Huang W Y, Liew C C
Laboratory for Molecular Cardiology, Departments of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada.
Biochem J. 1998 Mar 1;330 ( Pt 2)(Pt 2):871-6. doi: 10.1042/bj3300871.
To investigate the role of chromatin structure in cardiac gene expression, we used the DNase I and micrococcal nuclease to probe the chromatin structure of the hamster cardiac beta-MyHC gene. Two cardiac-specific DNase I hypersensitive sites (DHS) were identified, one of which was mapped to the -2.3 kb (beta-2.3 kb) region and the other to the proximal promoter region of the beta-MyHC gene. The two sites were readily detectable using nuclei from neonatal hamster heart; however, the proximal promoter site disappeared when adult hamster heart nuclei were used, and the -2.3 kb site decreased in intensity. We were able to demonstrate the gradual disappearance of this proximal promoter DHS by comparing heart nuclei isolated from animals at late-gestation and 1-day-old stages. Furthermore, injecting thyroid hormone caused the disappearance of the proximal promoter DHS in late gestational fetal ventricular nuclei. Digestion of nuclei from various tissues by micrococcal nuclease revealed that the beta-MyHC gene proximal promoter exists in an array of three specifically-positioned nucleosomes only in fetal heart chromatin. The beta-MyHC gene proximal promoter is DNase I hypersensitive within one of the nucleosomal particles. Our data suggest that chromatin structure may participate actively in cardiac gene expression.
为了研究染色质结构在心脏基因表达中的作用，我们使用脱氧核糖核酸酶I（DNase I）和微球菌核酸酶来探测仓鼠心脏β-肌球蛋白重链（beta-MyHC）基因的染色质结构。确定了两个心脏特异性的DNase I超敏位点（DHS），其中一个定位在-2.3 kb（β-2.3 kb）区域，另一个定位在β-MyHC基因的近端启动子区域。使用新生仓鼠心脏的细胞核很容易检测到这两个位点；然而，当使用成年仓鼠心脏细胞核时，近端启动子位点消失，而-2.3 kb位点的强度降低。通过比较从妊娠后期和1日龄动物分离的心脏细胞核，我们能够证明这个近端启动子DHS的逐渐消失。此外，注射甲状腺激素导致妊娠后期胎儿心室细胞核中近端启动子DHS消失。用微球菌核酸酶消化来自各种组织的细胞核表明，β-MyHC基因近端启动子仅在胎儿心脏染色质中以三个特定定位核小体的阵列形式存在。β-MyHC基因近端启动子在其中一个核小体颗粒内对DNase I敏感。我们的数据表明，染色质结构可能积极参与心脏基因表达。
