Transcription factor gene AP-2 gamma essential for early murine development

Transcription factor AP-2delta regulates the expression of polysialyltransferase ST8SIA2 in chick retina

The AP-2δ transcription factor is restricted to a subset of retinal ganglion cells. Overexpression of AP-2δ in chick retina results in induction of polysialylated neural cell adhesion molecule (PSA-NCAM) accompanied by misrouting and bundling of ganglion cell axons. Two polysialyltransferases, ST8SIA2 and ST8SIA4, are responsible for polysialylation of NCAM. Here, we investigate the mechanism driving the increase in PSA-NCAM observed upon AP-2δ overexpression. We show that ST8SIA2 is induced by AP-2δ overexpression in chick retina. We use chromatin immunoprecipitation and gel shift assays to demonstrate direct interaction between AP-2δ and the ST8SIA2 promoter. We propose that up-regulation of ST8SIA2 upon AP-2δ overexpression in retina increases ectopic polysialylation of NCAM which in turn causes premature bundling of axons and alters axonal response to guidance cues.

Ectopic expression of transcription factor AP-2δ in developing retina: effect on PSA-NCAM and axon routing

Retinal ganglion cells transmit the visual signal from the retina to the brain. We have previously shown that the activator protein 2 (AP-2)δ (TFAP2D) transcription factor is expressed in one third of ganglion cells in developing retina suggesting a specialized role for these AP-2δ-expressing cells. Here, we address the role of AP-2δ in retina by in ovo electroporation of RCAS/AP-2δ retroviral constructs into the eyes of chick embryos at day 2 of gestation. Ectopic expression of AP-2δ does not affect lineage differentiation in the developing retina. However, immunostaining of retinal tissue with markers associated with axonal growth such as growth-associated protein 43 and polysialic acid-neural cell adhesion molecule (PSA-NCAM) demonstrates axonal misrouting and abnormal axonal bundling. Treatment of AP-2δ-misexpressing retinal cell cultures with endoneuraminidase, an enzyme that removes PSA from NCAM, decreases AP-2δ-induced axonal bundling. Our data suggest a role for AP-2δ in polysialylation of NCAM, with ectopic expression of AP-2δ resulting in premature bundling of emerging axons and misrouting of axons. We propose that expression of AP-2δ in a subset of ganglion cells contributes to the fine-tuning of axonal growth in the developing retina.

Context-dependent wiring of Sox2 regulatory networks for self-renewal of embryonic and trophoblast stem cells

Sox2 is a transcription factor required for the maintenance of pluripotency. It also plays an essential role in different types of multipotent stem cells, raising the possibility that Sox2 governs the common stemness phenotype. Here we show that Sox2 is a critical downstream target of fibroblast growth factor (FGF) signaling, which mediates self-renewal of trophoblast stem cells (TSCs). Sustained expression of Sox2 together with Esrrb or Tfap2c can replace FGF dependency. By comparing genome-wide binding sites of Sox2 in embryonic stem cells (ESCs) and TSCs combined with inducible knockout systems, we found that, despite the common role in safeguarding the stem cell state, Sox2 regulates distinct sets of genes with unique functions in these two different yet developmentally related types of stem cells. Our findings provide insights into the functional versatility of transcription factors during embryogenesis, during which they can be recursively utilized in a variable manner within discrete network structures.

Curcumin inhibits AP-2γ-induced apoptosis in the human malignant testicular germ cells in vitro

AIM

To investigate the effects of curcumin on proliferation and apoptosis in testicular cancer cells in vitro and to investigate its molecular mechanisms of action.

METHODS

NTera-2 human malignant testicular germ cell line and F9 mouse teratocarcinoma stem cell line were used. The anti-proliferative effect was examined using MTT and colony formation assays. Hoechst 33258 staining, TUNEL and Annexin V-FITC/PI staining assays were used to analyze cell apoptosis. Protein expression was examined with Western blot analysis and immunocytochemical staining.

RESULTS

Curcumin (5, 10 and 15 μmol/L) inhibited the viability of NTera-2 cells in dose- and time-dependent manners. Curcumin significantly inhibited the colony formation in both NTera-2 and F9 cells. Curcumin dose-dependently induced apoptosis of NTera-2 cells by reducing FasL expression and Bcl-2-to-Bax ratio, and activating caspase-9, -8 and -3. Furthermore, curcumin dose-dependently reduced the expression of AP transcription factor AP-2γ in NTera-2 cells, whereas the pretreatment with the proteasome inhibitor MG132 blocked both the curcumin-induced reduction of AP-2γ and antiproliferative effect. Curcumin inhibited ErbB2 expression, and decreased the phosphorylation of Akt and ERK in NTera-2 cells.

CONCLUSION

Curcumin induces apoptosis and inhibits proliferation in NTera-2 cells via the inhibition of AP-2γ-mediated downstream cell survival signaling pathways.

Landscape of transcriptional deregulations in the preeclamptic placenta

Preeclampsia is a pregnancy disease affecting 5 to 8% of pregnant women and a leading cause of both maternal and fetal mortality and morbidity. Because of a default in the process of implantation, the placenta of preeclamptic women undergoes insufficient vascularization. This results in placental ischemia, inflammation and subsequent release of placental debris and vasoactive factors in the maternal circulation causing a systemic endothelial activation. Several microarray studies have analyzed the transcriptome of the preeclamptic placentas to identify genes which could be involved in placental dysfunction. In this study, we compared the data from publicly available microarray analyses to obtain a consensus list of modified genes. This allowed to identify consistently modified genes in the preeclamptic placenta. Of these, 67 were up-regulated and 31 down-regulated. Assuming that changes in the transcription level of co-expressed genes may result from the coordinated action of a limited number of transcription factors, we looked for over-represented putative transcription factor binding sites in the promoters of these genes. Indeed, we found that the promoters of up-regulated genes are enriched in putative binding sites for NFkB, CREB, ANRT, REEB1, SP1, and AP-2. In the promoters of down-regulated genes, the most prevalent putative binding sites are those of MZF-1, NFYA, E2F1 and MEF2A. These transcriptions factors are known to regulate specific biological pathways such as cell responses to inflammation, hypoxia, DNA damage and proliferation. We discuss here the molecular mechanisms of action of these transcription factors and how they can be related to the placental dysfunction in the context of preeclampsia.

Overlapping expression patterns and redundant roles for AP-2 transcription factors in the developing mammalian retina

BACKGROUND

We have previously shown that the transcription factor AP-2α (Tcfap2a) is expressed in postmitotic developing amacrine cells in the mouse retina. Although retina-specific deletion of Tcfap2a did not affect retinogenesis, two other family members, AP-2β and AP-2γ, showed expression patterns similar to AP-2α.

RESULTS

Here we show that, in addition to their highly overlapping expression patterns in amacrine cells, AP-2α and AP-2β are also co-expressed in developing horizontal cells. AP-2γ expression is restricted to amacrine cells, in a subset that is partially distinct from the AP-2α/β-immunopositive population. To address possible redundant roles for AP-2α and AP-2β during retinogenesis, Tcfap2a/b-deficient retinas were examined. These double mutants showed a striking loss of horizontal cells and an altered staining pattern in amacrine cells that were not detected upon deletion of either family member alone.

