It is concluded that flies deficient in S6k exhibit an extreme delay in development and a severe reduction in body size. These flies have smaller cells rather than fewer cells. The effect is cell-autonomous, displayed throughout larval development, and distinct from that of ribosomal protein mutants. In Drosophila, the process of oogenesis is initiated with the asymmetric division of a germline stem cell. This division results in the self-renewal of the stem cell and the generation of a daughter cell that undergoes four successive mitotic divisions to produce a germline cyst of 16 cells.
Clonal analysis indicates that shutdown functions autonomously in the germline.
Consistent with its function, the RNA and protein are strongly expressed in the germline stem cells and in 16-cell cysts. The RNA is also present in the germ cells throughout embryogenesis. Like immunophilins, Shutdown contains an FK506-binding protein domain and a tetratricopeptide repeat. In the peripheral nervous system, tap is expressed exclusively in one of the neurons that innervate each larval chemosensory organ, possibly controlling the specific properties of that neuron.