Translational control during early development.

The regulation of gene expression during early development is controlled predominantly at the translational level. This becomes necessary due to transcriptional arrest during maturation of the oocyte and the rapid early cleavage divisions of the embryo. Consequently, early events involved in pattern formation, germ cell specification, cell fate, and cell division are programmed by maternal messenger ribonucleic acid (RNA). The majority of these transcripts are stored as masked ribonucleoproteins particles during oogenesis but undergo sequence-specific translational activation during oocyte maturation and embryogenesis. Translational regulation occurs in the male germ line and, though not a prominent feature, in the soma as well. Evidence suggests that the assembly of ribonucleoprotein (RNP) particles may be coupled to transcription. Specific translational regulatory sequences are found in the 5' and 3' untranslated regions of maternal mRNA, but the majority occur downstream of the coding region. Most of the known cis-acting sequences and associated proteins are implicated in translational repression. Antisense RNA also has been implicated in specific mRNA translational regulation. Although little is known about message-specific unmasking, in general, one exception is cytoplasmic polyadenylation-mediated translational activation. A widespread phenomenon, it occurs in both vertebrates and invertebrates.