The product of the imprinted gene IPL marks human villous cytotrophoblast and is lost in complete hydatidiform mole

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.

Reproductive Immunology and Pregnancy 3.0

This Special Issue, the third dedicated to reproductive immunology and pregnancy, is another review of the latest trends in research topics in this field [...].

Diagnostic Utility of TSSC3 and RB1 Immunohistochemistry in Hydatidiform Mole

The general notion of complete hydatidiform moles is that most of them consist entirely of paternal DNA; hence, they do not express p57, a paternally imprinted gene. This forms the basis for the diagnosis of hydatidiform moles. There are about 38 paternally imprinted genes. The aim of this study is to determine whether other paternally imprinted genes could also assist in the diagnostic approach of hydatidiform moles. This study comprised of 29 complete moles, 15 partial moles and 17 non-molar abortuses. Immunohistochemical study using the antibodies of paternal-imprinted (RB1, TSSC3 and DOG1) and maternal-imprinted (DNMT1 and GATA3) genes were performed. The antibodies' immunoreactivity was evaluated on various placental cell types, namely cytotrophoblasts, syncytiotrophoblasts, villous stromal cells, extravillous intermediate trophoblasts and decidual cells. TSSC3 and RB1 expression were observed in all cases of partial moles and non-molar abortuses. In contrast, their expression in complete moles was identified in 31% (TSSC3) and 10.3% (RB1), respectively (p < 0.0001). DOG1 was consistently negative in all cell types in all cases. The expressions of maternally imprinted genes were seen in all cases, except for one case of complete mole where GATA3 was negative. Both TSSC3 and RB1 could serve as a useful adjunct to p57 for the discrimination of complete moles from partial moles and non-molar abortuses, especially in laboratories that lack comprehensive molecular service and in cases where p57 staining is equivocal.

Auxiliary and experimental diagnostic techniques for hydatidiform moles

Hydatidiform moles are classified into complete hydatidiform moles (CHMs), which are androgenetic and diploid, and partial hydatidiform moles (PHM), which are triploid with two paternal chromosomes and one maternal chromosome. The incidence of gestational trophoblastic neoplasia differs substantially between CHM and PHM. However, they are occasionally difficult to diagnose. In this review, auxiliary and experimental methods based on cytogenetic features and advanced molecular detection techniques applied to the diagnosis and analysis of hydatidiform moles are summarized, including basic principles, characteristics, and clinical implications. Short tandem repeat polymorphism analysis is considered the gold standard for the genetic diagnosis of hydatidiform moles. In clinical settings, immunohistochemical analyses of p57^KIP2 , an imprinted gene product, are widely used to differentiate CHMs from other conceptuses, including PHMs. Recently, new molecular genetic techniques, such as single nucleotide polymorphism arrays, have been applied to research on hydatidiform moles. In addition to insights from classical methods, such as chromosome analysis, recently developed approaches have yielded novel findings related to the mechanism underlying the development of androgenetic CHMs.

Challenges in diagnosing hydatidiform moles: a review of promising molecular biomarkers

INTRODUCTION

Hydatidiform moles (HMs) are pathologic conceptions with unique genetic bases and abnormal placental villous tissue. Overlapping ultrasonographical and histological manifestations of molar and non-molar (NM) gestations and HMs subtypes makes accurate diagnosis challenging. Currently, immunohistochemical analysis of p57 and molecular genotyping have greatly improved the diagnostic accuracy.

AREAS COVERED

The differential expression of molecular biomarkers may be valuable for distinguishing among the subtypes of HMs and their mimics. Thus, biomarkers may be the key to refining HMs diagnosis. In this review, we summarize the current challenges in diagnosing HMs, and provide a critical overview of the recent literature about potential diagnostic biomarkers and their subclassifications. An online search on PubMed, Web of Science, and Google Scholar databases was conducted from the inception to 1 April 2022.

EXPERT OPINION

the emerging biomarkers offer new possibilities to refine the diagnosis for HMs and pregnancy loss. Although the additional studies are required to be quantified and investigated in clinical trials to verify their diagnostic utility. It is important to explore, validate, and facilitate the wide adoption of newly developed biomarkers in the coming years.

RhoGDI1 interacts with PHLDA2, suppresses the proliferation, migration, and invasion of trophoblast cells, and participates in the pathogenesis of preeclampsia

