Stochastic loss of silencing of the imprinted Ndn/NDN allele, in a mouse model and humans with prader-willi syndrome, has functional consequences

Hormonal Imbalances in Prader-Willi and Schaaf-Yang Syndromes Imply the Evolution of Specific Regulation of Hypothalamic Neuroendocrine Function in Mammals

The hypothalamus regulates fundamental aspects of physiological homeostasis and behavior, including stress response, reproduction, growth, sleep, and feeding, several of which are affected in patients with Prader-Willi (PWS) and Schaaf-Yang syndrome (SYS). PWS is caused by paternal deletion, maternal uniparental disomy, or imprinting defects that lead to loss of expression of a maternally imprinted region of chromosome 15 encompassing non-coding RNAs and five protein-coding genes; SYS patients have a mutation in one of them, MAGEL2. Throughout life, PWS and SYS patients suffer from musculoskeletal deficiencies, intellectual disabilities, and hormonal abnormalities, which lead to compulsive behaviors like hyperphagia and temper outbursts. Management of PWS and SYS is mostly symptomatic and cures for these debilitating disorders do not exist, highlighting a clear, unmet medical need. Research over several decades into the molecular and cellular roles of PWS genes has uncovered that several impinge on the neuroendocrine system. In this review, we will discuss the expression and molecular functions of PWS genes, connecting them with hormonal imbalances in patients and animal models. Besides the observed hormonal imbalances, we will describe the recent findings about how the loss of individual genes, particularly MAGEL2, affects the molecular mechanisms of hormone secretion. These results suggest that MAGEL2 evolved as a mammalian-specific regulator of hypothalamic neuroendocrine function.

Magel2 truncation alters select behavioral and physiological outcomes in a rat model of Schaaf-Yang syndrome

Previous studies in mice have utilized Magel2 gene deletion models to examine the consequences of its absence. We report the generation, molecular validation and phenotypic characterization of a novel rat model with a truncating Magel2 mutation modeling variants associated with Schaaf-Yang syndrome-causing mutations. Within the hypothalamus, a brain region in which human MAGEL2 is paternally expressed, we demonstrated, at the level of transcript and peptide detection, that rat Magel2 exhibits a paternal, parent-of-origin effect. In evaluations of behavioral features across several domains, juvenile Magel2 mutant rats displayed alterations in anxiety-like behavior and sociability measures. Moreover, the analysis of peripheral organ systems detected alterations in body composition, cardiac structure and function, and breathing irregularities in Magel2 mutant rats. Several of these findings are concordant with reported mouse phenotypes, indicating the conservation of MAGEL2 function across rodent species. Our comprehensive analysis revealing impairments across multiple domains demonstrates the tractability of this model system for the study of truncating MAGEL2 mutations.

Recent Updates on Corticosteroid-Induced Neuropsychiatric Disorders and Theranostic Advancements through Gene Editing Tools

The vast use of corticosteroids (CCSs) globally has led to an increase in CCS-induced neuropsychiatric disorders (NPDs), a very common manifestation in patients after CCS consumption. These neuropsychiatric disorders range from depression, insomnia, and bipolar disorders to panic attacks, overt psychosis, and many other cognitive changes in such subjects. Though their therapeutic importance in treating and improving many clinical symptoms overrides the complications that arise after their consumption, still, there has been an alarming rise in NPD cases in recent years, and they are seen as the greatest public health challenge globally; therefore, these potential side effects cannot be ignored. It has also been observed that many of the neuronal functional activities are regulated and controlled by genomic variants with epigenetic factors (DNA methylation, non-coding RNA, and histone modeling, etc.), and any alterations in these regulatory mechanisms affect normal cerebral development and functioning. This study explores a general overview of emerging concerns of CCS-induced NPDs, the effective molecular biology approaches that can revitalize NPD therapy in an extremely specialized, reliable, and effective manner, and the possible gene-editing-based therapeutic strategies to either prevent or cure NPDs in the future.

MKRN3 circulating levels in Prader-Willi syndrome: a pilot study

CONTEXT

Hypogonadism in Prader-Willi syndrome (PWS) is generally attributed to hypothalamic dysfunction or to primary gonadal defect. MKRN3, a maternal imprinted gene located on 15q11.2-q13 region, encodes makorin ring finger protein 3, whose deficiency causes precocious puberty, an extremely rare symptom in PWS.

OBJECTIVE

This study aimed to evaluate MKRN3 levels in patients with PWS and to analyze its correlation with sexual hormone levels, insulin resistance and Body Mass Index (BMI).

METHODS

We performed an observational cross-sectional study and enrolled 80 patients with genetically confirmed diagnosis of PWS with median age of 9.6 years.

