A novel imprinted locus on bovine chromosome 18 homologous with human chromosome 16q24.1.

Genomic imprinting is an epigenetic regulation mechanism in mammals resulting in the parentally dependent monoallelic expression of genes. Imprinting disorders in humans are associated with several congenital syndromes and cancers and remain the focus of many medical studies. Cattle is a better model organism for investigating human embryo development than mice. Imprinted genes usually cluster on chromosomes and are regulated by different methylation regions (DMRs) located in imprinting control regions that control gene expression in cis. There is an imprinted locus on human chromosome 16q24.1 associated with congenital lethal developmental lung disease in newborns. However, genomic imprinting on bovine chromosome 18, which is homologous with human chromosome 16 has not been systematically studied. The aim of this study was to analyze the allelic expressions of eight genes (CDH13, ATP2C2, TLDC1, COTL1, CRISPLD2, ZDHHC7, KIAA0513, and GSE1) on bovine chromosome 18 and to search the DMRs associated gene allelic expression. Three transcript variants of the ZDHHC7 gene (X1, X2, and X5) showed maternal imprinting in bovine placentas. In addition, the monoallelic expression of X2 and X5 was tissue-specific. Five transcripts of the KIAA0513 gene showed tissue- and isoform-specific monoallelic expression. The CDH13, ATP2C2, and TLDC1 genes exhibited tissue-specific imprinting, however, COTL1, CRISLPLD2, and GSE1 escaped imprinting. Four DMRs, established after fertilization, were found in this region. Two DMRs were located between the ZDHHC7 and KIAA0513 genes, and two were in exon 1 of the CDH13 and ATP2C2 genes, respectively. The results from this study support future studies on the molecular mechanism to regulate the imprinting of candidate genes on bovine chromosome 18.

ZFAT (isoform-specific) and its antisense RNA 1 (ZFAT-AS1) are two allele-specific monoallelically expressed genes in cattle.

In mammals, imprinted genes are characterised by a monoallelic expression, which is based on parental origin and is essential for both foetal and placental development. The ZFAT gene encodes a transcriptional factor, and its non-coding antisense RNA, ZFAT-AS1, overlaps with the ZFAT locus. Both ZFAT and ZFAT-AS1 are maternally imprinted in human placentas. In bovines, the imprinting status of the ZFAT and ZFAT-AS1 genes has yet to be reported. In this study, we analysed the allelic expression of three transcript variants (X1-X3) of the bovine ZFAT and ZFAT-AS1 genes in somatic tissues and placentas using a single nucleotide polymorphism-based method. The results showed that bovine ZFAT exhibited isoform-specific paternal expression. The ZFAT X2 variant exhibited monoallelic expression in the bovine placentas and biallelic expression in the six bovine somatic tissues (heart, liver, spleen, lung, kidney and brain). However, the ZFAT X1 and X3 variants were biallelically expressed in both bovine tissues and placentas. A 311 bp bovine ZFAT-AS1 complementary DNA (cDNA) sequence was obtained by aligning the human ZFAT-AS1 cDNA sequence with the bovine genome and conducting reverse transcription polymerase chain reaction amplification. Bovine ZFAT-AS1 have monoallelic expression in bovine placentas and somatic tissues. In addition, the DNA methylation of two regions was characterised, including the partial promoter, and exon 1 and intron 1 regions of ZFAT, and there were no differentially methylated regions.

The landscape of allelic expression and DNA methylation at the bovine SGCE/PEG10 locus.

Genomic imprinting is an epigenetic regulation in mammals in which a small subset of genes is monoallelically expressed dependent on their parental origin. A large imprinted domain, SGCE/PEG10 locus, is located on human chromosome 7q21s and mouse proximal chromosome 6. However, genomic imprinting of bovine SGCE/PEG10 cluster has not been systematically studied. In this study, we investigated allele expression of 14 genes of the SGCE/PEG10 locus in bovine somatic tissues and term placenta using a single nucleotide polymorphism (SNP)-based sequencing method. In addition to SGCE and PEG10, two conserved paternally expressed genes in human and mice, five other genes (TFPI2, GNG11, ASB4, PON1, and PON3) were paternally expressed. Three genes, BET1, COL1A2, and CASD1, exhibited tissue-specific monoallelic expression. CALCR showed monoallelic expression in tissues but biallelic expression in the placenta. Three genes, GNGT1, PPP1R9A, and PON2, showed biallelic expression in cattle. Five differentially methylated regions (DMRs) were found to be associated with the allelic expression of TFPI2, COL1A2, SGCE/PEG10, PON3, and ASB4 genes, respectively. The SGCE/PEG10 DMR is a maternally hypermethylated germline DMR, but TFPI2, COL1A2, PON3, and ASB4 DMRs are secondary DMRs. In summary, we identified five novel bovine imprinted genes (GNG11, BET1, COL1A2, CASD1, and PON1) and four secondary DMRs at the SGCE/PEG10 locus.