The polyadenylation of mRNAs is usually thought of as a process that occurs in the nucleus, and indeed this is the cellular compartment in which pre-mRNA processing and polyadenylation does occur. However, mRNA polyadenylation is not restricted to the nucleus. Indeed, one of the more fascinating and important mechanisms that control gene expression during oogenesis and early development, stages in some organisms (such as animals) when the nucleus is not “active”, is mRNA polyadenylation. In these cases, the process occurs in the cytoplasm.
During oocyte development, a large population of maternally-encoded mRNAs are synthesized and stored for “use” in particular stages of development. These maternal mRNAs typically possess short poly(A) tails (20-40 nts) and are not available for translation (being “masked” by a complex of RNA-binding proteins). During oocyte maturation or following fertilization, these masked mRNAs become polyadenylated and thus activated for translation. This activation is a regulated process that helps to coordinate the ballet of gene expression attendant with meiotic maturation and early development. As such, it touches on many tangential phenomena (such as movement of stored mRNAs within the cell).
What is of particular interest for this blog is the nature of the mechanism that mediates polyadenylation in the cytoplasm. As indicated in the following figure, this mechanism includes some familiar players as well as some equally-intriguing partners. Read the rest of this entry »