Fig. 1

Schematic drawing of the analysed stages of oogenesis. The somatic follicle-cell epithelium (FCE) that surrounds the 15 nurse cells (NC, anterior) and the oocyte (Oo, posterior) is highlighted in blue. During vitellogenic stages 8–12 (S8–12), the FCE undergoes morphological changes and differentiates into several distinct follicle-cell (FC) populations: squamous FC, surrounding the NC, border cells, centripetally migrating FC (cFC), mainbody FC (mbFC) and posterior FC (pFC), surrounding the Oo. From S10b onward, the dorsal FCE (defined by the position of the Oo nucleus) becomes thicker than the ventral FCE. Now, the Oo constitutes almost one half of the follicle’s volume