Homeobox gene Distal-less 3 (DLX3) is a regulator of villous cytotrophoblast differentiation

Sexually dimorphic gene expression responses of bovine embryos to the maternal microenvironment on day 13 of gestation

BACKGROUND

Various studies have highlighted significant differences in developmental kinetics and sensitivity to developmental conditions between male and female bovine embryos. These differences are thought to be caused in part by the sexually dimorphic expression of genes located on the sex or autosomal chromosomes. However, little is known about the dimorphic gene expression patterns of bovine embryos at the initiation of elongation, which is one of the critical stages of development. Furthermore, to the best of our knowledge, there is little or no data available on the sexually dimorphic gene expression patterns in bovine embryos in relation to maternal environmental conditions during the initiation of elongation. Therefore, the main objective of this study was to investigate the sexually dimorphic gene expression responses of embryos to the maternal environment at the initiation of elongation in embryos developed in lactating dairy cows and nonlactating nulliparous heifers.

RESULTS

Gene expression analysis showed that 159 genes including those involved in steroid biosynthesis and gastrulation were differentially expressed exclusively between male and female embryos developed in cows. Among these, 61 genes including CYP39 A1, CYP2R1 and CYP27B1 were upregulated and 98 genes including HSD17B1, HSD17B10 and aromatase (CYP19 A1) were downregulated in male embryos. Chromosomal analysis showed that 31.2% of the differentially expressed genes (DEGs) including glucose-6-phosphate dehydrogenase (G6PD) were located on the X chromosome, and 96% of those were upregulated in female embryos. Similarly, 254 genes including those involved in female sex differentiation, placenta development, transmembrane transport, and cell adhesion were differentially expressed exclusively between the male and female embryos developed in heifers. Of these, 108 genes including HSD17B11, HSD17B12, and HSD3B1 were upregulated, and 146 genes including SLC16 A9, SLC10 A1, SLC10 A3, SLC16 A5, SLC22 A23, SLC25 A43, SLC35 A2, SLC35 C1, and SLC4 were downregulated in male compared to female embryos. In addition, 17.3% of the DEGs were located on the X chromosome and 75% of the DEGs located on the X chromosome were upregulated in female embryos. On the other hand, 38 genes including SLC30 A10, SLC10 A4, ATP6 AP1, and KDM5 C showed sexually dimorphic expression patterns in day 13 bovine embryos irrespective of the maternal environment. These genes accounted for only 19% and 13% of the genes that showed sexually dimorphic expression in embryos developed in cows and heifers, respectively and the expression difference of these genes in male and female embryos was then likely influenced by the sex of the embryo.

CONCLUSION

This study revealed that embryos developed in lactating cows showed sexually dimorphic expression of genes involved in various functions including steroid biosynthesis and gastrulation. In contrast, embryos developed in heifers displayed sexually dimorphic expression of genes related to placental development, female sex differentiation, and transmembrane transport. This suggests that the reproductive tract environments of cows and heifers differently affect the sex specific expression of genes in bovine embryos. A higher proportion of genes that showed sexually dimorphic expression in cow embryos were located on the X chromosome, and the majority of these genes were upregulated in female embryos. Overall, this study provides insight into genes that exhibit sexually dimorphic expression patterns in day 13 bovine embryos due to the maternal reproductive tract microenvironment or solely due to the sex of the embryo.

Genomic Patterns of Homozygosity and Genetic Diversity in the Rhenish German Draught Horse

BACKGROUND/OBJECTIVES

The Rhenish German draught horse is an endangered German horse breed, originally used as working horse in agriculture. Therefore, the objective of this study was to evaluate the breed's genetic diversity using pedigree and genomic data in order to analyze classical and ancestral pedigree-based inbreeding, runs of homozygosity, ROH islands, and consensus ROH.

METHODS

We studied the genome-wide genotype data of 675 Rhenish German draught horses and collated pedigree-based inbreeding coefficients for these horses. The final dataset contained 64,737 autosomal SNPs.

