The expressions of two myostatin paralogs in turbot Scophthalmus maximus fasted for 2 weeks and fed diets containing graded levels of fish protein hydrolysate

Myostatin (MSTN), a member of the transforming growth factor-β (TGF-β) superfamily, has retained the function of inhibiting muscle growth in fish. Turbot Scophthalmus maximus possesses two MSTN paralogs (MSTNa and MSTNb), but their respective response to dietary nutrients is still unclear. To clarify the effects of fish protein hydrolysate (FPH) on MSTNa and MSTNb, their mRNA levels were quantified in the muscle using the fasting–refeeding experiment and long-term feeding trial. Gene expressions in various tissues showed that MSTNb but not MSTNa was expressed mostly in the muscle. After 2 weeks of starvation, MSTNa expression was up-regulated in the muscle by refeeding FPH diet at 3 h and 6 h, while MSTNb expression was affected from 3 h to 3 days. Moreover, changes in MSTNb expression over time showed that significant reduction was observed at 3 h in fish refed optimal levels of FPH, but at 6 h in fish refed excessive levels of FPH. The expressions of two MSTN paralogs and related gene expressions of TGF-β/SMAD-dependent signalling pathway were not significantly altered by graded levels of FPH after 7 days of refeeding, while the expressions of MSTNb as well as the upstream FMODa and downstream SMAD4 were significantly affected after the long-term feeding trial (8 weeks). In conclusion, FPH mainly modulated the expression of MSTNb in the muscle, whereas MSTNa was only affected in the early stage of refeeding. Furthermore, during the refeeding period, optimal levels of FPH in diets may regulate MSTNb more rapidly to initiate compensatory growth.