Cdkn1c (p57Kip2) is the major regulator of embryonic growth within its imprinted domain on mouse distal chromosome 7

Protein restriction during pregnancy alters Cdkn1c silencing, dopamine circuitry and offspring behaviour without changing expression of key neuronal marker genes

We tracked the consequences of in utero protein restriction in mice throughout their development and life course using a luciferase-based allelic reporter of imprinted Cdkn1c. Exposure to gestational low-protein diet (LPD) results in the inappropriate expression of paternally inherited Cdkn1c in the brains of embryonic and juvenile mice. These animals were characterised by a developmental delay in motor skills, and by behavioural alterations indicative of reduced anxiety. Exposure to LPD in utero resulted in significantly more tyrosine hydroxylase positive (dopaminergic) neurons in the midbrain of adult offspring as compared to age-matched, control-diet equivalents. Positron emission tomography (PET) imaging revealed an increase in striatal dopamine synthesis capacity in LPD-exposed offspring, where elevated levels of dopamine correlated with an enhanced sensitivity to cocaine. These data highlight a profound sensitivity of the developing epigenome to gestational protein restriction. Our data also suggest that loss of Cdkn1c imprinting and p57KIP2 upregulation alters the cellular composition of the developing midbrain, compromises dopamine circuitry, and thereby provokes behavioural abnormalities in early postnatal life. Molecular analyses showed that despite this phenotype, exposure to LPD solely during pregnancy did not significantly change the expression of key neuronal- or dopamine-associated marker genes in adult offspring.

Deficiency of the paternally-expressed imprinted Peg3 gene in mice has sexually dimorphic consequences for offspring communication and social behaviour

Introduction

Imprinted genes are expressed from one parental allele as a consequence of epigenetic processes initiated in the germline. Consequently, their ability to influence phenotype depends on their parent-of-origin. Recent research suggests that the sex of the individual expressing the imprinted gene is also important. We have previously reported that genetically wildtype (WT) dams carrying and caring for pups mutant for PEG3 exhibit anxiety-like behaviours and their mutant pups show a reduction in ultrasonic vocalisation when separated from their mothers. Sex-specificity was not examined.

Methods

WT female mice were mated with WT, heterozygous Peg3-/+ or homozygous Peg3-/- studs to generate all WT (control), 50:50 mixed or 100% mutant litters, respectively, followed by behavioural assessment of both dams and their pups.

Results

We reproduced our original finding that WT dams carrying and caring for 100% mutant litters exhibit postpartum anxiety-like symptoms and delayed pup retrieval. Additionally, these WT dams were found to allocate less time to pup-directed care behaviours relative to controls. Male Peg3-deficient pups demonstrated significantly reduced vocalisation with a more subtle communication deficit in females. Postweaning, male mutants exhibited deficits across a number of key social behaviours as did WT males sharing their environment with mutants. Only modest variations in social behaviour were detected in experimental females.

Discussion

We have experimentally demonstrated that Peg3 deficiency confined to the offspring causes anxiety in mouse mothers and atypical behaviour including deficits in communication in their male offspring. A male-specific reduction in expression PEG3 in the fetally-derived placenta has previously been associated with maternal depression in human pregnancy. Maternal mood disorders such as depression and anxiety are associated with delays in language development and neuroatypical behaviour more common in sons. Peg3 deficiency could drive the association of maternal and offspring behavioural disorders reported in humans.

United by Conflict: Convergent Signatures of Parental Conflict in Angiosperms and Placental Mammals

Endosperm in angiosperms and placenta in eutherians are convergent innovations for efficient embryonic nutrient transfer. Despite advantages, this reproductive strategy incurs metabolic costs that maternal parents disproportionately shoulder, leading to potential inter-parental conflict over optimal offspring investment. Genomic imprinting-parent-of-origin-biased gene expression-is fundamental for endosperm and placenta development and has convergently evolved in angiosperms and mammals, in part, to resolve parental conflict. Here, we review the mechanisms of genomic imprinting in these taxa. Despite differences in the timing and spatial extent of imprinting, these taxa exhibit remarkable convergence in the molecular machinery and genes governing imprinting. We then assess the role of parental conflict in shaping evolution within angiosperms and eutherians using four criteria: (1) Do differences in the extent of sibling relatedness cause differences in the inferred strength of parental conflict? (2) Do reciprocal crosses between taxa with different inferred histories of parental conflict exhibit parent-of-origin growth effects? (3) Are these parent-of-origin growth effects caused by dosage-sensitive mechanisms and do these loci exhibit signals of positive selection? (4) Can normal development be restored by genomic perturbations that restore stoichiometric balance in the endosperm/placenta? Although we find evidence for all criteria in angiosperms and eutherians, suggesting that parental conflict may help shape their evolution, many questions remain. Additionally, myriad differences between the two taxa suggest that their respective biologies may shape how/when/where/to what extent parental conflict manifests. Lastly, we discuss outstanding questions, highlighting the power of comparative work in quantifying the role of parental conflict in evolution.

Epigenetic control of the imprinted growth regulator Cdkn1c in cadmium-induced placental dysfunction

Cadmium (Cd) is a toxic metal ubiquitous in the environment. In utero, Cd is inefficiently transported to the foetus but causes foetal growth restriction (FGR), likely through impairment of the placenta where Cd accumulates. However, the underlying molecular mechanisms are poorly understood. Cd can modulate the expression of imprinted genes, defined by their transcription from one parental allele, which play critical roles in placental and foetal growth. The expression of imprinted genes is governed by DNA methylation at Imprinting Control Regions (ICRs), which are susceptible to environmental perturbation. The imprinted gene Cdkn1c/CDKN1C is a major regulator of placental development, is implicated in FGR, and shows increased expression in response to Cd exposure in mice. Here, we use a hybrid mouse model of in utero Cd exposure to determine if the increase in placental Cdkn1c expression is caused by changes to ICR DNA methylation and loss of imprinting (LOI). Consistent with prior studies, Cd causes FGR and impacts placental structure and Cdkn1c expression at late gestation. Using polymorphisms to distinguish parental alleles, we demonstrate that increased Cdkn1c expression is not driven by changes to DNA methylation or LOI. We show that Cdkn1c is expressed primarily in the placental labyrinth which is proportionally increased in size in response to Cd. We conclude that the Cd-associated increase in Cdkn1c expression can be fully explained by alterations to placental structure. These results have implications for understanding mechanisms of Cd-induced placental dysfunction and, more broadly, for the study of FGR associated with increased Cdkn1c/CDKN1C expression.

Assessing the influence of distinct culture media on human pre-implantation development using single-embryo transcriptomics

The use of assisted reproductive technologies is consistently rising across the world. However, making an informed choice on which embryo culture medium should be preferred to ensure satisfactory pregnancy rates and the health of future children critically lacks scientific background. In particular, embryos within their first days of development are highly sensitive to their micro-environment, and it is unknown how their transcriptome adapts to different embryo culture compositions. Here, we determined the impact of culture media composition on gene expression in human pre-implantation embryos. By employing single-embryo RNA-sequencing after 2 or 5 days of the post-fertilization culture in different commercially available media (Ferticult, Global, and SSM), we revealed medium-specific differences in gene expression changes. Embryos cultured pre-compaction until day 2 in Ferticult or Global media notably displayed 266 differentially expressed genes, which were related to essential developmental pathways. Herein, 19 of them could have a key role in early development, based on their previously described dynamic expression changes across development. When embryos were cultured after day 2 in the same media considered more suitable because of its amino acid enrichment, 18 differentially expressed genes thought to be involved in the transition from early to later embryonic stages were identified. Overall, the differences were reduced at the blastocyst stage, highlighting the ability of embryos conceived in a suboptimal in vitro culture medium to mitigate the transcriptomic profile acquired under different pre-compaction environments.