RESULTS

MKRN3 levels were measurable in 49 PWS patients with a geometric mean of 34.9 ± 22 pg/ml (median: 28.4). Unmeasurable levels of MKRN3 were found in 31 patients. No statistically significant differences were found between patients with and without measurable MKRN3 levels for any clinical, biochemical, or genetic characteristics. However, MKRN3 levels were inversely correlated with HOMA-IR index (p: 0.005) and HbA1c (p: 0.046) values. No statistically significant correlations were found between MKRN3 and LH, estradiol and testosterone concentrations, pubertal development and genetic defect, whereas a direct correlation with FSH was found (p: 0.007).

CONCLUSIONS

The typical genetic defect of PWS should lead to unmeasurable levels of the MKRN3 protein due to the inactivation of the paternal allele. Measurable circulating MKRN3 could suggest the possible involvement of tissue-specific imprinting mechanisms and other regulatory factors in gene expression. Correlations with HOMA-IR index, HbA1c, and FSH suggest peripheral actions of MKRN3, but future studies are warranted to investigate this topic.

Oxytocin-based therapies for treatment of Prader-Willi and Schaaf-Yang syndromes: evidence, disappointments, and future research strategies

The prosocial neuropeptide oxytocin is being developed as a potential treatment for various neuropsychiatric disorders including autism spectrum disorder (ASD). Early studies using intranasal oxytocin in patients with ASD yielded encouraging results and for some time, scientists and affected families placed high hopes on the use of intranasal oxytocin for behavioral therapy in ASD. However, a recent Phase III trial obtained negative results using intranasal oxytocin for the treatment of behavioral symptoms in children with ASD. Given the frequently observed autism-like behavioral phenotypes in Prader-Willi and Schaaf-Yang syndromes, it is unclear whether oxytocin treatment represents a viable option to treat behavioral symptoms in these diseases. Here we review the latest findings on intranasal OT treatment, Prader-Willi and Schaaf-Yang syndromes, and propose novel research strategies for tailored oxytocin-based therapies for affected individuals. Finally, we propose the critical period theory, which could explain why oxytocin-based treatment seems to be most efficient in infants, but not adolescents.

Necdin: A purposive integrator of molecular interaction networks for mammalian neuron vitality

Necdin was originally found in 1991 as a hypothetical protein encoded by a neural differentiation‐specific gene transcript in murine embryonal carcinoma cells. Virtually all postmitotic neurons and their precursor cells express the necdin gene (Ndn) during neuronal development. Necdin mRNA is expressed only from the paternal allele through genomic imprinting, a placental mammal‐specific epigenetic mechanism. Necdin and its homologous MAGE (melanoma antigen) family, which have evolved presumedly from a subcomplex component of the SMC5/6 complex, are expressed exclusively in placental mammals. Paternal Ndn‐mutated mice totally lack necdin expression and exhibit various types of neuronal abnormalities throughout the nervous system. Ndn‐null neurons are vulnerable to detrimental stresses such as DNA damage. Necdin also suppresses both proliferation and apoptosis of neural stem/progenitor cells. Functional analyses using Ndn‐manipulated cells reveal that necdin consistently exerts antimitotic, anti‐apoptotic and prosurvival effects. Necdin interacts directly with a number of regulatory proteins including E2F1, p53, neurotrophin receptors, Sirt1 and PGC‐1α, which serve as major hubs of protein–protein interaction networks for mitosis, apoptosis, differentiation, neuroprotection and energy homeostasis. This review focuses on necdin as a pleiotropic protein that integrates molecular interaction networks to promote neuronal vitality in modern placental mammals.

The Diagnostic Journey of a Patient with Prader-Willi-Like Syndrome and a Unique Homozygous SNURF-SNRPN Variant; Bio-Molecular Analysis and Review of the Literature

Prader–Willi syndrome (PWS) is a rare genetic condition characterized by hypotonia, intellectual disability, and hypothalamic dysfunction, causing pituitary hormone deficiencies and hyperphagia, ultimately leading to obesity. PWS is most often caused by the loss of expression of a cluster of genes on chromosome 15q11.2-13. Patients with Prader–Willi-like syndrome (PWLS) display features of the PWS phenotype without a classical PWS genetic defect. We describe a 46-year-old patient with PWLS, including hypotonia, intellectual disability, hyperphagia, and pituitary hormone deficiencies. Routine genetic tests for PWS were normal, but a homozygous missense variant NM_003097.3(SNRPN):c.193C>T, p.(Arg65Trp) was identified. Single nucleotide polymorphism array showed several large regions of homozygosity, caused by high-grade consanguinity between the parents. Our functional analysis, the ‘Pipeline for Rapid in silico, in vivo, in vitro Screening of Mutations’ (PRiSM) screen, showed that overexpression of SNRPN-p.Arg65Trp had a dominant negative effect, strongly suggesting pathogenicity. However, it could not be confirmed that the variant was responsible for the phenotype of the patient. In conclusion, we present a unique homozygous missense variant in SNURF-SNRPN in a patient with PWLS. We describe the diagnostic trajectory of this patient and the possible contributors to her phenotype in light of the current literature on the genotype–phenotype relationship in PWS.

