Biased usage of two restricted VH gene segments in VH replacement

AT8-1-12-5, an intracytoplasmic gamma 2b-producing (mu- gamma 2b+) pre-B cell line transformed with Abelson murine leukemia virus continuously generated intracytoplasmic mu, gamma 2b-producing (mu+ gamma 2b+) cells during propagation in culture. Southern blotting, DNA cloning and sequence analysis showed that these mu+ gamma 2b+ cells were generated from the mu- gamma 2b+ pre-B cells by VH replacement events. The gene segments involved in these replacement events were restricted to only two VH gene segments, VH7.1 (VH7183 family) and VH6.2 (VHQ52 family). Cell staining using the monoclonal anti-VH141 antibody 3-5-6f that specifically recognized the VH6.2 but not VH7.1 gene products indicated that half of the VH replacement events occurring in AT8-1-12-5 used the VH6.2 gene segment. Deletion mapping indicated that the incoming VH gene segments, VH7.1 and VH6.2 were proximal to the resident VH gene segment, VH12.5 (VH7183 family). These results provided direct evidence of the biased usage of VH gene segments in VH replacement and have several implications for the mechanisms of VH replacement.