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At least 649 records · Page 36Linked to original sources
PubMed2003

Histology-based screen for zebrafish mutants with abnormal cell differentiation.

The power of histology to define states of cell differentiation was used as the basis of a mutagenesis screen in zebrafish. In this screen, 7-day-old parthenogenetic half-tetrad larvae from potential carrier females were screened for mutations affecting cell differentiation in hematoxylin and eosin-stained tissue sections. Seven, noncomplementing, recessive mutations were found. Two mutations affect only the retina: segmented photoreceptors (spr) show a discontinuous photoreceptor cell layer; vestigial outer segments (vos) has fewer photoreceptor cells and degenerated outer segments within this cell layer. Three mutants have gut-specific defects: the epithelial cells of kirby (kby) are replaced by ballooned cells; the intestines of stuffy (sfy) and stuffed (sfd) contain increased luminal mucus. Two mutations affect multiple organs: disordered neural retina (dnr) has disrupted retinal layering and mild nuclear abnormalities in the gut and liver; and in huli hutu (hht), the retinal cell layers are disorganized and multiple organs have mild to severe nuclear abnormalities that are reminiscent of the atypia of human neoplasia. Each mutation appears to be homozygous lethal. This screen is proof of principle for the feasibility of histologic screens to yield novel mutations, including potential models of human disease. The throughput for this type of screen may be enhanced by automation.

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PubMed1987

Ovarian teratocarcinomas in LT/Sv mice carrying t-mutations.

Ovarian teratomas that result from parthenogenetic activation of oocytes provide a double tool for developmental genetics. First, they provide a way of measuring recombination between a gene and its centromere. Second, in the absence of crossing over there is the potential of producing tumors that are homozygous for genes that would be lethal in the course of in utero embryonic development. We have applied both aspects to several t-haplotypes containing different early acting t-lethal genes. In a study of 26 tumors, genotyped by Southern blot analysis of the major histocompatibility complex (MHC), we measured the distance between the centromere and the start of the t-complex as 5.6 +/- 2.3 cM. We found a marked deficiency of t-homozygous genotypes among the tumors we studied, although T/T genotypes formed teratomas at levels comparable to controls. None of the lethal t-haplotypes we studied permit homozygous embryos to develop to the primitive streak stage, while T/T embryos do develop essentially normally through that stage. Thus, although the total number of tumors observed from t-bearing mice was small, the great difference in the incidence of t/t tumors versus the incidence of T/T tumors suggests strongly that the parthenogenetic embryos that convert to teratocarcinomas must first pass through some of the stages of normal early development, including the formation of three germ layers and the primitive streak.

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PubMed1993

Site of action of imprinted genes revealed by phenotypic analysis of parthenogenetic embryos.

The phenotypes of early post-implantation parthenogenetic embryos were examined. The spectrum of phenotypes suggested that three stages are adversely affected by imprinting--implantation, pregastrulation, and postgastrulation. Survival of parthenogenetic embryos past these developmental blocks can be improved but not completely overcome by experimental asynchrony. These results suggest that imprinting may be "leaky" at early stages.

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PubMed1995

Identification of genes showing altered expression in preimplantation and early postimplantation parthenogenetic embryos.

Uniparental embryos have been instrumental in studying imprinting because contributions from the parental genomes can be determined unambiguously. In this study, we set out to identify imprinted genes showing differential expression between parthenogenetic and fertilized embryos during preimplantation and early postimplantation stages of development. We identified three genes--apolipoprotein E, pyruvate kinase-3, and protein phosphatase 1 gamma--that represent excellent candidates for imprinted genes, based on the results of the differential screen, their function in differentiation and the cell cycle, and their location within imprinted chromosomal regions. In addition, two novel genes expressed in trophoblast were identified, 1661 and RA81. These genes, together with four known imprinted genes, H19, Igf2r, Igf2, and Snrpn, showed evidence of expression from both parental alleles in early stage embryos, indicating a role for postfertilization processes in regulating imprinted gene function.

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PubMed1994

Suppression of DNA replication via Mos function during meiotic divisions in Xenopus oocytes.

Meiosis is characterized by the absence of DNA replication between the two successive divisions. In Xenopus eggs, the ability to replicate DNA develops during meiotic maturation, but is normally suppressed until fertilization. Here we show that development of the DNA-replicating ability depends on new protein synthesis during meiosis I, and that mere ablation of the endogenous c-mos product Mos allows maturing oocytes to enter interphase and replicate DNA just after meiosis I. Moreover, we demonstrate that during normal maturation cdc2 kinase undergoes precocious inactivation in meiosis I and then premature reactivation before meiosis II; importantly, this premature cdc2 reactivation absolutely requires Mos function and its direct inhibition by a dominant-negative cdc2 mutant also results in nuclear reformation and DNA replication immediately after meiosis I. These findings indicate that suppression of DNA replication during meiotic divisions in Xenopus oocytes is accomplished by the Mos-mediated premature reactivation of cdc2 kinase. We suggest that these mechanisms for suppressing DNA replication may be specific for meiosis in animal oocytes, and that the ultimate biological function, including the well known cytostatic factor activity, of Mos during meiotic maturation may be to prevent undesirable DNA replication or parthenogenetic activation before fertilization.

