摘要：

Somatic hypermutation (SHM) and gene conversion (GCV) are two closely related processes that increase the diversity of the primary immunoglobulin (Ig) repertoire. Both processes are initiated by the activation-induced cytidine deaminase (AID) that converts cytosine residues to uracils in a transcription-dependent manner and processed by direct replication and error-prone DNA repair. It is unknown how this mutagenic activity is targeted almost exclusively to Ig loci. To identify cis-acting elements involved in targeting SHM and GCV to the chicken Ig light chain (IgL), we used DT40 cells and systematically deleted non-coding sequences from the IgL locus using standard gene targeting strategies. We identified a novel as of yet uncharacterized regulatory region (named 3′RR) in the chicken IgL gene, containing a classical transcriptional enhancer and also cis-acting DNA elements essential for targeting AID-mediated sequence diversification. We are continuing our systematic deletion strategy to identify the minimal sequence required for targeting and to determine the trans-acting factors that bind to it. To identify similar targeting elements in the murine Igκ locus, we use a cross-complementation approach replacing the 3′RR in DT40 cells with murine Igκ sequences. Previous mouse transgenic studies indicated that both iEκ and 3'Eκ were necessary for the SHM of Igκ transgenes, and we are currently testing the ability of these enhancers to restore SHM/GCV in the chicken locus.

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