Activation of four homeobox gene clusters in human embryonal carcinoma cells induced to differentiate by retinoic acid

Homeobox protein A1-like and DNA methylation regulate embryo-specific Zinc finger protein 615 gene expression and embryonic development in the silkworm Bombyx mori

DNA methylation and transcription factors play roles in gene expression and animal development. In insects, DNA methylation modifies gene bodies, but how DNA methylation and transcription factors regulate gene expression is unclear. In this study, we investigated the mechanism that regulates the expression of Bombyx mori Zinc finger protein 615 (ZnF 615), which is a downstream gene of DNA methyltransferase 1 (Dnmt1), and its effects on the regulation of embryonic development. By progressively truncating the ZnF 615 promoter, it was found that the -223 and -190 nt region, which contains homeobox (Hox) protein cis-regulatory elements (CREs), had the greatest impact on the transcription of ZnF 615. RNA interference (RNAi)-mediated knockdown and overexpression of Hox family genes showed that Hox A1-like can enhance the messenger RNA level of ZnF 615. Further studies showed that Hox A1-like regulates ZnF 615 expression by directly binding to the -223 and -190 nt region of its promoter. Simultaneous RNAi-mediated knockdown or overexpression of Hox A1-like and Dnmt1 significantly inhibited or enhanced the regulatory effect of either gene alone on ZnF 615 expression, suggesting that both DNA methylation of gene bodies and binding of transcription factors to promoters are essential for gene expression. RNAi-mediated knockdown of Hox A1-like and Dnmt1 showed that the embryonic development was retarded and the hatching rate was decreased. Taken together, these data suggest that Hox A1-like and DNA methylation enhance the expression of ZnF 615, thereby affecting the development of B. mori embryos.

Chromosome 1p status in neuroblastoma correlates with higher expression levels of miRNAs targeting neuronal differentiation pathway

Neuroblastoma (NB) is characterized by acquired segmental and numerical chromosome aberrations. Although deletions of distal 1p and 11q are frequent alterations, no candidate tumor suppressor gene residing in these chromosomal sites could be identified so far. In the present study, we detected the genomic imbalances of six neuroblastoma cell lines using the multiplex ligation-dependent probe amplification (MLPA) technique and the microRNA (miRNA) expression profiles of the cell lines by a microarray study. According to MLPA results, we aimed to assess the miRNA expression profiles of the cell lines harboring 11q and 1p deletions. The cell lines with 1p deletions revealed statistically significant higher levels of expression for 29 miRNAs in contrast to the cell lines without 1p deletion in microarray study. We also performed GO enrichment analysis for predicted targets of the differentially expressed miRNAs. According to GO enrichment analysis, miRNAs that showed the high change in expression was associated with neuronal differentiation. We showed that hsa-miR-494, hsa-miR-495, and hsa-miR-543 target most of mRNAs in neuronal differentiation pathway. Although limited to the cell lines, our results highly suggest that NBs with different segmental chromosome abnormalities may have different dysregulated miRNA expression signatures that target the genes involved in neuronal differentiation.

FAT1 cadherin controls neuritogenesis during NTera2 cell differentiation

Fat1 cadherin is broadly expressed throughout the nervous system and has been implicated in neuronal differentiation. Here we examined the functional contribution of FAT1 during neuronal differentiation of the Ntera2 cell line model. FAT1 expression was increased during the retinoic acid (RA)-induced differentiation of NTera2 cells. Depletion of FAT1 with siRNA decreased the number of neurites produced after RA treatment. Moreover, FAT1 silencing also led to decreased Ser127-phosphorylation of YAP along with transcriptional increases in the Hippo target genes CTGF and ANKRD1, suggesting FAT1 alters Hippo signalling during differentiation. In the context of the Ntera2 model, FAT1 is required for efficient neuritogenesis, acting as a regulator of neurite formation during the early stages of differentiation.

