Internal IgH class switch region deletions are position-independent and enhanced by AID expression.
Ig heavy chain class switch recombination (CSR) involves a recombination/deletion mechanism that exchanges the expressed C(H) gene with a downstream C(H) gene. CSR is mediated by highly repetitive switch (S) region sequences and requires the activation-induced deaminase (AID). The S region 5' of the C mu gene (S mu) can undergo high-frequency internal deletions in normal B cells and B cell lines activated for CSR, although the relationship of these deletions and CSR has not been elucidated. In this study, we introduced constitutively transcribed S mu or S gamma 2b regions into a pro-B cell line that can be activated for AID expression, CSR, and endogenous S mu deletions. We find that randomly integrated S region transcription units in these cells also undergo increased levels of internal rearrangements after cellular activation, indicating that the deletion process is independent of location within the Ig heavy chain locus and potentially AID-promoted. To test the latter issue, we generated hybridomas from wild-type and AID-deficient activated B cells and assayed them for internal S mu deletions and S region mutations. These studies demonstrated that efficient intra-S region recombination depends on AID expression and that internal S region deletions are accompanied by frequent mutations, indicating that most S region deletions occur by the same mechanism as CSR.
Howard Hughes Medical Institute, Children's Hospital, Department of Genetics, Harvard Medical School, and Center for Blood Research, Boston, MA 02115, USA.
Darryll D
DD
Dudley
John P
JP
Manis
Ali A
AA
Zarrin
Lianne
L
Kaylor
Ming
M
Tian
Frederick W
FW
Alt
D000483:Alleles; D001402:B-Lymphocytes / Q000276:immunology*; D001483:Base Sequence; D002478:Cells, Cultured; D003001:Cloning, Molecular; D003564:Cytidine Deaminase / Q000235:genetics* / Q000378:metabolism*; D017931:DNA Primers; D015321:Gene Rearrangement; D005803:Genes, Immunoglobulin; D006801:Humans; D006825:Hybridomas / Q000276:immunology; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007134:Immunoglobulin Switch Region / Q000235:genetics*; D008213:Lymphocyte Activation; D011994:Recombinant Proteins / Q000378:metabolism; D011995:Recombination, Genetic; D015183:Restriction Mapping; D017384:Sequence Deletion; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D017931:DNA Primers; D007143:Immunoglobulin Heavy Chains; D011994:Recombinant Proteins; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase