New University of Colorado Boulder-led research finds that the traits that make vertebrates distinct from invertebrates were made possible by the emergence of a new set of genes 500 million years ago, documenting an important episode in evolution where new genes played a significant role in the evolution of novel traits in vertebrates.
由美國科羅拉多大學博爾德分校領導的新研究發現，因5億年前出現一組新基因，使脊椎動物可能成為，截然不同於無脊椎動物的特徵。這佐證了一項，在演化上，新基因於脊椎動物新特徵之演化中，扮演重大角色的重要部分。
The findings, published today in Nature, show that a gene family only found in vertebrates is critical for forming the head skeleton and other traits unique to them during embryonic development.
此些發表於2020年9月16日版《自然》期刊的研究發現，證實一群僅在脊椎動物中被發現的基因，就胚胎發育期間，形成頭部骨骼及它們其他獨特的特徵而言，是不可或缺的。
"Every animal essentially has the same basic core set of Lego pieces to make them. What this paper shows is that vertebrates have a few special pieces in addition to that, and we identify those special pieces," said Daniel Medeiros, senior author of the paper and associate professor of ecology and evolutionary biology.
該項論文資深撰文人，生態及演化生物學副教授，Daniel Medeiros宣稱：「每一種動物本質上，具有相同的基本核心樂高積木組，來組成它們。該項論文所證實的是，除了上述之外，脊椎動物具有幾個特殊積木，且他們確認了那些特殊積木。」
These special pieces in vertebrates are known as the Endothelin signaling pathway, a set of genes that influence how cells talk to each other. The researchers found this gene family is responsible for allowing neural crest cells -- cells that develop into unique vertebrate traits like skeletal parts, pigment cells and our peripheral nervous system -- to proliferate and specialize into different roles throughout the body.
此些在脊椎動物中的積木，被通稱為內皮素發信號途徑。這是一組影響細胞，如何互相溝通的基因。此些研究人員發現，該基因群是導致，使神經嵴細胞(發展諸如骨骼部分、色素細胞及周邊神經系統等，脊椎動物獨特特徵的細胞)得以增殖，並特化成全身諸多不同角色物的原因。
Evolutionary theories have given weight to the role of genome duplication in the evolution of new traits, and for good reason. When a genome duplicates, new copies of existing genes can take on new roles in an organism. But since previous ideas were based mostly on observation, Medeiros wanted to test if gene duplication could have allowed vertebrates to become so special, or if the appearance of brand new genes could have played a role.
諸多演化理論一直重視基因體複製，在新特徵之演化中的角色，且有充分理由。當基因體複製時，現有基因的新複製物，在生物體中，能承擔新的角色。不過，由於先前的概念主要是根據觀察。因此，Medeiros想驗證，基因複製是否可能，曾經使脊椎動物得以變得如此特殊，或全新基因的出現是否可能，曾經扮演一種角色。
Medeiros and his colleagues tested the hypothesis that new gene families could also give rise to new traits by genetically modifying the larvae of sea lamprey, a type of jawless fish, through identifying and removing this specific gene family. If their prediction was correct, removing it would revert a sea lamprey during its larval development into a more invertebrate-like worm, a close evolutionary ancestor.
藉由遺傳改造海七鰓鰻(一種無顎魚)的幼體，透過確認及移除新基因群，Medeiros及其同僚們試驗了，此特殊基因群可能也導致新特徵的推測。倘若他們的預測正確，則移除新基因群，會在海七鰓鰻幼體發育期間，使其返祖成為一種，接近演化之原種，更像無脊椎動物的蠕蟲。
圖1. 海七鰓鰻 (圖援用自：https://www.reddit.com/r/AIDKE/comments/gfcznw/the_sea_lamprey_petromyzon_marinus_is_a_jawless/)
"And we found that by knocking out this new gene family, you can almost erase most of the key vertebrate traits that make vertebrates special," said Medeiros.
Medeiros宣稱：「結果，他們發現，藉由剔除此新基因群，幾乎能消除，使脊椎動物特有之大多數關鍵的脊椎動物特徵。」
While gene duplication is still an important part of the evolutionary process -- as this new gene family is also duplicated in vertebrates -- they found that duplication was not as critical in giving rise to the special neural crest cell types that vertebrates evolved as was the emergence of this new gene family.
儘管基因複製仍然是，演化過程的一個重要部分(因為該新基因群也在脊椎動物中被複製)。不過他們發現，在導致脊椎動物演化之特殊神經嵴細胞類型上，並不如該新基因群的出現般，不可或缺。
This finding is significant in part because it's rare to find clear roles for genes that are unique to vertebrates, said lead author Tyler Square, who recently completed his PhD in the Medeiros lab and is now at the University of California Berkeley.
