Regulation of EGF receptor signaling establishes pattern across the developing Drosophila retina

Developing epithelia use a variety of patterning mechanisms to place indivi dual cells into their correct positions, However, the means by which patter n elements are established are poorly understood. Here, we report evidence that regulation of Drosophila EGF receptor (DER) activity plays a central r ole in propagating the evenly spaced array of ommatidia across the developi ng Drosophila retina. DER activity is essential for establishing the first ommatidial cell fate, the RS photoreceptor neuron, R8s in turn appear to si gnal through Rhomboid and Vein to create a patterned array of 'proneural cl usters' which contain high levels of phosphorylated ERKA and the bHLH prote in Atonal. Finally, secretion by the proneural clusters of Argos represses DER activity in less mature regions to create a new pattern of R8s, Propaga tion of this process anteriorly results in a retina with a precise array of maturing ommatidia.