Germline transcripts of immunoglobulin light chain variable regions are structurally diverse and differentially expressed

Abstract

The murine pre-B cell line R2-bfl, which can be induced to differentiate in vitro, was used to study germline transcription of variable regions of the light chain loci. RNA from these cells was subjected to a 3′-RACE and germline transcripts from 17 individual Vκ gene segments belonging to 12 Vκ families were characterized. Germline transcripts of all three Vλ regions were similarly analyzed. The synchronous differentiation of R2-bfl cells was then used to investigate the order of appearance of germline transcripts of the V and JC clusters of both light chain loci. This was taken as indicator for accessibility of a particular locus to rearrangement. Germline transcripts of the JCκ cluster and the Vκ family most proximal to JCκ was detectable already at day 0, while transcripts of the most distal Vκ family became apparent after initiation of differentiation at day 1. Transcripts of the JCλ cluster could be found at day 2, whereas transcripts of the Vλ region were already present at day 1. Thus, the λ locus becomes accessible to rearrangement later during development than κ, confirming and extending our previous findings. The V and JC clusters open at the same stage of development although slight asynchronicities were found for the Vλ and the distal Vκ gene segments.