Fig. 3. Stretch cells are a substrate for DA-forming cells and exhibit morphogenetic behaviors. Confocal images of Canton-S egg chambers expressing UAS-GFP^S65T in the stretch cells and a nuclear ß-galactosidase in the anterior columnar cells. (A,A',C,E) Anti-GFP, (B,B',D,F) merge of anti-GFP (green) and anti-ß-gal (red) images. (A,B) The stretch cells cover the exterior of the nurse cells. The posterior-most stretch cells (asterisk in A) move inwards along with the centripetally migrating columnar cells. In the lower right of panels A and B, centripetal migration is commencing in a stage-10B egg chamber (white arrow in B). (A',B') Magnified views of the boxed areas in A,B show that the stretch-cell layer is thickest near the stretch-cell nuclei (blue triangle, A') and at the valleys between nurse cells (blue arrowhead, A'). (C,D) Stretch-cell staining is present around the shrinking nurse cells (NC). The DA-forming cells have formed a tube and are moving anteriorly on the stretch cells (green arrowhead, C). (E,F) A magnified view of an interface between the front of a DA-cell wedge and the stretch cells at stage 12. Note the thin cellular projections extending towards the DA cells (arrow). Scale bars: 25 µm.