological reorganization to a vacuolated stage. the bulk of the processed secretory ... | 1986 | 3782298 |
| identification of the locations of the methyl groups in 18 s ribosomal rna from xenopus laevis and man. | the 18 s ribosomal rna from a variety of vertebrate species contains some 40 to 47 methyl groups. the majority of these are 2'-o-ribose substituents; the remaining few are on bases. several lines of evidence have permitted the identification of the precise locations of the methyl groups in the primary structure of 18 s ribosomal rna of xenopus laevis and man. digestion of rna with t1 ribonuclease, followed by analysis of the methylated oligonucleotides yielded data on sequences immediately surro ... | 1986 | 3783688 |
| upstream domains of the xenopus laevis rdna promoter are revealed in microinjected oocytes. | the dna sequences involved in promoting transcription of the xenopus laevis rrna genes were determined by microinjecting a series of deletion mutants into oocyte nuclei. a very small promoter region is sufficient to direct efficient transcription when templates are microinjected at high rdna concentration, since 5'delta- 9 and 3'delta +6 templates are fully active. however, as the concentration of injected template is decreased, an increasing requirement for upstream domains, extending to nucleo ... | 1986 | 3785161 |
| delimitation and characterization of cis-acting dna sequences required for the regulated expression and transcriptional control of the chicken skeletal alpha-actin gene. | we have previously observed that dna sequences within the 5'-flanking region of the chicken skeletal alpha-actin gene harbor a cis-acting regulatory element that influences cell type and developmental stage-specific expression (j. m. grichnik, d. j. bergsma, and r. j. schwartz, nucleic acids res 14:1683-1701, 1986). in this report we have constructed unidirectional 5'-deletion and region-specific deletion-insertion mutations of the chicken skeletal alpha-actin upstream region and inserted these ... | 1986 | 3785201 |
| effects of nabam on developing xenopus laevis embryos: minimum concentration, biological stability, and degradative products. | | 1986 | 3789809 |
| the 5s gene internal control region is composed of three distinct sequence elements, organized as two functional domains with variable spacing. | systematic oligonucleotide-directed mutagenesis within the internal control region of the xenopus laevis somatic 5s rna gene identifies three distinct sequence elements that regulate transcription activity: box a, containing the common, conserved class iii promoter domain, and two 5s-gene-specific segments, termed intermediate element and box c. analysis of the individual steps in the formation of the stable initiation complex reveals that the two 5s-gene-specific elements are the main determina ... | 1987 | 3791417 |
| the effects of thiosemicarbazide on development in the wood frog, rana sylvatica. i. concentration effects. | the effects of exposure of rana sylvatica tadpoles to varying concentrations (10-75 mg/liter for 4 days) of thiosemicarbazide (tsc) was studied. exposure to concentrations of 25 mg/liter or more caused a curvature of digits, abnormal limb articulations, difficulty in swimming, and death. for all of these parameters, effects were dose dependent. tadpoles exposed to 10 mg/liter metamorphosed significantly slower than controls while those exposed to 50 mg/liter metamorphosed significantly faster th ... | 1986 | 3792267 |
| free calcium wave upon activation in xenopus eggs. | eggs of xenopus laevis were preloaded with aequorin and the spatial and temporal pattern of free calcium release in the egg cortex on artificial activation was determined by the aequorin luminescence emitted from the thin cortical layer of naturally opaque eggs. the aequorin luminescence was detected with a photonic microscope system consisting of a light microscope and a two-dimensional photon-counting system with an image processor. a free calcium increase was initiated around the point of pri ... | 1987 | 3792626 |
| eye factors and lens-forming transformations of outer cornea in xenopus laevis larvae. | outer cornea of lensectomized xenopus laevis tadpoles at state 50 (according to nieuwkoop, p.d. and faber, j., ('56) normal table of xenopus laevis, daudin, north-holland, amsterdam, pp. 1-243) was removed 3, 7 and 10 days after lensectomy and implanted between the outer and the inner cornea of larvae of the same species at stage 51-52. in these conditions, the implanted outer cornea remained isolated from the retinal factor of the vitreous chamber, although it received the nutritional factors n ... | 1986 | 3794628 |
| myoblasts and myoblast-conditioned medium attract the earliest spinal neurites from frog embryos. | a study was made of the capacity of newly segmented somites, unsegmented mesoderm and medium conditioned by each of these tissues to attract the growth of the earliest spinal neurites from the neural tube of xenopus laevis in tissue culture. when presented with segmented somitic myoblasts or sheets of skin, spinal neurites grew selectively towards the somitic myoblasts. neurites were not attracted specifically to somitic myoblasts from their own rostrocaudal level. a variable proportion of myobl ... | 1986 | 3795063 |
