A transcriptional chain linking eye specification to terminal determination of cone cells in the Drosophila eye.

Lozenge (Lz) is a multifunctional transcription factor that is activated in a pool of pluripotent cells at the beginning of a wave of morphogenesis during Drosophila eye development. Lozenge belongs to the Runx class of transcription factors that includes the mammalian proteins AML1, Runx 2, and Runx 3. These proteins allow a tissue-specific precursor population of cells to attain multiple terminally differentiated fates. We investigated the transcriptional control of lz to determine the mechanism by which precursor populations achieve their identity. We have identified a 251-bp region in the second intron of the lz gene that functions as a minimal eye-specific enhancer. We provide evidence that Sine oculis and Glass are the two major activators of Lz expression during eye development. This work establishes a bridge between early eye specification genes and late cell-specific transcription factors required for terminal determination of cone cells in the eye.