RESULTS

The average number of ROH per individual was 43.17 ± 9.459 with an average ROH length of 5.087 Mb ± 1.03 Mb. The average genomic inbreeding coefficient FROH was 0.099 ± 0.03, the pedigree-based classical inbreeding coefficient FPED 0.016 ± 0.021, and ancestral inbreeding coefficients ranged from 0.03 (Fa_Kal) to 0.51 (Ahc). Most ROH (55.85%) were classified into the length category of 2-4 Mb, and the minority (0.43%) into the length category of >32 Mb. The effective population size (Ne) decreased in the last seven generations (~65 years) from 189.43 to 58.55. Consensus ROH shared by 45% of the horses were located on equine chromosomes 3 and 7, while ROH islands exceeding the 99th percentile threshold were identified on chromosomes 2, 3, 5, 7, 9, 10, and 11. These ROH islands contained genes associated with morphological development (HOXB cluster), fertility (AURKC, NLRP5, and DLX3), muscle growth, and skin physiology (ZNF gene cluster).

CONCLUSIONS

This study highlights how important it is to monitor genetic diversity in endangered populations with genomic data. The results of this study will help to develop breeding strategies to ensure the conservation of the German Rhenish draught horse population and show whether favorable alleles from the overrepresented candidate genes within ROH were transmitted to the next generation.

Homeobox genes in the human placenta: Twists and turns on the path to find novel targets

Fetal growth restriction (FGR) is a clinically important human pregnancy disorder that is thought to originate early in pregnancy and while its aetiology is not well understood, the disorder is associated with placental insufficiency. Currently treatment for FGR is limited by increased surveillance using ultrasound monitoring and premature delivery, or corticosteroid medication in the third trimester to prolong pregnancy. There is a pressing need for novel strategies to detect and treat FGR at its early stage. Homeobox genes are well established as master regulators of early embryonic development and increasing evidence suggests they are also important in regulating early placental development. Most important is that specific homeobox genes are abnormally expressed in human FGR. This review focusses on identifying the molecular pathways controlled by homeobox genes in the normal and FGR-affected placenta. This information will begin to address the knowledge gap in the molecular aetiology of FGR and lay the foundation for identifying potential diagnostic and therapeutic targets.

How trophoblasts fuse: an in-depth look into placental syncytiotrophoblast formation

In humans, cell fusion is restricted to only a few cell types under normal conditions. In the placenta, cell fusion is a critical process for generating syncytiotrophoblast: the giant multinucleated trophoblast lineage containing billions of nuclei within an interconnected cytoplasm that forms the primary interface separating maternal blood from fetal tissue. The unique morphology of syncytiotrophoblast ensures that nutrients and gases can be efficiently transferred between maternal and fetal tissue while simultaneously restricting entry of potentially damaging substances and maternal immune cells through intercellular junctions. To maintain integrity of the syncytiotrophoblast layer, underlying cytotrophoblast progenitor cells terminate their capability for self-renewal, upregulate expression of genes needed for differentiation, and then fuse into the overlying syncytium. These processes are disrupted in a variety of obstetric complications, underscoring the importance of proper syncytiotrophoblast formation for pregnancy health. Herein, an overview of key mechanisms underlying human trophoblast fusion and syncytiotrophoblast development is discussed.

The Imbalance Expression of DLX3 May Perform Critical Function in the Occurrence and Progression of Preeclampsia

BACKGROUND

The present research focuses on preeclampsia (PE), a clinically relevant pregnancy disease. To date, the majority of research on PE was centered on placental insufficiency. However, the genes that regulate these processes, and the exact molecular mechanisms modulating these processes, are still unclear.

METHODS

We obtained placentae from a clinically well-specified group of patients with preeclampsia and gestationally matched control pregnancies in order to evaluate the expression of homeobox gene DLX3 by immunohistochemical staining, real-time PCR, and Western immunoblotting and determine the function of DLX3 utilizing lentivirus transfection in HTR-8/SVneo cells.

