Enforced expression of activated Notch1 or Myc partially rescued the DN-DP transition defect following Zmiz1 deprivation. (A) Schematic cartoon showing the DN3 cell rescue experiments using the OP9-DL1 culture assay. Murine stem cell virus–based retroviral vectors contain complementary DNA (cDNA) of genes cloned 5′ to the internal ribosome entry site (IRES) sequence followed by the nerve growth factor receptor (NGFR) marker. OP9-DL1 cells are green fluorescent protein positive (GFP⁺). (B-G) Representative CD4/CD8 flow cytometry plots (B,E), absolute total cell number counts (C,F), and DP (CD4⁺CD8⁺) cell counts (D,G) of transduced cells after 6 days of culture in the OP9-DL1 assay described in panel A. Cells counts are shown for 1000 seeded NGFR⁺ DN3 cells. One-way analysis of variance (ANOVA) on log2-transformed values. **P < .01; ****P < .0001.