title: Left-right lineage analysis of AV cushion tissue in normal and laterality defective Xenopus hearts.
abstract: The majority of complex congenital heart defects occur in individuals who are afflicted by laterality disease. We hypothesize that the prevalence of valvuloseptal defects in this population is due to defective left-right patterning of the embryonic atrioventricular (AV) canal cushions, which are the progenitor tissue for valve and septal structures in the mature heart. Using embryos of the frog Xenopus laevis, this hypothesis was tested by performing left-right lineage analysis of myocytes and cushion mesenchyme cells of the superior and inferior cushion regions of the AV canal. Lineage analyses were conducted in both wild-type and laterality mutant embryos experimentally induced by misexpression of ALK4, a type I TGF-beta receptor previously shown to modulate left-right axis determination in Xenopus. We find that abnormalities in overall amount and left-right cell lineage composition are present in a majority of ALK4-induced laterality mutant embryos and that much variation in the nature of these abnormalities exists in embryos that exhibit the same overall body situs. We propose that these two parameters of cushion tissue formation-amount and left-right lineage origin-are important for normal processes of valvuloseptal morphogenesis and that defective allocation of cells in the AV canal might be causatively linked to the high incidence of valvuloseptal defects associated with laterality disease.
authors.affiliation: Department of Cell and Developmental Biology and Anatomy, School of Medicine, University of South Carolina, Columbia, South Carolina, USA. ramsdell@musc.edu
authors.forename: Ann F
authors.initials: AF
authors.lastname: Ramsdell
authors.forename: Jayne M
authors.initials: JM
authors.lastname: Bernanke
authors.forename: John
authors.initials: J
authors.lastname: Johnson
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Trusk
mesh_terms: D029404:Activin Receptors / Q000235:genetics / Q000378:metabolism; D030201:Activin Receptors, Type I; D000818:Animals; D019521:Body Patterning / Q000235:genetics; D002454:Cell Differentiation; D019070:Cell Lineage; D004694:Endocardial Cushion Defects / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D005318:Fetal Heart / Q000196:embryology* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008648:Mesoderm / Q000166:cytology* / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D012857:Situs Inversus / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D012333:RNA, Messenger; D029867:Xenopus Proteins; D029404:Activin Receptors; D030201:Activin Receptors, Type I; C481805:acvr1b protein, Xenopus