RESULTS

In the present study, we detected DLX3 expression in a clinically well defined cohort of preeclampsia-affected and gestation-matched control pregnancies. As opposed to the controls, DLX3 was overexpressed in preeclampsia-affected placentae. Moreover, we found that the in vitro cell growth and invasive ability of HTR8/SVneo cells was enhanced by the exogenous overexpression of DLX3 (P < 0.05). It can be seen that DLX3 influences the cell cycle of HTR-8/SVneo cells in vitro.

CONCLUSIONS

DLX3 has been shown to be strongly related to normal placental growth as well as the pathophysiology of preeclampsia. The imbalanced expression of DLX3 may perform an integral function in the occurrence and progression of preeclampsia.

Cell dynamics in human villous trophoblast

BACKGROUND

Villous cytotrophoblast (vCTB) is a precursor cell population that supports the development of syncytiotrophoblast (vSTB), the high surface area barrier epithelium of the placental villus, and the primary interface between maternal and fetal tissue. In light of increasing evidence that the placenta can adapt to changing maternal environments or, under stress, can trigger maternal disease, we consider what properties of these cells empower them to exert a controlling influence on pregnancy progression and outcome.

OBJECTIVE AND RATIONALE

How are cytotrophoblast proliferation and differentiation regulated in the human placental villus to allow for the increasing demands of the fetal and environmental challenges and stresses that may arise during pregnancy?

SEARCH METHODS

PubMed was interrogated using relevant keywords and word roots combining trophoblast, villus/villous, syncytio/syncytium, placenta, stem, transcription factor (and the individual genes), signalling, apoptosis, autophagy (and the respective genes) from 1960 to the present. Since removal of trophoblast from its tissue environment is known to fundamentally change cell growth and differentiation kinetics, research that relied exclusively on cell culture has not been the main focus of this review, though it is mentioned where appropriate. Work on non-human placenta is not systematically covered, though mention is made where relevant hypotheses have emerged.

OUTCOMES

The synthesis of data from the literature has led to a new hypothesis for vCTB dynamics. We propose that a reversible transition can occur from a reserve population in G0 to a mitotically active state. Cells from the in-cycle population can then differentiate irreversibly to intermediate cells that leave the cycle and turn on genes that confer the capacity to fuse with the overlying vSTB as well as other functions associated with syncytial barrier and transport function. We speculate that alterations in the rate of entry to the cell cycle, or return of cells in the mitotic fraction to G0, can occur in response to environmental challenge. We also review evidence on the life cycle of trophoblast from the time that fusion occurs, and point to gaps in knowledge of how large quantities of fetal DNA arrive in maternal circulation. We critique historical methodology and make a case for research to re-address questions about trophoblast lifecycle and dynamics in normal pregnancy and the common diseases of pre-eclampsia and fetal growth restriction, where altered trophoblast kinetics have long been postulated.

WIDER IMPLICATIONS

The hypothesis requires experimental testing, moving research away from currently accepted methodology towards a new standard that includes representative cell and tissue sampling, assessment of cell cycle and differentiation parameters, and robust classification of cell subpopulations in villous trophoblast, with due attention to gestational age, maternal and fetal phenotype, disease and outcome.

The role of insulin-like growth factor 2 receptor-mediated homeobox gene expression in human placental apoptosis, and its implications in idiopathic fetal growth restriction

