Figure 7. Model for Egfr acting as a brake on DC.

Egfr negatively regulates the production and/or secretion of a diffusible signal “X” in the AS (AS) and is itself negatively regulated by Ack through endocytosis. “X” signals into both the AS and the DME cells where it activates a pathway promoting transcription of myosin from the zip locus. Previous work from our group and others, and unpublished results from our group, suggest that Dpp from the DME cells diffuses to the AS where it regulates production of a second diffusible signal “Y” providing a parallel input into zip transcription. Myosin produced through the cooperation of the two pathways then drives morphogenesis of the AS and DME cells. Egfr additionally regulates this signaling network by negatively regulating dpp transcription in the epidermis, including the DME cells. Egfr further regulates AS morphogenesis by inhibiting apoptosis in this tissue.