Mostoslavsky R, Singh N, Kirillov A, Pelanda R, Cedar H, Chess A, Bergman Y
The Hubert H. Humphrey Center for Experimental Medicine and Cancer Research, The Hebrew University Hadassah Medical School, Jerusalem 91120, Israel.
Genes Dev. 1998 Jun 15;12(12):1801-11. doi: 10.1101/gad.12.12.1801.
Allelic exclusion in kappa light-chain synthesis is thought to result from a feedback mechanism by which the expression of a functional kappa light chain on the surface of the B cell leads to an intracellular signal that down-regulates the V(D)J recombinase, thus precluding rearrangement of the other allele. Whereas such a feedback mechanism clearly plays a role in the maintenance of allelic exclusion, here we provide evidence suggesting that the initial establishment of allelic exclusion involves differential availability of the two kappa alleles for rearrangement. Analysis of kappa+ B-cell populations and of individual kappa+ B cells that have rearranged only one allele demonstrates that in these cells, critical sites on the rearranged allele are unmethylated, whereas the nonrearranged allele remains methylated. This pattern is apparently generated by demethylation that is initiated at the small pre-B cell stage, on a single allele, in a process that occurs prior to rearrangement and requires the presence in cis of both the intronic and 3' kappa enhancers. Taken together with data demonstrating that undermethylation is required for rearrangement, these results indicate that demethylation may actually underly the process of allelic exclusion by directing the initial choice of a single kappa allele for rearrangement.
κ轻链合成中的等位基因排斥被认为是由一种反馈机制导致的，通过这种机制，B细胞表面功能性κ轻链的表达会引发一种细胞内信号，该信号会下调V(D)J重组酶，从而阻止另一个等位基因的重排。虽然这种反馈机制显然在维持等位基因排斥中发挥作用，但在这里我们提供的证据表明，等位基因排斥的最初建立涉及两个κ等位基因重排的不同可用性。对κ+B细胞群体以及仅重排了一个等位基因的单个κ+B细胞的分析表明，在这些细胞中，重排等位基因上的关键位点未甲基化，而非重排等位基因仍保持甲基化。这种模式显然是由在小前B细胞阶段开始的去甲基化产生的，在单个等位基因上，这个过程发生在重排之前，并且需要内含子κ增强子和3'κ增强子在顺式中同时存在。结合表明重排需要去甲基化的数据，这些结果表明去甲基化实际上可能通过指导单个κ等位基因重排的初始选择而成为等位基因排斥过程的基础。
