Global genome decompaction leads to stochastic activation of gene expression as a first step toward fate commitment in human hematopoietic cells [scRNA-seq]

When human cord blood derived CD34+ cells are induced to differentiate in vitro, they undergo rapid and dynamic morphological and molecular transformation that are critical for the fate commitment. Using ATAC-seq and single-cell RNA sequencing we detected two phases of this process. We show that a rapid and widespread chromatin opening - that makes most of the gene promoters in the genome accessible - precedes the high and unrestrained transcription of a large variety of genes. This phase results in a quasi-random gene expression profile unique to each cell. During the second phase, slow chromatin closing precedes the downregulation of transcription and the emergence of coherent expression profiles. Transcription factors may play a role in the maintenance of the transcription activity of their target genes rather than in their initial activation. These observations are consistent with a model based on the spontaneous probabilistic organization of the cellular process of fate commitment. Overall design: Evolution of single cell mRNA profile and DNA accessibility profile of HSC after cytokine stimulation