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

Concise review: parthenote stem cells for regenerative medicine: genetic, epigenetic, and developmental features

Embryonic stem cells (ESCs) have the potential to provide unlimited cells and tissues for regenerative medicine. ESCs derived from fertilized embryos, however, will most likely be rejected by a patient's immune system unless appropriately immunomatched. Pluripotent stem cells (PSCs) genetically identical to a patient can now be established by reprogramming of somatic cells. However, practical applications of PSCs for personalized therapies are projected to be unfeasible because of the enormous cost and time required to produce clinical-grade cells for each patient. ESCs derived from parthenogenetic embryos (pESCs) that are homozygous for human leukocyte antigens may serve as an attractive alternative for immunomatched therapies for a large population of patients. In this study, we describe the biology and genetic nature of mammalian parthenogenesis and review potential advantages and limitations of pESCs for cell-based therapies.

Functional expression study of igf2 antisense transcript in mouse

Insulin-like growth factor antisense gene (Igf2as) expression was investigated in different mouse tissues during development, in differentiating C2C12 cells and in a ΔDMR1-U2 knockout mouse model. The expression levels of Igf2as were high in fetal and newborn liver and muscle tissues compared to adults. The Igf2as gene was also expressed in placenta and in brain. The expression data suggests that the Igf2as gene plays a role in early development of the mouse and in placenta. There was no consistent evidence for an interaction between Igf2 and Igf2as transcripts. Furthermore, in knockout placentas lacking Igf2as transcription, Igf2 expression was comparable to that in wild type. These results indicate that Igf2as does not regulate Igf2 sense transcripts. In previous studies, it was suggested that the ΔDMR1-U2 knockout mouse showing intrauterine growth restriction was caused by the absence of placenta-specific Igf2 P0 transcription. We conclude that the ΔDMR1-U2 deletion phenotype should be reconsidered in the light of a functional Igf2as gene.

Genome-wide analysis of DNA methylation in bovine placentas

Background

DNA methylation is an important epigenetic modification that is essential for epigenetic gene regulation in development and disease. To date, the genome-wide DNA methylation maps of many organisms have been reported, but the methylation pattern of cattle remains unknown.

Results

We showed the genome-wide DNA methylation map in placental tissues using methylated DNA immunoprecipitation combined with high-throughput sequencing (MeDIP-seq). In cattle, the methylation levels in the gene body are relatively high, whereas the promoter remains hypomethylated. We obtained thousands of highly methylated regions (HMRs), methylated CpG islands, and methylated genes from bovine placenta. DNA methylation levels around the transcription start sites of genes are negatively correlated with the gene expression level. However, the relationship between gene-body DNA methylation and gene expression is non-monotonic. Moderately expressed genes generally have the highest levels of gene-body DNA methylation, whereas the highly, and lowly expressed genes, as well as silent genes, show moderate DNA methylation levels. Genes with the highest expression show the lowest DNA methylation levels.

Conclusions

We have generated the genome-wide mapping of DNA methylation in cattle for the first time, and our results can be used for future studies on epigenetic gene regulation in cattle. This study contributes to the knowledge on epigenetics in cattle.

Sildenafil citrate increases fetal weight in a mouse model of fetal growth restriction with a normal vascular phenotype

Fetal growth restriction (FGR) is defined as the inability of a fetus to achieve its genetic growth potential and is associated with a significantly increased risk of morbidity and mortality. Clinically, FGR is diagnosed as a fetus falling below the 5(th) centile of customised growth charts. Sildenafil citrate (SC, Viagra™), a potent and selective phosphodiesterase-5 inhibitor, corrects ex vivo placental vascular dysfunction in FGR, demonstrating potential as a therapy for this condition. However, many FGR cases present without an abnormal vascular phenotype, as assessed by Doppler measures of uterine/umbilical artery blood flow velocity. Thus, we hypothesized that SC would not increase fetal growth in a mouse model of FGR, the placental-specific Igf2 knockout mouse, which has altered placental exchange capacity but normal placental blood flow. Fetal weights were increased (by 8%) in P0 mice following maternal SC treatment (0.4 mg/ml) via drinking water. There was also a trend towards increased placental weight in treated P0 mice (P = 0.056). Additionally, 75% of the P0 fetal weights were below the 5(th) centile, the criterion used to define human FGR, of the non-treated WT fetal weights; this was reduced to 51% when dams were treated with SC. Umbilical artery and vein blood flow velocity measures confirmed the lack of an abnormal vascular phenotype in the P0 mouse; and were unaffected by SC treatment. (14)C-methylaminoisobutyric acid transfer (measured to assess effects on placental nutrient transporter activity) per g placenta was unaffected by SC, versus untreated, though total transfer was increased, commensurate with the trend towards larger placentas in this group. These data suggest that SC may improve fetal growth even in the absence of an abnormal placental blood flow, potentially affording use in multiple sub-populations of individuals presenting with FGR.

Adaptations in placental phenotype depend on route and timing of maternal dexamethasone administration in mice

Synthetic glucocorticoids, like dexamethasone (dex), restrict growth of the fetus and program its adult physiology, in part by altering placental phenotype. The route and timing of dex administration determine the fetal and adult outcomes, but whether these factors affect placental phenotype remains unknown. This study compared placental morphology, amino acid transport, and gene expression in mice given dex orally or by subcutaneous injection over the periods of most rapid placental (Days [D] 11-16) or fetal (D14-19) growth (term is D21). Compared with untreated and saline-injected controls, both dex treatments reduced placental weight at D16 and 19 and fetal weight and total labyrinthine volume at D19 to a similar extent. Only oral dex treatment from D11 to D16 reduced labyrinthine fetal capillary volume on D16 and increased placental ¹⁴C-methylaminoisobutyric acid (MeAIB) clearance at D19, 3 days after treatment ended. Neither route of dex treatment altered placental expression of Slc38a, Hsd11b, or the glucocorticoid receptor, Nr3c1, at D16. In contrast, both routes of dex treatment from D14 to D19 increased placental Hsd11b2 expression and labyrinthine maternal vessel volume. Furthermore, injection per se altered placental expression of Nr3c1, Hsd11b1, and specific Slc38a isoforms in an age-related manner. Overall, MeAIB clearance was not related to Slc38a transporter expression but was correlated inversely with maternal corticosterone concentrations when dex was undetectable in maternal plasma at D19. The effects of dex on placental phenotype, therefore, depend on both the route and timing of administration and may relate to local glucocorticoid availability during and after the treatment period.

Placental weight: relation to maternal weight and growth parameters of full-term babies at birth and during childhood

Human growth is a continuous process. Studies defining placental effect on prenatal and postnatal human growth are few. We studied the anthropometric data of hundred mothers who gave birth at term after an uncomplicated singleton pregnancy, and their infants in relation to their placental weight using linear regression analysis. Mother weight, placental weight, and infant length (BL), weight (BW), and head circumference (HC) were obtained at birth and during childhood period (4.5 ± 2 years) of age. At birth, placental weights were correlated significantly with maternal weights (r = 0.21, P = 0.031). Placental weights were significantly correlated with growth parameters of the child at birth and during childhood. Infant BW (r = 0.71, r < 0.001), body mass index SDS (BMI SDS) (r = 0.589, P < 0.001), length SDS (LSDS) (0.567, P < 0.001) and HC (r = 0.699, P < 0.001). During childhood, placental weights were correlated with BMI SDS (r = 0.296, P = 0.002) and HtSDS = (r = 0.254, P = 0.009). LSDS at birth was correlated significantly with HtSDS during childhood (r = 0.445, P < 0.001). Placental weight represents a good marker of fetal growth (at birth) and significantly correlates with early childhood growth in full-term infants.