Preeclampsia (PE) is a pregnancy-associated disease, which is the major cause of mortality on maternity and perinatal infants. It is hypothesized that PE is a consequence of the dysfunction of the trophoblast cells. Pleckstrin homology-like domain, family A, member 2 (PHLDA2) was shown to inhibit the proliferation, migration, and invasion of trophoblast cells in our previous studies. However, the mechanism by which PHLDA2 affects trophoblast cell function has not been clarified. In the current study, co-immunoprecipitation (Co-IP) with mass spectroscopy analysis was used to explore the proteins that interacted with PHLDA2. A total of 291 candidate proteins were found to be associated with PHLDA2. The interaction between PHLDA2 and Rho guanine nucleotide dissociation inhibitor (RhoGDI) 1 was identified by Co-IP and immunofluorescence staining. Western blot analysis indicated that overexpression of PHLDA2 resulted in upregulation of the RhoGDI1 protein levels, which were stabilized in the presence of cycloheximide. Similarly, overexpression of RhoGDI1 promoted PHLDA2 expression and its stability. Furthermore, pull-down and Co-IP results indicated that PHLDA2 repressed the activity of Rho guanosine triphosphate hydrolase family proteins by regulating RhoGDI1 expression. In addition, RhoGDI1 expression was upregulated in the placental tissues of patients with PE. The effects of the suppression of PHLDA2 expression on proliferation, migration, and invasion of trophoblast cells were partly abrogated following knockdown of RhoGDI1. Taken together, the data indicated that RhoGDI1 mediated regulation of PHLDA2 on the biological behavior of trophoblast cells and may participate in the pathophysiology of PE.

Deletion of the Imprinted Phlda2 Gene Increases Placental Passive Permeability in the Mouse

Genomic imprinting, an epigenetic phenomenon that causes the expression of a small set of genes in a parent-of-origin-specific manner, is thought to have co-evolved with placentation. Many imprinted genes are expressed in the placenta, where they play diverse roles related to development and nutrient supply function. However, only a small number of imprinted genes have been functionally tested for a role in nutrient transfer capacity in relation to the structural characteristics of the exchange labyrinthine zone. Here, we examine the transfer capacity in a mouse model deficient for the maternally expressed Phlda2 gene, which results in placental overgrowth and a transient reduction in fetal growth. Using stereology, we show that the morphology of the labyrinthine zone in Phlda2^−/+ mutants is normal at E16 and E19. In vivo placental transfer of radiolabeled solutes ¹⁴C-methyl-D-glucose and ¹⁴C-MeAIB remains unaffected at both gestational time points. However, placental passive permeability, as measured using two inert hydrophilic solutes (¹⁴C-mannitol; ¹⁴C-inulin), is significantly higher in mutants. Importantly, this increase in passive permeability is associated with fetal catch-up growth. Our findings uncover a key role played by the imprinted Phlda2 gene in modifying placental passive permeability that may be important for determining fetal growth.

PHLDA2 gene polymorphisms and risk of HELLP syndrome and severe preeclampsia

OBJECTIVE

Pleckstrin homology-like domain, family A, member 2 (PHLDA2) is a maternally expressed imprinted gene. Loss of imprinting in PHLDA2 is associated with abnormal placental development and fetal growth restriction. Our objective was to determine whether genetic variation in PHLDA2 is also associated with risk of HELLP syndrome and preeclampsia (PE) with severe features.

STUDY DESIGN

Case (n = 162) and control (n = 33) mother-father-child triads were recruited using an internet-based method. Medical records were reviewed to verify clinical diagnosis of self-reported cases. DNA was genotyped for three polymorphisms in the PHLDA2 gene using TaqMan assays: rs13390, rs1056819, rs2583435.

MAIN OUTCOME MEASURES

To examine the association between minor alleles and haplotypes with HELLP syndrome and PE with severe features, relative risks and 95% confidence intervals were estimated using log-linear models, adjusting for the correlation between familial genotypes, using HAPLIN.

RESULTS

There was no association identified between PHLDA2 gene polymorphisms or haplotypes and HELLP syndrome and PE with severe features. No parent-of-origin effects were observed.

CONCLUSION

Genetic variation in the PHLDA2 gene is not associated with HELLP syndrome or PE with severe features.

Clinical Usefulness of Immunohistochemical Staining of p57 kip2 for the Differential Diagnosis of Complete Mole

Objective. Can polymer-based immunohistochemical staining of p57^kip2 replace DNA analysis as an inexpensive means of differentiating complete mole from partial mole or hydropic abortion? Methods and Materials. Original paraffin-embedded tissue blocks from 14 equivocal cases were turned over to our laboratory and examined by immunohistochemical staining of p57^kip2. Results. Four of the 14 cases showed clearly negative nuclear staining in cytotrophoblasts and villous stromal cells: these results were fully concordant with the control staining. The remaining 10 cases showed apparently positive staining in cytotrophoblasts and villous stromal cells. Without DNA analysis we are able to clearly differentiate the 4 cases of complete mole among the 14 equivocal cases. During follow-up, secondary low-risk gestational trophoblastic neoplasia (GTN) developed in 1 of the 4 cases of complete mole: the GTN was treated by single-agent chemotherapy. No subsequent changes were observed during follow-up in the other cases. Conclusion. Polymer-based immunohistochemical staining of p57^kip2 (paternally imprinted gene, expressed from maternal allele) is a very effective method that can be used to differentiate androgenetic complete mole from partial mole and hydropic abortion. We might be able to avoid the cost of DNA analysis.

