From the smallest single-celled organism to the largest creatures on earth, every living thing is defined by its genes. The DNA contained in our genes acts like an instruction manual for our cells. Four building blocks called bases are strung together in precise sequences, which tell the cell how to behave and form the basis for our every trait. But with recent advancements in gene editing tools, scientists can change an organism’s fundamental features in record time. They can engineer drought-resistant crops and create apples that don’t brown. They might even prevent the spread of infectious outbreaks and develop cures for genetic diseases. CRISPR is the fastest, easiest, and cheapest of the gene editing tools responsible for this new wave of science. But where did this medical marvel come from? How does it work? And what can it do?
从最小的单细胞有机体, 到地球上最大的生物, 每一个生命都由其基因决定。 基因中包含的DNA遗传物质 就像是细胞的使用说明。 4种碱基以精确的顺序连结成串, 指挥细胞的行为, 构成我们每项特质的基础。 但通过运用最先进的 基因编辑工具, 科学家可以用最短的时间 改变有机体的根本特征。 他们可以开发出抗旱的农作物, 创造出不会氧化变色的苹果。 他们甚至能够 防止传染病大规模扩散, 并研发出遗传性疾病的治疗方法。 CRISPR是最快、最简单、 最便宜的基因编辑工具, 引领了新一波科学研究潮流。 这个医学奇迹从何而来? 它是如何工作的? 它能做些什么?
Surprisingly, CRISPR is actually a natural process that’s long functioned as a bacterial immune system. Originally found defending single-celled bacteria and archaea against invading viruses, naturally occurring CRISPR uses two main components. The first are short snippets of repetitive DNA sequences called “clustered regularly interspaced short palindromic repeats,” or simply, CRISPRs. The second are Cas, or “CRISPR-associated” proteins which chop up DNA like molecular scissors. When a virus invades a bacterium, Cas proteins cut out a segment of the viral DNA to stitch into the bacterium’s CRISPR region, capturing a chemical snapshot of the infection. Those viral codes are then copied into short pieces of RNA. This molecule plays many roles in our cells, but in the case of CRISPR, RNA binds to a special protein called Cas9. The resulting complexes act like scouts, latching onto free-floating genetic material and searching for a match to the virus. If the virus invades again, the scout complex recognizes it immediately, and Cas9 swiftly destroys the viral DNA.
令人惊奇的是,CRISPR实际上是一种自然现象, 长久以来其功能是 作为细菌的免疫系统。 人们最早发现 单细胞细菌和古生菌 利用CRISPR抵抗入侵病毒。 自然界中的CRISPR 有两个主要组成部分: 一个是基因序列的重复片段, 称为 “常间回文重复序列丛集”, 简写为CRISPRs。 第二个是Cas蛋白, 也称"常间回文重复序列丛集关联蛋白"。 它像一把分子剪刀将DNA切断。 当病毒侵入细菌, Cas蛋白剪下 一段病毒DNA片段, 将其缝合到细菌的CRISPR区域, 捕捉到侵染的化学快照。 这些病毒编码 会被复制到一小段RNA上。 这个分子在我们细胞中有众多功能, 但对于CRISPR来说, RNA与一种特殊蛋白质Cas9结合。 形成的复合物仿佛是一群侦查员, 它们与遗传物质结合, 寻找与病毒配对。 如果病毒再次入侵, 这些侦查物质会立刻将其识别, Cas9可以迅速摧毁病毒的DNA。
Lots of bacteria have this type of defense mechanism. But in 2012, scientists figured out how to hijack CRISPR to target not just viral DNA, but any DNA in almost any organism. With the right tools, this viral immune system becomes a precise gene-editing tool, which can alter DNA and change specific genes almost as easily as fixing a typo.
许多细菌都有这种防御机制。 但在2012年,科学家找出了 如何让CRISPR 不仅仅针对病毒DNA, 而是用于 几乎所有组织中的DNA。 通过运用适当的工具, 病毒免疫系统成为了 一个精细的基因编辑工具。 它能够改变DNA和特定基因, 这一过程简单地如同修改错别字。
Here’s how it works in the lab: scientists design a “guide” RNA to match the gene they want to edit, and attach it to Cas9. Like the viral RNA in the CRISPR immune system, the guide RNA directs Cas9 to the target gene, and the protein’s molecular scissors snip the DNA. This is the key to CRISPR’s power: just by injecting Cas9 bound to a short piece of custom guide RNA scientists can edit practically any gene in the genome.
在实验室中,其运用方法如下: 科学家设计出一个向导RNA 来匹配他们想要编辑的基因, 并将其附着在Cas9上。 它如同CRISPR 免疫系统中的病毒RNA一样, 向导RNA会引导Cas9到目标DNA, 蛋白质的分子剪刀将DNA切断。 这是CRISPR强大的关键, 仅通过注入Cas9 与一小段定制的RNA绑定, 科学家就能够改变几乎任何基因。
Once the DNA is cut, the cell will try to repair it. Typically, proteins called nucleases trim the broken ends and join them back together. But this type of repair process, called nonhomologous end joining, is prone to mistakes and can lead to extra or missing bases. The resulting gene is often unusable and turned off. However, if scientists add a separate sequence of template DNA to their CRISPR cocktail, cellular proteins can perform a different DNA repair process, called homology directed repair. This template DNA is used as a blueprint to guide the rebuilding process, repairing a defective gene or even inserting a completely new one.
DNA一旦被切断, 细胞会试图进行修复。 通常,一种叫做核酸酶的蛋白质 会修整断掉的两段 并将其重新连接。 这种类型的修补过程 也称做非同源性末端接合 很容易产生错误, 并导致多余或丢失碱基。 产生的基因通常无法使用或表达。 但是如果科学家 将一条模板DNA序列 增加到CRISPR组合中, 分子蛋白就能够 执行一个不同的DNA修复过程, 称为同源介质的双链DNA修复。 这个模板DNA能够引导重建过程, 修复有缺陷的基因, 甚至插入一个全新的基因。
The ability to fix DNA errors means that CRISPR could potentially create new treatments for diseases linked to specific genetic errors, like cystic fibrosis or sickle cell anemia. And since it’s not limited to humans, the applications are almost endless. CRISPR could create plants that yield larger fruit, mosquitoes that can’t transmit malaria, or even reprogram drug-resistant cancer cells. It’s also a powerful tool for studying the genome, allowing scientists to watch what happens when genes are turned off or changed within an organism.
这种修复基因错误的能力 意味着CRISPR 能够用于创造新的疗法, 用于特定基因错误导致的疾病 如囊肿性纤维化或镰刀型红细胞贫血症。 这项应用不只局限与人类, 它有几乎无限的可能。 CRISPR能够创造 长出更大水果的植物, 无法传播疟疾的蚊子, 甚至是重新编辑拥有抗药性的癌细胞。 它也是一个研究基因组的有力工具, 使得科学家能够观察在有机体中 停止或改变基因表达会发生什么。
CRISPR isn’t perfect yet. It doesn’t always make just the intended changes, and since it’s difficult to predict the long-term implications of a CRISPR edit, this technology raises big ethical questions. It’s up to us to decide the best course forward as CRISPR leaves single-celled organisms behind and heads into labs, farms, hospitals, and organisms around the world.
CRISPR尚不完美, 它无法总是做出人们想要的改变, 由于难以预测 CRISPR编辑的长期影响, 这项技术引起了巨大的道德争议。 随着CRISPR脱离单细胞生物, 进入实验室、农场、医院, 以及世界上的各类有机体, 决定前进的最好道路 取决于我们自己。