Drug-induced loss of imprinting revealed using bioluminescent reporters of Cdkn1c

Genomic imprinting is an epigenetically mediated mechanism that regulates allelic expression of genes based upon parent-of-origin and provides a paradigm for studying epigenetic silencing and release. Here, bioluminescent reporters for the maternally-expressed imprinted gene Cdkn1c are used to examine the capacity of chromatin-modifying drugs to reverse paternal Cdkn1c silencing. Exposure of reporter mouse embryonic stem cells (mESCs) to 5-Azacytidine, HDAC inhibitors, BET inhibitors or GSK-J4 (KDM6A/B inhibitor) relieved repression of paternal Cdkn1c, either selectively or by inducing biallelic effects. Treatment of reporter fibroblasts with HDAC inhibitors or GSK-J4 resulted in similar paternal Cdkn1c activation, whereas BET inhibitor-induced loss of imprinting was specific to mESCs. Changes in allelic expression were generally not sustained in dividing cultures upon drug removal, indicating that the underlying epigenetic memory of silencing was maintained. In contrast, Cdkn1c de-repression by GSK-J4 was retained in both mESCs and fibroblasts following inhibitor removal, although this impact may be linked to cellular stress and DNA damage. Taken together, these data introduce bioluminescent reporter cells as tools for studying epigenetic silencing and disruption, and demonstrate that Cdkn1c imprinting requires distinct and cell-type specific chromatin features and modifying enzymes to enact and propagate a memory of silencing.

Sexually Dimorphic Alterations in the Transcriptome and Behavior with Loss of Histone Demethylase KDM5C

Chromatin dysregulation has emerged as a major hallmark of neurodevelopmental disorders such as intellectual disability (ID) and autism spectrum disorders (ASD). The prevalence of ID and ASD is higher in males compared to females, with unknown mechanisms. Intellectual developmental disorder, X-linked syndromic, Claes-Jensen type (MRXSCJ), is caused by loss-of-function mutations of lysine demethylase 5C (KDM5C), a histone H3K4 demethylase gene. KDM5C escapes X-inactivation, thereby presenting at a higher level in females. Initially, MRXSCJ was exclusively reported in males, while it is increasingly evident that females with heterozygous KDM5C mutations can show cognitive deficits. The mouse model of MRXSCJ, male Kdm5c-hemizygous knockout animals, recapitulates key features of human male patients. However, the behavioral and molecular traits of Kdm5c-heterozygous female mice remain incompletely characterized. Here, we report that gene expression and behavioral abnormalities are readily detectable in Kdm5c-heterozygous female mice, demonstrating the requirement for a higher KDM5C dose in females. Furthermore, we found both shared and sex-specific consequences of a reduced KDM5C dose in social behavior, gene expression, and genetic interaction with the counteracting enzyme KMT2A. These observations provide an essential insight into the sex-biased manifestation of neurodevelopmental disorders and sex chromosome evolution.

Clinical and Molecular Heterogeneity of Silver-Russell Syndrome and Therapeutic Challenges: A Systematic Review

BACKGROUND

Silver-Russell syndrome (SRS) is a developmental disorder involving extreme growth failure, characteristic facial features and underlying genetic heterogeneity. As the clinical heterogeneity of SRS makes diagnosis a challenging task, the worldwide incidence of SRS could vary from 1:30,000 to 1:100,000. Although various chromosomal, genetic, and epigenetic mutations have been linked with SRS, the cause had only been identified in half of the cases.

MATERIAL AND METHODS

To have a better understanding of the SRS clinical presentation and mutation/ epimutation responsible for SRS, a systematic review of the literature was carried out using appropriate keywords in various scientific databases (PROSPERO protocol registration CRD42021273211). Clinical features of SRS have been compiled and presented corresponding to the specific genetic subtype. An attempt has been made to understand the recurrence risk and the role of model organisms in understanding the molecular mechanisms of SRS pathology, treatment, and management strategies of the affected patients through the analysis of selected literature.

RESULTS

156 articles were selected to understand the clinical and molecular heterogeneity of SRS. Information about detailed clinical features was available for 228 patients only, and it was observed that body asymmetry and relative macrocephaly were most prevalent in cases with methylation defects of the 11p15 region. In about 38% of cases, methylation defects in ICRs or genomic mutations at the 11p15 region have been implicated. Maternal uniparental disomy of chromosome 7 (mUPD7) accounts for about 7% of SRS cases, and rarely, uniparental disomy of other autosomes (11, 14, 16, and 20 chromosomes) has been documented. Mutation in half of the cases is yet to be identified. Studies involving mice as experimental animals have been helpful in understanding the underlying molecular mechanism. As the clinical presentation of the syndrome varies a lot, treatment needs to be individualized with multidisciplinary effort.

CONCLUSION

SRS is a clinically and genetically heterogeneous disorder, with most of the cases being implicated with a mutation in the 11p15 region and maternal disomy of chromosome 7. Recurrence risk varies according to the molecular subtype. Studies with mice as a model organism have been useful in understanding the underlying molecular mechanism leading to the characteristic clinical presentation of the syndrome. Management strategies often need to be individualized due to varied clinical presentations.

Comprehensive expression analysis for the core cell cycle regulators in the chicken embryo reveals novel tissue-specific synexpression groups and similarities and differences with expression in mouse, frog and zebrafish

The core cell cycle machinery is conserved from yeast to humans, and hence it is assumed that all vertebrates share the same set of players. Yet during vertebrate evolution, the genome was duplicated twice, followed by a further genome duplication in teleost fish. Thereafter, distinct genes were retained in different vertebrate lineages; some individual gene duplications also occurred. To which extent these diversifying tendencies were compensated by retaining the same expression patterns across homologous genes is not known. This study for the first time undertook a comprehensive expression analysis for the core cell cycle regulators in the chicken, focusing in on early neurula and pharyngula stages of development, with the latter representing the vertebrate phylotypic stage. We also compared our data with published data for the mouse, Xenopus and zebrafish, the other established vertebrate models. Our work shows that, while many genes are expressed widely, some are upregulated or specifically expressed in defined tissues of the chicken embryo, forming novel synexpression groups with markers for distinct developmental pathways. Moreover, we found that in the neural tube and in the somite, mRNAs of some of the genes investigated accumulate in a specific subcellular localisation, pointing at a novel link between the site of mRNA translation, cell cycle control and interkinetic nuclear movements. Finally, we show that expression patterns of orthologous genes may differ in the four vertebrate models. Thus, for any study investigating cell proliferation, cell differentiation, tissue regeneration, stem cell behaviour and cancer/cancer therapy, it has to be carefully examined which of the observed effects are due to the specific model organism used, and which can be generalised.

The imprinted Zdbf2 gene finely tunes control of feeding and growth in neonates

Genomic imprinting refers to the mono-allelic and parent-specific expression of a subset of genes. While long recognized for their role in embryonic development, imprinted genes have recently emerged as important modulators of postnatal physiology, notably through hypothalamus-driven functions. Here, using mouse models of loss, gain and parental inversion of expression, we report that the paternally expressed Zdbf2 gene controls neonatal growth in mice, in a dose-sensitive but parent-of-origin-independent manner. We further found that Zdbf2-KO neonates failed to fully activate hypothalamic circuits that stimulate appetite, and suffered milk deprivation and diminished circulating Insulin Growth Factor 1 (IGF-1). Consequently, only half of Zdbf2-KO pups survived the first days after birth and those surviving were smaller. This study demonstrates that precise imprinted gene dosage is essential for vital physiological functions at the transition from intra- to extra-uterine life, here the adaptation to oral feeding and optimized body weight gain.

Cell-fate transition and determination analysis of mouse male germ cells throughout development

Mammalian male germ cell development is a stepwise cell-fate transition process; however, the full-term developmental profile of male germ cells remains undefined. Here, by interrogating the high-precision transcriptome atlas of 11,598 cells covering 28 critical time-points, we demonstrate that cell-fate transition from mitotic to post-mitotic primordial germ cells is accompanied by transcriptome-scale reconfiguration and a transitional cell state. Notch signaling pathway is essential for initiating mitotic arrest and the maintenance of male germ cells' identities. Ablation of HELQ induces developmental arrest and abnormal transcriptome reprogramming of male germ cells, indicating the importance of cell cycle regulation for proper cell-fate transition. Finally, systematic human-mouse comparison reveals potential regulators whose deficiency contributed to human male infertility via mitotic arrest regulation. Collectively, our study provides an accurate and comprehensive transcriptome atlas of the male germline cycle and allows for an in-depth understanding of the cell-fate transition and determination underlying male germ cell development.

