Identification of mouse inbred strains through mitochondrial DNA single-nucleotide extension

Differential accumulation of tau pathology between reciprocal F1 hybrids of rTg4510 mice

Tau, a family of microtubule-associated proteins, forms abnormal intracellular inclusions, so-called tau pathology, in a range of neurodegenerative diseases collectively known as tauopathies. The rTg4510 mouse model is a well-characterized bitransgenic F1 hybrid mouse model of tauopathy, which was obtained by crossing a Camk2α-tTA mouse line (on a C57BL/6 J background) with a tetO-MAPT*P301L mouse line (on a FVB/NJ background). The aim of this study was to investigate the effects of the genetic background and sex on the accumulation of tau pathology in reciprocal F1 hybrids of rTg4510 mice, i.e., rTg4510 on the (C57BL/6 J × FVB/NJ)F1 background (rTg4510_CxF) and on the (FVB/NJ × C57BL/6 J)F1 background (rTg4510_FxC). As compared with rTg4510_CxF mice, the rTg4510_FxC mice showed marked levels of tau pathology in the forebrain. Biochemical analyses indicated that the accumulation of abnormal tau species was accelerated in rTg4510_FxC mice. There were strong effects of the genetic background on the differential accumulation of tau pathology in rTg4510 mice, while sex had no apparent effect. Interestingly, midline-1 (Mid1) was identified as a candidate gene associated with this difference and exhibited significant up/downregulation according to the genetic background. Mid1 silencing with siRNA induced pathological phosphorylation of tau in HEK293T cells that stably expressed human tau with the P301L mutation, suggesting the role of Mid1 in pathological alterations of tau. Elucidation of the underlying mechanisms will provide novel insights into the accumulation of tau pathology and is expected to be especially informative to researchers for the continued development of therapeutic interventions for tauopathies.

Mitochondrial DNA Haplotypes as Genetic Modifiers of Cancer

Mitochondria play an essential role in cellular metabolism, generation of reactive oxygen species (ROS), and the initiation of apoptosis. These properties enable mitochondria to be crucial integrators in the pathways of tumorigenesis. An open question is to what extent variation in the mitochondrial genome (mtDNA) contributes to the biological heterogeneity observed in human tumors. In this review, we summarize our current understanding of the role of mtDNA genetics in relation to human cancers.

Mitochondrial polymorphisms contribute to aging phenotypes in MNX mouse models

Many inbred strains of mice develop spontaneous tumors as they age. Recent awareness of the impacts of mitochondrial DNA (mtDNA) on cancer and aging has inspired developing a mitochondrial-nuclear exchange (MNX) mouse model in which nuclear DNA is paired with mitochondrial genomes from other strains of mouse. MNX mice exhibit mtDNA influences on tumorigenicity and metastasis upon mating with transgenic mice. However, we also wanted to investigate spontaneous tumor phenotypes as MNX mice age. Utilizing FVB/NJ, C57BL/6J, C3H/HeN, and BALB/cJ wild-type inbred strains, previously documented phenotypes were observed as expected in MNX mice with the same nuclear background. However, aging nuclear matched MNX mice exhibited decreased occurrence of mammary tumors in C3H/HeN mice containing C57BL/6J mitochondria compared to wild-type C3H/HeN mice. Although aging tumor phenotypes appear to be driven by nuclear genes, evidence suggesting that some differences are modified by the mitochondrial genome is presented.

Evaluating purifying selection in the mitochondrial DNA of various mammalian species

Mitochondrial DNA (mtDNA), the circular DNA molecule inside the mitochondria of all eukaryotic cells, has been shown to be under the effect of purifying selection in several species. Traditional testing of purifying selection has been based simply on ratios of nonsynonymous to synonymous mutations, without considering the relative age of each mutation, which can be determined by phylogenetic analysis of this non-recombining molecule. The incorporation of a mutation time-ordering from phylogeny and of predicted pathogenicity scores for nonsynonymous mutations allow a quantitative evaluation of the effects of purifying selection in human mtDNA. Here, by using this additional information, we show that purifying selection undoubtedly acts upon the mtDNA of other mammalian species/genera, namely Bos sp., Canis lupus, Mus musculus, Orcinus orca, Pan sp. and Sus scrofa. The effects of purifying selection were comparable in all species, leading to a significant major proportion of nonsynonymous variants with higher pathogenicity scores in the younger branches of the tree. We also derive recalibrated mutation rates for age estimates of ancestors of these various species and proposed a correction curve in order to take into account the effects of selection. Understanding this selection is fundamental to evolutionary studies and to the identification of deleterious mutations.

Malaria: looking for selection signatures in the human PKLR gene region

The genetic component of susceptibility to malaria is both complex and multigenic and the better-known protective polymorphisms are those involving erythrocyte-specific structural proteins and enzymes. In vivo and in vitro data have suggested that pyruvate kinase deficiency, which causes a nonspherocytic haemolytic anaemia, could be protective against malaria severity in humans, but this hypothesis remains to be tested. In the present study, we conducted a combined analysis of Short Tandem Repeats (STRs) and Single Nucleotide Polymorphisms (SNPs) in the pyruvate kinase-encoding gene (PKLR) and adjacent regions (chromosome 1q21) to look for malaria selective signatures in two sub-Saharan African populations from Angola and Mozambique, in several groups with different malaria infection outcome. A European population from Portugal, including a control and a pyruvate kinase-deficient group, was used for comparison. Data from STR and SNP loci spread along the PKLR gene region showed a considerably higher differentiation between African and Portuguese populations than that usually found for neutral markers. In addition, a wider region showing strong linkage disequilibrium was found in an uncomplicated malaria group, and a haplotype was found to be associated with this clinical group. Altogether, this data suggests that malaria selective pressure is acting in this genomic region.