Monitoring and interpreting the intrinsic features of somatic hypermutation.

We have used both normal and transgenic mice to analyse the recruitment and targeting of somatic hypermutation to the immunoglobulin loci. We compare methods for analysing hypermutation and discuss how large databases of mutations can be assembled by PCR amplification of the rearranged V-gene flanks from the germinal centre B cells of normal mice as well as by transgene-specific amplification from transgenic B cells. Such studies confirm that hypermutation is preferentially targeted to the immunoglobulin V gene with the bcl6 gene, for example, escaping this intense mutational targeting in germinal centre B cells. We review our data concerning the nature of the hypermutation domain and the targeting of hotspots within that domain. We consider how enhancer-mediated recruitment of hypermutation to the immunoglobulin loci operates in a clonally maintained fashion and illustrate how both the degree of expression and demethylation of the transgene broadly correlate with its mutability.