Executioner caspase is proximal to Fasciclin 3 which facilitates non-lethal activation in Drosophila olfactory receptor neurons

Executioner caspases are activated by initiator caspases, resulting in lethal and non-lethal cellular outcomes. Despite the identification of numerous caspase-dependent non-lethal cellular processes (CDPs), the molecular mechanism that enables precise regulation of the non-lethal functions of executioner caspases remains unclear. Here, we conducted a comprehensive analysis of endogenous proximal proteins of Drosophila executioner caspases in vivo using TurboID. We discovered that in the adult brain, the executioner caspase Drice is, as an inactive proform, primarily proximal to cell membrane proteins, including the cell adhesion molecule Fasciclin 3 (Fas3). Notably, Drice is proximal to the specific alternative splicing isoforms of Fas3, Fas3G. To investigate whether Fas3G modulates caspase activity, we developed a Gal4-Manipulated Area-Specific CaspaseTracker/CasExpress (MASCaT) system for highly sensitive monitoring of non-lethal caspase activity near cell membrane compartments. Using MASCaT, we demonstrated that Fas3G overexpression promotes caspase activation near cell membrane compartments in olfactory receptor neurons without killing them. Mechanistically, Fas3G overexpression induces the expression of initiator caspase Dronc, which also comes close to Fas3G, regulating non-lethal caspase activation. Physiologically, Fas3G overexpression-facilitated caspase activation regulates innate olfactory attraction behavior. Collectively, our findings suggest that caspase activation is subcellularly restricted, the platform of which is defined by caspase proximal proteins, for non-lethal functions. ### Competing Interest Statement The authors have declared no competing interest.