Mitochondria and Cell Growth

 

Identification of Pathways Regulating Mitochondrial DNA Copy Number in S. cerevisiae

 

 

 

 

 

 

 

 

 

        The copy number of the Saccharomyces cerevisiae mitochondrial genome varies. Two major influences on mitochondrial DNA (mtDNA) copy number are genetic background and carbon source. While genes required for maintenance of mtDNA have been thoroughly investigated, genes that increase mtDNA copy number have not been systematically identified. We report a screen to determine mtDNA copy number in the yeast haploid deletion collection, focusing subsequent work on strains with elevated mtDNA copy number. Deletion strains were grown on glucose and on glycerol, and total DNA was quantitatively isolated. Nuclear DNA and mtDNA copy numbers were quantified by multiplex quantitative PCR. Several classes of genes were identified with increased mtDNA copy number. Nine members of the glucose sensing pathway had high mtDNA copy number, as predicted for cells defective in glucose-mediated repression of mitochondrial biogenesis. Another class of genes slows the cell cycle at various points, producing larger yeast with a larger mitochondrial volume. A third class consists of deletions of mitochondrial ribosomal proteins. These mutations may compromise mitochondrial function, inducing mitochondrial proliferation. Other functional classes of genes were also identified. We are characterizing growth rate, cell size, mitochondrial volume, and mitochondrial membrane potential in the strains with significantly altered mtDNA copy number to better understand the pathways that promote mtDNA biogenesis.

 

Regulation of the Mitochondrial Compartment in S. cerevisiae

 

Mitochondrial proliferation (mitochondria stained with red with Giemsa Trichome stain) observed in muscle fibers from a patient with a mitochondrial DNA mutation. A number of different mutations that compromise oxidative phosphorylation can trigger an increase in the mitochondrial compartment. Image courtesy of Washington University.

       Mitochondrial function has been genetically linked to aging through screens in the the yeast Saccharomyces cerevisiae, the worm C. elegans, and the fruit fly Drosophila melanogaster. Mutations that alter the efficiency of respiration can dramatically increase lifespan in many organisms. The number of mitochondria per cell is affected by the conditions under which cells are grown and the metabolic state of the cell. Although many mutations are known that result in the loss of mitochondrial DNA, little is known about the pathways that upregulate the number of mitochondria per cell or the copy number of the mitochondrial genome.