生物谷：美國(guó)康奈爾大學(xué)研究人員在7月6日的網(wǎng)絡(luò)雜志《PLoS遺傳學(xué)》上發(fā)表文章稱(chēng),，他們?cè)谝恍┕夡w內(nèi)發(fā)現(xiàn)了一種不與其它任何已知基因有關(guān)系的新基因。  

    領(lǐng)導(dǎo)該項(xiàng)研究的是康奈爾大學(xué)分子生物學(xué)與遺傳學(xué)系的Hsiao-Pei  Yang博士。她及同事發(fā)現(xiàn)的這種新基因命名為hydra，它只存在于果蠅很少量的種屬中。這說(shuō)明這種基因誕生的年代在1300萬(wàn)年前，它存在的果蠅種屬便是在那個(gè)時(shí)候脫離了共同祖先開(kāi)始單獨(dú)進(jìn)化。  

    Hydra具有自己的功能,，它能夠表達(dá)一種蛋白參與精子的后期生成。Yang表示,，人們習(xí)慣于認(rèn)為新基因是由已有基因改造而來(lái),，但是hydra不是這樣，這就是它的特別之處,。  

    科學(xué)家目前還不能確定hydra是如何產(chǎn)生的,。他們推測(cè)它可能是由一段“垃圾DNA”發(fā)展而成。這段“垃圾DNA”稱(chēng)為轉(zhuǎn)位因子,，又稱(chēng)跳躍基因,，它可以經(jīng)由病毒插入到果蠅基因組內(nèi)。此外,，hydra含有9個(gè)復(fù)制的外顯子（exon,，含蛋白質(zhì)編碼信息區(qū)域），任何一個(gè)外顯子都可以激活hydra,。研究人員發(fā)現(xiàn)大多數(shù)外顯子的旁邊都有一個(gè)轉(zhuǎn)位因子,，從而推測(cè)，由轉(zhuǎn)位因子產(chǎn)生復(fù)制序列可能是產(chǎn)生新基因的部分機(jī)制,，因?yàn)閺?fù)制提供了基因更多的進(jìn)化機(jī)會(huì),。（科學(xué)網(wǎng)  梅進(jìn)/編譯）

原始出處:

PLoS Genetics

Received: January 10, 2007; Accepted: May 15, 2007; Published: July 6, 2007

Evolution of hydra, a Recently Evolved Testis-Expressed Gene with Nine Alternative First Exons in Drosophila melanogaster
Shou-Tao Chen1, Hsin-Chien Cheng1, Daniel A. Barbash2, Hsiao-Pei Yang1,2*

1 Faculty of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan, Republic of China, 2 Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America

We describe here the Drosophila gene hydra that appears to have originated de novo in the melanogaster subgroup and subsequently evolved in both structure and expression level in Drosophila melanogaster and its sibling species. D. melanogaster hydra encodes a predicted protein of ~300 amino acids with no apparent similarity to any previously known proteins. The syntenic region flanking hydra on both sides is found in both D. ananassae and D. pseudoobscura, but hydra is found only in melanogaster subgroup species, suggesting that it originated less than ~13 million y ago. Exon 1 of hydra has undergone recurrent duplications, leading to the formation of nine tandem alternative exon 1s in D. melanogaster. Seven of these alternative exons are flanked on their 3′ side by the transposon DINE-1 (Drosophila interspersed element-1). We demonstrate that at least four of the nine duplicated exon 1s can function as alternative transcription start sites. The entire hydra locus has also duplicated in D. simulans and D. sechellia. D. melanogaster hydra is expressed most intensely in the proximal testis, suggesting a role in late-stage spermatogenesis. The coding region of hydra has a relatively high Ka/Ks ratio between species, but the ratio is less than 1 in all comparisons, suggesting that hydra is subject to functional constraint. Analysis of sequence polymorphism and divergence of hydra shows that it has evolved under positive selection in the lineage leading to D. melanogaster. The dramatic structural changes surrounding the first exons do not affect the tissue specificity of gene expression: hydra is expressed predominantly in the testes in D. melanogaster, D. simulans, and D. yakuba. However, we have found that expression level changed dramatically (~ >20-fold) between D. melanogaster and D. simulans. While hydra initially evolved in the absence of nearby transposable element insertions, we suggest that the subsequent accumulation of repetitive sequences in the hydra region may have contributed to structural and expression-level evolution by inducing rearrangements and causing local heterochromatinization. Our analysis further shows that recurrent evolution of both gene structure and expression level may be characteristics of newly evolved genes. We also suggest that late-stage spermatogenesis is the functional target for newly evolved and rapidly evolving male-specific genes.

Figure 1.Evolution of hydra in Drosophila Species

(A) The hydra region of the X-chromosome of D. melanogaster, based on FlyBase genome browser release 4.3. The hydra gene was previously annotated as producing two alternative transcripts, RA and RB, derived from alternative exon 1s. The proposed annotation of seven additional exon 1s is based on evidence presented here.

(B) Evolution of hydra region and hydra gene structure in seven Drosophila species. hydra and the flanking gene CG1835 are located in a recently expanded region between run and cyp6v1. hydra originated in the common ancestor of the melanogaster subgroup (arrow A). In D. melanogaster, this region between run and cyp6v1 is ~32 kb (10 kb from the 3′ end of hydra to cyp6v1 and 17 kb from the 5′ end of hydra to run), but is only ~26 kb apart in D. ananassae and D. pseudoobscura, where both hydra and CG1835 are missing. hydra has gone through multiple cycles of duplication and rearrangement in D. melanogaster and its sibling species, and accumulated insertions of the transposon DINE-1 and other repetitive sequences (arrow B). CG1835 is on the opposite strand from all other genes, as indicated by its leftward-pointing arrow. Three copies of hydra are found on two unlinked scaffolds in D. sechellia. Note that the distances are not to scale.

全文鏈接：

http://genetics.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pgen.0030107