Biomedical subjects

A C Ferguson-Smith

Publications and source records attributed to A C Ferguson-Smith.

At least 19 recordsLinked to original sources

PubMed2007

Oxidative stress and the induction of cyclooxygenase enzymes and apoptosis in the murine placenta.

Placental oxidative stress has been implicated in many complications of human pregnancy, including preterm delivery and preeclampsia. It is now appreciated that reactive oxygen species can induce a spectrum of changes, ranging from homeostatic induction of enzymes to apoptotic cell death. Little is known regarding the occurrence of placental oxidative stress in other species. We investigated markers of oxidative stress in the labyrinthine (LZ) and junctional (JZ) zones of the murine placenta across gestational age, and correlated these with expression of the cyclooxygenase enzymes COX-1 and COX-2, and apoptosis. We tested a causal link between the two by subjecting placental explants to hypoxia-reoxygenation (H/R) in vitro, a known stimulus for generation of oxidative stress. Western blotting demonstrated significant increases in the concentrations of hydroxynonenal (HNE), COX-1 and COX-2 with gestational age. Dual-labelling demonstrated co-localisation of HNE, and COX-1 and COX-2 within the trophoblast of the LZ, and glycogen cells of the JZ. An apoptotic index based on TUNEL-positivity demonstrated an increase with gestational age, and dual-labelling showed co-localisation of TUNEL labelling with HNE and active caspase-3 within the trophoblast of the LZ. H/R significantly increased oxidative stress, induction of COX-1 and COX-2, and the apoptotic index. Co-localisation demonstrated the increases in COX to be within the trophoblast of the LZ, and in particular the glycogen cells of the JZ. Apoptosis was restricted to the LZ. We speculate that the induction of COX enzymes is a physiological response to oxidative stress, and may play a role in initiating or augmenting parturition. Generation of oxidative stress may also play a role in influencing the growth trajectory of the placenta, and its component cell types. The mouse may provide an experimental genetic model in which to investigate these phenomena.

Aldehydes↗

PubMed2006

Epigenetics and imprinting of the trophoblast -- a workshop report.

Genomic imprinting is a remarkable process that causes genes to be expressed or repressed depending on their parental-origin. Imprinted genes play important roles in prenatal growth and organ development. Postnatally, imprinted genes can contribute to the regulation of metabolic pathways and behaviour associated with the control of resources. One of the most important sites of imprinted gene action is the placenta. During this workshop at the 11th meeting of the International Federation of Placenta Associations/European Placenta Group held in Glasgow, a series of short talks were presented providing an overview of the evolution, function and mechanisms of imprinting in mammals with particular reference to the placenta. In addition, epigenetic control of trophoblast development and function were considered. This report summarises the contributions to the workshop.

Animals↗

PubMed2006

Origin and characteristics of glycogen cells in the developing murine placenta.

The junctional zone (Jz) of the mouse placenta consists of two main trophoblast populations, spongiotrophoblasts and glycogen cells (GCs), but the development and function of both cell types are unknown. We conducted a quantitative analysis of GC size, number, and invasion of cells into the decidua across gestation. Furthermore, we identified markers of GC function to investigate their possible roles in the placenta. While the spongiotrophoblast cell volume doubles, and cell number increases steadily from E12.5 to E16.5, there is a remarkable 80-fold increase in GC numbers. This finding is followed by a notable decrease by E18.5. Surprisingly, the accumulation of GCs in the decidua did not fully account for the decrease in GC number in the Jz, suggesting loss of GCs from the placenta. Glucagons were detected on GCs, suggesting a steady glucose release throughout gestation. Connexin31 staining was shown to be specific for GCs. GC migration and invasion may be facilitated by temporally regulated expression of matrix metalloproteinase 9 and the imprinted gene product, Decorin. Expression of the clearance receptor for type II insulin-like growth factor (IGF-II), IGF2R, in a short developmental window before E16.5 may be associated with regulating the growth effects of IGF-II from glycogen cells and/or labyrinthine trophoblast on the expansion of the Jz. Thus stereology and immunohistochemistry have provided useful insights into Jz development and function of the glycogen cells.