Embryo-maternal communication: signalling before and during placentation in cattle and pig

Communication during early pregnancy is essential for successful reproduction. In this review we address the beginning of the communication between mother and developing embryo; including morphological and transcriptional changes in the endometrium as well as epigenetic regulation mechanisms directing the placentation. An increasing knowledge of the embryo-maternal communication might not only help to improve the fertility of our farm animals but also our understanding of human health and reproduction.

Maternal inheritance of a promoter variant in the imprinted PHLDA2 gene significantly increases birth weight

Birth weight is an important indicator of both perinatal and adult health, but little is known about the genetic factors contributing to its variability. Intrauterine growth restriction is a leading cause of perinatal morbidity and mortality and is also associated with adult disease. A significant correlation has been reported between lower birth weight and increased expression of the maternal PHLDA2 allele in term placenta (the normal imprinting pattern was maintained). However, a mechanism that explains the transcriptional regulation of PHLDA2 on in utero growth has yet to be described. In this study, we sequenced the PHLDA2 promoter region in 263 fetal DNA samples to identify polymorphic variants. We used a luciferase reporter assay to identify in the PHLDA2 promoter a 15 bp repeat sequence (RS1) variant that significantly reduces PHLDA2-promoter efficiency. RS1 genotyping was then performed in three independent white European normal birth cohorts. Meta-analysis of all three (total n = 9,433) showed that maternal inheritance of RS1 resulted in a significant 93 g increase in birth weight (p = 0.01; 95% confidence interval [CI] = 22-163). Moreover, when the mother was homozygous for RS1, the influence on birth weight was 155 g (p = 0.04; 95% CI = 9-300), which is a similar magnitude to the reduction in birth weight caused by maternal smoking.

TSSC3 overexpression associates with growth inhibition, apoptosis induction and enhances chemotherapeutic effects in human osteosarcoma

Loss of expression of TSSC3, an apoptosis-related imprinted gene, has been reported in several cases of malignant tumors. However, the roles and mechanisms of TSSC3 in human osteosarcoma remain to be defined. In this study, we found TSSC3 to be downregulated during osteosarcoma transformation and progression in osteosarcoma cell lines and tissues. The SaOS2 cell line was used to further evaluate the precise role of TSSC3 in osteosarcoma development. Overexpression of TSSC3 markedly reduced cell vitality and growth, colony formation, Ki67 expression as well as cell cycle arrest in the G(0)/G(1) phase. Consistently, TSSC3 overexpression was associated with increased apoptosis assayed by annexin V/propidium iodide and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining. Subcutaneous injection of TSSC3 overexpressing SaOS2 cells into athymic nude mice showed that TSSC3 also inhibited tumorigenesis through growth inhibition and apoptosis induction in vivo. Further mechanistic studies revealed that the mitochondrial apoptosis pathway was required for TSSC3-mediated cell apoptosis. These findings support a suppressor role for TSSC3 in osteosarcoma development by regulating apoptosis. In addition, constitutive TSSC3 expression greatly enhanced the sensitivity of human osteosarcoma cells to the chemotherapeutic drugs cisplatin and epirubicin. Conversely, TSSC3 knockdown increased SaOS2 cell growth and decreased apoptosis in vitro and in vivo and reduced sensitivity of the cells to chemotherapy. This is the first study to demonstrate that TSSC3 has a potent tumor suppressor role in osteosarcoma, probably by inhibition of growth and induction of apoptosis via the mitochondrial apoptosis pathway.

General imprinting status is stable in assisted reproduction-conceived offspring

OBJECTIVE

To evaluate whether the genomic imprinting status of assistant reproductive technology (ART)-conceived offspring is stable.

DESIGN

Prospective clinical observational study.

SETTING

In vitro fertilization (IVF) center, university-affiliated teaching hospital.

PATIENT(S)

Sixty ART-conceived babies (30 IVF and 30 intracytoplasmic sperm injection [ICSI]) and 60 naturally conceived babies.

INTERVENTION(S)

Collection of umbilical cord blood and peripheral blood samples.

MAIN OUTCOME MEASURE(S)

Expression profile was examined by microarray and real-time reverse-transcription polymerase chain reaction (PCR), allele-specific expression was studied by direct sequencing after PCR, and DNA methylation status was investigated by sodium bisulfite sequencing.

RESULT(S)

Hierarchic clustering demonstrated no obvious clustering between the ART- and naturally conceived offspring, suggesting similar genomic imprinting expression between the two groups. Three differentially expressed genes were identified in ART-conceived offspring, with PEG10 and L3MBTL up-regulated and PHLDA2 down-regulated. Allele-specific expression of the differentially expressed imprinted genes was maintained in the majority of the ART- and naturally conceived offspring. However, in one ICSI case, monoallelic expression of L3MBTL was disrupted and all CpGs were completely unmethylated. These were not inherited from the parents.

CONCLUSION(S)

The global profile of imprinting is stable in children conceived through ART. However, imprinting of a few specific imprinted genes may be vulnerable in a fraction of ART-conceived children.