High Maternal Serum Estradiol in First Trimester of Multiple Pregnancy Contributes to Small for Gestational Age via DNMT1-Mediated CDKN1C Upregulation

High maternal serum estradiol (E₂) levels in the first trimester of pregnancy are associated with a high incidence of low birth weight (LBW) and small for gestational age (SGA). This study aimed to investigate the effect of first-trimester high maternal serum E₂ levels on fetal growth and the underlying mechanisms in multiple pregnancies. Maternal serum E₂ levels of women at 8 weeks of gestation were measured. The expression levels of imprinted genes and DNMT1 were determined by RT-qPCR, and KvDMR1 methylation in embryo tissue, placenta, and newborn cord blood samples was examined by bisulfite sequencing PCR. The effect of E₂ on CDKN1C expression was investigated in HTR8 cells. The incidence of SGA was significantly higher in multiple pregnancies reduced to singleton than that in primary singleton pregnancies (11.4% vs. 2.9%) (P < 0.01) and multiple pregnancies reduced to twins than primary twins (38.5% vs. 27.3%) (P < 0.01). The maternal serum E₂ level at 8 weeks of gestation increased with the number of fetuses and was negatively correlated with offspring birth weight. CDKN1C and DNMT1 expression was significantly upregulated in embryo tissue, placenta, and cord blood from multiple pregnancies. Furthermore, there was a positive correlation between CDKN1C mRNA expression and KvDMR1 methylation levels. In HTR8 cells, DNMT1 mediated the estrogen-induced upregulation of CDKN1C, which might contribute to SGA. To minimize the risks of LBW and SGA, our findings suggest that abnormally high maternal serum E₂ levels should be avoided during the first trimester of multiple pregnancies from assisted reproductive technology (ART).

Sex Differences in Behavioral and Brainstem Transcriptomic Neuroadaptations following Neonatal Opioid Exposure in Outbred Mice

The opioid epidemic led to an increase in the number of neonatal opioid withdrawal syndrome (NOWS) cases in infants born to opioid-dependent mothers. Hallmark features of NOWS include weight loss, severe irritability, respiratory problems, and sleep fragmentation. Mouse models provide an opportunity to identify brain mechanisms that contribute to NOWS. Neonatal outbred Swiss Webster Cartworth Farms White (CFW) mice were administered morphine (15 mg/kg, s.c.) twice daily from postnatal day 1 (P1) to P14, an approximation of the third trimester of human gestation. Female and male mice underwent behavioral testing on P7 and P14 to determine the impact of opioid exposure on anxiety and pain sensitivity. Ultrasonic vocalizations (USVs) and daily body weights were also recorded. Brainstems containing pons and medulla were collected during morphine withdrawal on P14 for RNA sequencing. Morphine induced weight loss from P2 to P14, which persisted during adolescence (P21) and adulthood (P50). USVs markedly increased at P7 in females, emerging earlier than males. On P7 and P14, both morphine-exposed female and male mice displayed hyperalgesia on the hot plate and tail-flick assays, with females showing greater hyperalgesia than males. Morphine-exposed mice exhibited increased anxiety-like behavior in the open-field arena on P21. Transcriptome analysis of the brainstem, an area implicated in opioid withdrawal and NOWS, identified pathways enriched for noradrenergic signaling in females and males. We also found sex-specific pathways related to mitochondrial function and neurodevelopment in females and circadian entrainment in males. Sex-specific transcriptomic neuroadaptations implicate unique neurobiological mechanisms underlying NOWS-like behaviors.

Glucocorticoid receptor triggers a reversible drug-tolerant dormancy state with acquired therapeutic vulnerabilities in lung cancer

The glucocorticoid receptor (GR) regulates gene expression, governing aspects of homeostasis, but is also involved in cancer. Pharmacological GR activation is frequently used to alleviate therapy-related side-effects. While prior studies have shown GR activation might also have anti-proliferative action on tumours, the underpinnings of glucocorticoid action and its direct effectors in non-lymphoid solid cancers remain elusive. Here, we study the mechanisms of glucocorticoid response, focusing on lung cancer. We show that GR activation induces reversible cancer cell dormancy characterised by anticancer drug tolerance, and activation of growth factor survival signalling accompanied by vulnerability to inhibitors. GR-induced dormancy is dependent on a single GR-target gene, CDKN1C, regulated through chromatin looping of a GR-occupied upstream distal enhancer in a SWI/SNF-dependent fashion. These insights illustrate the importance of GR signalling in non-lymphoid solid cancer biology, particularly in lung cancer, and warrant caution for use of glucocorticoids in treatment of anticancer therapy related side-effects.

Variable Expressivity of the Beckwith-Wiedemann Syndrome in Four Pedigrees Segregating Loss-of-Function Variants of CDKN1C

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder characterized by prenatal and/or postnatal overgrowth, organomegaly, abdominal wall defects and tumor predisposition. CDKN1C is a maternally expressed gene of the 11p15.5 chromosomal region and is regulated by the imprinting control region IC2. It negatively controls cellular proliferation, and its expression or activity are frequently reduced in BWS. In particular, loss of IC2 methylation is associated with CDKN1C silencing in the majority of sporadic BWS cases, and maternally inherited loss-of-function variants of CDKN1C are the most frequent molecular defects of familial BWS. We have identified, using Sanger sequencing, novel CDKN1C variants in three families with recurrent cases of BWS, and a previously reported variant in a woman with recurrent miscarriages with exomphalos. Clinical evaluation of the patients showed variable manifestation of the disease. The frameshift and nonsense variants were consistently associated with exomphalos, while the missense variant caused a less severe phenotype. Pregnancy loss and perinatal lethality were found in the families segregating nonsense mutations. Intrafamilial variability of the clinical BWS features was observed, even between siblings. Our data are indicative of severe BWS phenotypes that, with variable expressivity, may be associated with both frameshift and nonsense variants of CDKN1C.

Dynamic Expression of Imprinted Genes in the Developing and Postnatal Pituitary Gland

In mammals, imprinted genes regulate many critical endocrine processes such as growth, the onset of puberty and maternal reproductive behaviour. Human imprinting disorders (IDs) are caused by genetic and epigenetic mechanisms that alter the expression dosage of imprinted genes. Due to improvements in diagnosis, increasing numbers of patients with IDs are now identified and monitored across their lifetimes. Seminal work has revealed that IDs have a strong endocrine component, yet the contribution of imprinted gene products in the development and function of the hypothalamo-pituitary axis are not well defined. Postnatal endocrine processes are dependent upon the production of hormones from the pituitary gland. While the actions of a few imprinted genes in pituitary development and function have been described, to date there has been no attempt to link the expression of these genes as a class to the formation and function of this essential organ. This is important because IDs show considerable overlap, and imprinted genes are known to define a transcriptional network related to organ growth. This knowledge deficit is partly due to technical difficulties in obtaining useful transcriptomic data from the pituitary gland, namely, its small size during development and cellular complexity in maturity. Here we utilise high-sensitivity RNA sequencing at the embryonic stages, and single-cell RNA sequencing data to describe the imprinted transcriptome of the pituitary gland. In concert, we provide a comprehensive literature review of the current knowledge of the role of imprinted genes in pituitary hormonal pathways and how these relate to IDs. We present new data that implicate imprinted gene networks in the development of the gland and in the stem cell compartment. Furthermore, we suggest novel roles for individual imprinted genes in the aetiology of IDs. Finally, we describe the dynamic regulation of imprinted genes in the pituitary gland of the pregnant mother, with implications for the regulation of maternal metabolic adaptations to pregnancy.

