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At least 19 recordsLinked to original sources
PubMed1979

Detecting mutations expressed during early development of cultured mammalian embryos.

Mammalian embryo culture systems can be used to study dominant lethal, recessive lethal, and visible mutations that are expressed between fertilization and early stages of organogenesis. The incidence of dominant lethal mutations has been determined for cultured mouse embryos by morphological observations during pre-implantation and early post-implantation growth in vitro, and the mechanisms of dominant lethal mutations have been studied cytogenetically. Recessive lethal mutations have been studied with cultured embryos, although they can be initially detected only with appropriate breeding protocols. Visible mutations that are due to deletions or single-site base alterations in the DNA can be detected in embryos by isoelectric focusing and gel-electrophoresis techniques.--The principal advantage of cultured embryos for detecting mutations and studying the mechanism of action of particular mutagens is that embryos are accessible for analysis before death with a minimum of indirect maternal effects. The primary disadvantages, which may be alleviated with improved culture conditions, are that only a limited amount of tissue is available, attrition and retardation occur, and offspring are not recovered for further breeding studies.

Animals↗
PubMed2006

DNA repair in mammalian embryos.

Mammalian cells have developed complex mechanisms to identify DNA damage and activate the required response to maintain genome integrity. Those mechanisms include DNA damage detection, DNA repair, cell cycle arrest and apoptosis which operate together to protect the conceptus from DNA damage originating either in parental gametes or in the embryo's somatic cells. DNA repair in the newly fertilized preimplantation embryo is believed to rely entirely on the oocyte's machinery (mRNAs and proteins deposited and stored prior to ovulation). DNA repair genes have been shown to be expressed in the early stages of mammalian development. The survival of the embryo necessitates that the oocyte be sufficiently equipped with maternal stored products and that embryonic gene expression commences at the correct time. A Medline based literature search was performed using the keywords 'DNA repair' and 'embryo development' or 'gametogenesis' (publication dates between 1995 and 2006). Mammalian studies which investigated gene expression were selected. Further articles were acquired from the citations in the articles obtained from the preliminary Medline search. This paper reviews mammalian DNA repair from gametogenesis to preimplantation embryos to late gestational stages.

Animals↗
PubMed1997

Nuclear translocation and carboxyl-terminal domain phosphorylation of RNA polymerase II delineate the two phases of zygotic gene activation in mammalian embryos.

In mammalian embryos, zygotic gene transcription initiates after a limited number of cell divisions through a two-step process termed the zygotic gene activation (ZGA). Here we report that RNA polymerase II undergoes major changes in mouse and rabbit preimplantation embryos during the ZGA. In transcriptionally inactive unfertilized oocytes, the RNA polymerase II largest subunit is predominantly hyperphosphorylated on its carboxy-terminal domain (CTD). The CTD is markedly dephosphorylated several hours after fertilization, before the onset of a period characterized by a weak transcriptional activity. The largest subunit of RNA polymerase II then lacks immunological and drug-sensitivity characteristics related to its phosphorylation by the TFIIH-associated kinase and gradually translocates into the nuclei independently of DNA replication and mitosis. A phosphorylation pattern of the largest subunit, close to that observed in somatic cells, is established in both mouse and rabbit embryos at the stage when transcription becomes a requirement for further development (respectively at the 2- and 8/16-cell stage). As these events occurred in the presence of actinomycin D, the nuclear translocation of RNA polymerase II and the phosphorylation of the CTD might be major determinants of ZGA.

Animals↗
PubMed1989

Using the amniotic cavity of the developing chick embryo for the in vivo culture of early-stage mammalian embryos.

The fertile chicken egg may provide an effective, inexpensive method for promoting the development of early-stage embryos from other species. Presently, the loss of viability associated with the in vitro culture of mammalian embryos is hindering the use of in vitro fertilization with farm animals. Consequently, alternative in vitro laboratory methods are needed for the culture of mammalian embryos. A new method has been developed that involves the culture of mammalian embryos in the amniotic cavity of a developing chick embryo. Chick embryos were placed into shell-less incubation (37 C) at the 72-h developmental stage. After 24 h of shell-less incubation, agarose-embedded mammalian embryos were injected into the amniotic cavity of the chick embryo. The mammalian embryos were first placed into a drop of liquid agarose. One to four embryos were then aspirated into a beveled injection pipette and cooled, allowing the agarose to harden. Following penetration of the amnion with the beveled pipette, the agarose cylinder containing the embryos was expelled into the amniotic cavity. The shell-less culture system was then returned to incubation at 37 C for an additional 72 to 96 h. Following incubation, the amniotic cavity containing both chick and mammalian embryos was isolated and the agarose-embedded mammalian embryos were harvested. Significantly more embryos developed in the chick embryo amnion than in the control medium alone. Results obtained using this method on laboratory animals (mice) and on domestic mammals (goats and cattle) indicate that the chick-embryo amnion can support the development of early-stage, mammalian embryos to the blastocyst stage of development.(ABSTRACT TRUNCATED AT 250 WORDS)

