The study investigates the role of dynamin-related protein Drp1 in mitochondrial division in mammalian cells. Mutations in Drp1 cause mitochondria to form perinuclear clusters, indicating a block in mitochondrial division. Immunofluorescence and subcellular fractionation show that endogenous Drp1 is localized to mitochondria. Time-lapse photography of transfected cells reveals that Drp1 localizes to spots on mitochondria that coincide with actual mitochondrial division events. Purified human Drp1 forms multimeric ring-like structures similar to dynamin, suggesting that Drp1 wraps around the constriction points of dividing mitochondria. The findings conclude that Drp1 contributes to mitochondrial division in mammalian cells.The study investigates the role of dynamin-related protein Drp1 in mitochondrial division in mammalian cells. Mutations in Drp1 cause mitochondria to form perinuclear clusters, indicating a block in mitochondrial division. Immunofluorescence and subcellular fractionation show that endogenous Drp1 is localized to mitochondria. Time-lapse photography of transfected cells reveals that Drp1 localizes to spots on mitochondria that coincide with actual mitochondrial division events. Purified human Drp1 forms multimeric ring-like structures similar to dynamin, suggesting that Drp1 wraps around the constriction points of dividing mitochondria. The findings conclude that Drp1 contributes to mitochondrial division in mammalian cells.