The epaxial-hypaxial subdivision of the avian somite

Dev Biol. 2004 Oct 15;274(2):348-69. doi: 10.1016/j.ydbio.2004.07.020.


In all jaw-bearing vertebrates, three-dimensional mobility relies on segregated, separately innervated epaxial and hypaxial skeletal muscles. In amniotes, these muscles form from the morphologically continuous dermomyotome and myotome, whose epaxial-hypaxial subdivision and hence the formation of distinct epaxial-hypaxial muscles is not understood. Here we show that En1 expression labels a central subdomain of the avian dermomyotome, medially abutting the expression domain of the lead-lateral or hypaxial marker Sim1. En1 expression is maintained when cells from the En1-positive dermomyotome enter the myotome and dermatome, thereby superimposing the En1-Sim1 expression boundary onto the developing musculature and dermis. En1 cells originate from the dorsomedial edge of the somite. Their development is under positive control by notochord and floor plate (Shh), dorsal neural tube (Wnt1) and surface ectoderm (Wnt1-like signalling activity) but negatively regulated by the lateral plate mesoderm (BMP4). This dependence on epaxial signals and suppression by hypaxial signals places En1 into the epaxial somitic programme. Consequently, the En1-Sim1 expression boundary marks the epaxial-hypaxial dermomyotomal or myotomal boundary. In cell aggregation assays, En1- and Sim1-expressing cells sort out, suggesting that the En1-Sim1 expression boundary may represent a true compartment boundary, foreshadowing the epaxial-hypaxial segregation of muscle.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Body Patterning*
  • Carbocyanines / metabolism
  • Cell Lineage
  • Chick Embryo* / anatomy & histology
  • Chick Embryo* / physiology
  • Chimera / anatomy & histology
  • Chimera / physiology
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Ectoderm / cytology
  • Ectoderm / physiology
  • Fluorescent Dyes / metabolism
  • Gene Expression Regulation, Developmental
  • Hedgehog Proteins
  • In Situ Hybridization
  • Mesoderm / cytology
  • Mesoderm / physiology
  • Muscle Development / physiology*
  • Muscle, Skeletal / cytology
  • Muscle, Skeletal / embryology*
  • Muscle, Skeletal / metabolism
  • Proto-Oncogene Proteins / metabolism
  • Quail / anatomy & histology
  • Quail / embryology
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Signal Transduction / physiology
  • Somites* / cytology
  • Somites* / physiology
  • Trans-Activators / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Wnt Proteins
  • Wnt1 Protein


  • Carbocyanines
  • DNA-Binding Proteins
  • Fluorescent Dyes
  • Hedgehog Proteins
  • Proto-Oncogene Proteins
  • Repressor Proteins
  • Trans-Activators
  • Transcription Factors
  • Wnt Proteins
  • Wnt1 Protein