DNA甲基化调控牛AQP1基因的胎盘特异性印记

为揭示牛AQP1（aquaporin 1）基因在不同组织及胎盘中的印记状态，以及DNA甲基化修饰在印记中的调控机制，本研究采用基于SNP的PCR产物直接测序的方法，对32头健康雌性成年荷斯坦奶牛心组织及15个自然分娩后的胎盘试验样本进行检测，确定了5头杂合子个体牛和3个杂合子胎盘，对其组织（心、肝、脾、肺、肾、肌肉和脂肪）和胎盘进行AQP1等位基因表达分析及印记状态分析，利用亚硫酸氢盐测序法分析AQP1基因位于启动子和第一个外显子区的CpG岛在牛心、肝组织、2个胎盘和对应精子中的DNA甲基化状态。结果发现，在杂合子牛被检测的7个组织中，AQP1基因呈现双等位基因表达；而在胎盘中，AQP1基因为单等位基因表达。通过分析杂合子胎盘对应的亲本基因型，发现AQP1基因为母源等位基因表达，即父源印记。进一步比较分析AQP1基因启动子区CpG岛在牛组织、胎盘及对应精子中的甲基化状态，在双等位基因表达的心脏、肝脏组织中，该区域未发现差异甲基化区（differentially methylated regions，DMR）；而在单等位基因表达的胎盘中，存在差异甲基化区，同时父源等位基因精子中为重甲基化状态。以上结果说明，牛AQP1基因为胎盘特异性单等位基因表达的父源印记基因，且AQP1基因位于启动子和第一个外显子区的CpG岛甲基化修饰参与调控牛胎盘的印记表达；在被检测的组织中为双等位基因表达。

DNA Methylation Regulate the Genomic Imprinting of AQP1 Gene Specific in Bovine Placenta

The study aimed to explore the imprinting status of AQP1 gene in various tissues and placenta of bovine and to determine the role of DNA methylation in regulating imprinted expression of AQP1 gene. The direct sequencing of RT-PCR products was used based on SNP, 5 heterozygous cows and 3 heterozygous placentas were identified from the heart tissues of 32 healthy female adult Holstein cows and 15 placentas after natural delivery, respectively. The allele expression and imprinting status of AQP1 gene in 7 tissues(heart, liver, spleen, lung, kidney, muscle and fat) and placentas of heterozygous cattle were analyzed. The DNA methylation status of the CpG island located the promoter and exon 1 of AQP1 gene was analyzed in heart, liver, two placentas and corresponding sperms by bisulfite sequencing. The results showed that AQP1 gene was in biallelic expression in 7 tissues tested of heterozygous cows. In the placenta, AQP1 gene was in maternal monoallelic expression by analyzing the parental genotype of heterozygous placenta. Furthermore, analysis of the DNA methylation status of CpG island in AQP1 gene promoter in tissues, placenta and corresponding sperms of bovine showed that there were no differentially methylated regions (DMR) in the biallele expressed heart and liver tissues, but in placenta with monoallelic expression, there were DMR, while in sperm with paternal allele expression, there was hyper-methylation. These results suggest that AQP1 gene is a paternal imprinting gene, and DNA methylation modification of the AQP1 CpG island is involved in the regulation of imprinting expression in bovine placenta.The expression of AQP1 gene is biallelic in the tested tissues.