Embryonic poly(A)-binding protein stimulates translation in germ cells

The function of poly(A)-binding protein 1 (PABP1) in poly(A)-mediated translation has been extensively characterized. Recently, Xenopus laevis oocytes and early embryos were shown to contain a novel poly(A)-binding protein, ePABP, which has not been described in other organisms. ePABP was identified as a protein that binds AU-rich sequences and prevents shortening of poly(A) tails. Here, we show that ePABP is also expressed in X. laevis testis, suggesting a more general role for ePABP in gametogenesis. We find that ePABP is conserved throughout vertebrates and that mouse and X. laevis cells have similar tissue-specific ePABP expression patterns. Furthermore, we directly assess the role of ePABP in translation. We show that ePABP is associated with polysomes and can activate the translation of reporter mRNAs in vivo. Despite its relative divergence from PABP1, we find that ePABP has similar functional domains and can bind to several PABP1 partners, suggesting that they may use similar mechanisms to activate translation. In addition, we find that PABP1 and ePABP can interact, suggesting that these proteins may be bound simultaneously to the same mRNA. Finally, we show that the activity of both PABP1 and ePABP increases during oocyte maturation, when many mRNAs undergo polyadenylation.