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. 2023 Nov 24;226(1):iyad183. doi: 10.1093/genetics/iyad183

Fig. 6.

Fig. 6.

Patterning and morphogenesis. Representative stages showing progressive patterning and movements of follicle cells. All drawings are lateral cross sections, except the lower S10B example, which is a dorsolateral surface view. By S2, Notch signaling has defined 2 polar cells (dark green) at the anterior and posterior of the egg chamber. During S1–S5, the polar follicle cells secrete the JAK/STAT ligand Upd to pattern terminal regions. At the anterior (yellow), the gradient will specify border cells (light green), squamous stretch cells (yellow), and centripetal cells (orange) (see S8 and S9), while at the posterior, Gurken (Grk, EGF) signaling converts these cells to a posterior fate (purple). At S6, an unknown signal from posterior cells to the oocyte induces a microtubule rearrangement that moves the oocyte nucleus to the anterior. grk RNA and protein (crescent) move with the oocyte nucleus. Rotation of the egg chamber by migration of follicle cells on the ECM, which begins slowly at S1 but speeds up at S6, alters egg chamber shape from round to elongated, particularly during S6–S8. At S9, the border cells move between nurse cells toward the oocyte, carrying the polar cells, while the stretch cells flatten. At the transition from S10A to S10B, dorsal anterior follicle cells begin to express markers responding to Grk (EGF) and Dpp (BMP) signals (red, floor cells; blue, roof cells; orange, midline cells). At S10B, the centripetal and midline cells move inward. At S11, the dorsal appendage-forming cells wrap to make 2 tubes while the nurse cells dump their contents into the oocyte, and at S12–S13 the dorsal appendage-forming cells move out over the stretch cells, which envelope the degenerating nurse cells. Scanning electron microscope image of a laid egg (wild-type, Oregon R) reveals structures synthesized by the anterior cells (operculum, micropyle, collar), roof and floor cells (dorsal appendages), main body cells (majority of eggshell), and posterior cells (aeropyle). Image courtesy of Dr. Miriam Osterfield. All black bars = 50 µ.