TEMPORAL PATTERNS OF EMBRYONIC GENE-EXPRESSION AND THEIR DEPENDENCE ON OOGENETIC FACTORS

Successful development of a fertilized egg beyond early cleavage divis ions requires the de novo initiation and subsequent regulation of embr yonic transcription. The egg provides the specialized environment with in which the newly formed zygotic nucleus initiates its developmental program and as a result plays an obligatory role in its regulation. Al though the precise timing of the onset of embryonic transcription in m ammals varies during early cleavage divisions, several common elements exist. In the present essay we review the current literature on the t iming and control of embryonic gene expression in mammals, and discuss recent findings from our laboratory on gene expression patterns in bo vine embryos and their relation to other species, and zygotic gene act ivation (ZGA). Lastly, we discuss the putative role of maternally inhe rited factors in conferring developmental competence to the blastocyst stage, and a method to identify such factors present in oocytes as mR NA. (C) 1998 by Elsevier Science Inc.