Two Cell-free Systems Constructed from Xenopus laevis Oocytes: Generalized Genetic Recombination; DNA Supercoiling

An old hypothesis in the field of developmental biology (Boveri 1902) states that in early development, genetically equivalent nuclei are programmed by the surrounding cytoplasm and that this nucleocytoplasmic interaction is responsible for the differences among the cells of an early embryo. The investigation of problems of this kind has, up to now, involved the transplantation of nuclei or of cytoplasm into eggs and some of these studies have demonstrated the existence of cytoplasmic determinants (Illmensee and Mahowald 1974). What is the nature of the determinants? How do they act? How are they localized? It seems that in order to arrive at a more thorough understanding of the relevant features of the egg cytoplasm, the problems of development must be approached by in vitro experimentation with cell-free systems. So much has yet to be learned about the machinery of the egg cytoplasm, that it seems crucial to focus current investigations...