Gna13 deletion results in expansion of GC B cells, reduced apoptosis, and increased SHM-related mutational burden. (A) Bar graph comparing the GC populations across genotypes in splenic cells isolated from 2-month-old AID-Cre⁺Gna13 mice. GC cells were calculated as a percentage of total B cells (B220⁺ cells). Data are representative of 3 experiments. Fluorescence-activated cell sorting analysis of active caspase-3 (B) and 5-bromo-2′-deoxyuridine (BrdU) (C) in B cells isolated from spleen of 3-month-old AID-Cre⁺Gna13 mice. In each graph, GC cells are depicted on the left, with FO cells on the right as a control. Dots represent individual mice. Data are representative of 3 experiments. (D) Representative histogram of pAKT (T308) expression in GC and FO B cells from spleen of AID-Cre⁺Gna13 cohort mice. Wild-type and null GC B cells are depicted by blue and red traces, respectively. (E) MFI for pAKT (T308) expression in AID-Cre⁺Gna13 cohort mice as measured by flow cytometry in spleen. Data are representative of 3 experiments. (F-G) SHM analysis of the J_H4 intronic region of the V_H immunoglobulin locus. Data are depicted as mutational frequency per base across an amplified segment of the J_H4 intronic region of GC B cells (F) and quantitated in bar-graph form (G), along with FO controls. WCRY/RGYW hotspot motifs are depicted with black triangles (F) and quantitated separately (G, right). Data reflect an average depth of ∼7500 reads per genotype from GC B cells and from FO B cells isolated from Peyer patches of wild-type or null AID-Cre⁺Gna13 animals.