Developmental restriction of Mash-2 expression in trophoblast correlates with potential activation of the notch-2 pathway

Physiology, Development, and Disease Modeling in the Drosophila Excretory System

The insect excretory system contains two organ systems acting in concert: the Malpighian tubules and the hindgut perform essential roles in excretion and ionic and osmotic homeostasis. For over 350 years, these two organs have fascinated biologists as a model of organ structure and function. As part of a recent surge in interest, research on the Malpighian tubules and hindgut of Drosophila have uncovered important paradigms of organ physiology and development. Further, many human disease processes can be modeled in these organs. Here, focusing on discoveries in the past 10 years, we provide an overview of the anatomy and physiology of the Drosophila excretory system. We describe the major developmental events that build these organs during embryogenesis, remodel them during metamorphosis, and repair them following injury. Finally, we highlight the use of the Malpighian tubules and hindgut as accessible models of human disease biology. The Malpighian tubule is a particularly excellent model to study rapid fluid transport, neuroendocrine control of renal function, and modeling of numerous human renal conditions such as kidney stones, while the hindgut provides an outstanding model for processes such as the role of cell chirality in development, nonstem cell-based injury repair, cancer-promoting processes, and communication between the intestine and nervous system.

Differential Regulation of TLE3 in Sertoli Cells of the Testes during Postnatal Development

Spermatogenesis is a process by which haploid cells differentiate from germ cells in the seminiferous tubules of the testes. TLE3, a transcriptional co-regulator that interacts with DNA-binding factors, plays a role in the development of somatic cells. However, no studies have shown its role during germ cell development in the testes. Here, we examined TLE3 expression in the testes during spermatogenesis. TLE3 was highly expressed in mouse testes and was dynamically regulated in different cell types of the seminiferous tubules, spermatogonia, spermatids, and Sertoli cells, but not in the spermatocytes. Interestingly, TLE3 was not detected in Sertoli cells on postnatal day 7 (P7) but was expressed from P10 onward. The microarray analysis showed that the expression of numerous genes changed upon TLE3 knockdown in a Sertoli cell line TM4. These include 1597 up-regulated genes and 1452 down-regulated genes in TLE3-knockdown TM4 cells. Ingenuity Pathway Analysis (IPA) showed that three factors were up-regulated and two genes were down-regulated upon TLE3 knockdown in TM4 cells. The abnormal expression of the three factors is associated with cellular malfunctions such as abnormal differentiation and Sertoli cell formation. Thus, TLE3 is differentially expressed in Sertoli cells and plays a crucial role in regulating cell-specific genes involved in the differentiation and formation of Sertoli cells during testicular development.

Notch signalling in placental development and gestational diseases

Activation of Notch signalling upon cell-cell contact of neighbouring cells controls a plethora of cellular processes such as stem cell maintenance, cell lineage determination, cell proliferation, and survival. Accumulating evidence suggests that the pathway also critically regulates these events during placental development and differentiation. Herein, we summarize our present knowledge about Notch signalling in murine and human placentation and discuss its potential role in the pathophysiology of gestational disorders. Studies in mice suggest that Notch controls trophectoderm formation, decidualization, placental branching morphogenesis and endovascular trophoblast invasion. In humans, the particular signalling cascade promotes formation of the extravillous trophoblast lineage and regulates trophoblast proliferation, survival and differentiation. Expression patterns as well as functional analyses indicate distinct roles of Notch receptors in different trophoblast subtypes. Altered effects of Notch signalling have been detected in choriocarcinoma cells, consistent with its role in cancer development and progression. Moreover, deregulation of Notch signalling components were observed in pregnancy disorders such as preeclampsia and fetal growth restriction. In summary, Notch plays fundamental roles in different developmental processes of the placenta. Abnormal signalling through this pathway could contribute to the pathogenesis of gestational diseases with aberrant placentation and trophoblast function.

TLE3 represses colorectal cancer proliferation by inhibiting MAPK and AKT signaling pathways

Background

Transducin-like enhancer of Split3 (TLE3) serves as a transcriptional corepressor during cell differentiation and shows multiple roles in different kinds of cancers. Recently, TLE3 together with many other genes involved in Wnt/β-catenin pathway were detected hyper-methylated in colorectal cancer (CRC). However, the potential role and the underlying mechanism of TLE3 in CRC progression remain scarce.

Methods

Gene expression profiles were analyzed in The Cancer Genome Atlas (TCGA) microarray dataset of 41 normal colorectal intestine tissues and 465 CRC tissues. Western blot and Real-time Quantitative PCR (RT-qPCR) were respectively performed to detect protein and mRNA expression in 8 pairs of CRC tissue and matched adjacent normal mucosa. Immunohistochemistry (IHC) was conducted to evaluate TLE3 protein expression in 105 paraffin-embedded, archived human CRC tissues from patients, whose survival data were analyzed with Kaplan-Meier method. In vitro experiments including MTT assay, colony formation assay, and soft agar formation assay were used to investigate the effects of TLE3 on CRC cell growth and proliferation. Additionally, subcutaneous tumorigenesis assay was performed in nude mice to confirm the effects of TLE3 in vivo. Furthermore, gene set enrichment analysis (GSEA) was run to explore potential mechanism of TLE3 in CRC, and then we measured the distribution of CRC cell cycle phases and apoptosis by flow cytometry, as well as the impacts of TLE3 on MAPK and AKT signaling pathways by Western blot and RT-qPCR.

Results

TLE3 was significantly down-regulated in 465 CRC tissues compared with 41 normal tissues. Both protein and mRNA expressions of TLE3 were down-regulated in CRC compared with matched adjacent normal mucosa. Lower expression of TLE3 was significantly associated with poorer survival of patients with CRC. Besides, knock down of TLE3 promoted CRC cell growth and proliferation, while overexpression of TLE3 showed suppressive effects. Furthermore, overexpression of TLE3 caused G1-S phase transition arrest, inhibition of MAPK and AKT pathways, and up-regulation of p21Cip1/WAF1 and p27Kip1.

Conclusion

This study indicated that TLE3 repressed CRC proliferation partly through inhibition of MAPK and AKT signaling pathways, suggesting the possibility of TLE3 as a biomarker for CRC prognosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0426-8) contains supplementary material, which is available to authorized users.

