Establishment of the epaxial-hypaxial boundary in the avian myotome

M. Ahmed, L. Cheng, Susanne Dietrich

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Trunk skeletal muscles are segregated into dorsomedial epaxial and ventrolateral hypaxial muscles, separated by a myoseptum. In amniotes, they are generated from a transient structure, the dermomyotome, which lays down muscle, namely the myotome underneath. However, the dermomyotome and myotome are dorsoventrally continuous, with no morphologically defined epaxial-hypaxial boundary. The transcription factors En1 and Sim1 have been shown to molecularly subdivide the amniote dermomyotome, with En1 labeling the epaxial dermomyotome and Sim1 the hypaxial counterpart. Here, we demonstrate that En1 and Sim1 expression persists in cells leaving the dermomyotome, superimposing the expression boundary onto muscle and skin. En1-expressing cells colonize the myotome initially from the rostral and caudal lips, and slightly later, directly from the de-epithelializing dermomyotomal center. En1 expression in the myotome is concomitant with the appearance of Fgfr4/Pax7-expressing mitotically active myoblasts. This finding suggests that Fgfr4+/Pax7+/En1+ cells carry their expression with them when entering the myotome. Furthermore, it suggests that the epaxial-hypaxial boundary of the myotome is established through the late arising, mitotically active myoblasts.
Original languageEnglish
Pages (from-to)1884-94
Number of pages11
JournalDevelopmental Dynamics
Issue number7
Publication statusPublished - Jul 2006


  • Animals
  • Basic Helix-Loop-Helix Transcription
  • Factors/metabolism
  • Body Patterning
  • Cell Differentiation
  • Cell Lineage
  • Chick Embryo
  • Homeodomain Proteins/metabolism
  • *Muscle Development
  • Muscle
  • Skeletal/*embryology/metabolism
  • Myoblasts/cytology/metabolism
  • PAX7 Transcription
  • Factor/metabolism
  • Repressor Proteins/metabolism
  • Somites/cytology/metabolism


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