| contractile activation in myotomes from developing larvae of xenopus laevis. | contractile activation in response to application of different perfusing solutions was observed in developing myotomes from larvae of xenopus laevis. contractures resulted from treatment with isotonic solutions containing high k+ concentrations in myotomes from embryos from stage 24 onwards. these developed over 5-10 s and inactivated over 20-30 s. contractures persisted in curarized preparations. the applied k+ concentrations at the estimated mechanical threshold in embryos at stages 26 and 34 ... | 1986 | 3795064 |
| dynamic aspects of amphibian neurite growth and the effects of an applied electric field. | the dynamics of growth of earliest spinal neurites from xenopus laevis have been studied in vitro in the presence and absence of an applied d.c. electric field. control and cathode-directed neurites grew at a rate of about 30 micron/h: growth of anodal-facing neurites was 8 times slower. periods of arrested growth were common in cultured neurones; these lasted 2-3 times longer in an applied electric field. the likelihood and the severity of neurite reabsorption was greatest in neurites directed ... | 1986 | 3795068 |
| two distant and precisely positioned domains promote transcription of xenopus laevis rrna genes: analysis with linker-scanning mutants. | to examine the internal organization of the promoter of the xenopus laevis rrna gene, we constructed a series of linker-scanning mutants that traverse the rdna initiation region. the mutant genes, which have 3 to 11 clustered base substitutions set within an otherwise unaltered rdna promoter sequence, were injected into xenopus oocyte nuclei, and their transcriptional capacity was assessed by s1 nuclease analysis of the resultant rna. the data demonstrate that there are two essential promoter do ... | 1986 | 3796610 |
| exafs study of the zinc-binding sites in the protein transcription factor iiia. | the protein transcription factor iiia (tfiiia) is involved in the synthesis of 5s rna in vitro by rna polymerase iii. it can be isolated from xenopus laevis oocytes as a 7s particle in which the protein is associated with 5s rna. recently it has been shown that the native particle contains 7-11 zinc atoms. analysis of the amino-acid sequence of tfiiia revealed nine similar domains of approximately 30 amino acids, each containing two invariant pairs of histidines and cysteines, which have been im ... | 1986 | 3796733 |
| cells from xenopus laevis gastrulae adhere to fibronectin-sepharose beads and other lectin coated beads. | cells from xenopus laevis blastulae have a poorly developed ability to adhere to sepharose beads covalently coupled to bovine plasma fibronectin (fn-beads). they do, however, have the ability to adhere to con a-beads and cytodex-1 and cytodex-3 beads. beginning at the early gastrula stage, there is a progressively increasing ability of cells to adhere to fn-beads. gastrula cells adhere to fn-beads by the formation of large ruffling lamellipodia. these cells can translocate on the surface of fn-b ... | 1986 | 3798003 |
| the migration of amphibian primordial germ cells in the chick embryo. | a fibrous band of extracellular materials on the chick embryo area pellucida/area opaca border is a preferential migratory pathway for chick embryo primordial germ cells (pgc). this band contains fibronectin, collagen type i and sulphated glycosaminoglycans. it is known that pgcs from xenopus laevis interact with fibronectin as they undergo migration in the embryo from their site of origin to the gonads. to establish whether this pathway is species specific in chick embryos it was decided to tra ... | 1986 | 3798020 |
| transcription of genomic bovine and xenopus laevis dna species by rna polymerase iii in hela-cell cytosol extracts. | rna transcribed from genomic xenopus laevis dna by rna polymerase iii in hela-cell extract was found in discrete size classes and was transcribed from at least two different xenopus repeat dna species. very little 5s ribosomal rna was transcribed, contrasting with results obtained on transcription of genomic xenopus dna by xenopus extract [bogenhagen et al. (1982) cell 28, 413-421]. the low transcription was not due to an inability to use 5s rdna templates, since the cloned xenopus 5s ribosomal ... | 1986 | 3800921 |
| sequence and transcription of trnaval gene from xenopus laevis. | a dna fraction enriched in trna genes has been prepared by cscl density gradient centrifugation of xenopus laevis dna in the presence of actinomycin d. this dna fraction was cut with the restriction endonuclease ecori and the fragments 800-900 base pairs in size were cloned into the plasmid pbr325. recombinant dnas were screened by hybridization to labeled trna and for the ability to support transcription in vitro. the entire sequence of one fragment was determined by sequencing the ends of an o ... | 1987 | 3801487 |
| toxicity of mixtures of heavy metals and petrochemicals to xenopus laevis. | | 1987 | 3801708 |
| gaba and dopamine act directly on melanotropes of xenopus to inhibit msh secretion. | the release of melanophore stimulating hormone (msh) from the pars intermedia of the amphibian xenopus laevis is regulated by multiple factors of hypothalamic origin. the aim of this study was to determine if potential secretagogues function through a direct action on the melanotrope cell. for this purpose an in vitro superfusion system containing isolated melanotropes (cell suspension) was utilized. the viability of the cells in suspension was tested by examining their ability to synthesize, pr ... | 1986 | 3801932 |
