Fig. 6. Model for Sens action in R8. Spi induces Egfr activation and the signal transduction cascade is induced normally. However, Sens prevents transcription of pnt-P1, thereby blocking the pathway at the final step. This relationship is likely to specifically mediate cell differentiation in R8 (see text). Sens also represses ro, an early target of the Egfr pathway. This second relationship regulates the cell fate decision in the founder photoreceptor between R8 and R2/R5 (see text).