| conversion of a phosphoseryl/threonyl phosphatase into a phosphotyrosyl phosphatase. | by use of the autophosphorylated epidermal-growth-factor receptor and the synthetic peptide rrlie-daey(p)aarg, representing an autophosphorylation site of the transforming protein of rous-sarcoma virus, it is demonstrated that the phosphotyrosyl phosphatase activity of the polycation-stimulated phosphatases is substantially increased by an enzyme-directed effect of atp or ppi. concomitant with this increase in phosphotyrosyl phosphatase activity, the phosphorylase phosphatase activity is decreas ... | 1988 | 2852001 |
| expression of the human serum apolipoprotein ai and aii genes in xenopus laevis oocytes. lipid-associated secretion of gene products. | the two major apolipoproteins of plasma high-density lipoproteins (hdl) are apolipoprotein ai (apo ai) and aii (apo aii). the apo ai and the correctly oriented apo ciii genes separated by 2.6 kb were obtained by fusion of two human lambda-genomic clones. the apo aii gene was isolated as a 3 kb clone. these apolipoprotein genes have been injected independently and together into xenopus laevis oocytes and their expression studied. both apolipoprotein genes were transcribed and translated into thei ... | 1988 | 2852015 |
| several hypothalamic peptides stimulate in vitro thyrotropin secretion by pituitaries of anuran amphibians. | the effects of several hypothalamic peptides on hormone secretion by pituitaries of three species of anuran amphibians were investigated using in vitro techniques. secretion of thyrotropic bioactivity (designated thyrotropin or tsh) was quantified by bioassay of the pituitary incubation medium using thyroxine (t4) production by paired thyroids from the same animals. pituitaries from adult male rana pipiens were cultured in medium alone, 10 or 100 ng/ml thyrotropin-releasing hormone (trh), 1000 n ... | 1988 | 2853681 |
| fast calcium currents in cut skeletal muscle fibres of the frogs rana temporaria and xenopus laevis. | | 1988 | 2853684 |
| a dna helicase from xenopus laevis ovaries. | a dna helicase was extensively purified from xenopus laevis ovaries. the most purified fraction was free of dna topoisomerase, dna polymerase, and nuclease activities. the enzyme had a stokes radius of 54 a and a sedimentation coefficient of 6-7.3 s, from which a native molecular weight of 140,000-170,000 was calculated. dna helicase activity required mg2+ or mn2+ and was dependent on hydrolysis of atp or datp. monovalent cations, k+ and na+, stimulated dna unwinding with an optimum at 130 mm. d ... | 1988 | 2853968 |
| assembly of spaced chromatin involvement of atp and dna topoisomerase activity. | undiluted extracts from eggs or oocytes of xenopus laevis support the assembly of chromatin with physiologically spaced nucleosomes. micrococcal nuclease and dnase i digestion experiments show that nucleosome formation as well as supercoiling of circular dna concomitant to assembly do not require atp or mg2+. however these factors are essential for the stability and the physiological spacing of the assembled chromatin. gamma-s-atp can substitute for atp in this process. with topoisomers of defin ... | 1988 | 2854062 |
| effect of antibodies against the gap junction protein on differentiation of induced embryonic cells. | microinjections of antibodies against gap junction protein to early blastomeres of xenopus laevis were succeeded by the treatments of mesodermal inductor. it was found that induction was not affected by the injection of the antibodies but the differentiation of notochord and muscle was impeded at different degrees. cell interactions via gap junction communication seem to be involved in the differentiation of the induced cells. | 1988 | 2855456 |
| functional expression of the oxytocin receptor in xenopus laevis oocytes primed with mrna from bovine endometrium. | synthesis of the uterine receptor for the hypothalamic hormone oxytocin has been induced in oocytes from xenopus laevis previously primed with bovine endometrium mrna. the injected oocytes responded to oxytocin by showing dose-dependent oscillations in membrane currents as recorded by the voltage-clamp method. the response was specific in that it was not elicited by several other peptides tested. the oxytocin-induced membrane changes were suppressed when oocytes were pretreated with an oxytocin ... | 1988 | 2855710 |
| mechanism of membrane electrical response to thyrotropin-releasing hormone in xenopus oocytes injected with gh3 pituitary cell messenger ribonucleic acid. | trh evoked a complex electrical membrane response in xenopus laevis oocytes injected with either total cytosolic or poly(a)(+)-enriched rna from gh3 pituitary cells but not in uninjected oocytes. a typical response consisted of a transient, rapid depolarizing current followed by a prolonged depolarizing current with superimposed current fluctuations. the reversal potentials of the rapid and the slow components of the response were -23.0 and -22.6 mv, respectively, and were markedly affected by c ... | 1987 | 2856406 |
| structural effects of external media on isolated myelinated axons. | myelinated axons were isolated from the sciatic nerve of xenopus laevis by desheathing and teasing, and were mounted for short-term light microscope observation in different media. fibres mounted in a conventional physiological saline showed a tendency to gross structural changes, including collapse of axons and separation of the axon from the myelin sheath. with isotonic media based on 120mm potassium aspartate, or 120mm potassium glutamate, structural stability and axoplasmic function (assesse ... | 1985 | 2858303 |
| [nle4, d-phe7]-alpha-msh: a superpotent melanotropin with prolonged action on vertebrate chromatophores. | the in vitro and in vivo responses of integumental chromatophores to alpha-msh and a related analogue, [nle4, d-phe7] -alpha-msh, were studied in a number of vertebrate species: the teleost, lebistes reticulatus; the amphibians, rana pipiens, r. catesbeiana, xenopus laevis, bufo alvarius, and b. cognatus; the lizard, anolis carolinensis; the rattlesnake, crotalus atrox. the alpha-melanotropin analogue was a superpotent agonist in the in vitro frog (r. pipiens, r. catesbeiana) and lizard (a. caro ... | 1985 | 2859941 |
| comparative actions of gaba and acetylcholine on the xenopus laevis lateral line. | the effects of gaba, acetylcholine and carbachol on the spontaneous activity of afferent nerve fibers in the lateral line of xenopus laevis are characterized. atropine and bicuculline were also tested on drug- and water motion-evoked activity. gaba (0.019-1.25 mm) suppressed and both acetylcholine (1.25-80 microm) and carbachol (1.25-40 microm) increased spontaneous activity. these actions were blocked by bicuculline (100 microm) and atropine (4 microm) respectively. atropine (20 microm) and bic ... | 1985 | 2861015 |