Cell Fate and Differentiation of Bone Marrow Mesenchymal Stem Cells

Osteoblasts and bone marrow adipocytes originate from bone marrow mesenchymal stem cells (BMMSCs) and there appears to be a reciprocal relationship between adipogenesis and osteoblastogenesis. Alterations in the balance between adipogenesis and osteoblastogenesis in BMMSCs wherein adipogenesis is increased relative to osteoblastogenesis are associated with decreased bone quality and quantity. Several proteins have been reported to regulate this reciprocal relationship but the exact nature of the signals regulating the balance between osteoblast and adipocyte formation within the bone marrow space remains to be determined. In this review, we focus on the role of Transducin-Like Enhancer of Split 3 (TLE3), which was recently reported to regulate the balance between osteoblast and adipocyte formation from BMMSCs. We also discuss evidence implicating canonical Wnt signalling, which plays important roles in both adipogenesis and osteoblastogenesis, in regulating TLE3 expression. Currently, there is demand for new effective therapies that target the stimulation of osteoblast differentiation to enhance bone formation. We speculate that reducing TLE3 expression or activity in BMMSCs could be a useful approach towards increasing osteoblast numbers and reducing adipogenesis in the bone marrow environment.

Adaptive mechanisms controlling uterine spiral artery remodeling during the establishment of pregnancy

Implantation of the embryo into the uterus triggers the initiation of hemochorial placentation. The hemochorial placenta facilitates the acquisition of maternal resources required for embryo/fetal growth. Uterine spiral arteries form the nutrient supply line for the placenta and fetus. This vascular conduit undergoes gestation stage-specific remodeling directed by maternal natural killer cells and embryo-derived invasive trophoblast lineages. The placentation site, including remodeling of the uterine spiral arteries, is shaped by environmental challenges. In this review, we discuss the cellular participants controlling pregnancy-dependent uterine spiral artery remodeling and mechanisms responsible for their development and function.

Development of the hemochorial maternal vascular spaces in the placenta through endothelial and vasculogenic mimicry

The maternal vasculature within the placenta in primates and rodents is unique because it is lined by fetal cells of the trophoblast lineage and not by maternal endothelial cells. In addition to trophoblast cells that invade the uterine spiral arteries that bring blood into the placenta, other trophoblast subtypes sit at different levels of the vascular space. In mice, at least five distinct subtypes of trophoblast cells have been identified which engage maternal endothelial cells on the arterial and venous frontiers of the placenta, but which also form the channel-like spaces within it through a process analogous to formation of blood vessels (vasculogenic mimicry). These cells are all large, post-mitotic trophoblast giant cells. In addition to assuming endothelial cell-like characteristics (endothelial mimicry), they produce dozens of different hormones that are thought to regulate local and systemic maternal adaptations to pregnancy. Recent work has identified distinct molecular pathways in mice that regulate the morphogenesis of trophoblast cells on the arterial and venous sides of the vascular circuit that may be analogous to specification of arterial and venous endothelial cells.

Expression of TLE3 by bone marrow stromal cells is regulated by canonical Wnt signaling

Transducing-like enhancer of split 3 (TLE3), one of the Groucho/TLE family members, targets Runx2 transcription and suppresses osteoblast differentiation in bone marrow stromal cells (BMSCs). Here, we identify Wnt responsive elements of the TLE3 promoter region through comparative genomic and functional analyses and show that expression of TLE3 is increased by Wnt signaling, which is important for osteoblast differentiation. We also demonstrated that TLE3 is able to suppress canonical Wnt signaling in BMSCs. Taken together, our data suggest that induction of TLE3 by Wnt signaling is part of a negative feedback loop active during osteoblast differentiation.

The transcriptional co-repressor TLE3 regulates development of trophoblast giant cells lining maternal blood spaces in the mouse placenta

TLE3 is a transcriptional co-repressor that interacts with several DNA-binding repressors, including downstream effectors of the Notch signaling pathway. We generated Tle3-deficient mice and found that they die in utero and their death is associated with abnormal development of the placenta with major defects in the maternal vasculature. In the normal placenta, maternal blood spaces are lined, not as usual in the mammalian circulation by endothelial cells, but rather by specialized embryo-derived cells of the trophoblast cell lineage named trophoblast giant cells (TGC). Tle3 mRNA is expressed in those specialized TGC and Tle3 mutants show severe defects in differentiation of TGC-lined channels and lacunar spaces that take blood out of the labyrinth zone of the placenta and into the uterine veins. The mutants also show somewhat milder defects on the arterial-side of the maternal vascular circuit in spiral arteries and canals that take blood into the labyrinth. Notch2 and Tle3 expression patterns overlap in several TGC subtypes and we found that Tle3 and Notch2 mutants have some overlapping features. However, they also show differences implying that TLE3 may mediate some but not all of the effects of Notch2 signaling during placenta development. Therefore, formation of the different types of maternal blood spaces by different TGC subtypes is regulated by distinct molecular mechanisms.

Spatiotemporal expression of Notch receptors and ligands in developing mouse placenta

Notch signaling is involved in cell lineage specification in many developing organs. In mice there are four known Notch receptor genes (Notch1-4) and five ligands genes (Dll1, 3, 4 and Jagged1 and 2). Notch2 is essential for development of placenta, an organ that mediates feto-maternal nutrient and gas exchange as well as maternal adaptations to pregnancy. However the role of other Notch receptors and ligands in placentation is not known. In order to gain better insight into the role of Notch signaling in mouse placenta we thoroughly analyzed mRNA expression of all Notch receptors and ligands in all trophoblast cell types from the embryonic day (E) 7.5 to E12.5, the period during which all of the substructures of the placenta develop. Here we show that Notch receptors and ligands are specifically and dynamically expressed in multiple cell layers of developing placenta. We found that the Notch2 receptor and Jagged1 and Jagged2 ligand genes are complementarily expressed in trophoblast cells of the chorion and its later derivatives in the labyrinth. Dll4 and Notch2 expression complement each other in the ectoplacental cone, while Dll1 and Notch2 are expressed in an ectoplacental cone derivative, the junctional zone. Moreover Dll4 and Notch2 are expressed at the ectoplacental cone-decidua interface at early stages of placentation. Additionally we show that Notch2 is dynamically expressed in all trophoblast giant cell subtypes, which is consistent with previous reports. Overall these expression pattern results suggest that Notch signaling may play several diverse roles during placenta development.

Groucho: a corepressor with instructive roles in development

Drosophila Groucho (Gro) is the founding member of a family of metazoan corepressors. Gro mediates repression through interactions with a myriad of DNA-binding repressor proteins to direct the silencing of genes involved in many developmental processes, including neurogenesis and patterning of the main body axis, as well as receptor tyrosine kinase/Ras/MAPK, Notch, Wingless (Wg)/Wnt, and Decapentaplegic (Dpp) signaling. Gro mediates repression by multiple molecular mechanisms, depending on the regulatory context. Because Gro is a broadly expressed nuclear factor, whereas its repressor partners display restricted temporal and spatial distribution, it was presumed that this corepressor played permissive rather than instructive roles in development. However, a wide range of studies demonstrates that this is not the case. Gro can sense and integrate many cellular inputs to modulate the expression of variety of genes, making it a versatile corepressor with crucial instructive roles in development and signaling.