Inducible uniparental chromosome disomy to probe genomic imprinting at single-cell level in brain and beyond

Genomic imprinting is an epigenetic mechanism that results in parental allele-specific expression of ~1% of all genes in mouse and human. Imprinted genes are key developmental regulators and play pivotal roles in many biological processes such as nutrient transfer from the mother to offspring and neuronal development. Imprinted genes are also involved in human disease, including neurodevelopmental disorders, and often occur in clusters that are regulated by a common imprint control region (ICR). In extra-embryonic tissues ICRs can act over large distances, with the largest surrounding Igf2r spanning over 10 million base-pairs. Besides classical imprinted expression that shows near exclusive maternal or paternal expression, widespread biased imprinted expression has been identified mainly in brain. In this review we discuss recent developments mapping cell type specific imprinted expression in extra-embryonic tissues and neocortex in the mouse. We highlight the advantages of using an inducible uniparental chromosome disomy (UPD) system to generate cells carrying either two maternal or two paternal copies of a specific chromosome to analyze the functional consequences of genomic imprinting. Mosaic Analysis with Double Markers (MADM) allows fluorescent labeling and concomitant induction of UPD sparsely in specific cell types, and thus to over-express or suppress all imprinted genes on that chromosome. To illustrate the utility of this technique, we explain how MADM-induced UPD revealed new insights about the function of the well-studied Cdkn1c imprinted gene, and how MADM-induced UPDs led to identification of highly cell type specific phenotypes related to perturbed imprinted expression in the mouse neocortex. Finally, we give an outlook on how MADM could be used to probe cell type specific imprinted expression in other tissues in mouse, particularly in extra-embryonic tissues.

Functional Versatility of the CDK Inhibitor p57Kip2

The cyclin/CDK inhibitor p57^Kip2 belongs to the Cip/Kip family, with p21^Cip1 and p27^Kip1, and is the least studied member of the family. Unlike the other family members, p57^Kip2 has a unique role during embryogenesis and is the only CDK inhibitor required for embryonic development. p57^Kip2 is encoded by the imprinted gene CDKN1C, which is the gene most frequently silenced or mutated in the genetic disorder Beckwith-Wiedemann syndrome (BWS), characterized by multiple developmental anomalies. Although initially identified as a cell cycle inhibitor based on its homology to other Cip/Kip family proteins, multiple novel functions have been ascribed to p57^Kip2 in recent years that participate in the control of various cellular processes, including apoptosis, migration and transcription. Here, we will review our current knowledge on p57^Kip2 structure, regulation, and its diverse functions during development and homeostasis, as well as its potential implication in the development of various pathologies, including cancer.

The Role of CDKs and CDKIs in Murine Development

Cyclin-dependent kinases (CDKs) and their inhibitors (CDKIs) play pivotal roles in the regulation of the cell cycle. As a result of these functions, it may be extrapolated that they are essential for appropriate embryonic development. The twenty known mouse CDKs and eight CDKIs have been studied to varying degrees in the developing mouse, but only a handful of CDKs and a single CDKI have been shown to be absolutely required for murine embryonic development. What has become apparent, as more studies have shone light on these family members, is that in addition to their primary functional role in regulating the cell cycle, many of these genes are also controlling specific cell fates by directing differentiation in various tissues. Here we review the extensive mouse models that have been generated to study the functions of CDKs and CDKIs, and discuss their varying roles in murine embryonic development, with a particular focus on the brain, pancreas and fertility.

Modeling human epigenetic disorders in mice: Beckwith-Wiedemann syndrome and Silver-Russell syndrome

Genomic imprinting, a phenomenon in which the two parental alleles are regulated differently, is observed in mammals, marsupials and a few other species, including seed-bearing plants. Dysregulation of genomic imprinting can cause developmental disorders such as Beckwith-Wiedemann syndrome (BWS) and Silver-Russell syndrome (SRS). In this Review, we discuss (1) how various (epi)genetic lesions lead to the dysregulation of clinically relevant imprinted loci, and (2) how such perturbations may contribute to the developmental defects in BWS and SRS. Given that the regulatory mechanisms of most imprinted clusters are well conserved between mice and humans, numerous mouse models of BWS and SRS have been generated. These mouse models are key to understanding how mutations at imprinted loci result in pathological phenotypes in humans, although there are some limitations. This Review focuses on how the biological findings obtained from innovative mouse models explain the clinical features of BWS and SRS.

Imprinted Cdkn1c genomic locus cell-autonomously promotes cell survival in cerebral cortex development

The cyclin-dependent kinase inhibitor p57^KIP2 is encoded by the imprinted Cdkn1c locus, exhibits maternal expression, and is essential for cerebral cortex development. How Cdkn1c regulates corticogenesis is however not clear. To this end we employ Mosaic Analysis with Double Markers (MADM) technology to genetically dissect Cdkn1c gene function in corticogenesis at single cell resolution. We find that the previously described growth-inhibitory Cdkn1c function is a non-cell-autonomous one, acting on the whole organism. In contrast we reveal a growth-promoting cell-autonomous Cdkn1c function which at the mechanistic level mediates radial glial progenitor cell and nascent projection neuron survival. Strikingly, the growth-promoting function of Cdkn1c is highly dosage sensitive but not subject to genomic imprinting. Collectively, our results suggest that the Cdkn1c locus regulates cortical development through distinct cell-autonomous and non-cell-autonomous mechanisms. More generally, our study highlights the importance to probe the relative contributions of cell intrinsic gene function and tissue-wide mechanisms to the overall phenotype.

How the imprinted Cdkn1c locus regulates corticogenesis is unclear. Here, the authors dissect the level of cell-autonomy of imprinted Cdkn1c gene function in mouse corticogenesis and identify this as regulating radial glial progenitor cell and projection neuron survival.

Role of genomic imprinting in mammalian development

Non-mendelian inheritance refers to the group of phenomena and observations related to the inheritance of genetic information that cannot be merely explained by Mendel's laws of inheritance. Phenomenon including Genomic imprinting, X-chromosome Inactivation, Paramutations are some of the best studied examples of non-mendelian inheritance. Genomic imprinting is a process that reversibly marks one of the two homologous loci, chromosome or chromosomal sets during development, resulting in functional non-equivalence of gene expression. Genomic imprinting is known to occur in a few insect species, plants, and placental mammals. Over the years, studies on imprinted genes have contributed immensely to highlighting the role of epigenetic modifications and the epigenetic circuitry during gene expression and development. In this review, we discuss the phenomenon of genomic imprinting in mammals and the role it plays especially during fetoplacental growth and early development.

Abundances of placental imprinted genes CDKN1C, PHLDA2 and IGF-2 are related to low birth weight and early catch-up growth in full-term infants born small for gestational age

Children born small for gestational age (SGA) generally have a catch-up growth and rapid weight gain in the first years of life, which is a high risk of insulin resistance and cardiovascular diseases later in life. It was reported that the level of imprinted genes IGF-2, CDKN1C and PHLDA2 regulates placental growth. We assessed these imprinted genes expression levels in placental tissue and their influences on catch-up growth of full-term SGA infants. The protein and mRNA levels of placental CDKN1C, PHLDA2 and IGF-2 were analyzed in 29 full-term SGA and 29 full-term infants born appropriate for gestational age (AGA) using quantitative RT-PCR and Western blot assay, respectively. Catch-up growth was indicated by increased standard deviation score (ΔSDS) of weight at 1, 3 and 6 months relative to birth weight (BW). Correlations between indicated variables were evaluated using Pearson correlation coefficient analysis. Compared to AGA infants, CDKN1C and PHLDA2 levels were significantly increased, whereas IGF-2 was significantly reduced in SGA infants. The value of ΔSDS was significantly higher in SGA than that in AGA infants. For SGA status, Pearson analysis shows i) a negative correlation of CDKN1C and PHLDA2 abundances with BW, and a positive correlation of IGF-2 with BW, ii) no correlation between the three imprinted gene abundances and placental weight (PW), and between PW and BW, iii) a positive correlation of PHLDA2 abundance with CDKN1C, and iv) a positive correlation of CDKN1C and PHLDA2 abundances with ΔSDS, and a negative correlation of IGF-2 with ΔSDS at 1, 3 and 6 months. Taken together, increased CDKN1C and PHLDA2 and reduced IGF-2 abundances in placental tissue were related to BW and early period catch-up growth in full-term SGA infants. Placental CDKN1C, PHLDA2 and IGF-2 level monitoring may be useful for predicting and preventing the development of SGA.

