Investigation of a potential regulator of mitochondrial fission identified by genome-wide screening.

Mitochondria are dynamic organelles that constantly change their morphology through fusion and fission events. The balance among these processes is critical for their function and for cellular homeostasis. Among the many roles they play in cell biology, mitochondria are central to energy conversion, calcium signalling and the regulation of cell death. Mitochondrial fission is driven by DRP1, a GTPase mechanoenzyme which assembles into helical rings around the mitochondrial tubule to drive its constriction and division. The recruitment of DRP1 to fission sites depends on four canonical adaptor proteins (FIS1, MFF, MiD49 and MiD51), whose roles have been extensively studied. However, whether additional proteins contribute to the regulation of this process in specific physiological contexts remains an open question. To address this, a genome-wide RNAi screening was carried out in OPA1-deficient mouse embryonic fibroblasts, a system where mitochondrial shape reflects only fission activity. This approach identified DNAJC5, encoding the co-chaperone CSPα, as a candidate regulator. CSPα is known to regulate dynamin 1, a GTPase of the same superfamily as DRP1, which makes it a compelling candidate for a non-canonical role in fission. This thesis investigates whether CSPα is a non-canonical regulator of mitochondrial fission and explores the molecular basis of this interaction.