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In the early vertebrate embryo, cardiac progenitor/precursor cells (CPs) give rise to cardiac structures. Better understanding their biological character is critical to understand the heart development and to apply CPs for the clinical arena. However, our knowledge remains incomplete. With the use of single-cell expression profiling, we have now revealed rapid and dynamic changes in gene expression profiles of the embryonic CPs during the early phase after their segregation from the cardiac mesoderm. Progressively, the nascent mesodermal gene Mesp1 terminated, and Nkx2-5+/Tbx5+ population rapidly replaced the Tbx5low+ population as the expression of the cardiac genes Tbx5 and Nkx2-5 increased. At the Early Headfold stage, Tbx5-expressing CPs gradually showed a unique molecular signature with signs of cardiomyocyte differentiation. Lineage-tracing revealed a developmentally distinct characteristic of this population. They underwent progressive differentiation only towards the cardiomyocyte lineage corresponding to the first heart field rather than being maintained as a progenitor pool. More importantly, Tbx5 likely plays an important role in a transcriptional network to regulate the distinct character of the FHF via a positive feedback loop to activate the robust expression of Tbx5 in CPs. These data expands our knowledge on the behavior of CPs during the early phase of cardiac development, subsequently providing a platform for further study. [ABSTRACT FROM AUTHOR]

The endocardium is the endothelial component of the vertebrate heart and plays a key role in heart development. Where, when, and how the endocardium segregates during embryogenesis have remained largely unknown, however. We now show that Nkx2-5+ cardiac progenitor cells (CPCs) that express the Sry-type HMG box gene Sox17 from embryonic day (E) 7.5 to E8.5 specifically differentiate into the endocardium in mouse embryos. Although Sox17 is not essential or sufficient for endocardium fate, it can bias the fate of CPCs toward the endocardium. On the other hand, Sox17 expression in the endocardium is required for heart development. Deletion of Sox17 specifically in the mesoderm markedly impaired endocardium development with regard to cell proliferation and behavior. The proliferation of cardiomyocytes, ventricular trabeculation, and myocardium thickening were also impaired in a non-cell-autonomous manner in the Sox17 mutant, likely as a consequence of down-regulation of NOTCH signaling. An unknown signal, regulated by Sox17 and required for nurturing of the myocardium, is responsible for the reduction in NOTCH-related genes in the mutant embryos. Our results thus provide insight into differentiation of the endocardium and its role in heart development. [ABSTRACT FROM AUTHOR]

The abundance of retinoic acid (RA) is determined by the balance between its synthesis by retinaldehyde dehydrogenase (RALDH) and its degradation by CYP26. In particular, the dynamic expression of three CYP26 genes controls the regional level of RA within the body. Pregastrulation mouse embryos express CYP26 but not RALDH. We now show that mice lacking all three CYP26 genes manifest duplication of the body axis as a result of expansion of the Nodal expression domain throughout the epiblast. Mouse Nodal was found to contain an RA-responsive element in intron 1 that is highly conserved among mammals. In the absence of CYP26, maternally derived RA activates Nodal expression in the entire epiblast of pregastrulation embryos via this element. These observations suggest that maternal RA must be removed by embryonic CYP26 for correct Nodal expression during embryonic patterning. [ABSTRACT FROM AUTHOR]

Abstract: Left–right (L–R) asymmetry in the mouse embryo is generated in the node and is dependent on cilia-driven fluid flow, but how the initial asymmetry is transmitted from the node to the lateral plate has remained unknown. We have now identified a transcriptional enhancer (ANE) in the human LEFTY1 gene that exhibits marked L>R asymmetric activity in perinodal cells of the mouse embryo. Dissection of ANE revealed that it is activated in the perinodal cells on the left side by Nodal signaling, suggesting that Nodal activity in the node is asymmetric at a time when Nodal expression is symmetric. Phosphorylated Smad2/3 (pSmad2) indeed manifested an L–R asymmetric distribution at the node, being detected in perinodal cells preferentially on the left side. This asymmetry in pSmad2 distribution was found to be generated not by unidirectional transport of Nodal but rather as a result of LR distribution of active Nodal in the node is translated into the asymmetry in LPM. [Copyright &y& Elsevier]

Summary: The bilateral symmetry of the mouse embryo is broken by leftward fluid flow in the node. However, it is unclear how this directional flow is then translated into the robust, left side-specific Nodal gene expression that determines and coordinates left-right situs throughout the embryo. While manipulating Nodal and Lefty gene expression, we have observed phenomena that are indicative of the involvement of a self-enhancement and lateral-inhibition (SELI) system. We constructed a mathematical SELI model that not only simulates, but also predicts, experimental data. As predicted by the model, Nodal expression initiates even on the right side. These results indicate that directional flow represents an initial small difference between the left and right sides of the embryo, but is insufficient to determine embryonic situs. Nodal and Lefty are deployed as a SELI system required to amplify this initial bias and convert it into robust asymmetry. [Copyright &y& Elsevier]

Background: Biomarkers for selecting human induced pluripotent stem cell (hiPSC) lines with high differentiation capacity into cardiomyocytes are required for drug screening and regenerative therapy, but existing pluripotency markers such as Oct-4, Lin28 and Nanog cannot distinguish their differentiation directivity. We hypothesized that hiPSCs with high cardiomyogenic potential can be predicted by gene expression analysis of undifferentiated hiPS cells. Objective: The present study aims to investigate the biomarker to predict cardiogenicity of individual hiPSC lines by comparing differential gene expression profiles in undifferentiated hiPSC lines with high and low cardiomyogenesis differentiation potential. Methods and Results: We comprehensively analyzed gene expression in six undifferentiated hiPSCs using the cap analysis gene expression (CAGE) method, GeneChip array and microRNA array to screen biomarkers related to cardiac differentiation. Subsequently, we subjected all hiPSC lines to cardiac differentiation. The differentiation capacity was quantified based on the percentage of cardiac troponin T-positive cell populations using flow cytometry and cardiac-related genes using quantitative polymerase chain reaction (qPCR). We observed that the difference in purity of cardiac troponin T among different hiPSC lines ranged from 7.7% ± 2.6% in RIKEN-12A to 92.3% ± 1.2% in 409B2. Similarly, the hiPSC lines in the high differentiation group expressed TNT2 and Nkx2.5 at >20- and >50-fold higher levels, respectively, compared with cardiomyocyetes derived from hiPSC lines with low differentiation potential. Differential global gene expression within the undifferentiated hiPSCs revealed 22 distinguishing candidate genes among hiPSC lines with cardiac propensity. Next, we verified the utility of biomarker candidate genes in the differentiation of 13 additional hiPSC lines. Finally, global gene profiling and validation showed that CXCL4 was positively correlated with cardiac differentiation propensity. Conclusions: hiPSCs with high cardiomyogenic potential were marked by higher expression levels of CXCL4 in the undifferentiated state, suggesting that these genes may be used as a biomarker for the selection of hiPSCs appropriate for the manufacture of cardiomyocytes. [ABSTRACT FROM AUTHOR]