A novel salmonid myoD gene is distinctly regulated during development and probably arose by duplication after the genome tetraploidization.

A novel myoD paralogue was characterised in Salmo salar (smyoD1c) and S. trutta (btmyoD1c). SmyoD1c had 78.2/90.6% protein sequence identity to smyoD1a/smyoD1b, respectively. Each paralogue was differentially expressed throughout somitogenesis. In adult fish, smyoD1a was the predominant gene expressed in fast muscle, whereas smyoD1c was 2-3 times upregulated in slow muscle compared to smyoD1a/1b. A maximum likelihood analysis indicated that myoD1c arose by duplication of myoD1b after the salmonid tetraploidization. Another myoD paralogue (myoD2) is present in at least some teleosts, reflecting a more ancient genome duplication. To accommodate these findings we propose a simplified teleost-myoD nomenclature.