Blocking Notch1 or Notch2 negatively affects HSC development. (A) Both Notch1 and Notch2 are involved in HSC development in the E10.5 AGM region. E10.5 AGM were cultured as reaggregates for 5 days without cytokines in the presence of anti-NRR1 (10 μg/mL) or anti-NRR2 (10 μg/mL) antibodies before transplantation into irradiated mice (0.3 ee per recipient); n = 2, *P < .05, Mann-Whitney test. (B) Blocking Notch1 or Notch2 affects pre-HSC type II maturation. E11.5 pre-HSCs type II (VC⁺CD45⁺) were coaggregated with OP9 cells with cytokines and cultured for 5 days with anti-NRR1 (10 μg/mL) or anti-NRR2 (10 μg/mL) antibodies before transplantation (0.1 ee per recipient); n = 2, *P < .05, Mann-Whitney test. (C) Blocking Notch1 or Notch2 does not disrupt CFU-C development. The development of hematopoietic progenitors in the presence of Notch-blocking antibodies after 5 days in culture, in E10.5 AGM reaggregates was assessed by CFU-C assay. The number of hematopoietic progenitors per 1 ee and standard errors are shown (n = 2). GEMM, granulocyte-erythrocyte-macrophage-megakaryocyte.