Fig. 1. Drosophila ovarian cyst and germarium. (A) The 16 cells of an ovarian cyst are connected in an invariant pattern via actin-rich ring canals (rc, ring canal). The single oocyte (black) always develops from one of the two cells with four ring canals. The other 15 cells in the cyst, including the other cell with four ring canals (asterisk), enter the endocycle and develop as highly polyploid nurse cells. (B) A germarium. The four mitotic cyst divisions take place in region 1 of the germarium. In region 2a, all 16 cells enter premeiotic S phase. In region 2b, a meiotic gradient forms with the two cells with four canals progressing to pachytene. By the time cysts enter region 3 of the germarium (stage 1) only the cell that is destined to become the oocyte (black) remains in the meiotic cycle. By contrast, the 15 mitotic sisters of the oocyte enter the S phase of the first endocycle on their way to becoming highly polyploid nurse cells. NC, nurse cell.

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