| polyadenylation of the xenopus beta 1 globin mrna at a downstream minor site in the absence of the major site and utilization of an aauaca polyadenylation signal. | we show that adult reticulocytes of xenopus laevis produce two forms of the beta 1 globin mrna that differ in their site of polyadenylation. the minor site of polyadenylation is located 46 nucleotides downstream of the major site and is used in approximately 1% of mrna molecules. a fusion gene was constructed containing the promoter from the thymidine kinase gene of herpes simplex virus fused to the protein coding, 3'-noncoding and 3'-flanking sequences of the x. laevis beta 1 globin gene. when ... | 1985 | 2862026 |
| isolation, partial characterization and translation of mrnas for chymosin and pepsin, the two main aspartyl proteinases of bovine stomach. | poly(a) rna from the mucosa of the fundal region of the fourth stomach of suckling calf and adult cattle was isolated by the phenol or guanidine thiocyanate procedure. the mrnas for chymosin and pepsin were present in the 15s fraction of poly(a) rna. they were active both in cell-free translation systems and in oocytes of xenopus laevis and directed the synthesis of either chymosin or pepsin precursor, depending upon the age of the donor animal. in the reticulocyte and wheat germ system only pre ... | 1985 | 2862064 |
| calcium paradox from cyclostome to man: a comparative study. | in seven poikilotherm species, i.e. cyclostome, myxine glutinosa; teleosts, gadus morrhua; platichtys flesus; amphibia, r. pipiens; r. temporaria; xenopus laevis; reptiles, vipera berus. ca paradox could not be obtained in ventricular strips at 8-12 degrees c. in similar preparations from human atria at 30 degrees c and 37 degrees, ca paradox was obtained similarly as in other homoiotherms. in homoiotherms, lowered temperature (below 30 degrees c) has a protective effect. viper myocardium did no ... | 1985 | 2863069 |
| accurate and efficient transcription of human c-myc genes injected into xenopus laevis oocytes. | we investigated the expression of the cloned human c-myc gene in xenopus laevis oocytes microinjected with different recombinants. we found that microinjected plasmid dna carrying an intact human c-myc gene directs efficient and faithful transcription from its own two promoters in x. laevis oocytes. this active transcription was unaffected by the presence of previously identified enhancing elements such as simian virus 72-base pair repeats or mouse immunoglobulin heavy-chain gene enhancer sequen ... | 1985 | 2863748 |
| messenger rna from bovine retina induces kainate and glycine receptors in xenopus oocytes. | the retina contains several types of nerve cells that communicate through chemical synapses. the transmitter and receptor molecules that mediate signal transmission across these synapses need further characterization. for this purpose, poly (a)+ mrna was isolated from bovine retinas and injected into xenopus laevis oocytes. translation of the foreign mrna induced the oocyte membrane to acquire functional receptors to kainate and, to a lesser extent, also receptors to glycine, gamma-aminobutryic ... | 1985 | 2863826 |
| a comparative study of the membrane potential from before fertilization through early cleavage in two frogs, rana pipiens and xenopus laevis. | the membrane potential of rana pipiens eggs (-55.0 mv +/- 11.2(16)) was more likely to recover from impalement and was always more negative than that of eggs of xenopus laevis (-19.3 mv +/- 4.2(68)). it was also much more negative than previously reported. essentially similar membrane resistance changes were measured in the two frog species through fertilization and cleavage. small transient depolarizations only associated with the onset of the fertilization potential in xenopus could be prevent ... | 1985 | 2864209 |
| stimulation of photoreceptor disc shedding and pigment epithelial phagocytosis by glutamate, aspartate, and other amino acids. | it has been reported that aspartate and glutamate selectively impair the structure (olney, '82) and function (e.g., furakawa and hanawa, '55) of second- and third-order retinal neurons while leaving the photoreceptor unaffected. either amino acid may mimic the endogenous photoreceptor neurotransmitter (ehinger, '82). we report here that excitatory amino acids also induce massive rod photoreceptor disc shedding in eyecups of xenopus laevis maintained in vitro. disc shedding is the process whereby ... | 1985 | 2864363 |
| identification of microtubule-associated proteins (maps) in xenopus oocyte. | microtubules were isolated from prophase-blocked oocytes of xenopus laevis with the use of the anti-tumor drug taxol. in addition to tubulin, 5 microtubule-associated proteins (maps) were characterized. among them, 2 high molecular mass proteins (200-300 kda) are phosphorylated in ovo. the oocyte map extract promotes the assembly of rat brain 6 s purified tubulin. | 1985 | 2865168 |
| t-lymphocyte regulation of humoral immunity in xenopus laevis, the south african clawed toad. | | 1985 | 2867941 |
| microtubules in immature oocytes of xenopus laevis. | previous work indicated that immature oocytes of xenopus were incapable of assembling microtubules but that competence was achieved during maturation. we report here that small numbers of microtubules do exist in immature oocytes. consistent with this finding, ultrastructural observations indicate that brain microtubules injected into immature oocytes persist in large numbers for at least 30 min. we report that the tubulin dimers of mature and immature oocytes are equally capable of assembling w ... | 1985 | 2868018 |
| the role of the jelly coat in amino acid transport in embryos of bombina orientalis. | the obligatory role of the jelly coat for maximal transport of all amino acids, including those found to be jelly coat-independent in xenopus laevis embryos, has been shown in bombina orientalis embryos. amino acid transport in dejellied embryos (without fertilization membrane and jelly coats) of bombina, reconstituted with either intact or homogenized jelly coats, was similar to the values in normal embryos. amino acid transport in totally dejellied embryos, and those surrounded with fertilizat ... | 1986 | 2871977 |
| the influence of second messengers and related substances on the sensitivity of early embryos to cytostatic neurochemicals. | "prenervous" neurotransmitters interact with second messengers in the regulation of early embryogenesis of sea urchins and the clawed frog xenopus laevis. propranolol and atropine inhibit cleavage divisions of x. laevis only after their intracellular administration. the level of the membrane potential (including a zero level) of the embryos studied is not essential for the cleavage divisions. possible mechanisms of action of the "prenervous" neurotransmitters at the intracellular level and their ... | 1986 | 2872009 |