Notch signaling pathway and human placenta

Notch signaling was evolutionarily conserved and critical for cell-fate determination, differentiation and many other biological processes. Growing evidences suggested that Notch signaling pathway played an important role in the mammalian placental development. All of the mammalian Notch family proteins had been identified in human placenta except Delta-like 3, which appeared to affect the axial skeletal system. However the molecular mechanisms that regulated the Notch signaling pathway remained largely unknown in human placenta. Therefore, additional research was needed to investigate expression pattern of Notch family members and the mechanisms for activation of Notch signaling pathway in human placenta, which might help elucidate the roles of Notch signaling pathway in human placentation. This review would focus on the roles of Notch receptors and ligands in the human placental trophoblasts function and placental angiogenesis. It might hopefully provide perspectives for future research about human placentation of pregnancy complicated by preeclampsia and other placenta associated diseases.

A role for Notch signaling in trophoblast endovascular invasion and in the pathogenesis of pre-eclampsia

Placental trophoblasts (TBs) invade and remodel uterine vessels with an arterial bias. This process, which involves vascular mimicry, re-routes maternal blood to the placenta, but fails in pre-eclampsia. We investigated Notch family members in both contexts, as they play important roles in arterial differentiation/function. Immunoanalyses of tissue sections showed step-wise modulation of Notch receptors/ligands during human TB invasion. Inhibition of Notch signaling reduced invasion of cultured human TBs and expression of the arterial marker EFNB2. In mouse placentas, Notch activity was highest in endovascular TBs. Conditional deletion of Notch2, the only receptor upregulated during mouse TB invasion, reduced arterial invasion, the size of maternal blood canals by 30-40% and placental perfusion by 23%. By E11.5, there was litter-wide lethality in proportion to the number of mutant offspring. In pre-eclampsia, expression of the Notch ligand JAG1 was absent in perivascular and endovascular TBs. We conclude that Notch signaling is crucial for TB vascular invasion.

Distribution of Notch family proteins in intrauterine growth restriction and hypertension complicated human term placentas

Members of the Notch family have been detected in many developmental and cell specification processes during placental development. However, Notch protein expression in Intrauterine Growth Restriction (IUGR) and Pregnancy Induced Hypertension (PIH) is not clear. In this study we aimed to clarify the immunolocalization of Notch proteins in full-term placentas after IUGR and PIH in comparison with normal placentas. Formalin-fixed, paraffin-embedded term placentas obtained by caesarean operations were processed for immunohistochemical localization of Notch 1, 2, 4 and Jagged 2. Transmission electron microscopy was also performed. In normal term placentas, all Notch proteins were intensely immunostained in the brush border of cells of the syncytiotrophoblast layer of the basal (maternal) side and the chorionic plate (fetal) side. The endothelial cells were also intensely immunostained in both sides for Notch 1. However, in IUGR and PIH placentas, the immunoreactivities of all Notch proteins were decreased significantly in the brush border of cells of the syncytiotrophoblast layer and the reaction was generally observed in the cytoplasm of syncytiotrophoblast cells in the basal and chorionic plate sides. The reactivity in endothelial cells was also significantly decreased. Our results have shown that the immunoreactivity and localization of Notch proteins is altered in pathologic placentas. Therefore, we propose that deregulated expression of Notch proteins may contribute to the disruption of trophoblast differentiation, endothelial cell function and/or feto-maternal traffic down-regulation during pregnancy or vice versa in such pathologic conditions.

Endoreplication: polyploidy with purpose

A great many cell types are necessary for the myriad capabilities of complex, multicellular organisms. One interesting aspect of this diversity of cell type is that many cells in diploid organisms are polyploid. This is called endopolyploidy and arises from cell cycles that are often characterized as "variant," but in fact are widespread throughout nature. Endopolyploidy is essential for normal development and physiology in many different organisms. Here we review how both plants and animals use variations of the cell cycle, termed collectively as endoreplication, resulting in polyploid cells that support specific aspects of development. In addition, we discuss briefly how endoreplication occurs in response to certain physiological stresses, and how it may contribute to the development of cancer. Finally, we describe the molecular mechanisms that support the onset and progression of endoreplication.

Genes and signals regulating murine trophoblast cell development

A fundamental step in embryonic development is cell differentiation whereby highly specialised cell types are developed from a single undifferentiated, fertilised egg. One of the earliest lineages to form in the mammalian conceptus is the trophoblast, which contributes exclusively to the extraembryonic structures that form the placenta. Trophoblast giant cells (TGCs) in the rodent placenta form the outermost layer of the extraembryonic compartment, establish direct contact with maternal cells, and produce a number of pregnancy-specific cytokine hormones. Giant cells differentiate from proliferative trophoblasts as they exit the cell cycle and enter a genome-amplifying endocycle. Normal differentiation of secondary TGCs is a critical step toward the formation of the placenta and normal embryonic development. Trophoblast development is also of particular interest to the developmental biologist and immunobiologist, as these cells constitute the immediate cellular boundary between the embryonic and maternal tissues. Abnormalities in the development of secondary TGCs results in severe malfunction of the placenta. Herein we review new information that has been accumulated recently regarding the molecular and cellular regulation of trophoblast and placenta development. In particular, we discuss the molecular aspects of murine TGC differentiation. We also focus on the role of growth and transcription factors in TGC development.

Transcriptional regulator BPTF/FAC1 is essential for trophoblast differentiation during early mouse development

The putative transcriptional regulator BPTF/FAC1 is expressed in embryonic and extraembryonic tissues of the early mouse conceptus. The extraembryonic trophoblast lineage in mammals is essential to form the fetal part of the placenta and hence for the growth and viability of the embryo in utero. Here, we describe a loss-of-function allele of the BPTF/FAC1 gene that causes embryonic lethality in the mouse. BPTF/FAC1-deficient embryos form apparently normal blastocysts that implant and develop epiblast, visceral endoderm, and extraembryonic ectoderm including trophoblast stem cells. Subsequent development of mutants, however, is arrested at the early gastrula stage (embryonic day 6.5), and virtually all null embryos die before midgestation. Most notably, the ectoplacental cone is drastically reduced or absent in mutants, which may cause the embryonic lethality. Development of the mutant epiblast is also affected, as the anterior visceral endoderm and the primitive streak do not form correctly, while brachyury-expressing mesodermal cells arise but are delayed. The mutant phenotype suggests that gastrulation is initiated, but no complete anteroposterior axis of the epiblast appears. We conclude that BPTF/FAC1 is essential in the extraembryonic lineage for correct development of the ectoplacental cone and fetomaternal interactions. In addition, BPTF/FAC1 may also play a role either directly or indirectly in anterior-posterior patterning of the epiblast.

