来自该遗址的野牛骨骼尚存有DNA，研究者们将这些DNA提取出来，并分析其中有哪些特征使野牛发生了表观上的改变，并帮助它们适应气候的剧烈变化。这种现象叫做表观遗传现象，此时生物的DNA序列并不发生改变，但基因表达了可遗传的变化，多发生于剧烈变化的环境中，对表现型的影响能持续数代。
“这是我们验证表观遗传现象能驱动自然种群演化的第一步，”研究的参与者，澳洲张任谦研究所（Victor Chang Institute）的C.Suter说。
表观遗传学是一个比较年轻的学科，旨在研究DNA在合成或修饰时，其所处的环境对基因表达水平的影响。一个典型的例子是DNA甲基化，它能起到开启或关闭一段序列的作用，进而改变个体的表现型。这种现象与人类的发育和肿瘤疾病密切相关。
“表观遗传现象改变着我们对于适应进化的看法，也帮助我们对动物的传衍并表达DNA的方式有了新的认识。”研究的参与者，A.Cooper说。
气候变化对基因型和种群结构的影响已经被研究得很充分了，但受限于技术，表观遗传现象的研究才刚刚兴起。“我们对这批冰期材料的研究证实了气候波动对基因的作用，”Cooper说。“随着工作的进行，我们发现末次冰期的气候变化非常剧烈，动物们承受着很强的选择压，需要迅速地做出反应。表观遗传现象能帮助它们做到这一点，但令我们惊讶的是，末次冰期中动物对环境的适应竟然主要依靠了表观遗传，很少涉及DNA序列的改变。”
High-Resolution Analysis of Cytosine Methylation in Ancient DNA
Bastien Llamas, Michelle L. Holland, Kefei Chen, Jennifer E. Cropley, Alan Cooper, Catherine M. Suter
Epigenetic changes to gene expression can result in heritable phenotypic characteristics that are not encoded in the DNA itself, but rather by biochemical modifications to the DNA or associated chromatin proteins. Interposed between genes and environment, these epigenetic modifications can be influenced by environmental factors to affect phenotype for multiple generations. This raises the possibility that epigenetic states provide a substrate for natural selection, with the potential to participate in the rapid adaptation of species to changes in environment. Any direct test of this hypothesis would require the ability to measure epigenetic states over evolutionary timescales. Here we describe the first single-base resolution of cytosine methylation patterns in an ancient mammalian genome, by bisulphite allelic sequencing of loci from late Pleistocene Bison priscus remains. Retrotransposons and the differentially methylated regions of imprinted loci displayed methylation patterns identical to those derived from fresh bovine tissue, indicating that methylation patterns are preserved in the ancient DNA. Our findings establish the biochemical stability of methylated cytosines over extensive time frames, and provide the first direct evidence that cytosine methylation patterns are retained in DNA from ancient specimens. The ability to resolve cytosine methylation in ancient DNA provides a powerful means to study the role of epigenetics in evolution.
文献链接：https://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0030226
