ATONAL, ROUGH AND THE RESOLUTION OF PRONEURAL CLUSTERS IN THE DEVELOPING DROSOPHILA RETINA

In the developing Drosophila retina, the proneural gene for photorecep tor neurons is atonal, a basic helix-loop-helix transcription factor, Using atonal as a marker for proneural maturation, we examine the step wise resolution of proneural clusters during the initiation of ommatid ial differentiation in the developing eye disc, In addition, evidence is provided that atonal is negatively regulated by rough, a homeobox-c ontaining transcription factor expressed exclusively in the retina, Th is interaction leads to the refinement of proneural clusters to specif y R8, the first neuron to emerge in the retinal neuroepithelium, Ectop ic expression of atonal or removal of rough results in the transformat ion of a discrete 'equivalence group' of cells into R8s, In addition, ectopic expression of rough blocks atonal expression and proneural clu ster formation within the morphogenetic furrow, Thus, rough provides r etina-specific regulation to the more general atonal-mediated proneura l differentiation pathway, The opposing roles of atonal and rough are not mediated through the Notch pathway, as their expression remains co mplementary when Notch activity is reduced, These observations suggest that homeobox-containing genes can provide tissue-specific regulation to bHLH factors.