An obesogenic diet during mouse pregnancy modifies maternal nutrient partitioning and the fetal growth trajectory

In developed societies, high-sugar and high-fat (HSHF) diets are now the norm and are increasing the rates of maternal obesity during pregnancy. In pregnant rodents, these diets lead to cardiovascular and metabolic dysfunction in their adult offspring, but the intrauterine mechanisms involved remain unknown. This study shows that, relative to standard chow, HSHF feeding throughout mouse pregnancy increases maternal adiposity (+30%, P<0.05) and reduces fetoplacental growth at d 16 (-10%, P<0.001). At d 19, however, HSHF diet group pup weight had normalized, despite the HSHF diet group placenta remaining small and morphologically compromised. This altered fetal growth trajectory was associated with enhanced placental glucose and amino acid transfer (+35%, P<0.001) and expression of their transporters (+40%, P<0.024). HSHF feeding also up-regulated placental expression of fatty acid transporter protein, metabolic signaling pathways (phosphoinositol 3-kinase and mitogen-activated protein kinase), and several growth regulatory imprinted genes (Igf2, Dlk1, Snrpn, Grb10, and H19) independently of changes in DNA methylation. Obesogenic diets during pregnancy, therefore, alter maternal nutrient partitioning, partly through changes in the placental phenotype, which helps to meet fetal nutrient demands for growth near term. However, by altering provision of specific nutrients, dietary-induced placental adaptations have important roles in programming development with health implications for the offspring in later life.

Fetal growth factors and fetal nutrition

Optimal fetal growth is important for a healthy pregnancy outcome and also for lifelong health. Fetal growth is largely regulated by fetal nutrition, and mediated via the maternal and fetal glucose/insulin/insulin-like growth factor axes. Fetal nutrition may reflect maternal nutrition, but abnormalities of placental function can also affect fetal growth, as the placenta plays a key intermediary role in nutritional signalling between mother and fetus. Fetal nutrition also impacts on the development of key fetal endocrine systems such as the glucose-insulin and insulin-like growth factor axes. This is likely to contribute to the link between both fetal growth restriction and fetal overgrowth, and increased risks of obesity and impaired glucose tolerance in later life. This review focuses on the associations between maternal and fetal nutrition, fetal growth and later disease risk, with particular emphasis on the role of insulin-like growth factors and the importance of the periconceptional period.

The genome of the platyfish, Xiphophorus maculatus, provides insights into evolutionary adaptation and several complex traits

Several attributes intuitively considered to be typical mammalian features, such as complex behavior, live birth, and malignant diseases like cancer, also appeared several times independently in so-called “lower” vertebrates. The genetic mechanisms underlying the evolution of these elaborate traits are poorly understood. The platyfish, Xiphophorus maculatus, offers a unique model to better understand the molecular biology of such traits. Herein we detail sequencing of the platyfish genome. Integrating genome assembly with extensive genetic maps uncovered that fish, in contrast to mammals, exhibit an unexpected evolutionary stability of chromosomes. Genes associated with viviparity show signatures of positive selection identifying new putative functional domains and rare cases of parallel evolution. We also discovered that genes implicated in cognition possess an unexpected high rate of duplicate gene retention after the teleost genome duplication suggesting a hypothesis for the evolution of the great behavioral complexity in fish, which exceeds that in amphibians and reptiles.

Differential gene expression in the endometrium on gestation day 12 provides insight into sow prolificacy

BACKGROUND

Erhualian pigs, one of Chinese Taihu pig breeds, are known to have the largest recorded litter size in the world. A lower prenatal death rate is the major contributing factor to the prolificacy of Taihu pigs. Cross-breeding experiments have demonstrated that Taihu sows exhibit a strong maternal effect and that their large litter sizes are mainly caused by maternal genes. The growth and development of porcine embryos on gestation day (GD) 12 are dependent on histotroph secreted by endometrium. Embryonic loss of Taihu pigs on GD12 is lower than that of Western pigs. Here, endometrial samples were collected from pregnant Erhualian sows (parity 3) and Landrace × Large White (LL) sows (parity 3) on GD12. Digital gene expression profiling (DGE) was used to measure the gene expression in the endometrium of the two breeds.

RESULTS

A total of 13,612 genes were differentially expressed between the two breeds (P < 0.001, FDR < 0.001). Gene Ontology (GO) analysis showed that the differential genes involved in reproduction and growth. Pathway analysis revealed that the differentially expressed genes significantly enriched in 24 KEGG pathways. Quantitative real-time RT-PCR confirmed the differential expression of eight genes. Analyses of the differentially expressed genes suggested possible reasons for the difference in embryonic survival ratio between the two breeds. Specifically, these findings point to a higher ratio of PGE2:PGF2α in the endometrium of Erhualian pigs, which facilitates the establishment and maintenance of pregnancy. We also suggest that the differences in the uterine environment lead to higher uterine capacity in Erhualian pigs.

CONCLUSIONS

The DGE expression profiles of Erhualian and LL endometrium demonstrated differential expression of genes. Our results will increase understanding of the molecular mechanisms of the low rate of embryonic loss in Chinese Taihu pigs, facilitate the identification of major genes that affect litter size, and be valuable for porcine transcriptomic studies.

Quantitative allele-specific expression and DNA methylation analysis of H19, IGF2 and IGF2R in the human placenta across gestation reveals H19 imprinting plasticity

Imprinted genes play important roles in placental differentiation, growth and function, with profound effects on fetal development. In humans, H19 and IGF2 are imprinted, but imprinting of IGF2R remains controversial. The H19 non-coding RNA is a negative regulator of placental growth and altered placental imprinting of H19-IGF2 has been associated with pregnancy complications such as preeclampsia, which have been attributed to abnormal first trimester placentation. This suggests that changes in imprinting during the first trimester may precede aberrant placental morphogenesis. To better understand imprinting in the human placenta during early gestation, we quantified allele-specific expression for H19, IGF2 and IGF2R in first trimester (6–12 weeks gestation) and term placentae (37–42 weeks gestation) using pyrosequencing. Expression of IGF2R was biallelic, with a mean expression ratio of 49∶51 (SD = 0.07), making transient imprinting unlikely. Expression from the repressed H19 alleles ranged from 1–25% and was higher (P<0.001) in first trimester (13.5±8.2%) compared to term (3.4±2.1%) placentae. Surprisingly, despite the known co-regulation of H19 and IGF2, little variation in expression of the repressed IGF2 alleles was observed (2.7±2.0%). To identify regulatory regions that may be responsible for variation in H19 allelic expression, we quantified DNA methylation in the H19-IGF2 imprinting control region and H19 transcription start site (TSS). Unexpectedly, we found positive correlations (P<0.01) between DNA methylation levels and expression of the repressed H19 allele at 5 CpG’s 2000 bp upstream of the H19 TSS. Additionally, DNA methylation was significantly higher (P<0.05) in first trimester compared with term placentae at 5 CpG’s 39–523 bp upstream of the TSS, but was not correlated with H19 repressed allele expression. Our data suggest that variation in H19 imprinting may contribute to early programming of placental phenotype and illustrate the need for quantitative and robust methodologies to further elucidate the role of imprinted genes in normal and pathological placental development.