CONCLUSIONS

These studies have uncovered critical roles for AP-2 activity in retinogenesis, delineating the overlapping expression patterns of Tcfap2a, Tcfap2b, and Tcfap2c in the neural retina, and revealing a redundant requirement for Tcfap2a and Tcfap2b in horizontal and amacrine cell development.

Embryonic stem cell-derived trophoblast differentiation: a comparative review of the biology, function, and signaling mechanisms

The development of the placenta is imperative for successful pregnancy establishment, yet the earliest differentiation events of the blastocyst-derived trophectoderm that forms the placenta remain difficult to study in humans. Human embryonic stem cells (hESC) display a unique ability to form trophoblast cells when induced to differentiate either by the addition of exogenous BMP4 or by the formation of cellular aggregates called embryoid bodies. While mouse trophoblast stem cells (TSC) have been isolated from blastocyst outgrowths, mouse ESC do not spontaneously differentiate into trophoblast cells. In this review, we focus on addressing the similarities and differences between mouse TSC differentiation and hESC-derived trophoblast differentiation. We discuss the functional and mechanistic diversity that is found in different species models. Of central importance are the unique signaling events that trigger downstream gene expression that create specific cellular fate decisions. We support the idea that we must understand the nuances that hESC differentiation models display so that investigators can choose the appropriate model system to fit experimental needs.

Induction of the inner ear: stepwise specification of otic fate from multipotent progenitors

Despite its complexity in the adult, during development the inner ear arises from a simple epithelium, the otic placode. Placode specification is a multistep process that involves the integration of various signalling pathways and downstream transcription factors in time and space. Here we review the molecular events that successively commit multipotent ectodermal precursors to the otic lineage. The first step in this hierarchy is the specification of sensory progenitor cells, which can contribute to all sensory placodes, followed by the induction of a common otic-epibranchial field and finally the establishment the otic territory. In recent years, some of the molecular components that control this process have been identified, and begin to reveal complex interactions. Future studies will need to unravel how this information is integrated and encoded in the genome. This will form the blueprint for stem cell differentiation towards otic fates and generate a predictive gene regulatory network that models the earliest steps of otic specification.

Primordial germ cells in mice

Germ cell development creates totipotency through genetic as well as epigenetic regulation of the genome function. Primordial germ cells (PGCs) are the first germ cell population established during development and are immediate precursors for both the oocytes and spermatogonia. We here summarize recent findings regarding the mechanism of PGC development in mice. We focus on the transcriptional and signaling mechanism for PGC specification, potential pluripotency, and epigenetic reprogramming in PGCs and strategies for the reconstitution of germ cell development using pluripotent stem cells in culture. Continued studies on germ cell development may lead to the generation of totipotency in vitro, which should have a profound influence on biological science as well as on medicine.

Genome-scale study of transcription factor expression in the branching mouse lung

BACKGROUND

Mammalian lung development consists of a series of precisely choreographed events that drive the progression from simple lung buds to the elaborately branched organ that fulfills the vital function of gas exchange. Strict transcriptional control is essential for lung development. Among the large number of transcription factors encoded in the mouse genome, only a small portion of them are known to be expressed and function in the developing lung. Thus a systematic investigation of transcription factors expressed in the lung is warranted.

RESULTS

To enrich for genes that may be responsible for regional growth and patterning, we performed a screen using RNA in situ hybridization to identify genes that show restricted expression patterns in the embryonic lung. We focused on the pseudoglandular stage during which the lung undergoes branching morphogenesis, a cardinal event of lung development. Using a genome-scale probe set that represents over 90% of the transcription factors encoded in the mouse genome, we identified 62 transcription factor genes with localized expression in the epithelium, mesenchyme, or both. Many of these genes have not been previously implicated in lung development.

CONCLUSIONS

Our findings provide new starting points for the elucidation of the transcriptional circuitry that controls lung development.

Cell fate regulation in early mammalian development

Preimplantation development in mammals encompasses a period from fertilization to implantation and results in formation of a blastocyst composed of three distinct cell lineages: epiblast, trophectoderm and primitive endoderm. The epiblast gives rise to the organism, while the trophectoderm and the primitive endoderm contribute to extraembryonic tissues that support embryo development after implantation. In many vertebrates, such as frog or fish, maternally supplied lineage determinants are partitioned within the egg. Cell cleavage that follows fertilization results in polarization of these factors between the individual blastomeres, which become restricted in their developmental fate. In contrast, the mouse oocyte and zygote lack clear polarity and, until the eight-cell stage, individual blastomeres retain the potential to form all lineages. How are cell lineages specified in the absence of a maternally supplied blueprint? This is a fundamental question in the field of developmental biology. The answer to this question lies in understanding the cell-cell interactions and gene networks involved in embryonic development prior to implantation and using this knowledge to create testable models of the developmental processes that govern cell fates. We provide an overview of classic and contemporary models of early lineage development in the mouse and discuss the emerging body of work that highlights similarities and differences between blastocyst development in the mouse and other mammalian species.

Health during pregnancy and beyond: Fetal trophoblast cells as chief co-ordinators of intrauterine growth and reproductive success

Abstract Differentiation of extra-embryonic tissues and organs, notably the placenta, is vital for embryonic development and growth throughout gestation, starting from a few days after fertilization when the trophoblast cell lineage arises until parturition. In utero metabolic programming events may even extend the impact of placental function well into adulthood as they may predispose the offspring to common pathologies such as diabetes and cardiovascular disease. This review summarizes key steps that lead up to formation of a functional placenta. It highlights recent insights that have advanced our view of how early trophoblast expansion is achieved and how sufficient maternal blood supply to the developing fetus is secured. Exciting cumulative data have revealed the importance of a close cross-talk between the embryo proper and extra-embryonic trophoblast cells that involves extracellular matrix components in the establishment of a stem cell-like niche and proliferation compartment. Remarkably, placental function also relies on beneficial interactions between trophoblast cells and maternal immune cells at the implantation site. Our growing knowledge of the molecular mechanisms involved in trophoblast differentiation and function will help to devise informed approaches aimed at deciphering how placentation is controlled in humans as an essential process for reproductive success and long-term health.

The role of transcription factor Tcfap2c/TFAP2C in trophectoderm development

In recent years, knowledge regarding the genetic and epigenetic programmes governing specification, maintenance and differentiation of the extraembryonic lineage has advanced substantially. Establishment and analysis of mice deficient in genes implicated in trophoblast lineage and the option to generate and manipulate murine stem cell lines from the inner cell mass and the trophectoderm in vitro represent major advances. The activating enhancer binding protein 2 (AP2) family of transcription factors is expressed during mammalian development and in certain malignant diseases. This article summarizes the data regarding expression and function of murine Tcfap2 and human TFAP2 in extraembryonic development and differentiation. It also presents a model integrating Tcfap2c into the framework of trophoblast development and highlights the requirement of Tcfap2c to maintain trophoblast stem cells. With regard to human trophoblast cell-lineage restriction, the role of TFAP2C in lineage specification and maintenance is speculated upon. Furthermore, an overview of target genes of AP2 in mouse and human affecting placenta development and function is provided and the evidence suggesting that defects in regulating TFAP2 members might contribute to placental defects is discussed.

