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Trout, Your Mama Was a Salmon
Scientists have for the first time coaxed salmon to produce trout sperm and eggs. These special deliveries might allow researchers to resurrect extinct species from frozen cells.
The study clears a major conservation hurdle. Scientists often freeze eggs and sperm of endangered animals to keep viable genetic material around in case of extinction. However, fish eggs cannot be preserved this way because of their large size and high fat content. But undeveloped male sperm cells, called spermatogonia, do fine in a freezer. When thawed and implanted into another fish, they migrate to the gonads and grow into either sperm or eggs, depending on the sex of their host. This technique works within a species, but no one had tried transfers between fish species.
Researchers at the Tokyo University of Marine Science and Technology collected spermatogonia from adult rainbow trout and injected them into sterile salmon embryos. The researchers raised the fish to sexual maturity and found that 10 of the 29 male salmon produced trout sperm, and five of the 50 female salmon produced trout eggs. In comparison, a control group of sterile salmon that did not receive transplants had no mature sex cells at all. As the team reports in the 14 September issue of Science, when it combined eggs and sperm from the recipients, a new generation of healthy trout hatched. Co-author Goro Yoshizaki says his team used sterile recipient fish so that only donor-derived sex cells could be produced. That way, when the researchers mixed eggs from the female salmon with sperm produced by the males, they got "100% trout."
Fish geneticist Gary Thorgaard of Washington State University in Pullman says he is "very excited" by the study because it "opens up new directions both in research with salmon and trout and in conservation approaches." But, he warns, only a small percentage of salmon in the study produced sperm and eggs, and that could create a "genetic bottleneck" where inbreeding occurs. To prevent this, Thorgaard says, researchers will need to get more surrogates reproducing so that enough genetic diversity is available to keep endangered fish safely in the gene pool.
濒危鱼类保护新方法
科学家已首次利用三纹鱼产生鳟鱼精子和卵细胞。这可能使科学家从冷冻细胞复活灭绝物种。
通常科学家会冷冻濒危动物的卵细胞和精子，以保持有效的遗传物质不灭绝。不过，鱼的卵细胞不能这样保存，因为它们“个头”太大和脂肪含量太高。但未发育的雄性精子细胞，即精原细胞，能够较好的冷冻保存。当将其解冻植入另一条鱼中后，他们在鱼的性腺中发育成精子或卵子，这取决于受体鱼的性别。这一技术只在同一物种中实施过，没有人曾试图在不同种的鱼之间进行移植。
研究人员在东京大学海洋科学与技术部门收集成熟虹鳟鱼精原细胞注入到不育的三纹鱼胚胎。研究者在三纹鱼性成熟后，发现29条雄性三纹鱼中有10条产生了鳟鱼产生精子，50条三纹鱼中有5条产生了鳟鱼卵细胞。相较之下，对照组的没有接受移植的不育三纹鱼没有成熟性细胞。发表在9月14日的science上的研究结果显示，结合受体三纹鱼产生的卵子与精子，孵化出了新一代的健康鳟鱼。Goro Yoshizaki说，他的研究小组利用不育的受体鱼，那样就只会产生移植的性细胞。因此，当研究者混合雌性三纹鱼产生的鳟鱼卵子与雄性三纹鱼产生的鳟鱼精子，便得到了"百分之百的鳟鱼" 。
华盛顿州立大学的鱼类遗传学家Gary Thorgaard说“这个结果非常令人兴奋” ，因为"无论是在三纹鱼还是鳟鱼和保护办法上，都开辟了新的方向" 。但是，他警告说，只有一小部分的比例三纹鱼研究产生精子和卵子，这可能形成一个"遗传瓶颈" –-发生近亲繁殖。为防止这种情况， thorgaard说，研究者将需要获得更多的移植受体，使具有足够的遗传多样性，来保持濒危鱼类安全。
鳟鱼（trout）属鲑目，鲑科，是一类很有价值的垂钓鱼和食用鱼，全世界大约也只有10种左右。由于世界各地每年都大量捕捞，因此，全世界大多数野生山海鳟、山鳟等鳟鱼都数量锐减，陷入濒危状。三纹鱼（Salmon）、鳟鱼（Trout）和鲑鱼（Char）三大类统称为鲑鱼。
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