Multiple transcription factors mediating the expressional regulation of myosin heavy chain gene involved in the indeterminate muscle growth of fish.

Torafugu myosin heavy chain gene, MYH, is specifically expressed in neonatal slow and fast muscle fibers, suggesting its functional role in indeterminate muscle growth in fish. However, the transcriptional regulatory mechanisms of MYH involved in indeterminate muscle growth in fish remained unknown. We previously isolated a 2100 bp 5'- flanking sequence of torafugu MYH that showed sufficient promoter activity to allow specific gene expression in neonatal muscle fibers of zebrafish. Here, we examined the cis-regulatory mechanism of 2100 bp 5'-flanking region of torafugu MYH using deletion-mutation analysis in zebrafish embryo. We discovered that myoblast determining factor (MyoD) binding elements play a key role and participate in the transcriptional regulation of MYH expression in zebrafish embryos. We further discovered that paired box protein (Pax3) are required for promoting MYH expression and myocyte enhancer factor-2 (MEF2) binding sites participate in the transcriptional regulation of MYH expression in slow/fast skeletal muscles. Our study also confirmed that the nuclear factor of activated T-cell (NFAT) binding sites take part in the transcriptional regulation of MYH expression in slow and fast muscles fiber in relation to indeterminate muscle growth. These results obviously confirmed that multiple cis-elements in the 5'-flanking region of MYH function in the transcriptional regulation of its expression.