A Comprehensive Review of Genetically Engineered Mouse Models for Prader-Willi Syndrome Research

Prader-Willi syndrome (PWS) is a neurogenetic multifactorial disorder caused by the deletion or inactivation of paternally imprinted genes on human chromosome 15q11-q13. The affected homologous locus is on mouse chromosome 7C. The positional conservation and organization of genes including the imprinting pattern between mice and men implies similar physiological functions of this locus. Therefore, considerable efforts to recreate the pathogenesis of PWS have been accomplished in mouse models. We provide a summary of different mouse models that were generated for the analysis of PWS and discuss their impact on our current understanding of corresponding genes, their putative functions and the pathogenesis of PWS. Murine models of PWS unveiled the contribution of each affected gene to this multi-facetted disease, and also enabled the establishment of the minimal critical genomic region (PWScr) responsible for core symptoms, highlighting the importance of non-protein coding genes in the PWS locus. Although the underlying disease-causing mechanisms of PWS remain widely unresolved and existing mouse models do not fully capture the entire spectrum of the human PWS disorder, continuous improvements of genetically engineered mouse models have proven to be very powerful and valuable tools in PWS research.

Hypogonadism in Patients with Prader Willi Syndrome: A Narrative Review

Prader-Willi syndrome (PWS) is a multisystemic complex genetic disorder related to the lack of a functional paternal copy of chromosome 15q11-q13. Several clinical manifestations are reported, such as short stature, cognitive and behavioral disability, temperature instability, hypotonia, hypersomnia, hyperphagia, and multiple endocrine abnormalities, including growth hormone deficiency and hypogonadism. The hypogonadism in PWS is due to central and peripheral mechanisms involving the hypothalamus-pituitary-gonadal axis. The early diagnosis and management of hypogonadism in PWS are both important for physicians in order to reach a better quality of life for these patients. The aim of this study is to summarize and investigate causes and possible therapies for hypogonadism in PWS. Additional studies are further needed to clarify the role of different genes related to hypogonadism and to establish a common and evidence-based therapy.

Complex Economic Behavior Patterns Are Constructed from Finite, Genetically Controlled Modules of Behavior

Complex ethological behaviors could be constructed from finite modules that are reproducible functional units of behavior. Here, we test this idea for foraging and develop methods to dissect rich behavior patterns in mice. We uncover discrete modules of foraging behavior reproducible across different strains and ages, as well as nonmodular behavioral sequences. Modules differ in terms of form, expression frequency, and expression timing and are expressed in a probabilistically determined order. Modules shape economic patterns of feeding, exposure, activity, and perseveration responses. The modular architecture of foraging changes developmentally, and different developmental, genetic, and parental effects are found to shape the expression of specific modules. Dissecting modules from complex patterns is powerful for phenotype analysis. We discover that both parental alleles of the imprinted Prader-Willi syndrome gene Magel2 are functional in mice but regulate different modules. Our study found that complex economic patterns are built from finite, genetically controlled modules.

The principles and mechanisms involved in constructing complex behavior patterns are not well defined. Stacher Hörndli et al. find that complex foraging patterns in mice are constructed from finite modules, defined as significantly reproducible behavioral sequences. Modules are expressed in a probabilistically defined order to construct complex patterns and controlled by genetic mechanisms.

P2X3 receptor antagonism reduces the occurrence of apnoeas in newborn rats

Hyperreflexia of the peripheral chemoreceptors is a potential contributor of apnoeas of prematurity (AoP). Recently, it was shown that elevated P2X3 receptor expression was associated with elevated carotid body afferent sensitivity. Therefore, we tested whether P2X3 receptor antagonism would reduce AoP known to occur in newborn rats. Unrestrained whole-body plethysmography was used to record breathing and from this the frequency of apnoeas at baseline and following administration of either a P2X3 receptor antagonist - AF-454 (5 mg/kg or 10 mg/kg s.c.) or vehicle was derived. In a separate group, we tested the effects of AF-454 (10 mg/kg) on the hypoxic ventilatory response (10 % FiO2). Ten but not 5 mg/kg AF-454 reduced the frequency of AoP and improved breathing regularity significantly compared to vehicle. Neither AF-454 (both 5 and 10 mg/kg) nor vehicle affected baseline respiration. However, P2X3 receptor antagonism (10 mg/kg) powerfully blunted hypoxic ventilatory response to 10 % FiO2. These data suggest that P2X3 receptors contribute to AoP and the hypoxic ventilatory response in newborn rats but play no role in the drive to breathe at rest.

