Genetic analysis reveals an intrinsic property of the germinal center B cells to generate A:T mutations.
The immunoglobulin genes undergo a high frequency of point mutations at both C:G and A:T pairs in the germinal center (GC) B cells. This hypermutation process is initiated by the activation-induced cytidine deaminase (AID), which converts cytosine to uracil and generates a U:G lesion. Replication of this lesion, or its repair intermediate the abasic site, could introduce C:G mutations but the mechanisms leading to mutations at non-damaged A:T pairs remain elusive. Using a lacZ-transgenic system in which endogenous genome mutations can be detected with high sensitivity, we found that GC B cells exhibited a much higher ratio of A:T mutations as compared to naïve B, non-GC B, and cells of other tissues. This property does not require AID or active transcription of the target gene, and is dependent on DNA polymerase eta. These in vivo results demonstrate that GC B cells are unique in having an intrinsic propensity to generate A:T mutations during repair of endogenous DNA damage. These findings have important implications in understanding how AID, which can only target C:G base pairs, is able to induce the entire spectrum of mutations observed in immunoglobulin variable region genes in GC B cells.
Laboratory for Immune Diversity, Research Center for Allergy and Immunology, RIKEN Yokohama Institute, Tsurumi, Yokohama, Japan.
Rika
R
Ouchida
Akiko
A
Ukai
Hiromi
H
Mori
Kiyoko
K
Kawamura
Martijn E T
ME
Dollé
Masatoshi
M
Tagawa
Akemi
A
Sakamoto
Takeshi
T
Tokuhisa
Tadashi
T
Yokosuka
Takashi
T
Saito
Masayuki
M
Yokoi
Fumio
F
Hanaoka
Jan
J
Vijg
Ji-Yang
JY
Wang
D000225:Adenine / Q000737:chemistry*; D000818:Animals; D001402:B-Lymphocytes / Q000648:ultrastructure*; D001483:Base Sequence; D017931:DNA Primers; D051379:Mice; D017354:Point Mutation; D013941:Thymine / Q000737:chemistry*; D014158:Transcription, Genetic
D017931:DNA Primers; D000225:Adenine; D013941:Thymine