Cell-to-cell heterogeneity in gene expression is a widespread phenomenon, and may play important roles in cellular differentiation, function and disease development. Human Cell Atlas aims to profile gene expression in every single human cells. Recent studies have implicated a potential role of chromatin in the heterogeneity in gene expression. Understanding the mechanisms of cellular heterogeneity requires simultaneous measurement of RNA and occupancy of histone modifications and transcription factors on chromatin due to their critical roles in transcriptional regulation. However, methods for simultaneous profiling of chromatin occupancy and RNA in the same single cell are not available currently. Scientists at the National Heart, Lung, and Blood Institute have developed a technique, called scPCORseq (single-cell Profiling of Chromatin Occupancy and RNAs Sequencing), for simultaneously profiling genome-wide chromatin protein binding or histone modification marks and RNA expression in the same cell.