Mechanisms in the regulation of aromatase in developing ovary and placenta

During human gestation, the placental syncytiotrophoblast develops the capacity to synthesize large amounts of estrogen from C(19)-steroids secreted by the fetal adrenals. The conversion of C(19)-steroids to estrogens is catalyzed by aromatase P450 (P450arom), product of the CYP19 gene. The placenta-specific promoter of the hCYP19 gene lies approximately 100,000 bp upstream of the translation initiation site in exon II. In studies using transgenic mice and transfected human trophoblast cells we have defined a 246-bp region upstream of placenta-specific exon I.1 that mediates placental cell-specific expression. Using transgenic mice, we also observed that as little as 278 bp of DNA flanking the 5'-end of ovary-specific hCYP19 exon IIa was sufficient to target ovary-specific expression. This ovary-specific promoter contains response elements that bind cAMP-response element-binding protein (CREB) and the orphan nuclear receptors SF-1 and LRH-1, which are required for cAMP-mediated stimulation of CYP19 expression in granulosa and luteal cells during the estrous cycle and pregnancy. In this article, we review our studies to define genomic regions and response elements that mediate placenta-specific expression of the hCYP19 gene. The temporal and spatial expression of LRH-1 versus SF-1 in the developing gonad during mouse embryogenesis and in the postnatal ovary also will be considered.

Notch2 is required for formation of the placental circulatory system, but not for cell-type specification in the developing mouse placenta

We have previously reported that a mutation in the ankyrin repeats of mouse Notch2 results in embryonic lethality by embryonic day 11.5 (E11.5), showing developmental retardation at E10.5. This indicated that Notch2 plays an essential role in postimplantation development in mice. Here, we demonstrate that whole embryo culture can circumvent developmental retardation of Notch2 mutant embryos for up to 1 day, suggesting that the lethality was primarily caused by extraembryonic defects. Histological examinations revealed delayed entry of maternal blood into the mutant placenta and poor blood sinus formation at later stages. Notch2-expressing cells appeared around maternal blood sinuses. Specification of trophoblast subtypes appeared not to be drastically disturbed and expression of presumptive downstream genes of Notch2 signaling was not altered by the Notch2 mutation. Thus, in the developing mouse placenta, Notch2 is unlikely to be involved in cell fate decisions, but rather participates in formation of maternal blood sinuses. In aggregation chimeras with wild-type tetraploid embryos, the mutant embryos developed normally until E12.5, but died before E13.5. The chimeric placentas showed a restored maternal blood sinus formation when compared with the mutant placentas, but not at the level of wild-type diploid placentas. Therefore, it was concluded that the mutant suffers from defects in maternal blood sinus formation. Thus, Notch2 is not cell autonomously required for the early cell fate determination of subtypes of trophoblast cells, but plays an indispensable role in the formation of maternal blood sinuses in the developing mouse placenta.

Analysis of Oct4-dependent transcriptional networks regulating self-renewal and pluripotency in human embryonic stem cells

The POU domain transcription factor OCT4 is a key regulator of pluripotency in the early mammalian embryo and is highly expressed in the inner cell mass of the blastocyst. Consistent with its essential role in maintaining pluripotency, Oct4 expression is rapidly downregulated during formation of the trophoblast lineage. To enhance our understanding of the molecular basis of this differentiation event in humans, we used a functional genomics approach involving RNA interference-mediated suppression of OCT4 function in a human ESC line and analysis of the resulting transcriptional profiles to identify OCT4-dependent genes in human cells. We detected altered expression of >1,000 genes, including targets regulated directly by OCT4 either positively (NANOG, SOX2, REX1, LEFTB, LEFTA/EBAF DPPA4, THY1, and TDGF1) or negatively (CDX2, EOMES, BMP4, TBX18, Brachyury [T], DKK1, HLX1, GATA6, ID2, and DLX5), as well as targets for the OCT4-associated stem cell regulators SOX2 and NANOG. Our data set includes regulators of ACTIVIN, BMP, fibroblast growth factor, and WNT signaling. These pathways are implicated in regulating human ESC differentiation and therefore further validate the results of our analysis. In addition, we identified a number of differentially expressed genes that are involved in epigenetics, chromatin remodeling, apoptosis, and metabolism that may point to underlying molecular mechanisms that regulate pluripotency and trophoblast differentiation in humans. Significant concordance between this data set and previous comparisons between inner cell mass and trophectoderm in human embryos indicates that the study of human ESC differentiation in vitro represents a useful model of early embryonic differentiation in humans.

Branching morphogenesis during development of placental villi

The placenta forms a complex interface between the mother and fetus during development that is designed for efficient nutrient exchange. A large surface area is created by extensive branching morphogenesis of the trophoblast-derived epithelium to create a villous network, called the labyrinth in rodents. These villi are subsequently vascularized with an elaborate capillary network. Morphogenesis begins with selection of a subset of trophoblast cells in the basal layer of the chorion that express the Gcm1 transcription factor. These cells leave the cell cycle and undergo cell shape changes that initiate a process of involution to create primary villi into which fetal blood vessels grow. Much less is known about the regulation of subsequent events in branching, certainly compared with other organs. However, over 60 different mouse mutants have defects during later labyrinth development. Some of these mutant genes encode components of signaling pathways such as the fibroblast growth factor and Wnt pathways that play evolutionarily conserved roles in other branched organs, These mutants represent a still largely untapped resource as most of them have not been studied in detail in relation to placental morphogenesis.

Generation of new Notch2 mutant alleles

The Notch signaling pathway is an evolutionarily conserved intercellular signaling mechanism, and mutations in its components disrupt embryonic development in many organisms and cause inherited diseases in humans. We previously described construction and analysis of a hypomorphic allele of the Notch2 gene. Homozygosity for this allele leads to embryonic and perinatal lethality due to cardiovascular and kidney defects. We report here novel Notch2 mutant alleles generated by gene targeting in embryonic stem cells, including a conditional null allele in which exon 3 of the Notch2 gene is flanked by loxP sequences. These new Notch2 mutant alleles expand the set of tools available for studying the myriad roles of the Notch pathway during mammalian development and will enable analysis of Notch2 function at additional stages of embryogenesis and in adult mice.

