Fig. 8. Schematic representation of signals required for patterning the follicle. Cells are identified by the color of their nuclei, as in Fig. 1. (A) Germarium. In region IIb, the posterior polar cells contact the oocyte. In region III, the oocyte is at the posterior of the cyst, in contact with the polar cells. (B) Before stage 6, signal(s) from the polar cells (large red arrow) establish terminal fates in surrounding cells. In the anterior, they will become border, stretched or centripetal cells. In the posterior, they will become posterior after receiving the germline Grk signal from the oocyte at stage 6. (C) After stage 6, the posterior cells send an unknown signal to the oocyte (black arrows) to reorganize the cytoskeleton, which establishes the later localization of positional determinants, including mRNAs for bcd (light blue lines), nanos (violet lines) and gurken (brown lines). Grk signaling from the germline to central follicle cells establishes dorsal follicle fate. DPP signaling from the stretched cells (pink arrow) is required to establish centripetal cell fate.

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