Mitochondria (green) in Peg1 mutants aggregate (left), whereas wild-type mitochondria are more spread out (right).
Mitochondria rely on microtubules to move around the cell and for distribution into daughter cells. Many cell types use microtubule-bound motors to move mitochondria. Yeast cells instead depend on microtubule growth to do the job, but how mitochondria are lashed onto the growing microtubules was unknown.
In normal yeast cells, mitochondria are evenly distributed throughout the cell. In a screen of temperature-sensitive yeast mutants, the authors discovered one in which mitochondria aggregated at the ends of the cell, a phenomenon that also occurs when microtubules depolymerize. The mutant gene that caused this phenotype was peg1, which encodes a homologue of the mammalian microtubule plus end–binding protein CLASP.
Mitochondrial aggregation could not be recapitulated by mutants of either the motor protein dynein or other plus end–binding proteins. The Peg1 mutation did not affect the cytoskeleton, and the changes were independent of the cell cycle, suggesting the aggregation was not due to other changes in microtubules.
Peg1 was found to be a mitochondrial peripheral membrane protein. As CLASP links membranes to microtubules in mammalian cells, Chiron proposes a similar function for Peg1 in yeast, and suggests that it hitches mitochondria to microtubules.
