Uracil excision by endogenous SMUG1 glycosylase promotes efficient Ig class switching and impacts on A:T substitutions during somatic mutation

来自 EBSCO

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作者：

FA Dingler，K Kemmerich，MS Neuberger，C Rada

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摘要：

Excision of uracil introduced into the immunoglobulin loci by AID is central to antibody diversification. While predominantly carried out by the UNG uracil-DNA glycosylase as reflected by deficiency in immunoglobulin class switching in Ung/ mice, the deficiency is incomplete, as evidenced by the emergence of switched IgG in the serum of Ung/ mice. Lack of switching in mice deficient in both UNG and MSH2 suggested that mismatch repair initiated a backup pathway. We now show that most of the residual class switching in Ung/ mice depends upon the endogenous SMUG1 uracil-DNA glycosylase, with in vitro switching to IgG1 as well as serum IgG3, IgG2b, and IgA greatly diminished in Ung/Smug1/ mice, and that Smug1 partially compensates for Ung deficiency over time. Nonetheless, using a highly MSH2-dependent mechanism, Ung/Smug1/ mice can still produce detectable levels of switched isotypes, especially IgG1. While not affecting the pattern of base substitutions, SMUG1 deficiency in an Ung/ background further reduces somatic hypermutation at A:T base pairs. Our data reveal an essential requirement for uracil excision in class switching and in facilitating noncanonical mismatch repair for the A:T phase of hypermutation presumably by creating nicks near the U:G lesion recognized by MSH2.

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关键词：

Class switching DNA deamination Somatic hypermutation Uracil

DOI：

10.1002/eji.201444482

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年份：

2014