Human iPSC-derived MSCs (iMSCs) from aged individuals acquire a rejuvenation signature

BACKGROUND

Primary mesenchymal stem cells (MSCs) are fraught with aging-related shortfalls. Human-induced pluripotent stem cell (iPSC)-derived MSCs (iMSCs) have been shown to be a useful clinically relevant source of MSCs that circumvent these aging-associated drawbacks. To date, the extent of the retention of aging-hallmarks in iMSCs differentiated from iPSCs derived from elderly donors remains unclear.

METHODS

Fetal femur-derived MSCs (fMSCs) and adult bone marrow MSCs (aMSCs) were isolated, corresponding iPSCs were generated, and iMSCs were differentiated from fMSC-iPSCs, from aMSC-iPSCs, and from human embryonic stem cells (ESCs) H1. In addition, typical MSC characterization such as cell surface marker expression, differentiation capacity, secretome profile, and trancriptome analysis were conducted for the three distinct iMSC preparations-fMSC-iMSCs, aMSC-iMSCs, and ESC-iMSCs. To verify these results, previously published data sets were used, and also, additional aMSCs and iMSCs were analyzed.

RESULTS

fMSCs and aMSCs both express the typical MSC cell surface markers and can be differentiated into osteogenic, adipogenic, and chondrogenic lineages in vitro. However, the transcriptome analysis revealed overlapping and distinct gene expression patterns and showed that fMSCs express more genes in common with ESCs than with aMSCs. fMSC-iMSCs, aMSC-iMSCs, and ESC-iMSCs met the criteria set out for MSCs. Dendrogram analyses confirmed that the transcriptomes of all iMSCs clustered together with the parental MSCs and separated from the MSC-iPSCs and ESCs. iMSCs irrespective of donor age and cell type acquired a rejuvenation-associated gene signature, specifically, the expression of INHBE, DNMT3B, POU5F1P1, CDKN1C, and GCNT2 which are also expressed in pluripotent stem cells (iPSCs and ESC) but not in the parental aMSCs. iMSCs expressed more genes in common with fMSCs than with aMSCs. Independent real-time PCR comparing aMSCs, fMSCs, and iMSCs confirmed the differential expression of the rejuvenation (COX7A, EZA2, and TMEM119) and aging (CXADR and IGSF3) signatures. Importantly, in terms of regenerative medicine, iMSCs acquired a secretome (e.g., angiogenin, DKK-1, IL-8, PDGF-AA, osteopontin, SERPINE1, and VEGF) similar to that of fMSCs and aMSCs, thus highlighting their ability to act via paracrine signaling.

CONCLUSIONS

iMSCs irrespective of donor age and cell source acquire a rejuvenation gene signature. The iMSC concept could allow circumventing the drawbacks associated with the use of adult MSCs und thus provide a promising tool for use in various clinical settings in the future.

Paternally and maternally imprinted gene perturbed expression in parthenogenetic diploid embryos in Capra hircus

The present research work was undertaken to compare the expression of paternally imprinted (P57KIP2, Grb10 and Xist) and maternally imprinted gene (Dlk1) among diploid parthenogenetic (DIP), female sexed in vivo and female sexed in vitro produced embryonic cell colony. The good quality caprine oocytes were matured in presence of cytochalasin B (CCB) and activated by ethanol (7%) for 5 min followed by incubation with 2 mM 6-dimethyl amino purine (DMAP) for 4 h for DIP embryos production. In vivo embryo was collected by surgical method from 10 super ovulated goats using Pluset®. In vitro embryos were produced by maturation of good quality oocyte followed by fertilization with superior male germplasm from the institute flock. Embryonic cell colony were developed from 8 to 16 and morula stage DIP, IVF and in vivo derived embryos. These colonies were used for studying the paternal and maternal imprinted genes expression. Karyotyping and sexing of embryonic cell colony was done to get only female sexed colony for this purpose. Paternally imprinted genes (P57KIP2, Grb10 and Xist) showed more expression in DIP compared to in vivo and IVF derived embryonic cell colony. The expression of maternally imprinted genes (Dlk1) was low in DIP compared to in vivo and IVF derived embryonic cell colony. The present study demonstrated that the expression profile of both paternal and maternally imprinted genes were perturbed, which may be responsible for developmental failure of parthenogenetic embryos to full term following parthenogenetic embryo transfer in goat.

Loss of Imprinting of Cdkn1c Protects against Age and Diet-Induced Obesity

Cyclin dependent kinase inhibitor 1c (Cdkn1c) is a maternally expressed imprinted gene with roles in embryonic development, post-natal metabolism and behaviour. Using mouse models with altered dosages of Cdkn1c, we have previously identified a role for the gene in promoting brown adipose tissue formation. Here, we use these transgenic mouse lines to model the loss of imprinting of Cdkn1c in adulthood. We demonstrate that only a two-fold increase in the expression of Cdkn1c during development is sufficient to protect against age-related weight gain in addition to glucose and insulin intolerance. Further to this, we show that the loss of imprinting of Cdkn1c protects against diet-induced obesity. Bisulphite sequencing was performed to test the stability of the two differentially methylated regions that regulate Cdkn1c imprinting, and both were found to be unaltered in aged or diet-challenged adipose tissue, despite drastic reductions in Cdkn1c expression. These data demonstrate a critical role for Cdkn1c in regulating adult adipose tissue, with modest changes in expression capable of protecting against both age and diet-induced obesity and metabolic syndrome, with a natural decline in Cdkn1c expression observed that may contribute to less healthy metabolic aging. Finally, we have observed a post-natal insensitivity of the imprint to environmental factors, in contrast to recent observations of an in utero sensitivity.

Territorial Behavior and Social Stability in the Mouse Require Correct Expression of Imprinted Cdkn1c

Genomic imprinting, the epigenetic process by which transcription occurs from a single parental allele, is believed to influence social behaviors in mammals. An important social behavior is group living, which is enriched in Eutherian mammals relative to monotremes and marsupials. Group living facilitates resource acquisition, defense of territory and co-care of young, but requires a stable social group with complex inter-individual relationships. Co-occurring with increased group living in Eutherians is an increase in the number of imprinted loci, including that spanning the maternally expressed Cdkn1c. Using a 'loss-of-imprinting' model of Cdkn1c (Cdkn1cBACx1), we demonstrated that twofold over expression of Cdkn1c results in abnormal social behaviors. Although, our previous work indicated that male Cdkn1cBACx1 mice were more dominant as measured by tube test encounters with unfamiliar wild-type (WT) males. Building upon this work, using more ecologically relevant assessments of social dominance, indicated that within their normal social group, Cdkn1cBACx1 mice did not occupy higher ranking positions. Nevertheless, we find that presence of Cdkn1cBACx1 animals within a group leads to instability of the normal social hierarchy, as indicated by greater variability in social rank within the group over time and an increase in territorial behavior in WT cage-mates. Consequently, these abnormal behaviors led to an increased incidence of fighting and wounding within the group. Taken together these data indicate that normal expression of Cdkn1c is required for maintaining stability of the social group and suggests that the acquisition of monoallelic expression of Cdkn1c may have enhanced social behavior in Eutherian mammals to facilitate group living.

Visualizing Changes in Cdkn1c Expression Links Early-Life Adversity to Imprint Mis-regulation in Adults

Imprinted genes are regulated according to parental origin and can influence embryonic growth and metabolism and confer disease susceptibility. Here, we designed sensitive allele-specific reporters to non-invasively monitor imprinted Cdkn1c expression in mice and showed that expression was modulated by environmental factors encountered in utero. Acute exposure to chromatin-modifying drugs resulted in de-repression of paternally inherited (silent) Cdkn1c alleles in embryos that was temporary and resolved after birth. In contrast, deprivation of maternal dietary protein in utero provoked permanent de-repression of imprinted Cdkn1c expression that was sustained into adulthood and occurred through a folate-dependent mechanism of DNA methylation loss. Given the function of imprinted genes in regulating behavior and metabolic processes in adults, these results establish imprinting deregulation as a credible mechanism linking early-life adversity to later-life outcomes. Furthermore, Cdkn1c-luciferase mice offer non-invasive tools to identify factors that disrupt epigenetic processes and strategies to limit their long-term impact.

