Fig. 8. RTKs signaling downregulates Yan. (A) Yan (blue) is strongly expressed in BCs that delaminate from the follicular epithelium, but expression gradually decreases as BCs migrate along the increasing gradient of Pvf1 (orange). The inverse expression levels of Yan and Pvf1 suggest that PVR activity counteracts Yan expression in migrating BCs. (B-E') Egg chambers are stained with Alexa-568-phalloidin (red) to visualize actin. Arrows indicate BCs and arrowheads the squamous follicle cells. (B-E) Anti-Slbo (green) and actin (red) staining; (B'-E') anti-Yan (green) and actin (red) staining. (B,B') Slbo and Yan are strongly expressed in wild-type BCs that delaminate from the follicular epithelium. (C) Slbo is normally expressed in BCs that ectopically express activated PVR. (C') By contrast, Yan is undetectable in BCs but is expressed normally in squamous follicle cells where slbo-Gal4 is inactive. Similarly, expression of either activated EGFR (D,D') or activated Raf (E,E') in BCs downregulates Yan but not Slbo. All experiments and stainings were done in parallel, and images were taken with the same settings, together with experiments in Fig. 7F-H. The expression levels of Yan in squamous follicle cells serve as an internal control. (F,G) ß-Gal staining indicates yan expression in yan^P(lacZ) (F) and yan^P(lacZ)/slbo-Gal4; UAS-PVR (G) stage 10 egg chambers. Arrows indicate BCs; insets show yan mRNA expression by in situ hybridization. (H,I) Stage 10 egg chamber stained with anti-Slbo antibody (red), anti-ß-Gal antibody indicating pnt-lacZ expression (green), DAPI (blue) and Alexa-568-phalloidin (gray). (H) Pnt-lacZ is expressed in posterior cells and is absent in wild-type BCs. (I) Expression of activated PVR in BCs arrests their migration. These BCs express Slbo but do not express pnt-lacZ.