一項研究報告說,，從單細(xì)胞到多細(xì)胞的轉(zhuǎn)變的最初關(guān)鍵步驟的進(jìn)化速度可能比此前認(rèn)為得更快。
William C. Ratcliff及其同事讓單細(xì)胞酵母釀酒酵母（Saccharomyces cerevisiae）生活在一種環(huán)境中,，在這種環(huán)境中，多細(xì)胞被認(rèn)為是一種適應(yīng)性的性狀,，這是建立在一個事實的基礎(chǔ)上,，即酵母細(xì)胞集群比單個細(xì)胞在液體中的定居速度更快。在60天的快速定居選擇中,，全部實驗酵母種群都以多個附著細(xì)胞的雪花樣集群為主,，這是由在細(xì)胞分裂之后仍然相互粘著的細(xì)胞形成的,。
這種集群顯示出了幾種多細(xì)胞性狀,，包括通過產(chǎn)生雪花樣子代集群的多細(xì)胞“生殖芽”進(jìn)行繁殖以及一個幼年階段的出現(xiàn)。當(dāng)定居選擇的強(qiáng)度發(fā)生變化的時候,，雪花酵母通過在多細(xì)胞層次而非單細(xì)胞層次上對變化進(jìn)行了適應(yīng),，這表明整個細(xì)胞集群作為一個整體進(jìn)行進(jìn)化。
這組科研人員還觀察到了集群內(nèi)部的勞動分工的進(jìn)化：大多數(shù)細(xì)胞仍然活著并能進(jìn)行繁殖,，但是少部分細(xì)胞進(jìn)行了程序細(xì)胞死亡,，或者說細(xì)胞凋亡。凋亡的細(xì)胞起到了多細(xì)胞集群中的斷裂點的作用,，讓雪花酵母調(diào)控它們產(chǎn)生的后代的數(shù)量和尺寸,。
這些發(fā)現(xiàn)提示多細(xì)胞復(fù)雜性的關(guān)鍵特性可以在一種單細(xì)胞真核細(xì)胞中容易地進(jìn)化出來。(生物谷Bioon.com)
doi: 10.1073/pnas.1115323109
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Experimental evolution of multicellularity
William C. Ratcliffa,1, R. Ford Denisona, Mark Borrelloa, and Michael Travisanoa,b
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.
