Imprinting Analysis of RTL1 and DIO3 Genes and Their Association with Carcass Traits in Pigs (Sus scrofa)

Imprinted genes play significant roles in the regulation of fetal growth, development, function of the placenta and postnatal behavior in mammals, but little is known in pigs. In order to investigate the imprinting status of porcine retro-transposon like 1 （RTL1） and type 3 iodothyronine deiodinase （DIO3） genes, DNA or RNA samples of the parents and F1 animals, generated with reciprocal crosses between Large White and Meishan breeds, were isolated, and analyzed by reverse transcription polymerase chain reaction restriction fragment length polymorphism （RT-PCR-RFLP）. The results demonstrated that the RTL1 gene was paternally expressed in 10 tissues, such as the skeletal muscle, heart, spleen, liver, kidney, lung, stomach, fat, small intestine and brain, and D103 gene exhibited paternal expression in the skeletal muscle, heart, spleen, lung, stomach, and brain, in 2-month-old pigs. The association of RTL1 and DI03 with carcass traits was further analyzed in the F2 population of Large White×Meishan pigs. The statistical results showed that the R TL1 A1101G polymorphism （EU781029） was significantly associated with lean meat percentage （LMP） and fat meat percentage （FMP） （P〈0.05）, while the D103 A744C polymorphism （AY533208） was not significantly associated with any carcass traits. These results indicate that the imprinting status of RTL1 and DIO3 is well kept across the mammalian species, and porcine RTL1 may have important roles in muscle growth and fat deposition.

Characterization,Imprinting Status and Tissue Distribution of Porcine GTL2 Gene

The callipyge （CLPG） phenotype, exhibiting polar overdominance （POD）, is an inherited skeletal muscle hypertrophy described in sheep. The callipyge locus maps to the distal portion of ovine chromosome 18 within the DLKI-GTL2 region and corresponds to human chromosome 14 and mouse chromosome 12. The POD phenomenon is confirmed to the homologous region of swine chromosome 7. In order to clone and investigate the expression of porcine GTL2 gene, DNA and RNA samples from 60-day-old F1 animals, generated with reciprocal crosses between Large White and Meishan breeds and their parents, were used. The authors showed that porcine GTL2 acted as a uoncoding RNA. cDNA samples exhibited maternal expression of the gene in the heart, liver, spleen, lung, kidney, stomach, small intestine, skeletal muscle, and fat in pigs, and a unique tissue-specific expression different from that of humans and mice. These results indicated that the gene was conserved in the pig, human, mouse, and bovine. It will be of interest to further study the gene functions in muscle growth and fat deposition.

cDNA Cloning and Expression Analysis of Mest Gene in the Bufo gargarizans

The Mest （mesoderm-specific transcript） gene has been considered an imprinting gene in human and mouse, and was also confirmed in other mammals and flowering plants. To investigate the function and evolution of this gene, the cDNA of full length Mest gene was obtained using 5＇- and 3＇-RACE from the Chinese Large Toad （Bufo gargarizans）. The transcript is 1 325bp in length which contains a complete open reading frame （ORF） encoding a polypeptide of 326 amino acids （GenBank accession number： ABQ10905）. There is a typical 0./13 hydrolase fold domain in the putative gene product, and it shows high similarity to sequence of homologous protein of Xenopus tropicali （86%）, mammlian （70% - 80%）. RT-PCR （reverse transcriptase-polymerase chain reaction） analysis demonstrated that the Bufo gargarizans Mest （BgMest） gene is expressed widely in testis, ovary, liver, kidney, spleen, brain, stomach and lung. The conservation of the BgMest gene sequences, protein secondary structure of the BgMest protein, in addition to the expression pattern of the BgMest gene, suggested that the function of BgMest was conserved in amphibians. However, the phylogenetic tree of the imprinting gene of the mammals and other vertebrates examined in this study indicated their divergent origins.

