Thymic granulocyte development requires the Notch target gene Hes1. (A) Hes1 is expressed in the thymus, like another Notch target, Deltex1. Hes1 and Deltex1 expression in fetal liver are minimal. (B) The development of CD45.2⁺ thymic ETPs, granulocytes, and cDCs was examined in the absence of Hes1 in mixed fetal liver chimeras 8-10 weeks after reconstitution of lethally irradiated CD45.1⁺ hosts. (C) Mean percent CD45.2⁺ donor contribution to each intrathymic lineage by Hes1^+/+ (black bars) or Hes1^−/− (gray bars) fetal liver. Four mice per group were examined. ***P < .001 for the CD45.2⁺ donor chimerism of the indicated population compared with BM Lin⁻Sca1⁺Kit⁺ CD45.2⁺ donor chimerism. (D) The development of CD45.2⁺ BM Lin⁻Sca1⁺Kit⁺, splenic granulocytes, and cDCs was examined in the absence of Hes1 in mixed fetal liver chimeras 8-10 weeks after reconstitution of lethally irradiated CD45.1⁺ hosts. (E) Mean percentage CD45.2⁺ donor contribution to each lineage by Hes1^+/+ (black bars) or Hes1^−/− (gray bars) fetal liver. Four mice per group were examined. Error bars represent SEM.