Caspase-3/Drice as a critical regulator of actin dynamics through its dual control of small RhoGTPase family and Gelsolin in the Malpighian tubules of Drosophila

Caspases are well-known executioner enzymes that drive programmed cell death. However, growing evidence indicates their crucial non-apoptotic functions in regulating proliferation, differentiation, endocytic trafficking, cell polarity, morphogenesis, and immune responses. In this study, we uncover a novel role of the Drosophila caspase-3 homolog, Drice, in the spatial and dynamic regulation of actin filaments during the development and functional maintenance of Malpighian tubules (MTs). Our previous work demonstrated that Drice is crucial for the morphogenesis of the MTs. Its absence results in erroneous Rho GTPase signaling, driving disarray in actin organization, leading to the formation of multiple fluid-filled cysts in tubules. Here, we show that altered expression of two Rho family GTPases, Rho1 and Cdc42, perturbs downstream signaling in Drice null mutants. Reduced Rok expression aborts Rho1-mediated signaling, whereas elevated Cdc42 levels induce Arp2/3-dependent hyper-polymerization of actin in Drice null mutants. Comparative analyses between control and Drice null mutant MTs revealed loss of the Gelsolin-Rho1 interaction and significant downregulation of Gelsolin expression, disrupting the F-actin: G-actin balance in Drice null mutants. Together, our findings establish a previously unrecognized role of caspase-3/Drice in regulating actin homeostasis and tubule morphogenesis, underscoring its broader significance beyond apoptosis in developmental and physiological contexts.