Fetal growth restriction (FGR) is caused by poor placental development and function early in gestation. It is well known that placentas from women with FGR exhibit reduced cell growth, elevated levels of apoptosis and perturbed expression of the growth factors, cytokines and the homeobox gene family of transcription factors. Previous studies have reported that insulin-like growth factor-2 (IGF2) interacts with its receptor-2 (IGF2R) to regulate villous trophoblast survival and apoptosis. In this study, we hypothesized that human placental IGF2R-mediated homeobox gene expression is altered in FGR and contributes to abnormal trophoblast function. This study was designed to determine the association between IGF2R, homeobox gene expression and cell survival in pregnancies affected by FGR. Third trimester placentas were collected from FGR-affected pregnancies (n = 29) and gestation matched with control pregnancies (n = 30). Functional analyses were then performed in vitro using term placental explants (n = 4) and BeWo trophoblast cells. mRNA expression was determined by real-time PCR, while protein expression was examined by immunoblotting and immunohistochemistry. siRNA transfection was used to silence IGF2R expression in placental explants and the BeWo cell-line. cDNA arrays were used to screen for downstream targets of IGF2R, specifically homeobox gene transcription factors and apoptosis-related genes. Functional effects of silencing IGF2R were then verified by β-hCG ELISA, caspase activity assays and a real-time electrical cell-impedance assay for differentiation, apoptosis and cell growth potential, respectively. IGF2R expression was significantly decreased in placentas from pregnancies complicated by idiopathic FGR (P < 0.05 versus control). siRNA-mediated IGF2R knockdown in term placental explants and the trophoblast cell line BeWo resulted in altered expression of homeobox gene transcription factors, including increased expression of distal-less homeobox gene 5 (DLX5), and decreased expression of H2.0-Like Homeobox 1 (HLX) (P < 0.05 versus control). Knockdown of IGF2R transcription increased the expression and activity of caspase-6 and caspase-8 in placental explants, decreased BeWo proliferation and increased BeWo differentiation (all P < 0.05 compared to respective controls). This is the first study linking IGF2R placental expression with changes in the expression of homeobox genes that control cellular signalling pathways responsible for increased trophoblast cell apoptosis, which is a characteristic feature of FGR.

Super-enhancer-guided mapping of regulatory networks controlling mouse trophoblast stem cells

Trophectoderm (TE) lineage development is pivotal for proper implantation, placentation, and healthy pregnancy. However, only a few TE-specific transcription factors (TFs) have been systematically characterized, hindering our understanding of the process. To elucidate regulatory mechanisms underlying TE development, here we map super-enhancers (SEs) in trophoblast stem cells (TSCs) as a model. We find both prominent TE-specific master TFs (Cdx2, Gata3, and Tead4), and >150 TFs that had not been previously implicated in TE lineage, that are SE-associated. Mapping targets of 27 SE-predicted TFs reveals a highly intertwined transcriptional regulatory circuitry. Intriguingly, SE-predicted TFs show 4 distinct expression patterns with dynamic alterations of their targets during TSC differentiation. Furthermore, depletion of a subset of TFs results in dysregulation of the markers for specialized cell types in placenta, suggesting a role during TE differentiation. Collectively, we characterize an expanded TE-specific regulatory network, providing a framework for understanding TE lineage development and placentation.

Trophectoderm lineage development is essential for implantation, placentation, and healthy pregnancy. Here the authors map super-enhancers (SEs) in trophoblast stem cells and find both TE-specific master regulators and 150 previous uncharacterised transcription factors that are SE-associated, providing insight into trophectoderm-specific regulatory networks.

Human placental 3β-hydroxysteroid dehydrogenase/steroid Δ5,4-isomerase 1: Identity, regulation and environmental inhibitors

Human placental 3β-hydroxysteroid dehydrogenase/steroid Δ5, 4-isomerase 1 (HSD3B1), a high-affinity type I enzyme, uses pregnenolone to make progesterone, which is critical for maintenance of pregnancy. HSD3B1 is located in the mitochondrion and the smooth endoplasmic reticulum of placental cells and is encoded by HSD3B1 gene. HSD3B1 contains GATA and TEF-5 regulatory elements. Many endocrine disruptors, including phthalates, methoxychlor and its metabolite, organotins, and gossypol directly inhibit placental HSD3B1 thus blocking progesterone production. In this review, we discuss the placental HSD3B1, its gene regulation, biochemistry, subcellular location, and inhibitors from the environment.

