Humanized H19/Igf2 locus reveals diverged imprinting mechanism between mouse and human and reflects Silver–Russell syndrome phenotypes

Abstract

Genomic imprinting affects a subset of genes in mammals, such that they are expressed in a monoallelic, parent-of-origin-specific manner. These genes are regulated by imprinting control regions (ICRs), cis-regulatory elements that exhibit allele-specific differential DNA methylation. Although genomic imprinting is conserved in mammals, ICRs are genetically divergent across species. This raises the fundamental question of whether the ICR plays a species-specific role in regulating imprinting at a given locus. We addressed this question at the H19/insulin-like growth factor 2 (Igf2) imprinted locus, the misregulation of which is associated with the human imprinting disorders Beckwith-Wiedemann syndrome (BWS) and Silver-Russell syndrome (SRS). We generated a knock-in mouse in which the endogenous H19/Igf2 ICR (mIC1) is replaced by the orthologous human ICR (hIC1) sequence, designated H19 hIC1 . We show that hIC1 can functionally replace mIC1 on the maternal allele. In contrast, paternally transmitted hIC1 leads to growth restriction, abnormal hIC1 methylation, and loss of H19 and Igf2 imprinted expression. Imprint establishment at hIC1 is impaired in the male germ line, which is associated with an abnormal composition of histone posttranslational modifications compared with mIC1. Overall, this study reveals evolutionarily divergent paternal imprinting at IC1 between mice and humans. The conserved maternal imprinting mechanism and function at IC1 demonstrates the possibility of modeling maternal transmission of hIC1 mutations associated with BWS in mice. In addition, we propose that further analyses in the paternal knockin H19 +/hIC1 mice will elucidate the molecular mechanisms that may underlie SRS.G enomic imprinting is a conserved, epigenetic process in mammals that regulates the expression of a small number of genes in a monoallelic, parent-of-origin-specific manner. Typically clustered within domains, the parental-specific expression of imprinted genes is controlled by a cis-regulatory element, the imprinting control region (ICR). During gametogenesis, ICRs acquire differential DNA methylation patterns according to the sex of the germ cells. This DNA methylation is maintained in somatic cells after fertilization but is erased in primordial germ cells, allowing the establishment of sex-specific imprints in mature gametes. The proper establishment, maintenance, and erasure of imprints are crucial for the correct expression of imprinted genes. Misregulation of imprinted genes is associated with human imprinting disorders, including Beckwith-Wiedemann syndrome (BWS), an overgrowth disorder, and Silver-Russell syndrome (SRS), an undergrowth disorder (1-3).Mouse models have been valuable to the study of imprinting at the H19/insulin-like growth factor 2 (Igf2) locus, serving as a proxy for the orthologous human locus. On distal mouse chromosome 7, reciprocal imprinting of the paternally expressed fetal growth factor gene, Igf2, and the maternally expressed noncoding RNA, H19, is regulated by the ICR located between H...

Recapitulation of gametic DNA methylation and its post-fertilization maintenance with reassembled DNA elements at the mouse Igf2/H19 locus

“…Therefore, it is conceivable that a Zfp57-independent mechanism that is common to both H19 ICR and IG-DMR is operating at these paternal gDMRs through the 118-bp and the repeat array sequences, respectively, although they do not share significant sequence homology. In addition, the corresponding region of the human H19 ICR sequence (hIC1) is not strongly similar to the mouse 118-bp sequence, and Hur et al failed to recapitulate paternal methylation of the hIC1 (4.8 kb) when knocked into the mouse Igf2/H19 locus [28]. It remains an open question whether the mechanism of post-fertilization methylation maintenance we found in the mouse H19 ICR is conserved in other mammals, especially in humans, and whether it is also employed at other imprinted loci.…”

Reprogramming of Meiotic Chromatin Architecture during Spermatogenesis

“…To examine the 3D chromatin structure in spermatogenesis, we applied a low-input Hi-C method (sisHi-C) to spermatogenic cells in rhesus monkey. We collected spermatogonia (SPA), pachytene spermatocyte (PAC), round spermatid (RS), and mature sperm using STA-PUT, a widely used velocity sedimentation approach to purify spermatogenic cells (Bryant et al, 2013(Bryant et al, , 2015Hur et al, 2016;Korhonen et al, 2015;Liu et al, 2015;Luense et al, 2016) (Figures 1A and S1A; see STAR Methods). We confirmed the identities of these cells by immunofluorescence staining and morphology (Figures S1A and S1B; see legend for details).…”

An Update on Epigenetics in Mammalian Reproduction with Emphasis on Human Reproduction

“…Further role of environmental stressors in stresses. Role of famines in both Chinese as well as Dutch famines highlights immediate changes [3,6,156] and effects on future generations [171,172]. Epigenetic information can be inherited through the mammalian germ line and represents a plausible Tran's generational carrier of environmental information.…”

“…Why multilocus loss of methylation (MLOM), occurs is unclear. This also occurs is transient neonatal diabetes mellitus, having initial defect in PLAGL1DMR on C6q24, which is associated with LOM at other DMRs [156,157]. It is believed that this MLOM is due to homozygous mutation in the ZFP57 gene.…”