149. TRANSLATIONAL CONTROL IN FOLLICULOGENESIS AND OOCYTE DEVELOPMENT: A ROLE FOR RNA-BINDING PROTEIN MUSASHI-1

Abstract

Control of the maternal mRNA pool during oocyte maturation is crucial to the correct temporal and spatial expression of proteins, particularly during oocyte transcriptional quiescence. We have identified Musashi-1 as being present within the oocyte/ovary, where this RNA-binding protein is believed to act as a translational repressor of target mRNAs. Recent studies in mammalian neural and intestinal systems have identified a number of cell cycle regulators as potential targets of Msi-1. Using Msi-1 protein-RNA immunoprecipitation, we have also identified musashi-2 (msi-2) and c-mos as putative targets in the mouse oocyte. To further study these targets, a transgenic mouse was produced to overexpress Msi-1 exclusively in the oocyte. QPCR analysis, performed on intact ovaries of wild type (WT) and Tg mice, confirmed a 1.5-fold increase in msi-1 expression in tgMsi-1/+ ovaries in excess of WT ovary expression. QPCR analysis of Msi-1 target expression, performed on intact WT and Tg ovaries, in conjunction with transcript obtained from the Msi-1 protein-RNA immunoprecipitation, revealed an overall increase in expression in the tgMsi-1/+ and Msi-1 IP samples, respectively, of p21WAF-1 (~2.5-fold; undetected), cdkn2a (~2-fold; undetected), notch1 (~3-fold;undetected), c-mos (no difference; ~41-fold) and msi-2 (~7-fold; ~10-fold). Immunohistochemical analysis of Msi-2 protein expression in transgenic juvenile mouse ovaries,demonstrated a decrease in expression of Msi-2 in tgMsi-1/+ ovaries, when compared to WT ovary expression, suggesting that Msi-2 mRNA is translationally repressed by Msi-1. Therefore, preliminary analysis suggests that Msi-1 may play a role inregulating transcripts of genes necessary for processes characteristic of meiotic progression and oocyte development.