Characterisation of marsupial PHLDA2 reveals eutherian specific acquisition of imprinting

BACKGROUND

Genomic imprinting causes parent-of-origin specific gene expression by differential epigenetic modifications between two parental genomes. We previously reported that there is no evidence of genomic imprinting of CDKN1C in the KCNQ1 domain in the placenta of an Australian marsupial, the tammar wallaby (Macropus eugenii) whereas tammar IGF2 and H19, located adjacent to the KCNQ1 domain in eutherian mammals, are imprinted. We have now identified and characterised the marsupial orthologue of PHLDA2, another gene in the KCNQ1 domain (also known as IPL or TSSC3) that is imprinted in eutherians. In mice, Phlda2 is a dose-sensitive negative regulator of placental growth, as Cdkn1c is for embryonic growth.

RESULTS

Tammar PHLDA2 is highly expressed in the yolk sac placenta compared to other fetal tissues, confirming a similar expression pattern to that of mouse Phlda2. However, tammar PHLDA2 is biallelically expressed in both the fetus and yolk sac placenta, so it is not imprinted. The lack of imprinting in tammar PHLDA2 suggests that the acquisition of genomic imprinting of the KCNQ1 domain in eutherian mammals, accompanied with gene dosage reduction, occurred after the split of the therian mammals into the marsupials and eutherians.

CONCLUSIONS

Our results confirm the idea that acquisition of genomic imprinting in the KCNQ1 domain occurred specifically in the eutherian lineage after the divergence of marsupials, even though imprinting of the adjacent IGF2-H19 domain arose before the marsupial-eutherian split. These data are consistent with the hypothesis that genomic imprinting of the KCNQ1 domain may have contributed to the evolution of more complex placentation in the eutherian lineage by reduction of the gene dosage of negative regulators for both embryonic and placental growth.

Isolation and characterization of human trophoblast side-population (SP) cells in primary villous cytotrophoblasts and HTR-8/SVneo cell line

Recently, numerous studies have identified that immature cell populations including stem cells and progenitor cells can be found among “side-population” (SP) cells. Although SP cells isolated from some adult tissues have been reported elsewhere, isolation and characterization of human trophoblast SP remained to be reported. In this study, HTR-8/SVneo cells and human primary villous cytotrophoblasts (vCTBs) were stained with Hoechst 33342 and SP and non-SP (NSP) fractions were isolated using a cell sorter. A small population of SP cells was identified in HTR-8/SVneo cells and in vCTBs. SP cells expressed several vCTB-specific markers and failed to express syncytiotrophoblast (STB) or extravillous cytotrophopblast (EVT)-specific differentiation markers. SP cells formed colonies and proliferated on mouse embryonic fibroblast (MEF) feeder cells or in MEF conditioned medium supplemented with heparin/FGF2, and they also showed long-term repopulating property. SP cells could differentiate into both STB and EVT cell lineages and expressed several differentiation markers. Microarray analysis revealed that IL7R and IL1R2 were exclusively expressed in SP cells and not in NSP cells. vCTB cells sorted as positive for both IL7R and IL1R2 failed to express trophoblast differentiation markers and spontaneously differentiated into both STB and EVT in basal medium. These features shown by the SP cells suggested that IL7R and IL1R2 are available as markers to detect the SP cells and that vCTB progenitor cells and trophoblast stem cells were involved in the SP cell population.

Characterization of conserved and nonconserved imprinted genes in swine

To increase our understanding of imprinted genes in swine, we carried out a comprehensive analysis of this gene family using two complementary approaches: expression and phenotypic profiling of parthenogenetic fetuses, and analysis of imprinting by pyrosequencing. The parthenote placenta and fetus were smaller than those of controls but had no obvious morphological differences at Day 28 of gestation. By Day 30, however, the parthenote placentas had decreased chorioallantoic folding, decreased chorionic ruggae, and reduction of fetal-maternal interface surface in comparison with stage-matched control fetuses. Using Affymetrix Porcine GeneChip microarrays and/or semiquantitative PCR, brain, fibroblast, liver, and placenta of Day 30 fetuses were profiled, and 25 imprinted genes were identified as differentially expressed in at least one of the four tissue types: AMPD3, CDKN1C, COPG2, DHCR7, DIRAS3, IGF2 (isoform specific), IGF2AS, IGF2R, MEG3, MEST, NAP1L5, NDN, NNAT, OSBPL1A, PEG3, APEG3, PEG10, PLAGL1, PON2, PPP1R9A, SGCE, SLC38A4, SNORD107, SNRPN, and TFPI2. For DIRAS3, PLAGL1, SGCE, and SLC38A4, tissue-specific differences were detected. In addition, we examined the imprinting status of candidate genes by quantitative allelic pyrosequencing. Samples were collected from Day 30 pregnancies generated from reciprocal crosses of Meishan and White Composite breeds, and single-nucleotide polymorphisms were identified in candidate genes. Imprinting was confirmed for DIRAS3, DLK1, H19, IGF2AS, NNAT, MEST, PEG10, PHLDA2, PLAGL1, SGCE, and SNORD107. We also found no evidence of imprinting in ASB4, ASCL2, CD81, COMMD1, DCN, DLX5, and H13. Combined, these results represent the most comprehensive survey of imprinted genes in swine to date.

