YS contains unipotent T-cell progenitors that can engraft in the NOG neonates. (A) E9.5 YS reconstituted only T cells in the recipient spleen and BM on transplantation. Most of CD3⁺ cells were TCRβ⁺. The representative FACS dot plots from a recipient mouse 9 months after transplantation are depicted. The number of mice that received a transplant is shown in supplemental Table 3. (B) RT-PCR was performed with E9.5 WT YS and P-Sp for Notch ligand. The expression of Notch signaling genes (B left panel) and of genes that are important for T lymphoid development (B right panel) are shown.