Scientists just created female clones of male mice
Scientists just created female clones of male mice
科学家首次成功利用雄性小鼠克隆出雌性后代
EXECUTIVE SUMMARY 执行摘要
Scientists have deliberately turned male mouse embryos into females for the first time. A team based in Japan used a CRISPR-based approach to remove the Y chromosome from male cells and create female clones of male mice. 科学家首次成功地将雄性小鼠胚胎人为转化为雌性。日本的一个研究团队利用基于 CRISPR 的技术，去除了雄性细胞中的 Y 染色体，并成功克隆出了雄性小鼠的雌性后代。
“No one has done this before,” says Monika Ward, a reproductive biologist at the University of Hawaii, who was not involved in the research. The feat could change the way scientists think about reproduction, says Takashi Ishiuchi, a reproductive biologist at the University of Yamanashi, who co-led the work. 夏威夷大学的生殖生物学家莫妮卡·沃德（Monika Ward）表示：“此前从未有人做到过这一点。”她并未参与这项研究。该研究的共同负责人、山梨大学的生殖生物学家石内隆（Takashi Ishiuchi）认为，这一壮举可能会改变科学家对生殖的认知。
The findings were published in a preprint paper shared on bioRxiv earlier this month, which has not yet been through the peer-review process. “There’s a fixed concept in our scientific field that we need both females and males for reproduction,” says Ishiuchi. “I think we could change this concept.” 这项研究成果于本月初以预印本形式发布在 bioRxiv 上，目前尚未经过同行评审。石内隆表示：“在我们的科学领域中，存在一种固有的观念，即生殖需要雌雄双方共同参与。我认为我们可以改变这一观念。”
He and his colleague Shogo Matoba of the Riken BioResource Research Center in Ibaraki also hope their technique could help rescue endangered species, particularly in cases where only a few individuals remain. “It’s exciting to see,” says Ben Novak, lead scientist at the wildlife conservation organization Revive & Restore, who was not involved in the work. “I am confident there will be plenty of applications, particularly for conservation purposes.” 他和同事——位于茨城县的理化学研究所生物资源研究中心的的场章悟（Shogo Matoba）也希望，他们的技术能够帮助拯救濒危物种，特别是在仅存少量个体的情况下。野生动物保护组织“Revive & Restore”的首席科学家本·诺瓦克（Ben Novak）表示：“看到这一成果令人兴奋。我相信它会有很多应用场景，特别是在物种保护方面。”他并未参与此项研究。
Sex change 性别转换
Ishiuchi says he and his colleagues were inspired by the Okinawa rubble goby, a fish that can change its sex in certain situations. If no males are present, a female can do this in order to reproduce with the other females. Males can also change sex to female. This ability to change sex might be useful when it comes to rescuing endangered species, including mammals. 石内隆表示，他和同事的灵感来源于冲绳虾虎鱼，这种鱼在特定情况下可以改变性别。如果没有雄性存在，雌性可以转变为雄性以便与其他雌性繁殖。雄性也可以转变为雌性。这种改变性别的能力在拯救包括哺乳动物在内的濒危物种时可能非常有用。
There’s some precedent in the lab—albeit not intentional. In 2009, researchers reported the accidental birth of a single female pup in a batch of 27 clones created from male mouse cells. 实验室中曾有过类似的先例，尽管并非出于本意。2009 年，研究人员报告称，在利用雄性小鼠细胞进行的 27 例克隆实验中，意外诞生了一只雌性幼崽。
Sometimes the surviving population of a species falls so low that scientists will try to clone those animals. Cloning isn’t perfect—it can be tricky and inefficient, and it creates genetically identical individuals whose offspring might be more vulnerable to disease. But it has helped scientists with efforts to bring some species back from the brink of extinction, including black-footed ferrets and Przewalski’s horse. 有时，一个物种的存活数量会降至极低，科学家便会尝试克隆这些动物。克隆技术并不完美——它既复杂又低效，且产生的个体基因完全相同，其后代可能更容易受到疾病侵害。但它确实帮助科学家将一些物种从灭绝边缘拉了回来，包括黑足鼬和普氏野马。
Cloning an individual can only replicate its genes, so cloning a male animal will create all male offspring, for example. That won’t help much in the hypothetical situation where only male individuals of a species are left. Ishiuchi has been working on a way to overcome this challenge by altering the chromosomes in cells. 克隆个体只能复制其基因，因此克隆雄性动物只会产生雄性后代。在假设某种物种只剩下雄性个体的情况下，这并不能提供太大帮助。石内隆一直致力于通过改变细胞中的染色体来克服这一挑战。
Mammals’ DNA is organized in pairs of chromosomes, including one pair of sex chromosomes. These sex chromosomes are typically XX in females and XY in males. It’s the Y chromosome that makes mammals male. Ishiuchi and his colleagues have developed a CRISPR-based tool to get rid of it. Their approach targets a section of the Y chromosome that plays an important role in ensuring that, each time a cell divides, the “daughter” cells inherit the Y chromosome. 哺乳动物的 DNA 以染色体对的形式组织，其中包括一对性染色体。这些性染色体在雌性中通常为 XX，在雄性中为 XY。正是 Y 染色体决定了哺乳动物的雄性特征。石内隆及其同事开发了一种基于 CRISPR 的工具来去除它。他们的方法针对的是 Y 染色体上的一个片段，该片段在确保细胞每次分裂时“子细胞”都能遗传 Y 染色体方面起着重要作用。
