FIS1 and diabetes mellitus: To examine the causal role of mitochondrial dynamics in insulin resistance relevant to mtDNA variants, we established cybrid cell harboring diabetes mellitus- (DM-) susceptible mtDNA haplogroup B4 (thereafter DM cybrid) [18] and overexpressed Mfn1, Mfn2, Drp1, and Fis1 in cybrid B4.