Quantitative Changes in Gimap3 and Gimap5 Expression Modify Mitochondrial DNA Segregation in Mice

Abstract

Mammalian mitochondrial DNA (mtDNA) is a high-copy maternally inherited genome essential for aerobic energy metabolism. Mutations in mtDNA can lead to heteroplasmy, the co-occurence of two different mtDNA variants in the same cell, which can segregate in a tissue-specific manner affecting the onset and severity of mitochondrial dysfunction. To investigate mechanisms regulating mtDNA segregation we use a heteroplasmic mouse model with two polymorphic neutral mtDNA haplotypes (NZB and BALB) that displays tissue-specific and age-dependent selection for mtDNA haplotypes. In the hematopoietic compartment there is selection for the BALB mtDNA haplotype, a phenotype that can be modified by allelic variants of Gimap3. Gimap3 is a tail-anchored member of the GTPase of the immunity-associated protein (Gimap) family of protein scaffolds important for leukocyte development and survival. Here we show how the expression of two murine Gimap3 alleles from Mus musculus domesticus and M. m. castaneus differentially affect mtDNA segregation. The castaneus allele has incorporated a uORF (upstream open reading frame) in-frame with the Gimap3 mRNA that impairs translation and imparts a negative effect on the steady-state protein abundance. We found that quantitative changes in the expression of Gimap3 and the paralogue Gimap5, which encodes a lysosomal protein, affect mtDNA segregation in the mouse hematopoietic tissues. We also show that Gimap3 localizes to the endoplasmic reticulum and not mitochondria as previously reported. Collectively these data show that the abundance of protein scaffolds on the endoplasmic reticulum and lysosomes are important to the segregation of the mitochondrial genome in the mouse hematopoietic compartment. KEYWORDS mitochondria; mitochondrial DNA; mice; segregation; Gimap M AMMALIAN mitochondrial DNA (mtDNA) is a maternally inherited small circular multicopy genome that encodes 13 proteins that are essential subunits of four of the five complexes required for mitochondrial oxidative phosphorylation. Germline or somatic-cell mtDNA mutations lead to the co-occurrence of two or more sequence variants in a cell, a state known as heteroplasmy. In the absence of selection, the segregation of mtDNA sequence variants is neutral and can be modeled as a random walk (Chinnery and Samuels 1999); however, in some cases there is preferential selection for a mtDNA sequence variant that is dependent upon the nucleotide sequence, tissue, and nuclear background (Battersby and Shoubridge 2001;Battersby et al. 2003Battersby et al. , 2005Jokinen and Battersby 2013;Burgstaller et al. 2014). The majority of pathogenic mtDNA mutations are heteroplasmic and some mutations display skewed segregation patterns in somatic tissues. (Larsson et al. 1990;Boulet et al. 1992;Kawakami et al. 1994;Dunbar et al. 1995;Fu et al. 1996;Chinnery et al. 1997Weber et al. 1997), which can affect the onset and severity of mitochondrial dysfunction. Currently, the molecular basis for this regulation of the mitochondrial genome is largely un...

Systemic analyses of expression patterns and clinical features for GIMAPs family members in lung adenocarcinoma

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Pervasive within-Mitochondrion Single-Nucleotide Variant Heteroplasmy as Revealed by Single-Mitochondrion Sequencing

“…Among the 118 single mitochondrion samples from mice, there were on average 3.9 SNV sites per mitochondrion with a standard deviation of 5.71, indicating over-dispersion of SNV sites with some mitochondrion containing an unexpected high or low mutational load. Such over-dispersion might arise from preferential birth-death of certain multi-loci variant combinations leading to fitness effects (cf., Jokinen et al, 2015. ; Jenuth et al, 1997).…”

“…We note several complicating factors may influence our results including unusual cellular environment within in vitro cell cultures leading to de novo mutations as well as possible effects of somatic selection which may depend on variation at other genomic loci or tissue specific selection (e.g., Jokinen et al, 2015; Jenuth et al, 1997). Unusual environment leading to mutations can influence the total number of SNV loci but we believe it unlikely to lead to SNVs shared in multiple samples as those described in Table 1.…”

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