Reg1 and Reg3 are essential for early stage lymphopoiesis in a cell-intrinsic manner. (A-F) Competitive FL transplantation. (A) Experimental workflow of competitive transplantation using FL cells (E15.5). (B-C) Relative frequencies and cell numbers of donor immune cells in the peripheral blood. (B) Each dot represents the ratio of the percentage of CD45.2 in each population to the percentage of CD45.2 in SLAM⁺ Lin^–Sca1⁺Kit⁺ (LSK) from recipient mice. Donor B cells, T cells, and myeloid cells were defined as CD45.2⁺ B220⁺CD19⁺ cells, CD4/8⁺TCRβ⁺ cells, and CD11b⁺ cells, respectively. (D) Representative flow cytometric plots of CD45.1 and CD45.2 expression gated on CD150⁺ LSK, LMPP (Flt3^hiLSK), CLP (Ly6D^–Flt3⁺IL-7Rα⁺Sca1^dullKit^dull), and BLP (Ly6D⁺Flt3⁺IL-7Rα⁺Sca1^dullKit^dull). Numbers in plots indicate the percentage of CD45.1⁺ or CD45.2⁺ cells. (E-F) Relative frequencies of each population in the BM. Each dot represents the ratio of the percentage of CD45.2 in each population to the percentage of CD45.2 in CD150⁺ LSK from recipient mice. (G-H) in vivo BrdU incorporation and annexin V staining in CD150⁺ LSK, CD150^– LSK, Flt3⁺ MPP, CLP, CMP, GMP, and MEP in the BM of mice competitively transplanted with FL cells, as in panel A. (E-F) Data are a composite of 3 independent experiments. (G-H) Data are representative from 3 independent experiments. Data are presented as mean ± standard deviation (SD) (B-C,E-H). Statistical significance was calculated by unpaired 2-tailed Student t test (B-C,E-H). BrdU, Bromodeoxyuridine; BLP, B-cell-biased lymphoid progenitor; CLP, common lymphoid progenitor; CMP, granulocyte-monocyte progenitor; GMP, granulocyte-monocyte progenitor; MEP, megakaryocyte–erythroid progenitor; LMPP, lymphoid primed multipotent progenitor; ns, not significant.