The mtDNA-encoded COX2 protein: bivalves have the longest
Résumé
In contrast to all other animal species in which strict maternal inheritance (SMI) of mitochondria is the rule, bivalves possess a system known as doubly uniparental inheritance (DUI) of mitochondria in which maternal and paternal mitochondria (and their corresponding female- of F- and male- or M-transmitted mtDNAs) are transmitted within a species. Recently, DUI was discovered in two new species: Scrobicularia plana (family Semelidae) and Limecola balthica (family Tellinidae). The complete F and M mtDNAs were sequenced for both species. An intriguing difference of ~10,000 bp was observed between the F genome and M genomes in both species. A large part of this difference is due to the exceptionally long size of the male cox2gene, which possesses a >3,400 bp insertion. This observation raises several questions: (1) Is this gigantic cox2 gene in the male genome (or Mcox2) an artifact of the sequenced individuals or a conserved trait in each species? (2) Is this extension expressed or is it rather an intron-like sequence that is spliced? (3) If this sequence is conserved and expressed, how does it evolve relative to the rest of the gene and relative to other typical genes, and is it involved in the mito-nuclear network of epistatic interactions leading to OXPHOS functioning? Does it have a function aside from bioenergetics? The present research project attempts to answer these questions, the main objective being to characterize the molecular evolution and to analyze the structure of the Mcox2 gene of these species.