A zebrafish model of nondystrophic myotonia with sodium channelopathy

Nondystrophic myotonias are disorders of Na⁺ (Na_v1.4 or SCN4A) and Cl^- (CLCN1) channels in skeletal muscles, and frequently show phenotype heterogeneity. The molecular mechanism underlying their pathophysiology and phenotype heterogeneity remains unclear. As zebrafish models have been recently exploited for studies of the pathophysiology and phenotype heterogeneity of various human genetic diseases, a zebrafish model may be useful for delineating nondystrophic myotonias. Here, we generated transgenic zebrafish expressing a human mutant allele of SCN4A, referred to as Tg(mylpfa:N440K), and needle electromyography revealed increased number of myotonic discharges and positive sharp waves in the muscles of Tg(mylpfa:N440K) than in controls. In addition, forced exercise test at a water temperature of 24 °C showed a decrease in the distance moved, time spent in and number of visits to the zone with stronger swimming resistance. Finally, a forced exercise test at a water temperature of 18 °C exhibited a higher number of dive-bombing periods and drifting-down behavior than in controls. These findings indicate that Tg(mylpfa:N440K) is a good vertebrate model of exercise- and cold-induced human nondystrophic myotonias. This zebrafish model may contribute to provide insight into the pathophysiology of myotonia in sodium channelopathy and could be used to explore a new therapeutic avenue.

Screening for rare epigenetic variations in autism and schizophrenia

While many studies have led to the identification of rare sequence variants linked with susceptibility to autism and schizophrenia, the contribution of rare epigenetic variations (epivariations) in these disorders remains largely unexplored. Previously we presented evidence that epivariations occur relatively frequently in the human genome, and likely contribute to a subset of congenital and neurodevelopmental disorders through the disruption of dosage-sensitive genes. Here we extend this approach, studying methylation profiles from 297 samples with autism and 767 cases with schizophrenia, identifying 84 and 268 rare epivariations in these two cohorts, respectively, that were absent from 4,860 population controls. We observed multiple features associated with these epivariations that support their pathogenic relevance, including (a) a significant enrichment for epivariations in schizophrenic individuals at genes previously linked with schizophrenia, (b) increased brain expression of genes associated with epivariations found in autism cases compared with controls, (c) in autism families, a significant excess of epivariations found specifically in affected versus unaffected sibs, (d) Gene Ontology terms linked with epivariations found in autism, including "D1 dopamine receptor binding." Our study provides additional evidence that rare epivariations likely contribute to the mutational spectra underlying neurodevelopmental disorders.

Preclinical Testing in Translational Animal Models of Prader-Willi Syndrome: Overview and Gap Analysis

Prader-Willi syndrome (PWS) is a rare neurodevelopmental disorder causing endocrine, musculoskeletal, and neurological dysfunction. PWS is caused by the inactivation of contiguous genes, complicating the development of targeted therapeutics. Clinical trials are now underway in PWS, with more trials to be implemented in the next few years. PWS-like endophenotypes are recapitulated in gene-targeted mice in which the function of one or more PWS genes is disrupted. These animal models can guide priorities for clinical trials or provide information about efficacy of a compound within the context of the specific disease. We now review the current status of preclinical studies that measure the effect of therapeutics on PWS-like endophenotypes. Seven categories of therapeutics (oxytocin and related compounds, K⁺-ATP channel agonists, melanocortin 4 receptor agonists, incretin mimetics and/or GLP-1 receptor agonists, cannabinoids, ghrelin agents, and Caralluma fimbriata [cactus] extract) have been tested for their effect on endophenotypes in both PWS animal models and clinical trials. Many other therapeutics have been tested in clinical trials, but not preclinical models of PWS or vice versa. Fostering dialogs among investigators performing preclinical validation of animal models and those implementing clinical studies will accelerate the discovery and translation of therapies into clinical practice in PWS.