Amnion↗
PubMed1985

Manipulation of the mammalian embryo.

Technological advances in manipulation of mammalian embryos outside the maternal environment have resulted in opportunities for study of preimplantation embryo development, identification of developmental phenomena that are unique to mammals, and further improvement of technology. Mammalian embryos may be cultured in vitro at 37 C for up to several days or they may be stored at -196 C indefinitely. The mammalian embryo possesses the unique capacity to regulate its development and differentiate into a normal individual after being stimulated to incorporate foreign cells or after a portion of its cells are removed. This regulatory ability has proven useful in research dealing with the production of chimeras. It allows genetic copies of an embryo to be produced by dissociation of an early cleavage-stage embryo into its component blastomeres or by bisection of a morula. Production of large sets of identical animals may be possible in the future by serial transplantation of nuclei from one embryo into enucleated ova. Progress has been made in producing unique genetic combinations by manipulation of the pronuclei of fertilized ova. It is also possible in some cases to identify the sex of a living cleavage-stage embryo. Some of these manipulations have been carried out primarily in laboratory mice, but as animal scientists identify beneficial uses in farm animals, these procedures are being extended to embryos of the large domestic species.

Animal Husbandry↗
PubMed1986

Cryobiology: preservation of mammalian embryos.

The preservation of mammalian embryos has become a routine procedure. Thousands of live offspring have been produced from frozen-thawed embryos transferred into recipient foster mothers. Species whose embryos have been successfully preserved include mouse, rat, rabbit, sheep, goat, cattle, horse, antelope, baboon, and human. During the past few years, novel procedures have been introduced that permit embryos to be frozen and thawed rapidly, and to be transferred into recipients under field conditions almost immediately upon thawing. Thus, the transfer of frozen-thawed embryos of domestic animals is becoming almost as efficient as is artificial insemination using frozen-thawed semen. Because of both the inherent fundamental interest and the practical applications of embryo freezing, a substantial understanding of the mechanisms responsible for freezing damage of embryos has been achieved. To survive freezing, embryos must be exposed to protective compounds; to function after thawing, embryos must be washed free of these compounds. Based on fundamental physiology, efficient methods to accomplish such washing have been developed. Furthermore, to survive freezing, embryos must be cooled under conditions in which intracellular ice does not form. This can be accomplished either by pretreating the embryo or by cooling it in such a way as to cause it to dehydrate during freezing. Maximum survival of embryos appears to be achieved when intracellular water does not crystallize during cooling or during warming. As a result of the growing efficiency of embryo preservation, this method is being applied to a variety of practical situations. For example, large banks of frozen embryos of laboratory animals are being established to preserve valuable research resources. The freezing of cattle embryos is being used with increasing frequency as an adjunct to commercial embryo transfer. Preservation of endangered species by embryo preservation is beginning. And finally, the preservation of human embryos is finding application in the field of in vitro fertilization.

Animals↗
PubMedDate not supplied

The influence of growth factors on the development of preimplantation mammalian embryos.

The development of the preimplantation mammalian embryo from a fertilized egg to a blastocyst capable of implanting in the uterus is a complex process. Cell division must be carefully programmed. The embryonic genome must be activated at the appropriate stage of development, and the pattern of gene expression must be carefully coordinated for the initiation of the correct program of differentiation. Cell fates must be chosen to establish specific cell types such as the inner cell mass and the trophectoderm, which give rise to the embryo proper and the placenta, respectively. This review summarizes recent findings concerning the influence of growth factors on the development of preimplantation mammalian embryos. Maternal factors secreted into the lumen of the female reproductive tract as well as substances synthesized by the developing embryo itself help to regulate this process. Studies of embryos in culture and investigations using homologous recombination to create embryos and animals null for specific genes have enabled the identification of several growth factors that appear essential for preimplantation mammalian embryo development. Some of the factors are required maternal factors; others are embryo-derived autocrine and paracrine factors. Studies using molecular biology are beginning to identify differences in the patterns of genes expressed by naturally derived embryos and those developing in culture. The knowledge gained from studies on growth factors, media, embryonic development, and gene expression should help improve culture conditions for embryos and will provide for safer outcomes from assisted reproductive procedures in human and animal clinics.