| effects of minute doses of ethylenebisdithiocarbamate disodium salt (nabam) and its degradative products on connective tissue envelopes of the notochord in xenopus: an ultrastructural study. | the fungicide ethylenebisdithiocarbamate disodium salt (nabam) at 40 or 100 micrograms/l has deleterious effects on the survival of xenopus laevis embryos. the tissues of the notochordal enveloping layer show definite alterations at the ultrastructural level. there is a significant reduction or absence of the collagen fibres of the outer connective tissue cells. embryos treated with 100 micrograms/l nabam stored for 3 weeks developed more severe malformations of the enveloping connective tissue ... | 1986 | 3802916 |
| [analytical study of xenopus hindlimb regenerate with special reference to muscle regeneration]. | amputated hindlimbs of xenopus laevis, develop various types of regenerates in relation with amputation level as well as stage development. the present experiments is an attempt to study the histological characteristics of xenopus regenerations, i.e., rational changes of tissue components along the length of the regenerated part with special emphasis on the degree of muscle regeneration. four types of regenerates were studied viz; a 4th toe obtained from a completely restored regenerated limb at ... | 1986 | 3803428 |
| vegetal pole cells and commitment to form endoderm in xenopus laevis. | in order to compare their states of commitment with their normal developmental fate, single vegetal pole cells from early xenopus embryos were labeled and transplanted into the blastocoels of host embryos. in a previous study we showed, using this single cell transplantation assay, that vegetal pole cells become committed to endoderm by the early gastrula stage. in this paper we examine some properties of the commitment process. first, we show that it is gradual. when vegetal blastomeres are tak ... | 1987 | 3803714 |
| changes in states of commitment of single animal pole blastomeres of xenopus laevis. | the experiments described in this paper were designed to compare the normal fates of animal pole blastomeres of xenopus laevis with their state of commitment. single animal pole blastomeres were labeled with a lineage marker and transplanted into the blastocoels of host embryos of different stages. the distribution of labeled daughter cells in the tadpole reflects the state of commitment of the parent cell at the time of transplantation. it is known that cells from the animal pole of the early b ... | 1987 | 3803715 |
| prolactin binding sites in xenopus laevis tissues: comparison between normal and dehydrated animals. | the binding of 125i-labeled ovine prolactin (125i-oprl) to membranes from the kidney, epidermis, liver, and testis of xenopus laevis adult specimens either kept in an aquatic environment or exposed for 2 weeks to dehydrating conditions was studied. prolactin binding specificity was assayed through competition with several unlabeled hormones (oprl, hgh, rgh, rlh, and porcine insulin). in the animal exposed to dehydrating conditions a statistically highly significant reduction in prolactin binding ... | 1987 | 3803901 |
| functional elements of the human u1 rna promoter. identification of five separate regions required for efficient transcription and template competition. | we have determined the structure of the human u1 snrna promoter by microinjection of several mutant u1 templates into xenopus laevis oocytes. these deletion templates were assayed for their ability to express mature u1 rna and for their ability to compete for limiting transcription factors. we have mapped five separate regions, called promoter elements a, b, c, d, and e. element a, located between positions -8 and -50, stimulates transcription 3- to 5-fold increases the accuracy of initiation; e ... | 1987 | 3805053 |
| the occurrence of lampbrush chromosomes in early diplotene oocytes of xenopus laevis. | transmission electron microscopy has been used to study the chromosomes found in the early diplotene oocytes of xenopus laevis. chromosomes from 40 micron early diplotene oocytes were found to possess a normal lampbrush chromosome morphology. the contour length of the loops found on these chromosomes was measured, the mean value determined and compared with that for lampbrush chromosomes found on 300 micron mid-diplotene (dumont stage ii) oocytes. the mean contour length of the loops from 40 mic ... | 1986 | 3805141 |
| the development of the static vestibulo-ocular reflex in the southern clawed toad, xenopus laevis. i. intact animals. | in the clawed toad, xenopus laevis, the static vestibulo-ocular reflex appears in 3 days old tadpoles (developmental stage 42) (fig. 2). the amplitude and gain of this reflex increase up to stage 52, and then decrease to an almost constant value at stage 60 and older tadpoles (fig. 3). the most effective roll angle gradually increases during development (fig. 4). the size of the sensory epithelia reaches the final value at the end of the premetamorphic period (stage 56) (fig. 5). the small-cellu ... | 1986 | 3806442 |