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Allele-specific expression of imprinted Cdkn1c imaged in vivo using bioluminescence

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Chromatin-modifying drugs applied in utero transiently de-repress Cdkn1c imprinting

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In utero exposure to low-protein diet permanently disrupts the Cdkn1c imprint

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Folate supplements during gestation protect against loss of Cdkn1c imprinting

Maternal high estradiol exposure alters CDKN1C and IGF2 expression in human placenta

INTRODUCTION

The increased maternal estradiol (E₂) concentrations induced by assisted reproductive technology (ART) result in lower birth weight of offspring, which is associated with increased risk of adult diseases. However, the exact mechanism remains unknown. The present study investigated the effect of high E₂ exposure on the expression of imprinted genes CDKN1C and IGF2 in human placentas and the DNA methylation status of their differential methylation regions (DMRs).

METHODS

The mRNA expression of CDKN1C and IGF2 in human placentas and the human trophoblast cells (HTR8) treated with E₂ were investigated by reverse transcription-real time polymerase chain reaction (PCR). The DNA methylation of their DMRs were investigated by sodium bisulfite sequencing.

RESULTS

CDKN1C and IGF2 were significantly up-regulated in ART conceived placentas. The mean birth weight of ART singletons was significantly lower than that of naturally conceived (NC) ones, with the increased percentage of small-for-gestational-age (SGA) birth. The DNA methylation was significantly down-regulated in the DMR of CDKN1C (KvDMR1) and up-regulated in the DMR of IGF2 (H19 DMR) in ART placentas. The treatment of E₂ altered the expression of the two genes and the DNA methylation of their DMRs in HTR8 to a similar tendency as in vivo.

DISCUSSION

The maternal high E₂ levels after ART up-regulate the expression of imprinted genes in human placentas through epigenetic modifications, which influences the growth potential of the offspring. Further studies are needed to follow up the growth and development of the ART offspring.

Dopaminergic and behavioural changes in a loss-of-imprinting model of Cdkn1c

The imprinted gene Cdkn1c is expressed exclusively from the maternally inherited allele as a consequences of epigenetic regulation. Cdkn1c exemplifies many of the functional characteristics of imprinted genes, playing a role in foetal growth and placental development. However, Cdkn1c also plays an important role in the brain, being key to the appropriate proliferation and differentiation of midbrain dopaminergic neurons. Using a transgenic model (Cdkn1c^BACx1) with a twofold elevation in Cdkn1c expression that mimics loss‐of‐imprinting, we show that increased expression of Cdkn1c in the brain gives rise to neurobiological and behavioural changes indicative of a functionally altered dopaminergic system. Cdkn1c^BACX1 mice displayed altered expression of dopamine system‐related genes, increased tyrosine hydroxylase (Th) staining and increased tissue content of dopamine in the striatum. In addition, Cdkn1c^BACx1 animals were hypersensitive to amphetamine as showed by c‐fos expression in the nucleus accumbens. Cdkn1c^BACX1 mice had significant changes in behaviours that are dependent on the mesolimbic dopaminergic system. Specifically, increased motivation for palatable food stuffs, as indexed on a progressive ratio task. In addition, Cdkn1c^BACX1 mice displayed enhanced social dominance. These data show, for the first time, the consequence of elevated Cdkn1c expression on dopamine‐related behaviours highlighting the importance of correct dosage of this imprinted gene in the brain. This work has significant relevance for deepening our understanding of the epigenetic factors that can shape neurobiology and behaviour.

Placental Expressions of CDKN1C and KCNQ1OT1 in Monozygotic Twins with Selective Intrauterine Growth Restriction

CDKN1C and KCNQ1OT1 are imprinted genes that might be potential regulators of placental development. This study investigated placental expressions of CDKN1C and KCNQ1OT1 in monozygotic twins with and without selective intrauterine growth restriction (sIUGR). Seventeen sIUGR and fifteen normal monozygotic(MZ) twin pairs were examined. Placental mRNA expressions of CDKN1C and KCNQ1OT1 were detected by real-time fluorescent quantitative PCR. CDKN1C protein expression was detected by immunohistochemical assay and Western-blotting. In the sIUGR group, smaller fetuses had a smaller share of the placenta, and CDKN1C protein expression was significantly increased while KCNQ1OT1 mRNA expression was significantly decreased. The CDKN1C/KCNQ1OT1 mRNA ratio was lower in the larger fetus than in the smaller fetus (p < .05). In the control group, CDKN1C protein expression showed no difference between larger and smaller fetuses, while KCNQ1OT1 mRNA expression was significantly lower in the larger fetus, and the CDKN1C/KCNQ1OT1 mRNA ratio was higher in the larger fetus than in the smaller fetus (p < .05). Our findings showed that pathogenesis of sIUGR may be related to the co-effect of the up-regulated protein expression of CDKN1C and down-regulated mRNA expression of KCNQ1OT1 in the placenta.

Behavioural abnormalities in a novel mouse model for Silver Russell Syndrome

Silver Russell Syndrome (SRS) syndrome is an imprinting disorder involving low birth weight with complex genetics and diagnostics. Some rare SRS patients carry maternally inherited microduplications spanning the imprinted genes CDKN1C, PHLDA2, SLC22A18 and KCNQ1, suggesting that overexpression of one of more of these genes contributes to the SRS phenotype. While this molecular alteration is very rare, feeding difficulties are a very common feature of this condition. Given that SRS children also have very low body mass index, understanding the underpinning biology of the eating disorder is important, as well as potential co-occurring behavioural alterations. Here, we report that a mouse model of this microduplication exhibits a number of behavioural deficits. The mice had a blunted perception of the palatability of a given foodstuff. This perception may underpin the fussiness with food. We additionally report hypoactivity, unrelated to anxiety or motoric function, and a deficit in the appropriate integration of incoming sensory information. Importantly, using a second genetic model, we were able to attribute all altered behaviours to elevated expression of a single gene, Cdkn1c. This is the first report linking elevated Cdkn1c to altered behaviour in mice. Importantly, the findings from our study may have relevance for SRS and highlight a potentially underreported aspect of this disorder.

A p57 conditional mutant allele that allows tracking of p57-expressing cells

p57^Kip2 (p57) is a maternally expressed imprinted gene regulating growth arrest which belongs to the CIP/KIP family of cyclin-dependent kinase inhibitors. While initially identified as a cell cycle arrest protein through inhibition of cyclin and cyclin-dependent kinase complexes, p57 activity has also been linked to differentiation, apoptosis, and senescence. In addition, p57 has recently been shown to be involved in tumorigenesis and cell fate decisions in stem cells. Yet, p57 function in adult tissues remains poorly characterized due to the perinatal lethality of p57 knock-out mice. To analyze p57 tissue-specific activity, we generated a conditional mouse line (p57^FL-ILZ/+ ) by flanking the coding exons 2-3 by LoxP sites. To track p57-expressing or mutant cells, the p57^FL-ILZ allele also contains an IRES-linked β-galactosidase reporter inserted in the 3' UTR of the gene. Here, we show that the β-galactosidase reporter expression pattern recapitulates p57 tissue specificity during development and in postnatal mice. Furthermore, we crossed the p57^FL-ILZ/+ mice with PGK-Cre mice to generate p57^cKO-ILZ/+ animals with ubiquitous loss of p57. p57^cKO-ILZ/+ mice display developmental phenotypes analogous to previously described p57 knock-outs. Thus, p57^FL-ILZ/+ is a new genetic tool allowing expression and functional conditional analyses of p57.

Placental 5-methylcytosine and 5-hydroxymethylcytosine patterns associate with size at birth

Altered placental function as a consequence of aberrant imprinted gene expression may be one mechanism mediating the association between low birth weight and increased cardiometabolic disease risk. Imprinted gene expression is regulated by epigenetic mechanisms, particularly DNA methylation (5mC) at differentially methylated regions (DMRs). While 5-hydroxymethylcytosine (5hmC) is also present at DMRs, many techniques do not distinguish between 5mC and 5hmC. Using human placental samples, we show that the expression of the imprinted gene CDKN1C associates with birth weight. Using specific techniques to map 5mC and 5hmC at DMRs controlling the expression of CDKN1C and the imprinted gene IGF2, we show that 5mC enrichment at KvDMR and DMR0, and 5hmC enrichment within the H19 gene body, associate positively with birth weight. Importantly, the presence of 5hmC at imprinted DMRs may complicate the interpretation of DNA methylation studies in placenta; future studies should consider using techniques that distinguish between, and permit quantification of, both modifications.

