Background-Induced pluripotent stem (iPS) cells are a novel stem cell population induced from mouse and human adult somatic cells through reprogramming by transduction of defined transcription factors. However, detailed differentiation properties and the directional differentiation system of iPS cells have not been demonstrated. Methods and Results-Previously, we established a novel mouse embryonic stem (ES) cell differentiation system that can reproduce the early differentiation processes of cardiovascular cells. We applied our ES cell system to iPS cells and examined directional differentiation of mouse iPS cells to cardiovascular cells. Flk1 (also designated as vascular endothelial growth factor receptor-2)-expressing mesoderm cells were induced from iPS cells after Ϸ4-day culture for differentiation. Purified Flk1 ϩ cells gave rise to endothelial cells and mural cells by addition of vascular endothelial growth factor and serum. Arterial, venous, and lymphatic endothelial cells were also successfully induced. Self-beating cardiomyocytes could be induced from Flk1 ϩ cells by culture on OP9 stroma cells. Time course and efficiency of the differentiation were comparable to those of mouse ES cells. Occasionally, reexpression of transgene mRNAs, including c-myc, was observed in long-term differentiation cultures. Conclusions-Various

RationaleHuman embryonic and induced pluripotent stem cells (hESCs/hiPSCs) are promising cell sources for cardiac regenerative medicine. To realize hESC/hiPSC-based cardiac cell therapy, efficient induction, purification, and transplantation methods for cardiomyocytes are required. Though marker gene transduction or fluorescent-based purification methods have been reported, fast, efficient and scalable purification methods with no genetic modification are essential for clinical purpose but have not yet been established. In this study, we attempted to identify cell surface markers for cardiomyocytes derived from hESC/hiPSCs.Method and ResultWe adopted a previously reported differentiation protocol for hESCs based on high density monolayer culture to hiPSCs with some modification. Cardiac troponin-T (TNNT2)-positive cardiomyocytes appeared robustly with 30–70% efficiency. Using this differentiation method, we screened 242 antibodies for human cell surface molecules to isolate cardiomyocytes derived from hiPSCs and identified anti-VCAM1 (Vascular cell adhesion molecule 1) antibody specifically marked cardiomyocytes. TNNT2-positive cells were detected at day 7–8 after induction and 80% of them became VCAM1-positive by day 11. Approximately 95–98% of VCAM1-positive cells at day 11 were positive for TNNT2. VCAM1 was exclusive with CD144 (endothelium), CD140b (pericytes) and TRA-1-60 (undifferentiated hESCs/hiPSCs). 95% of MACS-purified cells were positive for TNNT2. MACS purification yielded 5−10×105 VCAM1-positive cells from a single well of a six-well culture plate. Purified VCAM1-positive cells displayed molecular and functional features of cardiomyocytes. VCAM1 also specifically marked cardiomyocytes derived from other hESC or hiPSC lines.ConclusionWe succeeded in efficiently inducing cardiomyocytes from hESCs/hiPSCs and identifying VCAM1 as a potent cell surface marker for robust, efficient and scalable purification of cardiomyocytes from hESC/hiPSCs. These findings would offer a valuable technological basis for hESC/hiPSC-based cell therapy.

Notch is an ancient transmembrane receptor with critical roles in cell-fate choices. While the “canonical” Notch pathway and its core members are well established -- involving ligand-induced cleavage of Notch for transcriptional regulation -- it has been unclear whether Notch can also function independent of ligand and transcription (‘non-canonically’) through a common mechanism. Recent studies suggest that Notch can non-canonically exert its biological functions by posttranslationally targeting Wnt/β-catenin signaling, an important cellular and developmental regulator. The non-canonical Notch pathway appears to be highly conserved from flies to mammals. Here, we discuss the emerging conserved mechanism and role of ligand/transcription-independent Notch signaling in cell and developmental biology.

SUMMARY Decades of progress in developmental cardiology has advanced our understanding of the early aspects of heart development, including cardiomyocyte (CM) differentiation. However, control of CM maturation which is subsequently required to generate adult myocytes, remains elusive. Here, we analyzed over 200 microarray datasets from early embryonic to adult hearts and identified a large number of genes whose expression shifts gradually and continuously during maturation. We generated an atlas of integrated gene expression, biological pathways, transcriptional regulators, and gene regulatory networks (GRNs), which show discrete sets of key transcriptional regulators and pathways activated or suppressed during CM maturation. We developed a GRN-based program named MatStatCM that indexes CM maturation status. MatStatCM reveals that pluripotent stem cell-derived CMs mature early in culture, but are arrested at the late embryonic stage with aberrant regulation of key transcription factors. Our study provides a foundation for understanding CM maturation.