Kappa light chain rearrangement in mouse fetal liver

Ig variable domains are generated by the recombination of V, D, and J segments (V(D)J rearrangement). V(D)J rearrangement is capable of generating a vast repertoire of different variable domains. In this report, we quantify and characterize the repertoire of kappa rearrangements in fetal liver ontogeny. VJ kappa rearrangements are first observable at approximately day 14 of gestation. Characterization of these rearrangements indicates that only 33% are in a productive reading frame, which supports the argument that they have been generated recently and have not as yet undergone significant Ag-driven selection. Further analysis of rearrangements from a pool of 133 cloned VJ kappa junctions (from both day 14 and day 16 of gestation) indicates that the repertoire is fairly diverse with respect to the V kappa gene families used, as well as the number of members from each gene family. The frequency of V kappa 4 family use in rearrangements to J kappa 5, however, was approximately twice that of the frequency of V kappa 4 family use in rearrangement to other J kappa s. The fine structure of fetal VJ kappa junctions was also diverse, which indicates that precise deletion of sequence identities shared between rearranging V kappa J kappa pairs does not significantly reduce junctional diversity, as has been observed in DJH rearrangements. Lastly, a number of junctions contained P nucleotides, in contrast to the repertoire of expressed VJ kappa junctions.