C6orf15 and cyst: Expression of the cdc25 phosphatase string (stg), required for the G2/M transition in mitotic cells (Alphey et al., 1992; Edgar and O’Farrell, 1990), and escargot (esg), a gene expressed in diploid proliferative cells (Fuse et al., 1994), marked CySCs in the cyst cell lineage and proliferating GSCs and spermatogonia in the germ line lineage (Figure 1E and F).