Map position and usage of 3' VH family members: usage is not position dependent

The primary repertoire in mice, in large part, is determined by the Ig gene segments joined to form the variable region genes-VDJ for the heavy chain genes and VJ for the light chain genes. However, the mechanisms that determine which VH gene, of several hundred available, is joined to a DJH structure remain unexplained. One theory proposes that the VH gene segments closest to the 3' end of the VH locus are chosen because of their location, i.e. that proximity to a DJH structure is a prime determinant for VH selection. Alternatively, the content of the DNA may be the determining factor regardless of chromosomal position. According to this hypothesis 3' preference is due to the coincidence of preferred content and proximity to DJH structures. Since the 3' VH families span more than a centimorgan of DNA we were able to distinguish between these concepts by determining VH usage of gene segments within this region. The BALB/c strain is ideal for this study since it uses 3' VH families at a very high frequency. We therefore mapped the positions of the 3' VH gene families and used this map to investigate the usage of these gene segments in BALB/c fetal liver derived A-MuLV transformed cell lines. We found that while VH gene segments throughout the Ig locus, both 3' and 5' were used, there was a clear preference for 3' VH families. However, within the 3' VH segments the most proximal were not preferred, indicating that proximity to DJH structure was not a strict determinant of VH utilization.