BACKGROUND:The rodent specific reproductive homeobox (Rhox) gene cluster on the X chromosome has been reported to contain twelve homeobox-containing genes, Rhox1-12. RESULTS:We have identified a 40 kb genomic region within the Rhox cluster that is duplicated eight times in tandem resulting in the presence of eight paralogues of Rhox2 and Rhox3 and seven paralogues of Rhox4. Transcripts have been identified for the majority of these paralogues and all but three are predicted to produce full-length proteins with functional potential. We predict that there are a total of thirty-two Rhox genes at this genomic location, making it the most gene-rich homoeobox cluster identified in any species. From the 95% sequence similarity between the eight duplicated genomic regions and the synonymous substitution rate of the Rhox2, 3 and 4 paralogues we predict that the duplications occurred after divergence of mouse and rat and represent the youngest homoeobox cluster identified to date. Molecular evolutionary analysis reveals that this cluster is an actively evolving region with Rhox2 and 4 paralogues under diversifying selection and Rhox3 evolving neutrally. The biological importance of this duplication is emphasised by the identification of an important role for Rhox2 and Rhox4 in regulating the initial stages of embryonic stem (ES) cell differentiation. CONCLUSION:The gene rich Rhox cluster provides the mouse with significant biological novelty that we predict could provide a substrate for speciation. Moreover, this unique cluster may explain species differences in ES cell derivation and maintenance between mouse, rat and human.

译文

背景:据报道,X染色体上的啮齿动物特异性生殖同源盒(Rhox)基因簇含有十二个包含同源盒的基因,Rhox1-12。
结果:我们在Rhox簇中鉴定出一个40 kb的基因组区域,该区域串联重复八次,导致存在八个Rhox2和Rhox3旁系同源物和七个Rhox4旁系同源物。已为大多数这些旁系同源物确定了转录本,除三个外,均预测会产生具有功能潜力的全长蛋白质。我们预测在该基因组位置总共有32个Rhox基因,使其成为任何物种中鉴定到的最丰富的基因同源盒簇。从八个重复的基因组区域之间95%的序列相似性以及Rhox2、3和4个旁系同源物的同义取代率,我们预测重复发生在小鼠和大鼠分化后,并且代表了迄今确定的最年轻的同源盒簇。分子进化分析表明,该簇是一个活跃进化的区域,在选择多样化的情况下,Rhox2和4个旁系同源物,而Rhox3则是中性进化的。通过鉴定Rhox2和Rhox4在调节胚胎干(ES)细胞分化的初始阶段中的重要作用,强调了这种重复的生物学重要性。
结论:富含基因的Rhox簇为小鼠提供了重要的生物学新奇,我们预测可以为物种形成提供底物。而且,这种独特的簇可以解释小鼠,大鼠和人之间ES细胞衍生和维持中的物种差异。

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