Epigenetic Characterization of CDKN1C in Placenta Samples from Non-syndromic Intrauterine Growth Restriction

The cyclin-dependent kinase (CDK)-inhibitor 1C (CDKN1C) gene is expressed from the maternal allele and is located within the centromeric imprinted domain at chromosome 11p15. It is a negative regulator of proliferation, with loss-of-function mutations associated with the overgrowth disorder Beckwith–Wiedemann syndrome. Recently, gain-of-function mutations within the PCNA domain have been described in two disorders characterized by growth failure, namely IMAGe (intra-uterine growth restriction, metaphyseal dysplasia, adrenal hypoplasia congenita and genital abnormalities) syndrome and Silver–Russell syndrome (SRS). Over-expression of CDKN1C by maternally inherited microduplications also results in SRS, suggesting that in addition to activating mutations this gene may regulate growth by changes in dosage. To determine if CDKN1C is involved in non-syndromic IUGR we compared the expression and DNA methylation levels in a large cohort of placental biopsies from IUGR and uneventful pregnancies. We observe higher levels of expression of CDKN1C in IUGR placentas compared to those of controls. All placenta biopsies heterozygous for the PAPA repeat sequence in exon 2 showed appropriate monoallelic expression and no mutations in the PCNA domain were observed. The expression profile was independent of both genetic or methylation variation in the minimal CDKN1C promoter interval and of methylation of the cis-acting maternally methylated region associated with the neighboring KCNQ1OT1 non-coding RNA. Chromatin immunoprecipitation revealed binding sites for CTCF within the unmethylated CDKN1C gene body CpG island and putative enhancer regions, associated with the canonical enhancer histone signature, H3K4me1 and H3K27ac, located ∼58 and 360 kb away. Using 3C-PCR we identify constitutive higher-order chromatin loops that occur between one of these putative enhancer regions and CDKN1C in human placenta tissues, which we propose facilitates expression.

Cdkn1c Boosts the Development of Brown Adipose Tissue in a Murine Model of Silver Russell Syndrome

The accurate diagnosis and clinical management of the growth restriction disorder Silver Russell Syndrome (SRS) has confounded researchers and clinicians for many years due to the myriad of genetic and epigenetic alterations reported in these patients and the lack of suitable animal models to test the contribution of specific gene alterations. Some genetic alterations suggest a role for increased dosage of the imprinted CYCLIN DEPENDENT KINASE INHIBITOR 1C (CDKN1C) gene, often mutated in IMAGe Syndrome and Beckwith-Wiedemann Syndrome (BWS). Cdkn1c encodes a potent negative regulator of fetal growth that also regulates placental development, consistent with a proposed role for CDKN1C in these complex childhood growth disorders. Here, we report that a mouse modelling the rare microduplications present in some SRS patients exhibited phenotypes including low birth weight with relative head sparing, neonatal hypoglycemia, absence of catch-up growth and significantly reduced adiposity as adults, all defining features of SRS. Further investigation revealed the presence of substantially more brown adipose tissue in very young mice, of both the classical or canonical type exemplified by interscapular-type brown fat depot in mice (iBAT) and a second type of non-classic BAT that develops postnatally within white adipose tissue (WAT), genetically attributable to a double dose of Cdkn1c in vivo and ex-vivo. Conversely, loss-of-function of Cdkn1c resulted in the complete developmental failure of the brown adipocyte lineage with a loss of markers of both brown adipose fate and function. We further show that Cdkn1c is required for post-transcriptional accumulation of the brown fat determinant PR domain containing 16 (PRDM16) and that CDKN1C and PRDM16 co-localise to the nucleus of rare label-retaining cell within iBAT. This study reveals a key requirement for Cdkn1c in the early development of the brown adipose lineages. Importantly, active BAT consumes high amounts of energy to generate body heat, providing a valid explanation for the persistence of thinness in our model and supporting a major role for elevated CDKN1C in SRS.

Silver Russell syndrome is a severe developmental disorder characterised by low birth weight, sparing of the head and neonatal hypoglycemia. SRS adults are small and can be extremely thin, lacking body fat. Numerous genetic and epigenetic mutations have been linked to SRS primarily involving imprinted genes, but progress has been hampered by the lack of a suitable animal model. Here we describe a mouse model of the rare micro duplications reported in some SRS patients, which recapitulated many of the defining features of SRS, including extreme thinness. We showed that these mice possessed substantially more of the energy consuming brown adipose tissue (BAT), driven by a double dose of the imprinted Cdkn1c gene. We further show that Cdkn1c is required for the postranscriptional accumulation of the BAT determinant PRDM16 and that these proteins co-localise to the nucleus of in a rare label-retaining cell within BAT. These data suggest that Cdkn1c contributes to the development of BAT by modulating PRDM16 and supports a major role for this gene in SRS.

The imprinted Phlda2 gene modulates a major endocrine compartment of the placenta to regulate placental demands for maternal resources

Imprinted genes, which are expressed from a single parental allele in response to epigenetic marks first established in the germline, function in a myriad of processes to regulate mammalian development. Recent work suggests that imprinted genes may regulate the signalling function of the placenta by modulating the size of the endocrine compartment. Here we provide in vivo evidence that this hypothesis is well founded. Elevated expression of the imprinted Pleckstrin homology-like domain, family a, member 2 (Phlda2) gene drives a reduction of the spongiotrophoblast endocrine compartment, diminished placental glycogen and asymmetric foetal growth restriction. Using both loss-of-function and gain-in-expression mouse models, here we further show that Phlda2 exclusively modulates the spongiotrophoblast compartment of the placenta without significantly altering the composition of the trophoblast giant cell endocrine lineages that share a common progenitor with this lineage. Additionally, we show that Phlda2 loss-of-function placentae contain nearly three times more placental glycogen than non-transgenic placentae. Remarkably, relative to a fully wild type scenario, wild type placentae also accumulate excessive glycogen. While loss-of-function of Phlda2 increased both placental weight and placental glycogen, the weight of both mutant and non-transgenic fetuses was lower than that found in a fully wild type scenario indicating that excessive glycogen accumulation comes at the cost of foetal growth. This work firstly highlights a novel signalling function for the spongiotrophoblast in stimulating the global accumulation of placental glycogen. Furthermore, this work suggests that Phlda2 manipulates the placenta's demands for maternal resources, a process that must be tightly regulated by epigenetic marks to ensure optimal foetal growth.

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Phlda2 specifically restrains development of the spongiotrophoblast.

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The spongiotrophoblast is a major endocrine compartment of the placenta.

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The spongiotrophoblast locally and globally boosts glycogen accumulation.

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Excessive glycogen accumulation is associated with foetal growth restriction.

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Phlda2 regulates placental demands from maternal resources.

Partial Loss of Genomic Imprinting Reveals Important Roles for Kcnq1 and Peg10 Imprinted Domains in Placental Development

Mutations in imprinted genes or their imprint control regions (ICRs) produce changes in imprinted gene expression and distinct abnormalities in placental structure, indicating the importance of genomic imprinting to placental development. We have recently shown that a very broad spectrum of placental abnormalities associated with altered imprinted gene expression occurs in the absence of the oocyte-derived DNMT1o cytosine methyltransferase, which normally maintains parent-specific imprinted methylation during preimplantation. The absence of DNMT1o partially reduces inherited imprinted methylation while retaining the genetic integrity of imprinted genes and their ICRs. Using this novel system, we undertook a broad and inclusive approach to identifying key ICRs involved in placental development by correlating loss of imprinted DNA methylation with abnormal placental phenotypes in a mid-gestation window (E12.5-E15.5). To these ends we measured DNA CpG methylation at 15 imprinted gametic differentially methylated domains (gDMDs) that overlap known ICRs using EpiTYPER-mass array technology, and linked these epigenetic measurements to histomorphological defects. Methylation of some imprinted gDMDs, most notably Dlk1, was nearly normal in mid-gestation DNMT1o-deficient placentas, consistent with the notion that cells having lost methylation on these DMDs do not contribute significantly to placental development. Most imprinted gDMDs however showed a wide range of methylation loss among DNMT1o-deficient placentas. Two striking associations were observed. First, loss of DNA methylation at the Peg10 imprinted gDMD associated with decreased embryonic viability and decreased labyrinthine volume. Second, loss of methylation at the Kcnq1 imprinted gDMD was strongly associated with trophoblast giant cell (TGC) expansion. We conclude that the Peg10 and Kcnq1 ICRs are key regulators of mid-gestation placental function.

