title: A Notch-dependent transcriptional hierarchy promotes mesenchymal transdifferentiation in the cardiac cushion.
abstract: BACKGROUND
  Valvuloseptal defects are the most common congenital heart defects. Notch signaling-induced endothelial-to-mesenchymal transition (EMT) in the atrioventricular canal (AVC) cushions at murine embryonic day (E)9.5 is a required step during early valve development. Insights to the transcriptional network that is activated in endocardial cells (EC) during EMT and how these pathways direct valve maturation are lacking.
  
  
  RESULTS
  We show that at E11.5, AVC-EC retain the ability to undergo Notch-dependent EMT when explanted on collagen. EC-Notch inhibition at E10.5 blocks expression of known mesenchymal genes in E11.5 AVC-EC. To understand the genetic network and AVC development downstream of Notch signaling beyond E9.5, we constructed Tag-Seq libraries corresponding to different cell types of the E11.5 AVC and atrium in wild-type mice and in EC-Notch inhibited mice. We identified 1,400 potential Notch targets in the AVC-EC, of which 124 are transcription factors (TF). From the 124 TFs, we constructed a transcriptional hierarchy and identify 10 upstream TFs within the network.
  
  
  CONCLUSIONS
  We validated 4 of the upstream TFs as Notch targets that are enriched in AVC-EC. Functionally, we show these 4 TFs regulate EMT in AVC explant assays. These novel signaling pathways downstream of Notch are potentially relevant to valve development.
authors.affiliation: Michael Smith Genome Sciences Centre, British Columbia Cancer Agency, Vancouver, Canada.
authors.forename: Alex C Y
authors.initials: AC
authors.lastname: Chang
authors.forename: Victoria C
authors.initials: VC
authors.lastname: Garside
authors.forename: Michele
authors.initials: M
authors.lastname: Fournier
authors.forename: Justin
authors.initials: J
authors.lastname: Smrz
authors.forename: Pavle
authors.initials: P
authors.lastname: Vrljicak
authors.forename: Patricia
authors.initials: P
authors.lastname: Umlandt
authors.forename: Megan
authors.initials: M
authors.lastname: Fuller
authors.forename: Gordon
authors.initials: G
authors.lastname: Robertson
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Zhao
authors.forename: Angela
authors.initials: A
authors.lastname: Tam
authors.forename: Steven J M
authors.initials: SJ
authors.lastname: Jones
authors.forename: Marco A
authors.initials: MA
authors.lastname: Marra
authors.forename: Pamela A
authors.initials: PA
authors.lastname: Hoodless
authors.forename: Aly
authors.initials: A
authors.lastname: Karsan
mesh_terms: D000818:Animals; D002460:Cell Line; D054338:Cell Transdifferentiation / Q000235:genetics* / Q000502:physiology; D054089:Endocardial Cushions / Q000196:embryology* / Q000378:metabolism*; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000235:genetics* / Q000502:physiology; D053263:Gene Regulatory Networks / Q000235:genetics* / Q000502:physiology; D006801:Humans; D008297:Male; D051379:Mice; D011247:Pregnancy; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism*
chemical_list: D051880:Receptors, Notch
keywords: EMT; Notch; cardiac cushion