17 Dynamics of Poly(A) Addition and Removal during Development

Abstract

Nuclear polyadenylation of pre-mRNA generally occurs without regard to RNA sequence or cell type. Cytoplasmic polyadenylation of messenger RNA, on the other hand, is both mRNA sequence-specific and cell-type-specific. With few exceptions, the consequence of cytoplasmic polyadenylation, which occurs in the eggs and embryos of many species, is a highly ordered activation of translationally dormant mRNAs that is essential for normal development. Antithetically, the silencing of certain translating mRNAs is also under developmental control and, perhaps not surprisingly, is the result of message-specific deadenylation. This chapter reviews the current state of our knowledge of poly(A) addition and removal during development. For related aspects of polyadenylation and translational control, see Wickens et al. and Jacobson (both this volume).

To place cytoplasmic polyadenylation in context, it is worthwhile to consider its historical antecedent. In an interpretive review of late 19th and early 20th century embryology, Wilson (1925) noted that “the behavior of nuclei in eggs is determined by the cytoplasm in which they lie.” Although Wilson was speaking at that time specifically of the continuity of germ plasm, we now know that cytoplasmic components inherited by the egg at the time of fertilization program early development, probably in all metazoans. These components, for the most part mRNAs, are generally quiescent in oocytes, but they are translationally activated following the resumption of meiosis (oocyte maturation) or after fertilization. How these “masked” or “maternal” mRNAs are translationally regulated has been the subject of much speculation since they were first discovered in the 1960s. Although...