| pituitary extract of the ricefield eel monopterus albus (synbranchidae, teleostei) exhibits gonadotropic activity in the classes mammalia, aves, reptilia and amphibia. | pituitary extract of the ricefield eel monopterus albus demonstrated gonadotropic activity in mammals and non-mammalian vertebrates. using the rat as the recipient, fsh activity was detected in monopterus pituitaries in the hcg augmentation test and lh activity in the ovarian ascorbic acid depletion test. cyclic amp level in superovulated ovaries, ovarian lactate production and glucose uptake in vitro, plasma testosterone level in males, testicular enzymes, ventral prostate weight and other andr ... | 1986 | 2873938 |
| linkage arrangement in the vitellogenin gene family of xenopus laevis as revealed by gene segregation analysis. | using restriction fragment length polymorphism (rflp) we have analyzed the segregation of alleles of the different vitellogenin genes of xenopus laevis. the results demonstrate that the four genes whose expression is controlled by oestrogen, form two linkage groups. the genes a1, a2 and b1 are linked genetically whereas the fourth gene, the gene b2, segregates independently. the possible origin of this unexpected arrangement is discussed. | 1986 | 2878417 |
| cholinergic antagonists in a solitary wasp venom. | the venom of the solitary wasp philanthus triangulum contains a cholinergic antagonist of the nicotinic receptor of the rectus abdominis muscle of the frog, xenopus laevis. the venom of african p. triangulum contains two different cholinergic factors, a competitive and a non-competitive antagonist. the venom of the european p. triangulum may not contain a competitive antagonist of the nicotinic receptor of x. laevis, but only a very strong non-competitive antagonist. the possible non-synonymity ... | 1986 | 2879703 |
| immunocytochemical localization and spatial relation to the adenohypophysis of a somatostatin-like and a corticotropin-releasing factor-like peptide in the brain of four amphibian species. | the distribution of somatostatin (srif) - and corticotropin-releasing factor (crf)-like - immunoreactive material was studied in the brain of four amphibian species (ambystoma mexicanum, pleurodeles waltlii, xenopus laevis, rana ridibunda) by use of immunocytochemistry. a wide network of srif-immunoreactive fibers and numerous perikarya were observed in all amphibians examined, with a dense accumulation of nerve endings in the external layer of the median eminence (elme). in the representatives ... | 1987 | 2880668 |
| amino acids, including neurotransmitter candidates, in a hair cell-enriched fraction from the lateral line of xenopus laevis. | a hair cell-enriched neuromast fraction from the lateral line of xenopus laevis was compared with adjacent tactile organ and epidermis for content of primary amine-containing components. of 32 components quantitated by cation-exchange hplc with fluorescence detection of orthophthalaldehyde adducts, l-alpha-amino adipic acid, o-phosphoethanolamine, l-alpha-glycerophosphorylethanolamine, o-phospho-l-serine, and l-lysine were elevated in concentration in the neuromast relative to the tactile organ ... | 1987 | 2881697 |
| rat brain 5-ht1c receptors are encoded by a 5-6 kbase mrna size class and are functionally expressed in injected xenopus oocytes. | injection of rat brain rna into xenopus laevis oocytes induces synthesis of receptors that show an electrophysiological response to bath application of serotonin. while there are at least 4 pharmacologically distinct subtypes of 5-ht binding sites in the rat brain, we find that the pharmacological characteristics of the predominant electrophysiologically active receptor synthesized in xenopus oocytes are most consistent with those of the 5-ht1c subtype. additional electrophysiologically active 5 ... | 1987 | 2883267 |
| an npy-like peptide may function as msh-release inhibiting factor in xenopus laevis. | this study demonstrates the presence of a rich plexus of neuropeptide y (npy) immunoreactive fibers in the hypothalamus and in the intermediate lobe of the pituitary of xenopus laevis. during superfusion of neurointermediate lobe tissue, synthetic npy induces a rapid, powerful and dose-dependent inhibition of in vitro release of msh, endorphin and other proopiomelanocortin (pomc) derived peptides. therefore, npy undoubtedly is one of the growing number of neuropeptides that are likely involved i ... | 1987 | 2883634 |
| in vitro formation of neuromuscular junctions between adult rana muscle fibres and embryonic xenopus neurons. | adult muscle fibres of the frog rana temporaria were cultured with neurons from embryos of the frog xenopus laevis. electron microscopical and electro-physiological examination of the cultures showed that hetero-specific (xenopus-rana) neuromuscular junctions were formed in vitro. nerve processes, without any schwann cell covering, made contacts anywhere along a muscle fibre, and the junctions resembled those seen during early regeneration of neuromuscular synapses in situ. functional contacts, ... | 1987 | 2885850 |
| calcium and magnesium dependence of spontaneous and evoked afferent neural activity in the lateral-line organ of xenopus laevis. | 1. rates of spontaneous and mechanically evoked neural impulses from the xenopus laevis lateral line were compared in the presence of calcium and/or magnesium or in the absence of either divalent cation, bath-applied to the synaptic side of the mechanoreceptors. 2. spontaneous activity and total activity during mechanical stimulation decreased with increasing calcium or magnesium concentration. 3. activity during stimulation minus spontaneous activity increased with increasing calcium concentrat ... | 1987 | 2886271 |
| neuroactive substances in inner ear extracts. | to identify the neurotransmitter released by sensory hair cells, as well as to find other substances that might influence neural function of the inner ear, we have prepared extracts from inner ears of fishes (which have large numbers of hair cells), fractionated the extracts, and studied the effects of the fractionated extracts on the discharge rate of afferent fibers innervating hair cells in the lateral line organ of the african clawed frog xenopus laevis. the extracts contain active substance ... | 1987 | 2886566 |
| accumulation of free amino acids in growing xenopus laevis oocytes. | the sizes of amino acid pools in growing xenopus laevis oocytes have been measured. the total free amino acid content per oocyte increases nearly 25-fold during oocyte growth. together, glutamic acid and aspartic acid account for approximately 59-75% of the total amino acid pool in xenopus oocytes. on the other hand, methionine and cysteine are the least abundant of the amino acids detected, each accounting for less than 0.7% of the total pool in developing oocytes. it is argued that the acid-ex ... | 1987 | 2889640 |
