Differential regulation of myosin heavy chains defines new muscle domains in the zebrafish

Numerous muscle lineages are formed during myogenesis, both within the slow- and the fast specific cell groups. In this study, we show that six fast muscle specific myosin heavy chain genes have unique expression patterns in the zebrafish embryo. The expression of a tail specific myosin heavy chain (fmyhc2.1), requires wnt signaling and is essential for the fast muscle organisation within the tail. Retinoic acid treatment results in reduced wnt signaling, which leads to loss of the fmyhc2.1 domain. Retinoic acid treatment also results in a shift of muscle identity within two trunk domains defined by the expression of fmyhc1.2 and fmyhc1.3, in favor for the anteriormost myosin isoform fmyhc1.2. In summary, we have identified new muscle domains along the anteroposterior axis in the zebrafish, which are defined by their individual non-overlapping differentially regulated expression of myosin heavy chain isoforms.