MyocardialNotch-Rbpjdeletion does not affect heart development or function

Abstract

23 24 25 2 26 Abstract 27 During vertebrate cardiac development NOTCH signaling activity in the endocardium is essential for the crosstalk 28 between endocardium and myocardium that initiates ventricular trabeculation and valve primordium formation.29 This crosstalk leads later to the maturation and compaction of the ventricular chambers and the morphogenesis of 30 the cardiac valves, and its alteration may lead to disease. Although endocardial NOTCH signaling has been shown 31 to be crucial for heart development, its physiological role in the myocardium has not been clearly established.32 Here we have used a genetic strategy to evaluate the role of NOTCH in myocardial development. We have 33 inactivated the unique and ubiquitous NOTCH effector RBPJ in the early cardiomyocytes progenitors, and 34 examined its consequences in cardiac development and function. Our results demonstrate that mice with cTnT-35 Cre-mediated myocardial-specific deletion of Rbpj develop to term, with homozygous mutant animals showing 36 normal expression of cardiac development markers, and normal adult heart function. Similar observations have 37 been obtained after Notch1 deletion with cTnT-Cre. We have also deleted Rbpj in both myocardial and endocardial 38 progenitor cells, using the Nkx2.5-Cre driver, resulting in ventricular septal defect (VSD), double outlet right 39 ventricle (DORV), and bicuspid aortic valve (BAV), due to NOTCH signaling abrogation in the endocardium of 40 cardiac valves territories. Our data demonstrate that NOTCH-RBPJ inactivation in the myocardium does not affect 41 heart development or adult cardiac function.42 43 44 3 45 Introduction 46 47 The heart is the first organ to form and function during vertebrate development. At embryonic day 7.0 (E7.0) in48 the mouse, cardiac progenitor cells, migrating from the primitive streak, reach the head folds on either side of the 49 midline (1) and by E8.0, fuse and form the primitive heart tube (2). The heart tube consists internally of the 50 endocardium, that is separated from the primitive myocardium by an extracellular matrix termed cardiac jelly (3). 51The NOTCH signaling pathway is crucial for the endocardial-myocardial interactions that regulate the patterning, 52 growth and differentiation of chamber and non-chamber tissues that will develop from E8.5 onwards (4-8). The 53 main components of the pathway are the single-pass transmembrane NOTCH receptors (NOTCH1-4 in mammals) 54 that interact with membrane-bound ligands of the JAGGED (JAG1 and JAG2) and DELTA families (DELTA 55 LIKE1, 3 and 4), expressed in neighboring cells (9, 10). Ligand-receptor interactions leads to three consecutive 56 cleavage events that generate the NOTCH intracellular domain (NICD), which can translocate to the nucleus of 57 the signaling-receiving cell (11). In the nucleus, NICD binds directly to the DNA-binding protein CSL 58 (CBF1/RBPJ/Su(H)/Lag1) (12) and recruits the co-activator Mastermind-like (13, 14). In the absence of N1ICD, 59 ubiquitously expressed RBPJ (recombination signal bi...