7 Translational Control of Developmental Decisions

Abstract

At fertilization, the calm of oogenesis ends and the egg abruptly begins a flurry of activity. Many crucial steps—decisions concerning when and where to divide, specification of cell fates, and establishment of body axes—rely on materials the egg contains at that moment. In many animals, the first few hours of life proceed with little or no transcription. As a result, developmental regulation at these early stages is dependent on maternal cytoplasm rather than the zygotic nucleus. The regulatory molecules accumulated during oogenesis might, in principle, be of any type, including RNA and protein. It is clear that mRNAs present in the egg before fertilization—so-called maternal mRNAs—play a particularly prominent role in early decisions. Viewed from this perspective, it is not surprising that oocytes and early embryos display an impressive array of posttranscriptional regulatory mechanisms, controlling mRNA stability, localization, and translation.

The mechanisms by which translation of specific maternal mRNAs is controlled, and how those controls contribute to proper development, are the main focus of this chapter. Translational regulation is vital throughout development, in somatic as well as germ cells. The predominant mode of tissue-specific regulation in adult tissues is transcriptional; yet several of the examples we discuss hint that the importance of translational control may be currently underestimated, perhaps dramatically so.

One conclusion emerges exceptionally clearly from studies of translational control during early development: The region between the termination codon and the poly(A) tail—the 3′ untranslated region, or 3′UTR—is a key repository for the...