Single-cell mass cytometry analysis reveals stem cell heterogeneity.

Cellular heterogeneity is fundamental to both developmental differentiation and disease establishment. Recent advances in high-throughput single-cell technology have been rapidly revolutionizing the resolution of our understanding of development and disease. However, while the study of single-cell transcriptomes is easily accessible, the analysis of single-cell proteomes is still in its infancy. In this study, we describe simultaneous profiling of multiple regulatory proteins at a single-cell level using mass cytometry or cytometry by time of flight. We develop mass cytometry reagents to study key transcription factors, signaling proteins and chromatin modifiers that regulate mouse embryonic stem cells. Our data reveal that the protein level of stem cell regulators significantly varies and that cell signaling pathways are extensively cross-activated across defined culture conditions of embryonic stem cells. In addition, the mass cytometry data enabled us to identify distinct multiple cell states of embryonic stem cells and determine their variation across culture conditions. We discuss the mass cytometry method, our results of the multi-protein analysis in embryonic stem cells and potential future perspectives for single-cell protein analysis.