Hemochorial placentation: development, function, and adaptations

Placentation is a reproductive adaptation that permits fetal growth and development within the protected confines of the female reproductive tract. Through this important role, the placenta also determines postnatal health and susceptibility to disease. The hemochorial placenta is a prominent feature in primate and rodent development. This manuscript provides an overview of the basics of hemochorial placental development and function, provides perspectives on major discoveries that have shaped placental research, and thoughts on strategies for future investigation.

Expression of Homeobox Gene HLX and its Downstream Target Genes are Altered in Placentae From Discordant Twin Pregnancies

A discordant twin gestation, in which one fetus is significantly growth restricted, compared to the other normal twin, is a unique model that can be used to elucidate the mechanism(s) by which the intrauterine environment affects fetal growth. In many model systems, placental transcription factor genes regulate fetal growth. Transcription factors regulate growth through their activation or repression of downstream target genes that mediate important cell functions. The objective of this study was to determine the expression of the placental HLX homeobox gene transcription factor and its downstream target genes in dizygotic twins with growth discordance. In this cross-sectional study, HLX and its downstream target genes' retinoblastoma 1 (RB1) and cyclin kinase D (CDKN1C) expression levels were determined in placentae obtained from dichorionic diamniotic twin pregnancies (n = 23) where one of the twins was growth restricted. Fetal growth restriction (FGR) was defined as small for gestational age with abnormal umbilical artery Doppler indices when compared with the normal control co-twin. Homeobox gene HLX expression was significantly decreased at both the mRNA and protein levels in FGR twin placentae compared with the normal control co-twin placentae (p < .05). Downstream target genes CDKN1C and RB1 were also significantly decreased and increased, respectively, at both the mRNA and protein levels in FGR twin placentae compared with normal control co-twin placentae (p < .05). Together, these observations suggest an important association between HLX transcription factor expression and abnormal human placental development in discordant twin pregnancies.

Increased methylation and decreased expression of homeobox genes TLX1, HOXA10 and DLX5 in human placenta are associated with trophoblast differentiation

Homeobox genes regulate embryonic and placental development, and are widely expressed in the human placenta, but their regulatory control by DNA methylation is unclear. DNA methylation analysis was performed on human placentae from first, second and third trimesters to determine methylation patterns of homeobox gene promoters across gestation. Most homeobox genes were hypo-methylated throughout gestation, suggesting that DNA methylation is not the primary mechanism involved in regulating HOX genes expression in the placenta. Nevertheless, several genes showed variable methylation patterns across gestation, with a general trend towards an increase in methylation over gestation. Three genes (TLX1, HOXA10 and DLX5) showed inverse gains of methylation with decreasing mRNA expression throughout pregnancy, supporting a role for DNA methylation in their regulation. Proteins encoded by these genes were primarily localised to the syncytiotrophoblast layer, and showed decreased expression later in gestation. siRNA mediated downregulation of DLX5, TLX1 and HOXA10 in primary term villous cytotrophoblast resulted in decreased proliferation and increased expression of differentiation markers, including ERVW-1. Our data suggest that loss of DLX5, TLX1 and HOXA10 expression in late gestation is required for proper placental differentiation and function.

An EG-VEGF-Dependent Decrease in Homeobox Gene NKX3.1 Contributes to Cytotrophoblast Dysfunction: A Possible Mechanism in Human Fetal Growth Restriction

