title: Mouse myotomes pairs exhibit left-right asymmetric expression of MLC3F and alpha-skeletal actin.
abstract: Most muscle originates from the myotomal compartment of the somites, paired structures flanking the neural tube. Whereas vertebrate embryos show molecular and morphological asymmetry about the left-right body axis, somitic myogenesis is thought to occur symmetrically. Here, we provide the first evidence that myotome pairs are transiently left-right asymmetric, with higher expression of alpha-skeletal actin and myosin light chain 3F (MLC3F) on the left side between embryonic day 9.5-10.25. In iv mutants with situs inversus, the asymmetric expression of alpha-skeletal actin and MLC3F was inverted, showing that this process is regulated by global left-right axis cues, initiated before gastrulation. However, although left-sided identity is later maintained by Pitx2 genes, we found that Pitx2c null embryos have normal left-biased expression of alpha-skeletal actin and MLC3F. Myotome asymmetry, therefore, is downstream of the iv mutation but upstream of, or unrelated to, the Pitx2c pathway.
authors.affiliation: Muscle Cell Biology Group, Medical Research Council Clinical Sciences Centre, London, United Kingdom. jon.golding@csc.mrc.ac.uk
authors.forename: Jon P
authors.initials: JP
authors.lastname: Golding
authors.forename: Terence A
authors.initials: TA
authors.lastname: Partridge
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Beauchamp
authors.forename: Tim
authors.initials: T
authors.lastname: King
authors.forename: Nigel A
authors.initials: NA
authors.lastname: Brown
authors.forename: Martin
authors.initials: M
authors.lastname: Gassmann
authors.forename: Peter S
authors.initials: PS
authors.lastname: Zammit
mesh_terms: D000199:Actins / Q000235:genetics*; D000818:Animals; D047108:Embryonic Development / Q000502:physiology*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D018482:Muscle, Skeletal / Q000196:embryology* / Q000502:physiology; D018994:Myosin Light Chains / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics; D011247:Pregnancy; D012857:Situs Inversus / Q000235:genetics / Q000503:physiopathology*; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2
chemical_list: D000199:Actins; D018398:Homeodomain Proteins; D018994:Myosin Light Chains; D009687:Nuclear Proteins; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2