Animals↗
PubMedDate not supplied

Transport mechanisms in the preimplantation mammalian embryo.

Compaction is associated with major changes in the transport processes in preimplantation embryos. Before this time the processes are homocellular, in which all the component cells exchange materials across their cell membranes with a common environment. After compaction the outer trophoblast cells become organized into a simple, squamous epithelium which is capable of transcellular vectorial transport, that selectively controls the movement of materials into the embryo. Measurements of the intracellular concentrations and membrane permeabilities of Na+, K+ and Cl- in the mouse oocyte and two-cell embryo have demonstrated that they undergo significant changes during this period of development. The development of transcellular transport across the trophectoderm is fundamental in the regionalization of the embryo. These physiological mechanisms are involved in the formation of the blastocoele fluid, and may be dependent on the development of regionally located Na+, K+-ATPase on the juxtacoelic surfaces of the trophoblast cells.

Adenosine Triphosphatases↗
PubMed2004

BMP receptor IA is required in the mammalian embryo for endodermal morphogenesis and ectodermal patterning.

BMPRIA is a receptor for bone morphogenetic proteins with high affinity for BMP2 and BMP4. Mouse embryos lacking Bmpr1a fail to gastrulate, complicating studies on the requirements for BMP signaling in germ layer development. Recent work shows that BMP4 produced in extraembryonic tissues initiates gastrulation. Here we use a conditional allele of Bmpr1a to remove BMPRIA only in the epiblast, which gives rise to all embryonic tissues. Resulting embryos are mosaics composed primarily of cells homozygous null for Bmpr1a, interspersed with heterozygous cells. Although mesoderm and endoderm do not form in Bmpr1a null embryos, these tissues are present in the mosaics and are populated with mutant cells. Thus, BMPRIA signaling in the epiblast does not restrict cells to or from any of the germ layers. Cells lacking Bmpr1a also contribute to surface ectoderm; however, from the hindbrain forward, little surface ectoderm forms and the forebrain is enlarged and convoluted. Prechordal plate, early definitive endoderm, and anterior visceral endoderm appear to be expanded, likely due to defective morphogenesis. These data suggest that the enlarged forebrain is caused in part by increased exposure of the ectoderm to signaling sources that promote anterior neural fate. Our results reveal critical roles for BMP signaling in endodermal morphogenesis and ectodermal patterning.

Animals↗
PubMed2002

Hedgehog-mediated patterning of the mammalian embryo requires transporter-like function of dispatched.

The dispatched (disp) gene is required for long-range Hedgehog (Hh) signaling in Drosophila. Here, we demonstrate that one of two murine homologs, mDispA, can rescue disp function in Drosophila and is essential for all Hh patterning activities examined in the early mouse embryo. Embryonic fibroblasts lacking mDispA respond normally to exogenously provided Sonic hedgehog (Shh) signal, but are impaired in stimulation of other responding cells when expressing Shh. We have developed a biochemical assay that directly measures the activity of Disp proteins in release of soluble Hh proteins. This activity is disrupted by alteration of residues functionally conserved in Patched and in a related family of bacterial transmembrane transporters, thus suggesting similar mechanisms of action for all of these proteins.

Alleles↗
PubMed1990

A POU-domain transcription factor in early stem cells and germ cells of the mammalian embryo.

The murine oct-3 gene encodes a transcription factor containing a POU-specific domain and a homeodomain. In marked contrast to other homeodomain-encoding genes, oct-3 is expressed in the totipotent and pluripotent stem cells of the pregastrulation embryo and is down-regulated during differentiation to endoderm and mesoderm, suggesting that it has a role in early development. The oct-3 gene is also expressed in primordial germ cells and in the female germ line.

Amino Acid Sequence↗