Single-cell data analysis
Cell Ranger (version 3.1.0) was used for raw data pre-processing. Each library was aligned to an indexed hg19 genome using Cell Ranger count. Output from Cell Ranger was loaded into R and further analyzed using the Seurat pipeline (version 3.1.2). Dimensional reduction, clustering and differential expression analysis of scRNA-seq data were performed with the R package Seurat (version 3.2.0)To determine differentiation trajectories for cells from all clusters, we used the R package Monocle 2 (ref. 