美实验用啤酒酵母菌揭示单细胞变多细胞过程

sunsong7

2012年01月18日11:24科技日报
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/ x( H; x2 ?/ W/ ~& N0 k' y [导读]美国明尼苏达大学研究人员在实验室用普通的啤酒酵母菌复制了这一关键进化步骤，演示了这一过渡的发生过程。$ b; J  @% W. W7 R$ m- T3 r6 ~$ ?! B
　　从单细胞生物到多细胞体这一过渡是怎么发生的？据美国物理学家组织网1月16日报道，5亿多年前，地球表面的单细胞生物开始形成多细胞簇，最终变成了植物和动物。美国明尼苏达大学研究人员在实验室用普通的啤酒酵母菌复制了这一关键进化步骤，演示了这一过渡的发生过程。相关论文发表在近期出版的《美国国家科学院院刊》上。6 r; a4 g* z: D9 t
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　　研究人员将啤酒酵母菌加入到培养基中，在试管内生长了一天，然后用离心机搅动使试管中的成份分层。当混合物稳定下来，细胞簇会更快地落在试管底部，因为它们最重。研究人员把这些细胞簇取出来，转移到新的培养基中，然后再次搅动它们。六轮循环后，细胞簇已经包含了几百个细胞，看起来就像球形的雪花。* e8 |6 t7 x; ?) a/ W5 T- Z% f' X
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　　酵母菌“进化”成了多细胞簇，能协同合作、繁殖并改变它们的环境，基本上变成了今天地球生命的初期形式。分析显示，细胞簇并不是随机粘在一起的细胞群，而是互相关联的，它们随着细胞分裂而保持连接。这表示它们具有遗传相似性以促进合作。当细胞簇达到临界大小时，一些细胞就会进入凋亡过程而死亡，将后代细胞分隔开来。而后代细胞簇的繁殖扩展也只能到达它们“父母”所达到的大小。“这种劳动分工进化得非常快，以雪花状集簇的形式不断繁殖。”国家科学基金会环境生物学分部代理副主管乔治·吉尔克利斯特说，“通向多细胞复合体的第一步，好像并没有理论认为的那么艰巨。”
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　　“一个细胞簇还不能称为多细胞体，只有当其中的细胞开始合作，自我牺牲以达成公共利益并能适应变化，这就是向多细胞体进化的一种过渡。” 论文作者之一、明尼苏达州立大学科学家威尔·拉特克利夫解释说，要形成多细胞生物，大部分细胞要牺牲它们的繁殖能力，这是一种有利整体却不利于个体的行为。比如人体的几乎所有细胞从本质上说就是一个支持系统，只有精子和卵子负责把DNA传到下一代。所以多细胞体是由其合作性来定义的。+ e2 @. ~% a% Y4 f: z
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　　进化生物学家们估计，这种多细胞体独立地进化成了25个体系，将来通过对比多细胞簇留下来的化石，可进一步揭示每个体系中相应的发展机制和基因异同。
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　　新实验方法可用于对许多医疗和生物重要课题的研究，比如多细胞体在癌症、老化及其他生物学关键领域中的功能。论文合著者、明尼苏达大学的迈克尔·特拉维萨诺说，最近有人提出，癌症是一种源自最初的多细胞体的化石，而老化的起源也与此类似，通过多细胞酵母菌可以直接对此进行研究。5 `* Y  k* w% x: g
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Evolving Multicellularity  http://the-scientist.com/2012/01/16/evolving-multicellularity/# D; n5 ^$ D/ \8 |' @& M
Using an artificial selection paradigm, researchers watch as unicellular yeast evolve into snowflake-like clusters with distinct multicellular characteristics./ A  A: l7 K& [% T* a% Z8 J
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By Jef Akst | January 16, 2012 ( v5 c: s& k# j* B

