Figure 5.

Oocyte development: stages 1–10. In the premeiotic region 1 of the germarium, a germline stem cell (asterisk) divides to produce a cystoblast, which then undergoes four incomplete mitotic divisions to produce a 16-cell interconnected cyst. Synaptonemal complex (SC) components (orange) begin loading next to unpaired centromeres (blue) in two-cell cysts, and centromeres begin pairing in four-cell cysts and clustering in eight-cell cysts. Prophase I of meiosis begins in 16-cell cysts in region 2A with the initiation of the euchromatic SC in up to four nuclei, followed by double-strand break (DSB) formation (purple). DSB formation and repair are dynamic processes that occur throughout early and early/midprophase. DSBs marked by γ-H2AV are mostly absent by midprophase in region 3 (stage 1), at which time one nucleus has been chosen as the oocyte nucleus. The other cells in the cyst serve as nurse cells. Around stages 2–3, chromosomes are reorganized and condense to form the karyosome. Euchromatic SC begins to disassemble in midprophase around stage 5 and will be completely absent by stages 7–9 during the transition from mid to late prophase (mid/late prophase). Centromeres remain clustered and centromeric SC persists through at least stage 9. In late prophase, chromosomes briefly decondense in stage 10 oocytes and transcription is upregulated before chromosomes recondense in stage 11.