👤 Emre Seli

Oocyte maturation and early embryonic development require the cytoplasmic polyadenylation and concomitant translational activation of stored maternal mRNAs. ePAB [embryonic poly(A)-binding protein, also known as ePABP and PABPc1-like] is a multifunctional post-transcriptional regulator that binds to poly(A) tails. In the present study we find that ePAB is a dynamically modified phosphoprotein in Xenopus laevis oocytes and show by mutation that phosphorylation at a four residue cluster is required for oocyte maturation. We further demonstrate that these phosphorylations are critical for cytoplasmic polyadenylation, but not for ePAB's inherent ability to promote translation. Our results provide the first insight into the role of post-translational modifications in regulating PABP protein activity in vivo. Show less

Gene expression during oocyte maturation, fertilization, and early embryo development until zygotic gene activation is regulated mainly by translational activation of maternally derived mRNAs. This process requires the presence of a poly(A)-binding protein. However, the cytoplasmic somatic cell poly(A)-binding protein (PABP1) is not expressed until later in embryogenesis. We recently identified an embryonic poly(A)-binding protein (ePAB) in Xenopus. ePAB is the predominant cytoplasmic PABP in Xenopus oocytes and early embryos and prevents deadenylation of mRNAs, suggesting its importance in the regulation of gene expression during early Xenopus development. Here we report the identification of the mouse ortholog of Xenopus ePAB. The mouse ePAB gene on chromosome 2 contains 14 exons that specify an alternatively spliced mRNA encoding a protein of 608 or 561 aa with approximately 65% identity to Xenopus ePAB. Mouse ePAB mRNA is expressed in ovaries and testis but not in somatic tissues. In situ hybridization localizes ePAB RNA to oocytes and confirms its absence from surrounding somatic cells in the mouse ovary. During early development, mouse ePAB is expressed in prophase I and metaphase II oocytes and one-cell and two-cell embryos and then becomes undetectable in four-or-more-cell embryos. In contrast, PABP1 mRNA expression is minimal in oocytes and early embryos until the eight-cell stage when it increases, becoming predominant at the blastocyst stage. The expression of mouse ePAB before zygotic gene activation argues for its importance in translational activation of maternally derived mRNAs during mammalian oocyte and early preimplantation embryo development. Show less