Fig. 5. PVF/PVR signals direct cell migration during Drosophila development. (A) Hemocyte migration. Hemocytes (red) originate as bilateral clusters in the anterior region of Drosophila embryos. These cells migrate anteriorly, posteriorly and ventrally to populate the wild-type embryo (red arrows indicate migration routes). PVF ligands are expressed along the embryonic hemocyte migration routes and guide or enable hemocyte migration: in Pvr mutant or Pvf1, 2, 3 knockdown embryos, hemocytes cluster in the head region and fail to enter the caudal region of the embryo. (B) Border cell cluster migration in response to PVF1. In the left-most panel, a stage 9 Drosophila egg chamber expressing lacZ in border cells is stained with anti-ß-galactosidase (green; border cells) and phalloidin (red; actin), and shows a long cellular extension (LCE; white arrow), which protrudes from one cell of the border cell cluster toward the oocyte. PVF1 is expressed by oocytes in Drosophila egg chambers, and PVR is expressed by all follicle cells, including the border cell cluster (red, green). In response to a graded PVF1 signal (blue), one border cell of the cluster protrudes a long cellular extension (LCE, green) toward the source of PVF1. This LCE guides the migration of the border cell cluster from the anterior cortex of the egg chamber to its final posterior location next to the oocyte. The panel on the left is copied with permission from Fulga and Rørth (Fulga and Rørth, 2002). Scale bar: 20 µm.

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