Genesis of muscle fiber-type diversity during mouse embryogenesis relies on Six1 and Six4 gene expression

► Genetic and embryologic origin of muscle fiber-type diversity remains unknown in mammals. ► We investigate the role of Six proteins in the genetic of muscle fiber-type diversity. ► We establish the gene network controlled by Six1/4 proteins in mouse E18 embryo. ► Six control crosstalk between slow and fast type determinant genes. ► Six are required for genesis of muscle fiber type diversity during embryogenesis.