| a possible neurotransmitter role for cgrp in a hair-cell sensory organ. | we report that calcitonin gene-related peptide (cgrp) increases the discharge rate of afferent fibers innervating hair cells in the lateral line organ of xenopus laevis. we have localized cgrp-like immunoreactivity in small, presumably efferent, fibers innervating the lateral line organ. in addition to providing evidence for a neurotransmitter role for cgrp in a sensory system, these results may help explain the non-cholinergic excitatory effect seen with efferent stimulation in this and other h ... | 1987 | 2890408 |
| a highly evolutionarily conserved mitochondrial protein is structurally related to the protein encoded by the escherichia coli groel gene. | we recently reported that a tetrahymena thermophila 58-kilodalton (kda) mitochondrial protein (hsp58) was selectively synthesized during heat shock. in this study, we show that hsp58 displayed antigenic similarity with mitochondrially associated proteins from saccharomyces cerevisiae (64 kda), xenopus laevis (60 kda), zea mays (62 kda), and human cells (59 kda). furthermore, a 58-kda protein from escherichia coli also exhibited antigenic cross-reactivity to an antiserum directed against the t. t ... | 1988 | 2892128 |
| effect of osmolality on the initiation of sperm motility in xenopus laevis. | 1. seminal plasma of the south african clawed toad xenopus laevis exhibited osmolality around 250 mosmol/kg isotonic to blood plasma. 2. spermatozoa remained immotile when the semen was diluted in solutions of 100 mm nacl, 100 mm kcl or 200 mm glucose containing 20 mm hepes-naoh buffer which exhibited almost the same osmolalities (approximately 240 mosmol/kg) as seminal plasma. 3. the spermatozoa became motile in these three solutions if the osmolalities were decreased. 4. these suggest that mot ... | 1987 | 2892629 |
| rna 3' cleavage and polyadenylation in oocytes and unfertilized eggs of xenopus laevis. | xenopus laevis histone h4 and h1 genes were transcribed in vitro to generate artificial precursor mrnas (pre-mrnas). these pre-mrnas were microinjected into oocytes, matured oocytes, and unfertilized eggs of xenopus laevis and their 3' cleavage and polyadenylation were investigated. in the oocyte nucleus both h4 and h1 pre-mrnas were 3' cleaved but were not detectably polyadenylated. in the oocyte cytoplasm there was neither 3' cleavage nor polyadenylation of these histone pre-mrnas. when inject ... | 1988 | 2892746 |
| biosynthesis of the neurofilament heavy subunit in xenopus oocytes microinjected with rat brain poly(a)+ rna. | in order to study the expression of the major subunit of neurofilaments (nfs), rat brain poly(a)+ rna was purified by three different procedures and was injected in xenopus laevis oocytes. this system was able to translate efficiently the 200 kda nf subunit as shown by a dot-blot immunoassay and by immunoprecipitation of labeled nf polypeptides. | 1987 | 2893252 |
| responses of trout fry (salmo gairdneri) and xenopus laevis tadpoles to cadmium and zinc. | 1. toxicity of cadmium chloride and zinc sulphate in solution has been determined for xenopus tadpoles and rainbow trout fry in recirculated water systems. 2. both animals show approximately equal tolerance of zinc but xenopus tadpoles tolerate cadmium at approximately 10 times the lethal concentration for trout fry. 3. in the case of xenopus tadpoles, pre-treatment with sub-lethal concentrations of cadmium or zinc protects against subsequent exposure to either metal. for trout fry, cadmium give ... | 1988 | 2894280 |
| xenopus homeobox-containing cdnas expressed in early development. | we report the isolation of six different homeobox-containing genes in xenopus laevis which are expressed during early embryogenesis. cdna clones of all of them were partially sequenced including two from previously isolated xenopus genomic loci and found to contain homeodomains which share a high degree of homology with the antennapedia protein (50 to 59 out of 60 amino acids). we find a short region of homology (consensus ile tyr pro trp met) in four of the cdnas, which is also present in anten ... | 1988 | 2894634 |
| chromosome replication in cell-free systems from xenopus eggs. | cell-free systems from eggs of the frog xenopus laevis are able to perform most of the acts of eukaryotic chromosome replication in vitro. this now includes the crucial regulatory step of initiation, which had only been achieved for viral systems previously. purified dna or nuclei are able to initiate and complete semi-conservation replication in egg extracts in vitro (blow & laskey, cell 47, 557-587 (1986). replication does not require specialized dna sequences either in vitro or in microinject ... | 1987 | 2894683 |
| a xenopus laevis gene encodes both homeobox-containing and homeobox-less transcripts. | a cdna clone (p52) that contains all the protein-coding region from the maternally expressed xlhbox 2 locus of the frog xenopus laevis has been isolated and sequenced. a probe containing the exon preceding the homeobox detected transcripts which arise from a splicing event in which the homeobox-containing exon is replaced by another exon lying 5' to it in the genome. both the homeobox-containing and homeobox-less splicing event occur in the same tissues, with the homeobox-less rna representing t ... | 1987 | 2894983 |
| unmyelinated cutaneous afferent neurons activate two types of excitatory amino acid receptor in the spinal cord of xenopus laevis embryos. | the trunk and tail skin of xenopus laevis embryos near the time of hatching is innervated by the mechanoreceptive free nerve endings of rohon-beard neurons, a homogeneous class of cutaneous primary afferent fibers. rohon-beard neurons have cell bodies and axons in the dorsal spinal cord, where they monosynaptically excite a population of dorsolaterally situated interneurons (clarke and roberts, 1984). epsps can be recorded in these dorsolateral interneurons following electrical stimulation of th ... | 1988 | 2895802 |
| gaba release from xenopus retina does not correlate with horizontal cell membrane potential. | the relationship between horizontal cell membrane potential and the release of gaba was explored in the retina of xenopus laevis. the intracellularly recorded membrane potential of horizontal cells was monitored while the retina was exposed to different concentrations of depolarizing agents. the dose-response curves obtained revealed a rise from 5 to 95% maximum depolarization in 0.5-1.5 log unit concentration change. the molar concentrations that elicited a 20 mv depolarization were 40 mm (pota ... | 1988 | 2897092 |
| responses to gaba, glycine and beta-alanine induced in xenopus oocytes by messenger rna from chick and rat brain. | poly (a)+ messenger rna (mrna) was extracted from rat and chick brains, and injected into oocytes of xenopus laevis. this led to the expression of receptors that evoked membrane currents in response to gamma-aminobutyric acid (gaba), glycine and beta-alanine. these currents all inverted at about the chloride equilibrium potential in the oocyte, and showed a marked rectification at negative potentials. oocytes injected with mrna from chick optic lobe gave large responses to gaba and beta-alanine, ... | 1988 | 2898147 |
