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Replication and Subnuclear Location Dynamics of the Immunoglobulin Heavy-Chain Locus in B-Lineage Cells

机译：B系细胞中免疫球蛋白重链基因座的复制和亚核位置动态

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The murine immunoglobulin heavy-chain (Igh) locus provides an important model for understanding the replication of tissue-specific gene loci in mammalian cells. We have observed two DNA replication programs with dramatically different temporal replication patterns for the Igh locus in B-lineage cells. In pro- and pre-B-cell lines and in ex vivo-expanded pro-B cells, the entire locus is replicated early in S phase. In three cell lines that exhibit the early-replication pattern, we found that replication forks progress in both directions through the constant-region genes, which is consistent with the activation of multiple initiation sites. In contrast, in plasma cell lines, replication of the Igh locus occurs through a triphasic pattern similar to that previously detected in MEL cells. Sequences downstream of the Igh-Cα gene replicate early in S, while heavy-chain variable (Vh) gene sequences replicate late in S. An ～500-kb transition region connecting sequences that replicate early and late is replicated progressively later in S. The formation of the transition region in different cell lines is independent of the sequences encompassed. In B-cell lines that exhibit a triphasic-replication pattern, replication forks progress in one direction through the examined constant-region genes. Timing data and the direction of replication fork movement indicate that replication of the transition region occurs by a single replication fork, as previously described for MEL cells. Associated with the contrasting replication programs are differences in the subnuclear locations of Igh loci. When the entire locus is replicated early in S, the Igh locus is located away from the nuclear periphery, but when Vh gene sequences replicate late and there is a temporal-transition region, the entire Igh locus is located near the nuclear periphery.
机译：鼠免疫球蛋白重链（Igh）基因座为理解哺乳动物细胞中组织特异性基因位点的复制提供了重要模型。我们已经观察到两个DNA复制程序，它们在B谱系细胞中的Igh基因座具有明显不同的时间复制模式。在前B细胞和前B细胞系以及离体扩增的前B细胞中，整个基因座都在S期早期复制。在表现出早期复制模式的三个细胞系中，我们发现复制叉通过恒定区基因在两个方向上进行，这与多个起始位点的激活是一致的。相反，在浆细胞系中，Igh基因座的复制通过类似于先前在MEL细胞中检测到的三相模式发生。 Igh-Cα基因下游的序列在S早期复制，而重链可变（Vh）基因序列在S晚期复制。连接早复制和晚复制的序列的〜500-kb过渡区在S后期复制。不同细胞系中过渡区的形成与所涵盖的序列无关。在表现出三重复制模式的B细胞系中，复制叉通过检查的恒定区基因沿一个方向前进。时序数据和复制叉移动的方向指示过渡区域的复制是由单个复制叉进行的，如先前针对MEL单元所述。与对比复制程序有关的是Igh基因座亚核位置的差异。当整个基因座在S早期复制时，Igh基因座位于远离核外围的位置，但是当Vh基因序列复制到较晚且有一个时间过渡区域时，整个Igh基因座位于核外围附近。

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