Tumas-Brundage K M, Vora K A, Manser T
Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson Medical College, Philadelphia, PA 19107, U.S.A.
Mol Immunol. 1997 Apr;34(5):367-78. doi: 10.1016/s0161-5890(97)00065-5.
Previous work on the cis-acting elements that control heavy chain variable region (VH) gene somatic hypermutation has indicated the presence of an as yet unidentified element(s) 3' of the intron enhancer that is necessary for high rate mutation. Examination of cis-acting elements involved in kappa light chain V gene hypermutation has demonstrated a requirement for both the intronic and 3' kappa enhancers in this process. To examine whether the 3'alpha heavy chain enhancer [3'alpha E(hs1,2)] is required for somatic hypermutation of VH genes, we generated two types of transgenic mice. One type was generated using a construct containing a VH promoter, a rearranged VDJ, the heavy chain intronic enhancer, and the murine heavy chain 3'alpha E(hs1,2). The transgenes in the second lines were similar to the transgenes in the first with the addition of a second complete matrix attachment region (MAR) 3' of the heavy chain intronic enhancer, and splice acceptor and polyadenylation sites between the two enhancers. Analysis of both transgenes revealed levels of mutation at least 10-fold lower than endogenous VH genes. These data suggest that the 3'alpha E(hs1,2) does not play a role analogous to the 3' kappa enhancer in the regulation of the hypermutation process. Moreover, in one of the transgenes, the presence of the 3'alpha E(hs1,2) resulted in a lack of transcription in vivo, suggesting a negative regulatory role for this enhancer in certain contexts.
先前关于控制重链可变区（VH）基因体细胞超突变的顺式作用元件的研究表明，在内含子增强子的3'端存在一个尚未确定的元件，它是高频率突变所必需的。对参与κ轻链V基因超突变的顺式作用元件的研究表明，在此过程中，内含子增强子和3'κ增强子都是必需的。为了研究3'α重链增强子[3'αE(hs1,2)]是否是VH基因体细胞超突变所必需的，我们构建了两种转基因小鼠。一种转基因小鼠使用的构建体包含一个VH启动子、一个重排的VDJ、重链内含子增强子和小鼠重链3'αE(hs1,2)。第二种品系的转基因与第一种相似，但在重链内含子增强子的3'端增加了第二个完整的基质附着区域（MAR），并在两个增强子之间添加了剪接受体和聚腺苷酸化位点。对这两种转基因的分析表明，其突变水平比内源性VH基因至少低10倍。这些数据表明，3'αE(hs1,2)在超突变过程的调控中并不发挥类似于3'κ增强子的作用。此外，在其中一种转基因中，3'αE(hs1,2)的存在导致体内转录缺失，这表明该增强子在某些情况下具有负调控作用。