| the development of the static vestibulo-ocular reflex in the southern clawed toad, xenopus laevis. iii. chronic hemilabyrinthectomized tadpoles. | the static vestibulo-ocular reflex was investigated in tadpoles at different times following unilateral destruction of the labyrinth during the period of early organogenesis and premetamorphosis. balance compensation is completed after a few weeks, while gain compensation only occurs partially (figs. 2-4). tadpoles hemilabyrinthectomized in the age of 2.5 days (stage 38) develop no vestibular nuclei on their lesioned side, while tadpoles operated later in their life, possess these nuclei (figs. ... | 1986 | 3806443 |
| thymic involvement in memory responses after primary challenge with tnp-ficoll in xenopus laevis, the south african clawed toad. | memory to tnp-ficoll in xenopus laevis is demonstrable as a more rapid secondary response rather than an augmented response. while adult thymectomy abrogates ability to respond to both primary and secondary challenge with soluble tnp-ficoll, memory to this antigen can be revealed in thymectomized animals by challenge with tnp-ficoll on bentonite beads. memory to tnp-ficoll cannot be revealed by secondary challenge with tnp-lps or tnp-rbc, but memory to tnp-lps is revealed by tnp-ficoll challenge ... | 1986 | 3810777 |
| the sexually dimorphic larynx of xenopus laevis: development and androgen regulation. | the aims of this study were to characterize sexual dimorphism in the larynx of adult xenopus laevis and to determine how sex differences arise during postmetamorphic development. the larger male larynx is a result of greater cell numbers in both cartilage and muscle. the dilator laryngis muscle of the male larynx has 6-7 times more muscle fibers than that of the female. at metamorphosis, the larynx is sexually monomorphic and feminine in phenotype. the dna content of the male larynx doubles duri ... | 1986 | 3812330 |
| expression of agrobacterium tumefaciens t-dna gene 7 in xenopus laevis oocytes. | the expression of agrobacterium tumefaciens t-dna gene 7 was investigated in xenopus laevis oocytes. cloned dna injected into oocytes consisted of t-dna sequences derived from octopine type ti plasmid b6-806 and t-dna attached to plant dna sequences at the left junction in crown gall tumors. transcription initiation sites observed in oocytes were similar to those for transcript 7 in crown gall tumors. quantitative differences in transcription occurred depending on the flanking sequences of the i ... | 1986 | 3814121 |
| reexamination of the 'regulative development' of amphibian embryos. | in this article, we have reviewed a series of our recent results of isolation, defect and transplantation experiments on early embryos of xenopus laevis. the results show that as early as the 8-cell stage an embryo consists of several kinds of cells which differ distinctly in developmental capacities and that their capacities are much more restricted than previously thought. thus, for the formation of complete embryos a certain set of cells is necessary; and no regulation occurs whenever any one ... | 1987 | 3815529 |
| weak bases inhibit cleavage and embryogenesis in amphibians and echinoderms. | the action of weak bases was studied on the early embryonic development of a number of species. gastrulation was disrupted in the frog, xenopus laevis, the newt, pleurodeles watlii, the sea urchins, paracentrotus lividus and sphaerechinus granularis and the starfish, asterias rubens. this required only submillimolar amounts of either nh+4 (ph 9.0) or procaine (ph 8.2). at higher concentrations even early cell division was inhibited in all the species with furrow regression particularly noticeabl ... | 1987 | 3815530 |
| upstream sequences required for tissue-specific activation of the cardiac actin gene in xenopus laevis embryos. | the entire dna sequence of the xenopus laevis cardiac actin gene was determined. a recombinant plasmid comprising the cardiac actin gene promoter fused to the bacterial chloramphenicol acetyl transferase (cat) gene is correctly regulated after introduction into fertilized xenopus eggs. the fusion gene shows a temporal and tissue-specific pattern of expression in the early embryo which is indistinguishable from that of the endogenous cardiac actin gene. the fusion gene is also activated in cultur ... | 1986 | 3816759 |
| the membrane attack complex of xenopus laevis complement. | rabbit erythrocyte membranes lyzed by xenopus laevis serum exhibited a typical ultrastructural complement lesion with an inner diameter of 80 +/- 9 a. the protein pattern associated with lyzed membrane is compared to a similar human preparation. | 1987 | 3817103 |
| partial characterization of different cell types found in the xenopus laevis lymphoreticular tumor based on the presence or absence of surface immunoglobulins and fc molecules. | cells of xenopus laevis lymphoreticular tumor induced by tumor tissue transplantation were examined for surface ig and fc receptor molecules in order to evaluate the different cell types found in the tumor. direct immunofluorescent technique, using fluorochrome conjugated rabbit antisera to xenopus ig's, detected ig molecules on the surface of a mean of 31.7 +/- 11.3% of cells in tumor suspensions. most of these molecules were of igm isotype, reversibly bound to the cell membrane (cytophilic) an ... | 1986 | 3817250 |
