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Temperature strongly modulates muscle development and growth in ectothermic teleosts; however, the underlying mechanisms remain largely unknown. In this study, primary cultures of skeletal muscle cells of Lateolabrax maculatus were conducted and reared at different temperatures (21, 25, and 28 °C) in both the proliferation and differentiation stages. CCK-8, EdU, wound scratch and nuclear fusion index assays revealed that the proliferation, myogenic differentiation, and migration processes of skeletal muscle cells were significantly accelerated as the temperature raises. Based on the GO, GSEA, and WGCNA, higher temperature (28 °C) induced genes involved in HSF1 activation, DNA replication, and ECM organization processes at the proliferation stage, as well as HSF1 activation, calcium activity regulation, myogenic differentiation, and myoblast fusion, and sarcomere assembly processes at the differentiation stage. In contrast, lower temperature (21 °C) increased the expression levels of genes associated with DNA damage, DNA repair and apoptosis processes at the proliferation stage, and cytokine signaling and neutrophil degranulation processes at the differentiation stage. Additionally, we screened several hub genes regulating myogenesis processes. Our results could facilitate the understanding of the regulatory mechanism of temperature on fish skeletal muscle growth and further contribute to utilizing rational management strategies and promoting organism growth and development. [ABSTRACT FROM AUTHOR]

Long noncoding RNAs (lncRNAs) play an important role in many life activities, but the expression pattern and function of lncRNAs in Japanese flounder skeletal muscle are unclear. In this study, 751 lncRNAs were selected from skeletal muscle in different development stages of the Japanese flounder [stage A: larval 7 days post hatching (dph); stage B: juvenile about 90 dph; stage C (female) and stage D (male): adult about 24 months] using coding potential analysis methods. In total, 232, 211, 194, 28, 29, and 14 differentially expressed lncRNAs and 9549, 8673, 9181, 1821, 1080, and 557 differentially expressed mRNAs were identified in comparisons of A versus B, A versus C, A versus D, B versus C, B versus D, and C versus D, respectively. We identified the cis - and trans -regulatory target genes of differentially expressed lncRNAs, and lncRNA–gene interaction networks were constructed using the Cytoscape program. In total, there were 200, 200, 200, 93, 47, and 11 cis -regulation relationships, and 29, 19, 24, 38, 8, and 47 trans -regulation relationships in the comparisons between A versus B, A versus C, A versus D, B versus C, B versus D, and C versus D, respectively. These results indicate that lncRNA may participate in the development of Japanese flounder skeletal muscle through cis - or trans -acting mechanisms, thus providing a scientific basis for further study of the biological function of lncRNA in Japanese flounder skeletal muscle. Based on these relationships, functional annotation of the related lncRNAs was performed by gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. Differentially expressed genes associated with muscle development were enriched in multiple pairs of comparisons (e.g., differentially expressed genes LOC109640370, LOC109634180, LOC109643555, rusc1, and LOC109626999 were enriched in the actin-binding term, and differentially expressed genes LOC109640370, was, LOC109644970, LOC109643555, and itga9 were enriched in the regulation of the actin cytoskeleton pathway in the KEGG pathway analysis in the comparison of stages C and D). We predicted lncRNA–mRNA, miRNA–mRNA, and lncRNA–miRNA regulatory relationships and constructed interactive networks using Cytoscape software. Co-expression networks show that most lncRNAs interact with one or two predicted miRNAs involved in muscle growth and development. These results provide a basis for further study of the function of lncRNAs on skeletal muscle in different developmental stages of Japanese flounder. [ABSTRACT FROM AUTHOR]

Many genes related to muscle growth modulate myoblast proliferation and differentiation and promote muscle hypertrophy. MyoD is a myogenic determinant that contributes to myoblast determination, and insulin-like growth factor 1 (IGF-I) interacts with MyoD to regulate muscle hypertrophy and muscle mass. In this study, we aimed to assess DNA methylation and mRNA expression patterns of MyoD and IGF-I during different developmental stages of Japanese flounder, and to examine the relationship between MyoD and IGF-I gene. DNA and RNA were extracted from muscles, and DNA methylation of MyoD and IGF-I promoter and exons was detected by bisulfite sequencing. The relative expression of MyoD and IGF-I was measured by quantitative polymerase chain reaction. IGF-I was measured by radioimmunoassay. Interestingly, the lowest expression of MyoD and IGF-I emerged at larva stage, and the mRNA expression was negatively associated with methylation. We hypothesized that many skeletal muscle were required to complete metamorphosis; thus, the expression levels of MyoD and IGF-I genes increased from larva stage and then decreased. The relative expression levels of MyoD and IGF-I exhibited similar patterns, suggesting that MyoD and IGF-I regulated muscle growth through combined effects. Changes in the concentrations of IGF-I hormone were similar to those of IGF-I gene expression. Our results the mechanism through which MyoD and IGF-I regulate muscle development and demonstrated that MyoD interacted with IGF-I to regulate muscle growth during different developmental stages. [ABSTRACT FROM AUTHOR]

• The methylation and expression of myomaker was assessed in Paralichthys olivaceus. • Myomaker expression increased throughout postnatal development. • Methylation was negatively correlated with myomaker expression. • Myomaker is likely a key myoblast fusion and muscle formation gene in P. olivaceus. Myomaker is a membrane protein that plays a crucial role in the fusion of myoblasts during muscle growth. DNA methylation, a significant factor, regulates gene expression. The aim of this study was to examine the methylation and mRNA expression patterns of the myomaker gene during 8 different postnatal developmental stages in the Japanese flounder (L: 7 days post hatch (dph); M1: 21 dph; M2: 28 dph; M3: 35 dph; J1: 90 dph; J2: 180 dph; A1: 24 months; A2: 36 months). Muscle tissue samples were taken from Japanese flounder at different postnatal development stages to measure the extent of DNA methylation and gene expression. Methylation level in the promoter and exon 1 of myomaker was measured using bisulfite sequencing, and the relative expression of myomaker during each developmental stage was measured by quantitative PCR. The relative expression levels of myomaker were up-regulated from stages L to M2, M3 to J2, and methylation of myomaker was negatively correlated with mRNA expression. Furthermore, the CpG site located at −26 bp in the promoter was the lowest methylated region in all developmental stages. These results offer a basis for understanding the mechanism by which myomaker regulates muscle formation during postnatal development. [ABSTRACT FROM AUTHOR]