Regulation of Notch signaling by miR-79 in Drosophila eye development

The Notch signaling pathway is crucial for cell fate determination and tissue morphogenesis. In Drosophila, Notch signaling regulates eye size, but the mechanisms that fine-tune its activity during eye development remain unclear. Here, we established a Notch-sensitized Drosophila model to identify novel regulators of this pathway. Using the Gal4/UAS system, we overexpressed fringe (fng) under ey-Gal4 control (ey > fng) in Drosophila eyes, disrupting Notch signaling and resulting in a small-eye phenotype. In this sensitizing background, a genetic screening identified miR-79 as a key modulator of Notch signaling. miR-79 overexpression rescued ey > fng-induced small-eye phenotype, whereas loss-of-function analysis using a mir-79 sponge exacerbated the phenotype, confirming its regulatory role. Furthermore, co-expression of miR-79 with the Notch ligands Delta or Serrate induced eye disc overgrowth near the equator, where Notch signaling is typically active, suggesting a strong genetic interaction between miR-79 and the Notch pathway. Functional studies revealed that miR-79 directly targets Beaded (Brd) by binding to specific Brd-Box motifs in its 3' UTR. RNAi-mediated Brd knockdown phenocopied the rescue effect of miR-79 overexpression, whereas Brd gain-of-function enhanced the ey > fng phenotype. RNA in situ hybridization demonstrated complementary expression patterns of miR-79 and Brd during eye development. Although Tom, another Brd family member, was identified as a potential miR-79 target, luciferase assays confirmed that Tom is not directly regulated by miR-79. However, genetic interactions between Tom and Notch components suggest function redundancy with Brd. These findings establish miR-79 as a novel activator of Notch signaling in Drosophila eye development, primary through Brd regulation. This study provides new insights into molecular mechanisms governing Notch-mediated development and highlights the regulatory role of miR-79 in tissue growth and differentiation.