title: Evolution of the immunoglobulin heavy chain class switch recombination mechanism.
abstract: To mount an optimum immune response, mature B lymphocytes can change the class of expressed antibody from IgM to IgG, IgA, or IgE through a recombination/deletion process termed immunoglobulin heavy chain (IgH) class switch recombination (CSR). CSR requires the activation-induced cytidine deaminase (AID), which has been shown to employ single-stranded DNA as a substrate in vitro. IgH CSR occurs within and requires large, repetitive sequences, termed S regions, which are parts of germ line transcription units (termed "C(H) genes") that are composed of promoters, S regions, and individual IgH constant region exons. CSR requires and is directed by germ line transcription of participating C(H) genes prior to CSR. AID deamination of cytidines in S regions appears to lead to S region double-stranded breaks (DSBs) required to initiate CSR. Joining of two broken S regions to complete CSR exploits the activities of general DNA DSB repair mechanisms. In this chapter, we discuss our current knowledge of the function of S regions, germ line transcription, AID, and DNA repair in CSR. We present a model for CSR in which transcription through S regions provides DNA substrates on which AID can generate DSB-inducing lesions. We also discuss how phosphorylation of AID may mediate interactions with cofactors that facilitate access to transcribed S regions during CSR and transcribed variable regions during the related process of somatic hypermutation (SHM). Finally, in the context of this CSR model, we further discuss current findings that suggest synapsis and joining of S region DSBs during CSR have evolved to exploit general mechanisms that function to join widely separated chromosomal DSBs.
authors.affiliation: Immunology Program, Memorial Sloan Kettering Cancer Center, New York, New York, USA.
authors.forename: Jayanta
authors.initials: J
authors.lastname: Chaudhuri
authors.forename: Uttiya
authors.initials: U
authors.lastname: Basu
authors.forename: Ali
authors.initials: A
authors.lastname: Zarrin
authors.forename: Catherine
authors.initials: C
authors.lastname: Yan
authors.forename: Sonia
authors.initials: S
authors.lastname: Franco
authors.forename: Thomas
authors.initials: T
authors.lastname: Perlot
authors.forename: Bao
authors.initials: B
authors.lastname: Vuong
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.forename: Ryan T
authors.initials: RT
authors.lastname: Phan
authors.forename: Abhishek
authors.initials: A
authors.lastname: Datta
authors.forename: John
authors.initials: J
authors.lastname: Manis
authors.forename: Frederick W
authors.initials: FW
authors.lastname: Alt
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology; D005075:Biological Evolution; D003564:Cytidine Deaminase / Q000502:physiology*; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D006801:Humans; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D027041:Somatic Hypermutation, Immunoglobulin / Q000235:genetics*; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D007143:Immunoglobulin Heavy Chains; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase