Cortical organoids reveal human-specific role of METTL5 in neurodevelopment via regulation of CHCHD2.

Methyltransferase-like 5 (METTL5) catalyzes N6-methyladenosine (m6A) modification on 18S rRNA. In humans, loss-of-function mutations in METTL5 cause severe microcephaly and intellectual disability, whereas Mettl5 knockout (KO) animal models display inconsistent and milder phenotypes. To better model human disease, we generated METTL5-KO human-induced pluripotent stem cell (hiPSC)-derived cortical organoids, which exhibit impaired neural progenitor cell (NPC) proliferation and differentiation, leading to reduced ventricle-like structures and significant reductions in cortical organoid diameter. Mechanistically, Ribo-seq analysis revealed broad translational changes in METTL5-KO NPCs consistent with cellular stress responses rather than transcript-specific translational changes. Single-cell RNA-seq identified downregulation of coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2), a mitochondrial regulator of oxidative metabolism. Overexpression of CHCHD2 in METTL5-KO NPCs rescued proliferation and partially rescued oxidative metabolism in NPCs and ventricle formation in organoids. This highlights a previously uncharacterized connection between CHCHD2, oxidative metabolism, and METTL5-mediated regulation of human neurogenesis.