Mutation frequencies and AID activation state in B-cell lymphomas from Ung-deficient mice

B-cell lymphomas arising in lymph nodes and spleen of aging mice deficient in the Ung DNA glycosylase were recovered, dispersed, grown in short-term culture, and CD19-positive B-cells retrieved and analysed. Several tumors as well as controls only expressed detectable amounts of the Aid deaminase after mitogenic stimulation, as estimated by real-time PCR of transcripts. However, one unusually large lymph node tumor expressed a high level of Aid constitutively. This particular tumor also showed a substantially increased mutation frequency in the Aid gene itself as well as in the bcl-6 and c-myc genes, but not in the p53 gene, consistent with aberrant somatic hypermutation. Other B-cell lymphomas from Ung(-/-) mice exhibited a modest increase in mutation frequency.