Trophoblast development

This review summarises current knowledge about the specification, commitment and maintenance of the trophoblast lineage in mice and cattle. Results from gene expression studies, in vivo loss-of-function models and in vitro systems using trophoblast and embryonic stem cells have been assimilated into a model seeking to explain trophoblast ontogeny via gene regulatory networks. While trophoblast differentiation is quite distinct between cattle and mice, as would be expected from their different modes of implantation, recent studies have demonstrated that differences arise much earlier during trophoblast development.

AP-2δ is a crucial transcriptional regulator of the posterior midbrain

Ap-2 transcription factors comprise a family of 5 closely related sequence-specific DNA binding proteins that play pivotal and non-redundant roles in embryonic organogenesis. To investigate the function of Ap-2δ, wδe analyzed its expression during embryogenesis and generated Ap-2δ-deficient mice. In line with the specific expression pattern of Ap-2δ in the mesencephalic tectum and the dorsal midbrain, Ap-2δ-deficient mice failed to maintain the colliculus inferior, a derivative of the dorsal midbrain, as a consequence of increased apoptotic cell death. To identify specific Ap-2δ target genes in cells of the developing dorsal midbrain, we performed whole genome analysis of cDNA expression levels. This approach identified a set of 12 putative target genes being expressed in the developing midbrain, including the transcription factors Pitx2, Mef2c, Bhlhb4 and Pou4f3. Using chromatin immunoprecipitation (CHIP) we showed that some of these genes are direct targets of Ap-2δ. Consistently, we demonstrate that Ap-2δ occupies and activates the Pou4f3 and Bhlhb4 promoters. In addition, known Pou4f3 target genes were downregulated in the posterior midbrain of Ap-2δ-deficient mice. Despite the absence of a central part of the auditory pathway, the presence of neuronal responses to sounds in the neocortex of Ap-2δ-deficient mice indicates that auditory information from the brainstem still reaches the neocortex. In summary, our data define Ap-2δ as an important transcription factor, specifying gene expression patterns required for the development of the posterior midbrain.

Transgenic overexpression of Tcfap2c/AP-2gamma results in liver failure and intestinal dysplasia

Background

The transcription factor Tcfap2c has been demonstrated to be essential for various processes during mammalian development. It has been found to be upregulated in various undifferentiated tumors and is implicated with poor prognosis. Tcfap2c is reported to impinge on cellular proliferation, differentiation and apoptosis. However, the physiological consequences of Tcfap2c-expression remain largely unknown.

Methodology/Principal Findings

Therefore we established a gain of function model to analyze the role of Tcfap2c in development and disease. Induction of the transgene led to robust expression in all tissues (except brain and testis) and lead to rapid mortality within 3–7 days. In the liver cellular proliferation and apoptosis was detected. Accumulation of microvesicular lipid droplets and breakdown of major hepatic metabolism pathways resulted in steatosis. Serum analysis showed a dramatic increase of enzymes indicative for hepatic failure. After induction of Tcfap2c we identified a set of 447 common genes, which are deregulated in both liver and primary hepatocyte culture. Further analysis showed a prominent repression of the cytochrome p450 system, PPARA, Lipin1 and Lipin2. These data indicate that in the liver Tcfap2c represses pathways, which are responsible for fatty acid metabolism. In the intestine, Tcfap2c expression resulted in expansion of Sox9 positive and proliferative active epithelial progenitor cells resulting in dysplastic growth of mucosal crypt cells and loss of differentiated mucosa.

Conclusions

The transgenic mice show that ectopic expression of Tcfap2c is not tolerated. Due to the phenotype observed, iTcfap2c-mice represent a model system to study liver failure. In intestine, Tcfap2c induced cellular hyperplasia and suppressed terminal differentiation indicating that Tcfap2c serves as a repressor of differentiation and inducer of proliferation. This might be achieved by the Tcfap2c mediated activation of Sox9 known to be expressed in intestinal and hepatic stem/progenitor cell populations.

Aberrant expressions of AP-2α splice variants in pancreatic cancer

OBJECTIVES

The present study was conducted to evaluate the expression and function of AP-2α isoforms in pancreatic ductal adenocarcinoma.

METHODS

The expression of AP-2α was evaluated at the RNA level by reverse transcription-polymerase chain reaction and at the protein level by Western blotting and immunofluorescence. Its function as a transcription factor was evaluated in transient transfection experiments: DNA binding properties by electromobility shift assay and transactivation capabilities by luciferase assay.

RESULTS

Multiple alternative splicing events of AP-2α messenger occurred in all human pancreatic cancer cell lines, including a novel isoform, termed variant 6, which was not present in HeLa cells. At the protein level, except for 1 cell line, all pancreatic cancer cell lines expressed high nuclear levels of AP-2α. We also showed that AP-2α expressed by the pancreatic cancer cell lines could bind its cognate recognition site and activate transcription. However, variant 6, although not able to activate transcription, did not act in a dominant negative manner when cotransfected with the full-length protein.

CONCLUSIONS

Multiple isoforms of AP-2α are highly expressed in pancreatic cancer cell lines including a new isoform, AP-2α variant 6, which seems to be pancreatic cancer specific and is deprived of transcriptional activity.

Graded Nodal/Activin signaling titrates conversion of quantitative phospho-Smad2 levels into qualitative embryonic stem cell fate decisions

Nodal and Activin are morphogens of the TGFbeta superfamily of signaling molecules that direct differential cell fate decisions in a dose- and distance-dependent manner. During early embryonic development the Nodal/Activin pathway is responsible for the specification of mesoderm, endoderm, node, and mesendoderm. In contradiction to this drive towards cellular differentiation, the pathway also plays important roles in the maintenance of self-renewal and pluripotency in embryonic and epiblast stem cells. The molecular basis behind stem cell interpretation of Nodal/Activin signaling gradients and the undertaking of disparate cell fate decisions remains poorly understood. Here, we show that any perturbation of endogenous signaling levels in mouse embryonic stem cells leads to their exit from self-renewal towards divergent differentiation programs. Increasing Nodal signals above basal levels by direct stimulation with Activin promotes differentiation towards the mesendodermal lineages while repression of signaling with the specific Nodal/Activin receptor inhibitor SB431542 induces trophectodermal differentiation. To address how quantitative Nodal/Activin signals are translated qualitatively into distinct cell fates decisions, we performed chromatin immunoprecipitation of phospho-Smad2, the primary downstream transcriptional factor of the Nodal/Activin pathway, followed by massively parallel sequencing, and show that phospho-Smad2 binds to and regulates distinct subsets of target genes in a dose-dependent manner. Crucially, Nodal/Activin signaling directly controls the Oct4 master regulator of pluripotency by graded phospho-Smad2 binding in the promoter region. Hence stem cells interpret and carry out differential Nodal/Activin signaling instructions via a corresponding gradient of Smad2 phosphorylation that selectively titrates self-renewal against alternative differentiation programs by direct regulation of distinct target gene subsets and Oct4 expression.

