Myocardial Pitx2 Differentially Regulates the Left Atrial Identity and Ventricular Asymmetric Remodeling Programs

Abstract

Abstract-The Pitx2 gene regulates left-right (L/R) asymmetrical cardiac morphogenesis. Constitutive Pitx2 knock out (ko) mice die before birth and display, among other defects, right atrial isomerism, atrial and ventricular septal defects, and double outlet right ventricle. The myocardial role of the gene has not been dissected. In particular, how Pitx2 regulates the differential L/R cardiac identity program is not clear. Additionally, the relation between Pitx2 ko ventricular defects and the gene expression pattern is not understood. In this article we analyze Pitx2 myocardial function during mouse heart development. By in situ hybridization analysis we show that myocardial Pitx2 expression delineates the remodeling of the left atrioventricular canal, the inner curvature, the ventral part of the interventricular ring, and the ventral portion of the right and left ventricle. By genetic analysis using an allelic series of Pitx2 mutants, among which a myocardial specific ko (ko myo ) we show it has a crucial role in this process. Pitx2 ko myo mutants survive to adulthood, when they present strong cardiac morphological and functional defects.

Expression patterns and immunohistochemical localization of PITX2B transcription factor in the developing mouse heart

“…Overall, these findings indicate that during the developmental window comprising interventricular septum formation (E11.5-E15.5) (Miquerol et al, 2012) PITX2B positive cells displayed a dynamic distribution within this ventricular compartment. At E13.5, we found that a major proportion of PITX2B ventricular positive nuclei are located in the interventricular septum and these cells shift to minimal PITX2B expression at E15.5 when ventricular septation is fully completed (Miquerol et al, 2012).In addition, and based on recent reports that pointed out a possible participation of PITX2 in the development of atrioventricular (AV) canal (Tessari et al, 2008), we investigated whether PITX2B could be involved in AV canal formation by analysing the number of PITX2B positive cells in those structures. At stages E9.5 and E11.5 the proportion of PITX2B positive mesenchymal cells in AV cushions is clearly low, around 4% (Fig.…”

“…In addition, we cannot rule out the possibility that different PITX2 isoforms could be coexpressed in the same cardiac cells, according to the fact that different isoforms of PITX2 can act together forming homo and heterodimers leading to transcriptional synergism (Cox et al, 2002;Saadi et al, 2003). Current studies suggest that Pitx2-mediated signalling during cardiogenesis is conducted within three different cell types: the myocardium, the cardiac neural crest (CNC) cells, and the pharyngeal arch mesenchyme (Campione et al, 1999;Chinchilla et al, 2011; Franco et al, 2003;Kioussi et al, 2002;Liu et al, 2002;Tessari et al, 2008), minimizing the possible role that Pitx2 a, b or c, may have during development of epicardial and endocardial derivatives. In addition, it was previously reported only that Pitx2c expression is never detected in endocardium (Liu et al, 2002).…”

“…In addition, and based on recent reports that pointed out a possible participation of PITX2 in the development of atrioventricular (AV) canal (Tessari et al, 2008), we investigated whether PITX2B could be involved in AV canal formation by analysing the number of PITX2B positive cells in those structures. At stages E9.5 and E11.5 the proportion of PITX2B positive mesenchymal cells in AV cushions is clearly low, around 4% (Fig.…”

“…Notably, we reported here the presence of PITX2B in epicardium and endocardium during heart development, opening new putative roles for this gene during heart organogenesis. Concerning the possible role of Pitx2 in myocardium, Tessari et al, (Tessari et al, 2008) reported how myocardial Pitx2 expression delineates the remodelling of the left atrioventricular canal, contributing to atrio-ventricular septation. Interestingly our results show that in the atrioventricular canal compartment PITX2B protein is mainly present in the mural primordium of the mitral valve during heart development, suggesting a role of PITX2B in the maturation of the right portion of the atrioventricular canal.…”

Sequence variations of NKX2-5 and HAND1 genes in patients with atrial isomerism

“…Asymmetric distributions of secreted factors and asymmetric expression of transcription factors guide the asymmetric development of the organs in digestive, circulatory and respiratory systems. Nodal is one of these asymmetrically distributed secreted factors and Pitx2 is one of these asymmetrically expressed transcription factors (10,11). Some studies have demonstrated that human orthologue of the Nodal signaling genes, ACVR2B (12), LEFTYA (13) and CFC1 (14), were mutated in patients with heterotaxia.…”