Animals↗

PubMed2006

Analysis of mouse conceptuses with uniparental duplication/deficiency for distal chromosome 12: comparison with chromosome 12 uniparental disomy and implications for genomic imprinting.

Distal mouse chromosome 12 is imprinted. Phenotypic analysis of mouse embryos with maternal or paternal uniparental disomy for the whole of chromosome 12 has characterized the developmental defects associated with the altered dosage of imprinted genes on this chromosome. Here we conduct a characterization of maternal and paternal Dp(dist12) mice using the reciprocal translocation T(4;12)47H. This limits the region analysed to the chromosomal domain distal to the T47H breakpoint in B3 on mouse chromosome 12. Both MatDp(dist12)T47H and PatDp(dist12)T47H conceptuses are non-viable and the frequency of recovery of Dp(dist12) conceptuses by 10.5 days post coitum (dpc) was lower than expected after normal adjacent-1 disjunction. A subset of MatDp(dist12) embryos can survive up to one day post partum. In contrast to paternal uniparental disomy 12 embryos, no live PatDp (dist12) embryos were recovered after 16.5 days of gestation. Other phenotypes observed in maternal and paternal chromosome 12 uniparental disomy mice are recapitulated in the Dp(dist12) mice and include placental, muscle and skeletal defects. Additional defects were also noted in the skin of both MatDp(dist12) and maternal uniparental disomy 12 embryos. This study shows that the developmental abnormalities associated with the altered parent of origin for mouse chromosome 12 can be attributed to the genomic region distal to the T47H breakpoint.

Animals↗

PubMed2005

Epigenetic alteration at the DLK1-GTL2 imprinted domain in human neoplasia: analysis of neuroblastoma, phaeochromocytoma and Wilms' tumour.

Epigenetic alterations in the 11p15.5 imprinted gene cluster are frequent in human cancers and are associated with disordered imprinting of insulin-like growth factor (IGF)2 and H19. Recently, an imprinted gene cluster at 14q32 has been defined and includes two closely linked but reciprocally imprinted genes, DLK1 and GTL2, that have similarities to IGF2 and H19, respectively. Both GTL2 and H19 are maternally expressed RNAs with no protein product and display paternal allele promoter region methylation, and DLK1 and IGF2 are both paternally expressed. To determine whether methylation alterations within the 14q32 imprinted domain occur in human tumorigenesis, we investigated the status of the GTL2 promoter differentially methylated region (DMR) in 20 neuroblastoma tumours, 20 phaeochromocytomas and, 40 Wilms' tumours. Hypermethylation of the GTL2 promoter DMR was detected in 25% of neuroblastomas, 10% of phaeochromocytoma and 2.5% of Wilms' tumours. Tumours with GTL2 promoter DMR hypermethylation also demonstrated hypermethylation at an upstream intergenic DMR thought to represent a germline imprinting control element. Analysis of neuroblastoma cell lines revealed that GTL2 DMR hypermethylation was associated with transcriptional repression of GTL2. These epigenetic findings are similar to those reported in Wilms' tumours in which H19 repression and DMR hypermethylation is associated with loss of imprinting (LOI, biallelic expression) of IGF2. However, a neuroblastoma cell line with hypermethylation of the GTL2 promoter and intergenic DMR did not show LOI of DLK1 and although treatment with a demethylating agent restored GTL2 expression and reduced DLK1 expression. As described for IGF2/H19, epigenetic changes at DLK1/GTL2 occur in human cancers. However, these changes are not associated with DLK1 LOI highlighting differences in the imprinting control mechanisms operating in the IGF2-H19 and DLK1-GTL2 domains. GTL2 promoter and intergenic DMR hypermethylation is associated with the loss of GTL2 expression and this may contribute to tumorigenesis in a subset of human cancers.

Base Sequence↗

PubMed2005

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.

Animals↗

PubMed2005

Ultrastructural changes in the interhaemal membrane and junctional zone of the murine chorioallantoic placenta across gestation.

