Temporal pattern of expression of EMT molecular markers in the chicken embryo heart.

Abstract

In the atrioventricular canal (AVC) of the embryonic heart, endothelia undergo an epithelial‐mesenchymal transition (EMT) and migrate into the underlying extracellular matrix. EMT in this region is a multi‐step event, wherein TGFβ2 acts on the activation of endothelia while TGFβ3 acts on invasion. We explore here the temporal pattern of expression of several genes previously related to EMT in other models and the effect of TGFβ family members by qPCR. EMT in the chick heart becomes visible at stage 17 although signaling processes are known to occur as early as stage 14. We looked at transcription factors, intracellular proteins and secreted proteins. Starting at stage 14 in AVC tissues we saw 4 developmental patterns. One expression pattern was down at stage 16 and 20, but up at stage 18 (VE‐cadherin, β‐catenin, TβRIII). A second pattern showed downregulation at stage 16, 18 and 20 (α‐smooth‐muscle actin, fibrillin2 and sox11). A third pattern showed increased expression at each stage (sox8) or increased expression at stages 18 and 20 (periostin, collagen I, snail2). A few genes showed changes only at one specific stage. TβRII was down only at stage 16, runx2 was upregulated at stage 16 and collagen VI was upregulated only at stage 16. These data confirm EMT as a multi‐step event. Experiments are underway to explore the growth factor regulation of these markers in an in vitro culture system.