Ontogenesis of Ap-2γ expression in rat testes

Searching for useful markers of spermatogonial stem cells and their differentiation, we used rat testes from ages representing different stages of testicular maturation to investigate the expression profile of transcription factor activation protein-2γ (Ap-2γ). The immunohistochemical and immunocytochemical evaluation using Ap-2γ and promyelocytic leukemia zinc finger in combination with sorting of CD9 and CD90 positive cells (undifferentiated spermatogonia) by fluorescence-activated cell sorting was performed. Our experiments revealed that Ap-2γ is detectable in testes of late fetal age and up to 60 days postnatally and is expressed in gonocytes and spermatogonia from late fetal age throughout all maturational stages. Restricted nuclear expression of Ap-2γ to undifferentiated male germ cells was verified by coexpression of Ap-2γ with promyelocytic leukemia zinc finger in sections of paraffin-embedded testes as well as in cells sorted positive for CD9 and CD90 expression. Our study demonstrated clearly that nuclear expression of Ap-2γ is a useful marker for identifying undifferentiated male germ cells, although its functional role is yet to be fully explored.

Two regions within the proximal steroidogenic factor 1 promoter drive somatic cell-specific activity in developing gonads of the female mouse

Targets of steroidogenic factor 1 (SF1; also known as NR5A1 and AD4BP) have been identified within cells at every level of the hypothalamic-pituitary-gonadal and -adrenal axes, revealing SF1 to be a master regulator of major endocrine systems. Mouse embryos express SF1 in the genital ridge until Embryonic Day 13.5 (E13.5). Thereafter, expression persists in the male and is substantially lower in the female gonad until birth. We hypothesize that the sexually dimorphic expression of Sf1 during gonadogenesis is mediated by sex-specific regulation of its promoter. To investigate dimorphic regulation within the fetal gonad, we developed an experimental strategy using transient transfection of E13.5 gonad explant cultures and evaluated various Sf1 promoter constructs for sexually dimorphic DNA elements. The proximal Sf1 promoter correctly targeted reporter activity to SF1-expressing cells in both XY and XX gonads. Stepwise deletion of sequences from the Sf1 promoter revealed two regions that affected regulation within female gonads. Mutation of both sequences together did not cause further disruption of reporter activity, suggesting the two sites might work in concert to promote activity in female somatic cells. Results from gel mobility shift assays and fetal gonad-chromatin immunoprecipitation showed that TCFAP2 binds to one of the two female-specific sites within the proximal promoter of Sf1. Together, we show that transient transfection experiments performed within developing testes and ovaries are a powerful tool to uncover elements within the Sf1 promoter that contribute to sex-specific expression.

Loss of transcription factor AP-2gamma/TFAP2C impairs branching morphogenesis of the murine mammary gland

Extensive development of the mammary gland occurs during puberty, when rising levels of ovarian hormones induce the formation of highly proliferative terminal end buds (TEBs) at the tips of mammary ducts. TEBs consist of an outer layer of cap cells and of inner body cells. TEBs invade the adipose stroma and bifurcate while extending the ducts to generate an arborized ductal network. We show that in murine mammary glands transcription factor AP-2gamma is strongly expressed in the cap cell layer and in a subset of body cells of TEBs. To decipher AP-2gamma functions during mammary development we generated AP-2gamma-deficient mice. Their mammary glands displayed impaired ductal branching and elongation. Cellular proliferation within TEBs was reduced. Although estrogen receptor was expressed, exogenously administered ovarian hormones could not restore normal development. Therefore, AP-2gamma is functionally involved in branching morphogenesis of the mammary epithelium, possibly by controlling genetic processes downstream of ovarian hormones.

Trophoblast stem cells

Trophoblast stem cells (TSC) are the precursors of the differentiated cells of the placenta. In the mouse, TSC can be derived from outgrowths of either blastocyst polar trophectoderm (TE) or extraembryonic ectoderm (ExE), which originates from polar TE after implantation. The mouse TSC niche appears to be located within the ExE adjacent to the epiblast, on which it depends for essential growth factors, but whether this cellular architecture is the same in other species remains to be determined. Mouse TSC self-renewal can be sustained by culture on mitotically inactivated feeder cells, which provide one or more factors related to the NODAL pathway, and a medium supplemented with FGF4, heparin, and fetal bovine serum. Repression of the gene network that maintains pluripotency and emergence of the transcription factor pathways that specify a trophoblast (TR) fate enables TSC derivation in vitro and placental formation in vivo. Disrupting the pluripotent network of embryonic stem cells (ESC) causes them to default to a TR ground state. Pluripotent cells that have acquired sublethal chromosomal alterations may be sequestered into TR for similar reasons. The transition from ESC to TSC, which appears to be unidirectional, reveals important aspects of initial fate decisions in mice. TSC have yet to be derived from domestic species in which remarkable TR growth precedes embryogenesis. Recent derivation of TSC from blastocysts of the rhesus monkey suggests that isolation of the human equivalents may be possible and will reveal the extent to which mechanisms uncovered by using animal models are true in our own species.

AP2 transcription factor induces apoptosis in retinoblastoma cells

The underlying cause of human retinoblastoma is complete inactivation of both copies of the RB1 gene. Other chromosome abnormalities, with the most common being extra copies of chromosome arm 6p, are also observed in retinoblastoma. The RB protein has previously been shown to interact with TFAP2 transcription factors. Here, we show that TFAP2A and TFAP2B, which map to chromosome arm 6p, are expressed in the amacrine and horizontal cells of human retina. TFAP2A RNA can readily be detected in retinoblastoma cell lines and tumors; however, the great majority of retinoblastoma cell lines and tumors are completely devoid of TFAP2A protein and TFAP2B RNA/protein. Transfection of TFAP2A and TFAP2B expression constructs into retinoblastoma cells induces apoptosis and inhibits proliferation. Our results suggest that a consequence of loss of RB1 gene function in retinoblastoma cells is inactivation of TFAP2A and TFAP2B function. We propose that inability to differentiate along the amacrine/horizontal cell lineages may underlie retinoblastoma tumor formation.

Transcription factor AP-2β regulates the neurotransmitter phenotype and maturation of chromaffin cells

During development, sympathetic neurons and chromaffin cells originate from bipotential sympathoadrenal (SA) progenitors arising from neural crests (NC) in the trunk regions. Recently, we showed that AP-2β, a member of the AP2 family, plays a critical role in the development of sympathetic neurons and locus coeruleus and their norepinephrine (NE) neurotransmitter phenotype. In the present study, we investigated the potential role of AP-2β in the development of NC-derived neuroendocrine chromaffin cells of the adrenal medulla and the epinephrine (EPI) phenotype determination. In support of its role in chromaffin cell development, AP-2β is prominently expressed in both embryonic and adult adrenal medulla. In adrenal chromaffin cells of the AP-2β(-/-) mouse, the expression levels of catecholamine biosynthesizing enzymes, dopamine β-hydroxylase (DBH) and phenylethanolamine-N-methyl-transferase (PNMT), as well as the SA-specific transcription factor, Phox2b, are significantly reduced compared to wild type. In addition, ultrastructural analysis demonstrated that the formation of large secretory vesicles, a hallmark of differentiated chromaffin cells, is defective in AP-2β(-/-) mice. Furthermore, the level of EPI content is largely diminished (>80%) in the adrenal gland of AP-2β(-/-) mice. Chromatin immunoprecipitation (ChIP) assays of rat adrenal gland showed that AP-2β binds to the upstream promoter of the PNMT gene in vivo; strongly suggesting that it is a direct target gene. Overall, our data suggest that AP-2β plays critical roles in the epinephrine phenotype and maturation of adrenal chromaffin cells.