Microarray analysis of prothrombin knockdown in zebrafish

The serine protease thrombin is generated from its precursor, prothrombin, in the coagulation cascade and plays a central role in fibrin deposition and platelet activation mediated through the protease activated receptors. Knockdown of prothrombin in the zebrafish was previously shown to recapitulate the phenotype observed in prothrombin knockout mice, such as an absence of blood pericardial edema, and hemorrhage. However, the role of thrombin during embryogenesis is not fully understood. To find genes affected by potential thrombin signaling in embryogenesis before blood circulation, microarray analysis was performed using total RNA prepared from antisense-injected, knockdown embryos versus mismatch-injected at 20 h post fertilization. A total of 63 upregulated and downregulated genes were identified with duplicate microarrays using dye reversal and a two-fold difference limitation. Real time RT-PCR for 10 selected genes identified by the microarray confirmed the expression changes in these genes. One particular gene, phlda3, was at least eleven fold upregulated, and in situ hybridization revealed expansion of phlda3 expression in the central nervous system, branchial arches, and head endoderm in knockdown embryos. The identification of these genes regulated by thrombin according to microarray analysis should provide a greater understanding of the effects of thrombin activity in the early vertebrate embryo.

Androgenetic/biparental mosaicism in an infant with hepatic mesenchymal hamartoma and placental mesenchymal dysplasia

Androgenetic/biparental mosaicism, in which a subset of cells has complete paternal uniparental disomy, is associated with placental mesenchymal dysplasia (PMD), which is compatible with fetal development, indicating that fetal organs could also have androgenetic/biparental mosaicism, but few cases of somatic mosaicism have been described. A hepatic mesenchymal hamartoma (HMH) was resected from an otherwise healthy, nondysmorphic, 11-month-old girl, whose prenatal development was complicated by PMD. Placenta, HMH, histologically normal liver, and other tissues were examined for androgenetic/biparental mosaicism by analysis of (1) polymorphic DNA microsatellite markers, (2) the methylation status of an imprinted gene, SNRPN, and (3) immunohistochemically detectable protein products of the imprinted genes p57KIP2 and PHLDA2. The patient's liver, HMH, and 1 placental sample demonstrated an increased ratio of paternal to maternal alleles, indicating androgenetic/biparental mosaicism. The androgenetic component comprised 26% to 60% of the cells. Other tissues, including a 2nd placental sample, white blood cells, umbilical cord, and abdominal fascia, had no detectable androgenetic component. Methylation analysis confirmed a relative excess of the paternally imprinted SNRPN homolog in the normal liver, HMH, and placenta. Placental p57KIP2 immunoreactivity was consistent with androgenetic/biparental mosaicism, but neither p57KIP2 nor PHLDA2 immunohistochemistry were informative for HMH, because neither antigen was detected in control liver samples. We report androgenetic/biparental mosaicism in nonplacental tissues of an infant with PMD and provide the 1st description of genome-wide paternal uniparental disomy in HMH. Androgenetic/biparental mosaicism appears to play a role in the pathogenesis of HMH and other somatic lesions, particularly those associated with PMD.

Psychosis and autism as diametrical disorders of the social brain

Autistic-spectrum conditions and psychotic-spectrum conditions (mainly schizophrenia, bipolar disorder, and major depression) represent two major suites of disorders of human cognition, affect, and behavior that involve altered development and function of the social brain. We describe evidence that a large set of phenotypic traits exhibit diametrically opposite phenotypes in autistic-spectrum versus psychotic-spectrum conditions, with a focus on schizophrenia. This suite of traits is inter-correlated, in that autism involves a general pattern of constrained overgrowth, whereas schizophrenia involves undergrowth. These disorders also exhibit diametric patterns for traits related to social brain development, including aspects of gaze, agency, social cognition, local versus global processing, language, and behavior. Social cognition is thus underdeveloped in autistic-spectrum conditions and hyper-developed on the psychotic spectrum.;>We propose and evaluate a novel hypothesis that may help to explain these diametric phenotypes: that the development of these two sets of conditions is mediated in part by alterations of genomic imprinting. Evidence regarding the genetic, physiological, neurological, and psychological underpinnings of psychotic-spectrum conditions supports the hypothesis that the etiologies of these conditions involve biases towards increased relative effects from imprinted genes with maternal expression, which engender a general pattern of undergrowth. By contrast, autistic-spectrum conditions appear to involve increased relative bias towards effects of paternally expressed genes, which mediate overgrowth. This hypothesis provides a simple yet comprehensive theory, grounded in evolutionary biology and genetics, for understanding the causes and phenotypes of autistic-spectrum and psychotic-spectrum conditions.

