Figure 1.—

Schematic of the onset of Drosophila female meiosis. The germarium is the most anterior structure of the Drosophila ovariole, where germ-line stem cells produce cystoblasts by asymmetric division. Germaria are divided into three regions. In region 1, cystoblast formation is followed by four rounds of mitosis, which give rise to cysts of 16 interconnected cells. In region 2, several cells per cyst initiate the assembly of synaptic chromosomes and form DSBs through the activity of the Drosophila SPO11 homologs mei-W68 and mei-P22. In region 3A, cysts become surrounded by follicle cells (not shown) and reorient so that each oocyte is placed at the posterior pole of each cluster where it remains for the rest of oogenesis. At stage 2, meiotic restriction to the oocyte (oo) is completed. The other “synaptic” cystocytes regress from meiosis and become nurse cells (nc). As the oocyte leaves pachytene, the meiotic chromatin releases the synaptonemal complex components and condenses into a karyosome (blue doughnut). In mid-oogenesis, the oocyte nucleus moves anteriorly. Tightly associated with it, Grk will be secreted to the adjacent follicle cells (gray grid), which will acquire a dorsal fate and later synthesize the dorsal appendages of the chorion (not shown). Persistent DSB in spn-A and okr mutants activate Mei-41, which causes a decrease in Grk production and consequent ventralization of the eggshell. The link between this activation and delays in meiotic progression is unclear (blue question mark).