A Novel Interaction Between Stem Cell Factors FMRP and Zfrp8. William Tan, Tatyana Naryshkina, Neha Changela, Curtis Schauder, Ruth Steward. Waksman Institute, Rutgers University, Piscataway, NJ.

   Fragile-X Mental Retardation Protein (dFMRP) is a ubiquitously expressed protein required for a number of developmental processes, including neural differentiation and stem cell maintenance. Drosophila FMRP is required for the proper maintenance of both neural and ovary germline stem cells. FMRP functions by selectively binding mRNA targets co-transcriptionally in the nucleus, then subsequently inhibiting the initiation step of translation at the ribosome. We have identified stem cell factor Zfrp8 as a component of the dFMRP complex. Zfrp8 is an essential stem cell protein also required in the nucleus. As in the case of dFMRP, reduction of Zfrp8 results in loss of stem cells. We have also determined a direct physical interaction between Zfrp8 and Drosophila NUFIP (Nuclear FMRP Interacting-Protein), another RNA-binding protein. These interactions bring to light a novel mechanism for FMRP regulation.