Elevated placental expression of the imprinted PHLDA2 gene is associated with low birth weight

The identification of genes that regulate fetal growth will help establish the reasons for intrauterine growth restriction. Most autosomal genes are expressed biallelically, but some are imprinted, expressed only from one parental allele. Imprinted genes are associated with fetal growth and development. The growth of the fetus in utero relies on effective nutrient transfer from the mother to the fetus via the placenta. Some current research on the genetic control of fetal growth has focused on genes that display imprinted expression in utero. The expression levels of four imprinted genes, the paternally expressed insulin growth factor 2 (IGF2), the mesoderm-specific transcript isoform 1 (MEST); the maternally expressed pleckstrin homology-like domain, family A, member 2 (PHLDA2); and the polymorphically imprinted insulin-like growth factor 2 (IGF2R) gene are all known to have roles in fetal growth and were studied in the placentae of 200 white European, normal term babies. The quantitative expression analysis with real-time PCR showed the maternally expressing PHLDA2 but not the paternally expressing IGF2 and MEST, nor the polymorphic maternally expressing IGF2R placental levels to have a statistically significant effect on birth weight. PHLDA2 expression levels are negatively correlated with size at birth. These data implicate PHLDA2 as an imprinted gene important in fetal growth and also as a potential marker of fetal growth.

Hypoxia regulates the expression of PHLDA2 in primary term human trophoblasts

Hypoxia influences gene expression in placental trophoblasts. We sought to examine the effect of hypoxia on trophoblast expression of human PHLDA2 (also termed IPL, TSSC3 or BWR-1C), a product of an imprinted gene on human chromosome 11p15.5 whose murine ortholog plays a pivotal role in placental development. We initially confirmed that PHLDA2 was expressed in term placental villi, primarily in the trophoblast layer. Using quantitative PCR we found that the expression of PHLDA2 gradually declined during differentiation of primary term human trophoblasts. A similar expression pattern was seen for p57(Kip2) and IGF-II, both products of imprinted genes on chromosome 11p15.5. Exposure of trophoblasts to hypoxia in vitro (O(2)<or=2%) markedly reduced the expression of PHLDA2 mRNA and protein. This effect was not consistent among other chromosome 11p15.5 genes products, as the expression of p57(Kip2) decreased, but that of IGF-II increased in hypoxic trophoblasts. PHLDA2 expression in trophoblasts exposed to TGFbeta1, -beta2 or -beta3 was unchanged. We conclude that hypoxia down-regulates the expression of PHLDA2 in human term placental trophoblasts. As murine PHLDA2 limits placental growth, our results suggest that down-regulation of PHLDA2 attenuates the impact of hypoxia on placental growth.

Imprinted genes in placental growth and obstetric disorders

Genomic imprinting has a special role in placental biology. Imprinted genes are often strongly expressed in the placenta, and the allelic expression bias due to imprinting is sometimes stronger in this extraembryonic organ than in the embryo and adult. Mutations, epimutations, and uniparental disomies affecting imprinted loci cause placental stunting or overgrowth in mice and humans, and placental neoplasms (complete hydatidiform moles) are androgenetic. Whether imprinted genes might also play a role in the more common medical conditions that affect the placenta, including preeclampsia and intrauterine growth restriction (IUGR), is an important question that is now receiving some attention. Here we review this area and describe recent data indicating altered expression of imprinted genes in the placental response to maternal vascular underperfusion associated with IUGR.

Genomic imprinting in the placenta

Genomic imprinting is an epigenetic mechanism that is important for the development and function of the extra-embryonic tissues in the mouse. Remarkably all the autosomal genes which were found to be imprinted in the trophoblast (placenta) only are active on the maternal and repressed on the paternal allele. It was shown for several of these genes that their paternal silencing is not dependent on DNA methylation, at least not in its somatic maintenance. Rather, recent studies in the mouse suggest that placenta-specific imprinting involves repressive histone modifications and non-coding RNAs. This mechanism of autosomal imprinting is similar to imprinted X chromosome inactivation in the placenta. Although the underlying reasons remain to be explored, this suggests that imprinting in the placenta and imprinted X inactivation are evolutionarily related.

Imprinted genes and their role in human fetal growth

Growth is defined as the progressive increase in size and is listed as one of the eight main characteristics of life. In human gestation the most rapid growth phase is from 16 to 32 weeks when first there is both cell number and size increase and then from 32 weeks onwards there is continued size increase (Pollack and Divon, 1992). The mechanism of growth in utero is of fundamental interest to clinicians and scientists because of its implications for neonatal health. Growth is multifactorial in origin with both genetics and environment contributing equally large parts. Despite this complexity analysis of the candidate genes involved is possible using simple tissue biopsies at the relevant stages of development. Of particular interest in understanding fetal growth is the analysis of a group of genes that show a parent-of-origin effect known as genomic imprinting. Imprinted genes are not only found in eutherian (placental) and metatherian (marsupial) mammals but surprisingly also in plants. Nevertheless, their evolution in mammals appears to be linked primarily to placentation. It is thought to result from a potential conflict between the parents in terms of the drive to successfully propagate their own separate genes and the mother's added drive for her survival through the pregnancy to reproduce again. This means that the mother wants to restrict fetal growth and the father to enhance it.

