组蛋白H4K20去甲基化酶的鉴定和功能研究

组蛋白甲基化是重要的表观遗传修饰方式，与细胞重编程密切相关。近几年来，组蛋白去甲基化酶的不断发现证明了该修饰是可逆的，但H4K20me2/3的组蛋白去甲基化酶仍未找到。在前期工作中，我们用高通量方法筛选到一个H4K20的组蛋白去甲基化酶KDM9A：在细胞内高表达KDM9A可降低H4K20me1/2/3的水平;表达纯化的GST-KDM9A在体外可去除H4K20me1/2/3，产生甲醛和去掉甲基化的组蛋白产物。我们在该标书中申请继续研究KDM9A：（1）用缺失和突变体研究其催化结构域；（2）研究其对转录的调控，（3）研究其在胚胎干细胞分化中的功能。由于KDM9A与以前发现的两类酶不一样，该研究将鉴定一类新型的组蛋白去甲基化酶，为表观遗传调控和细胞重编程提供新的思路。

Histone methylation can be removed by demethylases. Up to now, two classes of 20 histone demethylases specific for different lysine residues have been identified, but demethylases for several other lysine residues including H4K20me2/3 have not been found. To identify histone demethylases for H4K20 me2/3, we performed a high-content cell-based screening and identified KDM9A. Overexpression of KDM9A caused a reduction of H4K20me1, me2 and me3 in vivo. Purified KDM9A could reduce the levels of H4K20me1, me2 and me3 in vitro, and the reaction produced formaldehyde and the respective histone products. These results indicate that KDM9A is a histone demethylase for H4K20. We propose (1) to identify the catalytic domain by domain mapping, (2) to study its role in transcription, and (3) to study its biological function in ES cell differentiation.