Regulation of early trophoblast differentiation - lessons from the mouse

The earliest stages of trophoblast differentiation are of tremendous importance to mediate implantation and to lay the anatomical foundations for normal placental development and function throughout gestation. Yet our molecular insights into these early developmental processes in humans have been limited by the inaccessibility of material and the unavailability of trophoblast cell lines that fully recapitulate the behaviour of early placental trophoblast. In this review we highlight recent advances that have come from the study of distinct stem cell types representative of the embryonic and extraembryonic lineages in the mouse, and from the study of mouse mutants. These models have revealed the presence of intricate transcriptional networks that are set up by signalling pathways, translating extracellular growth factor and cell positional information into distinct lineage-specific transcriptional programmes. The trophoblast specificity of these networks is ensured by epigenetic mechanisms including DNA methylation and histone modifications that complement each other to define trophoblast cell fate and differentiation. Despite the anatomical differences between mouse and human placentas, it seems that important aspects of early trophoblast specification are conserved between both species. Thus we may be able to build on our insights from the mouse to better understand early trophoblast differentiation in the human conceptus which is important for improving assisted reproductive technologies and may enable us in the future to derive human trophoblast stem cell lines. These advances will facilitate the investigation of genetic, epigenetic and environmental influences on early trophoblast differentiation in normal as well as in pathological conditions.

Identification of functional TFAP2A and SP1 binding sites in new TFAP2A-modulated genes

Background

Different approaches have been developed to dissect the interplay between transcription factors (TFs) and their cis-acting sequences on DNA in order to identify TF target genes. Here we used a combination of computational and experimental approaches to identify novel direct targets of TFAP2A, a key TF for a variety of physiological and pathological cellular processes. Gene expression profiles of HeLa cells either silenced for TFAP2A by RNA interference or not were previously compared and a set of differentially expressed genes was revealed.

Results

The regulatory regions of 494 TFAP2A-modulated genes were analyzed for the presence of TFAP2A binding sites, employing the canonical TFAP2A Positional Weight Matrix (PWM) reported in Jaspar http://jaspar.genereg.net/. 264 genes containing at least 2 high score TFAP2A binding sites were identified, showing a central role in "Cellular Movement" and "Cellular Development". In an attempt to identify TFs that could cooperate with TFAP2A, a statistically significant enrichment for SP1 binding sites was found for TFAP2A-activated but not repressed genes. The direct binding of TFAP2A or SP1 to a random subset of TFAP2A-modulated genes was demonstrated by Chromatin ImmunoPrecipitation (ChIP) assay and the TFAP2A-driven regulation of DCBLD2/ESDN/CLCP1 gene studied in details.

Conclusions

We proved that our computational approaches applied to microarray selected genes are valid tools to identify functional TF binding sites in gene regulatory regions as confirmed by experimental validations. In addition, we demonstrated a fine-tuned regulation of DCBLD2/ESDN transcription by TFAP2A.

Germ cell specification in mice: signaling, transcription regulation, and epigenetic consequences

The specification of germ cell fate in development initiates mechanisms essential for the perpetuation of genetic information across the generations. Recent studies in mice have shown that germ cell specification requires at least three key molecular/cellular events: repression of the somatic program, re-acquisition of potential pluripotency, and an ensuing genome-wide epigenetic reprogramming. Moreover, a signaling and transcriptional principle governing these processes has been identified, raising the possibility of inducing the germ cell fate precisely from pluripotent stem cells in culture. These advances will in turn serve as a basis to explore the mechanism of germ cell specification in other mammals, including humans. The recapitulation of germ cell development in humans in culture will provide unprecedented opportunities to understand the basis of the propagation of our genome, both under normal and diseased conditions.

The transcription factor TCFAP2C/AP-2gamma cooperates with CDX2 to maintain trophectoderm formation

In mammals, cell lineage specification is established at the blastocyst stage. At this stage, transcription factor Cdx2 represses pluripotency genes, thus promoting extraembryonic trophoblast fate. Recently, transcription factor Gata3 was shown to act in a parallel pathway in promoting trophoblast cell fate, suggesting that there are more factors working in the trophoblast lineage. Here, we report that the transcription factor Tcfap2c is expressed at a high level in the trophectoderm and is able to induce trophoblast fate in embryonic stem cells. Trophoblast fate induced by Tcfap2c does not require Cdx2 and vice versa, suggesting that the molecules act in alternative pathways. However, both Tcfap2c and Cdx2 are required for the upregulation of Elf5, a marker of trophoblast stem cell maintenance, suggesting that both factors are required for stable trophoblast induction. Tcfap2c-induced trophoblast-like cells are stable in long-term culture, indicating that they are capable of self-renewal. Tcfap2c-controlled trophoblast maintenance involves the induction of Cdx2 and the repression of the pluripotency factor Nanog. Tcfap2c-induced trophoblast-like cells differentiate to trophoblast derivatives in vitro and contribute to the trophectoderm in blastocysts in vivo. Taken together, these observations suggest that Tcfap2c and Cdx2 cooperate to override the pluripotency program and establish the extraembryonic trophoblast maintenance program in murine embryos.

Examination of transcriptional networks reveals an important role for TCFAP2C, SMARCA4, and EOMES in trophoblast stem cell maintenance

Trophoblast stem cells (TS cells), derived from the trophectoderm (TE) of blastocysts, require transcription factors (TFs) and external signals (FGF4, INHBA/NODAL/TGFB1) for self-renewal. While many reports have focused on TF networks that regulate embryonic stem cell (ES cell) self-renewal and pluripotency, little is know about TF networks that regulate self-renewal in TS cells. To further understand transcriptional networks in TS cells, we used chromatin immunoprecipitation with DNA microarray hybridization (ChIP-chip) analysis to investigate targets of the TFs-TCFAP2C, EOMES, ETS2, and GATA3-and a chromatin remodeling factor, SMARCA4. We then evaluated the transcriptional states of target genes using transcriptome analysis and genome-wide analysis of histone H3 acetylation (AcH3). Our results describe previously unknown transcriptional networks in TS cells, including TF occupancy of genes involved in ES cell self-renewal and pluripotency, co-occupancy of TCFAP2C, SMARCA4, and EOMES at a significant number of genes, and transcriptional regulatory circuitry within the five factors. Moreover, RNAi depletion of Tcfap2c, Smarca4, and Eomes transcripts resulted in a loss of normal colony morphology and down-regulation of TS cell-specific genes, suggesting an important role for TCFAP2C, SMARCA4, and EOMES in TS cell self-renewal. Through genome-wide mapping and global expression analysis of five TF target genes, our data provide a comprehensive analysis of transcriptional networks that regulate TS cell self-renewal.

