Defective thymocyte development in Cdk6 mutant mice. (A) Gross picture of thymi from the mutant mice and littermates. Images were acquired with Leica MZFL III dissection microscope at 2× magnification fitted with a SPOT RT KE/SE camera from Diagnostic Instruments Inc. SPOT software Version 4.1 for Macintosh was used for image production. (B) Total number of thymocytes from 1- to 3-month-old mice. The cell numbers are mean ± SE (n = 15 for WT and KO, n = 13 for R31C, n = 6 for K43M, and n = 17 for WT-Δ and DM). *P < .05, significantly different from the control levels. (C-D) Flow cytometric profiles of thymocytes from 2-month-old mice after staining with CD4 and CD8 antibodies. The percentage of cells in each quadrant is shown.