| metaphase protein phosphorylation in xenopus laevis eggs. | cytoplasmic extracts of metaphase (m-phase)-arrested xenopus laevis eggs support nuclear envelope breakdown and chromosome condensation in vitro. induction of nuclear breakdown is inhibited by ampp(nh)p, a nonhydrolyzable atp analog, but not by atp or gamma-s-atp, a hydrolyzable atp analog, suggesting that protein phosphorylation may be required for m-phase nuclear events in vitro. by addition of [gamma-32p]atp, we have identified in cytoplasmic extracts and in intact eggs at least six phosphopr ... | 1987 | 3821728 |
| characteristics of receptors for dopamine in the pars intermedia of the amphibian xenopus laevis. | while mammalian dopamine receptors have been extensively characterized, very little attention has been given to these receptors in lower vertebrates. dopamine is thought to be a physiologically important melanotropin release-inhibiting factor in amphibians. by administering selective dopamine receptor agonists and antagonists to superfused neurointermediate lobes of xenopus laevis and monitoring their effect on the release of melanophore-stimulating hormone (msh), we have examined the characteri ... | 1986 | 3822075 |
| relation between force and calcium ion concentration in different fibre types of the iliofibularis muscle of xenopus laevis. | calcium activated isometric force was measured in segments of single muscle fibres of the iliofibularis muscle of xenopus laevis skinned by freeze-drying. a subdivision in five different fibre types was made, based on the location of the fibres inside the muscle, fibre diameter and a quantitative histochemical assay for succinate dehydrogenase activity. the ca2+ sensitivity was characterized by fitting a hill curve to the force levels reached at different ca2+ concentrations. the parameter n of ... | 1987 | 3822771 |
| the nucleotide sequence of the ribosomal protein l14 gene of xenopus laevis. | | 1987 | 3822843 |
| respiratory physiology of fish, amphibian, and mammalian sperm. | teleost (liza dumerili) and toad (xenopus laevis) sperm consume oxygen optimally at high oxygen tensions (120-150 mm hg) close to the saturation level of the diluents. oxygen consumption of sperm of both species declines rapidly below a po2 of 60 mm hg. sperm of both species consume more oxygen per unit sperm in dilute than in dense sperm suspensions and conform to the so-called respiratory dilution effect. in contrast, ram sperm do not conform to the respiratory dilution effect and utilize oxyg ... | 1986 | 3827393 |
| examination of heat shock protein mrna accumulation in early xenopus laevis embryos. | elevation of the incubation temperature of xenopus laevis neurulae from 22 to 33-35 degrees c induced the accumulation of heat shock protein (hsp) 70 mrna (2.7 kilobases (kb)) and a putative hsp 87 mrna (3.2 kb). while constitutive levels of both hsp mrnas were detectable in unfertilized eggs and cleavage-stage embryos, heat-induced accumulation was not observed until after the mid-blastula stage. exposure of xenopus laevis embryos to other stressors, such as sodium arsenite or ethanol, also ind ... | 1987 | 3828114 |
| heat-shock gene expression in animal embryonic systems. | we have examined the expression of heat shock or stress genes in fish, echinoderm, amphibian, and mammalian embryonic systems. in a chinook salmon embryo cell line, elevation of the incubation temperature or exposure to metal ions (e.g., cadmium and zinc) induced a set of heat-shock proteins hsps. transcriptional inhibitor, in vitro translation, and northern hybridization studies suggest that fish hsp synthesis is regulated at the transcriptional level. the synthesis of hsps during early develop ... | 1986 | 3828897 |
| [mosaic formation of neurons in the neurogenesis zone in the xenopus laevis tectum]. | | 1987 | 3829896 |
| epidermal development in xenopus laevis: the definition of a monoclonal antibody to an epidermal marker. | a monoclonal antibody 2f7.c7 which identifies an epidermal antigen common to both anuran and urodele amphibia is described. this antigen has a high molecular weight and is expressed at stage 12 1/2 first inside and then on the surface of epidermal cells. it is not expressed on presumptive nervous tissue. it is expressed on all cells of the larval epidermis including ciliated and nonciliated cells and sucker. the relationship of the epidermal antigen to 'epimucin' is investigated by blocking expe ... | 1985 | 3831211 |
| the function and mechanism of convergent extension during gastrulation of xenopus laevis. | the processes thought to function in xenopus gastrulation include bottle cell formation, migration of cells on the roof of the blastocoel, and autonomous convergent extension of the circumblastoporal region. a review of recent and classical results shows that only the last accounts for the bulk of the tissue displacement of gastrulation, including spreading of the marginal zone toward the blastopore, involution of the marginal zone, and closure of the blastopore. microsurgical manipulation and e ... | 1985 | 3831213 |
| chromosome replication in early development of xenopus laevis. | eggs of xenopus laevis contain exceptionally large amounts of materials involved in chromosome replication. this maternal stockpile allows an embryo to produce about 80 000 cells in less than 24 h. the adaptations which achieve this involve the mechanisms of both dna replication and chromatin assembly. | 1985 | 3831215 |
