Oncogenic effect of deleting floxed Notch1 sequences from a single allele. (A) Survival curves of Ik^L/LNotch1^+/Δf (IN1^+/Δf) and Ik^L/LNotch1^+/+ (IN1^+/+) mice. The statistical significance was calculated by log-rank test. (B) Western blot of ICN1 expression in IN1^+/Δf tumors. The control sample is the IRC⁺ T99 tumor shown in Figure 1C, which expresses ICN1 proteins of normal size. α-Tubulin was used as a loading control. (C) Strategy to identify the allele harboring the PEST domain mutation. A single nucleotide polymorphism in exon 26 (rs27201809; Mouse Genome Informatics database) distinguishes the WT and deleted alleles, which are derived from the C57Bl/6 and 129/Sv strains, respectively. RT-PCR amplification and sequencing of exon 26 and the PEST region in exon 34 identifies the allele carrying the mutation. (D) Association of PEST region mutations with the N1^Δf allele in the 3 tumors shown in B. T3 had a single nt insertion. T7a had a duplication of 19 nt (in bold and italic). T123 had 2 separate mutations, both in the N1^Δf allele: a deletion of 6 nt, which were replaced by a single T, and a single nt insertion. Numbering according to the Notch1 reference sequence NM_008714.