title: The dermomyotome ventrolateral lip is essential for the hypaxial myotome formation.
abstract: BACKGROUND
  The myotome is the primitive skeletal muscle that forms within the embryonic metameric body wall. It can be subdivided into an epaxial and hypaxial domain. It has been shown that the formation of the epaxial myotome requires the dorsomedial lip of the dermomyotome (DML). Although the ventrolateral lip (VLL) of the dermomyotome is believed to be required for the formation of the hypaxial myotome, experimentally evidence for this statement still needs to be provided. Provision of such data would enable the resolution of a debate regarding the formation of the hypaxial dermomyotome. Two mechanisms have been proposed for this tissue. The first proposes that the intermediate dermomyotome undergoes cellular expansion thereby pushing the ventral lateral lip in a lateral direction (translocation). In contrast, the alternative view holds that the ventral lateral lip grows laterally.
  
  
  RESULTS
  Using time lapse confocal microscopy, we observed that the GFP-labelled ventrolateral lip (VLL) of the dermomyotome grows rather than translocates in a lateral direction. The necessity of the VLL for lateral extension of the myotome was addressed by ablation studies. We found that the hypaxial myotome did not form after VLL ablation. In contrast, the removal of an intermediate portion of the dermomyotome had very little effect of the hypaxial myotome. These results demonstrate that the VLL is required for the formation of the hypaxial myotome.
  
  
  CONCLUSIONS
  Our study demonstrates that the dermomyotome ventrolateral lip is essential for the hypaxial myotome formation and supports the lip extension model. Therefore, despite being under independent signalling controls, both the dorsomedial and ventrolateral lip fulfil the same function, i.e. they extend into adjacent regions permitting the growth of the myotome.
authors.affiliation: Institute of Anatomy, Department of Neuroanatomy, Medical Faculty Bonn, Rheinish Friedrich-Wilhelms-University of Bonn, Bonn, Germany. pujinshuo@hotmail.com.
authors.forename: Qin
authors.initials: Q
authors.lastname: Pu
authors.forename: Aisha
authors.initials: A
authors.lastname: Abduelmula
authors.forename: Maryna
authors.initials: M
authors.lastname: Masyuk
authors.forename: Carsten
authors.initials: C
authors.lastname: Theiss
authors.forename: Dieter
authors.initials: D
authors.lastname: Schwandulla
authors.forename: Michael
authors.initials: M
authors.lastname: Hans
authors.forename: Ketan
authors.initials: K
authors.lastname: Patel
authors.forename: Beate
authors.initials: B
authors.lastname: Brand-Saberi
authors.forename: Ruijin
authors.initials: R
authors.lastname: Huang
mesh_terms: D000818:Animals; D002642:Chick Embryo; D047108:Embryonic Development; D004848:Epithelium / Q000196:embryology; D018613:Microscopy, Confocal; D018482:Muscle, Skeletal / Q000196:embryology*; D019170:Somites / Q000196:embryology*