Transgenic mice with a tandem duplication of the Necdin gene overexpress Necdin

Necdin (Ndn) transgenic (Tg) mice were generated with a bacterial artificial chromosome (BAC) clone. Droplet digital PCR (ddPCR) and inverse PCR methods revealed that the transgene consisted of four fragments with a total length of 171 kb. Two of these fragments were tandem tail-to-tail duplicates of 77 kb and 37 kb that both contained a Ndn gene. The transgene was inserted in chromosome 15qD1. Ndn is a paternally expressed imprinted gene; however, the total expression level of Ndn in hemizygous Tg mice was approximately twofold higher than that in wild-type mice. ddPCR assays with locked nucleic acid (LNA) TaqMan probes revealed that transgenic Ndn expression was almost equal to endogenous Ndn expression, despite there being two copies of the Ndn gene in the transgene, indicating an interaction between the transcriptional regulation of endogenous Ndn and the transgene. ddPCR assays with LNA TaqMan probes were also applied for imprinting analysis to confirm exclusive paternal expression in tissues with low Ndn expression. This is the first report of a Tg mouse with a tandem duplication of a Ndn transgene and Ndn overexpression, which will be useful for the in vivo study of Ndn overexpression and for rescue experiments of the neonatal lethality seen in the Ndn knockout mouse.

Application of droplet digital PCR in the analysis of genome integration and organization of the transgene in BAC transgenic mice

Transgenic (Tg) mice containing bacterial artificial chromosome (BAC) DNA are widely used for gene expression analysis and gene therapy models because BAC transgenes provide gene expression at physiological levels with the same developmental timing as endogenous genes. To ensure correct interpretation of transgene functions, investigation of the genomic organisation and integration of the BAC transgene is required. Here, we describe a reliable method based on droplet digital PCR (ddPCR) and inverse PCR to estimate copy number, genomic organisation and insertion sites of BAC transgenes in the mouse genome. We generated BAC Tg mice containing fragments of BAC clone RP23-59P20. ddPCR and iPCR analysis showed that the transgene consisted of five fragments of the BAC clone containing the Mkrn3 gene region, and that the transgene was inserted into Bckdhb, homozygous deletion of which causes the maple syrup urine disease phenotype. The ddPCR method described here should prove useful for analysis of genomic organisation and integration of BAC transgenes.

Early-onset epileptic encephalopathy and severe developmental delay in an association with de novo double mutations in NF1 and MAGEL2

Advance in the exome-wide sequencing analysis contributes to identifying hundreds of genes that are associated with early-onset epileptic encephalopathy and neurodevelopmental disorders. On the basis of massive sequencing data, functional interactions among different genes are suggested to explain the common molecular pathway underlying the pathogenic process of these disorders. However, the relevance of such interactions with the phenotypic severity or variety in an affected individual remains elusive. In this report, we present a 45-year-old woman with neurofibromatosis type 1 (NF1), infantile-onset epileptic encephalopathy, and severe developmental delay. Whole-exome sequencing identified de novo pathogenic mutations in NF1 and the Schaaf-Yang syndrome-associated gene, MAGEL2. Literature-curated interaction data predicted that NF1 and MAGEL2 proteins were closely connected in this network via their common interacting proteins. Direct conversion of fibroblasts into neurons in vitro showed that neuronal cells from 9 patients with NF1 expressed significantly lower levels of MAGEL2 (54%, p = 0.0047) than those from healthy individuals. These data provide the first evidence that pathogenic mutations of NF1 deregulate the expression of other neurodevelopmental disease-associated genes. De novo mutations in multiple genes may lead to severe developmental phenotypes through their cumulative effects or synergistic interactions.

The Prader-Willi syndrome proteins MAGEL2 and necdin regulate leptin receptor cell surface abundance through ubiquitination pathways

In Prader-Willi syndrome (PWS), obesity is caused by the disruption of appetite-controlling pathways in the brain. Two PWS candidate genes encode MAGEL2 and necdin, related melanoma antigen proteins that assemble into ubiquitination complexes. Mice lacking Magel2 are obese and lack leptin sensitivity in hypothalamic pro-opiomelanocortin neurons, suggesting dysregulation of leptin receptor (LepR) activity. Hypothalamus from Magel2-null mice had less LepR and altered levels of ubiquitin pathway proteins that regulate LepR processing (Rnf41, Usp8, and Stam1). MAGEL2 increased the cell surface abundance of LepR and decreased their degradation. LepR interacts with necdin, which interacts with MAGEL2, which complexes with RNF41 and USP8. Mutations in the MAGE homology domain of MAGEL2 suppress RNF41 stabilization and prevent the MAGEL2-mediated increase of cell surface LepR. Thus, MAGEL2 and necdin together control LepR sorting and degradation through a dynamic ubiquitin-dependent pathway. Loss of MAGEL2 and necdin may uncouple LepR from ubiquitination pathways, providing a cellular mechanism for obesity in PWS.