| a mass spectrometric assay for novel peptides: application to xenopus laevis skin secretions. | the peptides secreted by the south african frog xenopus laevis were screened systematically using a strategy based on fast atom bombardment mass spectrometry (fab-ms). high performance liquid chromatography (hplc) of crude and sephadex g-10 chromatographed secretions showed that many more peptides were present in these secretions than those previously identified, i.e., xenopsin, caerulein, trh and pgla. fractions from the hplc were analyzed directly by fab-ms to determine the molecular weights o ... | 1985 | 3831964 |
| studies on the endogenous galactose-binding lectin during early development of the embryo of xenopus laevis. | embryos of the frog xenopus laevis at cleavage, blastula, gastrula and neurula stages contain a galactose-specific lectin. extracts of gastrula embryos show the highest specific activity for this lectin compared to the other stages. haemagglutinating activity of crude extracts is inhibited by lactose, alpha-galactose, beta-galactose, alpha gal(1----4) beta gal, beta gal(1----3) alpha galnac, beta gal(1----3) beta glcnac, beta gal (1----4) beta glcnac, and most effectively by the disaccharide alp ... | 1985 | 3833862 |
| factors guiding regenerating retinotectal fibres in the frog xenopus laevis. | i have examined the pathways of retinotectal fibres regenerating back to the contralateral tectum, and also to innervated and 'virgin' ipsilateral tecta in postmetamorphic xenopus. the fibres were visualized by hrp labelling of either the whole optic nerve, or a selected quadrant of the retina. most fibres grow into either the ipsilateral or contralateral optic tract, although a small proportion go down the outside of the contralateral optic nerve. in the tracts, many fibres grow superficially, ... | 1985 | 3834030 |
| cytological analyses of factors which determine the number of primordial germ cells (pgcs) in xenopus laevis. | correlation of the number of primordial germ cells (pgcs) at stage 47 with the amount of germ plasm at the 8-cell stage and with the number of the germ-plasm-containing cells (gpccs) was analysed using two different laboratory-raised colonies of xenopus laevis, hd and j groups. the average number of pgcs in j group tadpoles was significantly larger than that in hd group tadpoles. the amount of germ plasm in j group embryos was also demonstrated to be larger than in hd group embryos. the amount o ... | 1985 | 3834031 |
| the effect of egg rotation on the differentiation of primordial germ cells in xenopus laevis. | eggs of x. laevis were rotated (sperm entrance point downwards) either through 90 degrees (1 x 90 embryos) or 180 degrees in two 90 degrees steps (2 x 90 embryos) at approximately 25-30 min postfertilization after cooling to 13 degrees c. the embryos were kept in their off-axis orientation and cooled until the early gastrula stage. rotation resulted in relocation of egg constituents with slight changes in the distribution of outer cortical and subcortical components and major changes in inner co ... | 1985 | 3834040 |
| a proposed neural pathway for vocalization in south african clawed frogs, xenopus laevis. | vocalizations of south african clawed frogs are produced by contractions of laryngeal muscles innervated by motor neurons of the caudal medulla (within cranial nerve nucleus ix-x). we have traced afferents to laryngeal motor neurons in male and female frogs using retrograde axonal transport of horseradish peroxidase conjugated to wheat germ agglutinin (hrp-wga). after iontophoretic injection of hrp-wga into n. ix-x, retrogradely labelled neurons were seen in the contralateral n. ix-x, in rhomben ... | 1985 | 3837111 |
| stimulation of sea urchin h2b histone gene transcription by a chromatin-associated protein fraction depends on gene sequences downstream of the transcription start site. | we isolated a chromosomal protein fraction derived from chromatin of sea urchin embryos which specifically stimulated the expression of the histone h2b gene by a factor of 5- to 10-fold when the complete sea urchin histone gene repeat h22 was injected in xenopus laevis oocyte nuclei. gene manipulation experiments revealed the existence of two different target sites in the h2b gene which appear to mediate the response to injection of the stimulatory sea urchin chromatin-associated proteins; both ... | 1985 | 3837183 |
| coordinate estrogen induction of vitellogenin and a small serum protein mrna in xenopus laevis liver. | we have used plus-minus hybridization to identify xenopus liver cdna clones of mrnas whose levels are regulated by estrogen. one clone identified in this way was shown to be a nearly full-length cdna clone of the mrna coding for a small 22 000 dalton estrogen-inducible serum protein (eisp). quantitation of eisp mrna levels by in vitro translation and by hybridization to the cloned dna demonstrated a 7-12-fold estrogen induction of eisp mrna, both in vivo and in primary xenopus liver cultures. th ... | 1985 | 3838520 |
| solid-phase synthesis of pyla and isolation of its natural counterpart, pgla [pyla-(4-24)] from skin secretion of xenopus laevis. | from the nucleotide sequence of clones isolated from a cdna library constructed from skin of xenopus laevis, the existence of pyla, a peptide comprised of 24 amino acids, was predicted. this peptide was synthesized by solid-phase methods and purified to homogeneity with an overall yield of 61%. the synthetic peptide was used as reference substance to search for its natural counterpart in skin secretion of xenopus. two peptides were found which were very similar to pyla except for the absence of ... | 1985 | 3839186 |
