Minimal effects ofspargel(PGC-1α) overexpression in aDrosophilamitochondrial disease model

Abstract

PGC-1α and its homologues have been proposed to act as master regulators of mitochondrial biogenesis in animals. Most relevant studies have been conducted in mammals, where interpretation is complicated by the fact that there are three partially redundant members of the gene family. In Drosophila, only a single PGC-1α homologue, spargel (srl), is present in the genome. Here we analyzed the effects of srl overexpression on phenotype and on gene expression in tko 25t , a recessive bang-sensitive mutant with a global defect in oxidative phosphorylation, resulting in a deficiency of mitochondrial protein synthesis. In contrast to previous reports, we found only minimal effects of substantial overexpression of srl throughout development, on the expression of a representative set of both mtDNA-and nuclear-encoded OXPHOSrelated transcripts, both in tko 25t mutant flies and heterozygous controls. Sex and genetic background appeared to influence the expression of the tested genes, but srl overexpression or tko 25t itself did not have clear-cut or systematic effects thereon. These studies provide no support to the concept of spargel as a global regulator of mitochondrial biogenesis. Summary blurb: overexpression of spargel, the fly PGC-1α homologue proposed as a mitochondrial biogenesis regulator, has minimal effects on the phenotype of tko 25t , considered a fly model for mitochondrial disease Jacobs HT (2009) Expression of the Ciona intestinalis alternative oxidase (AOX) in Drosophila complements defects in mitochondrial oxidative phosphorylation, Cell Metab 9: 449-460 Finck BN, Kelly DP (2006) PGC-1 coactivators: inducible regulators of energy metabolism in health and disease. J Clin Invest 116: 615-622 17 Gill G (2004) SUMO and ubiquitin in the nucleus: different functions, similar mechanisms? Genes Dev 18: 2046-2059 González de Cózar JM, Gerards M, Teeri E, George J, Dufour E, Jacobs HT, Jõers P (2019) RNase H1 promotes replication fork progression through oppositely transcribed regions of Drosophila mitochondrial DNA. J Biol Chem doi: 10.1074/jbc.RA118.007015 [Epub before print] Handschin C, Kobayashi YM, Chin S, Seale P, Campbell KP, Spiegelman BM (2007) PGC-1alpha regulates the neuromuscular junction program and ameliorates Duchenne muscular dystrophy. Genes Dev 21: 770-783 Johnson LN (2009) The regulation of protein phosphorylation. Biochem Soc Trans 37: 627-641 Kemppainen E, George J, Garipler G, Tuomela T, Kiviranta E, Soga T, Dunn CD, Jacobs HT (2016) Mitochondrial dysfunction plus high-sugar diet provokes a metabolic crisis that inhibits growth. PLoS One 11: e0145836. Kemppainen E, Fernández-Ayala DJ, Galbraith LC, O'Dell KM, Jacobs HT (2009) Phenotypic suppression of the Drosophila mitochondrial disease-like mutant tko(25t) by duplication of the mutant gene in its natural chromosomal context. Mitochondrion 9: 353-363 Klein T, Eckhard U, Dufour A, Solis N, Overall CM (2018) Proteolytic cleavage-mechanisms, function, and "omic" approaches for a near-ubiquitous posttranslational modification. Chem Rev 118: 1137-...