A 5'-flanking region of embryonic-type myosin heavy chain gene, MYHM743-2, from torafugu Takifugu rubripes regulates developmental muscle-specific expression

The myosin heavy chain gene, MYHM743-2, is highly expressed in fast muscle fibers of torafugu embryos. However, the regulatory mechanisms involved in its expression have been unclear. In this study, we examined spatio-temporal expression patterns of this gene during development by injecting expression vectors containing the GFP reporter gene fused to the 5'-flanking region of MYHM743-2 into fertilized eggs of zebrafish and medaka. Although the -2.1 kb 5'-flanking region of torafugu MYHM743-2 showed no homology with the corresponding regions of zebrafish and medaka orthologous genes on the rVISTA analysis, the torafugu 5'-flanking region activated the GFP expression which was detected in the myotomal compartment for both zebrafish and medaka embryos. The GFP expression was localized to fast and slow muscle fibers in larvae as revealed by immunohistochemical analysis. In addition to the above tissues, GFP was also expressed in jaw, eye and pectoral fin muscles in embryos and larvae. These results clearly demonstrated that the 2.1 kb 5'-flanking region of MYHM743-2 contains essential cis-regulatory sequences for myogenesis that are conserved among torafugu, zebrafish and medaka.