Constitutive activation of β-catenin affects T-cell development. (A) Flow cytometry analysis of T cells from R26-βcat and control mice stained with anti-CD4 and anti-CD8 antibodies. (B) Absolute numbers of DN, DP, CD4⁺, and CD8⁺ T cells in the thymus and spleen (mean ± standard deviation [SD], 6 mice per genotype). **P < .01, Student t test. (C-D) Phenotypic analysis (C) and absolute numbers (D) of DN1, DN2, DN3, and DN4 cells from R26-βcat and control mice (mean ± SD, 4 mice per genotype). **P < .01; *P < .05, Student t test. (E) Polymerase chain reaction (PCR) analysis of excision of the stop cassette in R26 locus from DN cells and tail of R26-βcat and control mice. Note that most of the DN1-like cells from the R26-βcat mice carry excised R26-βcat alleles. (F) Phenotypic analysis of thymocytes from control and R26-βcat mice 48 hours after sublethal irradiation (6.5 Gy) or 24 hours after intraperitoneal injection of 25 mg/kg dexamethasone (Dex). Data were obtained with 6-week-old mice and are representative of >3 independent experiments. (G) Frequency of apoptotic thymocytes (Annexin V⁺) 6 hours after Dex injection (mean ± SD, 4 mice per genotype). *P < .05, Student t test.