Crossing mice deficient in eNOS with placental-specific Igf2 knockout mice: a new model of fetal growth restriction

We tested the hypothesis that crossing two mouse models of fetal growth restriction (FGR) of differing phenotype would induce more severe FGR than either model alone. Female endothelial nitric oxide synthase knockout mice (eNOS(-/-)) were mated with placental-specific Igf2 knockout males (P0). Resultant fetuses were no more growth restricted than those with P0 deletion alone. However, P0 deletion attenuated the reduced placental system A amino acid transporter activity previously observed in eNOS(-/-) mice. Manipulating maternal and fetal genotypes provides a means to compare maternal and fetal regulation of fetal growth.

Sertraline alters multidrug resistance phosphoglycoprotein activity in the mouse placenta and fetal blood-brain barrier

Phosphoglycoprotein (P-gp) is highly expressed in the placental syncytiotrophoblast and prevents xenobiotics from entering the fetus. In tumor cells, P-gp-mediated substrate efflux is inhibited by selective serotonin reuptake inhibitors (SSRIs). However, nothing is known regarding the effects of SSRIs on P-gp function in the placenta or fetal tissues. We hypothesized that the SSRI sertraline would decrease P-gp-mediated drug efflux at the placenta and fetal blood-brain barrier (BBB)-increasing P-gp substrate transfer from the mother to the fetus and fetal brain. In contrast to our hypothesis, this study presents the novel findings that sertraline (4 hours exposure) increases placental P-gp-mediated efflux (P < .001), resulting in decreased drug transfer to the fetus. Meanwhile, sertraline decreases fetal (P < .001) and maternal (P < .05) BBB P-gp-mediated efflux, resulting in increased drug transfer into the fetal and maternal brain from the circulation. This suggests that P-gp regulation by sertraline is tissue specific. These findings have important clinical implications with respect to fetal protection during maternal drug therapy in pregnancy.

Maternal corticosterone regulates nutrient allocation to fetal growth in mice

Stresses during pregnancy that increase maternal glucocorticoids reduce birth weight in several species. However, the role of natural glucocorticoids in the mother in fetal acquisition of nutrients for growth remains unknown. This study aimed to determine whether fetal growth was reduced as a consequence of altered amino acid supply when mice were given corticosterone in their drinking water for 5 day periods in mid to late pregnancy (day, D, 11-16 or D14-19). Compared to controls drinking tap water, fetal weight was always reduced by corticosterone. At D16, corticosterone had no effect on materno-fetal transfer of [(14)C]methylaminoisobutyric acid (MeAIB), although placental MeAIB accumulation and expression of the Slc38a1 and Slc38a2 transporters were increased. However, at D19, 3 days after treatment ended, materno-fetal transfer of MeAIB was increased by 37% (P < 0.04). During treatment at D19, placental accumulation and materno-fetal transfer of MeAIB were reduced by 40% (P < 0.01), although expression of Slc38a1 was again elevated. Permanent reductions in placental vascularity occurred during the earlier but not the later period of treatment. Placental Hsd11b2 expression, which regulates feto-placental glucocorticoid bioavailability, was also affected by treatment at D19 only. Maternal corticosterone concentrations inversely correlated with materno-fetal MeAIB clearance and fetal weight at D19 but not D16. On D19, weight gain of the maternal carcass was normal during corticosterone treatment but reduced in those mice treated from D11 to D16, in which corticosterone levels were lowest. Maternal corticosterone is, therefore, a physiological regulator of the amino acid supply for fetal growth via actions on placental phenotype.

Environmental regulation of placental phenotype: implications for fetal growth

Environmental conditions during pregnancy determine birthweight, neonatal viability and adult phenotype in human and other animals. In part, these effects may be mediated by the placenta, the principal source of nutrients for fetal development. However, little is known about the environmental regulation of placental phenotype. Generally, placental weight is reduced during suboptimal conditions like maternal malnutrition or hypoxaemia but compensatory adaptations can occur in placental nutrient transport capacity to help maintain fetal growth. In vivo studies show that transplacental glucose and amino acid transfer adapt to the prevailing conditions induced by manipulating maternal calorie intake, dietary composition and hormone exposure. These adaptations are due to changes in placental morphology, metabolism and/or abundance of specific nutrient transporters. This review examines environmental programming of placental phenotype with particular emphasis on placental nutrient transport capacity and its implications for fetal growth, mainly in rodents. It also considers the systemic, cellular and molecular mechanisms involved in signalling environmental cues to the placenta. Ultimately, the ability of the placenta to balance the competing interests of mother and fetus in resource allocation may determine not only the success of pregnancy in producing viable neonates but also the long-term health of the offspring.

Promoter-specific expression and imprint status of marsupial IGF2

In mice and humans, IGF2 has multiple promoters to maintain its complex tissue- and developmental stage-specific imprinting and expression. IGF2 is also imprinted in marsupials, but little is known about its promoter region. In this study, three IGF2 transcripts were isolated from placental and liver samples of the tammar wallaby, Macropus eugenii. Each transcript contained a unique 5' untranslated region, orthologous to the non-coding exons derived from promoters P1–P3 in the human and mouse IGF2 locus. The expression of tammar IGF2 was predominantly from the P2 promoter, similar to humans. Expression of IGF2 was higher in pouch young than in the adult and imprinting was highly tissue and developmental-stage specific. Interestingly, while IGF2 was expressed throughout the placenta, imprinting seemed to be restricted to the vascular, trilaminar region. In addition, IGF2 was monoallelically expressed in the adult mammary gland while in the liver it switched from monoalleleic expression in the pouch young to biallelic in the adult. These data suggest a complex mode of IGF2 regulation in marsupials as seen in eutherian mammals. The conservation of the IGF2 promoters suggests they originated before the divergence of marsupials and eutherians, and have been selectively maintained for at least 160 million years.

Impaired placental nutrient transport in mice generated by in vitro fertilization

More than 4.5 million children have been conceived by in vitro fertilization (IVF). Interestingly, singleton IVF offspring born at term have an increased incidence of low birth weight. The mechanism responsible for the lower birth weight is unknown, but alterations in placental function are possible. Hence, the goal of our study was to examine placental growth and function in mice generated in vivo or in vitro. To assess placental function, blastocysts were generated by IVF or produced by natural mating (control group); both IVF and control blastocysts were transferred to pseudopregnant recipients. Placental weights did not differ at embryonic d 15.5 (E15.5) but were increased at E18.5 in the IVF group (25.4%, P < 0.001) compared with control. Proliferation was increased in IVF placentae, whereas overall placental gross morphology and apoptosis were not affected. Both fetal weights (16.4% lower at E15.5 and 8.8% lower at E18.5, P < 0.05) and fetal to placental ratios were lower (P < 0.001) in the IVF compared with the control group at both time points, whereas birth weights did not differ. At E18.5, the mRNA for selected glucose, system A amino acid transporters, and imprinted genes were down-regulated in IVF placentae. GLUT3 protein level was decreased in the IVF group (P < 0.05). Importantly, intrajugular injections of (14)C-methyl-D-glucose or (14)C-MeAIB tracers (n = 6 litters per group) showed that placental transport of glucose and amino acids were 24.8% (not significant) and 58.1% (P < 0.05) lower in the IVF group. Fetal accumulation of glucose was not different, but amino acid accumulation was significantly (36 %) lower in IVF fetuses (P < 0.05). We conclude that IVF alters both fetal and placental growth and, importantly, decreases placental transport efficiency in mice conceived by IVF.