Parallel generation of easily selectable multiple nephronal cell types from human pluripotent stem cells

Human pluripotent stem cells (hPSCs) provide a source for the generation of defined kidney cells and renal organoids applicable in regenerative medicine, disease modeling, and drug screening. These applications require the provision of hPSC-derived renal cells by reproducible, scalable, and efficient methods. We established a chemically defined protocol by application of Activin A, BMP4, and Retinoic acid followed by GDNF, which steered hPSCs to the renal lineage and resulted in populations of SIX2+/CITED1+ metanephric mesenchyme- (MM) and of HOXB7+/GRHL2+ ureteric bud (UB)-like cells already by 6 days. Transcriptome analysis corroborated that the PSC-derived cell types at day 8 resemble their renal vesicle and ureteric epithelial counterpart in vivo, forming tubular and glomerular renal cells 6 days later. We demonstrate that starting from hPSCs, our in vitro protocol generates a pool of nephrogenic progenitors at the renal vesicle stage, which can be further directed into specialized nephronal cell types including mesangial-, proximal tubular-, distal tubular, collecting duct epithelial cells, and podocyte precursors after 14 days. This simple and rapid method to produce renal cells from a common precursor pool in 2D culture provides the basis for scaled-up production of tailored renal cell types, which are applicable for drug testing or cell-based regenerative therapies.

Reciprocal regulation of chromatin state and architecture by HOTAIRM1 contributes to temporal collinear HOXA gene activation

Thousands of long non-coding RNAs (lncRNAs) have been identified in mammals, many of which represent important regulators of gene expression. However, the mechanisms used by lncRNAs to control transcription remain largely uncharacterized. Here, we report on HOTAIRM1, a promising lncRNA biomarker in leukemia and solid tumors. We find that HOTAIRM1 contributes to three-dimensional chromatin organization changes required for the temporal collinear activation of HOXA genes. We show that distinct HOTAIRM1 variants preferentially associate with either UTX/MLL or PRC2 complexes to modulate the levels of activating and silencing marks at the bivalent domain. HOTAIRM1 contributes to physical dissociation of chromatin loops at the cluster proximal end, which delays recruitment of the histone demethylase UTX and transcription of central HOXA genes. Interestingly, we find overall proximal HOXA gene activation without chromatin conformation changes by HOTAIRM1 in a different cell type. Our results reveal a previously unappreciated relationship between chromatin structure, architecture and lncRNA function.

Quantification of Etoposide Hypersensitivity: A Sensitive, Functional Method for Assessing Pluripotent Stem Cell Quality

Human induced pluripotent stem cells (hiPSC) hold great promise in diagnostic and therapeutic applications. However, translation of hiPSC technology depends upon a means of assessing hiPSC quality that is quantitative, high‐throughput, and can decipher malignant teratocarcinoma clones from normal cell lines. These attributes are lacking in current approaches such as detection of cell surface makers, RNA profiling, and/or teratoma formation assays. The latter remains the gold standard for assessing clone quality in hiPSCs, but is expensive, time‐consuming, and incompatible with high‐throughput platforms. Herein, we describe a novel method for determining hiPSC quality that exploits pluripotent cells’ documented hypersensitivity to the topoisomerase inhibitor etoposide (CAS No. 33419‐42‐0). Based on a study of 115 unique hiPSC clones, we established that a half maximal effective concentration (EC50) value of <300 nM following 24 hours of exposure to etoposide demonstrated a positive correlation with RNA profiles and colony morphology metrics associated with high quality hiPSC clones. Moreover, our etoposide sensitivity assay (ESA) detected differences associated with culture maintenance, and successfully distinguished malignant from normal pluripotent clones independent of cellular morphology. Overall, the ESA provides a simple, straightforward method to establish hiPSC quality in a quantitative and functional assay capable of being incorporated into a generalized method for establishing a quality control standard for all types of pluripotent stem cells. Stem Cells Translational Medicine2017;6:1829–1839

Lovastatin Decreases the Expression of CD133 and Influences the Differentiation Potential of Human Embryonic Stem Cells

The lipophilic statin lovastatin decreases cholesterol synthesis and is a safe and effective treatment for the prevention of cardiovascular diseases. Growing evidence points at antitumor potential of lovastatin. Therefore, understanding the molecular mechanism of lovastatin function in different cell types is critical to effective therapy design. In this study, we investigated the effects of lovastatin on the differentiation potential of human embryonic stem (hES) cells (H9 cell line). Multiparameter flow cytometric assay was used to detect changes in the expression of transcription factors characteristic of hES cells. We found that lovastatin treatment delayed NANOG downregulation during ectodermal and endodermal differentiation. Likewise, expression of ectodermal (SOX1 and OTX2) and endodermal (GATA4 and FOXA2) markers was higher in treated cells. Exposure of hES cells to lovastatin led to a minor decrease in the expression of SSEA-3 and a significant reduction in CD133 expression. Treated cells also formed fewer embryoid bodies than control cells. By analyzing hES with and without CD133, we discovered that CD133 expression is required for proper formation of embryoid bodies. In conclusion, lovastatin reduced the heterogeneity of hES cells and impaired their differentiation potential.

