MiP2005: Session 5

Mitochondrial Physiology Network 10.9: 60-61 (2005) - download pdf

 

Functional significance of mtDNA evolution.

Pierre Blier

Laboratoire de Biologie Évolutive, Département de Biologie, Université du Québec, 300 Allée des Ursulines, Rimouski, Qc, Canada G5L 3A1. - pierre_blier@uqar.qc.ca

    Mitochondrial DNA is a powerful tool for the investigation of the population dynamics of animal species. Although evolutionary and population genetic studies often assume that mtDNA undergoes neutral or nearly neutral evolution, the important roles of all 13 mtDNA-encoded peptides in cellular ATP production suggest that mtDNA could have significant metabolic and fitness consequences [1]. Different methods have been used to detect natural selection. Statistical analysis of mtDNA sequences is a powerful analytical tool but possesses little power in detecting functional significance of specific mtDNA substitutions. Physiological studies on cellular or animal models can highlight how divergent combinations of mtDNA and nuclear background interact together, tease apart the relative roles of environmental and genetic factors in cytonuclear interactions and assess the adaptive value of different mitochondrial haplotypes. For example, various studies have shown that the repopulation of mtDNA-less cells with mtDNA of different species leads to different levels of respiratory function restoration depending on the phylogenetic distance between the mtDNA donor species and the recipient [2]. In populations of invertebrates (copepods and drosophila) laboratory crosses or microinjections revealed either an unpredictable pattern of hybrid breakdown, or fitness advantage of specific mitochondrial mitotypes (for a review see ref. 1). The former suggests that genomes co-adaptation arises during the course of stochastic population differentiation while the latter could suggest specific adaptations to local environments. Wild introgressed populations offer a rare opportunity to study the potential adaptive value of mtDNA in a natural environment. A natural population of brook char (Salvelinus fontinalis) has been found that possesses the mitochondrial DNA of Arctic char (Salvelinus alpinus) with no sign of nuclear introgression. This introgression could be highly significant because Arctic char is a cold adapted species, whereas brook char is more temperate and the introgressed population is found in the northern distribution range of brook char. Complete sequencing of the mitochondrial genome of Arctic and brook char revealed 47 amino acid substitutions between the species with only one in the cytochrome oxidase complex and 45 in the NADH oxidase complex. We therefore estimated the temperature sensitivity of muscle mitochondrial respiration rate as well as the maximal activity of enzymes of the electron transport system and Krebs cycle in both species and their hybrids to assess the functional impact of mitochondrial introgression on energy metabolism.

1.  Blier PU, Dufresne F, Burton R (2001) Natural selection and the evolution of mtDNA-encoded peptides: evidence for intergenomic co-adaptation. TIG 17: 400-4006

2.  Mckenzie et al. (2003) Functional respiratory chain analyses in murid xenomitochondrial cybrids expose coevolutionary constraints of cytochrome b and nuclear subunits of complex III. Mol. Biol. Evol. 20: 1117-1124.


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