MISO Regulates Mitochondria Dynamics and mtDNA Homeostasis by Establishing Inner Membrane Subdomains

Mitochondrial dynamics and mtDNA homeostasis are critical in various biological processes, including cell fate determination, metabolism, and aging. Although specialized mitochondrial membrane subdomains linking these two aspects have recently been reported, their structural and molecular characteristics have remained elusive. In this study, we discover MISO (Mitochondrial Inner Membrane-subdomain Organizer), a novel protein that initiates the formation of distinct MISO-enriched mitochondrial subdomains (MEMS) within the inner mitochondrial membrane. Our data demonstrate that MISO is an evolutionary conserved protein that regulates mitochondrial dynamics in Drosophila intestinal stem cells (ISCs) in vivo and various human and mouse cell lines in vitro. The functions of MISO depend on the formation of MEMS, which promote mitochondrial fission while inhibiting fusion, likely through the modulation of FIS1-DRP1 and OPA1 respectively. Further investigation reveals that MEMS recruit mtDNA nucleoids, facilitating their degradation via peripheral mitochondrial division. Additionally, we show that MISO orchestrates the assembly of MEMS through oligomerization mediated by its C-terminal domain, which drives contact between inner mitochondrial membranes to generate locally multilayered structures. Our findings collectively elucidate the molecular identity and functional mechanisms of specific mitochondrial subdomains in vivo and in vitro, revealing a structural link between the regulation of mitochondrial dynamics and mtDNA homeostasis.