part of part of develops_from embryo heart endocardial cushion (Cardiac valve formation in vertebrates) In response to a myocardial signal, endocardial cells at chamber boundaries take on a mesenchymal character, delaminate and migrate into the cardiac jelly. There, they form an endocardial cushion that is later remodelled into a valve.[well established][VHOG] AV cushion EHDAA2:0000434 EHDAA2:0004028 EHDAA:2586 EMAPA:16696 FMA:70302 GO graph seems to suggest this is an endothelium. WP: The endocardial cushions are thought to arise from a subset of endothelial cells that undergo epithelial to mesenchymal transformation, a process whereby these cells break cell-to-cell contacts and migrate into the cardiac jelly (towards to interior of the heart tube). Latest (2010-06-01) new def suggested for GO, added above. Note that EHDAA2 has a more detailed model which we may later adopt. JB: Patterning makes the cushions lay down connective tissue in three domains that force out the local endothelial lining and so the leaflets form MA:0000078 Swellings of tissue present between the endocardial and myocardial cell layers that will give rise to the interstitial cells of the cardiac valves.[TAO] TAO:0001317 The endocardial cushion is a specialized region of mesenchymal cells that will give rise to the heart septa and valves[GO]. Swellings of tissue present between the endocardial and myocardial cell layers that will give rise to the interstitial cells of the cardiac valves[ZFA]. UBERON:0002062 VHOG:0000932 XAO:0004189 ZFA:0001317 atrioventricular canal cushion atrioventricular cushion cardiac cushion endocardial cushion tissue endocardial cushions relationship loss: develops_from endocardial ring (TAO:0005072)[TAO] uberon endocardium neural crest trunk mesenchyme cardiac mesenchyme mesenchyme derived from neural crest