The Analysis Of Genomic Imprinting And DNA Methylation Status Of Bovine SGCE/PEG10 Locus

In mammals,genomic imprinting is an epigenetic phenomenon that leads to the preferential expression of genes from either the paternal or maternal allele.Although less than 1%of mammalian genes have been identified,genomic imprinting is critical for proper placental maturation,embryonic growth,and development,and as well as plays important roles in postnatal development.Imprinted genes are often expressed and imprinted in a tissue-and developmental stage-specific manner.Several mechanisms of genomic imprinting is shared by mammals,involving differential DNA methylation,noncoding RNA,and/or histone modification.Most imprinted genes exist in clusters in specific chromosome regions and are regulated by the same imprinting control region(ICR).Cattle is a better model organism for investigating human embryo development than mice,for it has a shorter evolutionary distance to humans and a similar timing of preimplantation development.However,in cattle,about 49 imprinted genes are identified using single nucleotide polymorphism(SNP)-based and high throughput sequencing methods.This number is much smaller than that in humans and mice.Sgce/Peg10 imprinted locus is mapped to mouse proximal chromosome 6,human chromosome 7q21.3 and cow chromosome 4,respectively.This domain involved 14 genes(CALCR,TFPI2,GNGT1,GNG11,BET1,COL1A2,CASD1,SGCE,PEG10,PPP1R9A,PON1,PON3,PON2,and ASB4),which are organized around a maternally methylated DMR(differentially methylated region)comprising the promoter of two adjacent paternally expressed genes of Sgce and Peg 10.At present,the research on this gene region mainly focuses on human and mouse,however,genomic imprinting of bovine SGCE/PEG10 cluster have not been systematically studied,but SGCE and PEG10 are identified as imprinted genes.Detailed comparative characterization of imprinted clusters between species is a useful tool for understanding the biological significance and epigenetic regulation of genomic imprinting.The aim of this study is to analyze the allelic expression pattern of SGCE/PEG10 in cattle and to determine whether DNA methylation is involved in regulating the expression of imprinted genes.In this study,we investigate allele expression of 14 genes(CALCR,TFPI2,GNG11,GNGT1,BET1,COL1A2,CASD1,SGCE,PEG10,PPP1R9A,PON1,PON3,PON2,and ASB4)in bovine adult somatic tissues and term placenta using single nucleotide polymorphism(SNP)-based sequencing method.Except for SGCE and PEG10,three other paternally expressed genes(TFPI2,ASB4,and PON1)are found.TFPI2 and ASB4 are paternally expressed in tissues and placenta,but PON1 shows paternal expression only in placenta.CALCR and GNG11 shows monoallelic expression in tissues but biallelic expression in the placenta.Four genes,BET1,COL1A2,CASD1,and PONS,exhibit tissue-specific monoallelic expression.Biallelic expression levels of GNGT1,PPP1R9A,and PON2 show both in tissues and placenta.To determine whether DNA methylation is involved in the regulation of single allele or imprinted expression of bovine SGCE/PEG10 imprinted cluster,the DNA methylation of the ten CpG islands is characterized using bisulfite sequencing polymerase chain reaction(PCR)analyses,which associated the promoter regions of TFPI2,CASD1,SGCE/PEG10,PON3,ASB4,CALCR,GNG11,BET1,COL1A2,and PON1 genes.Four differentially methylated regions are found to be associated with TFPI2,SGCE/PEG10,PON3,and ASB4 genes,respectively.This suggests that DNA methylation is involved in the regulation of monoallelic/imprinted expression of TFPI2,SGCE/PEG10,PON3,and ASB4 genes in cattle.These results suggest that the bovine imprinting of the SGCE/PEG10 region is more complex compared to that of humans and mice.