Antisense transcripts from immunoglobulin heavy-chain locus V(D)J and switch regions.
Activation-induced cytosine deaminase (AID) is essential for both somatic hypermutation (SHM) and class switch recombination (CSR), two processes involved in antibody diversification. Previously, various groups showed both in vitro and in vivo that AID initiates SHM and CSR by deaminating cytosines in DNA in a transcription-dependent manner. Although in vivo both DNA strands are equally targeted by AID, many in vitro and bacterial experiments found that AID almost exclusively targets the nontemplate strand of a transcribed substrate. Here, we report the detection of antisense transcripts in assembled Ig heavy chain (IgH) variable region exons and their immediate downstream region, as well as in switch regions, sequences that, respectively, are targets for SHM and CSR in vivo. In contrast, we did not detect antisense transcripts from the Cmu constant region exons, which lie between the IgH variable region exons and downstream S regions and which are not normally an AID target. Expression of the antisense variable region/flanking region and the S-region transcripts were found in all lymphocytes that transcribe these sequences in the sense direction. Steady-state levels of antisense transcripts appeared very low, and start sites potentially appeared heterogeneous. We discuss the potential implications of antisense IgH locus transcription for AID targeting or other processes.
Perlot
Thomas
T
The Howard Hughes Medical Institute, The Children's Hospital, Immune Disease Institute, and Department of Genetics, Harvard Medical School, 1 Blackfan Circle, Boston, MA 02115, USA.
Li
Gang
G
Alt
Frederick W
FW
D000818:Animals; D001483:Base Sequence; D005786:Gene Expression Regulation; D050438:Genes, Immunoglobulin Heavy Chain; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007135:Immunoglobulin Variable Region / Q000235:genetics; D007438:Introns / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D016372:RNA, Antisense / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D024363:Transcription Initiation Site; D014158:Transcription, Genetic; D050441:VDJ Exons / Q000235:genetics*
D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; D016372:RNA, Antisense; D012333:RNA, Messenger