The mouse is an extremely useful experimental model for the study of human disease owing to the ease of genetic and physiological manipulation. A more detailed knowledge of murine placental development will, we hope, increase our understanding of the pathogenesis of placentally related complications of human pregnancy. The murine placenta consists of two main fetally derived compartments: the labyrinthine zone and the junctional zone. Exchange in the labyrinthine zone takes place across an interhaemal membrane comprising an outer layer of cytotrophoblast cells and two inner layers of syncytial trophoblast. The cytotrophoblast layer thins as gestation advances, and in addition becomes highly perforated after embryonic day (E)12.5. Furthermore, as gestation advances cytotrophoblast nuclear volume and DNA content increase, suggesting the formation of labyrinthine trophoblast giant cells. The syncytial layers become increasingly microvillous, enlarging the surface area for exchange. Separate basement membranes support the syncytium and the fetal capillary endothelium throughout gestation, although these appear to fuse where the capillaries are closely approximated to the trophoblast. The junctional zone consists of two principal trophoblast cell types, spongiotrophoblasts and invasive glycogen cells, yet the functions of each remain elusive. Spongiotrophoblasts vary in their appearance even when not fully differentiated, but a striking feature is the extensive endoplasmic reticulum of the more mature cells. Early glycogen cells are distinguished by the presence of electron-dense glycogen granules, and large amounts of surrounding extracellular matrix. Later the accumulations of glycogen granules occupy almost all the cytoplasm and there are few organelles. This is the first study to use both scanning and transmission electron microscopy in an ultrastructural description of murine placental development and is complementary to contemporary genetic investigations.

Allantois↗

PubMed2004

Placental-specific insulin-like growth factor 2 (Igf2) regulates the diffusional exchange characteristics of the mouse placenta.

Restricted fetal growth is associated with postnatal mortality and morbidity and may be directly related to alterations in the capacity of the placenta to supply nutrients. We proposed previously that imprinted genes can regulate nutrient supply by the placenta. Here, we tested the hypothesis that the insulin-like growth factor 2 gene (Igf2) transcribed from the placental-specific promoter (P0) regulates the development of the diffusional permeability properties of the mouse placenta. Using mice in which placental-specific Igf2 had been deleted (P0), we measured the transfer in vivo of three inert hydrophilic solutes of increasing size (14C-mannitol, 51CrEDTA, and 14C-inulin). At embryonic day 19, placental and fetal weights in P0 conceptuses were reduced to 66% and 76%, respectively, of wild type. In P0 mutants, the permeability.surface area product for the tracers at this stage of development was 68% of that of controls; this effect was independent of tracer size. Stereological analysis of histological sections revealed the surface area of the exchange barrier in the labyrinth of the mouse placenta to be reduced and thickness increased in P0 fetuses compared to wild type. As a result, the average theoretical diffusing capacity in P0 knockout placentas was dramatically reduced to 40% of that of wild-type placentas. These data show that placental Igf2 regulates the development of the diffusional exchange characteristics of the mouse placenta. This provides a mechanism for the role of imprinted genes in controlling placental nutrient supply and fetal growth. Altered placental Igf2 could be a cause of idiopathic intrauterine growth restriction in the human.

Animals↗

PubMed2002

Comparative developmental anatomy of the murine and human definitive placentae.

The placenta of eutherian mammals is a remarkable biological structure. It is composed of both zygote-derived and maternal cells, and mediates the complex interactions between the mother and the fetus that are necessary for fetal growth and survival. While the genetic basis of human placental development and function is largely unknown, its understanding is of immense clinical importance because placentopathies of unknown genetic aetiology are thought to be the cause of many types of pregnancy complications including unexplained miscarriage and intrauterine growth retardation. The mouse is the best-studied mammalian experimental genetic model system and research is not restricted by the inherent ethical and practical limitations associated with the human. As a result, knowledge about the genetic control of mouse placental development has expanded greatly in recent years. In order for this to be of benefit to medical practice, extrapolations from murine to human placentation have to be made. However, comprehensive comparisons of the placentae of these two species are rare. This review therefore compares the developmental anatomy of the placenta between humans and mice with emphasis on structures and cell types that might be analogous between the two species. This could be of particular benefit to mouse developmental geneticists who study placental development and have an interest in the possible clinical implications of their work.

Adult↗

PubMed2001

Imprinting and the epigenetic asymmetry between parental genomes.

