自然界中有機生命體形態(tài)和大小的多樣性分異究竟如何而來,？科學(xué)家通過對果蠅進行研究解開了謎團：果蠅體內(nèi)一種基因強化因子通過逐步改變DNA序列來增加生物形貌分異度,。
圖：背部缺少毛發(fā)群的Drosophila sechellia
基因轉(zhuǎn)錄過程被嚴(yán)密控制，一系列錯綜復(fù)雜的DNA調(diào)控序列,、數(shù)量巨大的蛋白質(zhì)與其他各種因素共同影響著基因的激活與作用,。這一過程的研究曾令無數(shù)分子生物學(xué)家困惑。不過現(xiàn)在,，來自美國普林斯頓大學(xué)的D.Stern,，斯洛伐克獸醫(yī)大學(xué)的A.McGregor和法國圖盧茲大學(xué)的François Payre的共同研究，開啟了此項研究的新篇章,。
研究對象為兩種果蠅的幼蟲,，分別是Drosophila melanogaster和Drosophila sechellia，前者為廣泛分布的屬種,，后者則僅分布于塞舌爾,，兩者以毛狀體（trichomes）的不同區(qū)分。這種區(qū)別源自名為“光寶貝”（shaven baby, svb）的基因,，光寶貝基因的不表達使得Drosophila sechellia幼蟲的頭部和背部缺少毛發(fā)群,。McGregor更進一步發(fā)現(xiàn)，E強化因子對光寶貝基因的表達與否起著決定作用,，其中的E6段承擔(dān)著激活光寶貝基因的任務(wù),，而Drosophila sechellia的E6段與眾不同,。
Stern手下的兩名博士后系統(tǒng)檢測了E強化因子各種變化的影響。結(jié)果顯示,，E強化因子至少有五種對表達結(jié)果產(chǎn)生影響的變化,，它們其中的任何一個都僅能產(chǎn)生微弱的影響，但五種變化組合到一起,，則會產(chǎn)生巨大的影響,。因此，五種變化之間的任意組合,，都會產(chǎn)生形貌不同的果蠅種類,。研究結(jié)果對于理解形貌進化有重要的指示意義。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature DOI：10.1038/nature05988
Morphological evolution through multiple cis-regulatory mutations at a single gene
Alistair P. McGregor, Virginie Orgogozo, Isabelle Delon, Jennifer Zanet, Dayalan G. Srinivasan, Franois Payre & David L. Stern
One central, and yet unsolved, question in evolutionary biology is the relationship between the genetic variants segregating within species and the causes of morphological differences between species. The classic neo-darwinian view postulates that species differences result from the accumulation of small-effect changes at multiple loci. However, many examples support the possible role of larger abrupt changes in the expression of developmental genes in morphological evolution1, 2, 3. Although this evidence might be considered a challenge to a neo-darwinian micromutationist view of evolution, there are currently few examples of the actual genes causing morphological differences between species4, 5, 6, 7, 8, 9, 10. Here we examine the genetic basis of a trichome pattern difference between Drosophila species, previously shown to result from the evolution of a single gene, shavenbaby (svb), probably through cis-regulatory changes6. We first identified three distinct svb enhancers from D. melanogaster driving reporter gene expression in partly overlapping patterns that together recapitulate endogenous svb expression. All three homologous enhancers from D. sechellia drive expression in modified patterns, in a direction consistent with the evolved svb expression pattern. To test the influence of these enhancers on the actual phenotypic difference, we conducted interspecific genetic mapping at a resolution sufficient to recover multiple intragenic recombinants. This functional analysis revealed that independent genetic regions upstream of svb that overlap the three identified enhancers are collectively required to generate the D. sechellia trichome pattern. Our results demonstrate that the accumulation of multiple small-effect changes at a single locus underlies the evolution of a morphological difference between species. These data support the view that alleles of large effect that distinguish species may sometimes reflect the accumulation of multiple mutations of small effect at select genes.
