Small metallothionein MT-10 genes in coastal and hydrothermal mussels

Metallothioneins (MTs) are important proteins in the intracellular regulation of metals. In the Mytilidae family, which includes many economically important species, 2 major forms of MTs have been reported: MT-10 (10 kDa) and MT-20 (20 kDa). Many different MT-10 proteins have been isolated from the common species Mytilus edulis, which suggests that distinct MT-10 genes may occur in a single specimen. Some MT genes, involving 3 exons and 2 large introns, have been isolated in Mytilidae. Our aim was to determine whether intron-free forms of the MT-10 genes can exist, which could allow rapid transcription in response to exposure to metals. Our study focused on 2 species living under very different environmental conditions: Mytilus edulis (a coastal mussel) and Bathymodiolus thermophilus (a hydrothermal mussel). We report here the first description of small, intron-free MT-10 genes, possessing a correct open reading frame in these 2 species.