Idiopathic fetal growth restriction (FGR) is frequently associated with placental insufficiency. Previous reports have provided evidence that endocrine gland-derived vascular endothelial growth factor (EG-VEGF), a placental secreted protein, is expressed during the first trimester of pregnancy, controls both trophoblast proliferation and invasion, and its increased expression is associated with human FGR. In this study, we hypothesize that EG-VEGF-dependent changes in placental homeobox gene expressions contribute to trophoblast dysfunction in idiopathic FGR. The changes in EG-VEGF-dependent homeobox gene expressions were determined using a homeobox gene cDNA array on placental explants of 8-12 wks gestation after stimulation with EG-VEGF in vitro for 24 h. The homeobox gene array identified a greater-than-five-fold increase in HOXA9, HOXC8, HOXC10, HOXD1, HOXD8, HOXD9 and HOXD11, while NKX 3.1 showed a greater-than-two-fold decrease in mRNA expression compared with untreated controls. Homeobox gene NKX3.1 was selected as a candidate because it is a downstream target of EG-VEGF and its expression and functional roles are largely unknown in control and idiopathic FGR-affected placentae. Real-time PCR and immunoblotting showed a significant decrease in NKX3.1 mRNA and protein levels, respectively, in placentae from FGR compared with control pregnancies. Gene inactivation in vitro using short-interference RNA specific for NKX3.1 demonstrated an increase in BeWo cell differentiation and a decrease in HTR-8/SVneo proliferation. We conclude that the decreased expression of homeobox gene NKX3.1 downstream of EG-VEGF may contribute to the trophoblast dysfunction associated with idiopathic FGR pregnancies.

Decreased STAT3 in human idiopathic fetal growth restriction contributes to trophoblast dysfunction

Abnormal trophoblast function is associated with fetal growth restriction (FGR). The JAK-STAT pathway is one of the principal signalling mechanisms by which cytokines and growth factors modulate cell proliferation, differentiation, cell migration and apoptosis. The expression of placental JAK-STAT genes in human idiopathic FGR is unknown. In this study, we propose the hypothesis that JAK-STAT pathway genes are differentially expressed in idiopathic FGR-affected pregnancies and contribute to abnormal feto-placental growth by modulating the expression of the amino acid transporter SNAT2, differentiation marker CGB/human chorionic gonadotrophin beta-subunit (β-hCG) and apoptosis markers caspases 3 and 8, and TP53. Expression profiling of FGR-affected placentae revealed that mRNA levels of STAT3, STAT2 and STAT5B decreased by 69, 52 and 50%, respectively, compared with gestational-age-matched controls. Further validation by real-time PCR and immunoblotting confirmed significantly lower STAT3 mRNA and STAT3 protein (total and phosphorylated) levels in FGR placentae. STAT3 protein was localised to the syncytiotrophoblast (ST) in both FGR and control placentae. ST differentiation was modelled by in vitro differentiation of primary villous trophoblast cells from first-trimester and term placentae, and by treating choriocarcinoma-derived BeWo cells with forskolin in cell culture. Differentiation in these models was associated with increased STAT3 mRNA and protein levels. In BeWo cells treated with siRNA targeting STAT3, the mRNA and protein levels of CGB/β-hCG, caspases 3 and 8, and TP53 were significantly increased, while that of SNAT2 was significantly decreased compared with the negative control siRNA. In conclusion, we report that decreased STAT3 expression in placentae may contribute to abnormal trophoblast function in idiopathic FGR-affected pregnancies.

Review: placental homeobox genes and their role in regulating human fetal growth

The regulation of fetal growth is multifactorial and complex. Normal fetal growth is determined by the genetically predetermined growth potential and further modulated by maternal, fetal, placental, and environmental factors. The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface is controlled by several growth factors, cytokines and transcription factors including homeobox genes. This review summarizes our current knowledge regarding homeobox genes in the human placenta and their differential expression and functions in human idiopathic fetal growth restriction (FGR). The review also describes the research strategies that were used for the identification of homeobox genes, their expression in FGR, functional role and target genes of homeobox genes in the trophoblasts and the hormonal regulators of homeobox gene expression in vitro. A better understanding of molecular pathways driven by placental homeobox genes and further elucidation of signaling pathways underlying the hormone-mediated homeobox gene developmental programs may offer novel strategies of targeted therapy for improving feto-placental growth in idiopathic FGR pregnancies.

