6月 26, 2022

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Brown Rat

マンモスを忘れてください-これらの科学者は、そのDNAを編集することによって、絶滅したクリスマス島のネズミを復活させるために働いています

恐竜は6500万年前に絶滅し、マンモスは4、000年前に絶滅し、クリスマス島は119年前に絶滅しました。 1990年代に人気のある概念になって以来、絶滅の取り組みは伝説的な地位の大型動物に焦点を当ててきましたが、2022年3月9日にジャーナルに掲載された論文では 現在の生物学、古生物学者のチームが彼に注意を向けます Ratus McClearyそして彼らの発見は、すべての種にわたる絶滅を排除することの限界への洞察を提供します。

消滅の行為は未知のものによって定義されます。 絶滅した種のゲノムを配列決定するとき、科学者は衰退する種を扱うという課題に直面します[{” attribute=””>DNA, which doesn’t yield all the genetic information required to reconstruct a full genome of the extinct animal. With the Christmas Island rat, which is believed to have gone extinct because of diseases brought over on European ships, evolutionary geneticist Tom Gilbert at University of Copenhagen and his colleagues lucked out.

Not only was the team able to obtain almost all of the rodent’s genome, but since it diverged from other Rattus species relatively recently, it shares about 95% of its genome with a living rat, the Norway brown rat. “It was a quite a nice test model,” says Gilbert. “It’s the perfect case because when you sequence the genome, you have to compare it to a really good modern reference.”

Christmas Island Rat (Rattus macleari)

Maclear’s rat (Rattus macleari) is an extinct large rat endemic to Christmas Island in the Indian Ocean. Credit: Joseph Smit, Proceedings of the Zoological Society of London 1887

After the DNA has been sequenced as well as possible and the genome is matched up against the reference genome of the living species, the scientists identify the parts of the genomes that don’t match up and, in theory, would then use CRISPR technology to gene edit the DNA of the living species to match that of the extinct one. The brown-rat-to-Christmas-Island-rat scenario is a particularly good test case because the evolutionary divergence is similar to that of the elephant and the mammoth.

Though the sequencing of the Christmas Island rat was mostly successful, a few key genes were missing. These genes were related to olfaction, meaning that a resurrected Christmas Island Rat would likely be unable to process smells in the way as it would have originally. “With current technology, it may be completely impossible to ever recover the full sequence, and therefore it is impossible to ever generate a perfect replica of the Christmas Island rat,” says Gilbert.

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“It is very, very clear that we are never going to be able to get all the information to create a perfect recovered form of an extinct species,” he says. “There will always be some kind of hybrid.” Though a replica will never be perfect, the key is that scientists are able to edit for the DNA that makes the extinct animal functionally different from the living one.

Gilbert says that in order to make an ecologically functional mammoth, for example, it might be enough to edit elephant DNA to make the animal hairy and able to live in the cold. “If you’re making a weird fuzzy elephant to live in a zoo, it probably doesn’t matter if it is missing some behavioral genes,” he says. “But that brings up a whole lot of ethical questions.”

Gilbert plans to try doing the actual gene editing on rats but would like to start with species that are still living. He intends to begin by doing CRISPR edits on a black rat genome to change it to a Norway brown rat before attempting to resurrect the Christmas Island rat. Though he is excited about his future research, the whole process still gives him pause. “I think it’s a fascinating idea in technology, but one has to wonder if that’s the best use of money as opposed to keeping the things alive that are still here,” he says.

Reference: “Probing the genomic limits of de-extinction in the Christmas Island rat” by Jianqing Lin, David Duchêne, Christian Carøe, Oliver Smith, Marta Maria Ciucani, Jonas Niemann, Douglas Richmond, Alex D. Greenwood, Ross MacPhee, Guojie Zhang, Shyam Gopalakrishnan and M. Thomas P. Gilbert, 9 March 2022, Current Biology.
DOI: 10.1016/j.cub.2022.02.027

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This work was supported by the European Research Council and the Danish National Research Foundation.