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PubMed1982

Experimental genetics of the mammalian embryo.

Recent progress in experimental mouse embryology has provided new approaches to the genetic manipulation of the mammalian embryo. The production of uniparental embryos enables one to compare maternal and paternal gene activity during development, to study the biological consequences of homozygosity of mutant genes, and to further elucidate the unsolved problem of X chromosome inactivation. Transplantation of nuclei from somatic cells into mouse eggs is considered the most vigorous functional test for the developmental capacity of the nuclear genome and provides a bioassay for the study of possible genomic changes during cellular differentiation. Transplantation of cloned eukaryotic genes into mouse eggs will permit the molecular and genetic analysis of their integration and regulation during development and, eventually, their germ line transmission as new heritable elements.

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PubMed2001

Temporal and quantitative changes in sexual reproductive cycling of the cladoceran Daphnia magna by a juvenile hormone analog.

Cyclic parthenogens, such as the cladoceran, Daphnia magna, utilize both asexual (parthenogenetic) and sexual reproduction in order to maximize population fitness in variable environments. Parthenogenetic reproduction is the default strategy among D. magna, while various environmental cues trigger cycles of sexual reproduction. Experiments were conducted with the juvenile hormone analog methoprene to test the hypothesis that members of the insect juvenile hormone/vertebrate retinoic acid family of transcription factors are involved in the regulation of sexual reproduction in daphnids. Neither methoprene, food reduction, or crowding independently stimulated entry into the sexual reproductive phase of the daphnids. However, the combination of food deprivation and crowding stimulated entry into the sexual reproductive phase characterized by an initial high production of males and the subsequent intermittent production of haploid egg-containing ephippia. Exposure to 160 nM methoprene along with food deprivation and crowding caused a significant reduction in the percentage of males produced during the early phase of the sexual cycle and significantly increased the percentage of males produced during the later stages of the cycle. Methoprene concentrations as low as 6.4 nM significantly reduced the number of resting eggs produced and proportionately increased the production of parthenogenetically-produced neonates. These experiments demonstrate that methoprene uncouples the coordinate production of males and resting eggs during the sexual reproductive period of D. magna. Methoprene stimulates male offspring production and defers their production to latter stages of the sexual reproductive period, while inhibiting the production of resting eggs and promoting the continuance of parthenogenetic reproduction. J. Exp. Zool. 290:148-155, 2001.

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PubMed1975

Development and life cycle of the parthenogenetically activated sea urchin embryo.

A method is reported for inducing parthenogenetic development in eggs of the sea urchin Lytechinus pictus, a species which previously could not be artificially activated. NH4OH or the calcium ionophore A23187 are used as activating agents followed by hypertonic treatment. The ionophore is superior in activating large numbers of unfertilized eggs, whereas NH4OH produces a larger percent of embryos able to undergo gastrulation. Both feeding larvae and urchins arising from these artificially activated eggs are diploid. All individuals in which sex has been identified have been female. The viability of these completely homozygous organisms is low compared to their fertilized counterparts.

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PubMed1975

Parthenogenic development after chemical treatment of Xenopus laevis spermatozoa.

Eggs of Xenopus laevis were fertilized in vitro by spermatozoa pre-treated with various concentrations of aziridinyl urea (ethyleneurea) for between 30 and 120 minutes. At 2 and 4 mg/ml for 30 minutes there was a high incidence of abnormal embryos, few of which developed into tadpoles; after 6 and 8 mg/ml no tadpoles were produced. However, the highest concentration 10 mg/ml, yielded 66% of tadpoles, only 7% of which were obviously abnormal. With increasing time the same pattern of events was obtained except for a displacement towards the lower concentration ranges. Tadpoles developing from these latter experiments were found to be haploid. The results resemble those obtained by exposure of Rana pipiens spermatozoa to X-rays and ultraviolet light, with the production of gynogenetic embryos, usually referred to as the Hertwig effect.

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PubMed1975

Ultrastructural analysis of artificially activated rabbit eggs.

Ultrastructural investigations have been carried out on parthenogenetic rabbit eggs in an effort to elucidate events occurring during artificial activation and their similarity to processes of fertilization and embryogenesis. Rabbit eggs were artificially activated by culturing at 10 degrees C for 24 hours followed by incubation at 37 degrees C for 2 to 24 hours. Examination of eggs immediately after incubation at 10 degrees C for 24 hours indicates that activation is initiated when the chromosomes coalesce to form a reticulum which is either surrounded completely by two parallel membranes or incompletely by cisternae of smooth endoplasmic reticulum. Aggregation of the chromosomes occurs as a result of a reduction in the number of microtubules making up the meiotic spindle. When cold treated ova are subsequently incubated at 37 degrees C a nucleus is formed which moves central where it may participate in the cleavage of the egg. Formation of a second polar body and release of the contents of the cortical granules as reported for inseminated eggs was not found to be a part of activation of the egg by cold treatment. Approximately 95% of the ova cultured at 10 degrees C for 24 hours followed by 37 degrees C for 12 hours were activated, i.e., they possessed a nucleus or they had cleaved. Many of the activated eggs cultured for short periods at 37 degrees C were structurally similar to fertilized ova, with further incubation fragmented eggs and abnormal multicellular stages predominated.

