(A) Expression of AID in shark spleen (black bar), thymus (hashed bar), and forebrain (gray bar) using real-time quantitative PCR. Expression was measured using the delta delta Cq method and are normalized against shark muscle tissue using β2M as a reference gene. Data represent expression fold-change differences at four cDNA concentrations. (B) In situ hybridization of mRNA using ribo-probes on adult shark thymus sections. 1,2: Two different fields probing for TcRβ antisense. 3,4: AID antisense. 5,6: TcRβ sense. 7,8: AID sense. All micrographs at 10X magnification; black scale bar in lower right of each panel is 100 uM. Anatomical structures are designated on the top panels [c: cortex; m: medulla; sc: subcapsular region; cmj: corticomedullary junction].