Hand2 Is an Essential Regulator for Two Notch-Dependent Functions within the Embryonic Endocardium

Nathan J Vandusen,Jose Casanovas,Joshua W Vincentz,Beth A Firulli,Marco Osterwalder,Javier Lopez-Rios,Rolf Zeller,Bin Zhou,Joaquim Grego-Bessa,José Luis De La Pompa,Weinian Shou,Anthony B Firulli

doi:10.1016/j.celrep.2014.11.021

Abstract

The basic-helix-loop-helix (bHLH) transcription factor Hand2 plays critical roles during cardiac morphogenesis via expression and function within myocardial, neural crest, and epicardial cell populations. Here, we show that Hand2 plays two essential Notch-dependent roles within the endocardium. Endocardial ablation of Hand2 results in failure to develop a patent tricuspid valve, intraventricular septum defects, and hypotrabeculated ventricles, which collectively resemble the human congenital defect tricuspid atresia. We show endocardial Hand2 to be an integral downstream component of a Notch endocardium-to-myocardium signaling pathway and a direct transcriptional regulator of Neuregulin1. Additionally, Hand2 participates in endocardium-to-endocardium-based cell signaling, with Hand2 mutant hearts displaying an increased density of coronary lumens. Molecular analyses further reveal dysregulation of several crucial components of Vegf signaling, including VegfA, VegfR2, Nrp1, and VegfR3. Thus, Hand2 functions as a crucial downstream transcriptional effector of endocardial Notch signaling during both cardiogenesis and coronary vasculogenesis.

Highlights

In the primitive heart, communication between the endocardium, which is the endothelium-like tissue that lines the heart, and the myocardium, which is the muscular heart tissue, is essential for processes central to normal cardiac morphogenesis, including trabeculation, chamber septation, and coronary vasculogenesis (Bruneau, 2003; Brutsaert, 2003)
Hand2 functions as a crucial downstream transcriptional effector of endocardial Notch signaling during both cardiogenesis and coronary vasculogenesis
Our data reveal that either endothelial or endocardialspecific deletion of Hand2 (H2CKO) using either Tie2-Cre or Nfatc1Cre, respectively, results in Tricuspid atresia (TA). These data show that Hand2 functions downstream of endocardial Notch to mediate endocardium-to-myocardium signaling via direct transcriptional regulation of the growth factor Neuregulin1 (Nrg1)

Summary

Introduction

Communication between the endocardium, which is the endothelium-like tissue that lines the heart, and the myocardium, which is the muscular heart tissue, is essential for processes central to normal cardiac morphogenesis, including trabeculation, chamber septation, and coronary vasculogenesis (Bruneau, 2003; Brutsaert, 2003). Conditional ablation of the basic-helix-loop-helix (bHLH) factor Hand within the second heart field (SHF) via Mef2c-Cre results in TA (Tsuchihashi et al, 2011). Mef2c-Cre marks a pool of SHF progenitor cells that contribute to both the myocardium and endocardium (Tsuchihashi et al, 2011; Verzi et al, 2005), and SHF ablation of Hand causes TA via unknown mechanisms. Our data reveal that either endothelial or endocardialspecific deletion of Hand (H2CKO) using either Tie2-Cre or Nfatc1Cre, respectively, results in TA. These data show that Hand functions downstream of endocardial Notch to mediate endocardium-to-myocardium signaling via direct transcriptional regulation of the growth factor Neuregulin (Nrg1)

Results

Discussion

Conclusion