Roles of AP-2 transcription factors in the regulation of cartilage and skeletal development

During embryogenesis, most of the mammalian skeletal system is preformed as cartilaginous structures that ossify later. The different stages of cartilage and skeletal development are well described, and several molecular factors are known to influence the events of this enchondral ossification, especially transcription factors. Members of the AP-2 family of transcription factors play important roles in several cellular processes, such as apoptosis, migration and differentiation. Studies with knockout mice demonstrate that a main function of AP-2s is the suppression of terminal differentiation during embryonic development. Additionally, the specific role of these molecules as regulators during chondrogenesis has been characterized. This review gives an overview of AP-2s, and discusses the recent findings on the AP-2 family, in particular AP-2alpha, AP-2beta, and AP-2epsilon, as regulators of cartilage and skeletal development.

AP-2gamma promotes proliferation in breast tumour cells by direct repression of the CDKN1A gene

Overexpression of the activator protein (AP)-2gamma transcription factor in breast tumours has been identified as an independent predictor of poor outcome and failure of hormone therapy. To understand further the function of AP-2gamma in breast carcinoma, we have used an RNA interference and gene expression profiling strategy with the MCF-7 cell line as a model. Gene expression changes between control and silenced cells implicate AP-2gamma in the control of cell cycle progression and developmental signalling. A function for AP-2gamma in cell cycle control was verified using flow cytometry: AP-2gamma silencing led to a partial G1/S arrest and induction of the cyclin-dependent kinase inhibitor, p21cip/CDKN1A. Reporter and chromatin immunoprecipitation assays demonstrated a direct, functional interaction by AP-2gamma at the CDKN1A proximal promoter. AP-2gamma silencing coincided with acquisition of an active chromatin conformation at the CDKN1A locus and increased gene expression. These data provide a mechanism whereby AP-2gamma overexpression can promote breast epithelial proliferation and, coupled with previously published data, suggest how loss of oestrogen regulation of AP-2gamma may contribute to the failure of hormone therapy in patients.

Critical function of AP-2 gamma/TCFAP2C in mouse embryonic germ cell maintenance

Formation of the germ cell lineage involves multiple processes, including repression of somatic differentiation and reacquisition of pluripotency as well as a unique epigenetic constitution. The transcriptional regulator Prdm1 has been identified as a main coordinator of this process, controlling epigenetic modification and gene expression. Here we report on the expression pattern of the transcription factor Tcfap2c, a putative downstream target of Prdm1, during normal mouse embryogenesis and the consequences of its specific loss in primordial germ cells (PGCs) and their derivatives. Tcfap2c is expressed in PGCs from Embryonic Day 7.25 (E 7.25) up to E 12.5, and targeted disruption resulted in sterile animals, both male and female. In the mutant animals, PGCs were specified but were lost around E 8.0. PGCs generated in vitro from embryonic stem cells lacking TCFAP2C displayed induction of Prdm1 and Dppa3. Upregulation of Hoxa1, Hoxb1, and T together with lack of expression of germ cell markers such Nanos3, Dazl, and Mutyh suggested that the somatic gene program is induced in TCFAP2C-deficient PGCs. Repression of TCFAP2C in TCam-2, a human PGC-resembling seminoma cell line, resulted in specific upregulation of HOXA1, HOXB1, MYOD1, and HAND1, indicative of mesodermal differentiation. Expression of genes indicative of ectodermal, endodermal, or extraembryonic differentiation, as well as the finding of no change to epigenetic modifications, suggested control by other factors. Our results implicate Tcfap2c as an important effector of Prdm1 activity that is required for PGC maintenance, most likely mediating Prdm1-induced suppression of mesodermal differentiation.

AP2gamma regulates basal progenitor fate in a region- and layer-specific manner in the developing cortex

An important feature of the cerebral cortex is its layered organization, which is modulated in an area-specific manner. We found that the transcription factor AP2gamma regulates laminar fate in a region-specific manner. Deletion of AP2gamma (also known as Tcfap2c) during development resulted in a specific reduction of upper layer neurons in the occipital cortex, leading to impaired function and enhanced plasticity of the adult visual cortex. AP2gamma functions in apical progenitors, and its absence resulted in mis-specification of basal progenitors in the occipital cortex at the time at which upper layer neurons were generated. AP2gamma directly regulated the basal progenitor fate determinants Math3 (also known as Neurod4) and Tbr2, and its overexpression promoted the generation of layer II/III neurons in a time- and region-specific manner. Thus, AP2gamma acts as a regulator of basal progenitor fate, linking regional and laminar specification in the mouse developing cerebral cortex.

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.

Identification of target genes of transcription factor activator protein 2 gamma in breast cancer cells

Background

Activator protein 2 gamma (AP-2γ) is a member of the transcription factor activator protein-2 (AP-2) family, which is developmentally regulated and plays a role in human neoplasia. AP-2γ has been found to be overexpressed in most breast cancers, and have a dual role to inhibit tumor initiation and promote tumor progression afterwards during mammary tumorigensis.

Methods

To identify the gene targets that mediate its effects, we performed chromatin immunoprecipitation (ChIP) to isolate AP-2γ binding sites on genomic DNA from human breast cancer cell line MDA-MB-453.

Results

20 novel DNA fragments proximal to potential AP-2γ targets were obtained. They are categorized into functional groups of carcinogenesis, metabolism and others. A combination of sequence analysis, reporter gene assays, quantitative real-time PCR, electrophoretic gel mobility shift assays and immunoblot analysis further confirmed the four AP-2γ target genes in carcinogenesis group: ErbB2, CDH2, HPSE and IGSF11. Our results were consistent with the previous reports that ErbB2 was the target gene of AP-2γ. Decreased expression and overexpression of AP-2γ in human breast cancer cells significantly altered the expression of these four genes, indicating that AP-2γ directly regulates them.

Conclusion

This suggested that AP-2γ can coordinate the expression of a network of genes, involving in carcinogenesis, especially in breast cancer. They could serve as therapeutic targets against breast cancers in the future.

Expression of AP-2delta in the developing chick retina

AP-2 is a family of transcription factors that play important roles during embryonic development. Two AP-2 genes, AP-2alpha and AP-2beta, have previously been characterized in chick retina. Here, we demonstrate that a third member of the chicken AP-2 family, AP-2delta, is primarily expressed in the retina and brain, with highest levels at embryonic days 7 to 11. By in situ hybridization and immunohistochemical analysis, we show that AP-2delta RNA and protein are found in a subset of ganglion cells in embryonic chick retina. Co-immunostaining with anti-Brn3a and anti-AP-2delta antibodies indicates that approximately one-third of Brn3a-positive ganglion cells express AP-2delta. AP-2delta RNA but not AP-2delta protein is also found in cells located in the outer half of the inner nuclear layer. The spatial and temporal distribution of AP-2delta protein in the retina suggests a transient role in a subset of late-born ganglion cells likely involving axonal trafficking or pathfinding.