Imprinted genes in placental growth and obstetric disorders

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

Notch signaling through tramtrack bypasses the mitosis promoting activity of the JNK pathway in the mitotic-to-endocycle transition of Drosophila follicle cells

Background

The follicle cells of the Drosophila egg chamber provide an excellent model in which to study modulation of the cell cycle. During mid-oogenesis, the follicle cells undergo a variation of the cell cycle, endocycle, in which the cells replicate their DNA, but do not go through mitosis. Previously, we showed that Notch signaling is required for the mitotic-to-endocycle transition, through downregulating String/Cdc25, and Dacapo/p21 and upregulating Fizzy-related/Cdh1.

Results

In this paper, we show that Notch signaling is modulated by Shaggy and temporally induced by the ligand Delta, at the mitotic-to-endocycle transition. In addition, a downstream target of Notch, tramtrack, acts at the mitotic-to-endocycle transition. We also demonstrate that the JNK pathway is required to promote mitosis prior to the transition, independent of the cell cycle components acted on by the Notch pathway.

Conclusion

This work reveals new insights into the regulation of Notch-dependent mitotic-to-endocycle switch.

Mammalian Groucho homologs: redundancy or specificity?

The proteins termed TLE in humans, Grg in mice and Groucho in Drosophila constitute a family of transcriptional corepressors. In mammalians there are five different genes encoding an even larger number of proteins. Interactions between these TLE/Grg proteins and an array of transcription factors has been described. But is there any specificity? This review tries to make a case for a non-redundant function of individual TLE/Grg proteins. The specificity may be brought about by a tightly controlled temporo-spatial expression pattern, post-translational modifications, and subtle structural differences leading to distinct preferences for interacting transcription factors. A confirmation of this concept will ultimately need to come from genetic experiments.

JMJD2A is a novel N-CoR-interacting protein and is involved in repression of the human transcription factor achaete scute-like homologue 2 (ASCL2/Hash2)

Corepressor N-CoR (nuclear receptor corepressor) and the highly related protein SMRT (silencing mediator of retinoid and thyroid hormone receptor) play important roles in different biological processes including proliferation, differentiation, and development. Understanding the biological function of these corepressors requires identification and characterization of their interacting proteins. Here we report the characterization of a novel N-CoR-interacting protein, JMJD2A (previously known as KIAA0677). JMJD2A is an evolutionarily conserved nuclear protein containing many functionally unknown domains. JMJD2A directly interacts with the N-terminal region of N-CoR through a small NID (N-CoR interaction domain) both in vitro and in vivo. Despite its copurification with N-CoR, JMJD2A is not a core subunit of the stable multiprotein N-CoR complex and is not required for N-CoR-mediated repression by thyroid hormone receptor. By chromatin immunoprecipitation cloning, we identified the human achaete scute-like homologue 2 (ASCL2/Hash2) gene as a gene regulated by JMJD2A. ASCL2 is a basic helix-loop-helix transcription factor whose mouse homolog is encoded by an imprinted gene highly expressed during the development of extraembroynic trophoblast lineages but repressed in other tissues and is essential for proper placental development. We demonstrated that JMJD2A selectively represses the expression of the ASCL2 gene but not other imprinted genes in the same imprinted locus in HeLa cells and that this repression required a functional N-CoR complex and the tandem Tudor domain of JMJD2A. Like N-CoR, JMJD2A is widely expressed in various mouse tissues. Our data indicate that JMJD2A makes use of the N-CoR complex to repress transcription and suggest that JMJD2A together with N-CoR could play a role in repressing ASCL2 expression in various tissues.

Genomic regions that mediate placental cell-specific and developmental regulation of human Cyp19 (aromatase) gene expression in transgenic mice

The human aromatase (hCYP19) gene is controlled by tissue-specific promoters that lie upstream of tissue-specific first exons. Placenta-specific exon I.1 lies approximately 100,000 bp upstream of exon II. Previously, we observed that genomic sequences within 501 bp upstream of exon I.1 mediate placenta-specific expression. In the present study, transgenic mice were created carrying hCYP19I.1(-246):hGH/hGX, hCYP19I.1(-201):hGH, and hCYP19I.1(-125):hGH fusion genes to further delineate 5'-flanking sequences within 501 bp of exon I.1 that are required to mediate placenta-specific hCYP19 gene expression. As little as 246 bp of hCYP19 exon I.1 5'-flanking sequence was sufficient to direct placenta-specific expression in transgenic mice. By contrast, transgenes containing 201 or 125 bp of exon I.1 5'-flanking DNA were not expressed in mouse placenta. Furthermore, hCYP19I.1(-246):hGX transgene expression was developmentally regulated; expression was observed as early as embryonic d 7.5 (E7.5) in several cells of the trophoblast ectoderm, on E8.5 in some trophoblast giant cells, and by E9.5 in giant cells and the labyrinthine layer. By contrast, expression of the hCYP19I.1(-501):hGH transgene was first observed on E10.5 and was restricted to the labyrinthine layer, which is most analogous to the human syncytiotrophoblast. This suggests the presence of regulatory elements between -501 and -246 bp that may bind inhibitory transcription factors expressed in giant cells. These findings from transgenic experiments together with deletion mapping studies using transfected human placental cells indicate that the concerted interaction of strong placenta-specific enhancers and silencers within this 501-bp region mediate labyrinthine and syncytiotrophoblast-specific CYP19 gene expression.

Connexin31-deficient trophoblast stem cells: a model to analyze the role of gap junction communication in mouse placental development

The connexin (Cx) expression during placental development in rodents is subject to exacting spatiotemporal regulation. Following implantation, Cx31 characterizes the early trophoblast cell lineage and is expressed by the spongiotrophoblast during placental development until birth. Inactivation of the Cx31 gene results in a transient placental dysmorphogenesis with an imbalance in the trophoblast cell lineage differentiation in favor to giant cells [Dev. Biol. 231 (2001) 334]. In this study, we show that trophoblast stem (TS) cells exhibit the same connexin expression found in trophoblast cell lineage differentiation. Undifferentiated TS cells exclusively express Cx31 protein and Cx31.1 transcripts. Upon differentiation of TS cells, placental-specific Cx26 and Cx43 are induced. Cx31 knockout TS cells revealed an accelerated differentiation process to giant cells compared to controls, indicated by an overall shift in expression of connexins and marker genes such as Mash2, Pl-1, and Tpbpa. Moreover, proliferation was significantly reduced in Cx31 knockout TS cells upon differentiation. Both wild type and Cx31 knockout TS cells are able to invade and erode host vessels when injected into nude mice. We conclude that during trophoblast cell lineage differentiation, the Cx31 gap junction channel is involved in maintaining the proliferative diploid trophoblast cell population.

