Species-specific expression variation of fish MYH14, an ancient vertebrate myosin heavy chain gene orthologue
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MYH14 (MYH7b) is the most recently identified sarcomeric myosin heavy chain gene (MYH) from the human genome. Recent observations have revealed that MYHM5, a torafugu orthologue of MYH14, is one of the major components of the MYH repertoire expressed in torafugu embryos and adults, suggesting its pivotal role in fish muscle formation. We have examined the expression pattern of MYH14 in zebrafish, a model organism for the study of vertebrate development. In situ hybridization studies revealed that zebrafish MYH14 was expressed in the most myotomal region containing fast muscle fibers in the embryonic stage and in superficial slow muscle fibers in the adult stage. Weak signals of MYH14 transcripts were also detected in intermediate muscle fibers located between superficial slow and inner fast muscle fibers in the adult. Reverse transcription-PCR studies showed that MYH14 was not only expressed in skeletal muscles but also in cardiac muscles. These expression patterns are in a marked contrast to that of torafugu MYHM5, which is solely expressed in slow and cardiac muscle fibers in both the embryonic and adult stages. Our results imply species-specific functions of MYH14 in fish muscle formation.