Expression of a Targeted λ1 Light Chain Gene Is Developmentally Regulated and Independent of Igκ Rearrangements

Immunoglobulin light chain (IgL) rearrangements occur more frequently at Ig kappa than at Ig lambda. Previous results suggested that the unrearranged Ig kappa locus negatively regulates Ig lambda transcription and/or rearrangement. Here, we demonstrate that expression of a VJ lambda 1-joint inserted into its physiological position in the Ig lambda locus is independent of Ig kappa rearrangements. Expression of the inserted VJ lambda 1 gene segment is developmentally controlled like that of a VJ kappa-joint inserted into the Ig kappa locus and furthermore coincides developmentally with the occurrence of Ig kappa rearrangements in wild-type mice. We conclude that developmentally controlled transcription of a gene rearrangement in the Ig lambda locus occurs in the presence of an unrearranged Ig kappa locus and is therefore not negatively regulated by the latter. Our data also indicate light chain editing in approximately 30% of lambda 1 expressing B cell progenitors.