Genomic imprinting confers a developmental asymmetry on the parental genomes, through epigenetic modifications in the germ line and embryo. These heritable modifications regulate the monoallelic activity of parental alleles resulting in their functional differences during development. Specific cis-acting regulatory elements associated with imprinted genes carry modifications involving chromatin structural changes and DNA methylation. Some of these modifications are initiated in the germ line. Comparative genomic analysis at imprinted domains is emerging as a powerful tool for the identification of conserved elements amenable to more detailed functional analysis, and for providing insight into the emergence of imprinting during the evolution of mammalian species. Genomic imprinting therefore provides a model system for the analysis of the epigenetic control of genome function.

Alleles↗

PubMed2001

Roles for genomic imprinting and the zygotic genome in placental development.

The placenta contains several types of feto-maternal interfaces where zygote-derived cells interact with maternal cells or maternal blood for the promotion of fetal growth and viability. The genetic factors regulating the interactions between different cell types within feto-maternal interfaces and the relative contributions of the maternal and zygotic genomes are poorly understood. Genomic imprinting, the epigenetic process responsible for parental origin-dependent functional differences between homologous chromosomes, has been proposed to contribute to these events. Previous studies showed that mouse conceptuses with an absence of imprinted differences between the two copies of chromosome 12 (upon paternal inheritance of both copies) die late in gestation and have a variety of defects, including placentomegaly. Here we examined the role of chromosome 12 imprinting in these placentae in more detail. We show that the spatial interactions between different cell types within feto-maternal interfaces are defective and identify abnormal behaviors in both zygote-derived and maternal cells that are attributed to the genome of the zygote but not the mother. These include compromised invasion of the maternal decidualized endometrium and the central maternal artery situated within it by zygote-derived trophoblast, abnormalities in the wall of the central maternal artery, and defects within the zygote-derived cellular layer of the labyrinth, which is in direct contact with maternal blood. These findings demonstrate multiple roles for chromosome 12 imprinting in the placenta that have not previously been associated with imprinting effects. They provide insights into the function of imprinting in placental development and have evolutionary and clinical implications.

Animals↗

PubMed2001

DNA methylation in genomic imprinting, development, and disease.

Changes in DNA methylation profiles are common features of development and in a number of human diseases, such as cancer and imprinting disorders like Beckwith-Wiedemann and Prader-Willi/Angelman syndromes. This suggests that DNA methylation is required for proper gene regulation during development and in differentiated tissues and has clinical relevance. DNA methylation is also involved in X-chromosome inactivation and the allele-specific silencing of imprinted genes. This review describes possible mechanisms by which DNA methylation can regulate gene expression, using imprinted genes as examples. The molecular basis of methylation-mediated gene regulation is related to changes in chromatin structure and appears to be similar for both imprinted and biallelically expressed genes.

Abnormalities, Multiple↗

PubMed2001

Dynamic temporal and spatial regulation of the cdk inhibitor p57(kip2) during embryo morphogenesis.

The complete developmental expression pattern of the cyclin dependent kinase inhibitor (CDKI) p57(kip2) has not been reported, here we report a detailed study of the localization of p57(kip2) protein during mouse organogenesis. We show that p57(kip2) is coincident with key stages of differentiation of several organs, some but not all of which are affected in Beckwith-Weidermann syndrome, a human congenital syndrome characterized by foetal overgrowth and childhood tumours.

Animals↗

PubMed2001

Comparative sequence analysis of the imprinted Dlk1-Gtl2 locus in three mammalian species reveals highly conserved genomic elements and refines comparison with the Igf2-H19 region.

The Dlk1-Gtl2 domain on mouse chromosome 12 contains reciprocally imprinted genes with the potential to contribute to our understanding of common features involved in imprinting control. We have sequenced this conserved region in the mouse and sheep and included the human sequence in a three species comparison. This analysis resulted in a precise conservation map and identification of highly conserved sequence elements, some of which we have shown previously to be differentially methylated in the mouse. Additionally, this analysis facilitated identification of a CpG-rich tandem repeat array located approximately 13-15 kb upstream of Gtl2. Furthermore, we have identified a third imprinted transcript that overlaps with the last Dlk1 exon in the mouse. This transcript lacks a conserved open reading frame and is probably generated by cleavage of extended Dlk1 transcripts. Because Dlk1 and Gtl2 share many of the imprinting properties of the well-characterized Igf2-H19 domain, it has been proposed that the two regions may be regulated in the same way. Comparative genomic examination of the two domains indicates that although there are similarities, other features are very different, including the location of conserved CTCF-binding sites, and the level of conservation at regulatory regions.

