The thymic expansion in Rb family mutant mice does not originate from the hematopoietic compartment. (A) Control (Ctrl) and Mx1-Cre p107-Single (Mut) mice expressing the Ly5.1 surface marker were lethally irradiated and transplanted with BM from Ly5.1/Ly5.2 wild-type mice. (B) Thymic cellularity (×10⁸) of control and Mx1-Cre p107-Single chimeric mice (n = 5; P = 0.02). (C) Quantified (Ctrl: 95.23 ± 2.2% donor-derived; Mut: 97 ± 1.01% donor-derived; P = 0.19; n = 3). (D) Quantification of T cells in control and mutant chimeric mice (DN: Ctrl, 8.54 ± 2.44%; Mut, 11.88 ± 7.33% [P = 0.42]; DP: Ctrl, 80.68 ± 3.75%; Mut, 71.98 ± 5.87% [P = 0.046]; CD4⁺: Ctrl, 7.2 ± 1.26%; Mut, 10.74 ± 3.5% [P = 0.11]; CD8⁺: Ctrl, 3.59 ± 0.76%; Mut, 5.35 ± 1.87% [P = 0.13%]; n = 3). (E) PI analysis of cell cycle activity in control and mutant chimeric mice (G1: Ctrl, 80.65 ± 2.02%; Mut, 70.53 ± 1.13% [P = 0.0001]; S: Ctrl, 3.93 ± 0.16%; Mut, 5.00 ± 0.66% [P = 0.02]; G2: Ctrl, 15.30 ± 1.85%; Mut, 24.5 ± 5.40% [P = 0.0001]; n = 4). (F) Cytokine and receptor expression in thymic extracts from control and mutant mice after lethal irradiation and rescue with wild-type BM as assayed by RT-qPCR (p-values: Il7 = 0.41, Scf = 0.37, Fgfr2b = 0.58, Wnt4 = 0.97, and Dll4 = 0.64; n = 3). Asterisks indicate P < 0.05; ns indicates no significant difference. All error bars indicate standard error.