Necdin shapes serotonergic development and SERT activity modulating breathing in a mouse model for Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a genetic neurodevelopmental disorder that presents with hypotonia and respiratory distress in neonates. The Necdin-deficient mouse is the only model that reproduces the respiratory phenotype of PWS (central apnea and blunted response to respiratory challenges). Here, we report that Necdin deletion disturbs the migration of serotonin (5-HT) neuronal precursors, leading to altered global serotonergic neuroarchitecture and increased spontaneous firing of 5-HT neurons. We show an increased expression and activity of 5-HT Transporter (SERT/Slc6a4) in 5-HT neurons leading to an increase of 5-HT uptake. In Necdin-KO pups, the genetic deletion of Slc6a4 or treatment with Fluoxetine, a 5-HT reuptake inhibitor, restored normal breathing. Unexpectedly, Fluoxetine administration was associated with respiratory side effects in wild-type animals. Overall, our results demonstrate that an increase of SERT activity is sufficient to cause the apneas in Necdin-KO pups, and that fluoxetine may offer therapeutic benefits to PWS patients with respiratory complications.

Prader-Willi syndrome results from the disruption of a cluster of neighboring genes, including one called Necdin. Symptoms begin in early infancy and worsen with age. Affected children tend to develop an insatiable appetite, which often leads to obesity. They also experience serious problems with their breathing. Chest infections, high altitude and intense physical activity can be dangerous for children with Prader-Willi syndrome. This is because a slight shortage of oxygen may trigger breathing difficulties that could prove fatal.

The brain cells that produce a chemical messenger called serotonin help to control breathing. Several lines of evidence suggest that loss of Necdin may trigger breathing difficulties in Prader-Willi syndrome via effects on the serotonin system. First, serotonin neurons produce the Necdin protein. Second, laboratory mice that lack the gene for Necdin have abnormally shaped serotonin neurons. Third, these mice show breathing difficulties like those of individuals with Prader-Willi syndrome. But while this implies a connection between serotonin, Necdin and breathing difficulties, it falls short of establishing a causal link.

Matarazzo et al. now reveal an increase in the quantity and activity of a protein called the serotonin transporter in mutant mice that lacked the gene for Necdin compared to normal mice. Serotonin transporter proteins mop up the serotonin that neurons release when they signal to one another. Neurons in the mutant mice take up more serotonin than their counterparts in normal mice; this means they have less serotonin available for signaling. This may make it harder for the mutant mice to regulate their breathing.

Drugs called selective serotonin-reuptake inhibitors (or SSRIs for short) can block the serotonin transporter. These drugs, which include Fluoxetine (also called Prozac), are antidepressants. Matarazzo et al. show that SSRIs temporarily restore normal breathing in young mice that lack the gene for Necdin. However, these drugs have harmful long-term effects on breathing in non-mutant mice. Further studies should test whether short-term use of SSRIs could offer immediate relief for breathing difficulties in infants and children with Prader-Willi syndrome.

Cellular and disease functions of the Prader-Willi Syndrome gene MAGEL2

Melanoma antigen L2 (MAGEL2 or MAGE-L2) is a member of the MAGE family of ubiquitin ligase regulators. It is maternally imprinted and often paternally deleted or mutated in the related neurodevelopmental syndromes, Prader-Willi Syndrome (PWS) and Schaaf-Yang Syndrome (SHFYNG). MAGEL2 is highly expressed in the hypothalamus and plays an important role in a fundamental cellular process that recycles membrane proteins from endosomes through the retromer sorting pathway. MAGEL2 is part of a multi-subunit protein complex consisting of MAGEL2, the TRIM27 E3 ubiquitin ligase, and the USP7 deubiquitinating enzyme. The MAGEL2-USP7-TRIM27 (or MUST) complex facilitates the retromer recycling pathway through ubiquitination and activation of the WASH actin nucleation promoting factor. This review provides an overview of the MAGE protein family of ubiquitin ligases regulators and details the molecular and cellular role of MAGEL2 in ubiquitination, actin regulation and endosomal sorting processes, as well as MAGEL2 implications in PWS and SHFYNG disorders. The physiological functions of MAGEL2, elucidated through the study of Magel2 knockout mouse models, are also discussed.

DNA methylation differences between in vitro- and in vivo-conceived children are associated with ART procedures rather than infertility

Background

We, and others, have demonstrated previously that there are differences in DNA methylation and transcript levels of a number of genes in cord blood and placenta between children conceived using assisted reproductive technologies (ART) and children conceived in vivo. The source of these differences (the effect of ART versus the underlying infertility) has never been determined in humans. In this study, we have attempted to resolve this issue by comparing placental DNA methylation levels at 37 CpG sites in 16 previously identified candidate genes in independent populations of children conceived in vivo (‘fertile control’ group) with ART children conceived from two groups: either autologous oocytes with infertility in one or both parents (‘infertile ART’ group) or donor oocytes (obtained from young fertile donors) without male infertility (‘donor oocyte ART’ group).