首要撰文人，最近在Medeiros實驗室完成博士學位。目前，在加州大學柏克萊分校的Tyler Square表示，該項研究發現意義深遠，部分因為發現脊椎動物特有之基因的明確角色，這是很難得的。
"We thought that gene duplication was the most important thing. But here, we found both of those things [new genes and duplications] happening at once," said Square.
Square宣稱：「他們認為基因複製是最重要的。不過此時，他們發現那兩件事(新基因及複製)同時發生。」
Fish were the first vertebrates, from which all others evolved -- including humans. But there is a gap in the fossil record right when the first fish were evolving, because they had little, soft skeletons which were not preserved in the fossil record.
魚類是最早的脊椎動物，所有其他脊椎動物(包括人類)皆從其演化而來。不過，當最早的魚類演化時，在化石記錄中，就有一處缺口。因為，它們幾乎沒有，不被保存於化石記錄中的軟骨骼。
So how can scientists work out where the first fish came from, and therefore how all vertebrates came to be?
那麼，科學家們如何能確認最早魚類來自何處，及於是所有脊椎動物如何出現？
"Rather than looking at fossils, we use tools like molecular biology and genetics to try to understand how evolution has happened, kind of like genetic paleontology," said Medeiros. "In the deepest molecular genetic terms, we're trying to reverse engineer how a creature evolves. It's the closest you can get to Jurassic Park."
Medeiros宣稱：「並非檢視化石，他們使用像分子生物學及遺傳學，來試圖瞭解，像遺傳古生物學之類的演化，曾如何發生。在最深層的分子遺傳條件下，他們正嘗試進行，生物如何演化的反向工程。這是能最接近侏羅紀公園的方法。」
The creature they chose to reverse engineer, however, might seem a bit monstrous. "While most people think of a big ugly hurricane of teeth sticking on to fish and chewing on them, sea lamprey are surprisingly cute when they're little baby larvae," said Square.
不過，他們選擇來進行反向工程的生物，可能看起來有點怪物般。Square宣稱：「儘管大多數人認為，附著於魚上並啃食它們的牙齒，是一大醜陋之物。不過，當海七鰓鰻是小幼體時，它們是出人意料地可愛。」
The sea lamprey, a jawless fish, diverged in evolution from other fish 500 million years ago. Because they hold onto several older vertebrate features, this gives the researchers the best snapshot of the early stage of vertebrate evolution with a living organism today.
在演化上，5億年前，海七鰓鰻(一種無顎魚)與其他魚類分道揚鑣。因為，它們保留了若干較古老脊椎動物的特徵。這為此些研究人員提供了，當今現有生物，在脊椎動物演化初期的最佳快照(點滴見解)。
"A lamprey and a human are extremely different. But by doing these kinds of studies, we can know what makes them the same," said Square. "This is stuff that's really fundamental, not just to mammals and humans, but to every vertebrate that exists."
Square宣稱：「七鰓鰻與人類截然不同。不過，藉由進行這類的研究，能知曉什麼使其相同。這是真正固有的東西，不只是哺乳動物及人類，而且是所有存在的脊椎動物。」
Square and his colleagues used the gene-editing tool CRISPR during its early days to find out how important this new gene family is to making vertebrates, well, vertebrates.
在其初期幾天期間，Square及其同僚們使用了群聚、規律性間隔開的短迴文結構複製(CRISPR：Clustered Regularly Interspaced Short Palindromic Repeat)的基因編輯工具，來查明此新基因群，對導致脊椎動物有多重要。
"It was the wild west of CRISPR days," said Square. "But we couldn't have done this whatsoever if it weren't for CRISPR."
Square宣稱：「這是CRISPR時代的狂野西部。不過，倘若不是CRISPR，他們就不可能做到此。」
Not only did this technology allow the researchers to test hypotheses functionally, by knocking out genes, but they were also the first team to use CRISPR in sea lampreys. Previously, this technology had only been used in some vertebrates like mice, frogs and zebrafish.
不僅該項技術確實使此些研究人員得以，藉由剔除基因，從功能上試驗諸多假設。而且他們也是最先於海七鰓鰻中，使用CRISPR的團隊。先前，該項技術僅被使用於，諸如小鼠、青蛙及斑馬魚等，一些脊椎動物。
"And that's a really narrow view of life on the planet," said Medeiros. "What CRISPR has done is democratized genetic studies across diverse organisms. It's super powerful for answering evolutionary questions."
Medeiros宣稱：「不過，那是地球上之生物，一種很不充裕的概觀。CRISPR所做的是，大眾化跨不同生物的遺傳研究。就解答演化上的問題而言，這是超級強有力的。」
原文網址：https://www.colorado.edu/today/2020/09/16/scientists-identify-gene-family-key-unlocking-vertebrate-evolution
翻譯：許東榮
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