Characterization of B-cell lymphomas arising from AID-Cre⁺R26Stop^FLMYC Gna13–deficient mice. (A) Photograph of spleens and mesenteric lymph nodes from representative MYC⁺Gna13 genotypes. (B) Comparison of the weights of spleens and mesenteric lymph nodes (LN) from MYC⁻Gna13 wild-type (n = 2) mice and MYC⁺Gna13 wild-type (n = 4), heterozygous (n = 5 for spleen, 4 for mesenteric), and null (n = 4) mice. (C) Graph of GC B-cell and total B-cell populations in AID-Cre⁺MYC⁺Gna13 mice across genotypes. (D) Immunohistochemical staining of proliferation marker Ki67 (top row) or immunofluorescent staining of GC marker GL7 (bottom row) in FFPE sections of mouse lymph node from AID-Cre⁺MYC⁺Gna13 mice. (E) Tumor clonality as determined by IgH rearrangement patterns. Southern blot analysis was performed using a heavy-chain joining-region probe to detect changes in fragment patterns in EcoRI digested genomic DNA extracted from mouse tissue. The arrow indicates the 6.5-kb germ-line DNA fragment present in wild-type mouse tail DNA, and its presence in all samples reflects the relative contribution of non-B cells to a given sample. Tg, transgenic.