Insertion of Phosphoglycerine Kinase (Pgk)-Neo 5′ of Jλ1 Dramatically Enhances Vjλ1 Rearrangement

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Abstract
Gene-targeted mice were generated with a loxP-neomycin resistance gene (neor) cassette inserted upstream of the Jλ1 region and replacement of the glycine 154 codon in the Cλ1 gene with a serine codon. This insertion dramatically increases Vλ1-Jλ1 recombination. Jλ1 germline transcription levels in pre-B cells and thymus cells are also greatly increased, apparently due to the strong housekeeping phosphoglycerine kinase (PGK) promoter driving the neo gene. In contrast, deletion of the neo gene causes a significant decrease in VJλ1 recombination to levels below those in normal mice. This reduction is due to the loxP site left on the chromosome which reduces the Jλ1 germline transcription in cis. Thus, the correlation between germline transcription and variable (V), diversity (D), and joining (J) recombination is not just an all or none phenomenon. Rather, the transcription efficiency is directly associated with the recombination efficiency. Furthermore, Jλ1 and Vλ1 germline transcription itself is not sufficient to lead to VJ recombination in T cells or early pre-B cells. The findings may suggest that in vivo: (a) locus and cell type–specific transactivators direct the immunoglobulin or T cell receptor loci, respectively, to a “recombination factory” in the nucleus, and (b) transcription complexes deliver V(D)J recombinase to the recombination signal sequences.