表观遗传学

表观遗传学领域已经成为从事癌症、神经退行性疾病和成瘾研究的科学家关注的重要领域。表观遗传机制涉及暂时激活或抑制基因表达。值得关注的是，即使这些变化不会永久改变DNA序列，也可以代代相传。表观遗传学的三个主要机制是DNA甲基化、组蛋白修饰和RNA调控。   

DNA甲基化

DNA甲基化是最广为人知的表观遗传机制。DNA甲基化通常涉及甲基转移酶，利用这种酶可在胞嘧啶的第五个位点（C5）增加一个甲基。这一甲基主要加在胞嘧啶-磷酸-鸟嘌呤（CpG）二核苷酸上，但也存在非CpG甲基化的情况。为此，常常需要进行DNA甲基化分析以帮助理解基因表达。这类分析的示例包括：酶解DNA，然后通过HPLC、质谱分析定量甲基化；或者使用硫酸氢钠转化，然后再进行PCR测序和分析。

组蛋白修饰

组蛋白修饰是另一种经典的表观遗传机制。组蛋白修饰涉及多种改变组蛋白的方式，包括乙酰化、甲基化、磷酸化和其他影响基因表达的机制。组蛋白是可与DNA一起构成核小体的一类蛋白质。成束的核小体形成染色质，构成染色体。通常，组蛋白修饰发生组蛋白N末端尾部，氨基酸赖氨酸或精氨酸发生的比例较高。研究这种表观遗传调控的一种方法是染色质免疫共沉淀（ChIP）检测。

RNA 调控

与其他表观遗传机制相比，研究人员对RNA调控的了解甚少。人们普遍认为，RNA信号传导通过调节染色质结构影响表观遗传。目前学界研究人员正在研究mRNA——特别是非编码RNA（例如长链非编码RNA和微RNA）——在调控基因表达方面发挥的作用。此外，我们还可通过RNA纯化染色质分离（ChIRP）或RNA免疫沉淀（RIP）技术了解染色质与RNA之间的关系以及RNA的表观遗传学作用。

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