| expression of receptors for cholecystokinin and other ca2+-mobilizing hormones in xenopus oocytes. | the expression of receptors for cholecystokinin (cck) and other similar acting ca2+-mobilizing hormones was studied in xenopus laevis oocytes. poly(a)+ rna was prepared from pancreatic ar42j cells, which normally express receptors for cck and bombesin and the rna injected into oocytes. the presence of these pancreatic receptors on the oocytes was then demonstrated by hormone-induced mobilization of 45ca2+. cck receptors were present 1 day (maximum, 2 days) after injection of rna and were general ... | 1988 | 2898786 |
| in vitro reinnervation of adult rat muscle fibres by foreign neurons and transformed chromaffin pc12 cells. | adult rat muscle fibres were dissociated by using collagenase and maintained in culture. one to nine days later, neurons obtained from stages 22-30 xenopus laevis embryos, or neonatal spinal cord, or pheochromocytoma (pc12) cells treated with nerve growth factor were added. subsequently, the co-cultures were maintained for up to eight days. functional synapses were formed with variable efficiency: 12% in rat-xenopus nerve-muscle co-cultures, 23% in rat-rat and 33% in pc12 co-cultures. miniature ... | 1988 | 2901108 |
| long-term starvation in xenopus laevis daudin--ii. effects on several organs. | 1. the effect of starvation for 12 months on organo-somatic indices, glycogen, protein and water contents of several organs and the na+/k+ ratio in muscle was studied in the south african clawed toad xenopus laevis daudin. 2. the liver- and ovary-somatic index were reduced by 30 and 70% of the initial value after 12 months. fat bodies had disappeared after approximately 6 months of starvation. the indices of heart and kidney were not changed. 3. glycogen concentration of the liver, ovaries and m ... | 1988 | 2901321 |
| site-specific inversions in repeated xenopus laevis homeobox gene 2 sequences. | | 1988 | 2902559 |
| functional expression of brain cholecystokinin and bombesin receptors in xenopus oocytes. | total rna was extracted from 15-day-old whole rat brains. microinjection of the rna into xenopus laevis oocytes induced electrophysiological responsiveness to cholecystokinin-8 (cck) and bombesin (bbs) but not to corticotropin-releasing factor (crf) or somatostatin. the responses to cck and bbs were similar in shape, time course, and reversal potential to that induced by receptor mediated phospholipid breakdown and that which is induced by intracellular injection of ip3. these responses were not ... | 1988 | 2902910 |
| expression of k channels in xenopus laevis oocytes injected with poly(a+) mrna from the insulin-secreting beta-cell line, hit t15. | two types of exogenous k channel were identified in xenopus laevis oocytes injected with poly(a+) mrna from the insulin-secreting cell line hit t15. one of these was the atp-regulated k channel (g channel) as evidenced by its conductance and inhibition by tolbutamide. the other resembled the ca-activated k channel from beta-cells. | 1988 | 2903072 |
| organization and rearrangement of immunoglobulin m genes in the amphibian xenopus. | sequences of immunoglobulin (ig) cdna clones of xenopus laevis show that at least three different vh families are expressed in association with different jh elements and different isotypes of ig constant regions. in genomic southern blot analysis, the vh probes for each family hybridize to a distinct set of multiple dna fragments. in contrast, the genomic jh elements and the igm constant region gene are localized in a single dna fragment of approximately 15 kb. genomic vh elements contain regula ... | 1988 | 2903824 |
| isolation and characterization of a xenopus laevis c protein cdna: structure and expression of a heterogeneous nuclear ribonucleoprotein core protein. | the c proteins are major components of heterogeneous nuclear ribonucleoprotein complexes in nuclei of vertebrate cells. to begin to describe their structure, expression, and function we isolated and determined the dna sequence of xenopus laevis c protein cdna clones. the protein predicted from the dna sequence has a molecular mass of 30,916 kda and is very similar to its human counterpart. although mammalian genomes contain many copies of c protein sequence, the xenopus genome contains few copie ... | 1988 | 2904678 |
| expression of neurotransmitter transport from rat brain mrna in xenopus laevis oocytes. | to permit a molecular characterization of neurotransmitter transporter proteins, we have studied uptake activities induced in xenopus laevis oocytes after injection of adult rat forebrain, cerebellum, brainstem, and spinal cord poly(a)+ rna. l-glutamate uptake could be observed as early as 24 hr after injection, was linearly related to the quantity of mrna injected, and could be induced after injection of as little as 1 ng of cerebellar mrna. transport of radiolabeled l-glutamate, gamma-aminobut ... | 1988 | 2904681 |
| properties of two classes of rat brain acidic amino acid receptors induced by distinct mrna populations in xenopus oocytes. | the xenopus laevis oocyte expression system was used to study the molecular composition of mrnas encoding acidic amino acid (aa) receptors from rat brain. xenopus oocytes injected with poly(a) mrna express two general classes of aa receptors. one class consists of aa-gated cation channels. responses are evoked by n-methyl-d-aspartate (nmda), by kainate, and to a lesser extent by l-glutamate or quisqualate. the second class of receptor is coupled to an intracellular second messenger pathway activ ... | 1988 | 2905539 |
| evaluation of the developmental toxicity of nicotine and cotinine with frog embryo teratogenesis assay: xenopus. | the teratogenic potential of nicotine and a primary metabolite, cotinine, was examined with fetax (frog embryo teratogenesis assay: xenopus). early embryos of xenopus laevis were exposed for 96 hr to nicotine or cotinine in two separate static renewal tests of each compound without addition of the metabolic activation system (mas). two static renewal tests of nicotine with the mas were also conducted. addition of the mas to nicotine reduced the lc50 from an average of 136 to 20 mg/l. however, th ... | 1988 | 2905544 |
| peroxisomes in pigment epithelium and müller cells of amphibian retina possess d-amino acid oxidase as well as catalase. | in this paper we identify peroxisomes in müller cells and retinal pigment epithelial cells of rana pipiens and xenopus laevis by virtue of their content of cytochemically stainable catalase. these organelles have the form of an extensive, branched system of tubules in the retinal pigment epithelium and appear as discrete ovoid structures in the müller cells. in both the pigment epithelium and the müller cells a second peroxisomal enzyme, d-amino acid oxidase, can be detected in the same structur ... | 1988 | 2905671 |
