title: Impairment of endothelial-mesenchymal transformation during atrioventricular cushion formation in Tmem100 null embryos.
abstract: BACKGROUND
  Endothelial-mesenchymal transformation (EndMT) is essential for endocardial cushion formation during cardiac morphogenesis. We recently identified Tmem100 as an endothelial gene indispensable for vascular development. In this study, we further investigated its roles for EndMT during atrioventricular canal (AVC) cushion formation.
  
  
  RESULTS
  Tmem100 was expressed in AVC endocardial cells, and Tmem100 null embryos showed severe EndMT defect in the AVC cushions. While calcineurin-dependent suppression of vascular endothelial growth factor (VEGF) expression in the AVC myocardium is important for EndMT, significant up-regulation of Vegfa expression was observed in Tmem100 null heart. EndMT impaired in Tmem100 null AVC explants was partially but significantly restored by the expression of constitutively-active calcineurin A, suggesting dysregulation of myocardial calcineurin-VEGF signaling in Tmem100 null heart. Moreover, Tmem100 null endocardial cells in explant culture did not show EndMT in response to the treatment with myocardium-derived growth factors, transforming growth factor β2 and bone morphogenetic protein 2, indicating involvement of an additional endocardial-specific abnormality in the mechanism of EndMT defect. The lack of NFATc1 nuclear translocation in endocardial cells of Tmem100 null embryos suggests impairment of endocardial calcium signaling.
  
  
  CONCLUSIONS
  The Tmem100 deficiency causes EndMT defect during AVC cushion formation possibly via disturbance of multiple calcium-related signaling events.
authors.affiliation: Laboratory for Cardiovascular System Research, Nara Medical University Advanced Medical Research Center, Kashihara, Nara, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Mizuta
authors.forename: Masahide
authors.initials: M
authors.lastname: Sakabe
authors.forename: Aya
authors.initials: A
authors.lastname: Hashimoto
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ioka
authors.forename: Chihiro
authors.initials: C
authors.lastname: Sakai
authors.forename: Kazuki
authors.initials: K
authors.lastname: Okumura
authors.forename: Miwa
authors.initials: M
authors.lastname: Hattammaru
authors.forename: Masahide
authors.initials: M
authors.lastname: Fujita
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Araki
authors.forename: Satoshi
authors.initials: S
authors.lastname: Somekawa
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Saito
authors.forename: Osamu
authors.initials: O
authors.lastname: Nakagawa
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000235:genetics; D004622:Embryo, Mammalian / Q000378:metabolism*; D058750:Epithelial-Mesenchymal Transition; D018507:Gene Expression Regulation, Developmental; D006321:Heart / Q000196:embryology*; D006330:Heart Defects, Congenital / Q000196:embryology* / Q000235:genetics / Q000473:pathology; D008565:Membrane Proteins / Q000172:deficiency*; D051379:Mice; D008817:Mice, Mutant Strains; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; C556658:Tmem100 protein, mouse; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse
keywords: EndMT; NFATc1; cardiac development; endocardial cushion; mouse embryo; vascular endothelial growth factor