Emergence of Il7R⍺⁺expressing YS progenitors in E9.5 embryos. (A) Schematic representation of the anatomical sites analyzed in mouse embryos: YS, head, FL and the AGM region. (B) Representative flow cytometry plot showing YFP expression on live Lin⁻CD117⁺CD41⁺ E9.5 YS cells from Il7r^creROSA26^LSLYFP. (C) Number and percentage of YFP⁺ per YS (mean plus or minus SEM). Data representative of 14 embryos from 4 independent experiments. (D) Representative flow cytometry plot showing YFP expression on live Lin⁻CD117⁺ E9.5 placenta and AGM region cells. (E) Expression of CD115, CD127, CD135, CD16/32, and CD31 within the E9.5 YS Lin⁻CD117⁺CD41⁺ YFP⁺ and YFP⁻ populations. (F) Experimental strategy for single-cell lineage potential assay of E9.5 YS Lin⁻CD117⁺CD41⁺ YFP⁺ and YFP⁻ populations. Frequency of wells containing (G) B cells or (H) T cells in cultures of single-sorted E9.5 YS Lin⁻CD117⁺CD41⁺ YFP⁺ and YFP⁻ cells (180 cells from each population analyzed in 3 independent experiments). (I) Frequency of erythroid and megakaryocytic (E/Mk), myeloid (GM), or mixed E/Mk/GM colonies of single-sorted E9.5 YS Lin⁻CD117⁺CD41⁺ YFP⁺ and YFP⁻ cells. (J) Frequency of thymic lobes irradiated and reconstituted with CD117⁺ E9.5 YS YFP⁺ or YFP⁻, or with E12.5 LSK or E10.5 YS as controls that contained CD4/CD8 DP cells (left plot) or TCR-Vγ5⁺ T cells (right plot). FTOCs were analyzed at day 12 after reconstitution.