Fis1, Mff, MiD49 and MiD51 facilitate Drp1 recruitment for mitochondrial fission

Abstract

Several mitochondrial outer membrane proteins—Fis1, Mff, MiD49, and MiD51—have been proposed to promote mitochondrial fission by recruiting the cytosolic GTPase Drp1, but fundamental issues remain concerning their function. A recent study supported such a role for Mff, but not for Fis1. In addition, it is unclear whether MiD49 and MiD51 activate or inhibit fission because their overexpression causes extensive mitochondrial elongation. It is also unknown whether these proteins can act in the absence of one another to mediate fission. Using Fis1-null, Mff null, and Fis1/Mff -null cells, we show that both Fis1 and Mff have roles in mitochondrial fission. We employ several independent, quantitative techniques to show that these cell lines have significantly different mitochondrial elongation phenotypes. Using a specialized image analysis technique, we find that Fis1 and Mff are important for regulating the number and size of Drp1 fluorescent puncta on mitochondria. Finally, we find that either MiD49 or MiD51 can mediate Drp1 recruitment and mitochondrial fission in the absence of Fis1 and Mff. We also demonstrate that a significant enhancement of Drp1 phosphorylation at S637 is causal for the elongation phenotype during MiD overexpression. These results demonstrate that multiple receptors can recruit Drp1 to mediate mitochondrial fission, and suggest that these proteins may function in parallel pathways.

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