Reprogramming cell fate in the developing Drosophila retina: transformation of R7 cells by ectopic expression of rough.

In the developing eye of Drosophila, the homeo box gene rough is required in the developing photoreceptor cells R2 and R5 for the correct development of the neighboring R3 and R4 cells. We have expressed rough ectopically in a limited subset of developing ommatidial cells using the sevenless enhancer. Expression of rough in the presumptive R7 cell transforms this cell into an R1-6 type photoreceptor. This transformation is cell autonomous in contrast to the apparent nonautonomy of the rough mutant phenotype and depends on the presence of the sevenless gene. We propose that in wild type, rough functions autonomously in the specification of R2/5 photoreceptor cell identity but by itself cannot initiate neural development.