The Effect of the scid Mutation on Mechanism and Control of Immunoglobulin Heavy and Light Chain Gene Rearrangement

Summary

Most Abelson murine leukemia virus (A-MuLV)-transformed cell lines derived from scid (severe combined immune deficient) mice actively rearrange their endogenous immunoglobulin (Ig) heavy (H), but not light (L) chain variable region genes. Such cell lines express germline V_H segments and other RNA transcripts that are characteristically produced by early precursor (pre)-B lymphocytes, but do not express high levels of transcripts from the germline kappa (k) constant region (C _k ) locus. However, we have derived scid A-MuLV transformants that express germline C _k transcripts and attempt s gene assembly. In one case a gene expression and rearrangement occurred in the absence of μ H chain expression, and in another was not induced efficiently by introduction of a μ-expression vector. Although the vast majority of scid H and L chain coding sequence joins are grossly aberrant, scid A-MuLV transformants can form normal coding joins at a very low frequency. In contrast, these cells form generally normal signal sequence joins at an approximately normal efficiency. Thus, these findings mechanistically distinguish coding and signal join formation. Subcloning analyses suggest that scid A-MuLV transformants that do not attempt chromosomal coding sequence joining may have a relative survival advantage, and therefore that these events may often result in unrepaired chromosomal breakage and cell death.