4a). Given these results, and the delay in B-cell maturation selleck chemicals suggested by flow cytometric analysis of the bone marrow, we next considered the possibility that over-expression of the dnRAG1 transgene might render V(D)J recombination inefficient, resulting in a restricted B-cell repertoire. To test this possibility, we examined
the immunoglobulin heavy chain repertoire by amplifying VH-D-JH junctions from genomic DNA isolated from WT and dnRAG1 mouse spleens, and analysing nested runoff PCR products by sequencing gel electrophoresis as illustrated in Fig. 4(b).24 Three different VH gene families (J558, 7183, and Q52) were evaluated using this approach. In this assay, small differences in fragment length among amplicons from a given gene family reflect junctional diversification of CDR3 that occurs during V(D)J recombination: the pattern of the CDR3 length distribution is proportional to the fractional abundance of each rearrangement in the original sample. We found that the profile www.selleckchem.com/autophagy.html of runoff products from several WT animals shows a largely Gaussian distribution for all three VH families
tested, indicative of a highly diverse repertoire. In contrast, the CDR3 length distributions of all three VH gene families from three different dnRAG1 mice are clearly skewed toward a smaller number of fragment lengths (Fig. 4c,d). These data suggest that while splenic B cells in dnRAG1 mice are clonally diverse, the CDR3 repertoire among these cells is more restricted than in their normal counterparts. Thiamet G Because B220lo CD19+
B cells in 12-week-old dnRAG1 mice account for about 20% of splenic B cells at this age, we considered the possibility that the molecular features of the B220hi CD19+ B cells may partly mask those of the B220lo CD19+ B-cell population in a bulk splenic B-cell preparation. To address this issue, we sorted the two populations (Fig. 5a), and isolated genomic DNA or total RNA to compare immunoglobulin gene rearrangement patterns and immunoglobulin light chain gene sequences (Fig. 5b,c). Consistent with results obtained with bulk splenocytes, B220hi CD19+ B cells from WT and dnRAG1 mice showed fairly similar patterns of VH-to-DJH and Vκ-to-Jκ rearrangements (Fig. 5b). Interestingly, however, skewing was clearly evident in the rearrangement patterns detected from B220lo CD19+ B cells, particularly in the Igκ locus, where Jκ1 segment usage predominates over other Jκ rearrangements (Fig. 5b). This finding is confirmed by the preponderance of light chain genes containing the Jκ1 segment cloned from B220lo CD19+ B cells (11/15 clones sequenced), whereas Jκ usage is more evenly distributed between Jκ1, Jκ2 and Jκ5 segments among clones sequenced from B220hi CD19+ B cells sorted from WT and dnRAG1 mice (Fig. 5c, lower left panel).