RBP-J deletion delays T-ALL development. (A) Survival curves of Ik^L/LRBP-J^f/fCD4-Cre⁺ (IRC⁺) mice and Ik^L/LRBP-J^f/fCD4-Cre⁻ (IRC⁻) mice. The statistical significance was calculated by log-rank test. Note that the 2 IRC⁺ mice killed at 52 weeks did not show signs of disease. (B) Thymocyte CD4/CD8 profiles as determined by flow cytometry (top) and photos of the thoracic cavity (bottom) from 18-week-old IRC⁺ and IRC⁻ mice and a 7-week-old WT mouse. (C) Western blot of RBP-J and ICN1 (Val1744 antibody) expression in a panel of thymic tumors from IRC⁺ mice. Control samples are an IRC⁻ tumor and sorted CD4⁺CD8⁺ (DP) cells from 4-week-old IRC⁺ and WT mice. α-Tubulin was used as a loading control. The variable sizes of the ICN1 proteins are likely due to C-terminal truncations. Note that the deletion of the RBP-J floxed sequences effectively leads to loss of RBP-J proteins in nontransformed IRC⁺ DP cells. (D) PCR analysis of the deletion of the floxed sequences in the samples shown in C. The left panel shows amplification of control samples consisting of mixes of DNA from IRC⁺ and IRC⁻ thymocytes, at the indicated ratio. (E) CD4/CD8 profiles of samples shown in panel C, except for T22 where the FACS profile was not available.