The structure of aldolase isozyme genes and the regulation of their tissue-specific expression

通过检测表达或不表达醛缩酶B基因的组织和细胞，研究醛缩酶B基因的表达与染色质结构和DNA甲基化的关系。得到以下结果：(1)通过对醛缩酶B位点染色质结构的dna酶I超敏检测发现，在转录起始位点上游约0.3 Kb处对dna酶I敏感的特异结构是该基因转录所必需的。(2)在基因内及周围的15个Hpa <II>和Hha <I>位点中，位于基因3′-半和下游的位点被重度甲基化，与基因表达无关。在肝脏和分化型肝癌中，位于5'侧的一个Hha <I>位点和位于第一个内含子上的几个Hpa <II>位点低甲基化，而在脑和未分化型肝癌中，它们被重度甲基化。这些事实表明，在基因的5'-侧翼和5'-半区域的特定位点的胞嘧啶残基的低甲基化与该基因的表达有关。我们最近的研究结果表明，除了染色质结构松动和低甲基化外，一些与该区域元件相互作用的反式作用因子对该基因的转录是必需的。

By examining the tissues and cells which express or do not express aldolase B gene, the relationship between the gene expression and chromatin structure and DNA methylation of aldolase B gene was studied. Following results were obtained. (1) The examination of the chromatin structure of aldolase B locus by DNase I hypersensitivity revealed that the specific structure which is sensitive to DNase I at about 0.3 Kb upstream from the transcription-initiation site is necessary for transcription of the gene. (2) Out of 15 Hpa <II> and Hha <I> sites in and around the gene, those sites which located at 3'-half and at downstream of the gene were heavily methylated, regardless of the gene expression. A Hha <I> site in the 5'-flanking region, and several Hpa <II> sites in the first intron were hypomethylated in liver and differentiated hepatoma, while they were heavily methylated in brain and undifferentiated hepatoma. These facts suggest that the hypomethylation of cytosine residue at specific sites in the 5'-flanking and the 5'-half regions of the gene are related to the expression of this gene. Our recent results suggest that, besides loosened chromatin structure and hypomethylation, some trans-acting factor(s) which interact with the element in this region are necessary for the transcription of this gene.