Haploinsufficient lethality and formation of arteriovenous malformations in Notch pathway mutants

The Notch signaling pathway is essential for embryonic vascular development in vertebrates. Here we show that mouse embryos heterozygous for a targeted mutation in the gene encoding the DLL4 ligand exhibit haploinsufficient lethality because of defects in vascular remodeling. We also describe vascular defects in embryos homozygous for a mutation in the Rbpsuh gene, which encodes the primary transcriptional mediator of Notch signaling. Conditional inactivation of Rpbsuh function demonstrates that Notch activation is essential in the endothelial cell lineage. Notch pathway mutant embryos exhibit defects in arterial specification of nascent blood vessels and develop arteriovenous malformations. These results demonstrate that vascular remodeling in the mouse embryo is sensitive to Dll4 gene dosage and that Notch activation in endothelial cells is essential for embryonic vascular remodeling.

The Hand1, Stra13 and Gcm1 transcription factors override FGF signaling to promote terminal differentiation of trophoblast stem cells

The trophoblast cell lineage is an interesting model system because it is composed of a limited number of cell types that are spatially patterned. Trophoblast stem (TS) cells reside within a layer called the chorion and either remain as stem cells or differentiate into spongiotrophoblast (SpT), trophoblast giant (TG) cells or syncytiotrophoblast cells (SynT) of the labyrinth. Maintenance of the TS phenotype is dependent on stimulation by FGF4, whereas differentiation and/or maintenance of the differentiated derivatives are dependent on key transcription factors: Mash2 for SpT, Hand1 for TG cells and Gcm1 for SynT cells. TS cells proliferate and retain their stem cell phenotype in culture in response to FGF4 and an additional factor(s) that can be provided by conditioned medium from embryonic fibroblast feeder cells (CM). To understand the functions of Hand1, Mash2 and Gcm1 at a cellular level, we tested the effects of their ectopic and over-expression on the ability of TS cells to either continue to proliferate or differentiate into their alternative fates. Expression of Mash2 alone had no effects on TS cell differentiation. However, Mash2-transfected cells continued to divide longer after withdrawal of FGF/CM. Hand1 promoted TGC differentiation, even in the continued presence of FGF4/CM. Stra13, another bHLH factor gene that is expressed in TG cells, also induced TG differentiation. Gcm1 induced a rapid arrest of TS proliferation but, in contrast to Hand1 and Stra13, blocked TG cell differentiation. Although Gcm1 was not sufficient to promote SynT formation, expression of an antisense Gcm1 transcript blocked SynT differentiation. These data suggest that Mash2 functions to promote transient FGF4-independent amplification of trophoblast cells that are progressing towards the SpT and TG cell phenotype. By contrast, Hand1 and Stra13 promote cell cycle exit and restrict cells towards the TG fate, whereas Gcm1 promotes cell cycle exit and restriction towards the SynT fate.

The mitotic-to-endocycle switch in Drosophila follicle cells is executed by Notch-dependent regulation of G1/S, G2/M and M/G1 cell-cycle transitions

The Notch signaling pathway controls the follicle cell mitotic-to-endocycle transition in Drosophila oogenesis by stopping the mitotic cycle and promoting the endocycle. To understand how the Notch pathway coordinates this process, we have identified and performed a functional analysis of genes whose transcription is responsive to the Notch pathway at this transition. These genes include the G2/M regulator Cdc25 phosphatase, String; a regulator of the APC ubiquitination complex Hec/CdhFzr and an inhibitor of the CyclinE/CDK complex, Dacapo. Notch activity leads to downregulation of String and Dacapo, and activation of Fzr. All three genes are independently responsive to Notch. In addition, CdhFzr, an essential gene for endocycles, is sufficient to stop mitotic cycle and promote precocious endocycles when expressed prematurely during mitotic stages. In contrast, overexpression of the growth controller Myc does not induce premature endocycles but accelerates the kinetics of normal endocycles. We also show that Archipelago (Ago), a SCF-regulator is dispensable for mitosis, but crucial for endocycle progression in follicle epithelium. The results support a model in which Notch activity executes the mitotic-to-endocycle switch by regulating all three major cell cycle transitions. Repression of String blocks the M-phase, activation of Fzr allows G1 progression and repression of Dacapo assures entry into the S-phase. This study provides a comprehensive picture of the logic that external signaling pathways may use to control cell cycle transitions by the coordinated regulation of the cell cycle.

Chorioallantoic morphogenesis and formation of the placental villous tree

The placenta is a highly specialized organ whose primary function is to promote the exchange of nutrients and oxygen between maternal and fetal blood, essential for survival and growth of the baby. The surface area for nutrient transport is a highly convoluted villous structure that forms by branching morphogenesis. In mice, this process begins after embryonic day 8.5, following attachment of allantoic mesoderm to the chorion, and continues through the end of gestation. Gene targeting studies in mice have identified a large number of genes that are essential for chorioallantoic development to give rise to the layer of the placenta called the labyrinth. Collectively, these studies reveal that a number of signaling pathways regulate four distinct phases of labyrinth development: chorioallantoic attachment (involving VCAM1 and its receptor alpha4 integrin, Bmp5/7, and Wnt7b, as well as the cochaperone Mrj), initiation of branching (involving the Gcm1 transcription factor to select sites of branch initiation), extension of villous branching (involving FGF, EGF, and HGF/Met signaling, through the Grb2/Sos1/Mek1/p38alpha MAPK pathway), followed by vascularization of the villous tree. The restricted expression and/or action of the signaling components indicate that a series of intercellular interactions regulate chorioallantoic development.

Chimeric analysis ofNotch2 function: A role for Notch2 in the development of the roof plate of the mouse brain

Notch proteins are transmembrane receptors involved in cell-fate determination throughout development. Targeted disruption of either the Notch1 or Notch2 gene in mice results in embryonic lethality around embryonic day (E) 10.5 with widespread cell death. Although Notch1-deficient mice show disorganized somitogenesis, Notch2 mutants did not show definitive abnormalities in any tissue expressing high levels of the Notch2 gene, including the central nervous system. To study Notch2 function in development beyond the embryonic lethal stage, we performed chimeric analysis between Notch2 mutant and wild-type mouse embryos. Chimeric embryos developed normally and homozygous Notch2 mutant-specific cell death was not observed. Although chimeric embryos showed normal mosaicism until E9.5 in all tissues studied to date, Notch2 homozygous mutant cells failed to contribute to formation of the roof plate of the diencephalon and mesencephalon at later developmental stages, when Notch2 is normally expressed at high levels at there. Furthermore, Notch2 heterozygous mutant cells were also excluded from the roof plate of the chimera, however, Notch2 heterozygous mutant mice developed normally. We also showed that Wnt-1 and Mash1 expression patterns at the roof plate were disorganized in Notch2 homozygous mutant embryos. These results indicate that Notch2 plays an important role in development of the roof plate of the diencephalon and mesencephalon, and suggest that cellular rearrangement is involved in this process.

