Recent evidence from yeast and mammals suggest that dynamin-related proteins affect mitochondrial morphology. We analyzed C. elegans
drp-1 , which is a structural and functional homologue of yeast and mammalian dynamin-related proteins. The injection of C. elegans
drp-1 inhibitory RNA (RNAi) into adult hermaphrodites was lethal to ensuing progeny, suggesting that the
drp-1 gene is required during embryogenesis. High levels of expression in the neurons and muscle cells of adult worms suggested that
drp-1 was also important at later stages in life. We investigated the function of C. elegans
drp-1 using transgenic animals that overexpress mutant
drp-1 . Mutant
drp-1 disrupted the mitochondrial distributions in muscle cells, but the ER morphologies in those same cells were not affected. To investigate the nature of the mitochondrial defect, we labeled the mitochondrial matrix and the mitochondrial outer membrane with different GFP variants. Double labeling showed that the collapsed blebs of mitochondrial matrix were connected by thin tubules of mitochondrial outer membrane. Therefore, mutant
drp-1 could block scission of the mitochondrial outer membrane, while scission of the mitochondrial inner membrane was unaffected. GFP-tagged mutant
drp-1 was localized to the connecting tubules of outer membrane, suggesting that the block in scission of the outer membrane was a direct consequence of interference by mutant
drp-1 . In contrast, GFP-tagged wild type
drp-1 was localized in spots along normal mitochondria where it might be primed for mitochondrial severing. Together, these results suggest that the
drp-1 protein controls the severing of the mitochondrial outer membrane, analogous to the role of dynamin in vesicle formation.