Cutting the Y 切除 Y 染色体
When the researchers tested their technique—which they call Y-CUT—in early-stage mouse embryos, they found they were able to eliminate the Y chromosome. Treated XY embryos were transferred to surrogate mice, which gave birth to female pups. The effect can be described as a “sex reversal,” say the researchers. 当研究人员在早期小鼠胚胎中测试他们称之为“Y-CUT”的技术时，发现他们能够消除 Y 染色体。经过处理的 XY 胚胎被移植到代孕小鼠体内，最终产下了雌性幼崽。研究人员称，这种效果可以被描述为“性别逆转”。
The female pups had XO chromosomes, which means they had one X chromosome rather than the usual two. But this didn’t seem to affect the animals, which grew up healthy and fertile, say Ishiuchi and Matoba. 这些雌性幼崽拥有 XO 染色体，这意味着它们只有一条 X 染色体，而不是通常的两条。石内隆和的场章悟表示，这似乎并没有影响这些动物，它们健康成长并具有生育能力。
In a second experiment, the researchers found they could also use Y-CUT to create female clones from male mice. A standard approach to cloning involves taking the DNA-containing nucleus of a cell from an adult animal and inserting it into an egg cell that has had its own DNA removed. Under the right conditions, the resulting cell can develop into an animal that is genetically identical to the original donor. 在第二次实验中，研究人员发现他们还可以利用 Y-CUT 技术从雄性小鼠身上克隆出雌性后代。标准的克隆方法是提取成年动物细胞中含有 DNA 的细胞核，并将其植入已去除自身 DNA 的卵细胞中。在适当的条件下，由此产生的细胞可以发育成与原始供体基因完全相同的动物。
Matoba and his colleagues used a similar method. Once they had a glut of these cloned cells, they treated some with Y-CUT before transferring them to surrogate mice to carry the pregnancies. This allowed them to create female clones of male mice. The females are genetically identical to the original male, apart from the missing Y chromosome, says Matoba. 的场章悟及其同事使用了类似的方法。在获得大量此类克隆细胞后，他们用 Y-CUT 处理了其中一部分，然后将其移植到代孕小鼠体内进行妊娠。这使他们能够克隆出雄性小鼠的雌性后代。的场章悟表示，除了缺失 Y 染色体外，这些雌性个体与原始雄性在基因上是完全相同的。
“It’s like sci-fi,” says Ishiuchi. Courtesy of Takashi Ichiushi and Shogo Matoba, as published in their bioRxiv preprint. “这就像科幻小说一样，”石内隆说。（图片由石内隆和的场章悟提供，发表于他们的 bioRxiv 预印本中。）
In other experiments, the scientists were able to create female clones from male cells that had been cryopreserved—and the cloned males and females could mate to produce healthy pups. This suggests the Y-CUT approach might allow scientists to create female clones from male samples in “frozen zoos” that store cryopreserved cells and tissues from a range of animal species. 在其他实验中，科学家们成功地利用冷冻保存的雄性细胞克隆出了雌性后代，并且这些克隆出的雌性与雄性交配后产下了健康的幼崽。这表明 Y-CUT 技术或许能让科学家利用“冷冻动物园”（存储了各种动物物种的冷冻细胞和组织）中的雄性样本克隆出雌性个体。
It could have uses beyond conservation efforts, too. “This could be used potentially for producing genetically engineered animals,” says Ward. Creating an animal with multiple genetic edits can be time-consuming and expensive; creating male and female clones of that animal could help scientists time and money. Ward also hopes the technique could be a useful tool to study the biology of sex chromosomes. 它在物种保护之外也可能具有用途。沃德表示：“这可能被用于生产基因工程动物。”创造一个经过多次基因编辑的动物既耗时又昂贵；克隆出该动物的雄性和雌性后代可以帮助科学家节省时间和金钱。沃德还希望这项技术能成为研究性染色体生物学的有用工具。
Complementary techniques 互补技术
The Y-CUT approach isn’t perfect. For now, it still requires hollowed-out egg cells, which need to come from females of the same species or at least a closely related one. And it won’t be useful for endangered species in which only females survive. The technique works well in mice, partly because XO female mice are fertile. But while the approach might help some of the 355 endangered and vulnerable species of rodents, other mammals with XO chromosomes tend to experience infertility. Y-CUT 技术并不完美。目前，它仍然需要去核的卵细胞，这些卵细胞必须来自同物种或至少是亲缘关系相近的雌性个体。而且，对于仅存雌性的濒危物种，该技术也无法发挥作用。该技术在小鼠身上效果良好，部分原因是 XO 型雌性小鼠具有生育能力。然而，虽然这种方法可能有助于 355 种濒危和易危啮齿动物中的一部分，但其他拥有 XO 染色体的哺乳动物往往会出现不育问题。
But other new technologies could complement Y-CUT. In 2023, Katsuhiko Hayashi of Osaka University and his colleagues showed they could turn cells taken from male mice into egg cells. This enabled them to create… 但其他新技术可以与 Y-CUT 形成互补。2023 年，大阪大学的林克彦（Katsuhiko Hayashi）及其同事展示了他们可以将从雄性小鼠身上提取的细胞转化为卵细胞。这使他们能够创造出……