The root of the transmissible cancer: first description of a widespreadMytilus trossulus-derived cancer lineage inM. trossulus

Abstract

AbstractTwo lineages of bivalve transmissible neoplasia (BTN), BTN1 and BTN2, are known in blue musselsMytilus. Both lineages derive from the Pacific musselM. trossulusand are identified primarily by the unique genotypes of the nuclear gene EF1α. BTN1 is found in populations ofM. trossulusfrom the Northeast Pacific, while BTN2 has been detected in populations of otherMytilusspecies worldwide but not inM. trossulusitself. The aim of our study was to examine musselsM. trossulusfrom the Sea of Japan (Northwest Pacific) for the presence of BTN. Using hemocytology and flow cytometry of the hemolymph, we confirmed disseminated neoplasia in our specimens. Cancerous mussels possessed the unique BTN2 EF1α genotype and two mitochondrial haplotypes with different recombinant control regions, similar to that of common BTN2 lineages. This is the first report of BTN2 in its original host speciesM. trossuluspopulations in West Pacific may be the birthplace of BTN2 and a natural reservoir where it is maintained and whence it spreads worldwide. A comparison of all available BTN andM. trossulusCOI sequences suggests a common and recent, though presumably prehistoric origin of BTN2 diversity in populations ofM. trossulusoutside the Northeast Pacific.