Placental adaptations to the maternal-fetal environment: implications for fetal growth and developmental programming

The placenta is a transient organ found in eutherian mammals that evolved primarily to provide nutrients for the developing fetus. The placenta exchanges a wide array of nutrients, endocrine signals, cytokines and growth factors with the mother and the fetus, thereby regulating intrauterine development. Recent studies show that the placenta is not just a passive organ mediating maternal-fetal exchange. It can adapt its capacity to supply nutrients in response to intrinsic and extrinsic variations in the maternal-fetal environment. These dynamic adaptations are thought to occur to maximize fetal growth and viability at birth in the prevailing conditions in utero. However, some of these adaptations may also affect the development of individual fetal tissues, with patho-physiological consequences long after birth. Here, this review summarizes current knowledge on the causes, possible mechanisms and consequences of placental adaptive responses, with a focus on the regulation of transporter-mediated processes for nutrients. This review also highlights the emerging roles that imprinted genes and epigenetic mechanisms of gene regulation may play in placental adaptations to the maternal-fetal environment.

Biology and significance of signalling pathways activated by IGF-II

Insulin-like growth factor-II (IGF-II) affects many aspects of cellular function through its ability to activate several different receptors and, consequently, numerous intracellular signalling molecules. Thus, IGF-II is a key regulator of normal foetal development and growth. However, abnormalities in IGF-II function are associated with cardiovascular disease and cancer. Here, we review the cellular mechanisms by which IGF-II's physiological and pathophysiological actions are exerted by discussing the involvement of the type 1 and type 2 IGF receptors (IGF1R and IGF2R), the insulin receptor and the downstream MAP kinase, PI-3 kinase and G-protein-coupled signalling pathways in mediating IGF-II stimulated cellular proliferation, survival, differentiation and migration.

DNA methylation in the human placenta and fetal growth (review)

Throughout in utero development, the placenta plays a key role in controlling growth and development. The placenta acts not only as a gatekeeper of nutrient and waste exchange between mother and developing fetus, but also as a regulator of the intrauterine environment. Its functions can be influenced by the environment encountered throughout pregnancy, thereby altering the appropriate genetic programming needed to allow for appropriate fetal growth. Epigenetic alterations related to environmental exposures have been linked to aberrant fetal growth. DNA methylation, which is the best known DNA epigenetic modification, may provide an attractive mechanism linking environmental cues to placental pathology, with consequences for fetal growth and adult life. Alteration of the methylation patterns of genes expressed in the placenta has recently been found to modify gene expression and subsequently impair function of the placenta. Although there is strong evidence to demonstrate that the environment can affect the pattern of DNA methylation of the placenta during fetal development, a direct association between environmental conditions, methylation alterations and gene expression is difficult to confirm. DNA methylation in the placenta has mainly been investigated in the context of imprinted and non-imprinted genes transcription. Several environmental factors have also been assessed in regard to their association with changes to the epigenetic motives of embryonic and extraembryonic tissues and their impact on pregnancy outcome. In this review, we briefly present the available evidence regarding the role of DNA methylation patterns of the placenta on aberrant fetal growth.

Maternal protein restriction regulates IGF2 system in placental labyrinth

This study was to test the hypothesis that altered IGF2 system in the placental labyrinth zone (LZ) impairs feto-placental growth in response to maternal protein restriction. Rats were fed a 20% protein diet and an isocaloric 6 % protein diet (LP) from day 1 to days 14, 18, or 21 of pregnancy. The effects of diet, gender of placenta and fetus, and day of pregnancy on placental weight, fetal weight, and expression of the IGF2 axis in the placental LZ and amino acids in maternal plasma were analyzed. Growth restriction occurred in both female and male fetuses by LP, coincident with impaired LZ growth and efficiency. The expression of Igf2, Igf2P0, Igf1r, Igf2r, Insr, Igfbp1, and Igfbp2 in placental LZ were affected by diet, gender and/or day of pregnancy. Concentrations of total essential amino acids and total nonessential amino acids were reduced and increased, respectively, in maternal plasma of LP-fed rats. These results indicate that adaptation of the IGF2 system in rat LZ occurs in a sex- and time-dependent manner in response to maternal protein restriction; however, these adaptations cannot prevent the growth restriction of both male and female fetuses during late pregnancy.

Insulin-like growth factor-II: new roles for an old actor

Insulin-like growth factor-II (IGF-II), traditionally considered as a growth factor implicated in growth of fetal tissues and cancer cells, is now emerging as a potential metabolic regulator. The aim of this overview is to provide the available evidence, obtained in both experimental conditions and in humans, for a role of IGF-II in the fine-tuning of metabolism and body composition. The underlying mechanisms and the potential clinical implications are discussed.

Maternal protein restriction regulates IGF2 system in placental labyrinth

This study was to test the hypothesis that altered IGF2 system in the placental labyrinth zone (LZ) impairs feto-placental growth in response to maternal protein restriction. Rats were fed a 20% protein diet and an isocaloric 6 % protein diet (LP) from day 1 to days 14, 18, or 21 of pregnancy. The effects of diet, gender of placenta and fetus, and day of pregnancy on placental weight, fetal weight, and expression of the IGF2 axis in the placental LZ and amino acids in maternal plasma were analyzed. Growth restriction occurred in both female and male fetuses by LP, coincident with impaired LZ growth and efficiency. The expression of Igf2, Igf2P0, Igf1r, Igf2r, Insr, Igfbp1, and Igfbp2 in placental LZ were affected by diet, gender and/or day of pregnancy. Concentrations of total essential amino acids and total nonessential amino acids were reduced and increased, respectively, in maternal plasma of LP-fed rats. These results indicate that adaptation of the IGF2 system in rat LZ occurs in a sex- and time-dependent manner in response to maternal protein restriction; however, these adaptations cannot prevent the growth restriction of both male and female fetuses during late pregnancy.

Antenatal dexamethasone treatment in midgestation reduces system A-mediated transport in the late-gestation murine placenta

Clinically, approximately 30% of women who receive synthetic glucocorticoids (sGC) for risk of preterm labor carry to term. In vitro studies have shown that sGC acutely regulate the placental system A amino acid transporter, but there are no comparable data in vivo. Hence, the objective of our study was to examine the acute [embryonic day (E)15.5] and longer-term (E17.5 and E18.5) consequences of midgestation antenatal sGC [dexamethasone (DEX); 0.1 mg/kg on E13.5 and E14.5] on placental system A-mediated transfer in the mouse (measured in vivo as maternal-fetal unidirectional (14)C-methylaminoisobutyric acid transfer per gram of placenta). System A transfer and Slc38a mRNA expression significantly increased from E12.5 to E18.5 (P < 0.05), corresponding to increased fetal growth. DEX treatment had no acute effect at E15.5 or longer-term effect at E17.5 but significantly decreased system A-mediated transfer before term (E18.5; P < 0.05) in placentae of male and female fetuses. There was no effect of DEX on Slc38a gene expression. Administration of DEX in this regime had no effect on birth weight. We conclude that sGC treatment in midgestation leads to a substantial decrease in placental system A-mediated transport in late gestation, suggesting that prenatal sGC therapy may lead to a reduction in availability of neutral amino acids to the fetus if gestation persists to term.