Hox genes, evo-devo, and the case of the ftz gene

The discovery of the broad conservation of embryonic regulatory genes across animal phyla, launched by the cloning of homeotic genes in the 1980s, was a founding event in the field of evolutionary developmental biology (evo-devo). While it had long been known that fundamental cellular processes, commonly referred to as housekeeping functions, are shared by animals and plants across the planet-processes such as the storage of information in genomic DNA, transcription, translation and the machinery for these processes, universal codon usage, and metabolic enzymes-Hox genes were different: mutations in these genes caused "bizarre" homeotic transformations of insect body parts that were certainly interesting but were expected to be idiosyncratic. The isolation of the genes responsible for these bizarre phenotypes turned out to be highly conserved Hox genes that play roles in embryonic patterning throughout Metazoa. How Hox genes have changed to promote the development of diverse body plans remains a central issue of the field of evo-devo today. For this Memorial article series, I review events around the discovery of the broad evolutionary conservation of Hox genes and the impact of this discovery on the field of developmental biology. I highlight studies carried out in Walter Gehring's lab and by former lab members that have continued to push the field forward, raising new questions and forging new approaches to understand the evolution of developmental mechanisms.

BMP Inhibition in Seminomas Initiates Acquisition of Pluripotency via NODAL Signaling Resulting in Reprogramming to an Embryonal Carcinoma

Type II germ cell cancers (GCC) can be subdivided into seminomas and non-seminomas. Seminomas are similar to carcinoma in situ (CIS) cells, the common precursor of type II GCCs, with regard to epigenetics and expression, while embryonal carcinomas (EC) are totipotent and differentiate into teratomas, yolk-sac tumors and choriocarcinomas. GCCs can present as seminomas with a non-seminoma component, raising the question if a CIS gives rise to seminomas and ECs at the same time or whether seminomas can be reprogrammed to ECs. In this study, we utilized the seminoma cell line TCam-2 that acquires an EC-like status after xenografting into the murine flank as a model for a seminoma to EC transition and screened for factors initiating and driving this process. Analysis of expression and DNA methylation dynamics during transition of TCam-2 revealed that many pluripotency- and reprogramming-associated genes were upregulated while seminoma-markers were downregulated. Changes in expression level of 53 genes inversely correlated to changes in DNA methylation. Interestingly, after xenotransplantation 6 genes (GDF3, NODAL, DNMT3B, DPPA3, GAL, AK3L1) were rapidly induced, followed by demethylation of their genomic loci, suggesting that these 6 genes are poised for expression driving the reprogramming. We demonstrate that inhibition of BMP signaling is the initial event in reprogramming, resulting in activation of the pluripotency-associated genes and NODAL signaling. We propose that reprogramming of seminomas to ECs is a multi-step process. Initially, the microenvironment causes inhibition of BMP signaling, leading to induction of NODAL signaling. During a maturation phase, a fast acting NODAL loop stimulates its own activity and temporarily inhibits BMP signaling. During the stabilization phase, a slow acting NODAL loop, involving WNTs re-establishes BMP signaling and the pluripotency circuitry. In parallel, DNMT3B-driven de novo methylation silences seminoma-associated genes and epigenetically fixes the EC state.

