| Establishment of an embryo capable of development to term involves precisely regulated nuclear and cytoplasmic events. Interspecific hybrids provide unique embryo models with morphological, biochemical and temporal markers of development which enable investigation of these interactions. This study explores the feasibility of producing and utilizing interspecific hybrid embryos of cattle, sheep and goats as models to examine the respective roles of the maternal and paternal contributions to the embryo and the interactions of the nucleus and cytoplasm.; Interspecific hybrid embryos were created under in vivo and/or in vitro conditions. Ram spermatozoa penetrated intact bovine oocytes; under in vitro conditions, but the resulting embryos arrested at the 4-8-cell stage. This developmental arrest was exhibited even when bovine x ovine hybrid zygotes were transferred to sheep oviducts for in vivo culture, illustrating that the arrest was not an effect of the in vitro culture. Construction of nuclear transfer hybrids between ovine karyoplasts and bovine cytoplasts resulted in the same pattern of developmental arrest as in the bovine x ovine hybrid embryos. This indicates that the developmental arrest exhibited by the hybrid embryos is not an intragenomic incompatibility between the bovine and ovine components of the nucleus but an incompatibility between nucleus and cytoplasm.; Autoradiographic detection of {dollar}sp3{dollar}H-uridine incorporation provided evidence for low levels of genomic activity at the 2-cell stage of all types of embryos. In all but bovine x ovine hybrids, transcriptional activity increased through the 4-cell stage and culminated in a burst of transcriptional activity by the late 8-cell stage. Bovine x ovine hybrid embryos exhibited generous transcriptional activity at the 4-cell stage but no burst of activity as the embryos arrested at the 4-8-cell stage.; Ovine x caprine hybrid embryos develop to the blastocyst stage, hatch in vitro and establish pregnancies when transferred to sheep or goats. The pregnancies however, have retarded fetal development, incompletely formed placentomes and ultimately fail during the second month of gestation.; In summary, most interspecific hybrid embryos can be produced readily under in vivo or in vitro conditions. This study confirms the potential of producing and utilizing interspecific hybrid embryos from domestic ruminants as models to study embryonic development. |