System A activity and vascular function in the placental-specific Igf2 knockout mouse

OBJECTIVES

Deletion of the placental-specific P0 transcript of the insulin-like growth factor gene (Igf2) reduces placental growth from early pregnancy onwards. In Igf2 P0 knockout fetuses (P0), maternofetal flux of (14)C-methylaminoisobutyric acid ((14)C-MeAIB) mediated by system A amino acid transporter activity is increased at embryonic day 16 (E16), but this stimulation is not sustained, and by E19, fetal growth restriction (FGR) ensues. Here, we investigated whether upregulated (14)C-MeAIB transfer does occur concomitantly with a change in System A amino acid transporter activity and whether altered uteroplacental vascular function contributes to the FGR. We tested the hypothesis that FGR in P0 mice is attributable to altered nutrient transport rather than aberrant uteroplacental vascular function.

METHODS

Plasma membrane vesicles were isolated from placentas of P0 and wild-type (WT) fetuses at E16 and E19. System A amino acid transporter activity was measured as sodium-dependent (14)C-MeAIB uptake over 60s. Wire myography was performed on uterine artery branches supplying P0 or WT implantation sites and agonist-induced constriction and dilation measured.

RESULTS

Sodium-dependent uptake of (14)C-MeAIB (at 60s) was significantly (P < 0.05) higher in P0 compared to WT vesicles at E16; at E19 (14)C-MeAIB uptake was similar between P0 and WT. Uterine artery branch vascular reactivity was comparable between groups.

CONCLUSIONS

System A activity in the maternal-facing plasma membrane of syncytiotrophoblast layer II underpins the adaptations observed in the transplacental MeAIB flux of P0 mice. Unaltered uterine artery vascular function suggests that the FGR phenotype of P0 fetuses is primarily due to deficient placental nutrient exchange capacity.

Placental-specific Igf2 deficiency alters developmental adaptations to undernutrition in mice

The pattern of fetal growth is a major determinant of the subsequent health of the infant. We recently showed in undernourished (UN) mice that fetal growth is maintained until late pregnancy, despite reduced placental weight, through adaptive up-regulation of placental nutrient transfer. Here, we determine the role of the placental-specific transcript of IGF-II (Igf2P0), a major regulator of placental transport capacity in mice, in adapting placental phenotype to UN. We compared the morphological and functional responses of the wild-type (WT) and Igf2P0-deficient placenta in WT mice fed ad libitium or 80% of the ad libitium intake. We observed that deletion of Igf2P0 prevented up-regulation of amino acid transfer normally seen in UN WT placenta. This was associated with a reduction in the proportion of the placenta dedicated to nutrient transport, the labyrinthine zone, and its constituent volume of trophoblast in Igf2P0-deficient placentas exposed to UN on d 16 of pregnancy. Additionally, Igf2P0-deficient placentas failed to up-regulate their expression of the amino acid transporter gene, Slc38a2, and down-regulate phosphoinositide 3-kinase-protein kinase B signaling in response to nutrient restriction on d 19. Furthermore, deleting Igf2P0 altered maternal concentrations of hormones (insulin and corticosterone) and metabolites (glucose) in both nutritional states. Therefore, Igf2P0 plays important roles in adapting placental nutrient transfer capacity during UN, via actions directly on the placenta and/or indirectly through the mother.

Dietary composition programmes placental phenotype in mice

Dietary composition during pregnancy influences fetal and adult phenotype but its effects on placental phenotype remain largely unknown. Using molecular, morphological and functional analyses, placental nutrient transfer capacity was examined in mice fed isocaloric diets containing 23%, 18% or 9% casein (C) during pregnancy. At day 16, placental transfer of glucose, but not methyl-aminoisobutyric acid (MeAIB), was greater in C18 and C9 than C23 mice, in association with increased placental expression of the glucose transporter Slc2a1/GLUT1, and the growth factor Igf2. At day 19, placental glucose transport remained high in C9 mice while MeAIB transfer was less in C18 than C23 mice, despite greater placental weights in C18 and C9 than C23 mice. Placental System A amino acid transporter expression correlated with protein intake at day 19. Relative growth of transport verses endocrine zones of the placenta was influenced by diet at both ages without changing the absolute volume of the transport surface. Fetal weight was unaffected by diet at day 16 but was reduced in C9 animals by day 19. Morphological and functional adaptations in placental phenotype, therefore, occur to optimise nutrient transfer when dietary composition is varied, even subtly. This has important implications for the intrauterine programming of life expectancy.

Mammalian genomic imprinting

Normal mammalian development requires a maternal and paternal contribution, which is attributed to imprinted genes, or genes that are expressed from a single parental allele. Approximately 100 imprinted genes have been reported in mammals thus far. Imprinted genes are controlled by cis-acting regulatory elements, termed imprinting control regions (ICRs), which have parental-specific epigenetic modifications, including DNA methylation. ICRs are methylated by de novo DNA methyltransferases during germline development; these parental-specific modifications must be maintained following fertilization when the genome is extensively reprogrammed. Many imprinted genes reside in ∼1-megabase clusters, with two major mechanisms of imprinting regulation currently recognized, CTCF-dependent insulators and long noncoding RNAs. Unclustered imprinted genes are generally regulated by germline-derived differential promoter methylation. Here, we describe the identification and functions of imprinted genes, cis-acting control sequences, trans-acting factors, and imprinting mechanisms in clusters. Finally, we define questions that require more extensive research.

Imprinted genes and the epigenetic regulation of placental phenotype

Imprinted genes are expressed in a parent-of-origin manner by epigenetic modifications that silence either the paternal or maternal allele. They are widely expressed in fetal and placental tissues and are essential for normal placental development. In general, paternally expressed genes enhance feto-placental growth while maternally expressed genes limit conceptus growth, consistent with the hypothesis that imprinting evolved in response to the conflict between parental genomes in the allocation of maternal resources to fetal growth. Using targeted deletion, uniparental duplication, loss of imprinting and transgenic approaches, imprinted genes have been shown to determine the transport capacity of the definitive mouse placenta by regulating its growth, morphology and transporter abundance. Imprinted genes in the placenta are also responsive to environmental challenges and adapt placental phenotype to the prevailing nutritional conditions, in part, by varying their epigenetic status. In addition, interplay between placental and fetal imprinted genes is important in regulating resource partitioning via the placenta both developmentally and in response to environmental factors. By balancing the opposing parental drives on resource allocation with the environmental signals of nutrient availability, imprinted genes, like the Igf2-H19 locus, may act as nutrient sensors and optimise the fetal acquisition of nutrients for growth. These genes, therefore, have a major role in the epigenetic regulation of placental phenotype with long term consequences for the developmental programming of adult health and disease.

