Effect of fasting on protein metabolism in muscle tissue of Larimichthys crocea revealed by transcriptome and proteome

The large yellow croaker(Larimichthys crocea)is an important mariculture fish in China.Farmed large yellow croaker undergo periods of fasting to adapt to the environment or to improve meat quality.To better understand the physiological responses of their muscle tissues to fasting stresses,we analyzed the transcriptomes and proteome s of both normally-fed and fasting fish groups and identified 7578 differentially expressed genes(DEGs)and 297 differentially expressed proteins(DEPs)among them.Gene ontology and KEGG analysis showed that the enriched biological pathways were mainly involved in various synthetic and catabolic pathways,especially the protein metabolism.Based on the omics data,nine DEGs related to muscle composition(CAN3,MYL3,and TNNC2),growth(MSTN and MYF5),autophagy(TSC2 and ULK1),and the ubiquitin proteasome pathway(PRS6 B and UCHL3)were examined using qPCR.In response to fasting stress,MYL3 and TNNC2 were significantly downregulated,while genes associated with autophagy and the ubiquitin proteasome pathway were significantly upregulated.In re sponse to fasting stres s,MYL3,TNNC2,and MYF5 positively correlated with muscle growth were significantly downregulated,while inhibiting growth MSTN and genes associated with autophagy and the ubiquitin proteasome pathways were significantly upregulated.These results clarify the effects of fasting on metabolic changes in their muscle components and growth at the molecular level.

Functional Analysis of Slow Myosin Heavy Chain 1 and Myomesin-3 in Sarcomere Organization in Zebrafish Embryonic Slow Muscles

Myofibrillogenesis, the process of sarcomere formation, requires close interactions of sarcomeric proteins and various components of sarcomere structures. The myosin thick filaments and M-lines are two key components of the sarcomere. It has been suggested that myomesin proteins of M-lines interact with myosin and titin proteins and keep the thick and titin filaments in order. However, the function of myomesin in myofibrillogenesis and sarcomere organization remained largely enigmatic. No knockout or knockdown animal models have been reported to elucidate the role of myomesin in sarcomere organization in vivo. In this study, by using the gene-specific knockdown approach in zebrafish embryos, we carded out a loss-of-function analysis of myomesin-3 and slow myosin heavy chain 1 （smyhcl） expressed specifically in slow muscles. We demonstrated that knockdown of smyhcl abolished the sarcomeric localization of myomesin-3 in slow muscles. In contrast, loss of myomesin-3 had no effect on the sarcomeric organization of thick and thin filaments as well as M- and Z-line structures. Together, these studies indicate that myosin thick filaments are required for M-line organization and M-line localization of myomesin-3. In contrast, myomesin-3 is dispensable for sarcomere organization in slow muscles.