Fig. 4.

Combinatorial signalling during R1/R6, cone cell and primary pigment cell recruitment. a During larval development, Delta, the ligand for Notch, is produced in response to EGFR signalling in the R1/R6 photoreceptor cells. Rhomboid is also produced, leading to Spitz activation. Therefore, Spitz and Delta both signal from R1/R6 to induce the EGFR and Notch signalling pathways in adjacent cells. b These pathways lead to the activation of Pnt and Suppressor of Hairless (Su(H)) in the nucleus, which, together with the transcription factor Lozenge (Lz), activate Pax2 transcription, thereby inducing cone cell fate. Delta is also produced in the cone cell in response to EGFR signalling. c Finally, Delta activates the Notch pathway in adjacent cells during early pupal life (16–19 h after puparium formation). Su(H) and Lz induce the primary pigment cell fate