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

Dev Biol. 2011 Nov 15;359(2):303-20. doi: 10.1016/j.ydbio.2011.08.010. Epub 2011 Aug 22.


Adult skeletal muscles in vertebrates are composed of different types of myofibers endowed with distinct metabolic and contraction speed properties. Genesis of this fiber-type heterogeneity during development remains poorly known, at least in mammals. Six1 and Six4 homeoproteins of the Six/sine oculis family are expressed throughout muscle development in mice, and Six1 protein is enriched in the nuclei of adult fast-twitch myofibers. Furthermore, Six1/Six4 proteins are known to control the early activation of fast-type muscle genes in myocytes present in the mouse somitic myotome. Using double Six1:Six4 mutants (SixdKO) to dissect in vivo the genesis of muscle fiber-type heterogeneity, we analyzed here the phenotype of the dorsal/epaxial muscles remaining in SixdKO. We show by electron microscopy analysis that the absence of these homeoproteins precludes normal sarcomeric organization of the myofiber leading to a dystrophic aspect, and by immunohistochemistry experiments a deficiency in synaptogenesis. Affymetrix transcriptome analysis of the muscles remaining in E18.5 SixdKO identifies a major role for these homeoproteins in the control of genes that are specifically activated in the adult fast/glycolytic myofibers, particularly those controlling Ca(2+) homeostasis. Absence of Six1 and Six4 leads to the development of dorsal myofibers lacking expression of fast-type muscle genes, and mainly expressing a slow-type muscle program. The absence of restriction of the slow-type program during the fetal period in SixdKO back muscles is associated with a decreased HDAC4 protein level, and subcellular relocalization of the transcription repressor Sox6. Six genes thus behave as essential global regulators of muscle gene expression, as well as a central switch to drive the skeletal muscle fast phenotype during fetal development.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Blotting, Northern
  • Cells, Cultured
  • Drosophila Proteins / genetics*
  • Drosophila Proteins / metabolism
  • Embryo, Mammalian / embryology
  • Embryo, Mammalian / metabolism*
  • Embryo, Mammalian / ultrastructure
  • Embryonic Development / genetics
  • Gene Expression Regulation, Developmental
  • Homeodomain Proteins / genetics*
  • Homeodomain Proteins / metabolism
  • Immunohistochemistry
  • In Situ Hybridization
  • Mice
  • Mice, Knockout
  • Microscopy, Electron, Transmission
  • Muscle Development / genetics
  • Muscle Fibers, Fast-Twitch / metabolism
  • Muscle Fibers, Fast-Twitch / ultrastructure
  • Muscle Fibers, Skeletal / classification
  • Muscle Fibers, Skeletal / cytology
  • Muscle Fibers, Skeletal / metabolism*
  • Muscle Fibers, Slow-Twitch / metabolism
  • Muscle Fibers, Slow-Twitch / ultrastructure
  • Myofibrils / metabolism
  • Myofibrils / ultrastructure
  • Nerve Tissue Proteins / genetics*
  • Nerve Tissue Proteins / metabolism
  • Oligonucleotide Array Sequence Analysis
  • Time Factors
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism
  • Transcriptome


  • Drosophila Proteins
  • Homeodomain Proteins
  • Nerve Tissue Proteins
  • Six1 protein, mouse
  • Six4 protein, Drosophila
  • Transcription Factors