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nerve-independent dna synthesis and mitosis in regenerating hindlimbs of larval xenopus laevis.xenopus laevis larvae at stage 52-53 (according to nieuwkoop and faber 1956) were subjected to amputation of both limbs at the thigh level as well as to repeated denervations of the right limb. results obtained in larvae sacrificed during wound healing (1 after amputation), blastema formation (3 days) and blastema growth (5 and 7 days) showed that denervated right limbs have undergone the same histological modifications observed in innervated left limbs and have formed a regeneration blastema co ...199228305578
partial characterization of neural-inducing factors from xenopus gastrulae evidence for a larger protein complex containing the factor.high (mr ≈ 90-110 kda) and low (mr ≈ 15-30 kda) molecular weight forms of neural-inducing factors have been found in the supernatant of xenopus gastrula homogenate. the factors, which are protein in nature, have been partially purified by size exclusion high-performance liquid chromatography (hplc) and sodium dodecyl sulphate (sds)-polyacrylamide gel electrophoresis. the factor of smaller size, which could be derived from a precursor, is associated with other proteins in a larger complex. the ne ...199228305609
dynamic distribution of region-specific maternal protein during oogenesis and early embryogenesis of xenopus laevis.for analysing spatial distribution of maternal proteins in an amphibian egg, monoclonal antibodies specific to certain regions were raised. one monoclonal antibody was found (moab xa5b6) which reacted specifically with the animal hemisphere of the mature xenopus laevis egg. the maternal protein that reacted with the moab xa5b6 was shown to be distributed asymmetrically along the dorso-ventral axis in the upper region of the equatorial zone of the fertilized egg. at late blastula stage, the antig ...199128305969
in vitro evidence that interactions betweenxenopus blastomeres restrict cell migration.the consistency of the frog blastula's fate map is produced, in part, because the progeny of blastomeres located in dfferent regions do not intermix with one another. we examined the cause for this restriction of intermixing in two types of cultures. in one type of culture, two groups of cells were excised from blastulae and stuck together; the movement of cells between the groups was monitored. cells migrated more extensively between groups derived from the same region than between groups deriv ...199028306109
mesodermal induction in early amphibian embryos by activin a (erythroid differentiation factor).recently the mesoderm-inducing effects of the transforming growth factor β (tgf-β) family of proteins have been widely examined. in an attemt to elucidate the functions of these proteins, porcine inhibin a and activin a (erythroid differentiation factor; edf) were examined. treatment of explants with activin a led to differentiation of mesodermal derivatives such as mesenchyme, notochord, blood cells and muscle, but inhibin a had a much lesser effect. the mesodermal differentiation induced by ac ...199028305412
expression of exogenously introduced bacterial chloramphenicol acetyltransferase genes in xenopus laevis embryos before the midblastula transition.previous papers have reported that dnas exogenously injected into xenopus laevis fertilized eggs are expressed only at and after the midblastula transition (mbt). we have injected fertilized eggs of xenopus laevis with circular plasmids that contained bacterial chloramphenicol acetyltransferase (cat) genes connected to the promoter of viral genes (psv2cat and pad12.e1acat) or the xenopus cardiac actin gene (actin-cat fusion gene), and examined whether these dnas are expressed during the stage be ...199028305411
epiboly connected with cleavage in morula and early blastula stages of xenopus laevis, a study using time-lapse photography.measurements were made of the external surface areas occupied by animal and vegetal blastomeres and their daughter cells at successive cleavage cycles in 15 embyros of xenopus laevis. on the animal side, after each cleavage a general area increase (epiboly) occurs from cycle 4 (16-cell stage, stage 5) to cycle 10 (stage 8 1/2), while on the vegetal side there is a slight general area decrease after each cleavage from cycle 6 to cycle 10. the comparison between the external surface areas of indiv ...199028305669
the expression of barley α-amylase genes in xenopus laevis oocytes.the synthesis and secretion of α-amylase (ec 3.2.1.1) from xenopus laevis oocytes injected with plasmids containing barley α-amylase complementary dna (cdna), genomic dna, or synthetic α-amylase mrna were studied. α-amylase accumulated within the oocytes beginning 12 h after injection of dna and in the medium 12 h later as a result of secretion. s1 mapping showed that the transcription of genomic dna was initiated at the same site in oocytes as in barley aleurone, but that the transcription of c ...199024202011
the metamorphic switch in hemoglobin phenotype ofxenopus laevis involves erythroid cell replacement.to elucidate the cellular basis of hemoglobin transition inxenopus laevis the distribution of larval and adult hemoglobins was analyzed by indirect immunofluorescence in the circulating erythrocytes during metamorphosis. in addition, the morphological characteristics as well as the capacity for synthesis of dna and hemoglobin in the erythrocytes were followed during the same developmental period. our quantitative analysis on the distribution of larval and adult hemoglobins suggests that they are ...198928305873
