Recycling of uridylated mRNAs in starfish embryos

Abstract

In eukaryotes, mRNAs with long poly(A) tails are translationally active, whereas deadenylation of the tails decreases translation and uridylation of the short poly(A) tails causes the mRNA to be degraded. In this study, we confirmed that maternal cyclin B mRNAs with long poly(A) tails in blastula embryos of invertebrate starfish were deadenylated and uridylated, followed by decay. In starfish oocytes, however, cyclin B mRNAs with uridylated short poly(A) tails are stable. They are polyadenylated and translationally active immediately following hormonal stimulation for resumption of meiosis. Similarly, maternal ribosomal protein mRNAs, Rps29 and Rpl27a, which become uridylated following deadenylation upon hormonal stimulation, remain stable even after fertilisation and early development. At the morula stage, the uridylated maternal ribosomal protein mRNAs are modified to yield non-canonical poly (A) tails rich in U and G residues in the 5 region and in A residues at the 3 end, rendering them translationally active. These results indicate that the fates of uridylated mRNAs in starfish are decay and/or recycling.