| development of a metabolic activation system for the frog embryo teratogenesis assay: xenopus (fetax). | fetax (frog embryo teratogenesis assay: xenopus) is a 96-hr teratogenesis screening assay using embryos of the south african clawed frog, xenopus laevis. since xenopus embryos have limited xenobiotic metabolism through 96 hr of development, we have developed an in vitro metabolic activation system employing aroclor 1254-induced rat liver microsomes. by adding an exogenous source of mixed functional oxidase (mfo) activity, we may more accurately assess the teratogenic risk of proteratogenic compo ... | 1988 | 2905834 |
| biogenic amines and active peptides in the skin of fifty-two african amphibian species other than bufonids. | 1. extracts prepared from dried or fresh skins of 52 african amphibian species, other than bufonids, were subjected to chemical (colour reactions) and biological screening, to determine occurrence and contents of aromatic biogenic amines and peptides active on smooth muscle preparations and blood pressure. 2. only indolealkylamines were detectable in the skins. they were represented by 5-hydroxytryptamine, its n-methylated derivatives and tryptamine. the indolealkylamines considered included the ... | 1988 | 2905943 |
| somatostatin-like immunoreactivity and glycine high-affinity uptake colocalize to an interplexiform cell of the xenopus laevis retina. | antibodies directed against somatostatin have been used to label a population of interplexiform cells (ipcs) in the xenopus laevis retina. these cells have spherical soma which lie in the inner nuclear layer (inl), adjacent to or one cell distal to the inner plexiform layer (ipl). processes from these cells project throughout the ipl, with a fairly dense accumulation of labeled dendrites in the upper two-fifths of the ipl and a dense, narrow band of labeled dendrites adjacent to the ganglion cel ... | 1988 | 2906071 |
| isolation and expression of cdna clones coding for two sequence variants of xenopus laevis histone h5. | we have cloned and characterized cdnas coding for two variants of xenopus laevis h5 histone protein (previously called h1s). cdna was synthesized from rna of immature erythrocytes in a single reaction using a modification of the method of gubler and hoffman [gene 25 (1983) 263-269], and blunt-end ligated into the hincii site of the phage vector m13mp9. immunological screening with a polyclonal antibody yielded two clones expressing h5 peptide. sequence characterization revealed that both clones ... | 1988 | 2907322 |
| development and hormone regulation of androgen receptor levels in the sexually dimorphic larynx of xenopus laevis. | development of the sexually dimorphic larynx in african clawed frogs is controlled by secretion of androgenic steroids (d. sassoon and d. kelley, 1986, amer. j. anat. 177, 457-472). adult laryngeal muscle shows high levels of androgen binding relative to other skeletal muscles and binding activity in males is three times that in females (n. segil, l. silverman, and d. kelley, 1987, gen. comp. endocrinol. 66, 95-101). to determine when androgen sensitivity and sex differences arise, we assayed [3 ... | 1989 | 2909399 |
| 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 |
| a test of 'polymerase handover' as a mechanism for stimulating initiation by rna polymerase i. | on the tandemly linked ribosomal genes of xenopus laevis, the rna polymerase transcribes past the 3' end of the 40s coding region and terminates at t3 just upstream of the gene promoter. the close proximity of t3 to the gene promoter, and the functional interdependence of these two elements, has led to the suggestion that polymerase terminating at t3 might be passed directly to the gene promoter. such a mechanism might be necessary to maintain the characteristic high rate of transcription initia ... | 1989 | 2911470 |
| structural and functional properties of reticulospinal neurons in the early-swimming stage xenopus embryo. | this study presents direct evidence that in xenopus laevis embryos ipsi- and contralaterally descending reticulospinal fibers from the caudal brain stem project to the spinal cord, where they directly contact primary motoneurons. at stage 30, occasional contacts between primary motoneurons and descending axons are present. these contacts are possibly already functional since presynaptic vesicles were sometimes observed. furthermore, the physiological data obtained in this study suggest that reti ... | 1989 | 2913206 |
| polyamine levels during xenopus laevis oogenesis: a role in oocyte competence to meiotic resumption. | the results presented here show that a decrease in the concentration of total polyamines, due to a decrease in putrescine and spermine, occurs during oogenesis in xenopus laevis. the microinjection of spermine or spermidine decreases the hormonal responsiveness (maturation) of the fully-grown oocytes. this effect is synergistic with that already described for the microinjection of casein kinase ii (mulner-lorillon, o. et al. (1987) eur. j. biochem. 171, 107-117), a polyamine dependent enzyme. th ... | 1989 | 2917000 |
| 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 |
| 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 |
| 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 |
| sex linkage of malic enzyme in xenopus laevis. | genetic analysis of mme variants (mitochondrial malic enzyme, e.c. 1.1.1.40) in xenopus laevis revealed sex linkage of the mme locus and indicated a wz/zz type of sex determination. codominant mme alleles occur on both w and z chromosomes, with a recombination frequency of 6.1% +/- 1.5% between mme and the sex-determining locus (or region). | 1989 | 2920808 |
| 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 |
| corticosteroid receptors in liver cytosol of the clawed toad, xenopus laevis: influence of thyroid and ovarian hormones. | the glucocorticoid receptor capacity ro and the dissociation constant kd were determined in the liver of xenopus laevis by scatchard analysis. in 5-year-old female toads ro was about three times higher than that in males (153.9, 54.3 fmol/mg protein) and kd was similar in both sexes (4.0, 4.1 nm). some of the animals used had abnormal enlarged thyroid glands, atrophic ovaries, or both defects in connection with different levels of ro, but not of kd, compared to those of normal animals. females w ... | 1989 | 2925084 |
| 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 |
| vesicular transport of newly synthesized opsin from the golgi apparatus toward the rod outer segment. ultrastructural immunocytochemical and autoradiographic evidence in xenopus retinas. | each day, rod photoreceptors of the vertebrate retina synthesize rhodopsin and insert it into new membranes of the rod outer segment (ros). the authors determined which components of the rod cell transport opsin from the golgi to the ros by a combined em autoradiographic and immunocytochemical study using radiolabeled amino acid precursors and antiopsin antibodies. radiolabeled proteins in the ellipsoid region of xenopus laevis retinal rods were localized by comparison of the distribution of sil ... | 1985 | 2931395 |
