Cyclin A associates with the fusome during germline cyst formation in the Drosophila ovary

Regulated changes in the cell cycle underlie many aspects of growth and dif ferentiation. Prior to meiosis, germ cell cycles in many organisms become a ccelerated, synchronized, and modified to lack cytokinesis. These changes c ause cysts of interconnected germ cells to form that typically contain 2 " cells. In Drosophila, developing germ cells during this period contain a di stinctive organelle, the fusome, that is required for normal cyst formation . We find that the cell cycle regulator Cyclin A transiently associates wit h the fusome during the cystocyte cell cycles, suggesting that fusome-assoc iated Cyclin A drives the interconnected cells within each cyst synchronous ly into mitosis. In the presence of a normal fusome, overexpression of Cycl in A forces cysts through an extra round of cell division to produce cysts with 32 germline cells. Female sterile mutations in UbcD1, encoding an E2 u biquitin-conjugating enzyme, have a similar effect. Our observations sugges t that programmed changes in the expression and cytoplasmic localization of key cell cycle regulatory proteins control germline cyst production. (C) 2 000 Academic Press.