AID alternative splicing is conserved among vertebrates. (A) Alignment of the AICDA exon organization of human (Homo sapiens), chimpanzee (P troglodytes), cattle (B taurus), mouse (M musculus), chicken (G gallus), and zebrafish (D rerio). (B) Murine B-cell AID alternative splicing. Agarose gel image of AID RT-PCR performed using mouse lymph node (LN) and spleen (SP) B cells.