Abstract
BackgroundAnimal mitochondrial genomes typically encode 37 genes: 13 proteins, 22 tRNAs and two rRNAs. However, many species represent exceptions to that rule. Bivalvia along with Nematoda and Platyhelminthes are often suspected to fully or partially lack the ATP synthase subunit 8 (atp8) gene. This raises the question as to whether they are really lacking this gene or is this maybe an annotation problem? Among bivalves, Mytilus edulis has been inferred to lack an ATP8 gene since the characterization of its mitochondrial genome in 1992. Even though recent bioinformatic analyses suggested that atp8 is present in Mytilus spp., due to high divergence in predicted amino acid sequences, the existence of a functional atp8 gene in this group remains controversial.ResultsHere we demonstrate that M. edulis mitochondrial open reading frames suggested to be atp8 (in male and female mtDNAs) are actively translated proteins. We also provide evidence that both proteins are an integral part of the ATP synthase complex based on in-gel detection of ATP synthase activity and two-dimensional Blue-Native and SDS polyacrylamide electrophoresis.ConclusionMany organisms (e.g., Bivalvia along with Nematoda and Platyhelminthes) are considered to be lacking certain mitochondrial genes often only based on poor similarity between protein coding gene sequences in genetically closed species. In some situations, this may lead to the inference that the ATP8 gene is absent, when it is in fact present, but highly divergent. This shows how important complementary role protein-based approaches, such as those in the present study, can provide to bioinformatic, genomic studies (i.e., ability to confirm the presence of a gene).
Highlights
The blue mussel Mytilus edulis is one of the bivalve species possessing the unusual system of doubly uniparental inheritance (DUI) of mitochondria (Skibinski, Gallagher & Beynon, 1994; Boore, Medina & Rosenberg, 2004)
Contrary to anti-MATP8, anti-FATP8 antibody gave signal for every tissue both for male and female specimens (Fig. 3). This signal corresponded to the predicted protein molecular weight of FATP8 (∼10 kDa)
The signal for FATP8 in male mantle/gonad tissue was visibly weaker than the signals for other tissues
Summary
The blue mussel Mytilus edulis is one of the bivalve species possessing the unusual system of doubly uniparental inheritance (DUI) of mitochondria (Skibinski, Gallagher & Beynon, 1994; Boore, Medina & Rosenberg, 2004). Bivalvia along with Nematoda and Platyhelminthes are often suspected to fully or partially lack the ATP synthase subunit 8 (atp8) gene. Mytilus edulis has been inferred to lack an ATP8 gene since the characterization of its mitochondrial genome in 1992. Many organisms (e.g., Bivalvia along with Nematoda and Platyhelminthes) are considered to be lacking certain mitochondrial genes often only based on poor similarity between protein coding gene sequences in genetically closed species. In some situations, this may lead to the inference that the ATP8 gene is absent, when it is present, but highly divergent. This shows how important complementary role protein-based approaches, such as those in the present study, can provide to bioinformatic, genomic studies (i.e., ability to confirm the presence of a gene)
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