Epigenetic alterations in sperm associated with male infertility

The most common form of male infertility is a low sperm count, known as oligozoospermia. Studies suggest that oligozoospermia is associated with epigenetic alterations. Epigenetic alterations in sperm, which may arise due to the exposure of gametes to environmental factors or those that pre-exist in the sperm of infertile individuals, may contribute to the increased incidence of normally rare imprinting disorders in babies conceived after assisted reproductive technology using the sperm of infertile men. Genomic imprinting is an important developmental process whereby the allelic activity of certain genes is regulated by DNA methylation established during gametogenesis. The aberrant expression of several imprinted genes has been linked to various diseases, malignant tumors, lifestyle and mental disorders in humans. Understanding how infertility and environmental factors such as reproductive toxicants, certain foods, and drug exposures during gametogenesis contribute to the origins of these disorders via defects in sperm is of paramount importance. In this review, we discuss the association of epigenetic alterations with abnormal spermatogenesis and the evidence that epigenetic processes, including those required for genomic imprinting, may be sensitive to environmental exposures during gametogenesis, fertilization and early embryonic development. In addition, we review imprinting diseases and their relationships with environmental factors. While the plasticity of epigenetic marks may make these more susceptible to modification by the environment, this also suggests that aberrant epigenetic marks may be reversible. A greater understanding of this process and the function of epidrugs may lead to the development of new treatment methods for many adult diseases in the future.

Placental expression of imprinted genes varies with sampling site and mode of delivery

Imprinted genes, which are monoallelically expressed by virtue of an epigenetic process initiated in the germline, are known to play key roles in regulating fetal growth and placental development. Numerous studies are investigating the expression of these imprinted genes in the human placenta in relation to common complications of pregnancy such as fetal growth restriction and preeclampsia. This study aimed to determine whether placental sampling protocols or other factors such as fetal sex, gestational age and mode of delivery may influence the expression of imprinted genes predicted to regulate placental signalling.

METHODS

Term placentas were collected from Caucasian women delivering at University Hospital of Wales or Royal Gwent Hospital within two hours of delivery. Expression of the imprinted genes PHLDA2, CDKN1C, PEG3 and PEG10 was assayed by quantitative real time PCR. Intraplacental gene expression was analysed (N = 5). Placental gene expression was compared between male (N = 11) and female (N = 11) infants, early term (N = 8) and late term (N = 10) deliveries and between labouring (N = 13) and non-labouring (N = 21) participants.

RESULTS

The paternally expressed imprinted genes PEG3 and PEG10 were resilient to differences in sampling site, fetal sex, term gestational age and mode of delivery. The maternally expressed imprinted gene CDKN1C was elevated over 2-fold (p < 0.001) in placenta from labouring deliveries compared with elective caesarean sections. In addition, the maternally expressed imprinted gene PHLDA2 was elevated by 1.8 fold (p = 0.01) in samples taken at the distal edge of the placenta compared to the cord insertion site.

CONCLUSION

These findings support the reinterpretation of existing data sets on these genes in relation to complications of pregnancy and further reinforce the importance of optimising and unifying placental collection protocols for future studies.

Mutations in the PCNA-binding site of CDKN1C inhibit cell proliferation by impairing the entry into S phase

CDKN1C (also known as P57 (kip2) ) is a cyclin-dependent kinase inhibitor that functions as a negative regulator of cell proliferation through G1 phase cell cycle arrest. Recently, our group described gain-of-function mutations in the PCNA-binding site of CDKN1C that result in an undergrowth syndrome called IMAGe Syndrome (Intrauterine Growth Restriction, Metaphyseal dysplasia, Adrenal hypoplasia, and Genital anomalies), with life-threatening consequences. Loss-of-function mutations in CDKN1C have been identified in 5-10% of individuals with Beckwith-Wiedemann syndrome (BWS), an overgrowth disorder with features that are the opposite of IMAGe syndrome. Here, we investigate the effects of IMAGe-associated mutations on protein stability, cell cycle progression and cell proliferation. Mutations in the PCNA-binding site of CDKN1C significantly increase CDKN1C protein stability and prevent cell cycle progression into the S phase. Overexpression of either wild-type or BWS-mutant CDKN1C inhibited cell proliferation. However, the IMAGe-mutant CDKN1C protein decreased cell growth significantly more than both the wild-type or BWS protein. These findings bring new insights into the molecular events underlying IMAGe syndrome.

Dysregulation of methylation and expression of imprinted genes in oocytes and reproductive tissues in mice of advanced maternal age

PURPOSE

To evaluate reproductive outcomes in aged compared to young female mice, and determine associated methylation and expression of imprinted genes in reproductive tissues.

METHODS

Fetal, placental, and ovarian tissue were collected on d16.5 of pregnancy from young (4-5 weeks) and aged (15 months) mice. Uterine tissue and in vivo matured oocytes were collected from non-pregnant females. Methylation of imprinted genes was determined by restriction enzyme based assays, and transcript abundance of imprinted and nutrient supply genes were analyzed by quantitative PCR (qPCR).

RESULTS

Maternal age was associated with fetal growth restriction and placental overgrowth. In maternally aged mice, methylation was minimally dysregulated in fetal tissue, while placental tissue showed aberrant methylation and transcript abundance of imprinted genes. Ovarian methylation and gene expression was severely dysregulated, although oocyte gene expression was only minimally altered. Abundance of Kcnq1 transcripts was significantly (P < 0.05) increased in oocytes obtained from aged females compared to young females. Gene expression was also severely dysregulated in the uterus, including nutrient transport genes.

CONCLUSION

Fetal and placental growth abnormalities correspond to aberrant methylation and gene expression in reproductive tissues from maternally aged mice. Significant alterations in gene expression and methylation in the aged ovary suggests that the follicular environment may be compromised. Aberrant methylation and expression of imprinted genes in the aged uterus may contribute to reduced implantation. Maternal age negatively affects imprinted gene methylation and expression in both germ cells and somatic cells of the reproductive tract, contributing to the reduced fertility observed with advanced maternal age.

Genomic imprinting in development, growth, behavior and stem cells

Genes that are subject to genomic imprinting in mammals are preferentially expressed from a single parental allele. This imprinted expression of a small number of genes is crucial for normal development, as these genes often directly regulate fetal growth. Recent work has also demonstrated intricate roles for imprinted genes in the brain, with important consequences on behavior and neuronal function. Finally, new studies have revealed the importance of proper expression of specific imprinted genes in induced pluripotent stem cells and in adult stem cells. As we review here, these findings highlight the complex nature and developmental importance of imprinted genes.

Dosage-sensitivity of imprinted genes expressed in the brain: 15q11-q13 and neuropsychiatric illness

Imprinted genes, those genes subject to parent-of-origin-specific epigenetic marking resulting in monoallelic parent-specific expression, are sensitive to subtle changes in expression dosage. This has been illustrated in a number of experimental models and the fact that both decreased (or complete loss) and increased imprinted gene expression can lead to human diseases. In the present paper, we discuss the consequence of increased dosage of imprinted genes for brain function, focusing on the PWS (Prader-Willi syndrome) locus on human chromosome 15q11-q13 and how predicted increases in dosage of maternally expressed imprinted genes from this interval are associated with a higher risk of developing psychotic illness. The evidence for this comes from individuals with PWS itself and also non-syndromic cases of psychosis in carriers of a maternally derived copy number variant spanning this locus. Of the known imprinted genes in this region, the prime candidate is maternally expressed UBE3A, which encodes E6-AP (E6-associated protein) ubiquitin ligase and has an influence on a number of important neurotransmitter systems. Furthermore, these findings point to the fact that brain function is exquisitely sensitive to both decreases and increases in the expression of imprinted genes.