The Function of the FERM Protein Okapi in Regulating the Number of Follicle Stem Cells and Interfollicular Stalk Cells in Drosophila Ovaries

The FERM domain protein Okapi (Oka) is important for normal Drosophila oogenesis. I found that Oka is required in the follicle stem cell (FSC) lineage to prevent an overgrowth of FSCs. To determine how Oka regulates FSCs, I analyzed interactions between oka and Hippo pathway genes, as they have similar mutant phenotypes. Hippo is known to limit nuclear translocation and activity of Yorkie, thereby suppressing cell proliferation. I found a higher proportion of FSCs with nuclear Yorkie in oka mutants than in wild-type. Reduction of Yorkie or Hippo overexpression partially rescued the FSC overgrowth in oka mutant ovaries. Interestingly, I found that oka mutant FSCs were lost when forced to compete with wild-type FSCs, whereas hippo mutant FSCs are known to be hyper-competitive. My findings indicate that Oka regulates the number of FSCs through the Hippo pathway and is required to make FSCs competitive through an unknown mechanism.M.Sc