Khatib Hasan, Zaitoun Ismail, Kim Eui-Soo
Department of Dairy Science, University of Wisconsin-Madison, 1675 Observatory Dr., Madison, Wisconsin, 53706, USA.
Mamm Genome. 2007 Jul;18(6-7):538-47. doi: 10.1007/s00335-007-9039-z. Epub 2007 Jul 26.
Genomic imprinting is an epigenetic mechanism that results in monoallelic expression of genes depending on parent-of-origin of the allele. Although the conservation of genomic imprinting among mammalian species has been widely reported for many genes, there is accumulating evidence that some genes escape this conservation. Most known imprinted genes have been identified in the mouse and human, with few imprinted genes reported in cattle. Comparative analysis of genomic imprinting across mammalian species would provide a powerful tool for elucidating the mechanisms regulating the unique expression of imprinted genes. In this study we analyzed the imprinting of 22 genes in human, mouse, and cattle and found that in only 11 was imprinting conserved across the three species. In addition, we analyzed the occurrence of the sequence elements CpG islands, C + G content, tandem repeats, and retrotransposable elements in imprinted and in nonimprinted (control) cattle genes. We found that imprinted genes have a higher G + C content and more CpG islands and tandem repeats. Short interspersed nuclear elements (SINEs) were notably fewer in number in imprinted cattle genes compared to control genes, which is in agreement with previous reports for human and mouse imprinted regions. Long interspersed nuclear elements (LINEs) and long terminal repeats (LTRs) were found to be significantly underrepresented in imprinted genes compared to control genes, contrary to reports on human and mouse. Of considerable significance was the finding of highly conserved tandem repeats in nine of the genes imprinted in all three species.
基因组印记是一种表观遗传机制，它导致基因的单等位基因表达，具体取决于等位基因的亲本来源。尽管许多基因在哺乳动物物种间的基因组印记保守性已被广泛报道，但越来越多的证据表明，一些基因并不遵循这种保守性。大多数已知的印记基因是在小鼠和人类中鉴定出来的，在牛中报道的印记基因很少。对哺乳动物物种间的基因组印记进行比较分析，将为阐明调控印记基因独特表达的机制提供一个有力工具。在本研究中，我们分析了人类、小鼠和牛中22个基因的印记情况，发现其中只有11个基因在这三个物种间的印记是保守的。此外，我们分析了印记和非印记（对照）牛基因中序列元件CpG岛、C + G含量、串联重复和逆转座元件的出现情况。我们发现，印记基因具有更高的G + C含量、更多的CpG岛和串联重复。与对照基因相比，印记牛基因中的短散在核元件（SINEs）数量明显较少，这与之前关于人类和小鼠印记区域的报道一致。与对照基因相比，印记基因中的长散在核元件（LINEs）和长末端重复序列（LTRs）明显较少，这与关于人类和小鼠的报道相反。在所有三个物种中均被印记的9个基因中发现高度保守的串联重复，这一发现具有相当重要的意义。
