大自然中也在上演“真人秀”：逆境生存,，蛭形輪蟲或許能夠成為最后幸存的動物,。這種微小的水生生物能從高輻射和多年干燥的環(huán)境中存活下來，并且它們已經(jīng)無性生活了數(shù)百萬年,。
前不久,，在線發(fā)表于《科學(xué)公共圖書館—遺傳學(xué)》上的一項(xiàng)新研究揭示了蛭形輪蟲是如何做到這些的。
科學(xué)家通過基因分析發(fā)現(xiàn),，蛭形輪蟲大約10%的活躍基因是剽竊自其他物種的,，例如真菌、細(xì)菌和植物,。這些外源基因賦予蛭形輪蟲其他動物沒有的才能,。這能解釋為何蛭形輪蟲能在極其惡劣的環(huán)境中生存,。尤其是，這些外源基因讓蛭形輪蟲能一直獨(dú)身生活——這通常能導(dǎo)致其他動物的滅絕,。
蛭形輪蟲是一種遺傳嵌合體,，它們到處獲取DNA片段，就如同馬賽克一樣,，英國劍橋大學(xué)分子生物學(xué)家Alan Tunnacliffe表示,。像其他一些擁有“超能力”的生物一樣，顯微鏡下的蛭形輪蟲在惡劣的環(huán)境中快樂地生活著,。
大約有400種蛭形輪蟲生活在淡水和微咸水中。當(dāng)它們的水家園突然消失不見時(shí),，蛭形輪蟲也有大把的辦法幸存下來,，最長干燥存活紀(jì)錄達(dá)9年。
從一個(gè)進(jìn)化生物學(xué)家視角而言,，蛭形輪蟲更“超強(qiáng)”的能力是長期的無性生活,。大約8000萬年以來，所有的蛭形輪蟲都是雌性,，并穩(wěn)定地進(jìn)行著無性繁殖,。
生物學(xué)家一直認(rèn)為，有性繁殖帶來基因變異,，并讓物種隨著環(huán)境的變化而調(diào)整基因表達(dá),。并且人們普遍認(rèn)為，動物放棄性,，最終等于走向滅絕,。但是，蛭形輪蟲打破了這些傳統(tǒng)觀點(diǎn),。
之后,，科學(xué)家排序了蛭形輪蟲的DNA，發(fā)現(xiàn)它從超過500種不同的物種那里借來了DNA,，最終蛭形輪蟲成為了“超級英雄”,。（生物谷Bioon.com）
doi:10.1371/journal.pgen.1003035
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Biochemical Diversification through Foreign Gene Expression in Bdelloid Rotifers
Chiara Boschetti, Adrian Carr, Alastair Crisp, Isobel Eyres, Yuan Wang-Koh, Esther Lubzens, Timothy G. Barraclough, Gos Micklem, Alan Tunnacliffe
Bdelloid rotifers are microinvertebrates with unique characteristics: they have survived tens of millions of years without sexual reproduction; they withstand extreme desiccation by undergoing anhydrobiosis; and they tolerate very high levels of ionizing radiation. Recent evidence suggests that subtelomeric regions of the bdelloid genome contain sequences originating from other organisms by horizontal gene transfer (HGT), of which some are known to be transcribed. However, the extent to which foreign gene expression plays a role in bdelloid physiology is unknown. We address this in the first large scale analysis of the transcriptome of the bdelloid Adineta ricciae: cDNA libraries from hydrated and desiccated bdelloids were subjected to massively parallel sequencing and assembled transcripts compared against the UniProtKB database by blastx to identify their putative products. Of ~29,000 matched transcripts, ~10% were inferred from blastx matches to be horizontally acquired, mainly from eubacteria but also from fungi, protists, and algae. After allowing for possible sources of error, the rate of HGT is at least 8%–9%, a level significantly higher than other invertebrates. We verified their foreign nature by phylogenetic analysis and by demonstrating linkage of foreign genes with metazoan genes in the bdelloid genome. Approximately 80% of horizontally acquired genes expressed in bdelloids code for enzymes, and these represent 39% of enzymes in identified pathways. Many enzymes encoded by foreign genes enhance biochemistry in bdelloids compared to other metazoans, for example, by potentiating toxin degradation or generation of antioxidants and key metabolites. They also supplement, and occasionally potentially replace, existing metazoan functions. Bdelloid rotifers therefore express horizontally acquired genes on a scale unprecedented in animals, and foreign genes make a profound contribution to their metabolism. This represents a potential mechanism for ancient asexuals to adapt rapidly to changing environments and thereby persist over long evolutionary time periods in the absence of sex.
