This study demonstrated that synergistic activation by two transcription factors, Pointed (Pnt) and Glass (Gl), drives a program of neuronal gene expression in developing Drosophila photoreceptors. Differentiation of photoreceptors R1–R7 requires epidermal growth factor (EGFR) signaling. The intrinsic zinc finger transcription factor Gl is expressed in all eye disc cells beginning just prior to their differentiation. In gl mutants, fewer cells in each ommatidial cluster express the neuronal marker Elav, suggesting that Gl contributes to neuronal fate specification. To understand which photoreceptor subtypes are affected by the loss of gl function, they performed single-cell RNA sequencing analysis of gl^60j mutant in Drosophila melanogaster on white prepupal eye discs.

RNA sequencing was carried out on wandering third instar larval wing discs that contained clones expressing GFP; GFP and Gl; GFP and RasV12; GFP, Gl and RasV12; GFP, Gl and RasV12 in pntdelta88 mutant clones; and GFP and Gl in cicQ219X mutant clones. The goal was to discover genes that are synergistically activated by Gl and EGFR signaling. In addition, RNA sequencing analysis was performed on temperature sensitive mutant egfrtsla/egfrf2 wandering third instar larval eye discs, where control samples were kept at 18^°C and mutant samples were shifted to 29^°C for 24 hours. The DNA adenine methyltransferase identification (DamID) experiment was performed on wandering third instar larval eye discs for two transcription factors, Gl and Pnt, as well as Dam-only controls. The GAL4 drivers used were atonal-GAL4, expressed in the morphogenetic furrow, and elav-GAL4, expressed in the committed photoreceptors.