Sustained platelet-derived growth factor receptor alpha signaling in osteoblasts results in craniosynostosis by overactivating the phospholipase C-gamma pathway

The development and growth of the skull is controlled by cranial sutures, which serve as growth centers for osteogenesis by providing a pool of osteoprogenitors. These osteoprogenitors undergo intramembranous ossification by direct differentiation into osteoblasts, which synthesize the components of the extracellular bone matrix. A dysregulation of osteoblast differentiation can lead to premature fusion of sutures, resulting in an abnormal skull shape, a disease called craniosynostosis. Although several genes could be linked to craniosynostosis, the mechanisms regulating cranial suture development remain largely elusive. We have established transgenic mice conditionally expressing an autoactivated platelet-derived growth factor receptor alpha (PDGFRalpha) in neural crest cells (NCCs) and their derivatives. In these mice, premature fusion of NCC-derived sutures occurred at early postnatal stages. In vivo and in vitro experiments demonstrated enhanced proliferation of osteoprogenitors and accelerated ossification of osteoblasts. Furthermore, in osteoblasts expressing the autoactivated receptor, we detected an upregulation of the phospholipase C-gamma (PLC-gamma) pathway. Treatment of differentiating osteoblasts with a PLC-gamma-specific inhibitor prevented the mineralization of synthesized bone matrix. Thus, we show for the first time that PDGFRalpha signaling stimulates osteogenesis of NCC-derived osteoblasts by activating the PLC-gamma pathway, suggesting an involvement of this pathway in the etiology of human craniosynostosis.

AP-2alpha and AP-2gamma regulate tumor progression via specific genetic programs

The events occurring during tumor formation and progression display similarities to some of the steps in embryonic morphogenesis. The family of AP-2 proteins consists of five different transcription factors (alpha, beta, gamma, delta, and epsilon) that play relevant roles in embryonic development, as demonstrated by the phenotypes of the corresponding knockout mice. Here, we show that AP-2alpha and AP-2gamma proteins play an essential role in tumorigenesis. Down-modulation of AP-2 expression in tumor cells by RNA interference (RNAi) led to enhanced tumor growth and reduced chemotherapy-induced cell death, as well as migration and invasion. Most of these biological modulations were rescued by AP-2 overexpression. We observed that increased xenotransplant growth was mostly due to highly enhanced proliferation of the tumor cells together with reduced innate immune cell recruitment. Moreover, we showed that migration impairment was mediated, at least in part, by secreted factors. To identify the genetic programs involved in tumorigenesis, we performed whole genome microarray analysis of AP-2alpha knockdown cells and observed that AP-2alpha regulates specific genes involved in cell cycle, cell death, adhesion, and migration. In particular, we showed that ESDN, EREG, and CXCL2 play a major role in AP-2 controlled migration, as ablation of any of these genes severely altered migration.

Immunohistochemical expression patterns of AP2alpha and AP2gamma in the developing fetal human breast

AIMS

AP2alpha (TFAP2A) and AP2gamma (TFAP2G) transcription factors have been implicated in the control of proliferation, differentiation and apoptosis of normal breast epithelium and in breast cancer. The aim of this study was to provide a comprehensive analysis of the expression patterns of TFAP2A and TFAP2G in the developing fetal breast anlage with other relevant markers.

METHODS AND RESULTS

Sixty fetal and one infant human breast specimens from 14 weeks of gestational age to 5 months old were examined. The primary breast outgrowth/nipple showed TFAP2A expression by the basal cells (week 14), followed later by cytokeratin (CK) 5 co-expression (week 17). Sprouting of the secondary outgrowths was characterized by HER-2+ invading cells. Preliminary ductal buds were lined by TFAP2G/HER-1-expressing myoepithelial precursors (week 19). Maturation of TFAP2A/CK18+ epithelia and TFAP2G/smooth muscle actin-positive myoepithelia proceeded in a distal-to-proximal manner beginning in the terminal end buds (week 22). CK5+ progenitor cells and CK5/TFAP2A or CK5/TFAP2G co-expressing intermediary glandular or myoepithelial cells were found in the terminal end buds of neonatal fetal breast tissue.

CONCLUSIONS

AP2 transcription factors may play decisive pacemaker roles in initiating and coordinating budding and branching processes during formation of the fetal breast anlage, possibly via modulation of an epidermal growth factor receptor.

Prospective isolation of functionally distinct radial glial subtypes--lineage and transcriptome analysis

Since the discovery of radial glia as the source of neurons, their heterogeneity in regard to neurogenesis has been described by clonal and time-lapse analysis in vitro. However, the molecular determinants specifying neurogenic radial glia differently from radial glia that mostly self-renew remain ill-defined. Here, we isolated two radial glial subsets that co-exist at mid-neurogenesis in the developing cerebral cortex and their immediate progeny. While one subset generates neurons directly, the other is largely non-neurogenic but also gives rise to Tbr2-positive basal precursors, thereby contributing indirectly to neurogenesis. Isolation of these distinct radial glia subtypes allowed determining interesting differences in their transcriptome. These transcriptomes were also strikingly different from the transcriptome of radial glia isolated at the end of neurogenesis. This analysis therefore identifies, for the first time, the lineage origin of basal progenitors and the molecular differences of this lineage in comparison to directly neurogenic and gliogenic radial glia.

Tfap2 transcription factors in zebrafish neural crest development and ectodermal evolution

Transcription factor AP2 (Tfap2) genes play essential roles in development of the epidermis and migratory cells of the neural crest (NC) in vertebrate embryos. These transcriptional activators are among the earliest genes expressed in the ectoderm and specify fates within the epidermis/crest through both direct and indirect mechanisms. The Tfap2 family arose from a single ancestral gene in a chordate ancestor that underwent gene duplication to give up to five family members in living vertebrates. This coincided with the acquisition of important roles in NC development by Tfap2 genes suggesting that this gene family was important in ectodermal evolution and possibly in the origin of NC. Here, we show that a zebrafish tfap2c is expressed in the nonneural ectoderm during early development and functions redundantly with tfap2a in NC specification. In zebrafish embryos depleted of both tfap2a and tfap2c, NC cells are virtually eliminated. Cell transplantation experiments indicate that tfap2c functions cell-autonomously in NC specification. Cells of the enveloping layer, which forms a temporary skin layer surrounding the ectoderm, also fail to differentiate or to express appropriate keratins in tfap2c deficient embryos. The role of Tfap2 genes in epidermal and NC development is considered here in the broader context of ectodermal evolution. Distinct, tissue-specific functions for Tfap2 genes in different vertebrates may reflect subfunctionalisation of an ancestral gene that consequently led to the gain of novel roles for different subfamily members in patterning the epidermis and NC.

Global gene expression analysis and regulation of the principal genes expressed in bovine placenta in relation to the transcription factor AP-2 family

BACKGROUND

Cell-cell communication is an important factor in feto-maternal units during placentogenesis. The placenta produces pivotal hormones and cytokines for communication between cotyledonary villi and the maternal caruncle. Gene expression in bovine placenta throughout pregnancy was comprehensively screened by a cDNA microarray, and we searched for a common transcription factor in a gene cluster that showed increasing expression throughout gestation in cotyledonary villi and caruncle.

METHODS

Placentomal tissues (villi and caruncle) were collected from Day 25 to Day 250 of gestation for microarray analysis. Global gene expression profiles were analyzed using the k-means clustering method. A consensus sequence cis-element that may control up-regulated genes in a characteristic cluster was examined in silico. The quantitative expression and localization of a specific transcription factor were investigated in each tissue using quantitative real-time RT-PCR and in situ hybridization.

