Characterization of two paralogous myostatin genes and evidence for positive selection in Tibet fish: Gymnocypris przewalskii

• We first cloned mstn1 and mstn2 from a Tibetan fish, G. przewalskii.
• We detect the selection pressure on the two mstn paralogues.
• We mapped the positively selected sites on the 3D structure of Mstn1 and Mstn2.
• We characterized the expression profiles of two genes in G. przewalskii embryo development stages and adult tissues.

Myostatin (mstn) is an important member of TGF-β superfamily, a muscle growth inhibitor. Though mstn has been identified in many organisms, little is known about this gene in highland fish, Gymnocypris przewalskii endemic to the Qinghai–Tibetan Plateau. In this study, we first cloned two paralogous mstn genes (mstn1 and mstn2) from G. przewalskii through homologue cloning. The 3D structures of both Mstn proteins varied in the numbers of β-sheets and conformations of α-helices. The branch-site model showed that mstn1 has undergone positive selection, and two positively selected sites (107M and 181T) were located on the random coils of the 3D protein structure. Expression patterns indicated that the mstn1 expressed widely, while the mstn2 only expressed in the muscle and brain. During the early stage of embryo development, the expression levels of both mstn paralogous genes showed different increasing trends. These results suggest that it is diverging in two mstn paralogues of G. przewalskii via specific differences in gene structure, protein structure, selection pressure and gene expression patterns. Taken together, this study provides novel contribution on the research topics of growth related gene function and mechanism of highland fish in extreme aquatic environment on the Qinghai–Tibetan Plateau.