A Notch-Dependent Transcriptional Hierarchy Promotes Mesenchymal Transdifferentiation in the Cardiac Cushion

作者：Chang Alex C Y; Garside Victoria C; Fournier Michele; Smrz Justin; Vrljicak Pavle; Umlandt Patricia; Fuller Megan; Robertson Gordon; Zhao Yongjun; Tam Angela; Jones Steven J M; Marra Marco A; Hoodless Pamela A; Karsan Aly^*

来源：Developmental Dynamics, 2014, 243(7): 894-905.

DOI：10.1002/DVDY.24127

• Notch
• EMT
• cardiac cushion

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.