Switch recombination and somatic hypermutation are controlled by the heavy chain 3' enhancer region.
Both class switch recombination (CSR) and somatic hypermutation (SHM) require transcription and the trans-acting factor activation-induced cytidine deaminase (AID), and must be up-regulated during antigen-dependent differentiation of B lymphocytes. To test the role of the heavy chain 3' enhancers in both CSR and SHM, we used a BAC transgene of the entire heavy chain constant region locus. Using Cre-loxP recombination to delete a 28-kb region that contains the four known 3' heavy chain enhancers, we isolated lines of BAC transgenic mice with an intact heavy chain locus and paired lines in the same chromosomal insertion site lacking the 3' enhancers. Intact heavy chain transgenes undergo CSR to all heavy chain genes and mutate their transgenic VDJ exon. In paired transgenes lacking the 3' enhancer region, CSR to most heavy chain genes is reduced to approximately 1% of the levels for intact heavy chain loci; SHM is also reduced. Finally, we find that in B cells with a transgene lacking the 3' enhancers, interchromosomal recombination between the transgenic VDJ exon and the endogenous heavy chain C genes is more easily detected than CSR within the transgene.
Dunnick
Wesley A
WA
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48103, USA.
Collins
John T
JT
Shi
Jian
J
Westfield
Gerwin
G
Fontaine
Clinton
C
Hakimpour
Paul
P
Papavasiliou
F Nina
FN
D020413:3' Untranslated Regions / Q000502:physiology*; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D002645:Chickens; D003564:Cytidine Deaminase / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000502:physiology*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D019426:Integrases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D040641:Quantitative Trait Loci / Q000235:genetics; D011995:Recombination, Genetic / Q000502:physiology*; D017384:Sequence Deletion; D027041:Somatic Hypermutation, Immunoglobulin / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology; D019076:Transgenes / Q000502:physiology; D050441:VDJ Exons / Q000235:genetics
D020413:3' Untranslated Regions; D007143:Immunoglobulin Heavy Chains; C045073:Cre recombinase; D019426:Integrases; D003564:Cytidine Deaminase