Epigenetic deregulation of genomic imprinting in human disorders and following assisted reproduction

Imprinted genes play important roles in the regulation of growth and development, and several have been shown to influence behavior. Their allele-specific expression depends on inheritance from either the mother or the father, and is regulated by "imprinting control regions" (ICRs). ICRs are controlled by DNA methylation, which is present on one of the two parental alleles only. These allelic methylation marks are established in either the female or the male germline, following the erasure of preexisting DNA methylation in the primordial germ cells. After fertilization, the allelic DNA methylation at ICRs is maintained in all somatic cells of the developing embryo. This epigenetic "life cycle" of imprinting (germline erasure, germline establishment, and somatic maintenance) can be disrupted in several human diseases, including Beckwith-Wiedemann syndrome (BWS), Prader-Willi syndrome (PWS), Angelman syndrome and Hydatidiform mole. In the neurodevelopmental Rett syndrome, the way the ICR mediates imprinted expression is perturbed. Recent studies indicate that assisted reproduction technologies (ART) can sometimes affect the epigenetic cycle of imprinting as well, and that this gives rise to imprinting disease syndromes. This finding warrants careful monitoring of the epigenetic effects, and absolute risks, of currently used and novel reproduction technologies.

Unbalanced placental expression of imprinted genes in human intrauterine growth restriction

Imprinted genes control fetal and placental growth in mice and in rare human syndromes, but the role of these genes in sporadic intrauterine growth restriction (IUGR) is less well-studied. We measured the ratio of mRNA from a maternally expressed imprinted gene, PHLDA2, to that from a paternally expressed imprinted gene, MEST, by Northern blotting in 38 IUGR-associated placentae and 75 non-IUGR placentae and found an increase in the PHLDA2/MEST mRNA ratio in IUGR (p=0.0001). Altered expression of PHLDA2 and MEST was not accompanied by changes in DNA methylation within their imprinting centers, and immunohistochemistry showed PHLDA2 protein appropriately restricted to villous and intermediate cytotrophoblast in the IUGR placentae. We next did a genome-wide survey of mRNA expression in 14 IUGR placentae with maternal vascular under-perfusion compared to 15 non-IUGR placentae using Affymetrix U133A microarrays. In this series six imprinted genes were differentially expressed by ANOVA with a Benjamini-Hochberg false discovery rate of 0.05, with increased expression of PHLDA2 and decreased expression of MEST, MEG3, GATM, GNAS and PLAGL1 in IUGR placentae. At lower significance, we found IGF2 mRNA decreased and CDKN1C mRNA increased in the IUGR cases. We confirmed the significant reduction in MEG3 non-translated RNA in IUGR placentae by Northern blotting. In addition to imprinted genes, the microarray data highlighted non-imprinted genes acting in endocrine signaling (LEP, CRH, HPGD, INHBA), tissue growth (IGF1), immune modulation (INDO, PSG-family genes), oxidative metabolism (GLRX), vascular function (AGTR1, DSCR1) and metabolite transport (SLC-family solute carriers) as differentially expressed in IUGR vs. non-IUGR placentae.

Placental growth retardation due to loss of imprinting of Phlda2

The maternally expressed/paternally silenced genes Phlda2 (a.k.a. Ipl/Tssc3), Slc22a1l, Cdkn1c, Kcnq1, and Ascl2 are clustered in an imprinted domain on mouse chromosome 7. Paternal deletion of a cis-acting differentially methylated DNA element, Kvdmr1, causes coordinate loss of imprinting and over-expression of all of these genes and the resulting conceptuses show intrauterine growth restriction (IUGR). To test the specific contribution of Phlda2 to IUGR in the Kvdmr1-knockout, we crossed Kvdmr1(+/-) males with Phlda2(+/-) females. Conceptuses with the (Phlda2(+/+); Kvdmr1(+/-)) genotype showed fetal and placental growth retardation. Restoration of Phlda2 dosage to normal, as occurred in the conceptuses with the (Phlda2(-/+); Kvdmr1(+/-)) genotype, had a marginally positive effect on fetal weights and no effect on post-natal weights, but significantly rescued the placental weights. As we previously reported, loss of Phlda2 expression in the wild-type background (Phlda2(-/+); Kvdmr1(+/+) genotype) caused placentomegaly. Thus Phlda2 acts as a true rheostat for placental growth, with overgrowth after gene deletion and growth retardation after loss of imprinting. Consistent with this conclusion, we observed significant placental stunting in BAC-transgenic mice that over-expressed Phlda2 and one flanking gene, Slc22a1l, but did not over-express Cdkn1c.