developmental pattern and molecular identification of globin chains in xenopus laevis.high-resolution electrophoresis of larval and adult hemoglobins of xenopus laevis reveals stage-specific differences in the number and mobility of the globin chains. to establish the relationship between the globin chains and the previously described globin genes, the corresponding mrnas were hybrid-selected from total erythroblast rna by representative cdna clones, and translated in vitro. electrophoretic separation of the translation products allowed identification of a major and a minor α-glo ...198828305747
protein kinases in amphibian ectoderm induced for neural differentiation.ectoderm explants from early gastrula stages of xenopus laevis were induced with a neutralizing factor. the factor was isolated from xenopus gastrulae and partially purified by chromatography on deae cellulose. the ectoderm was cultured for different periods of time and then homogenized. protein kinase activity was determined in the homogenates from induced and control explants with histone h 1 or c-terminal peptide derived from histone h 1 as substrates. the c-terminal peptide is a more specifi ...198828305429
xenopus skin mucus induces oral dyskinesias that promote escape from snakes.african clawed frogs fed to american water snakes induced yawning and gaping which slowed ingestion and facilitated the frogs' escape without inducing flavor aversion. the peptide and/or indolealkylamine contents of the frog's poison glands caused the effect because frogs with purged glands did not induce these behaviors and rarely escaped. poison gland mucus, applied orally, elicited similar oral movements. the frog's clear lubricating mucus was inactive. as several compounds in the poison glan ...19883227042
crystallins during xenopus laevis free lens formation.the ontogeny and localization of crystallins during free lens development (i.e. lens development without the optic vesicle) were investigated in xenopus laevis using the indirect immunofluorescence staining method with an antiserum raised against homologous total lens soluble proteins. since the developing free lenses pass through stages similar to those of the lenses regenerated from the inner cell layer of the outer cornea following lentectomy in the same species freeman's classification was u ...198828305564
cell proliferation in ectodermal explants from xenopus embryos.dissociated prospective ectoderm cells from xenopus laevis embryos divide autonomously up to the 17th division cycle of the embryo. to examine the requirements for the further proliferation of these cells, the continuation of cell division in compact ectodermal explants beyond the 17th division cycle has been studied. such explants develop into aggregates of epidermal cells, as can be shown immunohistochemically with an anti-serum against xenopus epidermal cytokeratin. cell division in these exp ...198828305558
binding of anti-fibronectin to early amphibian ectoderm does not result in inhibition of neural induction under in vitro conditions.antibodies directed to fibronectin (anti-fn) were injected into the blastocoel of late blastulae of xenopus laevis. two animal caps (ectoderm) were isolated, when control embryos reached the early gastrula stage, and were combined with untreated upper blastopore lip in the sandwich method. in two control series fibronectin or holtfreter solution was injected into the blastocoel. the results of the experiments suggest that neural induction cannot be prevented by binding anti-fn to fibronectin, wh ...198728305695
characterization of repetitive dna transcripts isolated from a xenopus laevis gastrula-stage cdna clone bank.by screening a cdna library prepared from polyadenylated nuclear rna of xenopus laevis gastrula-stage embryos with total genomic dna we have identified nine clones belonging to seven different families of repeated dna. two of these families exhibit partial sequence homologies and thus probably represent subfamilies of a common origin. the individual families comprise between 0.024% and 1.5% and, in total, about 2% of the x. laevis genome. six of the clones elements represent dispersed repetitive ...198728305657
the direction of cleavage waves and the regional variation in the duration of cleavage cycles on the dorsal side of the xenopus laevis blastula.the animal and the dorsal side of five embryos of xenopus laevis were studied in detail from the 7th to the 13th cleavage by means of time-lapse cinematography. at each cleavage the regionally ordered sequence of blastomere divisions is visible in the films as a "cleavage wave", propagating about three times slower in the dorsal than in the animal view. in the dorsal view the waves run in an animal-vegetal direction, initially with a left-to-right deviation and in later cleavages converging on t ...198628305687
the inducing capacity of the presumptive endoderm of xenopus laevis studied by transfilter experiments.the inducing capacity of the vegetal hemisphere of early amphibian blastulae was studied by placing a nucleopore filter (pore size 0.4 μm) between isolated presumptive endoderm and animal (ectodermal) caps. the inducing effect was shown to traverse the nucleopore membrane. the reacting ectoderm differentiated into mainly ventral mesodermal derivatives. expiants consisting of five animal caps also formed dorsal mesodermal and neural structures. those results together with data published elsewhere ...198628305409
