Fig. 8. A model for the asymmetric regulation of N by the tissue polarity proteins. At the junction of photoreceptors R3/R4, Fmi is anchored in both R3 and R4 via homophilic association. In the developing photoreceptor R3, Fmi, Diego, and Dsh form a complex in which N is bound to Dsh. However, in the developing R4, Fmi, Diego, and Dsh form a complex in which Pk and Stbm are bound to Dsh, thereby preventing N from binding to Dsh. Consequently, in R4, N is released from this membrane-bound complex and can signal at high levels.