Activation of paternally expressed imprinted genes in newly derived germline-competent mouse parthenogenetic embryonic stem cell lines

Parthenogenetic embryonic stem （pES） cells provide a valuable in vitro model system for studying the molecular mechanisms that underlie genomic imprinting. However, the pluripotency of pES cells and the expression profiles of paternally expressed imprinted genes have not been fully explored. In this study, three mouse pES cell lines were established and the differentiation potential of these cells in extended culture was evaluated. The undifferentiated cells had a normal karyotype and homozygous genome, and expressed ES-cell-specific molecular markers. The cells remained undifferentiated after more than 50 passages and exhibited pluripotent differentiation capacity. All three lines of the established ES cells produced teratomas; two lines of ES cells produced chimeras and germline transmission. Furthermore, activation of the paternally expressed imprinted genes Snrpn, U2afl-rsl, Peg3, Impact, Zfp127, Dlkl and Mest in these cells was detected. Some paternally expressed imprinted genes were found to be expressed in the blastocyst stage of parthenogenetically activated embryos in vitro and their expression level increased with extended pES cell culture. Furthermore, our data show that the activation of these paternally expressed imprinted genes in pES cells was associated with a change in the methylation of the related differentially methylated regions. These findings provide direct evidence for the pluripotency of pES cells and demonstrate the association between the DNA methylation pattern and the activa- tion of paternally expressed imprinted genes in pES cells. Thus, the established ES cell lines provide a valuable model for studying epigenetic regulation in mammalian development.

Specific changes in the expression of imprinted genes in prostate cancer--implications for cancer progression and epigenetic regulation

Epigenetic dysregulation comprising DNA hypermethylation and hypomethylation, enhancer of zeste homologue 2 （EZH2） overexpression and altered patterns of histone modifications is associated with the progression of prostate cancer. DNA methylation, EZH2 and histone modifications also ensure the parental-specific monoallelic expression of at least 62 imprinted genes. Although it is therefore tempting to speculate that epigenetic dysregulation may extend to imprinted genes, expression changes in cancerous prostates are only well documented for insulin-like growth factor 2 （IGF2）. A literature and database survey on imprinted genes in prostate cancer suggests that the expression of most imprinted genes remains unchanged despite global disturbances in epigenetic mechanisms. Instead, selective genetic and epigenetic changes appear to lead to the inactivation of a sub-network of imprinted genes, which might function in the prostate to limit cell growth induced via the PI3K/Akt pathway, modulate androgen responses and regulate differentiation. Whereas dysregulation of IGF2 may constitute an early change in prostate carcinogenesis, inactivation of this imprinted gene network is rather associated with cancer progression.

Tissue Expression Profiles of 5 Putative Imprinted Genes in Bovine Chromosome 29

Genomic imprinting is an epigenetic process that regulates gene expression in the mammalian genome. Although there are specific imprinting differences between the mammalian species, cattle present unique opportunity for characterizing imprinted genes because of its sub-species classification. Five putative imprinted genes (TSSC4, CDKN1C, KCNQ1, PHLDA2 and NAP1L4) on bovine chromosome 29 (Bta 29) which had been characterized to have promoter CGI were quantitatively assayed for their relative expression across eight tissues (muscle, brain, liver, kidney, spinal cord, heart, lymph and skin) sampled in Angus cattle. The differential abundance of these genes in muscle and skin tissues of Angus, White Fulani and N’Dama cattle breeds was comparatively analyzed. These three breeds are representative of the Bos taurus and Bos indicus cattle sub-species while the two tissues are selected based on their strategic economic importance in cattle production. All the genes, except TSSC4, were relatively expressed across all the tissues. It was observed that Angus had the highest differential abundance in muscle tissues for TSSC4, PHLDA2 and NAP1L4 while N’Dama and White Fulani were the most abundant for KCNQ1 and NAP1L4 in skin tissues. The study identified marked differences in the expression profiles of the genes in both muscle and skin tissues of the three breeds that were characteristics of their genetics, environment and nutrition.

Overexpression of IGF2R and IGF1R mRNA in SCNT-produced Goats Survived to Adulthood

The procedure of somatic cell nuclear transfer （SCNT） is likely to affect the expression level of growth-related genes especially imprinting genes. In this study, expressions of growth-related genes including three imprinting genes （H19, IGF2, and IGF2R） and four non-imprinting genes （IGF1, IGFIR, GHR, and GHSR） in adult nuclear transferred （NT） goats were investigated by real-time PCR. The expressions of these genes in adult clones were found largely normal, but IGF2R and IGFIR were more highly expressed in cloned goats than in non-NT goats （P 〈 0.01）. Analysis on mono-allelic expression pattern of imprinting genes indicated that mono-allelic expression patterns of H19 and IGF2 in cloned goats were similar to that in non-NT goats. In addition, the sequence of goat IGF2 gene and the putative amino acid sequence were obtained. The 986 nucleotide cDNA of goat IGF2 gene contained an open-reading frame of 540 nucleotides coding for 179 amino acids. Both cDNA sequence and amino acid sequence of IGF2 in goat showed their higher homology with that in sheep than in cattle; the partial cDNA fragments of H19, IGF2R, GHSR, IGFIR, and GHR in goat were also cloned and sequenced, which shared higher sequence identities with those in sheep than in cattle.

