Reduction of Foxn1 levels reverses the enlarged thymus phenotype in Mx1-Cre p107-Single mice. (A) Thymic cellularity in control (Ctrl) and Rb family mutant (Mut) mice in the presence and in the absence of the Foxn1^LacZ allele (n = 3; P = 0.02). (B) Representative images of whole thymus explants (top) and of H&E-stained sections (bottom; n = 5) from mice in A. (C) Representative immunofluorescence analysis of Foxn1 and K5 expression in sections prepared from control and Rb family mutant mice in the presence and absence of the Foxn1^LacZ allele (n = 2). Bars: (B, top) 500 µm; (B, bottom) 200 µm; (C) 100 µm. (D) Analysis by RT-qPCR of Foxn1 message level in TECs from p107-single Foxn1 ^+/+, P107-single Foxn1^Lacz/Lacz, Mx1-Cre p107-single Foxn1^+/+, and Mx1-Cre p107-single Foxn1^LacZ/LacZ (n = 3, none pI:pC injected; P = 0.023). (E) Evaluation of E2F target and S-phase genes in control, Mx1-Cre p107-single, and Mx1-Cre p107-single Foxn1^LacZ/LacZ TECs (n = 3; 15 wk). Genes analyzed included E2f1 (P = 0.031), p107 (P = 0.008), PCNA (P = 0.02), bMyb (P = 0.01), Ezh2 (P = 0.12), and Mcm3 (P = 0.043). Asterisks indicate P < 0.05; ns indicates no significant difference. All error bars indicate standard error.