Developmental protein required for cell fate determination in both the germline and seam cells of the developing epidermis. Specifically, involved in sex determination and may function in parallel or downstream of other sex determination factors, including tra-2 and fem-3, to promote oogenesis in its role in the regulation of the switch from spermatogenesis to oogenesis in the gonads. Also implicated in the mitosis to meiosis switch in distal tip cells. Expressed in the spermatheca. Expressed in seam cells throughout postembryonic development. Expressed in the developing gonad, distal tip cells and spermatheca from larval stage L3. High level of lethality with a significant reduction in seam cell number. RNAi-mediated knockdown results in defects linked to cell fate determination including impaired hypodermal differentiation, fewer seam cells, possibly due to a change in cell fate, a molting defect in 10% of animals and male tail abnormalities, including reduced sensory ray number. The germline exhibits a mog (masculinization of the germline) phenotype with increased sperm numbers and largely absent oocytes in the gonad. Defective mitosis to meiosis switching and general impaired morphology in distal tip cells with abnormal extending processes (cytonemes) that are thicker and extend further into the proximal gonad from early stages of development. Belongs to the TTC27 family.