Animals↗
PubMed1975

Development of parthenogenetic membranes in double-yolked and injected chicken eggs.

Development of parthenogenetic eggs is expressed in a Dark Cornish stock by either membrane or embryo formation. Double-yolked eggs have membranes developing in zero, one, or two yolks. The incidence of double-yolked eggs with two membranes was higher than expected when compared with the incidence of single-yolked eggs from the same hens. Membrane formation was increased over that of the controls by injecting saline, Ringer's solution, or ground crude membranes. Yolk and membranes filtered through a 3 mu filter or autoclaved did not increase membrane formation over that of the controls. Fertile membranes behaved like parthenogenetic membranes.

Animals↗
PubMed1975

Dietary tocopherol and sexual reproduction in the rotifers Brachionus calyciflorus and Asplanchna sieboldi.

Brachionus calyciflorus contained no detectable tocopherol (vitamin E) when cultured for long periods on the yeast Rhodotorula glutinis. Using a spectrofluorometric assay and the Asplanchna body-wall-outgrowth response bioassay the limits of detection were 6.4 ng and 3.78 pg alpha-tocopherol per g dry weight Brachionus, respectively. These tocopherol-free Brachionus reproduced normally both parthenogenetically and sexually, producing active and potent males and fertilized resting eggs which developed into viable young rotifers. The apparent lack of a tocopherol requirement for male fertility in B. calyciflorus probably also applies to Asplanchna sieboldi and A. brightwell -- rotifers whose male-producing (mictic) females are induced by dietary tocopherol and whose males therefore are never tocopherol-deficient. The adaptive significance of the tocopherol requirement for the initiation of sexual reproduction in Asplanchna sieboldi--formerly hypothesized to be the result of a tocopherol requirement for male fertility--is now thought to be related to the role of tocopherol in controlling female polymorphism in this species.

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PubMed1976

The fine structural development of preimplantation mouse parthenotes.

The normality of the preimplantation development of 2-cell to expanded blastocyst stage mouse parthenotes, derived from oocytes activated in vivo, or in vitro, has been assessed at the fine structural level. Major changes in the organization of the cellular organelles, i.e., nucleoli, mitochondria, ribosomes, RER and junctional complexes, follow the same developmental sequences observed in embryos obtained from normally fertilized oocytes. One difference between parthenotes and controls is the scarcity of crystalloid bodies in parthenotes at the blastocyst stage. Because the embryos examined in this study had been cultured in vitro, in a simple salt and albumin medium in the absence of maternal influences, our observations on parthenotes indicate that developmental, preimplantation changes in the subcellular organization of the embryo do not require the continued presence of "maternal" factors or the participation of the paternal genome.

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PubMed1976

Natural hybridization between parthenogenetic and bisexual lizards: detection of uniparental source of skin grafting.

Skin graft evidence is used to directly identify the unisexual parent of natural hybrids produced between the bisexual species Cnemidophorus inornatus and the unisexual Cnemidophorus neomexicanus. Reciprocal grafts transplanted among there suspected hybrids between Cnemidophorus inornatus and Cnemidophorus neomexicanus are rejected as well as grafts from the hybrids to C. neomexicanus, indicating that the hybrids are each genetically different from each other and that C. neomexicanus has the ability to reject foreign grafts. Allografts among C. neomexicanus and xenografts from C. neomexicanus to the hybrids are not rejected, indicating that C. neomexicanus is genetically homogeneous and that the hybrids possess genomes genetically identical to C. neomexicanus. Electrophoretic analysis of the hybrids and their probable parents supports the evidence obtained from skin grafting that C. neomexicanus is one of the parents, and suggests that C. inornatus, rather than C. tigris, is the bisexual parent. Chromosome spreads obtained from the hybrids reveal a triploid number of 69, a number consistent with their presumed origin from unreduced diploid ova (2N = 46) from C. neomexicanus and haploid serum (N = 23) from C. inornatus. Preliminary evidence is presented of the first hybrids known between Cnemidophorus inornatus and Cnemidophorus uniparens. Histological examination of the tests suggests that these hybrids are sterile. Included is a list summarizing all known hybrids between bisexual and unisexual species of the genus Cnemidophorus.

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PubMed1982

Gynogenesis caused by ultraviolet irradiation of salmonid sperm.

Gynogenetic rainbow trout lines can be produced easily with the simple UV sperm irradiation technique detailed in this study. The dose effect on embryonic survival rate is called a pseudo "Hertwig effect" because of major differences with results of gamma irradiation: Some mixing of various karyotypes (from diploid to haploid number) were obtained with mean doses, probably because of the weak penetrating power of the ultraviolet rays. Irradiations lasting 4 minutes of more are required to produce homogeneous haploid progeny; heat shock applied to such fertilized eggs results in diploid fry of the maternal phenotype.

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