Expression of AID transgene is regulated in activated B cells but not in resting B cells and kidney.
Activation-induced DNA cytidine deaminase (AID) is required for somatic hypermutation (SHM) and efficient class switch recombination (CSR) of immunoglobulin (Ig) genes. We created AID-transgenic mice that express AID ubiquitously under the control of a beta-actin promoter. When crossed with AID-/- mice, the AID-transgenic,AID-/- mice carried out SHM and CSR, showing that the AID transgenes were functional. However, the frequencies of SHM in V- and switch-regions, and CSR were reduced compared to those in a wild type AID background. Several criteria suggested that the inefficiency of SHM was due to reduced AID activity, rather than lack of recruiting error-prone DNA repair. High levels of AID mRNA were produced in resting B cells and kidney, cells that do not express AID in wild type mice. Compared with these cells, activated B cells expressed about an order of magnitude less AID mRNA suggesting that there may be a post-transcriptional mechanism that regulates AID mRNA levels in professional AID producers but not other cells. The AID protein expressed in resting B cells and kidney was phosphorylated at serine-38. Despite this modification, known to enhance AID activity, resting B cells did not undergo SHM. Apparently, the large amounts of AID in resting B cells are not targeted to Ig genes in vivo, in contrast to findings in vitro.
Shen
Hong Ming
HM
Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
Bozek
Grazyna
G
Pinkert
Carl A
CA
McBride
Kevin
K
Wang
Lili
L
Kenter
Amy
A
Storb
Ursula
U
D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology* / Q000201:enzymology*; D003564:Cytidine Deaminase / Q000235:genetics*; D005434:Flow Cytometry; D015971:Gene Expression Regulation, Enzymologic; D017578:Immunoglobulin Class Switching / Q000276:immunology; D007668:Kidney / Q000201:enzymology*; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D027041:Somatic Hypermutation, Immunoglobulin / Q000276:immunology; D019076:Transgenes; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D018809:Proliferating Cell Nuclear Antigen; D012333:RNA, Messenger; D012694:Serine; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase