Using transcriptome and phosphoproteome profiling to identify genes that regulate the egg-to-embryo transition in D. melanogaster. Caroline V. Sartain, Amber R. Krauchunas, Jun Cui, Vanessa L. Horner, Jeffrey A. Pleiss, Mariana F. Wolfner. Dept Molec Biol & Gen, Cornell Univ, Ithaca, NY.

   After oogenesis, Drosophila oocytes transition from arrest to the ability to initiate embryogenesis if fertilized. This egg activation involves resumption and completion of meiosis, translation of proteins from stored maternal mRNAs, degradation of other maternal mRNAs, and changes to the vitelline envelope. Genetic screens identified maternal-effect genes needed for egg activation or to initiate embryogenesis, but more genes are certainly involved. Since there is little or no transcription during this transition, egg activation must be regulated by post-transcriptional and post-translational modification of pre-existing maternal mRNAs and proteins. Thus, we used transcriptomic and proteomic approaches to identify new molecules needed for egg activation: (1)We identified mRNAs that become translationally-competent. Wed shown that the GLD2 cytoplasmic poly-A polymerase WISPY is essential for egg activation. GLD2s extend poly-A tails of stored mRNAs to allow recruitment of cellular translation machinery. Using microarrays we identified RNAs whose poly-A tails depend on WISPY; these are likely to be newly-translated upon egg activation. We find that WISPY regulates poly-A tail length of RNAs from thousands of genes during egg activation. WISPY-regulated RNAs encode proteins in GO classes with likely roles in egg activation and early embryogenesis. (2)We examined phospho-modification of the proteome during egg activation. Changing phosphorylation state can cause an array of regulatory effects, and kinase and phosphatase activities are modulated during egg activation. Thus, we hypothesized that simultaneously changes in phosphorylation states of many proteins could underlie the cellular changes from oocyte to activated egg. Using 2-D gels and IMAC we identified 311 proteins that are phospho-modulated during egg activation; 83%; are conserved to mammals. RNAi knockdown of these molecules is identifying new genes needed for the oocyte-to-embryo transition.