• myosin heavy chain gene;
  • muscle development;
  • hedgehog signaling pathway;
  • muscle pioneer;
  • horizontal myoseptum;
  • engrailed;
  • adaxial cell;
  • medaka;
  • Oryzias latipes


We cloned three full-length cDNAs encoding myosin heavy chains (MYHs) previously found to be expressed in embryos or larvae of medaka Oryzias latipes. Based on cDNA sequence information, the three medaka MYH genes, mMYHemb1, mMYHL1 and mMYHL2, were localized on the chromosomes. In vivo promoter assay using the gene encoding green or red fluorescent protein and linked to the 5′-flanking region of mMYH demonstrated that the transcripts of fast-type mMYHemb1, first expressed in embryos but belonging to the adult type in phylogenetic analysis, were located in the horizontal myoseptum. On the other hand, embryonic fast-type mMYHL1 and mMYHL2 were expressed in the whole myotomes. Interestingly, cells expressing mMYHemb1 were localized together with engrailed, and cyclopamine, which blocks hedgehog signaling, inhibited mMYHemb1 expression as well as the formation of the horizontal myoseptum, suggesting that muscle pioneer cells express mMYHemb1 as a key protein in the formation of the horizontal myoseptum. Developmental Dynamics 239:1807–1817, 2010. © 2010 Wiley-Liss, Inc.