Fig. 1. Yan is dynamically expressed in migrating border cells. (A) BCs are specified at stage 8 of oogenesis at the anterior pole of the ovarian follicle cell epithelium. They exit from the epithelium at stage 9 to migrate in between the NCs to reach the NC-oocyte (OOC) boundary at stage 10 of oogenesis. (B-D) Expression of yan^P(lacZ) in egg chambers. Arrows indicate BCs and arrowheads centripetal cells. (B) yan^P(lacZ) is expressed in anterior and posterior terminal cells at early stages of oogenesis, and in BCs that exit the epithelium. (C) At stage 9, yan^P(lacZ) is strongly expressed in outer BCs, while it is weakly detectable in the main body follicle cells. (D) At stage 10, yan^P(lacZ) expression broadens and shows the highest levels in BCs and centripetal cells. (E-G) Staining of egg chambers with anti-Yan antibodies (green) and Alexa-568-phalloidin (red). Arrows mark BCs. Magnified boxes show the progressive decrease in Yan protein (gray) levels during migration. (E) Yan is strongly expressed in BCs, whereas it is hardly detectable in polar cells (yellow arrowhead). (F). Yan expression becomes weaker after BCs exit from the epithelium and progressively decreases thereafter. (G) Yan is hardly detectable in BCs that have reached the NC-oocyte boundary at stage 10 of oogenesis.