| nucleotide sequence of cloned cdna for pro-opiomelanocortin in the amphibian xenopus laevis. | the function of alpha-melanocyte-stimulating hormone (alpha-msh) is not known in mammals. it is well-established in the amphibian xenopus laevis in which alpha-msh mediates the process of adaptation to a dark background. the amino acid sequence of this hormone is, however, not known in amphibians. in order to determine the primary structure of the precursor protein for alpha-msh, which in mammals has been called pro-opiomelancortin (pomc), we constructed a cdna library from xenopus pituitary mrn ... | 1985 | 3840481 |
| nucleotide sequence of the l1 ribosomal protein gene of xenopus laevis: remarkable sequence homology among introns. | ribosomal protein l1 is encoded by two genes in xenopus laevis. the comparison of two cdna sequences shows that the two l1 gene copies (l1a and l1b) have diverged in many silent sites and very few substitution sites; moreover a small duplication occurred at the very end of the coding region of the l1b gene which thus codes for a product five amino acids longer than that coded by l1a. quantitatively the divergence between the two l1 genes confirms that a whole genome duplication took place in xen ... | 1985 | 3841512 |
| biosynthesis of peptides in the skin of xenopus laevis: isolation of novel peptides predicted from the sequence of cloned cdnas. | from skin of xenopus laevis, a few peptides have been isolated which are identical or homologous to gastrointestinal hormones and/or neurotransmitters of mammalian origin. we have studied the biosynthesis of these peptides using recombinant dna techniques. from cdna librariers constructed from skin mrna, clones with inserts coding for the precursors of caerulein, thyrotropin releasing hormone and a new peptide termed pgla have been isolated and sequenced. in the case of caerulein, a small family ... | 1985 | 3841688 |
| biochemical research on oogenesis. aminoacyl trna turns over in the 42-s particles of xenopus laevis oocytes, but its ester bond is protected against hydrolysis. | the ester bond aminoacyl trna is protected against hydrolysis in the 42-s particles (thesaurisomes) present in xenopus laevis previtellogenic oocytes. deacylation of trna is very slow in vitro, unless atp is present. atp causes a partial turnover of aminoacyl trna in vitro, with no detectable decrease in the overall aminoacylation level of trna, which remains close to 100%. trna in the particles turns over rapidly in vivo. since the ester bond of aminoacyl trna is stabilized inside the 42-s part ... | 1985 | 3847348 |
| purification and characterization of an endonuclease from xenopus laevis ovaries which accurately processes the 3' terminus of human pre-trna-met(i) (3' pre-trnase). | we have previously reported that the primary transcript of the human trnameti gene undergoes accurate processing to a mature 72-nucleotide species by activities present in the high speed supernatant of xenopus laevis ovarian extracts (zasloff, m., santos, t., romeo, p., and rosenberg, m. (1982a) j. biol. chem. 257, 7857-7863). we now report the purification and characterization of the enzyme which processes the 3' terminus of the human pre-trnameti species. the activity has been purified about 5 ... | 1985 | 3848432 |
| trna nuclear transport: defining the critical regions of human trnaimet by point mutagenesis. | we recently described a carrier-mediated nuclear transport system for trna in xenopus laevis oocytes. a natural human trnaimet variant with a g to t transversion in position 57 is defective in transport across the nuclear membrane. in addition, processing of the primary transcript of the variant gene is much less efficient than the wild type. we now describe the nuclear transport and processing phenotypes of 30 different point mutants generated by in vitro mutagenesis of a wild-type human trnaim ... | 1985 | 3852693 |
| a protein kinase from xenopus eggs specific for ribosomal protein s6. | a protein kinase specific for ribosomal protein s6 has been purified from eggs of xenopus laevis. as visualized on a silver-stained polyacrylamide gel, the major protein in the preparation migrated with a mr of 90,000. incubation of the enzyme preparation with [gamma-32p]atp led to phosphorylation of this protein on serine residues. upon glycerol gradient centrifugation, the s6 kinase activity and the mr 90,000 protein both sedimented with a mr of 50,000-55,000. two-dimensional gel electrophores ... | 1985 | 3856226 |
| identification of a messenger ribonucleic acid fraction in human prostatic cancer cells coding for a novel osteoblast-stimulating factor. | prostatic cancer is frequently associated with new bone formation although the tumor-derived factors responsible for changes in bone cell function have not been identified. we have examined the synthesis of osteoblast-stimulating factors in a cultured human prostatic cancer cell line (pc-3) and show that conditioned medium from pc-3 cells stimulate mitogenesis and alkaline phosphatase in cells with the osteoblast phenotype (cultured rat osteosarcoma cells) and collagen synthesis in fetal rat cal ... | 1985 | 3861313 |
