Regulation and Function of Maternal Gene Products During the Maternal-to-Zygotic Transition in Drosophila.

Drosophila late-stage oocytes and early embryos are transcriptionally silent. Thus, control of gene expression during these developmental periods is posttranscriptional and posttranslational. Global changes in the transcriptome and proteome occur during oocyte maturation, after egg activation and fertilization, and upon zygotic genome activation. We review the scale, content, and dynamics of these global changes; the factors that regulate these changes; and the mechanisms by which they are accomplished. We highlight the intimate relationship between the clearance of maternal gene products and the activation of the embryo's own genome, and discuss the fact that each of these complementary components of the maternal-to-zygotic transition can be subdivided into several phases that serve different biological roles and are regulated by distinct factors.