Imprinted genes in the placenta – A review

Imprinted genes are expressed monoallelically depending on their parental origin. High expression of the majority of imprinted genes tested to date has been demonstrated in extraembryonic tissues; placenta and yolk sac. Several mouse models where specific imprinted genes have been disrupted demonstrate that fetal and placental growth may be regulated by imprinted genes, in which paternally expressed genes enhance, and maternally expressed genes restrain, growth. We review the current information on, and suggest possible functional roles for, imprinted genes in placental development.

Genomic Imprinting and Kinship: How Good is the Evidence?

The kinship theory of genomic imprinting proposes that parent-specific gene expression evolves at a locus because a gene's level of expression in one individual has fitness effects on other individuals who have different probabilities of carrying the maternal and paternal alleles of the individual in which the gene is expressed. Therefore, natural selection favors different levels of expression depending on an allele's sex-of-origin in the previous generation. This review considers the strength of evidence in support of this hypothesis for imprinted genes in four "clusters," associated with the imprinted loci Igf2, Igf2r, callipyge, and Gnas. The clusters associated with Igf2 and Igf2r both contain paternally expressed transcripts that act as enhancers of prenatal growth and maternally expressed transcripts that act as inhibitors of prenatal growth. This is consistent with predictions of the kinship theory. However, the clusters also contain imprinted genes whose phenotypes as yet remain unexplained by the theory. The principal effects of imprinted genes in the callipyge and Gnas clusters appear to involve lipid and energy metabolism. The kinship theory predicts that maternally expressed transcripts will favor higher levels of nonshivering thermogenesis (NST) in brown adipose tissue (BAT) of animals that huddle for warmth as offspring. The phenotypes of reciprocal heterozygotes for Gnas knockouts provide provisional support for this hypothesis, as does some evidence from other imprinted genes (albeit more tentatively). The diverse effects of imprinted genes on the development of white adipose tissue (WAT) have so far defied a unifying hypothesis in terms of the kinship theory.

Complete hydatidiform mole retaining a chromosome 11 of maternal origin: molecular genetic analysis of a case

Hydatidiform moles are pregnancies characterized by abnormal development of both embryonic and extraembryonic tissues and are associated with the misexpression of imprinted genes. The vast majority of complete hydatidiform moles are diploid and androgenetic, whereas partial hydatidiform moles are triploid, with an extra set of chromosomes of paternal origin. Here, we present an unusual complete mole that showed strong expression of two imprinted, maternally transcribed genes, CDKN1C (encoding p57(KIP2)) and PHLDA2 (TSSC3/IPL), both part of a large imprinted gene domain on chromosome 11. Using microsatellite genotyping and fluorescent in situ hybridization, we show that this paradoxical gene expression was due to retention of a maternal copy of chromosome 11 in addition to the two paternal copies normally present in complete moles. These findings demonstrate that, despite being predominantly androgenetic, some complete moles contain small amounts of DNA of maternal origin. Furthermore, these results provide an explanation for rare false negatives that can arise when p57(KIP2) is used as a diagnostic marker for complete moles.

p57KIP2 immunohistochemical staining of gestational trophoblastic tumours does not identify the type of the causative pregnancy

AIM

To determine whether immunohistochemical staining for p57(KIP2), the product of the maternally expressed gene CDKN1C, can be used to differentiate between gestational trophoblastic tumours arising from a complete hydatidiform mole and those originating from non-molar pregnancies.

METHODS

The immunohistochemical expression of p57(KIP2) was investigated in 23 cases of choriocarcinoma and 17 placental site trophoblastic tumours. Fourteen of the tumours examined were shown by DNA analysis to have arisen from complete hydatidiform moles and 26 from non-molar pregnancies.

RESULTS

Five of 11 (45%) post-complete hydatidiform mole choriocarcinomas and two of three (67%) post-complete hydatidiform mole placental site trophoblastic tumours were found to be p57(KIP2)+ and showed similar immunostaining characteristics to tumours that developed from non-molar pregnancies. Although there was a statistically significant reduction in the proportion of cases showing positive p57(KIP2) staining in post-complete hydatidiform mole tumours compared with those originating in non-molar pregnancies [proportion difference 0.35 [95% confidence interval (CI) 0.05, 0.61], P = 0.02], immunostaining did not provide diagnostically useful information to differentiate between these tumours in clinical practice. There was no significant difference between the extent of staining in choriocarcinoma versus placental site trophoblastic tumours [proportion difference 0.17 (95% CI - 12, 42), P = 0.19]. The majority of both types of gestational trophoblastic tumour were positive for the presence of the p57(KIP2) protein irrespective of their genetic origin.

CONCLUSION

Immunostaining for p57(KIP2) fails to discriminate between gestational trophoblastic tumours that have arisen from complete hydatidiform moles and those that have originated from other types of pregnancy.