Fetal BM PreProB-progenitors are molecularly distinct from ELPs and ProB-progenitors. (A) Bulk RNA-sequencing of 100 cells from each population (n = 3): PCA of each HSPC population using the top 500 most variably expressed genes. (B) Heat map summarizing differentially expressed genes (false discovery rate [FDR] <0.1) between fetal BM ELPs and PreProB-progenitors (292 differentially expressed genes) and PreProB-progenitors and ProB-progenitors (808 differentially expressed genes). Genes are detailed in supplemental Tables 5 and 6. (C) Log2-fold change of selected lymphoid and myeloid genes that are significantly differentially expressed between fetal BM ELPs and PreProB-progenitors. (D) Log2-fold change of selected lymphoid, myeloid, and stem cell genes that are significantly differentially expressed between fetal BM PreProB-progenitors and ProB-progenitors. (E) Differential chromatin accessibility analysis of ATAC-sequencing from PreProB-progenitors and ProB-progenitors summarized by using PCA and heat map. Details of differentially accessible genes are given in supplemental Table 7. (F) Using ATAC-sequencing, chromatin was more accessible around the promoter regions of genes differentially expressed between PreProB-progenitors and ProB-progenitors (P = .027; n = 2).