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Summary: To facilitate understanding of human cardiomyocyte (CM) subtype specification, and the study of ventricular CM biology in particular, we developed a broadly applicable strategy for enrichment of ventricular cardiomyocytes (VCMs) derived from human embryonic stem cells (hESCs). A bacterial artificial chromosome transgenic H9 hESC line in which GFP expression was driven by the human ventricular-specific myosin light chain 2 (MYL2) promoter was generated, and screened to identify cell-surface markers specific for MYL2-GFP-expressing VCMs. A CD77+/CD200− cell-surface signature facilitated isolation of >97% cardiac troponin I-positive cells from H9 hESC differentiation cultures, with 65% expressing MYL2-GFP. This study provides a tool for VCM enrichment when using some, but not all, human pluripotent stem cell lines. Tools generated in this study can be utilized toward understanding CM subtype specification, and enriching for VCMs for therapeutic applications. : In this article, Evans and colleagues generated an H9 BAC transgenic reporter cell line and performed a flow cytometry screen to identify a cell-surface signature specific for MYL2-GFP-expressing VCMs. The cell-surface signature, CD77+/CD200−, facilitated isolation of a nearly pure hESC-derived CM population, enriched for VCMs. VCM enrichment was achieved when using some, but not all, human pluripotent stem cell lines. Tools generated in this study serve to advance our understanding of CM subtype specification, commitment, and maturation. Keywords: cardiac differentiation, human embryonic stem cells, ventricular cardiomyocytes, cell-surface marker signature

Summary: Large-scale collections of induced pluripotent stem cells (iPSCs) could serve as powerful model systems for examining how genetic variation affects biology and disease. Here we describe the iPSCORE resource: a collection of systematically derived and characterized iPSC lines from 222 ethnically diverse individuals that allows for both familial and association-based genetic studies. iPSCORE lines are pluripotent with high genomic integrity (no or low numbers of somatic copy-number variants) as determined using high-throughput RNA-sequencing and genotyping arrays, respectively. Using iPSCs from a family of individuals, we show that iPSC-derived cardiomyocytes demonstrate gene expression patterns that cluster by genetic background, and can be used to examine variants associated with physiological and disease phenotypes. The iPSCORE collection contains representative individuals for risk and non-risk alleles for 95% of SNPs associated with human phenotypes through genome-wide association studies. Our study demonstrates the utility of iPSCORE for examining how genetic variants influence molecular and physiological traits in iPSCs and derived cell lines. : Working as part of the NHLBI NextGen consortium, Panopoulos and colleagues report the derivation and characterization of 222 publicly available iPSCs from ethnically diverse individuals with corresponding genomic data including SNP arrays, RNA-seq, and whole-genome sequencing. This collection provides a powerful resource to investigate the function of genetic variants. Keywords: iPSCORE, iPSC, GWAS, molecular traits, physiological traits, cardiac disease, NHLBI Next Gen, LQT2, KCNH2, iPSC-derived cardiomyocytes