| dorsal lateral plate mesoderm influences proliferation and differentiation of hemopoietic stem cells derived from ventral lateral plate mesoderm during early development of xenopus laevis embryos. | the developmental pattern of dorsal and ventral lateral plate mesoderm was examined by explanting these regions and culturing them in serum-free conditions for 10 days. under these circumstances, ventral lateral plate mesoderm gave rise to hemopoietic cells, and dorsal lateral plate mesoderm gave rise to stromal cells. comparison of the differentiation pattern observed when dorsal and ventral mesoderm were cultured separately versus the pattern observed when dorsal and ventral mesoderm were cult ... | 1985 | 3861753 |
| change of karyoskeleton during spermatogenesis of xenopus: expression of lamin liv, a nuclear lamina protein specific for the male germ line. | lamins are the major constituent proteins of the nuclear lamina. in the frog, xenopus laevis, they are the products of a multigene family whose expression can be correlated to certain routes of cell differentiation. for example, lamins li (mr, 72,000) and lii (mr, 68,000) is expressed, together with li/lii, in certain highly differentiated cell types such as neurons and muscle cells and is the only lamin present in diplotene oocytes. here we report the identification by means of two monoclonal a ... | 1985 | 3862126 |
| differentiating effects of murine nerve growth factor in the peripheral and central nervous systems of xenopus laevis tadpoles. | the present investigation was directed toward exploration of the spectrum of action of murine nerve growth factor (m-ngf) in peripheral cells and neurons in the central nervous system (cns) of xenopus laevis tadpoles. it was found that systemic m-ngf injections elicit growth and differentiative effects not only on sensory and sympathetic nerve cells but also on several populations in the cns. the finding that aminergic and peptidergic neurons in brain centers are highly receptive to m-ngf activi ... | 1985 | 3863142 |
| genomic organization and nucleotide sequence of two distinct histone gene clusters from xenopus laevis. identification of novel conserved upstream sequence elements. | we have performed a detailed analysis of the genomic organization and the nucleotide sequence of two distinct xenopus laevis histone gene clusters totaling approximately 23.5 x 10(3) base-pairs. each cluster contains at least one copy of each of the five histone genes. however, these genes are present in different arrangements within each cluster and different h1a, h2a and h2b proteins (variants) are encoded by the respective genes of each cluster. southern blot analysis of genomic x. laevis dna ... | 1985 | 3863963 |
| germ plasm and germ cell determination in xenopus laevis as studied by cell transplantation analysis. | | 1985 | 3868485 |
| regulation of the production of granulocyte-macrophage colony-stimulating factor by macrophage-like tumour cell lines. | macrophage tumour cell lines (pu5-1.8, p388d1) produced detectable granulocyte macrophage colony-stimulating (csf-2) activity measured using a factor-dependent cell line fdc-p1. the production of csf-2 was enhanced by endotoxin and inhibited by serum, and correlated inversely with [3h]tdr incorporation. mrna isolated from pu5-1.8 or p388d1 cells initiated csf-2 production when injected into xenopus laevis oocytes. the specific activity in this assay was unaltered in mrna isolated from endotoxin- ... | 1985 | 3871405 |
| transformed xenopus embryos as a transient expression system to analyze gene expression at the midblastula transition. | the onset of transcriptional activity during embryogenesis in xenopus laevis is at the 4000- to 8000-cell stage (stage 8-8.5) and is referred to as the midblastula transition (mbt). most exogenous circular dna that is microinjected into the fertilized egg also is expressed at the mbt. the transformed xenopus embryo at these early stages was used as a transient expression system in order to determine the effects of (1) promoter strength, (2) physical conformation, (3) degree of replication, and ( ... | 1985 | 3871711 |
| murine and human interleukin 2 can substitute for the thymus in immune responses to tnp-ficoll in xenopus laevis, the south african clawed toad. | extirpation of the thymuses of xenopus laevis abrogates the capacity to respond to trinitrophenol (tnp)-ficoll regardless of the age of the animal. this thymus requirement can be substituted for by a variety of treatments which stimulate thymus-derived (t)cell activity in the periphery, such as the rejection of allogeneic skin grafts, immunologic challenge with thymus-dependent immunogens, (e.g., heterologous erythrocytes), or plant-derived lectins (e.g., concanavalin a). here we report that int ... | 1985 | 3873289 |
| comparative studies on the electric nature of amphibian gonadotropin. | the isoelectric focusing (ief) profiles of pituitary gonadotropic (gth) activity in six species of adult male amphibians were examined in addition to the newt and bullfrog. the gth activity was measured by two radioreceptor assay (rra) systems; one with xenopus laevis testicular homogenate as the receptor preparation, and the other with anolis carolinensis testicular homogenate, both employing 125i-labeled rat fsh as the radioligand, or by a radioimmunoassay (ria) system for bullfrog basic gth ( ... | 1985 | 3874809 |