Loss of Msp1p in Schizosaccharomyces pombe induces a ROS‐dependent nuclear mutator phenotype that affects mitochondrial fission genes

Abstract

Mitochondria continually fuse and divide to dynamically adapt to changes in metabolism and stress. Mitochondrial dynamics are also required for mitochondrial DNA (mtDNA) integrity; however, the underlying reason is not known. In this study, we examined the link between mitochondrial fusion and mtDNA maintenance in Schizosaccharomyces pombe, which cannot survive without mtDNA, by screening for suppressors of the lethality induced by loss of the dynamin-related large GTPase Msp1p. Our findings reveal that inactivation of Msp1p induces a ROS-dependent nuclear mutator phenotype that affects mitochondrial fission genes involved in suppressing mitochondrial fragmentation and mtDNA depletion. This indicates that mitochondrial fusion is crucial for maintaining the integrity of both mitochondrial and nuclear genetic information. Furthermore, our study suggests that the primary roles of Msp1p are to organize mitochondrial membranes, thus making them competent for fusion, and maintain the integrity of mtDNA.

A yeast-based screening assay identifies repurposed drugs that suppress mitochondrial fusion and mtDNA maintenance defects

“…1A). As expected for a conditional mutation affecting the function of Msp1p, the P300S mutation causes severe growth retardation in dextrose medium at restrictive temperature (Delerue et al, 2016) (Fig. 1B), fragmentation of the mitochondrial network (Delerue et al, 2016), and a decrease in the amount of mtDNA (Delerue et al, 2016).…”

“…As expected for a conditional mutation affecting the function of Msp1p, the P300S mutation causes severe growth retardation in dextrose medium at restrictive temperature (Delerue et al, 2016) (Fig. 1B), fragmentation of the mitochondrial network (Delerue et al, 2016), and a decrease in the amount of mtDNA (Delerue et al, 2016). In addition, the msp1 P300S strain was unable to grow at the restrictive temperature in galactose medium, whereas the corresponding strain bearing the wild-type (WT) allele of the msp1 + gene ( msp1 WT ) grew normally in the same conditions (Fig.…”

“…We recently constructed a mutant S. pombe strain ( msp1 P300S ) expressing a thermosensitive version of Msp1p (Delerue et al, 2016). This strain has a point mutation leading to the replacement of the proline residue in position 300 in the Msp1p GTPase domain by a serine residue (Fig.…”

“…1B). The mitochondrial network of the msp1 P300S strain, as visualized by fluorescence microscopy using the mitochondrial protein Arg11p fused to the fluorescent protein mCherry (Arg11p-mCherry) (Delerue et al, 2016), appeared as dots and more fragmented than that of the msp1 WT strain, which consisted of short filaments (Fig. 1C, left column).…”

“…Msp1p inactivation leads to mitochondrial fragmentation and loss of the mitochondrial genome (Delerue et al, 2016; Guillou et al, 2005; Pelloquin et al, 1998). We therefore investigated whether the drugs identified as able to suppress the growth defect of the msp1 P300S strain also suppress these mitochondria-associated phenotypes.…”