neural-inducing activity of nuclei and nuclear fractions from xenopus laevis embryos.from embryos (xenopus laevis) of different developmental stages nuclei were isolated which exert neural inducing activity in the biological test. the active material could partly be extracted from the nuclei. experiments for the isolation of nuclear ribonucleoprotein (rnp) particles have shown that the activity is localized at least in part in these particles. on the other hand, some neural inducer is not detached from chromatin and the nuclear matrix even with ionic detergents. inducing activit ...198628305447
isolation of plasma membranes from xenopus embryos.plasma membranes were isolated in high yield from xenopus gastrulae by repeated sedimentation in discontinuous sucrose gradients. most of the yolk was separated by lowspeed sedimentation before centrifugation on the discontinuous sucrose gradients. the isolation of plasma membranes was followed by covalent labelling of the surface of dissociated gastrula cells with diazoniobenzene sulphonate, by electron microscopy and the distribution of enzymatic markers. the isolated plasma membranes have a l ...198628305446
two recessive mutations with maternal effect upon colour and cleavage ofxenopus l. laevis eggs."pale eggs" and "partial cleavage" are two mutations with a maternal effect that are found in the same family ofxenopus l. laevis. the pale eggs have animal hemispheres of a yellow to beige colour and give rise to normally pigmented tadpoles and frogs. the cells of pale embryos contain fewer melanosomes than those of controls. the partial cleavage eggs are characterized by an abnormality of cleavage visible from the eight-cell stage onwards, by abnormal yolk platelet distribution and abnormal cy ...198428305590
inducing activity of subcellular fractions from amphibian embryos.the homogenate from unfertilized eggs, gastrulae, neurulae and hatched embryos ofxenopus laevis was fractionated by differential centrifugation and subsequent repeated centrifugation on discontinuous sucrose gradients. a high archencephalic-neural inducing activity was found in rnp particles, which were released from the high-speed ("microsomal") sediment by treatment with edta, and in a fraction of heterogeneous small vesicles. the highest archencephalic inducing activity was observed in rnp pa ...198428305490
change in the differentiation pattern ofxenopus laevis ectoderm by variation of the incubation time and concentration of vegetalizing factor.early amphibian gastrula ectoderm (xenopus laevis) has been treated with vegetalizing factor using the sandwich technique, varying the period of incubation and the inducer concentration.the pattern of induced tissues depends on three factors: the inducer concentration, the size of inducer pellet and the time of exposure of ectodermal target cells to inducer.short treatment with inducer will result in the formation of blood cells and heart structures. an increase in incubation time or inducer con ...198328305118
repetitive sequences associated with polyadenylated rna of xenopus laevis embryos.electron microscopy revealed that transcripts of complementary repetitive sequence elements are widely distributed among long poly (a) containing rna molecules of xenopus laevis. cdna/rna hybridization experiments suggest that many of these polyadenylated transcripts carry protein coding sequences which are interrupted by repetitive elements. our in-vitro translation experiments indicate that removal of repetitive elements must precede the utilization of protein coding sequences associated with ...198228305260
the fate of oocyte nuclear proteins during early development ofxenopus laevis.the localization and movements of four nuclear proteins, originally contained in the germinal vesicle ofxenopus oocytes, were followed through early development from cleavage to late neurula. the study made use of monoclonal antibodies directed against germinal vesicle proteins. biochemical methods showed that all proteins persist in the embryo without a change in molecular size or gross concentration. at early stages the proteins are localized preferentially in the cytoplasm of the animal hemis ...198228305052
the presence of an endogenous lectin in early embryos ofxenopus laevis.xenopus laevis embryos were examined for the presence of endogenous carbohydrate binding proteins. soluble extracts of cleavage, gastrula and neurula embryos are able to agglutinate trypsinized rabbit erythrocytes. unlike other embryonic lectins this agglutination activity requires the presence of calcium ions but not of sulphydryl reducing agents. it is specifically inhibited by galactose and galactose containing derivatives. thiodigalactoside is the most potent disaccharide inhibitor followed ...198228305386
cloning of cdna sequences derived from poly(a)+ nuclear rna ofxenopus laevis at different developmental stages: evidence for stage specific regulation.nuclear poly(a)+ rna was isolated from gastrula and early tadpole stages ofxenopus laevis, transcribed into cdna and integrated as double stranded cdna by the g-c joining method into the pst cleavage site of plasmid pbr 322. after cloning ine. coli strain hb 101 the clone libraries were hybridized to32p labelled cdna derived from nuclear poly(a)+ rna of the two different developmental stages. about 20% of the clones gave a positive hybridization signal thus representing rna molecules of high and ...198128305358
