脱氧核糖核酸甲基化

Dog Years

你知道你的狗几岁了吗。一般认为,人每长大一岁,狗会长大七岁。加州大学圣地亚哥分校的研究生王缇娜却想更准确地测算狗的年龄。五年前,小王在救助站捡回一只小狗,她想知道这只狗多大了,当时有人告诉了她一个年纪,感觉差不多,但她无法确认这只狗到底多大,于是她开始研究。

王同学在特雷伊得克实验室研究人体脱氧核糖核酸甲基化的变化模式。有一种被称为甲基组的小型化合物会附着在脱氧核糖核酸上,从而影响哪些序列被激活。随着我们年龄增长,有些脱氧核糖核酸甲基化的程度更深,而另一些甲基化程度则较轻。而大多数人的一生中,这种甲基化的变化模式都非常一致,以至于我们可以把它当成一种判断年龄的生物钟。这一过程在狗身上也会发生。其它实验室已有实验表明,狗的甲基化变化模式也会随着年龄而改变。

因此王同学找了三百二十个人和一百零四只拉布拉多犬,将人和狗的甲基化变化模式进行比较。过去我们知道,通过脱氧核糖核酸甲基化,可以预测很多哺乳动物的年纪,但是我们无法准确得知,人和狗之间,有多少变化模式是一致的,也无法确定是否一致。而有了这些相似性,我们可以找出一个保存完整的年龄增长特征,基于这种分子特征,我们就可以推测相出,人长大一岁,狗长大了几岁。

研究人员表示,随着狗狗年龄增长,它们相对于人的岁数增幅也会发生变化。例如这种方法判断出,狗一岁相当于人三十岁,狗四岁相当于人五十二岁。自此之后,狗龄的年均增幅大大降低。他们的研究发表在生物学预印本杂志上,里面有一张图,教你怎么看狗的年龄。

原文

How old is your four-legged best friend? Common wisdom says that a dog ages seven years for every human year. But Tina Wang, a graduate student at the University of California, San Diego, wanted a more accurate assessment. Her quest started five years ago, when she rescued a dog from a shelter. “I kind of just wanted to ask how old she was because I felt like they were giving me an age that was very sensible, but I wasn’t sure she was actually that old. So that kind of started this whole project.”

Wang worked in Trey Ideker’s lab, where they study changing patterns of DNA methylation in humans. Small chemical entities called methyl groups attach to stretches of DNA, which affects what sequences are active. As we age, some stretches of DNA get more methylated, and others less. The pattern is so consistent over the course of most people’s lives that it can be used as an aging “clock.” The same process happens in dogs—and published reports existed from other labs about methylation patterns in dogs changing over time.

So Wang compared the age-related patterns in 320 humans and 104 Labrador retrievers.“We knew that DNA methylation can predict age in many mammals, but we didn’t know exactly how much of this was shared throughout the progression of life, and it wasn't clear if there was anything that was shared. And because of these similarities, we were able to identify a conserved aging signature that allows you to estimate dog years from human years based on this molecular profile.”

The researchers say that dog years per human year change over the lifetime of a dog. For example, their method has a one-year-old dog being the equivalent of a 30-year-old human. A four-year-old dog is about 52. And dog aging per year slows considerably after that. To see a chart of the aging estimates, check out the paper at the bioRxiv Web site.

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