College of Life Science, Agricultural University of Hebei, Baoding, Hebei, China.
College of Bioscience and Bioengineering, Hebei University of Science and Technology, Shijiazhuang, Hebei, China.
Theriogenology. 2022 Mar 1;180:121-129. doi: 10.1016/j.theriogenology.2021.12.013. Epub 2021 Dec 20.
Genomic imprinting is an epigenetic phenomenon that leads to genes monoallelically expressed in a parent-of-origin-specific manner and plays an important role in the embryonic development and postnatal growth of mammals. Imprinted genes usually occur in clusters in a chromosomal region and are regulated by a cis-acting imprinting control region that involves differential DNA methylation modification. Igf2r, Slc22a2 and Slc22a3 are three maternally expressed genes on mouse chromosome 17. The paternally expressed long noncoding RNA (lncRNA) Air and the nonimprinted gene Slc22a1 are also located in the imprinted region. Comparative characterization of imprinted clusters between species is useful for us to understand the biological significance and epigenetic regulating mechanism of genomic imprinting. The aim of this study was to analyze the allelic expression pattern of AIR and SLC22A1-3 genes in cattle and to determine the role of DNA methylation in regulating gene expression. Allelic expression analysis was performed in bovine adult tissues and term placenta using an SNP-based approach. We found that IGF2R, AIR and SLC22A3 were monoallelically expressed in all detected bovine somatic tissues, including heart, liver, spleen, lung, kidney, muscle, fat and brain. In bovine placenta, IGF2R and SLC22A3 are maternally expressed; however, the AIR gene is paternally expressed. Tissue-specific monoallelic expression of SLC22A2 is detected in bovines, with monoallelic expression in the spleen and brain but biallelic expression in kidney tissues. SLC22A1 is only detected in bovine liver and kidney tissues and is biallelicly expressed, which is consistent with the imprint expression in mice. To determine the possible role of DNA methylation in regulating the monoallelic/imprinted expression of bovine IGF2R, AIR, SLC22A2, and SLC22A3 genes, we analyzed the DNA methylation status of CpG islands in the first exon of SLC22A2, the promoter region of SLC22A3 and region 2 in the second intron of the IGF2R gene by bisulfite sequencing. Two differentially methylated regions (DMRs) were detected in the first exon of bovine SLC22A3 and the common regions of IGF2R and AIR. This suggests that DNA methylation is involved in the regulation of monoallelic/imprinted expression of IGF2R, AIR and SLC22A3 genes in cattle.
基因组印迹是一种表观遗传现象，导致基因以亲本来源特异性的方式单等位基因表达，并在哺乳动物的胚胎发育和出生后生长中发挥重要作用。印迹基因通常在染色体区域中以簇的形式出现，并受涉及差异 DNA 甲基化修饰的顺式作用印迹控制区调节。Igf2r、Slc22a2 和 Slc22a3 是小鼠 17 号染色体上三个母源表达的基因。父源表达的长非编码 RNA（lncRNA）Air 和非印迹基因 Slc22a1 也位于印迹区域。物种间印迹簇的比较特征对于我们理解基因组印迹的生物学意义和表观遗传调控机制非常有用。本研究的目的是分析牛中 AIR 和 SLC22A1-3 基因的等位基因表达模式，并确定 DNA 甲基化在调节基因表达中的作用。使用 SNP 为基础的方法在牛成体组织和足月胎盘中进行等位基因表达分析。我们发现 IGF2R、AIR 和 SLC22A3 在所有检测到的牛体细胞组织中均单等位基因表达，包括心脏、肝脏、脾脏、肺、肾脏、肌肉、脂肪和大脑。在牛胎盘中，IGF2R 和 SLC22A3 为母源表达；然而，AIR 基因则为父源表达。在牛中检测到 SLC22A2 的组织特异性单等位基因表达，在脾脏和大脑中单等位基因表达，而在肾脏组织中则为双等位基因表达。SLC22A1 仅在牛的肝脏和肾脏组织中检测到，并呈双等位基因表达，这与小鼠中的印迹表达一致。为了确定 DNA 甲基化在调节牛 IGF2R、AIR、SLC22A2 和 SLC22A3 基因的单等位基因/印迹表达中的可能作用，我们通过亚硫酸氢盐测序分析了 SLC22A2 第一外显子、SLC22A3 启动子区域和 IGF2R 基因第二内含子 2 中 CpG 岛的 DNA 甲基化状态。在牛 SLC22A3 的第一外显子和 IGF2R 和 AIR 的共同区域中检测到两个差异甲基化区域（DMRs）。这表明 DNA 甲基化参与了牛 IGF2R、AIR 和 SLC22A3 基因的单等位基因/印迹表达调控。
