生物谷報(bào)道：地球上最早的四足動(dòng)物出現(xiàn)在3.65億年前，通過(guò)對(duì)斑馬魚(yú)（zebrafish）和四足動(dòng)物體內(nèi)一種名為Hox的基因進(jìn)行研究,，科學(xué)家長(zhǎng)期以來(lái)認(rèn)為,，原始的魚(yú)類(lèi)不具有與四肢形成相關(guān)的Hox基因的另一個(gè)表達(dá)階段,，因而推斷四肢的進(jìn)化是由于遺傳變異形成了全新的基因功能。
然而,，科學(xué)家的一項(xiàng)最新研究顛覆了這一傳統(tǒng)的理論。比斑馬魚(yú)更加原始的魚(yú)類(lèi)就已經(jīng)具有與四肢分化相關(guān)的基因表達(dá)方式,，四肢的出現(xiàn)并不是一個(gè)全新的進(jìn)化事件,。這一成果發(fā)表在5月24日的《自然》雜志上。
進(jìn)行此項(xiàng)研究的是美國(guó)芝加哥大學(xué)的Neil Shubin,、Marcus Davis和Randall Dahn等,，他們?cè)谝环N十分古老的魚(yú)類(lèi)——匙吻鱘（paddlefish）體內(nèi)找到了上述的另一個(gè)表達(dá)階段,，證實(shí)了形成胸鰭與形成四肢的Hox基因活動(dòng)十分相似。該發(fā)現(xiàn)同時(shí)表明,，這種脊椎動(dòng)物特有的基因表達(dá)方式實(shí)際上更為古老,。
在此之前，Shubin等科學(xué)家發(fā)現(xiàn)并研究了一種3.75億年前的物種Tiktaalik roseae,，從形態(tài)學(xué)上填補(bǔ)了魚(yú)類(lèi)與陸生動(dòng)物之間的進(jìn)化缺失?，F(xiàn)在科學(xué)家無(wú)疑又從遺傳層面上揭示了四肢的演化。
不過(guò),，Shubin表示,，盡管這種基因表達(dá)方式肯定在現(xiàn)代四肢動(dòng)物的四肢進(jìn)化過(guò)程中起到了重要作用，但是在原始魚(yú)類(lèi)中,，這可能并不是它們的本意,。也就是說(shuō)，形成帶手腳趾的四肢的這種能力一直存在著,，但在一系列的環(huán)境刺激下,，這種能力才最終得到發(fā)展。
Shubin實(shí)驗(yàn)室目前已經(jīng)開(kāi)始對(duì)鯊魚(yú)進(jìn)行研究,，看類(lèi)似的基因表達(dá)是否存在于這種更古老的物種的進(jìn)化過(guò)程中,。（科學(xué)網(wǎng) 任霄鵬/編譯）
原始出處：
Nature 447, 473-476 (24 May 2007) | doi:10.1038/nature05838; Received 26 February 2007; Accepted 13 April 2007
An autopodial-like pattern of Hox expression in the fins of a basal actinopterygian fish
Marcus C. Davis1, Randall D. Dahn1 & Neil H. Shubin1,2
Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, Illinois 60637, USA
Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, Illinois 60605, USA
Correspondence to: Neil H. Shubin1,2 Correspondence and requests for materials should be addressed to N.H.S. (Email: [email protected]).
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Comparative analyses of Hox gene expression and regulation in teleost fish and tetrapods support the long-entrenched notion that the distal region of tetrapod limbs, containing the wrist, ankle and digits, is an evolutionary novelty1, 2, 3, 4. Data from fossils support the notion that the unique features of tetrapod limbs were assembled over evolutionary time in the paired fins of fish5. The challenge in linking developmental and palaeontological approaches has been that developmental data for fins and limbs compare only highly derived teleosts and tetrapods; what is lacking are data from extant taxa that retain greater portions of the fin skeletal morphology considered primitive to all bony fish6, 7. Here, we report on the expression and function of genes implicated in the origin of the autopod in a basal actinopterygian, Polyodon spathula. Polyodon exhibits a late-phase, inverted collinear expression of 5' HoxD genes, a pattern of expression long considered a developmental hallmark of the autopod and shown in tetrapods to be controlled by a 'digit enhancer' region. These data show that aspects of the development of the autopod are primitive to tetrapods and that the origin of digits entailed the redeployment of ancient patterns of gene activity.
