Centromere clustering, pairing and cohesion in solo and WT germ cells.
(A) A schematic depiction of developmental stages of the germarium and early egg chambers of an ovariole , . Stages are not drawn to scale. Meiosis is initiated within the germarium, the most anterior section of each ovariole. The germarium is divided into 4 regions (1, 2a, 2b and 3, anterior-posterior). Region1 contains germline stem cells (anterior tip), cystoblasts (posterior daughters of stem cells) and mitotically proliferating 2-, 4- and 8- cell cysts. 16-cell cysts initiate meiosis in region 2a with up to 4 cells/cyst assembling SCs in zygotene while the remaining cells (pro-nurse cells) begin differentiating into nurse cells. Only two cells (the pro-oocytes) continue into meiosis and assemble full-length SC in early pachytene (still region 2a). Cysts continue moving posteriorally and by region 3, full-length SC is restricted to a single oocyte, which lies at the posterior end of the cyst. As cysts continue to grow and mature, they leave the germarium and enter the vitellarium where they are encapsulated by a single layer of somatic follicle cells to form egg chambers. The chromosomes in the oocyte begin to condense around stage 3 and SC begins to disassemble around stage 4–5. By about stage 7, SC proteins can no longer be detected on chromosome arms and the chromosomes are condensed into a compact structure called the karyosome. (B, C) Centromeres in WT and solo germ cell nuclei. Centromeres, SC and DNA were stained by anti-CID antibody (green), anti-C(3)G antibody (red) and DAPI (blue), respectively. solo: soloZ2-3534/Df(2L)A267. WT: sibling control. Scale bar: 5 µm. (B) 1–4 CID foci were present in WT pro-oocyte and oocyte nuclei in early (top panel) and late (bottom panel) pachytene. (C) In solo mutants, 5–8 nuclear CID foci were present in most early pachytene nuclei (top panel) and more than 8 CID foci were present in most late pachytene nuclei (bottom panel). (D, E) Percentages of nuclei with indicated numbers of CID foci in pro-oocytes from region 2a (D) and in oocytes from stage 5–7 egg chambers (E). N = number of nuclei scored.