Figure 1.

C. capitatais a useful species for comparison with D. melanogaster. Posterior is to the right; scale bar is 50 μm. (A) Stages of oogenesis were identifiable in C. capitata using criteria described in D. melanogaster. At stage 8 of oogenesis, the oocyte nucleus (on) is localized asymmetrically in the oocyte (oo), which at this stage is of roughly equal size to the nurse cells (nc). At stage 9 the follicle cells (fc) start their migration to posterior: anterior follicle cells stretching over the nurse cells, and posterior follicle cells forming a layer of columnar cells over the oocyte. At the same time, a cluster of border cells (bc) migrates between the nurse cells to the anterior end of the oocyte. Late stage 10 sees the columnar follicle cells migrating centripetally (cmfc), in between nurse cells and oocyte. Stage 11 shows a difference between D. melanogaster and C. capitata egg chambers in the relative thickness of dorsal and ventral follicle cell layers. (B) Eggs of D. melanogaster and C. capitata, the former bearing obvious structures: dorsal appendages (da), operculum (op), and an outward micropyle (mp). (C) Fas-II staining of stage 8 C. capitata egg chamber, identifying the polar cells, part of the border cell cluster. (D) In situ hybridization with a probe against slbo confirms the identity of the border cell cluster in the C. capitata egg chamber. (E) A small pore is visible in the newly formed eggshell of C. capitata, likely a structure homologous to the micropyle (mp).