A cellular atlas of Pitx2-dependent cardiac development

Abstract

The Pitx2 gene encodes a homeobox transcription factor that is required for mammalian development. Disruption of PITX2 expression in humans causes congenital heart diseases and is associated with atrial fibrillation; however, the cellular and molecular processes dictated by Pitx2 during cardiac ontogeny remain unclear. To characterize the role of Pitx2 during murine heart development we sequenced over 75,000 single cardiac cell transcriptomes between two key developmental timepoints in control and Pitx2 null embryos. We found that cardiac cell composition was dramatically altered in mutants at both E10.5 and E13.5. Interestingly, the differentiation dynamics of both anterior and posterior second heart field-derived progenitor cells were disrupted in Pitx2 mutants. We also uncovered evidence for defects in left-right asymmetry within atrial cardiomyocyte populations. Furthermore, we were able to detail defects in cardiac outflow tract and valve development associated with Pitx2. Our findings offer insight into Pitx2 function and provide a compilation of gene expression signatures for further detailing the complexities of heart development that will serve as the foundation for future studies of cardiac morphogenesis, congenital heart disease and arrhythmogenesis.

Reduced left atrial cardiomyocyte PITX2 and elevated circulating BMP10 predict atrial fibrillation after ablation

“…Our results also confirm recent data from mouse atria indicating that cardiomyocytes are the major cell type expressing PITX2 in the adult left atrium ( 36 ). Furthermore, we found that approximately one-quarter of nuclei in human left atrium are cardiomyocyte, consistent with prior data in mice ( 36 ).…”

“…Our results provide the first evidence to our knowledge that low left atrial cardiomyocyte PITX2 levels contribute to recurrent AF after ablation in patients in whom left atrial tissue was collected at the time of AF ablation. Our results also confirm recent data from mouse atria indicating that cardiomyocytes are the major cell type expressing PITX2 in the adult left atrium (36). Furthermore, we found that approximately one-quarter of nuclei in human left atrium are cardiomyocyte, consistent with prior data in mice (36).…”

“…Our results also confirm recent data from mouse atria indicating that cardiomyocytes are the major cell type expressing PITX2 in the adult left atrium (36). Furthermore, we found that approximately one-quarter of nuclei in human left atrium are cardiomyocyte, consistent with prior data in mice (36). The marked variability in cardiomyocyte content of the left atrium, dependent, e.g., on the degree of atrial fibrosis and atrial fatty infiltration (Figure 2E), can explain why PITX2 concentrations in whole atrial tissue were not associated with recurrent AF.…”

“…These results suggest that a common repressor/enhancer transcriptional network may exist between Bmp10 and Pitx2 whereby the loss of one of these genes results in the reciprocal upregulation of the other ( 18 , 38 ). Such findings are plausible given that PITX2 is known to be a key regulator of “leftness” in the heart during development ( 36 , 39 ) and BMP10 is a right atrial gene ( 11 , 40 ). Additional features supported our selection of increased BMP10 plasma concentrations as a surrogate marker for reduced left atrial PITX2 .…”

Single cell analyses of development in the modern era

“…Putting these ideas into play, the research papers in this Special Issue demonstrate a range of single cell techniques and the discoveries that they enable. Two papers apply live imaging to demonstrate the role of a signal transduction pathway in differentiation (Deathridge et al, 2019) or to demonstrate stochasticity in fate choice (Antolovićet al, 2019); several papers build transcriptomic maps of specific developing tissues that will prove useful resources and reveal new hypotheses for developmental regulation (Combes et al, 2019;Martin et al, 2019;Hulin et al, 2019;Li et al, 2019a,b); several studies computationally reconstruct developmental dynamics (Bastidas-Ponce et al, 2019;Delile et al, 2019;Guo and Li, 2019;Prior et al, 2019;van Gurp et al, 2019); and one study benchmarks in vitro differentiation to in vivo development and develops new computational tools to do so (Edri et al, 2019). Taking a slightly different approach, other papers use single cell analyses to characterize cell behaviors during morphogenesis (Amini et al, 2019;Yang et al, 2019), to investigate how cells respond to DNA or tissue damage (Miermont et al, 2019;Dell'Orso et al, 2019), and to understand how heterogeneities in gene and protein concentration influence development (Papadopoulos et al, 2019;Reznik et al, 2019;Velte et al, 2019).…”