Evolution patterns of Peg3 and H19-ICR

© 2018 Elsevier Inc. Mammalian imprinted domains are regulated through small genomic regions termed Imprinting Control Regions (ICRs). In the current study, the evolution patterns of the ICRs of Peg3 and H19-imprinted domains were analyzed using the genomic sequences derived from a large number of mammals. The results indicated that multiple YY1 and CTCF binding sites are localized within the Peg3 and H19-ICR in all the mammals tested. The numbers of YY1 and CTCF binding sites are variable among individual species, yet positively correlate with the presence of tandem repeats within the Peg3 and H19-ICRs. Thus, multiple YY1 and CTCF binding sites within the respective ICRs may have been maintained through tandem repeats/duplications. The unit lengths of tandem repeats are also non-random and locus-specific, 140 and 400 bp for the Peg3 and H19-ICRs. Overall, both Peg3 and H19-ICRs may have co-evolved with two unique features, multiple transcription factor binding sites and tandem repeats

Multiple YY1 and CTCF binding sites in imprinting control regions

Known imprinting control regions (ICRs) contain unusual tandem arrays of DNA-binding sites for transcription factors, including YY1 for the Peg3, Gnas and Xist/Tsix domains and CTCF for the H19/Igf2 domain. These multiple DNA-binding sites are known to be the only functionally shared and evolutionarily selected feature among these ICRs. However, it is not well understood why the imprinting control regions tend to maintain a high density of a particular transcription factor-binding site. We hypothesize that the multiplicity associated with the YY1 and CTCF binding sites may be designed for attracting and maintaining the relatively high levels of YY1 and CTCF proteins or for covering the relatively large genomic sizes of the associated ICRs. This idea remains to be tested in the near future, but it is one of the most likely explanations for all those unusual features that are associated with the functionally critical regions (ICRs) of genomic imprinting. © 2008 Landes Bioscience

Recruitment and biological consequences of histone modification of H3K27me3 and H3K9me3.

Two histone marks, H3K27me3 and H3K9me3, are well known for their repressive roles in the genic and nongenic regions of metazoan genomes. Several protein complexes are known to be responsible for generating these marks, including polycomb repression complex 2 and several H3K9 methylases. Recent studies have shown that the targeting of these histone-modifying complexes within mammalian genomes may be mediated through several DNA-binding proteins, including AEBP2, JARID2, and YY1. In this review, we discuss the potential targeting mechanisms in light of the recent results that have been derived from genome-wide chromatin immunoprecipitation sequencing data and the in vivo functions of these two histone marks in light of the results derived from mouse and human genetic studies

NGS-based deep bisulfite sequencing

© 2015 The Authors. Published by Elsevier B.V. We have developed an NGS-based deep bisulfite sequencing protocol for the DNA methylation analysis of genomes. This approach allows the rapid and efficient construction of NGS-ready libraries with a large number of PCR products that have been individually amplified from bisulfite-converted DNA. This approach also employs a bioinformatics strategy to sort the raw sequence reads generated from NGS platforms and subsequently to derive DNA methylation levels for individual loci. The results demonstrated that this NGS-based deep bisulfite sequencing approach provide not only DNA methylation levels but also informative DNA methylation patterns that have not been seen through other existing methods.This protocol provides an efficient method generating NGS-ready libraries from individually amplified PCR products.This protocol provides a bioinformatics strategy sorting NGS-derived raw sequence reads.This protocol provides deep bisulfite sequencing results that can measure DNA methylation levels and patterns of individual loci