Expression and methylation status of imprinted genes in placentas of deceased and live cloned transgenic calves

Placental deficiencies are linked with developmental abnormalities in cattle produced by somatic cell nuclear transfer (SCNT). To investigate whether the aberrant expression of imprinted genes in placenta was responsible for fetal overgrowth and placental hypertrophy, quantitative expression analysis of six imprinted genes (H19, XIST, IGF2R, SNRPN, PEG3, and IGF2) was conducted in placentas of: 1) deceased (died during perinatal period) transgenic calves (D group, n = 4); 2) live transgenic calves (L group, n = 15); and 3) conventionally produced (control) female calves (N group, n = 4). In this study, XIST, PEG3 and IGF2 were significantly over-expressed in the D group, whereas expression of H19 and IGF2R was significantly reduced in the D group compared to controls. The DNA methylation patterns in the differentially methylated region (DMR) from H19, XIST, and IGF2R were compared using Bisulfite Sequencing PCR (BSP) and Combined Bisulfite Restriction Analysis (COBRA). In the D group, H19 DMR was significantly hypermethylated, but XIST DMR and IGF2R ICR were significantly hypomethylated compared to controls. In contrast, there were no noticeable differences in the expression and DNA methylation status of imprinted genes (except DNA methylation level of XIST DMR) in the L group compared to controls. In conclusion, altered DNA methylation levels in the DMRs of imprinted genes in placentas of deceased transgenic calves, presumably due to aberrant epigenetic nuclear reprogramming during SCNT, may have been associated with abnormal expression of these genes; perhaps this caused developmental insufficiencies and ultimately death in cloned transgenic calves.

Sex- and diet-specific changes of imprinted gene expression and DNA methylation in mouse placenta under a high-fat diet

BACKGROUND

Changes in imprinted gene dosage in the placenta may compromise the prenatal control of nutritional resources. Indeed monoallelic behaviour and sensitivity to changes in regional epigenetic state render imprinted genes both vulnerable and adaptable.

METHODS AND FINDINGS

We investigated whether a high-fat diet (HFD) during pregnancy modified the expression of imprinted genes and local and global DNA methylation patterns in the placenta. Pregnant mice were fed a HFD or a control diet (CD) during the first 15 days of gestation. We compared gene expression patterns in total placenta homogenates, for male and female offspring, by the RT-qPCR analysis of 20 imprinted genes. Sexual dimorphism and sensitivity to diet were observed for nine genes from four clusters on chromosomes 6, 7, 12 and 17. As assessed by in situ hybridization, these changes were not due to variation in the proportions of the placental layers. Bisulphite-sequencing analysis of 30 CpGs within the differentially methylated region (DMR) of the chromosome 17 cluster revealed sex- and diet-specific differential methylation of individual CpGs in two conspicuous subregions. Bioinformatic analysis suggested that these differentially methylated CpGs might lie within recognition elements or binding sites for transcription factors or factors involved in chromatin remodelling. Placental global DNA methylation, as assessed by the LUMA technique, was also sexually dimorphic on the CD, with lower methylation levels in male than in female placentae. The HFD led to global DNA hypomethylation only in female placenta. Bisulphite pyrosequencing showed that neither B1 nor LINE repetitive elements could account for these differences in DNA methylation.

CONCLUSIONS

A HFD during gestation triggers sex-specific epigenetic alterations within CpG and throughout the genome, together with the deregulation of clusters of imprinted genes important in the control of many cellular, metabolic and physiological functions potentially involved in adaptation and/or evolution. These findings highlight the importance of studying both sexes in epidemiological protocols and dietary interventions.

Maternal-placental insulin-like growth factor (IGF) signaling and its importance to normal embryo-fetal development

As background for an antibody-based therapeutic program against the IGF receptor, we undertook a review of available information on the early pregnancy-specific regulation and localization of IGFs, IGF-binding proteins (BPs), IGFBP-specific proteases, and the type 1 IGF receptor relative to placental maintenance, function of placental nutrient transporters, placental cellular differentiation/turnover/apoptosis, and critical hormone signaling needed to maintain pregnancy. Possible adverse outcomes of altered IGF signaling include prenatal loss, fetal growth retardation, and maldevelopment are also discussed. It appears that the IGF axes in both the conceptus and mother are important for normal embryo-fetal growth. Thus, all molecules (i.e., both small and large) that disrupt the IGF axis could be expected to have some degree of fetal consequences.

IGF2 actions on trophoblast in human placenta are regulated by the insulin-like growth factor 2 receptor, which can function as both a signaling and clearance receptor

Insulin-like growth factor 2 (IGF2) enhances proliferation and survival of human first-trimester cytotrophoblasts (CTB) by signaling through the insulin-like growth factor 1 receptor (IGF1R). However, the role of the IGF2 receptor (IGF2R) in regulating trophoblast kinetics is unclear: It could act as a clearance receptor for trafficking excess ligand to lysosomes for degradation and/or directly mediate IGF2 signaling. We used an IGF2R knockdown strategy in BeWo cells and placental villous explants to investigate trophoblast proliferation and survival in response to stimulation by IGF. Both IGF1 and IGF2 significantly (P < 0.001) increased mitosis and reduced apoptosis in serum-starved BeWo cells. Small interfering RNA (siRNA)-mediated knockdown of IGF2R further enhanced IGF2-stimulated mitosis (P < 0.01), and IGF2-mediated rescue of apoptosis (P < 0.001) in these cells. Leu(27)IGF2, an IGF2 analogue that binds to IGF2R but not IGF1R, also protected IGF2R-expressing BeWo cells from apoptosis but did not increase mitosis. IGF treatment of term placental villous explants with reduced syncytial expression of IGF2R increased CTB proliferation (P < 0.001) and decreased apoptosis (P < 0.01) compared to untreated controls. Moreover, IGF2-mediated rescue of CTB apoptosis was significantly greater than that in tissue with normal IGF2R expression. Leu(27)IGF2 promoted mitogenesis and survival only in explants with intact IGF2R expression. Given that altered CTB turnover is observed in pregnancies complicated by fetal growth restriction, the development of strategies to manipulate the IGF2R signaling axis in the syncytiotrophoblast may provide a therapeutic avenue for treating this condition.

Epigenetics and the placenta

BACKGROUND

The placenta is of utmost importance for intrauterine fetal development and growth. Deregulation of placentation can lead to adverse outcomes for both mother and fetus, e.g. gestational trophoblastic disease (GTD), pre-eclampsia and fetal growth retardation. A significant factor in placental development and function is epigenetic regulation.

METHODS

This review summarizes the current knowledge in the field of epigenetics in relation to placental development and function. Relevant studies were identified by searching PubMed, Medline and reference sections of all relevant studies and reviews.

RESULTS

Epigenetic regulation of the placenta evolves during preimplantation development and further gestation. Epigenetic marks, like DNA methylation, histone modifications and non-coding RNAs, affect gene expression patterns. These expression patterns, including the important parent-of-origin-dependent gene expression resulting from genomic imprinting, play a pivotal role in proper fetal and placental development. Disturbed placental epigenetics has been demonstrated in cases of intrauterine growth retardation and small for gestational age, and also appears to be involved in the pathogenesis of pre-eclampsia and GTD. Several environmental effects have been investigated so far, e.g. ethanol, oxygen tension as well as the effect of several aspects of assisted reproduction technologies on placental epigenetics.

