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. Usually, the other ovarioles contain only one to three egg chambers and their numbers fail to increase as the females age. Those egg chambers with the correct number of germ cells may have arisen through the differentiation of prestem cells, i.e., germ cells that developed as cystoblasts without first being established as stem cells.