| location of influenza virus m, np and ns1 proteins in microinjected cells. | when microinjected as cloned dna, the nucleoprotein (np) of influenza virus a/nt/60/68 (h3n2) accumulated in the nuclei of xenopus laevis oocytes, and cultured cells of rodent and primate origin. this accumulation appeared to be specific and a property of the np itself (or conceivably np in association with unknown cellular constituents) since no other influenza virus components were present in dna-injected cells. in the oocyte nucleus, clonally derived np achieved an eightfold concentration ove ... | 1985 | 2932535 |
| trans effect of the e1 region of adenoviruses on the expression of a prokaryotic gene in mammalian cells: resistance to 5' -ccgg- 3' methylation. | the plasmid construct psvo-cat has been used to test adenovirus promoter activities in the unmethylated or methylated state. we have now observed that the e2a late promoter of adenovirus type 2 (ad2) dna also activated the chloramphenicol acetyltransferase (cat) gene upon transfection of the pad2e2a-cat construct into mammalian cells, and it was inactivated by specific methylations of three 5' -ccgg- 3' sites. similar results had been reported previously after microinjecting promoter-methylated ... | 1986 | 2937060 |
| changes in activity of the regulatory glycolytic enzymes and of the pyruvate-dehydrogenase complex during the development of xenopus laevis. | in this study we investigated the variations of the maximal activities of the rate-controlling glycolytic enzymes (i.e., hexokinase, hk; phosphofructokinase, pfk; pyruvate kinase, pk) and of the pyruvate-dehydrogenase complex (pdhc) during the early embryogenesis of xenopus laevis (from cleavage through hatching). all the enzymatic assays, using different coupled reactions, were performed spectrophotometrically on cytosolic and mitochondrial fractions. the maximal hk activity increases markedly ... | 1986 | 2937670 |
| the relationship between chromosomal origins of replication and the nuclear matrix during the cell cycle. | a cytological investigation into the dynamic behaviour of the origins of replication with respect to the nuclear matrix has been carried out on xenopus laevis cultured cells. in order to preferentially label origins or 'non-origin' regions along dna fibres, 5-fluoro-2'-deoxyuridine (fudr)-treated cells were pulsed with [3h]deoxyadenosine in early or late s phase. samples were then allowed to proceed through the cell cycle for increasing times. the dna loops were induced in situ to completely unc ... | 1986 | 2940105 |
| impaired rejection of minor-histocompatibility-antigen-disparate skin grafts and acquisition of tolerance to thymus donor antigens in allothymus-implanted, thymectomized xenopus. | we examine whether j strain xenopus laevis and x laevis/gilli (lg) isogeneic hybrids, thymectomized (tx) at 7 days and implanted with larval or postmetamorphic thymus (either normal or irradiated) in late larval life, can be used to explore the role of the developing thymus in the education of minor histocompatibility (h) antigen-reactive t cells and in the acquisition of tolerance to mhc (major histocompatibility complex) antigens. tx lg xenopus implanted with isogeneic thymus display fully res ... | 1986 | 2940739 |
| studies on dna polymerases of xenopus laevis oocytes: subcellular distribution and physical association of dna polymerase alpha inside the nucleus. | the localization of dna polymerases in xenopus laevis oocytes and eggs was studied. oocytes have a high level of dna polymerase alpha activity detected exclusively in the nuclei, while mitochondria contain all the dna polymerase activity of the gamma type. no dna polymerase beta activity is present in the nuclear fraction. moreover, the beta activity is not present in unfertilized eggs. in oocytes, dna polymerase alpha is weakly bound to the nucleoplasm. the leakage of the enzyme from whole nucl ... | 1986 | 2941095 |
| the development of inducer and effector immune suppressor cell function in xenopus laevis, the south african clawed toad: the effect of metamorphosis. | thymic capacity to induce suppression of antibody production by immunized xenopus laevis toadlet spleen fragments was tested in co-cultures for different developmental stages (nieuwkoop, p.d. and j. faber: normal table of xenopus laevis (daudin) (north holland, amsterdam) 1967). while thymuses of stages 52-54 (premetamorphosis) induced suppression, those of stages 58-62 (metamorphosis) did not. this capacity returned in metamorphic climax (stages 63-65). tests of lectin-induced suppressor functi ... | 1986 | 2941153 |
| monospecific antibodies reveal details of u2 snrnp structure and interaction between u1 and u2 snrnps. | monospecific antibodies directed against several u small nuclear ribonucleoprotein (u snrnp) particle proteins were affinity purified from a patient's anti-(u1,u2)rnp serum. these were used to demonstrate that: (i) proteins equivalent to the mammalian u2 snrnp-specific a' and b" proteins are present in xenopus laevis oocytes; (ii) both proteins a' and b" have the same structural requirements for binding to u2 snrna; (iii) proteins b, b' and d have the same structural requirement for binding to u ... | 1986 | 2941274 |
| formation of nucleus-like structure in the cytoplasm of lambda-dna-injected fertilized eggs and its partition into blastomeres during early embryogenesis in xenopus laevis. | the fate of bacteriophage lambda-dna was examined after injection into the fertilized eggs of xenopus laevis. injection of a large amount of lambda-dna (ca. 24 ng) into a fertilized xenopus egg induced the formation around the injected dna of a giant nucleus-like structure which was surrounded by an apparently normal bilayered nuclear membrane with nuclear pore complexes. southern blot analysis revealed the persistence of injected lambda-dna until the blastula stage. the nucleus-like structure w ... | 1986 | 2942430 |
| gene expression in transgenic xenopus laevis. | | 1986 | 2944126 |
| cap trimethylation of u snrna is cytoplasmic and dependent on u snrnp protein binding. | trimethyl capping of u2 snrna has been studied using u2 genes with mutations located in either the 5' flanking or the coding region. a monomethyl (7-methylguanosine) cap is added to u2 cotranscriptionally, trimethylation being posttranscriptional. the immediate 5' flanking sequences have no influence on trimethylation; furthermore, trimethylation is not affected by changing the position and sequence of the cap site. the efficiency of trimethylation is reduced by deleting the sm binding site from ... | 1986 | 2944599 |