CONCLUSIONS

Studies in both animals and humans have made it increasingly clear that proper epigenetic regulation of both imprinted and non-imprinted genes is important in placental development. Its disturbance, which can be caused by various environmental factors, can lead to abnormal placental development and function with possible consequences for maternal morbidity, fetal development and disease susceptibility in later life.

The importance of imprinting in the human placenta

As a field of study, genomic imprinting has grown rapidly in the last 20 years, with a growing figure of around 100 imprinted genes known in the mouse and approximately 50 in the human. The imprinted expression of genes may be transient and highly tissue-specific, and there are potentially hundreds of other, as yet undiscovered, imprinted transcripts. The placenta is notable amongst mammalian organs for its high and prolific expression of imprinted genes. This review discusses the development of the human placenta and focuses on the function of imprinting in this organ. Imprinting is potentially a mechanism to balance parental resource allocation and it plays an important role in growth. The placenta, as the interface between mother and fetus, is central to prenatal growth control. The expression of genes subject to parental allelic expression bias has, over the years, been shown to be essential for the normal development and physiology of the placenta. In this review we also discuss the significance of genes that lack conservation of imprinting between mice and humans, genes whose imprinted expression is often placental-specific. Finally, we illustrate the importance of imprinting in the postnatal human in terms of several human imprinting disorders, with consideration of the brain as a key organ for imprinted gene expression after birth.

Placental-specific Igf2 knockout mice exhibit hypocalcemia and adaptive changes in placental calcium transport

Evidence is emerging that the ability of the placenta to supply nutrients to the developing fetus adapts according to fetal demand. To examine this adaptation further, we tested the hypothesis that placental maternofetal transport of calcium adapts according to fetal calcium requirements. We used a mouse model of fetal growth restriction, the placental-specific Igf2 knockout (P0) mouse, shown previously to transiently adapt placental System-A amino acid transporter activity relative to fetal growth. Fetal and placental weights in P0 mice were reduced when compared with WT at both embryonic day 17 (E17) and E19. Ionized calcium concentration [Ca(2+)] was significantly lower in P0 fetal blood compared with both WT and maternal blood at E17 and E19, reflecting a reversal of the fetomaternal [Ca(2+)] gradient. Fetal calcium content was reduced in P0 mice at E17 but not at E19. Unidirectional maternofetal calcium clearance ((Ca) K (mf)) was not different between WT and P0 at E17 but increased in P0 at E19. Expression of the intracellular calcium-binding protein calbindin-D(9K), previously shown to be rate-limiting for calcium transport, was increased in P0 relative to WT placentas between E17 and E19. These data show an increased placental transport of calcium from E17 to E19 in P0 compared to WT. We suggest that this is an adaptation in response to the reduced fetal calcium accumulation earlier in gestation and speculate that the ability of the placenta to adapt its supply capacity according to fetal demand may stretch across other essential nutrients.

Gene expression in the placenta: maternal stress and epigenetic responses

Successful placental development is crucial for optimal growth, development, maturation and survival of the embryo/fetus into adulthood. Numerous epidemiologic and experimental studies have demonstrated the profound influence of intrauterine environment on life, and the diseases to which one is subject as an adult. For the most part, these invidious influences, whether maternal hypoxia, protein or caloric deficiency or excess, and others, represent types of maternal stress. In the present review, we examine certain aspects of gene expression in the placenta as a consequence of maternal stressors. To examine these issues in a controlled manner, and in a species in which the genome has been sequenced, most of these reported studies have been performed in the mouse. Although each individual maternal stress is characterized by up- or down-regulation of specific genes in the placenta, functional analysis reveals some patterns of gene expression common to the several forms of stress. Of critical importance, these genes include those involved in DNA methylation and histone modification, cell cycle regulation, and related global pathways of great relevance to epigenesis and the developmental origins of adult health and disease.

Adaptations in placental phenotype support fetal growth during undernutrition of pregnant mice

Undernutrition during pregnancy reduces birth weight and programmes adult phenotype with consequences for life expectancy, but its effects on the phenotype of the placenta, responsible for supplying nutrients for fetal growth, remain largely unknown. Using molecular, morphological and functional analyses, placental phenotype was examined in mice during restriction of dietary intake to 80% of control from day 3 of pregnancy. At day 16, undernutrition reduced placental, but not fetal, weight in association with decreased junctional zone volume and placental expression of glucose transporter Slc2a1. At day 19, both placental and fetal weights were reduced in undernourished mice (91% and 87% of control, respectively, P < 0.01), as were the volume and surface area of the labyrinthine zone responsible for placental nutrient transfer (85% and 86%, respectively, P < 0.03). However, unidirectional materno-fetal clearance of tracer glucose was maintained and methyl-aminoisobutyric acid increased 166% (P < 0.005) per gram of undernourished placenta, relative to controls. This was associated with an 18% and 27% increased placental expression of glucose and system A amino acid transporters Slc2a1 and Slc38a2, respectively, at day 19 (P < 0.04). At both ages, undernutrition decreased expression of the placental specific transcript of the Igf2 gene by 35% (P < 0.01), although methylation of its promoter was unaffected. The placenta, therefore, adapts to help maintain fetal growth when its own growth is compromised by maternal undernutrition. Consequently, placental phenotype is responsive to environmental conditions and may help predict the risk of adult disease programmed in utero.

Do maternal- or pregnancy-associated disease states affect blood pressure in the early neonatal period?

BACKGROUND

Placental vascular changes associated with maternal disease states may affect fetal vascular development. There is evidence suggesting that being born prematurely is associated with a higher blood pressure (BP) in later life.

AIM

To determine whether maternal disease state affects BP in the early neonatal period.

METHODS

Cohort study of neonates admitted to neonatal intensive care unit with exposure to maternal hypertension and diabetes. Inclusion criteria were neonates greater than 27 weeks gestation not ventilated or requiring inotropes for more than 24 h, materna l hypertension (pregnancy induced or essential) or diabetes of any kind requiring treatment, and spontaneous delivery. Exclusion criteria included chromosomal or congenital anomaly and illicit maternal drug use. Oscillometric BP measurements taken until discharge on days 1, 2, 3, 4, 7, 14, 21 and 28. Placental histopathology was performed.

RESULTS

One hundred and ninety infants enrolled, 104 in the control and 86 in the study group. Sixty-five infants were born between 28-31 weeks and 125 infants between 32-41 weeks gestation. Those born between 28-31 weeks with a history of diabetes had a statistically higher systolic, mean and diastolic BP throughout the first 28 days of life (P = 0.001; P = 0.007; P = 0.02). Those born between 32-41 weeks gestation with placental pathology associated with altered uteroplacental perfusion had a higher systolic BP (P = 0.005).

CONCLUSIONS

Maternal- or pregnancy-associated disease states appear to influence BP in the early neonatal period. Diabetes and altered placental perfusion were associated with higher BP readings. Clinical significance of these statistically elevated BPs in the early neonatal period is unknown.

