美國(guó)科學(xué)家進(jìn)行的一項(xiàng)最新研究,，為人們?cè)诨驅(qū)用嫔险J(rèn)識(shí)自然選擇過(guò)程提供了一幅精妙而詳盡的畫面,。相關(guān)論文發(fā)表在10月11日的《自然》雜志上,。
領(lǐng)導(dǎo)該項(xiàng)研究的是美國(guó)霍華德·休斯醫(yī)學(xué)研究所（Howard Hughes Medical Institute）的Sean B. Carroll,，他和同事證實(shí)了一個(gè)單獨(dú)的酵母菌基因如何經(jīng)過(guò)多代繁殖演變成兩種特異性基因,，并且刻畫出了這兩者如何分工,，從而使酵母菌成為適應(yīng)其生存環(huán)境的“居民”,。這項(xiàng)工作十分重要,，因?yàn)樗鼜淖罡镜膶用嫔详U明了進(jìn)化的驅(qū)動(dòng)力——生物如何變得更加適應(yīng)環(huán)境。Carroll表示,，“這實(shí)際上就是一個(gè)新的功能如何出現(xiàn),、如何進(jìn)化的問(wèn)題”。
利用特殊的分子手段,，研究人員重現(xiàn)了酵母菌體內(nèi)一個(gè)與糖類利用相關(guān)的重要基因,，在過(guò)去1億年的時(shí)間里所發(fā)生的一系列遺傳變化。Carroll說(shuō),，基因復(fù)制時(shí)產(chǎn)生的變異是創(chuàng)新之源,。同時(shí)，兩個(gè)基因肯定比一個(gè)好,，因?yàn)槿哂嗫梢源龠M(jìn)分工,，從而導(dǎo)致新的基因功能出現(xiàn)。比如,，人眼的顏色識(shí)別需要能夠區(qū)分紅綠色彩的不同蛋白受體來(lái)完成,，而這兩種受體都源于相同的視覺(jué)基因。
Carroll表示,，進(jìn)化研究中最大的困難是自然的遺傳變異發(fā)生的腳步太過(guò)緩慢,，即使經(jīng)過(guò)數(shù)千年甚至數(shù)百萬(wàn)年的積累，構(gòu)成基因的堿基對(duì)也沒(méi)有多少增量,。也正因?yàn)槿绱?，此次的研究選用了酵母菌這個(gè)繁殖周期短、能力強(qiáng)的理想模型,。
除了追溯酵母菌的整個(gè)進(jìn)化過(guò)程,，新的研究還包括交換酵母菌基因組中的不同區(qū)域片斷，評(píng)估這對(duì)兩種特異性基因表現(xiàn)的影響,，等等,。
Carroll表示，物種變得更有效率,、更加適應(yīng)環(huán)境的過(guò)程是“積跬步而致千里”,。隨著時(shí)間的流逝，微小的遺傳變化不斷疊加，最終導(dǎo)致一些生物成功地凌駕于其他同類之上,。“自然選擇讓一個(gè)基因擁有了兩個(gè)功能,，并且刻畫出了特異性基因的‘裝配線’，”他說(shuō),。（科學(xué)網(wǎng) 任霄鵬/編譯）
原始出處:
Nature 449, 677-681 (11 October 2007) | doi:10.1038/nature06151; Received 26 June 2007; Accepted 8 August 2007
Gene duplication and the adaptive evolution of a classic genetic switch
Chris Todd Hittinger1,2 & Sean B. Carroll1
Howard Hughes Medical Institute, Laboratory of Genetics, University of Wisconsin-Madison, 1525 Linden Drive, Madison, Wisconsin 53706, USA
Present address: Center for Genome Sciences, School of Medicine, Washington University in St Louis, 4444 Forest Park Avenue, St Louis, Missouri 63108, USA.
Correspondence to: Sean B. Carroll1 Correspondence and requests for materials should be addressed to S.B.C. (Email: [email protected]) and C.T.H. (Email: [email protected]).
How gene duplication and divergence contribute to genetic novelty and adaptation has been of intense interest, but experimental evidence has been limited. The genetic switch controlling the yeast galactose use pathway includes two paralogous genes in Saccharomyces cerevisiae that encode a co-inducer (GAL3) and a galactokinase (GAL1). These paralogues arose from a single bifunctional ancestral gene as is still present in Kluyveromyces lactis. To determine which evolutionary processes shaped the evolution of the two paralogues, here we assess the effects of precise replacement of coding and non-coding sequences on organismal fitness. We suggest that duplication of the ancestral bifunctional gene allowed for the resolution of an adaptive conflict between the transcriptional regulation of the two gene functions. After duplication, previously disfavoured binding site configurations evolved that divided the regulation of the ancestral gene into two specialized genes, one of which ultimately became one of the most tightly regulated genes in the genome.