the lens proteins in adult and embryos of the periodic albino mutant ofxenopus laevis.the crystallins of normal and ap mutants ofx. laevis have been studied using biochemical (electrophoresis in agar and polyacrylamide gels, isoelectric focusing) and immunochemical methods (immunoelectrophoresis, immunodiffusion, immunoabsorption, immunofluorescence, isoelectrofocusing with immunoidentification). the immunochemical analysis was carried out with rabbit antisera prepared against electrophoretic fractions of the mutant lens.crystallins of adultx. laevis (ap/ap; ++/++) are heterogeno ...198028305170
the effects of tunicamycin and 2-deoxy-d-glucose on the development ofxenopus laevis embryos.tunicamycin and 2-deoxy-d-glucose were applied toxenopus laevis embryos in the first cleavage furrow, blastula and early gastrula stages. no effect was observed with 2-deoxy-d-glucose up to the concentration 0.1 m. the effect of tunicamycin is dose- and stage-dependent. at the concentration of 5 μg/ml cleaving embryos are arrested at the onset of gastrulation and their cells exhibit decreased intercellular adhesivity, while embryos treated in the blastula and early gastrula stages may develop up ...198028305930
the role of tensile fields and contact cell polarization in the morphogenesis of amphibian axial rudiments.the role of stretching-generated tensile stresses upon the organization of axial rudiments have been studied. pieces of the dorsal wall ofxenopus laevis andrana temporaria embryos at the late gastrula stage were rotated through 90°, transplanted into the field of neurulation tensions of another embryo and replaced by ventral tissues already insensitive to inductive influences. the axial rudiments which developed from rotated and transplanted dorsal tissues oped from rotated and transplanted dors ...198028305148
quantitative aspects of rna synthesis in normal and lithium-treated embryos ofxenopus laevis.the treatment ofxenopus early embryos with lithium chloride produces exogastruale - embryos which fail to gastrulate normally and in which the rates of cell division are reduced. in the present study estimations of incorporations of (5-3h) uridine and the specific activities of the 5'-ribonucleotide precursor pools showed that exogastrulae have higher rates of rna synthesis per cell than control neurulae. sub-cellular fractionations showed that a greater proportion of labelled rna was retained i ...197928305001
changes in the cell surface coat during the development ofxenopus laevis embryos, detected by lectins.the composition of the surface coat in embryonic cells ofxenopus laevis was examined by agglutination and fluorescent staining with lectins.cells of early and mid gastrula stages were agglutinated by lectins specific for d-mannose, d-galactose, l-fucose, n-acetyl-d-glucosamine and n-acetyl-d-galactosamine. no differences in agglutinability among ectoderm, mesoderm and endoderm cells were observed with lectins specific for d-mannose, d-galactose and n-acetyl-d-galactosamine, though agglutination ...197828305035
melanin synthesis activation dependent on inductive influences.gene activity in melanin-synthesising cells of albino periodic (ap) mutants ofxenopus laevis is expressed phenotypically in the framework of the following cycle: a period of complete albinism succeeds the short peak of pigmentation, and melanosomes which have formed disappear. skin and choroid coat melanophores as well as pigmented epithelium melanocytes are involved in this cycle.parabiosis experiments allowed hormonal regulation of the melanin-synthesising gene activity to be excluded. neural ...197828305010
differentiated protein synthesis with polysomes from petunia ovaries before fertilization.polysomes from cross-, self- and unpollinated ovaries have been injected in xenopus laevis eggcells. the synthesised proteins have been identified by means of gel-electrophoresis. it appeared that few hours after pollination the protein pattern of the pollinated ovary has changed in comparison with that of unpollinated ones. however, in this early stage, there is only little difference found in the protein pattern of selfed and crossed ovaries. from 12 h after pollination and onwards, the differ ...197724425225
inducing activity of fractionated microsomal material from thexenopus laevis gastrula stage.the postmitochondrial supernatant fromxenopus gastrulae has been fractionated on sucrose gradients. part of the microsomal material was treated with edta, which dissociates most of the polysomal and monosomal material into ribosomal subunits. in addition, a series of pooled fractions from the edta treated gradients has been applied to discontinuous gradients in more concentrated sucrose to separate membranous material from the remaining microsomal components.pooled fractions from all gradients h ...197628305523
[a comparison of the inducing ability from the superficial layer of the yolk platelet coats and the microsomal fraction of cleavage, gastrula and neurula stages of xenopus laevis].deuterencephalic and spinocaudal inducing activity is extractable from the yolk platelet coats and the microsomal fraction of cleavage, gastrula and neurula stages ofxenopus laevis.extracts of both cell fractions from the gastrula and neurula cause a significantly stronger deuterencephalic and spinocaudal reaction than those from cleavage stages, when tested antriturus alpestus ectoderm.197428304839
[not available]. 194818891702
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