Description: Endosomal sorting complexes required for transport (ESCRTs) mediate sorting of ubiquitinated membrane proteins into multivesicular bodies en route to lysosomes for degradation. A mutation in CHMP2B (CHMP2B Intron5 , an ESCRT-III component) that is associated with a hereditary form of frontotemporal dementia (FTD3) disrupts the endosomal-lysosomal pathway and causes accumulation of autophagosomes and multilamellar structures. We previously demonstrated that expression of CHMP2B Intron5 in the Drosophila eye using GMR -Gal4 causes misregulation of the Toll receptor pathway. Here, we show that ectopic expression of CHMP2B Intron5 using eyeless -Gal4 ( ey 〉 CHMP2B Intron5 ), a driver with different spatiotemporal expression attributes than GMR -Gal4 in the Drosophila eye, causes eye deformities when compared to expression of wild-type CHMP2B (CHMP2B WT ) and the Drosophila homologue of CHMP2B ( CG4618 ). In addition, ey 〉 CHMP2B Intron5 flies showed defects in photoreceptor cell patterning and phototactic behavior. Furthermore, ey 〉 CHMP2B Intron5 flies showed accumulation of Notch in enlarged endosomes and up-regulation of Notch activity. Partial loss of Notch activity in ey 〉 CHMP2B Intron5 flies significantly rescued eye deformities, photoreceptor patterning defect, and phototactic behavior defect, indicating that these defects are primarily due to Notch misregulation. These results demonstrate that CHMP2B Intron5 preferentially affects different receptor signaling pathways in a cellular and developmental context-dependent manner.—Cheruiyot, A., Lee, J-A., Gao, F-B., Ahmad, S. T. Expression of mutant CHMP2B, an ESCRT-III component involved in frontotemporal dementia, causes eye deformities due to Notch misregulation in Drosophila .