RESULTS

The microarray expression profiles were classified into ten clusters. The genes with most markedly increased expression became concentrated in cluster 2 as gestation proceeded. Cluster 2 included placental lactogen (CSH1), pregnancy-associated glycoprotein-1 (PAG1), and sulfotransferase family 1E estrogen-preferring member 1 (SULT1E1), which were mainly detected in giant trophoblast binucleate cells (BNC). Consensus sequence analysis identified transcription factor AP-2 binding sites in some genes in this cluster. Quantitative real-time RT-PCR analysis confirmed that high level expression of transcription factor AP-2 alpha (TFAP2A) was common to cluster 2 genes during gestation. In contrast, the expression level of another AP-2 family gene, transcription factor AP-2 beta (TFAP2B), was extremely low over the same period. Another gene of the family, transcription factor AP-2 gamma (TFAP2C), was expressed at medium level compared with TFAP2A and TFAP2B. In situ hybridization showed that TFAP2A, TFAP2B and TFAP2C mRNAs were localized in trophoblast cells but were expressed by different cells. TFAP2A was expressed in cotyledonary epithelial cells including BNC, TFAP2B was specifically expressed in BNC, and TFAP2C in mononucleate cells.

CONCLUSION

We detected gestational-stage-specific gene expression profiles in bovine placentomes using a combination of microarray and in silico analysis. In silico analysis indicated that the AP-2 family may be a consensus regulator for the gene cluster that characteristically appears in bovine placenta as gestation progresses. In particular, TFAP2A and TFAP2B may be involved in regulating binucleate cell-specific genes such as CSH1, some PAG or SULT1E1. These results suggest that the AP-2 family is a specific transcription factor for clusters of crucial placental genes. This is the first evidence that TFAP2A may regulate the differentiation and specific functions of BNC in bovine placenta.

Establishment and controlled differentiation of neural crest stem cell lines using conditional transgenesis

Murine neural crest stem cells (NCSCs) are a multipotent transient population of stem cells. After being formed during early embryogenesis as a consequence of neurulation at the apical neural fold, the cells rapidly disperse throughout the embryo, migrating along specific pathways and differentiating into a wide variety of cell types. In vitro the multipotency is lost rapidly, making it difficult to study differentiation potential as well as cell fate decisions. Using a transgenic mouse line, allowing for spatio-temporal control of the transforming c-myc oncogene, we derived a cell line (JoMa1), which expressed NCSC markers in a transgene-activity dependent manner. JoMa1 cells express early NCSC markers and can be instructed to differentiate into neurons, glia, smooth muscle cells, melanocytes, and also chondrocytes. A cell-line, clonally derived from JoMa1 culture, termed JoMa1.3 showed identical behavior and was studied in more detail. This system therefore represents a powerful tool to study NCSC biology and signaling pathways. We observed that when proliferative and differentiation stimuli were given, enhanced cell death could be detected, suggesting that the two signals are incompatible in the cellular context. However, the cells regain their differentiation potential after inactivation of c-MycER(T). In summary, we have established a system, which allows for the biochemical analysis of the molecular pathways governing NCSC biology. In addition, we should be able to obtain NCSC lines from crossing the c-MycER(T) mice with mice harboring mutations affecting neural crest development enabling further insight into genetic pathways controlling neural crest differentiation.

Activator protein-2 in carcinogenesis with a special reference to breast cancer-A mini review

Activator protein-2 (AP-2) transcription factors are involved in the regulation of cell proliferation, differentiation, apoptosis and carcinogenesis. AP-2alpha has been suggested to function as a tumor suppressor in many cancers and AP-2gamma to be a marker of testicular and germ cell malignancies. At least 3 of the 5 AP-2 family members identified to date, AP-2alpha, AP-2beta and AP-2gamma, are known to be expressed in breast tissue and thought to coordinate the growth and development of the breast via regulation of several breast-related genes such as human epidermal growth factor receptor-2 (HER2) and estrogen receptor (ER). The function of AP-2alpha seems to be tumor suppressive in breast tissue, whereas the role of the other AP-2 family members is less well known. In this review, we summarize the current knowledge of AP-2 in carcinogenesis, especially in breast cancer.

Neural crest and mesoderm lineage-dependent gene expression in orofacial development

The present study utilizes a combination of genetic labeling/selective isolation of pluripotent embryonic progenitor cells, and oligonucleotide-based microarray technology, to delineate and compare the "molecular fingerprint" of two mesenchymal cell populations from distinct lineages in the developing embryonic orofacial region. The first branchial arches-bi-lateral tissue primordia that flank the primitive oral cavity-are populated by pluripotent mesenchymal cells from two different lineages: neural crest (neuroectoderm)- and mesoderm-derived mesenchymal cells. These cells give rise to all of the connective tissue elements (bone, cartilage, smooth and skeletal muscle, dentin) of the orofacial region (maxillary and mandibular portion), as well as neurons and glia associated with the cranial ganglia, among other tissues. In the present study, neural crest- and mesoderm-derived mesenchymal cells were selectively isolated from the first branchial arch of gestational day 9.5 mouse embryos using laser capture microdissection (LCM). The two different embryonic cell lineages were distinguished through utilization of a novel two component transgenic mouse model (Wnt1Cre/ZEG) in which the neural crest cells and their derivatives are indelibly marked (i.e., expressing enhanced green fluorescent protein, EGFP) throughout the pre- and post-natal lifespan of the organism. EGFP-labeled neural crest-derived, and non-fluorescent mesoderm-derived mesenchymal cells from the first branchial arch were visualized in frozen tissue sections from gestational day 9.5 mouse embryos and independently isolated by LCM under epifluorescence optics. RNA was extracted from the two populations of LCM-procured cells, and amplified by double-stranded cDNA synthesis and in vitro transcription. Gene expression profiles of the two progenitor cell populations were generated via hybridization of the cell-type specific cRNA samples to oligo-based GeneChip microarrays. Comparison of gene expression profiles of neural crest- and mesoderm-derived mesenchymal cells from the first branchial arch revealed over 140 genes that exhibited statistically significant differential levels of expression. The gene products of many of these differentially expressed genes have previously been linked to the development of mesoderm- or neural crest-derived tissues in the embryo. Interestingly, however, hitherto uncharacterized coding sequences with highly significant differences in expression between the two embryonic progenitor cell types were also identified. These lineage-dependent mesenchymal cell molecular fingerprints offer the opportunity to elucidate additional mechanisms governing cellular growth, differentiation, and morphogenesis of the embryonic orofacial region. The chemokine stromal cell-derived factor 1, (SDF-1), was found to exhibit greater expression in mesoderm-derived mesenchyme in the branchial arch when compared with neurectoderm, suggesting a possible chemotactic role for SDF-1 in guiding the migratory neural crest cells to their destination. The novel combination of genetic labeling of the neural crest cell population by EGFP coupled with isolation of cells by LCM for gene expression analysis has enabled, for the first time, the generation of gene expression profiles of distinct embryonic cell lineages.