| recombinant dna produced human il-2, injected in vivo, will substitute for carrier priming of helper function in the south african clawed toad, xenopus laevis. | the studied included in this report tested the ability of a recombinant dna produced human lymphokine (ril-2) to serve as a substitute for the carrier priming required for the in vivo generation of anti-hapten responses, in young adults of xenopus laevis, the south african clawed toad. heterologous erythrocyte carriers were used. immune reactivity was monitored with hapten-specific antigen binding cells (abc) in spleen cell suspensions, 8 days after injection i.p. of trinitrophenylated sheep ery ... | 1986 | 2945778 |
| calcium-stimulated myofibrillar atpase activity correlates with shortening velocity of muscle fibres in xenopus laevis. | the iliofibularis muscle of xenopus laevis is reported to contain five types of fibres which have different force-velocity relationships. ten fibres of each type were selected on the basis of succinate dehydrogenase activity, cross-sectional area and location in the muscle, in order to assess the validity of the fibre type classification. maximum calcium-stimulated myofibrillar atpase activity (vmax) and apparent michaelis constant (km) for atp were determined for these 50 fibres from serial sec ... | 1986 | 2946649 |
| efficient homologous recombination of linear dna substrates after injection into xenopus laevis oocytes. | when dna molecules are injected into xenopus oocyte nuclei, they can recombine with each other. with bacteriophage lambda dnas, it was shown that this recombination is stimulated greatly by introduction of double-strand breaks into the substrates and is dependent on homologous overlaps in the recombination interval. with plasmid dnas it was shown that little or no recombination occurs between circular molecules but both intra- and intermolecular events take place very efficiently with linear mol ... | 1986 | 2946937 |
| t cell receptor-homologous mrna from a suppressor t cell clone directs the synthesis of antigen-specific suppressive products. | the lh8-105 t cell clone, obtained by radiation leukemia virus-induced transformation of hen egg-white lysozyme (hel)-specific mouse suppressor t lymphocytes, constitutively releases in the culture supernatant products able to induce specific suppression of the immune response to hel. lh8-105 cells rearrange and express the genes encoding the alpha and beta chains of the antigen-specific t cell receptor and display membrane t cell receptor structures. lh8-105 mrna specific for the alpha and beta ... | 1987 | 2952515 |
| electron microscopic studies of giant nucleus-like structure formed by lambda dna introduced into the cytoplasm of xenopus laevis fertilized eggs and embryos. | when bacteriophage lambda dna was injected into the cytoplasm of the fertilized egg of xenopus laevis, giant nucleus-like structures were assembled around the injected dna. these nucleus-like structures survived during cleavage and were partitioned into blastomeres at the blastula stage. the nucleus-like structures formed in the uncleaved fertilized eggs and the blastula cells were both surrounded by a bilayer nuclear membrane with nuclear pore complexes. the ultrastructural features of the lamb ... | 1987 | 2953439 |
| 46 kd mannose 6-phosphate receptor: cloning, expression, and homology to the 215 kd mannose 6-phosphate receptor. | we have isolated cdna clones encoding the entire sequence of the bovine 46 kd cation-dependent mannose 6-phosphate (cd man-6-p) receptor. translation of cd man-6-p receptor mrna in xenopus laevis oocytes results in a protein that binds specifically to phosphomannan-sepharose, thus demonstrating that our cdna clones encode a functional receptor. the deduced 279 amino acid sequence reveals a single polypeptide chain that contains a putative signal sequence and a transmembrane domain. trypsin diges ... | 1987 | 2954652 |
| co-evolution of base composition and codon usage in xenopus laevis and human globin genes with long-range dna organization of their genome. | eucaryotic dna is punctuated by many a+t-rich segments that we named a+t-rich linkers. two types of these a+t-rich linkers can be distinguished: (i) isolated a+t-rich linkers, and (ii) a+t-rich linkers crowded in clusters. we have analysed the distribution of a+t-rich linker across the alpha- and beta-globin gene domain in xenopus laevis and human genomes using isodenaturation and electron microscopy. comparison of our data with those previously obtained for the avian globin genes leads us to co ... | 1987 | 2957230 |
| analysis of allotolerance in thymectomized xenopus restored with semiallogeneic thymus grafts. | the triploid j strain xenopus laevis (mhc haplotype, j/j/j) were thymectomized as early larvae, and in the adult stage each animal was given a pair of thymuses or lymphocytes from semiallogeneic diploid donor frogs (j/k). the alloreactivity of host frogs was restored to third-party donors in terms of skin graft rejection and mixed leukocyte reaction, but there was specific unresponsiveness against the k haplotype. grafting of heavily irradiated (10,000 rads) thymuses also restored host reactivit ... | 1987 | 2957832 |
| mitogen-activated xenopus laevis lymphocytes produce a t-cell growth factor. | mitogen-free and serum-free supernatants (sns) from cultures of phytohaemagglutinin (pha)-stimulated xenopus splenocytes, co-stimulated thymocytes, induced proliferation of splenic and thymic lymphoblast and supported growth of alloreactive t-cell lines. these sns had no effect on 'resting' splenocytes, as measured by uptake of tritiated thymidine ([3h]tdr). growth-promoting activity was also detected in sns of cultures containing alloreactive t-cell lines and either pha or irradiated stimulator ... | 1987 | 2958404 |
| atpase activity of intact single muscle fibres of xenopus laevis is related to the rate of force redevelopment after rapid shortening. | five different fibre types have been recognized in the iliofibularis muscle of xenopus laevis. the force-velocity and histochemical characteristics of these fibres vary considerably and differences are also found in their myosin composition. in this study a comparison was made between the rate of atp hydrolysis estimated from the stable maintenance heat rate and the mechanical performance of fibres of type 1, 2 and 3. in the experiments, firstly the force-velocity relation of a fibre was determi ... | 1987 | 2959253 |
| adenovirus e1a requires synthesis of a cellular protein to establish a stable transcription complex in injected xenopus laevis oocytes. | the escherichia coli-expressed adenovirus e1a 13s mrna product injected into xenopus oocytes was active, as assessed by its ability to stimulate the transcription of an injected gene which is normally responsive to e1a in mammalian cells. in the presence of the protein synthesis inhibitors pactamycin or cycloheximide, e1a was correctly posttranslationally modified (phosphorylated) and transported to the nucleus; but it failed to stimulate the transcription of an injected gene containing the huma ... | 1987 | 2959858 |