The cytoplasmic dynamin-related guanosine triphosphatase Drp1 is recruited to 
mitochondria and mediates mitochondrial fission. Although the mitochondrial 
outer membrane (MOM) protein Fis1 is thought to be a Drp1 receptor, this has not 
been confirmed. To analyze the mechanism of Drp1 recruitment, we manipulated the 
expression of mitochondrial fission and fusion proteins and demonstrated that 
(a) mitochondrial fission factor (Mff) knockdown released the Drp1 foci from the 
MOM accompanied by network extension, whereas Mff overexpression stimulated 
mitochondrial recruitment of Drp1 accompanied by mitochondrial fission; (b) 
Mff-dependent mitochondrial fission proceeded independent of Fis1; (c) a Mff 
mutant with the plasma membrane-targeted CAAX motif directed Drp1 to the target 
membrane; (d) Mff and Drp1 physically interacted in vitro and in vivo; (e) 
exogenous stimuli-induced mitochondrial fission and apoptosis were compromised 
by knockdown of Drp1 and Mff but not Fis1; and (f) conditional knockout of Fis1 
in colon carcinoma cells revealed that it is dispensable for mitochondrial 
fission. Thus, Mff functions as an essential factor in mitochondrial recruitment 
of Drp1.