Molecular characterisation and transcriptional regulation of muscle growth regulatory factors myogenin and myogenic factor 6 in the Trans-Himalayan cyprinid fish Schizothorax richardsonii.

In vertebrates, myogenic regulatory factors (MRFs) play an important role in muscle growth through the processes of cell determination and differentiation. Herein, we report the molecular characterisation of two MRFs, myogenin (myog) and myogenic factor 6 (myf6) in Indian snow trout Schizothorax richardsonii. The full length mRNA sequence of Srmyog and Srmyf6 was 1437 and 1296 bp, with an ORF of 762 and 720 bp, encoding a putative protein of 253 and 239 amino acids, respectively. In silico analysis and predicted tertiary protein structure revealed that both these nuclear localized MRFs contained the highly conserved basic helix loop helix motif, to potentially aid in dimerization with functional partners and DNA binding. Phylogenetically, the deduced protein sequences of Srmyog and Srmyf6 closely clustered with high altitude dwelling cyprinids, suggesting common ancestry. Tissue-wise, transcripts of Srmyog and Srmyf6 were abundant in skeletal muscle, affirming their muscle-specific role. Moreover, Srmyog was highly expressed in females as compared to males, whereas Srmyf6 expression was higher in older-bigger individuals as compared to younger-smaller fish. Nutritional status (fed-starved-refed) and diet composition (protein and lipid levels) had no significant influence on Srmyog expression. But, Srmyf6 expression was elevated in fishes re-fed after 3 weeks of starvation and in those fed low protein diet. Only rearing temperature was found to coherently influence Srmyog and Srmyf6 transcripts, with highest expression at 18 °C, which favoured growth. Overall, molecular characterisation of the structure and regulation of these MRFs is the first step taken towards deciphering slow growth in this important Himalayan cyprinid.