Fig. 3. The spatial pattern of tkv regulates the spatial pattern of Dpp signaling and is sensitive to EGFR signaling levels. (A-C) Dpp signaling is abolished in tkv^- cells. tkv^- cells are marked by the absence of GFP (green) and Dpp signaling is monitored by P-Mad staining (red). (D) Top: regulatory mechanism proposed for the formation of the spatial pattern of tkv expression: tkv is positively regulated by EGFR and negatively regulated by a midline repressor, potentially Pointed (Pnt), also controlled by EGFR. Bottom: schematic of the tkv patterns in the wild type, the EGFR hypomorph (QY1, anterior striped gray), and the mutant with extra copies of gurken (4PX, solid gray). The dashed line shows the boundary of the wild-type pattern of tkv; cells inside the red box express tkv in the wild-type background. In these cells, tkv expression is lost in both the 4PX and QY1 mutants. (E,F) tkv expression in the 4PX (E) and QY1 (F) backgrounds. The midline gap is marked by a double arrowhead and the midline is marked by an arrowhead. P-Mad (green) in 4PX (G) and QY1 (H) egg chambers, respectively. The wild-type patterns of Dpp signaling and tkv expression are shown in Fig. 1. Yellow dashed lines mark the anterior boundary of the oocyte.