Results

Of the 37 CpG sites analyzed, significant differences between the three groups were found in 11 CpGs (29.73 %), using ANOVA. Tukey’s post hoc test on the significant results indicated that seven (63.63 %) of these differences were significant between the donor oocyte ART and fertile control groups. In addition, 20 of the 37 CpGs analyzed had been identified as differentially methylated between ART and fertile control groups in an independent population in a prior study. Of these 20 CpG sites, 9 also showed significant differences in the present population. An additional 9 CpGs were found to be significantly different between the two groups. Of these 18 candidate CpGs, 12 CpGs (in seven candidate genes) also showed significant differences in placental DNA methylation levels between the donor oocyte ART and fertile control groups.

Conclusions

These data suggest strongly that the DNA methylation differences observed between ART and in vivo conceptions are associated with some aspect of ART protocols, not simply the underlying infertility.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-015-0071-7) contains supplementary material, which is available to authorized users.

Environmental epigenetic inheritance through gametes and implications for human reproduction

BACKGROUND

Traditional studies focused on DNA as the heritable information carrier that passes the phenotype from parents to offspring. However, increasing evidence suggests that information, that is independent of the DNA sequence, termed epigenetic information, can be inherited between generations. Recently, in our lab, we found that prediabetes in fathers increases the susceptibility to diabetes in offspring through gametic cytosine methylation changes. Paternal prediabetes changed overall methylation patterns in sperm, and a large portion of differentially methylated loci can be transmitted to pancreatic islets of offspring up to the second generation. In this review, we survey the extensive examples of environmentally induced epigenetic inheritance in various species, ranging from Caenorhabditis elegans to humans. We focus mainly on elucidating the molecular basis of environmental epigenetic inheritance through gametes, which is an emerging theme and has important implications for explaining the prevalence of obesity, type 2 diabetes and other chronic non-genetic diseases, which is also important for understanding the influence of environmental exposures on reproductive and overall health in offspring.

METHODS

For this review, we included relevant data and information obtained through a PubMed database search for all English language articles published up to August 2014 which included the term 'environmental epigenetic inheritance' and 'transgenerational epigenetic inheritance'. We focused on research papers using animal models including Drosophila, C. elegans, mouse and rat. Human data were also included.

RESULTS

Evidence from animal models suggests that environmental epigenetic inheritance through gametes exists in various species. Extensive molecular evidence suggests that epigenetic information carriers including DNA methylation, non-coding RNAs and chromatin proteins in gametes play important roles in the transmission of phenotypes from parents to offspring.

CONCLUSIONS

Given the large number of experimental evidence from various organisms, it is clear that parental environmental alterations can affect the phenotypes of offspring through gametic epigenetic alterations. This more recent thinking based on new data may have implications in explaining the prevalence of obesity, type 2 diabetes and other chronic non-genetic diseases. This also implies that, in the near future, epigenetic factors which are heritable should be regarded important in determining the risk of certain diseases. Moreover, identification of epigenetic markers in gametes (polar body or sperm) may hold great promise for predicting susceptibility to and preventing certain non-genetic diseases in offspring, as well as providing indications on parental environmental exposures.

Imprinting analysis of the mouse chromosome 7C region in DNMT1-null embryos

The mouse chromosome 7C, orthologous to the human 15q11-q13 has an imprinted domain, where most of the genes are expressed only from the paternal allele. The imprinted domain contains paternally expressed genes, Snurf/Snrpn, Ndn, Magel2, Mkrn3, and Frat3, C/D-box small nucleolar RNAs (snoRNAs), and the maternally expressed gene, Ube3a. Imprinted expression in this large (approximately 3-4 Mb) domain is coordinated by a bipartite cis-acting imprinting center (IC), located upstream of the Snurf/Snrpn gene. The molecular mechanism how IC regulates gene expression of the whole domain remains partially understood. Here we analyzed the relationship between imprinted gene expression and DNA methylation in the mouse chromosome 7C using DNA methyltransferase 1 (DNMT1)-null mutant embryos carrying Dnmt1(ps) alleles, which show global loss of DNA methylation and embryonic lethality. In the DNMT1-null embryos at embryonic day 9.5, the paternally expressed genes were biallelically expressed. Bisulfite DNA methylation analysis revealed loss of methylation on the maternal allele in the promoter regions of the genes. These results demonstrate that DNMT1 is necessary for monoallelic expression of the imprinted genes in the chromosome 7C domain, suggesting that DNA methylation in the secondary differentially methylated regions (DMRs), which are acquired during development serves primarily to control the imprinted expression from the maternal allele in the mouse chromosome 7C.

