據(jù)普渡大學教育網(wǎng)站2006年9月14日報道,，一種喜陰的嚙齒動物有可能揭示人類基因和進化的神秘性。普渡大學研究顯示,，一種類似老鼠的嚙齒類動物野鼠不僅是進化最快的哺乳動物,，而且還包含有許多挑戰(zhàn)當前科學理解中令人費解的遺傳特性。
“沒有人特別研究過野鼠,，”森林和自然資源系副教授,，其研究發(fā)表在本月《遺傳》雜志上的J•安德魯•代物第說，“但是當涉及到遺傳這方面的時候,，野鼠應受到更多的關(guān)注,。”小嚙齒動物經(jīng)常被誤認為是老鼠，除了有較短的尾巴和泡泡眼外,，其余與老鼠長得都很像,。野鼠生活范圍遍布整個北半球，經(jīng)常被認為是農(nóng)業(yè)害蟲,，因為它們以綠色素菜為食,。但是野鼠是包含許多奇怪特性的“進化中的謎”，代物第說道,。了解了造成這些特性的原因就能更好地了解出現(xiàn)在人類遺傳和遺傳障礙上的相似現(xiàn)象,，同時對基因治療也有積極的意義，他說,。
這項研究對象包括野鼠類Mocrotus中的60個種類,，野鼠類已經(jīng)進化了有50萬年到200萬年了。這意味著在創(chuàng)造不同物種方面,，野鼠的進化速度比脊椎動物的平均進化速度快60－100倍,。在類里面，野鼠的染色體的數(shù)量17—64不等,。代物第說這是個不尋常的發(fā)現(xiàn),，因為在單個類中的同種物體染色體數(shù)通常是相同的。存在于野鼠中的其他不尋常遺傳特性：
•在一種物種中,，X染色體,，兩個決定性別的染色體（另一個是Y染色體）之一，包含了整個基因組的20%,。通常性別染色體中包含更少的遺傳信息,。
•在另一種物種中，雌性體內(nèi)包含大比例的Y（雄）染色體,。
•在還有一種物種中,，雌性和雄性體的染色體數(shù)量不同,，這點在動物體內(nèi)是極不尋常的。
一個 “有悖常理的古怪” 結(jié)論是：雖然基因存在差異,，但是所有的野鼠長得都很相似,，代物第的前研究生和該研究的合著者代波•瑞特說。“所有的野鼠看起來都很相似,，甚至許多種是完全分辨不出差異,，”
在一種特別的情況，代物第甚至是在近距離觀察分析了它們的頭蓋骨結(jié)構(gòu)的情況下都不能辨別兩個種類的不同,；只有通過基因測試才能夠揭示它們的區(qū)別,。
然而，野鼠卻是很簡單就能認出同伴,。“我沒有發(fā)現(xiàn)不同種類的野鼠進行交配,。”瑞特說，“我們不知道它們是如何做到這點的,，但是氣味和行為舉止可能起作用了,。”
代物第說，“野鼠是一種能夠用于研究許多可能影響人類自然現(xiàn)象的模型系統(tǒng),。”
他的研究強調(diào)線粒體基因組,，是一組包含在負責產(chǎn)生能量（線粒體）的細胞間隔處的DNA。瑞特額外工作的一部分是探究野鼠線粒體DNA把自己植入到細胞核DNA中的獨特能力,。中心染色體組,，就像被知道的那樣，包含大多數(shù)的細胞DNA,，主要作用是控制細胞功能及其發(fā)展,。
“在這個領(lǐng)域，代波的工作可能對關(guān)于基因的基本科學知識產(chǎn)生潛在影響,，比如那些被運用到基因療法中的傳送機制方面的基本科學知識,。”代物第說。
在這個相對較新的理論里,，治療包括將基因植入患者的細胞中,，為了對抗一些像血友病之類的疾病。然而,，將特定基因植入到“正確”位置上或者期望它發(fā)揮作用的位置上通常是困難的,。對野鼠奇特行為的普遍性現(xiàn)象，以及這種行為的發(fā)生方式地更好了解,，可能對人類遺傳研究具有重要的意義。
代物第的研究獲國家科學基金和美國農(nóng)業(yè)部支助,。代物第希望以后可以繼續(xù)他關(guān)于野鼠基因的研究,。
英文原文:
Rodent's bizarre traits deepen mystery of genetics, evolution
Vole
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Purdue University research has shown that the vole, a mouselike rodent, is not only the fastest evolving mammal, but also harbors a number of puzzling genetic traits that challenge current scientific understanding.
"Nobody has posters of voles on their wall," said J. Andrew DeWoody, associate professor of genetics in the Department of Forestry and Natural Resources, whose study appears this month in the journal Genetica. "But when it comes down to it, voles deserve more attention."
Small rodents often confused for mice, except with shorter tails and beady eyes, voles live throughout the Northern Hemisphere and are often considered agricultural pests because they eat vegetation. Nevertheless, voles are an "evolutionary enigma" with many bizarre traits, DeWoody said. Understanding the basis for these traits could lead to better understanding of the same phenomena in human genetics and genetic disorders, and could have implications for gene therapy, he said.
The study focuses on 60 species within the vole genus Microtus, which has evolved in the last 500,000 to 2 million years. This means voles are evolving 60-100 times faster than the average vertebrate in terms of creating different species. Within the genus (the level of taxonomic classification above species), the number of chromosomes in voles ranges from 17-64. DeWoody said that this is an unusual finding, since species within a single genus often have the same chromosome number.
Among the vole's other bizarre genetic traits:
•In one species, the X chromosome, one of the two sex-determining chromosomes (the other being the Y), contains about 20 percent of the entire genome. Sex chromosomes normally contain much less genetic information.
•In another species, females possess large portions of the Y (male) chromosome.
•In yet another species, males and females have different chromosome numbers, which is uncommon in animals.
A final "counterintuitive oddity" is that despite genetic variation, all voles look alike, said DeWoody's former graduate student and study co-author Deb Triant.
"All voles look very similar, and many species are completely indistinguishable," DeWoody said.
In one particular instance, DeWoody was unable to differentiate between two species even after close examination and analysis of their cranial structure; only genetic tests could reveal the difference.
Nevertheless, voles are perfectly adept at recognizing those of their own species.
"I have seen absolutely no evidence of mating between different species," Triant said. "We don't know how they do this, but scent and behavior probably play a role."
DeWoody said, "The vole is a great a model system that could be used to study lots of natural phenomena that could impact humans."
His research focuses on the mitochondrial genome, the set of DNA within the cellular compartment responsible for generating energy (the mitochondria). Some of Triant's additional work explores the unique ability of vole's mitochondrial DNA to insert itself within DNA in the cell nucleus. The nuclear genome, as it is known, contains the vast majority of a cell's DNA and is responsible for controlling cellular function and development.
"Deb's work in this area could potentially have some basic science impact on gene delivery mechanisms, such as those used in gene therapy," DeWoody said.
In this relatively new therapy, treatment involves the insertion of a gene into human patients' cells in order to counter some illness or disease like hemophilia. However, it is often difficult to insert the desired gene in the "correct" location, or a location where it does what it is supposed to do. A better understanding of the unusual prevalence of this activity in voles, and the manner in which it happens, could have important human implications.
DeWoody's research was funded by the National Science Foundation and the U.S. Department of Agriculture. DeWoody hopes to continue his work on vole genetics at some point in the future.
