What is epigenetics? - Carlos Guerrero-Bosagna

譯者: Ann Chen 審譯者: Max Chern

Here's a conundrum:

這是個難題：

identical twins originate from the same DNA,

同卵雙胞胎源自相同的 去氧核醣核酸（DNA）

so how can they turn out so different

為什麼他們會變得如此不同 ──

even in traits that have a significant genetic component?

即使在有明顯遺傳成分的特徵下？

For instance, why might one twin get heart disease at 55,

例如，為什麼雙胞之一 在 55 歲得了心臟病

while her sister runs marathons in perfect health?

而她妹妹身體強健能跑馬拉松呢？

Nature versus nurture has a lot to do with it,

先天及後天與這個有很多關聯

but a deeper related answer can be found within something called epigenetics.

但在所謂 表徵遺傳學 (epigenetics) 裡 能找到更深一層相關答案

That's the study of how DNA interacts

那是有關 DNA 如何與細胞內 許多更小分子相互作用的研究

with the multitude of smaller molecules found within cells,

which can activate and deactivate genes.

這作用能活化及去活化基因

If you think of DNA as a recipe book,

假如你把 DNA 想成一本食譜

those molecules are largely what determine what gets cooked when.

那些分子主要是決定 什麼東西要在何時被烹煮

They aren't making any conscious choices themselves,

它們自己不會做任何有意識的選擇

rather their presence and concentration within cells makes the difference.

而是在細胞中 這些分子的存在與含量造成了不同

So how does that work?

所以這是如何運作的呢？

Genes in DNA are expressed when they're read and transcribed into RNA,

DNA 中的基因當被讀取並轉錄成 核糖核酸（RNA）時會表現出來

which is translated into proteins by structures called ribosomes.

RNA 會被 核醣體（ribosomes） 轉譯而製作出蛋白質

And proteins are much of what determines a cell's characteristics and function.

而蛋白質大致決定了 一個細胞的特徵與功能

Epigenetic changes can boost or interfere with the transcription of specific genes.

表徵遺傳變化 能促進或干擾特定基因的轉錄

The most common way interference happens is that DNA,

最常發生干擾的方式是當 DNA

or the proteins it's wrapped around,

或被它圍住的蛋白質

gets labeled with small chemical tags.

被貼上小化學標籤時

The set of all of the chemical tags that are attached to the genome

附在特定細胞基因組上的 整組化學標籤

of a given cell

is called the epigenome.

稱為 表徵基因組（epigenome）

Some of these, like a methyl group, inhibit gene expression

其中有些，如 甲基（methyl group）， 會抑制基因的表現

by derailing the cellular transcription machinery

即藉著擾亂細胞的轉錄機器

or causing the DNA to coil more tightly,

或造成 DNA 盤繞更緊

making it inaccessible.

使得它難以接近

The gene is still there, but it's silent.

基因仍在，但它是靜止的

Boosting transcription is essentially the opposite.

促進轉錄則基本上適得其反

Some chemical tags will unwind the DNA, making it easier to transcribe,

有些化學標籤會鬆開 DNA， 使得較容易轉錄

which ramps up production of the associated protein.

這會加速相關蛋白質的製造

Epigenetic changes can survive cell division,

表徵遺傳變化能在細胞分裂下留存

which means they could affect an organism for its entire life.

這意謂它們能影響生物體的整個生命

Sometimes that's a good thing.

有時那是一件好事

Epigenetic changes are part of normal development.

表徵遺傳變化是正常發育的一部分

The cells in an embryo start with one master genome.

胚胎上的細胞 始於一個最先的基因組

As the cells divide, some genes are activated

當細胞分裂，有些基因被活化

and others inhibited.

而有些被抑制

Over time, through this epigenetic reprogramming,

長久下來，經過表徵遺傳的重編程序

some cells develop into heart cells,

有些細胞發育成心臟細胞

and others into liver cells.

有些發育成肝臟細胞

Each of the approximately 200 cell types in your body

身體大約有 200 種的細胞

has essentially the same genome

基本上，每種都有相同的基因組

but its own distinct epigenome.

但各自擁有獨特的表徵基因組

The epigenome also mediates a lifelong dialogue

表徵基因組也會促成 基因與環境間終生的對話

between genes and the environment.

The chemical tags that turn genes on and off

開關基因的化學標籤

can be influenced by factors including diet,

會受一些因素影響，包括飲食、

chemical exposure,

化學物質的曝露

and medication.

和藥物

The resulting epigenetic changes can eventually lead to disease,

所造成的表徵遺傳變化 可能最後導致疾病 ──

if, for example, they turn off a gene that makes a tumor-suppressing protein.

例如，若它們關閉 製造抑制腫瘤蛋白質的基因

Environmentally-induced epigenetic changes are part of the reason

環境導致的表徵遺傳變化 部分解釋了

why genetically identical twins can grow up to have very different lives.

為什麼同卵雙胞胎 長大後會有極大不同的生活

As twins get older, their epigenomes diverge,

當雙胞年紀漸長， 他們的表徵基因組出現差異

affecting the way they age and their susceptibility to disease.

影響他們老化的方式 和對疾病的易感性

Even social experiences can cause epigenetic changes.

甚至社交經驗也能造成表徵遺傳變化

In one famous experiment,

在一個有名的實驗中

when mother rats weren't attentive enough to their pups,

當母鼠對其幼鼠關心不足

genes in the babies that helped them manage stress were methylated

幼鼠體內協助處理壓力的基因 會被甲基化且關閉

and turned off.

And it might not stop with that generation.

而且可能不會在那一代就停止

Most epigenetic marks are erased when egg and sperm cells are formed.

當卵子和精子細胞形成時， 大多數表徵遺傳的標記會被去除

But now researchers think that some of those imprints survive,

但現在研究者認為 有些印記會留存下來

passing those epigenetic traits on to the next generation.

將那些表徵遺傳的特徵傳到下一代

Your mother's or your father's experiences as a child,

你的父母小時候的經驗

or choices as adults,

或成人時的抉擇

could actually shape your own epigenome.

可能塑造你自己的表徵基因組

But even though epigenetic changes are sticky,

雖然表徵遺傳變化很黏人

they're not necessarily permanent.

但它們未必是永久的

A balanced lifestyle that includes a healthy diet,

一個均衡的生活形態， 包括健康的飲食、

exercise,

運動

and avoiding exposure to contaminants

和避免曝露到汚染物

may in the long run create a healthy epigenome.

從長遠看， 可以創造健康的表徵基因組

It's an exciting time to be studying this.

現在是研究這門科學的熱絡時刻

Scientists are just beginning to understand

科學家正開始去了解

how epigenetics could explain mechanisms of human development and aging,

表徵遺傳學 如何解釋人類發育和老化的機轉

as well as the origins of cancer,

以及癌症、心臟疾病、精神病、

heart disease,

mental illness,

addiction,

成癮和許多其他疾病的源起

and many other conditions.

Meanwhile, new genome editing techniques are making it much easier

同時，新的基因組編輯技術使得更容易

to identify which epigenetic changes really matter for health and disease.

辨識哪些表徵遺傳變化 對健康和疾病是真正重要的

Once we understand how our epigenome influences us,

一旦我們了解 表徵基因組是如何影響我們

we might be able to influence it, too.

我們可能也可以影響它

翻譯：Ann Chen