An antibody to the C‐terminus extension of cox2 in the male transmitted mitochondrial genome of Venustaconcha ellipsiformis (Bivalvia: Unionoidea)

Abstract

Doubly uniparental inheritance of mitochondrial DNA (DUI) has been observed in two orders of marine bivalves and in the freshwater bivalve superfamily Unionoidea. Cox2 is an inner mitochondrial membrane protein that functions in complex IV of the electron transport system. PCR amplification of the cox2-cox1 junction region from unionoidean male-transmitted (M) mtDNA genomes reveals an approximately 555 bp 3′ coding extension to cox2. The fixed presence of the cox2 3′ extension in unionoidean M genomes may be associated with the high stability of DUI in this taxon. We made an antibody against the M cox2 C-terminus extension from V. ellipsiformis. The antibody was characterized by blotting procedures using both soluble and insoluble extracts of testes. Attempts at detecting the lengthened cox2 protein were made using both male and female tissues and it was observed that the protein was predominantly expressed in testes. Weak expression was detected in other male tissues such as foot, mantle and gill. However, female tissues showed no immunoreactive band. Immunohistochemistry also verified that the expression of this protein is predominantly in male spermatogenic tissue. This is the first report documenting the expression of a significantly lengthened cox2 protein in the Unionoidea. We hypothesize that the expression of a lengthened cox2 protein in unionoidean bivalve testes has functional significance.