Mutational analyses of lymphocyte differentiation.

The site-specific recombination mechanism responsible for the assembly of antigen receptor variable region genes is only employed in lymphocyte development. Gene-targeted and other types of mutational analyses have implicated at least seven distinct gene products, some lymphoid-specific and others more generally expressed, as involved in aspects of this process. Mutation of the lymphocyte-specific activities required for VDJ recombination or mutation of the target gene segments of this process have created B and/or T cell-deficient mouse models that have provided new insights into the regulation of the VDJ recombination reaction and into how the successful achievement of this reaction at various loci helps lead lymphocytes through their early developmental program A second type of B lymphocyte-specific recombination process is involved in heavy-chain class switching; gene-targeted mutation approaches also have provided new insights into the cis-acting elements that target of this reaction to particular CH genes.