Maternally-inherited Grb10 reduces placental size and efficiency

The control of foetal growth is poorly understood and yet it is critically important that at birth the body has attained appropriate size and proportions. Growth and survival of the mammalian foetus is dependent upon a functional placenta throughout most of gestation. A few genes are known that influence both foetal and placental growth and might therefore coordinate growth of the conceptus, including the imprinted Igf2 and Grb10 genes. Grb10 encodes a signalling adapter protein, is expressed predominantly from the maternally-inherited allele and acts to restrict foetal and placental growth. Here, we show that following disruption of the maternal allele in mice, the labyrinthine volume was increased in a manner consistent with a cell-autonomous function of Grb10 and the enlarged placenta was more efficient in supporting foetal growth. Thus, Grb10 is the first example of a gene that acts to limit placental size and efficiency. In addition, we found that females inheriting a mutant Grb10 allele from their mother had larger litters and smaller offspring than those inheriting a mutant allele from their father. This grandparental effect suggests Grb10 can influence reproductive strategy through the allocation of maternal resources such that offspring number is offset against size.

The protein-tyrosine phosphatase, SRC homology-2 domain containing protein tyrosine phosphatase-2, is a crucial mediator of exogenous insulin-like growth factor signaling to human trophoblast

Adequate fetal growth depends on placental transfer of nutrients and gases from the mother; thus, as pregnancy progresses, the placenta must grow to meet the increasing demands of the developing fetus. IGFs control proliferation, differentiation, and survival of trophoblast in first-trimester placenta via intracellular tyrosine kinase signaling cascades, the activation of which is also regulated by tyrosine phosphatases. The protein-tyrosine phosphatase, Src homology-2 domain containing protein tyrosine phosphatase (SHP)-2, is crucial for mouse placental development and is known to mediate IGF actions in other systems. In this study we examined the role of SHP-2 in regulating IGF-mediated proliferation in human trophoblast. Immunohistochemical analysis demonstrated that SHP-2 is expressed strongly in cytotrophoblast and only weakly in syncytium. After small interfering RNA-mediated knockdown of SHP-2 in BeWo choriocarcinoma cells and human first-trimester placental explants, IGF-induced trophoblast proliferation, examined using immunohistochemical analysis of Ki67 and 5-bromo-2'-deoxyuridine incorporation, was significantly reduced (P < 0.05). Kinase activation assays suggested that SHP-2 interacts with the MAPK pathway to mediate these effects. Markers of trophoblast differentiation were elevated after SHP-2 knockdown. This study demonstrates a role for tyrosine phosphatases in human trophoblast and establishes SHP-2 as a component of the IGF signaling pathway that is required for normal placental growth.

IL-6 stimulates system A amino acid transporter activity in trophoblast cells through STAT3 and increased expression of SNAT2

Changes in placental nutrient transport are closely associated with abnormal fetal growth. However, the molecular mechanisms underlying the regulation of placental amino acid transporters are unknown. We demonstrate that physiological concentrations of the proinflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha stimulate the activity of amino acid transporter system A, but not system L, in cultured human primary trophoblast cells. Both cytokines increased the gene and protein expression of the Na(+)-coupled neutral amino acid transporter (SNAT)2 isoform and upregulated SNAT1 protein expression. IL-6 increased Tyr705 phosphorylation of signal transducer and activator of transcription 3 (STAT3). In cells transfected with small interfering RNA (siRNA) targeting STAT3, the RNA and protein expression of SNAT2, but not SNAT1, was reduced and the stimulating effect of IL-6 on system A activity was abolished. Despite eliciting similar responses in amino acid transport activity and transporter expression, TNF-alpha effects on system A activity were not mediated through the JAK/STAT pathway. In conclusion, we have identified a novel regulatory pathway involving increased gene expression of the SNAT2 isoform mediated by a STAT-dependent pathway, which links IL-6 to increased activity of system A, a ubiquitously expressed transporter of neutral amino acids. From these new findings, we propose that upregulation of amino acid transporters by cytokines may contribute to increased placental nutrient transport and fetal overgrowth, which are commonly found in pregnancies complicated by maternal diabetes and obesity.

Targeted gene knockdown in zebrafish reveals distinct intraembryonic functions for insulin-like growth factor II signaling

IGF-II is the predominant IGF ligand regulating prenatal growth in all vertebrates, including humans, but its central role in placental development has confounded efforts to fully elucidate its functions within the embryo. Here we use a nonplacental model vertebrate (zebrafish) to interrogate the intraembryonic functions of IGF-II signaling. The zebrafish genome contains two coorthologs of mammalian IGF2 (igf2a, igf2b), which exhibit distinct patterns of expression during embryogenesis. Expression of igf2a mRNA is restricted to the notochord, primarily during segmentation/neurulation. By contrast, igf2b mRNA is expressed in midline tissues adjacent to the notochord, with additional sites of expression in the ventral forebrain, and the pronephros. To identify their intraembryonic functions, we suppressed the expression of each gene with morpholino oligonucleotides. Knockdown of igf2a led to defects in dorsal midline development, characterized by delayed segmentation, notochord undulations, and ventral curvature. Similarly, suppression of igf2b led to defects in dorsal midline development but also induced ectopic fusion of the nephron primordia, and defects in ventral forebrain development. Subsequent onset of severe body edema in igf2b, but not igf2a morphants, further suggested a distinct role for igf2b in development of the embryonic kidney. Simultaneous knockdown of both genes increased the severity of dorsal midline defects, confirming a conserved role for both genes in dorsal midline development. Collectively, these data provide evidence that the zebrafish orthologs of IGF2 function in dorsal midline development during segmentation/neurulation, whereas one paralog, igf2b, has evolved additional, distinct functions during subsequent organogenesis.

Placental efficiency and adaptation: endocrine regulation

Size at birth is critical in determining life expectancy and is dependent primarily on the placental supply of nutrients. However, the fetus is not just a passive recipient of nutrients from the placenta. It exerts a significant acquisitive drive for nutrients, which acts through morphological and functional adaptations in the placenta, particularly when the genetically determined drive for fetal growth is compromised by adverse intrauterine conditions. These adaptations alter the efficiency with which the placenta supports fetal growth, which results in optimal growth for prevailing conditions in utero. This review examines placental efficiency as a means of altering fetal growth, the morphological and functional adaptations that influence placental efficiency and the endocrine regulation of these processes.

Understanding placental nutrient transfer--why bother? New biomarkers of fetal growth

The placenta, in general and the physiology of maternofetal nutrient transfer is under-researched compared to other organs with epithelial transport function, as evidenced, for example, by publication numbers. This report provides reasons why more researchers should become involved in this topic. First, the syncytiotrophoblast, the transporting epithelium of the placenta, though having many basic cell physiology properties similar to those of other transporting epithelia, has several properties which are markedly different. Better information on these might help fundamental understanding of how epithelia in general function as well as improving knowledge of how the syncytiotrophoblast operates. Second, the synctiotrophoblast has a key role in controlling fetal growth, not only by transporting nutrients and waste products of metabolism but also because it increasingly appears to be one site, perhaps even the dominant site, in which integration of, sometimes conflicting, signals between mother and fetus takes place. Finally, better understanding of placental nutrient transfer and especially of how it is regulated by maternal and fetal signals could provide better information on the placental phenotype in fetal growth disorders--information which might contribute to providing better biomarkers which the obstetrician could use to improve early diagnosis of these disorders.