# E  Z3 D  G6 lA yeast cluster with dead cells shown in red. t  L+ l3 D# J0 v
William Ratcliff, University of MinnesotaIn as little as 100 generations, yeast selected to settle more quickly through a test tube evolved into multicellular, snowflake-like clusters, according to a paper published today (January 16) in Proceedings of the National Academy of Sciences. Over the course of the experiment, the clusters evolved to be larger, produce multicellular progeny, and even show differentiation of the cells within the cluster—all key characteristics of multicellular organisms.' F! ^# i  a( X& y  }, [$ E  t" N7 @9 y
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“It’s very cool to demonstrate that [multicellularity] can happen so quickly,” said evolutionary biologist Mansi Srivastava of the Whitehead Institute for Biomedical Research in Massachusetts, who was not involved in the research. “Looking at the fossil record, we learned it took a very long time whenever these different transitions to multicellularity happened. Here they show it can happen very quickly.”5 O! P' i7 `9 q1 G  O7 T1 R+ E" C& G

! Q; }3 `& |& y“[The study] was provocative,” agreed biochemist Todd Miller of Stony Brook University in New York, who did not participate in the work. “It’s a different way of attacking the problem [of how multicellularity evolved]—coming from a simple system that doesn’t normally do this and seeing what it takes to make it do it.”
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The evolution of multicellular life has long intrigued evolutionary biologists. Cells coming together and cooperating for the good of the group goes against basic Darwinian principles. Yet multicellularity has evolved some two dozen times independently in nature, and has shaped the world as we know it.$ X4 l/ ?  l" K1 ?

, j# c7 [9 ~% u3 g: F% v8 xBut because most transitions to multicellularity happened more than 200 million years ago, many questions remain about how it happened. What were the ecological conditions that drove the transitions? And how did organisms overcome the conflicts of interest that accompany any sort of cooperative effort?
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To gain a better understanding of the initial leap from singularity, University of Minnesota evolutionary biologist Michael Travisano, his postdoc Will Ratcliff, and their colleagues decided to see if they could recreate such a transition in the lab. Their strategy was simple: grow yeast in test tubes, shake up those test tubes every 24 hours, and select those organisms that fell to the bottom quickest to transfer to new media and propagate the population. After 2 weeks and about 100 generations, the researchers began to see the yeast forming snowflake-like clusters that dropped to the bottom of the test tubes 34 percent faster than single cells.
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“We went to the microscope and were blown away,” Ratcliff said. “They form these clusters, and these clusters have these emergent properties of multicellular life.”
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The clusters continued to evolve over the course of the experiment, growing larger and asexually producing multicellular progeny. The yeast showed signs of having juvenile and adult life stages—only producing progeny once the cluster reached a certain size. They even evolved a kind of division of labor among the cells of the cluster, with certain yeast cells more readily undergoing apoptosis. Those apoptotic cells sacrificed their own reproductive output, but seemed to aid the reproduction of the entire cluster by allowing smaller cluster progeny to break off from the parent.# @8 _8 }# c0 F6 c
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Experimental evolution of multicellularity

9 ^2 C  p4 v: g* Xhttp://www.pnas.org/content/early/2012/01/10/11153231096 {. c: X5 Z( }2 P/ q- Z! L
William C. Ratcliffa,1, R. Ford Denisona, Mark Borrelloa, and Michael Travisanoa,baDepartment of Ecology, Evolution and Behavior and bBioTechnology Institute, University of Minnesota, Minneapolis, MN 55108 Edited* by Richard E. Lenski, Michigan State University, East Lansing, MI, and approved December 14, 2011 (received for review September 19, 2011) + O' s  {5 W  c2 j3 b" t8 E7 i

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Multicellularity was one of the most significant innovations in the history of life, but its initial evolution remains poorly understood. Using experimental evolution, we show that key steps in this transition could have occurred quickly. We subjected the unicellular yeast Saccharomyces cerevisiae to an environment in which we expected multicellularity to be adaptive. We observed the rapid evolution of clustering genotypes that display a novel multicellular life history characterized by reproduction via multicellular propagules, a juvenile phase, and determinate growth. The multicellular clusters are uniclonal, minimizing within-cluster genetic conflicts of interest. Simple among-cell division of labor rapidly evolved. Early multicellular strains were composed of physiologically similar cells, but these subsequently evolved higher rates of programmed cell death (apoptosis), an adaptation that increases propagule production. These results show that key aspects of multicellular complexity, a subject of central importance to biology, can readily evolve from unicellular eukaryotes.
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Tlexander

wonderful,thanks share

nmgnydxgy

同样的方法应用到某些细菌上，很可能达到相似的结果。做进化的孩子们，加油了！

Xenia

要是恩能用活细胞工作站类似的仪器拍到动态的效果，那真的了不起了哦