A functional composite cis-element for NF kappa b and RBJ kappa in the rat pregnancy-specific glycoprotein gene

The rat pregnancy-specific glycoprotein gene rnCGM3 is primarily expressed in the placenta. Previously, three DNase I footprinting sites (FPI, FPII, and FPIII) were identified in the rnCGM3 promoter region, a yeast one-hybrid screen was performed to identify the nuclear factors binding to the FPIII (5'-GCCTGGGAAAAAACTC-3') element, and RBPJ kappa, a downstream effector of the Notch signaling pathway, was identified as one of the FPIII-binding factors. In the present study, the NF kappa B member p65 was identified as another FPIII-binding factor. Electrophoretic mobility shift assays showed that NF kappa B members, including p50 and p65, bound to the FPIII site. The core binding sequence in the FPIII element for p50 and p65 is GGGAAA, which overlaps with that for RBPJ kappa. Competition exists between p50 and RBPJ kappa for binding to the FPIII element. Transient expression analyses revealed that p65 significantly stimulated the expression of a reporter gene directed by the NF kappa B core sequence in the FPIII element. However, RBPJ kappa could block this stimulation. These results suggest that the regulation of rnCGM3 expression involves both NF kappa B and RBPJ kappa, and they are mutually exclusive in the FPIII element.

Connexin31-deficiency in mice causes transient placental dysmorphogenesis but does not impair hearing and skin differentiation

Mutations in the human GJB3 gene that codes for Connexin31 (Cx31), a protein subunit of gap junction channels, have recently been reported to cause deafness and the skin disorder erythrokeratodermia variabilis. To study the function of this gene in mice, we generated animals with targeted replacement of the Cx31 gene (Gjb3) by a lacZ reporter gene. Although homozygous Cx31-deficient adult mice (Gjb3(-/-)) were found among the offspring of heterozygous Cx31-deficient parents (Gjb3(+/-)), 60% of the animals expected according to Mendelian inheritance were lost between ED 10.5 and 13.5. Placentas of Gjb3(-/-) embryos at ED 9.5 were smaller than controls as a result of severely reduced labyrinth and spongiotrophoblast size. From ED 10.5 onward, placentas of surviving Gjb3(-/-) embryos recovered progressively and reached normal size and morphology by ED 18.5. This corresponds to a time period in which another connexin isoform, Connexin43, is upregulated in spongiotrophoblast cells of Cx31-deficient and control placentas. No morphological or functional defects of skin or inner ear were observed in surviving adult Gjb3(-/-) mice. We conclude that Cx31 is essential for early placentation but can be compensated for by other connexins in the embryo proper and adult mouse.

Hypoxia prevents induction of aromatase expression in human trophoblast cells in culture: potential inhibitory role of the hypoxia-inducible transcription factor Mash-2 (mammalian achaete-scute homologous protein-2)

The human placenta has a remarkable capacity to aromatize C19-steroids, produced by the fetal adrenals, to estrogens. This reaction is catalyzed by aromatase P450 (P450arom), encoded by the CYP19 gene. In placenta, CYP19 gene expression is restricted to the syncytiotrophoblast layer. Cytotrophoblasts isolated from human placenta, when placed in monolayer culture in 20% O2, spontaneously fuse to form syncytiotrophoblast. These morphological changes are associated with a marked induction of aromatase activity and CYP19 gene expression. When cytotrophoblasts are cultured in an atmosphere containing 2% O2, they manifest increased rates of DNA synthesis and fail to fuse and form syncytiotrophoblast. The objective of the present study was to utilize cytotrophoblasts isolated from midterm human placenta to analyze the effects of O2 on CYP19 gene expression and the molecular mechanisms that mediate these effects. We observed that when trophoblast cells were maintained in 2% O2, there was only a modest induction of CYP19 expression as a function of time in culture, and aromatase activity was barely detectable. However, when cytotrophoblasts that had been maintained in 2% O2 for 3 days were placed in a 20% O2 environment, there was a rapid onset of cell fusion and induction of P450arom mRNA and aromatase activity. In addition, mRNAs for the helix-loop-helix factors Mash-2 (mammalian achaete-scute homologous protein-2) and Id1 (inhibitor of differentiation 1) were readily detectable in freshly isolated cytotrophoblasts and were markedly decreased upon differentiation to syncytiotrophoblast in 20% O2. By contrast, when cytotrophoblasts were cultured in 2% O2, mRNA levels for Mash-2 and Id1 remained elevated. Interestingly, overexpression of Mash-2 in primary cultures of human trophoblast cells markedly inhibited cell fusion and the spontaneous induction of P450arom mRNA levels and caused a marked decrease in expression of co-transfected fusion gene constructs containing either 125, 201, 246, or 501 bp of DNA flanking the 5'-end of the placenta-specific exon (exon I.1) of the human CYP19 gene linked to the human GH (hGH) structural gene, as reporter. In studies using BeWo, a human choriocarcinoma cell line, overexpression of Mash-2 also inhibited expression of cotransfected CYP19I.1:hGH fusion gene constructs. The findings that Mash-2 had no effect on the expression of a CYP19I.1(-42):hGH fusion gene in primary cultures of human trophoblast and BeWo cells suggest that Mash-2 exerts its inhibitory effects directly or indirectly though CYP19I.1 5'-flanking sequences that lie between -42 and -125 bp. By contrast, neither Id1 nor Id2 had an effect on CYP19I. 1 promoter activity in the transfected BeWo cells. These findings suggest that Mash-2 may serve as a hypoxia-induced transcription factor that prevents differentiation to syncytiotrophoblast and aromatase induction in human trophoblast cultured under low O2 conditions.