In vivo YY1 knockdown effects on genomic imprinting

The YY1 transcription factor is predicted to control several imprinted domains, including the Peg3, Gnas and Xist/Tsix regions. To test this possibility, we have used RNA interference strategies to generate transgenic mouse lines that express reduced levels of the cellular YY1 protein. As predicted, lowering YY1 levels resulted in global expression changes in these three imprinted domains. In neonatal brains, most imprinted genes of the Peg3 domain were up-regulated. In the Gnas domain, Nespas was down-regulated, whereas three other imprinted transcripts were up-regulated, including Nesp, Gnasxl and Exon1A. In the Xist/Tsix domain, no obvious change was detected in the expression levels of the two genes in female mice. However, male mice showed low-level coordinated, up- and down-regulation of Xist and Tsix, respectively, suggesting potential de-repression of Xist in a subset of male cell populations. YY1 knockdown also changed the methylation levels at the imprinting control regions (ICRs) of these domains in a target-specific manner. In addition, breeding experiments indicated that the birth weights of 20% of the transgenic females were much lower than those of normal female littermates. We surmise that this gender-specific outcome is caused by the YY1 knockdown effect on the Xist locus of females. In sum, these results demonstrate that YY1 indeed functions as a trans factor for transcriptional regulation and DNA methylation of these imprinted domains in vivo. © The Author 2007. Published by Oxford University Press. All rights reserved

Sexual differences of imprinted genes\u27 expression levels

In mammals, genomic imprinting has evolved as a dosage-controlling mechanism for a subset of genes that play critical roles in their unusual reproduction scheme involving viviparity and placentation. As such, many imprinted genes are highly expressed in sex-specific reproductive organs. In the current study, we sought to test whether imprinted genes are differentially expressed between the two sexes. According to the results, the expression levels of the following genes differ between the two sexes of mice: Peg3, Zim1, Igf2, H19 and Zac1. The expression levels of these imprinted genes are usually greater in males than in females. This bias is most obvious in the developing brains of 14.5-dpc embryos, but also detected in the brains of postnatal-stage mice. However, this sexual bias is not obvious in 10.5-dpc embryos, a developmental stage before the sexual differentiation. Thus, the sexual bias observed in the imprinted genes is most likely attributable by gonadal hormones rather than by sex chromosome complement. Overall, the results indicate that several imprinted genes are sexually different in terms of their expression levels, and further suggest that the transcriptional regulation of these imprinted genes may be influenced by unknown mechanisms associated with sexual differentiation. © 2013 Elsevier B.V

Inversion of the imprinting control region of the Peg3 domain

© 2017 Kim et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The imprinting of the mouse Peg3 domain is controlled through a 4-kb genomic region encompassing the bidirectional promoter and 1st exons of Peg3 and Usp29. In the current study, this ICR was inverted to test its orientation dependency for the transcriptional and imprinting control of the Peg3 domain. The inversion resulted in the exchange of promoters and 1st exons between Peg3 and Usp29. Paternal transmission of this inversion caused 10-fold down-regulation of Peg3 and 2-fold up-regulation of Usp29 in neonatal heads, consistent with its original promoter strength in each direction. The paternal transmission also resulted in reduced body size among the animals, which was likely contributed by the dramatic down-regulation of Peg3. Transmission through either allele caused no changes in the DNA methylation and imprinting status of the Peg3 domain except that Zfp264 became bi-allelic through the maternal transmission. Overall, the current study suggests that the orientation of the Peg3-ICR may play no role in its allele-specific DNA methylation, but very critical for the transcriptional regulation of the entire imprinted domain

Retroposition and evolution of the DNA-binding motifs of YY1, YY2 and REX1

YY1 is a DNA-binding transcription factor found in both vertebrates and invertebrates. Database searches identified 62 YY1 related sequences from all the available genome sequences ranging from flying insects to human. These sequences are characterized by high levels of sequence conservation, ranging from 66% to 100% similarity, in the zinc finger DNA-binding domain of the predicted proteins. Phylogenetic analyses uncovered duplication events of YY1 in several different lineages, including flies, fish and mammals. Retroposition is responsible for generating one duplicate in flies, PHOL from PHO, and two duplicates in placental mammals, YY2 and Reduced Expression 1 (REX1) from YY1. DNA-binding motif studies have demonstrated that YY2 still binds to the same consensus sequence as YY1 but with much lower affinity. In contrast, REX1 binds to DNA motifs divergent from YY1, but the binding motifs of REX1 and YY1 share some similarity at their core regions (5′-CCAT-3′). This suggests that the two duplicates, YY2 and REX1, although generated through similar retroposition events have undergone different selection schemes to adapt to new roles in placental mammals. Overall, the conservation of YY2 and REX1 in all placental mammals predicts that each duplicate has co-evolved with some unique features of eutherian mammals