美科学家称匙吻鲟可解释人类如何进化出四肢 - 未名空间MITBBS历史存档

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美科学家称匙吻鲟可解释人类如何进化出四肢

美科学家称匙吻鲟可解释人类如何进化出四肢# Animals - 动物园

i*s2012-08-13 07:08

1 楼

Key words: Hox genes, American paddlefish, Karen Crow
研究人员认为这种原始鱼类能够解释人类如何进化出四肢　　新浪科技讯北京时间8月
12日消息，据国外媒体12日报道，美国科学家指出美洲匙吻鲟能够解释人类如何进化出
四肢。根据他们发表在《基因组生物学与进化》杂志上的一篇新研究论文，这种鱼在大
约4200万年前复制了完整的基因组。这一现象能够帮助解释鳍如何进化。匙吻鲟是世界
上最怪异的鱼类之一，吻很长，呈扁平桨状，卵用于制作高级鱼子酱。
美国旧金山州立大学生物学助理教授卡伦-克劳表示：“我们的研究发现匙吻鲟拥
有自身基因组的副本。这种复制形成了额外的基因材料，提高了比较研究的复杂性。这
可能改变我们针对肢体发育的研究方式。”为了研究人类的肢体如何发育，科学家将老
鼠的肢体基因与鱼类的鳍基因进行比较。此前有关匙吻鲟的研究显示，这种鱼类在出现
四足动物前很久就拥有生长出肢体所需要的“基因包”。四足动物最后进化成爬行类、
鸟类、两栖类和哺乳动物。
研究中，克劳和同事对美洲匙吻鲟含有19个Hox基因的染色体片段进行了排序。Hox
基因决定体形和肢体发育，同时也是帮助科学发现整个基因族副本的主要指示器。完整
基因组副本被研究人员称之为进化史上“一个颠覆游戏规则的事件”，让一种物种出现
新种或者奇特种群创造了条件。
这种复制的出现是一系列看似不可能的条件同时满足的结果，让匙吻鲟的每一个基
因都拥有副本。完成复制后，基因对中的一个基因保持原有的功能，另一个要么消失，
要么拥有一个新功能。克劳表示：“额外的基因材料为进化提供了画布，让进化过程描
绘出各种景象。”克劳一直从事新奇物种和生物多样性研究。
科学家认为这种基因组复制在有颌类脊椎动物出现前就已发生。在进化树的特定枝
杈(谱系)也出现完整基因组复制现象，植物要比动物更为普遍。克劳说：“我们对匙吻
鲟进行的研究显示动物的完整基因组复制现象并没有此前认为的那么罕见。”(孝文)

I*i2012-08-13 07:08

2 楼

再来看个英文的，做个对照。
Washington: A new study has found that the American paddlefish -- known for
its bizarre, protruding snout and eggs harvested for caviar -- duplicated
its entire genome about 42 million years ago.
This finding may add a new twist to the way scientists study how fins
evolved into limbs since the paddlefish is often used as a proxy for a more
representative ancestor shared by humans and fishes.
“We found that paddlefish have had their own genome duplication. This
creates extra genetic material that adds complexity to comparative studies.
It may change the way we interpret studies on limb development,” said Karen
Crow, assistant professor of biology at San Francisco State University.
In order to study how human limbs develop, scientists compare the limb-
building genes found in mice with fin-building genes found in fishes.
Previous research on paddlefish has suggested that fishes possessed the
genetic toolkit required to grow limbs long before the evolution of the four
-limbed creatures (tetrapods) that developed into reptiles, birds,
amphibians and mammals.
In the last decade, paddlefish have become a useful benchmark in
evolutionary studies because their position on the evolutionary tree makes
them a reasonably good proxy for the ancestor of the bony fishes that
evolved into tetrapods such as humans. However, the fact that paddlefish
underwent a genome duplication could complicate what its genes tell us about
the fin-to-limb transition, said Crow.
“Our findings suggest that the results of previous studies using paddlefish
as a comparative species may need to be re-interpreted,” Crow said.
Crow and colleagues sequenced chromosomal regions containing 19 Hox genes in
the American paddlefish. Hox genes determine body shape and limb
development, and have become prime candidates for detecting whole genome
duplications.
Whole genome duplications are game-changing events in evolutionary history
that give rise to new species or novel features within a species. They occur
when a series of unlikely circumstances coincide, resulting in twin copies
of every gene. When this happens, one scenario that could take place is that
one gene in the pair keeps its designated function while the other is
either lost or takes on a new purpose.
“This extra genetic material provides the canvas for evolution to paint
with,” said Crow, who studies the evolution of novelty and diversity.
Two milestone genome duplications are believed to have taken place before
the evolution of jawed vertebrates. Additional whole genome duplications
have also taken place further down the evolutionary tree, in specific
lineages or branches, but it is a phenomenon more common in plants than
animals.
“Our findings on the paddlefish suggest that whole duplication is not as
uncommon in animals as previously thought,” Crow said.
The finding was published in the journal Genome Biology and Evolution.