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.

Reactivation of maternal SNORD116 cluster via SETDB1 knockdown in Prader-Willi syndrome iPSCs

Prader-Willi syndrome (PWS), a disorder of genomic imprinting, is characterized by neonatal hypotonia, hypogonadism, small hands and feet, hyperphagia and obesity in adulthood. PWS results from the loss of paternal copies of the cluster of SNORD116 C/D box snoRNAs and their host transcript, 116HG, on human chromosome 15q11-q13. We have investigated the mechanism of repression of the maternal SNORD116 cluster and 116HG. Here, we report that the zinc-finger protein ZNF274, in association with the histone H3 lysine 9 (H3K9) methyltransferase SETDB1, is part of a complex that binds to the silent maternal but not the active paternal alleles. Knockdown of SETDB1 in PWS-specific induced pluripotent cells (iPSCs) causes a decrease in the accumulation of H3K9 trimethylation (H3K9me3) at 116HG and corresponding accumulation of the active chromatin mark histone H3 lysine 4 dimethylation (H3K4me2). We also show that upon knockdown of SETDB1 in PWS-specific iPSCs, expression of maternally silenced 116HG RNA is partially restored. SETDB1 knockdown in PWS iPSCs also disrupts DNA methylation at the PWS-IC where a decrease in 5-methylcytosine is observed in association with a concomitant increase in 5-hydroxymethylcytosine. This observation suggests that the ZNF274/SETDB1 complex bound to the SNORD116 cluster may protect the PWS-IC from DNA demethylation during early development. Our findings reveal novel epigenetic mechanisms that function to repress the maternal 15q11-q13 region.

Imprinting genes associated with endometriosis

PURPOSE

Much work has been carried out to investigate the genetic and epigenetic basis of endometriosis and proposed that endometriosis has been described as an epigenetic disease. The purpose of this study was to extract the imprinting genes that are associated with endometriosis development.

METHODS

The information on the imprinting genes can be accessed publicly from a web-based interface at http://www.geneimprint.com/site/genes-by-species.

RESULTS

In the current version, the database contains 150 human imprinted genes derived from the literature. We searched gene functions and their roles in particular biological processes or events, such as development and pathogenesis of endometriosis. From the genomic imprinting database, we picked 10 genes that were highly associated with female reproduction; prominent among them were paternally expressed genes (DIRAS3, BMP8B, CYP1B1, ZFAT, IGF2, MIMT1, or MIR296) and maternally expressed genes (DVL1, FGFRL1, or CDKN1C). These imprinted genes may be associated with reproductive biology such as endometriosis, pregnancy loss, decidualization process and preeclampsia.

DISCUSSION

This study supports the possibility that aberrant epigenetic dysregulation of specific imprinting genes may contribute to endometriosis predisposition.

Natural breaking of the maternal silence at the mouse and human imprinted Prader-Willi locus: A whisper with functional consequences

Genomic imprinting is a normal process of epigenetic regulation leading some autosomal genes to be expressed from one parental allele only, the other parental allele being silenced. The reasons why this mechanism has been selected throughout evolution are not clear; however, expression dosage is critical for imprinted genes. There is a paradox between the fact that genomic imprinting is a robust mechanism controlling the expression of specific genes and the fact that this mechanism is based on epigenetic regulation that, per se, should present some flexibility. The robustness has been well studied, revealing the epigenetic modifications at the imprinted locus, but the flexibility has been poorly investigated.

 

Prader-Willi syndrome is the best-studied disease involving imprinted genes caused by the absence of expression of paternally inherited alleles of genes located in the human 15q11-q13 region. Until now, the silencing of the maternally inherited alleles was like a dogma. Rieusset et al. showed that in absence of the paternal Ndn allele, in Ndn +m/-p mice, the maternal Ndn allele is expressed at an extremely low level with a high degree of non-genetic heterogeneity. In about 50% of these mutant mice, this stochastic expression reduces birth lethality and severity of the breathing deficiency, correlated with a reduction in the loss of serotonergic neurons. Furthermore, using several mouse models, they reveal a competition between non-imprinted Ndn promoters, which results in monoallelic (paternal or maternal) Ndn expression, suggesting that Ndn monoallelic expression occurs in the absence of imprinting regulation. Importantly, specific expression of the maternal NDN allele is also detected in post-mortem brain samples of PWS individuals. Here, similar expression of the Magel2 maternal allele is reported in Magel2 +m/-p mice, suggesting that this loss of imprinting can be extended to other PWS genes. These data reveal an unexpected epigenetic flexibility of PWS imprinted genes that could be exploited to reactivate the functional but dormant maternal alleles in PWS.