Landscape of genomic imprinting and its functions in the mouse mammary gland

Genomic imprinting is an epigenetic modification of DNA,whereby gene expression is restricted to either maternally or paternally inherited alleles.Imprinted genes(IGs)in the placenta and embryo are essential for growth regulation and nutrient supply.However,despite being an important nutrition delivery organ,studies on mammary gland genomic imprinting remain limited.In this study,we found that both the number of IGs and their expression levels decreased during development of the mouse mammary gland.IG expression was lineage-specific and related to mammary gland development and lactation.Meta-analysis of single-cell RNA sequencing data revealed that mammary gland IGs were co-expressed in a network that regulated cell sternness and differentiation,which was confirmed by our functional studies.Accordingly,our data indicated that IGs were essential for the self-renewal of mammary gland stem cells and IG decline was correlated with mammary gland maturity.Taken together,our findings revealed the importance of IGs in a poorly studied nutrition-related organ,i.e.the mammary gland,thus providing a reference for further studies on genomic imprinting.

EARLY FLOWERING IN SHORT DAYS(EFS) regulates the seed size in Arabidopsis

Post-transcriptional modifications,including histone modifications and DNA methylation,alter the chromatin landscape to regulate gene expression,thus control various cellular processes in plants.EARLY FLOWERING IN SHORT DAYS(EFS)is the major contributor for H3K36 methylation in Arabidopsis and is important for plant development.Here,we find that EFS is expressed in different stages of embryo morphogenesis,and the efs mutant produces larger embryo that results in enlarged seeds.Further analysis reveals that an imprinted gene MOP9.5 is hypomethylated at the promoter region and its expression is derepressed in efs mutant.MOP9.5 promoter is marked by various epigenetic modifications,and we find that following the increase of H3K36me3,H3K27me3 and H3K9me2 levels are reduced in efs mutant.This data indicates an antagonistic regulation between H3K36me3 and DNA methylation,and/or H3K27me3 at MOP9.5.Our results further show that both maternal and paternal EFS alleles are responsible for the seed size regulation,which unraveled a novel function of EFS in plant development.

Genome-wide analysis of differential DNA methylation in Silver-Russell syndrome

Silver-Russell Syndrome(SRS) is clinically heterogeneous disorder characterized by low birth weight, postnatal growth restriction, and variable dysmorphic features. Current evidence strongly implicates imprinted genes as an important etiology of SRS. Although almost half of the patients showed DNA hypomethylation at the H19/IGF2 imprinted domain, and approximately7%–10% of SRS patients have maternal uniparental disomy of chromosome 7(UPD(7) mat); the rest of the SRS patients shows unknown etiology. In this study, we investigate whether there are further DNA methylation defects in SRS patients. We measured DNA methylation in seven SRS patients and five controls at more than 485,000 CpG sites using DNA methylation microarrays. We analyzed methylation changes genome-wide and identified the differentially methylated regions(DMRs) using bisulfite sequencing and digital PCR. Our analysis identifies epimutations at the previously characterized domains of H19/IGF2,providing proof of principle that our methodology can detect the changes in DNA methylation at imprinted loci. In addition,our results showed a novel SRS associated imprinted gene OSBPL5 located on chromosome 11p14 with the probe cg25963939,which is hypomethylated in 4/7 patients(P=0.023, β=.0.243). We also report DMRs in other genes including TGFβ3, HSF1,GAP43, NOTCH4 and MYH14. These DMRs were found to be associated with SRS using GO pathway analysis. In this study,we identified the probe cg25963939, located at the 5′UTR of imprinted gene OSBPL5, as a novel DMR that is associated with SRS. This finding provides new insights into the mechanism of SRS etiology and aid the further stratification of SRS patients by molecular phenotypes.