Bioscientifica Proceedings

In mammals, growing oocytes have characteristically high levels of RNA synthesis. After the initiation of meiosis, that is germinal vesicle breakdown, this RNA synthesis ceases. Although there is limited evidence for RNA synthesis by the zygote, significant amounts of RNA synthesis do not occur until a species-specific cell stage. In pigs, significant amounts of mRNA synthesis cannot be detected before the four-cell stage. There appear to be three qualitatively different ...

Fertilization of the egg, or oocyte, initiates the entire developmental process, but while the mechanism by which the spermatozoa triggers the oocyte to resume meiosis has been studied extensively, conclusions about this process are still elusive. Some workers have suggested that a molecule on the surface of the spermatozoon may interact with a receptor on the plasma membrane of the oocyte, thereby triggering the oocyte to resume meiosis. Other workers have focused on a ...

Summary. Nuclear transfer for the study of differentiation in amphibians has been used since the 1950s, but not until recently have the same procedures been applied successfully to some mammals. Nuclear transfer, as developed for the amphibian, is successful in sheep, cattle, rabbit, and pig, but not mouse embryos. This fact is discussed in relation to the species-specific timing of the activation of the zygotic genome. Nuclear transfer to an oocyte presu...