The Dynamin-related GTPase, Dnm1p, Controls Mitochondrial Morphology in Yeast

Abstract

The Saccharomyces cerevisiae Dnm1 protein is structurally related to dynamin, a GTPase required for membrane scission during endocytosis. Here we show that Dnm1p is essential for the maintenance of mitochondrial morphology. Disruption of the DNM1 gene causes the wild-type network of tubular mitochondrial membranes to collapse to one side of the cell but does not affect the morphology or distribution of other cytoplasmic organelles. Dnm1 proteins containing point mutations in the predicted GTP-binding domain or completely lacking the GTP-binding domain fail to rescue mitochondrial morphology defects in a dnm1 mutant and induce dominant mitochondrial morphology defects in wild-type cells. Indirect immunofluorescence reveals that Dnm1p is distributed in punctate structures at the cell cortex that colocalize with the mitochondrial compartment. These Dnm1p-containing structures remain associated with the spherical mitochondria found in an mdm10 mutant strain. In addition, a portion of Dnm1p cofractionates with mitochondrial membranes during differential sedimentation and sucrose gradient fractionation of wild-type cells. Our results demonstrate that Dnm1p is required for the cortical distribution of the mitochondrial network in yeast, a novel function for a dynamin-related protein.

Mitochondrial dynamics and division in budding yeast

“…The role of the Dnm1p GTPase in mitochondrial dynamics was first uncovered in a screen for yeast mutants with defective mitochondrial morphology [8]. Subsequent studies (described above) suggested that loss of Dnm1p function blocked mitochondrial fission but allowed the fusion of mitochondrial tips to continue, resulting in the formation of elaborate net-like structures [9,10].…”

“…Biochemical analyses detect a cytoplasmic pool of Dnm1p in yeast cells [8] and of Drp1 in mammalian cells [26]. In vivo, however, a large proportion of these proteins assembles into punctate structures on the outer mitochondrial membrane [8,26].…”

“…In vivo, however, a large proportion of these proteins assembles into punctate structures on the outer mitochondrial membrane [8,26]. Immunogold labeling in yeast revealed Dnm1p clustering at constricted sites on mitochondrial tubules that appear to be dividing [9].…”

“…The fission and fusion of the inner and outer mitochondrial membranes occur in tandem, although the mechanisms by which this coordination is accomplished are not understood. Fission can occur within a tubule or at a branchpoint in the reticulum and is regulated by a GTPase called Dnm1p [8][9][10]. Fusion always occurs between two mitochondrial tips or between the tip and the side of a tubule, and is regulated by the transmembrane GTPase Fzo1p [11,12].…”

Mitochondrial factors with dual roles in death and survival

“…Mitochondria also appear to be victimized by another protein complex, one that mediates mitochondrial fission. Fission and fusion of mitochondria occur every few minutes in healthy cells, both yeast and mammalian (Otsuga et al, 1998;Legros et al, 2002). Organelle fission may be required to send mitochondria to distant sites where ATP is required, whereas fusion appears to be required for genetic complementation and maintenance of healthy mitochondria.…”