Downstream targets of the homeobox gene DLX3 are differentially expressed in the placentae of pregnancies affected by human idiopathic fetal growth restriction

Human idiopathic fetal growth restriction (FGR) is associated with placental insufficiency. Previously, we reported that the expression of homeobox gene Distal-less 3 (DLX3) is increased in idiopathic FGR placentae and is a regulator of villous trophoblast differentiation. Here, we identify the downstream targets of DLX3 in trophoblast-derived cell lines. We modelled the high levels of DLX3 in FGR using an over-expression plasmid construct and complemented this using short-interference RNA (siRNA) for inactivation in cultured cells. Using a real-time PCR-based gene profiling, candidate target genes of DLX3 over-expression and inactivation were identified as regulators of trophoblast differentiation; GATA2 and PPARγ. The expression of GATA2 and PPARγ were further assessed in placental tissues and showed increased mRNA and protein levels in FGR-affected tissues compared with gestation-matched controls. We conclude that DLX3 orchestrates the expression of multiple regulators of trophoblast differentiation and that expression of these regulatory genes is abnormal in FGR.

Homeobox gene transforming growth factor β-induced factor-1 (TGIF-1) is a regulator of villous trophoblast differentiation and its expression is increased in human idiopathic fetal growth restriction

Abnormal trophoblast function is associated with human fetal growth restriction (FGR). Targeted disruption of homeobox gene transforming growth β-induced factor (TGIF-1) results in placental dysfunction in the mouse. The role of human TGIF-1 in placental cell function is unknown. The aims of this study were to determine the expression of TGIF-1 in human idiopathic FGR-affected placentae compared with gestation-matched controls (GMC), to elucidate the functional role of TGIF-1 in trophoblasts and to identify its downstream targets. Real-time PCR and immunoblotting revealed that TGIF-1 mRNA and protein expression was significantly increased in FGR-affected placentae compared with GMC (n = 25 in each group P < 0.05). Immunoreactive TGIF-1 was localized to the villous cytotrophoblasts, syncytiotrophoblast, microvascular endothelial cells and in scattered stromal cells in both FGR and GMC. TGIF-1 inactivation in BeWo cells using two independent siRNA resulted in significantly decreased mRNA and protein of trophoblast differentiation markers, human chorionic gonadotrophin (CGB/hCG), syncytin and 3β-hydroxysteroid dehydrogenase/3β-honest significant difference expression. Our data demonstrate that homeobox gene TGIF-1 is a potential up-stream regulator of trophoblast differentiation and the altered TGIF-1 expression may contribute to aberrant villous trophoblast differentiation in FGR.

Homeobox genes and down-stream transcription factor PPARγ in normal and pathological human placental development

The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface is controlled by nuclear transcription factors including homeobox genes. Here we summarize current knowledge regarding the expression and function of homeobox genes in the placenta. We also describe the identification of target transcription factors including PPARγ, biological pathways regulated by homeobox genes and their role in placental development. The role of the nuclear receptor PPARγ, ligands and target genes in human placental development is also discussed. A better understanding of these pathways will improve our knowledge of placental cell biology and has the potential to reveal new molecular targets for the early detection and diagnosis of pregnancy complications including human fetal growth restriction.

The role of homeobox genes in the development of placental insufficiency

Intrauterine growth restriction (IUGR) is an adverse pregnancy outcome associated with significant perinatal and pediatric morbidity and mortality, and an increased risk of chronic disease later in adult life. While a number of maternal, fetal and environmental factors are known causes of IUGR, the majority of IUGR cases are of unknown cause. These IUGR cases are frequently associated with placental insufficiency, possibly as a result of placental maldevelopment. Understanding the molecular mechanisms of abnormal placental development in IUGR associated with placental insufficiency is therefore of increasing importance. Here, we review our understanding of transcriptional control of normal placental development as well as human IUGR associated with placental insufficiency. We also assess the potential for understanding transcriptional control as a means for revealing new molecular targets for the detection, diagnosis and clinical management of IUGR associated with placental insufficiency.