Enhanced colony-forming ability of Rce1-deficient K-RAS^G12D–expressing hematopoietic cells. (A) Spleen weights of Rce1^fl/flK^LSLM mice (▪) and Rce1^fl/+K^LSLM mice (□) 3 and 5 weeks after pI-pC injections (n = 6 and n = 11 for Rce1^fl/flK^LSLM mice and n = 5 and n = 8 for Rce1^fl/+K^LSLM mice at 3 and 5 weeks, respectively). Dashed line indicates spleen weights of wild-type mice (4 ± 0.9 mg/g body weight; n =6). (B-C) Growth factor–independent colony growth of splenocytes from Rce1^fl/flK^LSLM (n = 3) and Rce1^fl/+K^LSLM (n = 3) mice. (B) Colony number. (C) Colony size. (D) Growth factor–independent colony growth of bone marrow cells (n = 2). (E, top) Photographs showing Rce1^Δ/ΔK^G12DM and Rce1^Δ/+K^G12DM splenocyte colonies from a typical experiment in panels B and C (magnification: 20×/0.30 NA objective lens). (Bottom) May-Grünwald-Giemsa–stained cytospins of individual colonies (magnification: 63×/1.40 NA objective lens). (F) PCR amplification of genomic DNA from individual colonies to detect the Rce1^fl and Rce1⁺ alleles (top) and the Kras2⁺ and Kras2^G12D alleles (bottom). Lane 1, Rce1-deficient Kras2^G12D colony; lane 2, heterozygous Rce1-deficient Kras2^G12D colony; lanes 3-4, control DNA from mouse tails. The same result was found in 5 additional colonies from spleens of Rce1^fl/flK^LSLM and Rce1^fl/+K^LSLM mice.