E-selectin expression and function in a unique placental trophoblast population at the fetal-maternal interface: regulation by a trophoblast-restricted transcriptional mechanism conserved between humans and mice

Trophoblast are the earliest differentiated cells to emerge during mammalian ontogeny. Proper differentiation and maturation of trophoblast contributes to the fetal-maternal vascular interface of the mature placenta and is required for all subsequent stages of embryogenesis. Although lineage commitment and early differentiation of trophoblast have been investigated experimentally, molecular markers and regulatory mechanisms operating later in trophoblast development remain uncertain. We now report that E-selectin is expressed in a unique pattern in secondary trophoblast giant cells, trophoblast lining the central artery, and a subpopulation of labyrinthine trophoblast all located at the fetal-maternal interface of the murine placenta. These cells line vascular channels but express a unique profile of gene products not displayed by vascular endothelium. Placentae lacking E-selectin show increased trophoblast glycogen cells and fewer labyrinthine neutrophils compared with normal placentae, suggesting that recognition of E-selectin on trophoblast by counter-receptors on other cells contributes to placental development. Novel, distant first exons direct E-selectin expression in both murine and human placentae, suggesting that evolutionarily conserved and lineage-restricted transcriptional mechanisms regulate expression in homologous trophoblast populations in both species. These results define, at molecular and anatomic levels, a unique population of trophoblast located at the physiologically critical fetal-maternal vascular interface in mice. We also present initial functional characterization of E-selectin in placenta. These results support the general hypothesis that endothelial-leukocyte adhesion molecules performing specialized functions in adults may also function in development of human and murine hemochorial placentae.

Distinct regulatory elements direct delta1 expression in the nervous system and paraxial mesoderm of transgenic mice

The Delta1 gene encodes one of the Notch ligands in mice. Delta1 is expressed during early embryogenesis in a complex and dynamic pattern in the paraxial mesoderm and neuroectoderm, and is essential for normal somitogenesis and neuronal differentiation. Molecular components thought to act in response to ligand binding and Notch activation have been identified in different species. In contrast, little is known about the transcriptional regulation of Notch receptors and their ligands. As a first step to identify upstream factors regulating Delta1 expression in different tissues, we searched for cis-regulatory regions in the Delta1 promoter able to direct heterologous gene expression in a tissue specific manner in transgenic mice. Our results show that a 4.3 kb genomic DNA fragment of the Delta1 gene is sufficient in a lacZ reporter transgene to reproduce most aspects of Delta1 expression from the primitive streak stage to early organogenesis. Using a minimal Delta1 promoter we also show that this upstream region contains distinct regulatory modules that individually direct tissue-specific transgene expression in subdomains of the endogenous expression pattern. It appears that expression in the paraxial mesoderm depends on the interaction of multiple positive and negative regulatory elements. We also find that at least some regulatory sequences required for transgene expression in subdomains of the neural tube have been maintained during the evolution of mammals and teleost fish, suggesting that part of the regulatory network that controls expression of Delta genes may be conserved.

Genetic insights into trophoblast differentiation and placental morphogenesis

The placenta is comprised of an inner vascular network covered by an outer epithelium, called trophoblast, all designed to promote the delivery of nutrients to the fetus. Several specialized trophoblast cell subtypes arise during development to promote this function, including cells that invade the uterus to promote maternal blood flow to the implantation site, and other cells that fuse into a syncytium, expand and fold to increase the surface area for efficient transport. Mutation of many genes in mice results in embryonic mortality or fetal growth restriction due to defects in placental development. Several important principles about placental development have emerged from these studies. First, distinct molecular pathways regulate the differentiation of the various trophoblast cell subtypes. Second, trophoblast proliferation, differentiation and morphogenesis are highly regulated by interactions with adjacent cell types. Finally, the specific classes of mutant phenotypes observed in the placenta of knockout mice resemble those seen in humans that are associated with preeclampsia and intrauterine growth restriction.

Active intracellular domain of Notch enhances transcriptional activation of CCAAT/enhancer binding protein beta on a rat pregnancy-specific glycoprotein gene

Pregnancy-specific glycoproteins (PSGs) are primarily expressed in the placenta and become the major glycoproteins at term. To understand the regulation of PSG expression, we characterized the promoter elements of a rodent PSG gene, rnCGM3, and delineated three nuclear protein binding sites: FPI, -II, and -III in the 5'-flanking region of the gene. The FPII-binding factor is shown to be C/EBPbeta, which positively regulates rnCGM3 expression [Chen, H., et al. (1995) DNA Cell Biol. 14, 681-688]. In the current study, we used the yeast one-hybrid system to isolate transcription factors binding to the FPIII site and demonstrated that a rodent J kappa recombination signal sequence binding protein, rRBPJ kappa-2N, bound to the FPIII site. Electrophoretic mobility shift assay with rat placental nuclear proteins revealed a constitutive occupancy of the FPIII site by RBPJ kappa. By transient expression analyses, we demonstrated that rRBPJ kappa-2N repressed the expression from an FPIII-driven SV40 promoter. However, this repression effect was counteracted by the active intracellular domain of Notch (NotchIC). Using the native rnCGM3 promoter construct, we demonstrated that the promoter activity stimulated by C/EBP beta was also repressed by rRBPJ kappa-2N but enhanced by NotchIC. Additionally, we found that NotchIC can stimulate expression through another RBPJkappa site within the FPI site. A functional interaction between factors binding to the FPI, FPII, and FPIII sites is proposed.

Id-2 regulates critical aspects of human cytotrophoblast differentiation, invasion and migration

During early human placental development, the conceptus attaches itself to the uterus through cytotrophoblast invasion. Invasive cytotrophoblast cells differentiate from precursor villous cytotrophoblasts, but the essential regulating factors in this process are unknown. Basic helix-loop-helix (bHLH) transcription factor dimers are essential regulators of mouse trophoblast development. We therefore examined the importance of this family of factors in the human placenta. In many cell lineages, bHLH factors are sequestered by members of the Id family, HLH proteins that lack the basic DNA binding domain (Inhibitor of DNA binding proteins (Id-1 to Id-4)). During differentiation of some tissues, Id expression declines, allowing bHLH factors to dimerize, bind DNA and trans-activate lineage-specific genes. To begin to study the role of bHLH transcription factors in human placental development, we first characterized Id expression in cytotrophoblast cells. The cells expressed Id-3 constitutively; Id-2 was downregulated, at the mRNA and protein levels, as the cells differentiated in culture and in situ, respectively. In cases when cytotrophoblast differentiation was compromised (in placentas from women with preeclampsia, or in cells grown under hypoxic conditions in culture), Id-2 expression was maintained. To assess the functional relevance of these correlations, we used an adenovirus vector to maintain Id-2 protein expression in cultured cytotrophoblasts. Compared to control (lacZ-expressing) cells, cytotrophoblasts transduced to constitutively express Id-2 retained characteristics of undifferentiated cells: (alpha)1 integrin expression was low and cyclin B expression was retained. Furthermore, invasion through Matrigel was partially inhibited and migration was strikingly enhanced in Id-2-expressing cells. These results suggest that Id-2 and the bHLH factors that it partners play important roles in human cytotrophoblast development.