Glass promotes the differentiation of both neuronal and non-neuronal cells in the Drosophila eye

Multiple cell types can be specified from a single pool of progenitors through the combinatorial activity of transcriptional regulators, which activate distinct developmental programs to establish different cell fates. The zinc finger transcription factor Glass is required for neuronal progenitors in the Drosophila eye imaginal disc to acquire a photoreceptor identity. Glass is also expressed in non-neuronal cone and pigment cells, but its role in these cells is unknown. To examine how Glass activity is affected by the cellular context, we misexpressed it in different tissues. When expressed in neuroblasts of the larval brain or in epithelial cells of the wing disc, Glass activated both a common core set of target genes and distinct gene sets specific to each tissue. In addition to photoreceptor-specific genes, Glass induced markers of cone and pigment cells. Cell type-specific glass mutations generated in cone or pigment cells using somatic CRISPR revealed autonomous developmental defects, and expressing Glass specifically in these cells partially rescued glass mutant phenotypes. Glass thus acts in both neuronal and non-neuronal cells to promote their differentiation into functional components of the eye, suggesting that it is a determinant of organ identity. 6 samples in triplicate, 2 experimental (Glass misexpression (Gl ME) in the wing and Gl ME in the brain), 4 controls (wild-type (WT) eye discs, WT wing discs and WT brains and gl60j brains) Drosophila melanogaster imaginal discs were isolated from Wandering 3rd Instar larvae (W3L) raised at 25C. Gl ME= Glass Misexpression, WT= wild-type. UAS-gl was expressed with tubulin (tub)-GAL4 in clones generated in the wing using Ultrabithorax-Flippase (Ubx-FLP). The inscuteable (insc)-GAL4 driver was used to misexpress Gl in the larval brain in a gl60j background.