Animals↗

PubMed2001

Balanced translocations for the analysis of imprinted regions of the mouse genome.

Experimental studies that investigate the functional and mechanistic properties of an imprinted locus require material in which the two parental chromosome homologs can be easily distinguished. The use of animals with uniparental duplications and deficiencies of imprinted regions of interest is one powerful approach. This material not only allows the successful analysis of the monoallelic expression and genome modifications associated with imprinting, but also is useful for studying the developmental roles of imprinted genes through the analysis of conceptuses in which the dosage of imprinted genes has been perturbed (1-3).

Animals↗

PubMed2000

Genetic imprinting: silencing elements have their say.

Tissue-specific silencing elements have been identified that are required for imprinting of the individual genes in the Igf2-H19 domain of the mouse genome. These elements further elaborate the differences between the two parental chromosomes, and add a new feature to parent-of-origin-specific gene regulatory complexes.

Animals↗

PubMed2000

Delta-like and gtl2 are reciprocally expressed, differentially methylated linked imprinted genes on mouse chromosome 12.

The distal portion of mouse chromosome 12 is imprinted. To date, however, Gtl2 is the only imprinted gene identified on chromosome 12. Gtl2 encodes multiple alternatively spliced transcripts with no apparent open reading frame. Using conceptuses with maternal or paternal uniparental disomy for chromosome 12 (UPD12), we found that Gtl2 is expressed from the maternal allele and methylated at the 5' end of the silent paternal allele. A reciprocally imprinted gene, Delta-like (Dlk), with homology to genes involved in the Notch signalling pathway was identified 80kb upstream of Gtl2. Dlk was expressed exclusively from the paternal allele in both the embryo and placenta, but the CpG-island promoter of Dlk was completely unmethylated on both parental alleles. Rather, a paternally methylated region was identified in the last exon of the active Dlk allele. The proximity, reciprocal imprinting and methylation in this domain are reminiscent of the co-ordinately regulated Igf2-H19 imprinted domain on mouse chromosome 7. Like H19 and Igf2, Gtl2 and Dlk were found to be co-expressed in the same tissues throughout development, though not after birth. These results have implications for the regulation, function and evolution of imprinted domains.

Alleles↗

PubMed2000

Increased IGF-II protein affects p57kip2 expression in vivo and in vitro: implications for Beckwith-Wiedemann syndrome.

In both human and mouse, the Igf2 gene, localized on chromosomes 11 and 7, respectively, is expressed from the paternally inherited chromosome in the majority of tissues. Insulin-like growth factor-II (IGF-II) plays an important role in embryonic growth, and aberrant IGF2 expression has been documented in several human pathologies, such as Beckwith-Wiedemann syndrome (BWS), and a wide variety of tumors. Human and mouse genetic data strongly implicate another gene, CDKN1C (p57(kip2)), located in the same imprinted gene cluster on human chromosome II, in BWS. p57(KIP2) is a cyclin-dependent kinase inhibitor and is required for normal mouse embryonic development. Mutations in CDKN1C (p57(kip2)) have been identified in a small proportion of patients with BWS, and removal of the gene from mice by targeted mutagenesis produces a phenotype with elements in common with this overgrowth syndrome. Patients with BWS with biallelic expression of IGF2 or with a CDKN1C (p57(kip2)) mutation, as well as overlapping phenotypes observed in two types of mutant mice, the p57(kip2) knockout and IGF-II-overexpressing mice, strongly suggest that the genes may act in a common pathway of growth control in situations where Igf2 expression is abnormal. Herein, we show that p57(kip2) expression is reduced on IGF-II treatment of primary embryo fibroblasts in a dose-dependent manner. In addition, p57(kip2) expression is down-regulated in mice with high serum levels of IGF-II. These data suggest that the effects of increased IGF-II in BWS may, in part, be mediated through a decrease in p57(kip2) gene expression.

3T3 Cells↗