The expression of multiple myosin heavy chain genes during skeletal muscle development of torafugu Takifugu rubripes embryos and larvae

In vertebrates, the development-dependent and tissue-specific expression of myosin heavy chain (MYH) genes (MYHs) contributes to the formation of diverged muscle fiber types. The expression patterns of developmentally regulated MYHs have been investigated in certain species of fish. However, the expression profiles of MYHs during torafugu Takifugu rubripes development, although extensively studied in adult tissues, have not been sufficiently studied, and also the expression orders of MYHs during development have remained unclear. In the present study, we comprehensively cloned four MYHs (MYHM743-2, MYHM86-2, MYHM5 and MYHM2126-1) from embryos, and two MYHs (MYHM2528-1 and MYHM1034) from larvae, and characterized their expression pattern in relation to developmental stages of torafugu by reverse transcription (RT)-PCR and in situ hybridization. The expression of MYHs from torafugu embryos and larvae appeared sequentially and varied largely in relation to the developmental stage-dependent and fibers-type-specific manners. The transcripts of MYHM743-2 appeared first in embryos at 3 days post fertilization (dpf) and were localized in the epaxial and hypaxial domains of fast muscle fibers of larval myotome, whereas those of MYHM5 and MYHM86-2 in 3 dpf and 4 dpf, respectively, and both were localized in superficial slow and horizontal myoseptum regions. The expression of MYHM1034 and MYHM2126-1 was quite low and mostly undetectable. Different MYHs from torafugu embryos and larvae have also been found to be expressed differentially in pectoral fin and craniofacial muscles. Interestingly, the transcripts of MYHM2528-1 first appeared at 6 dpf and were distinctly expressed at the dorsal and ventral extremes of larval myotome, suggesting its involvement in stratified hyperplasia. The novel involvement of MYHM2528-1 in mosaic hyperplasia was further confirmed in juvenile torafugu, where the transcripts were expressed in fast fibers with small diameters as well as the inner part of superficial slow fibers.

► Multiple myosin heavy chain genes (MYHs) are expressed during torafugu development.
► The expression of MYHs from torafugu embryos and larvae appeared sequentially.
► These MYHs showed strictly regulated spatial and temporal expression pattern.
► We confirmed the novel involvement of MYHM2528-1 in muscle hyperplasia