Induced pluripotency enables differentiation of human nullipotent embryonal carcinoma cells N2102Ep

Embryonal carcinoma (EC) cells, which are considered to be malignant counterparts of embryonic stem cells, comprise the pluripotent stem cell component of teratocarcinomas, a form of testicular germ cell tumors (GCTs). Nevertheless, many established human EC cell lines are nullipotent with limited or no capacity to differentiate under normal circumstances. In this study, we tested whether an over-expression of Yamanaka's reprogramming factors OCT4, SOX2, c-MYC and KLF4 might enable differentiation of the human nullipotent EC cells N2102Ep. Using OCT4 knockdown differentiated N2102Ep cells, we are able to derive reprogrammed N2102Ep cell lines. The induced pluripotency of N2102Ep allows the cells to differentiate toward neural lineage by retinoic acid; the expression of SSEA3 and SSEA4 is down-regulated, whereas that of neural surface markers is up-regulated. Consistent with the up-regulation of neural surface markers, the expression of the master neuroectodermal transcription factor PAX6 is also induced in reprogrammed N2102Ep. We next investigated whether PAX6 might induce spontaneous differentiation of nullipotent stem cells N2102Ep. However, while an ectopic expression of PAX6 promotes differentiation of NTERA2, it induces cell death in N2102Ep. We nevertheless find that upon induction of retinoic acid, the reprogrammed N2102Ep cells form mature neuronal morphology similar to differentiated pluripotent stem cells NTERA2 as determined by TUJ1 expression, which is absent in N2102Ep parental cells. Altogether, we conclude that the nullipotent state of human EC cells can be reprogrammed to acquire a more relaxed state of differentiation potential by Yamanaka's factors.

Design and biological evaluation of synthetic retinoids: probing length vs. stability vs. activity

All trans-retinoic acid (ATRA) is widely used to direct the differentiation of cultured stem cells. When exposed to the pluripotent human embryonal carcinoma (EC) stem cell line, TERA2.cl.SP12, ATRA induces ectoderm differentiation and the formation of neuronal cell types. We report in this study that novel polyene chain length analogues of ATRA require a specific chain length to elicit a biological responses of the EC cells TERA2.cl.SP12, with synthetic retinoid AH61 being particularly active, and indeed more so than ATRA. The impacts of both the synthetic retinoid AH61 and natural ATRA on the TERA2.cl.SP12 cells were directly compared using both RT-PCR and Fourier Transform Infrared Micro-Spectroscopy (FT-IRMS) coupled with multivariate analysis. Analytical results produced from this study also confirmed that the synthetic retinoid AH61 had biological activity comparable or greater than that of ATRA. In addition to this, AH61 has the added advantage of greater compound stability than ATRA, therefore, avoiding issues of oxidation or decomposition during use with embryonic stem cells.

Requirement for SNAPC1 in transcriptional responsiveness to diverse extracellular signals

Initiation of transcription of RNA polymerase II (RNAPII)-dependent genes requires the participation of a host of basal transcription factors. Among genes requiring RNAPII for transcription, small nuclear RNAs (snRNAs) display a further requirement for a factor known as snRNA-activating protein complex (SNAPc). The scope of the biological function of SNAPc and its requirement for transcription of protein-coding genes has not been elucidated. To determine the genome-wide occupancy of SNAPc, we performed chromatin immunoprecipitation followed by high-throughput sequencing using antibodies against SNAPC4 and SNAPC1 subunits. Interestingly, while SNAPC4 occupancy was limited to snRNA genes, SNAPC1 chromatin residence extended beyond snRNA genes to include a large number of transcriptionally active protein-coding genes. Notably, SNAPC1 occupancy on highly active genes mirrored that of elongating RNAPII extending through the bodies and 3' ends of protein-coding genes. Inhibition of transcriptional elongation resulted in the loss of SNAPC1 from the 3' ends of genes, reflecting a functional association between SNAPC1 and elongating RNAPII. Importantly, while depletion of SNAPC1 had a small effect on basal transcription, it diminished the transcriptional responsiveness of a large number of genes to two distinct extracellular stimuli, epidermal growth factor (EGF) and retinoic acid (RA). These results highlight a role for SNAPC1 as a general transcriptional coactivator that functions through elongating RNAPII.

Functional dissection of HOXD cluster genes in regulation of neuroblastoma cell proliferation and differentiation

Retinoic acid (RA) can induce growth arrest and neuronal differentiation of neuroblastoma cells and has been used in clinic for treatment of neuroblastoma. It has been reported that RA induces the expression of several HOXD genes in human neuroblastoma cell lines, but their roles in RA action are largely unknown. The HOXD cluster contains nine genes (HOXD1, HOXD3, HOXD4, and HOXD8-13) that are positioned sequentially from 3' to 5', with HOXD1 at the 3' end and HOXD13 the 5' end. Here we show that all HOXD genes are induced by RA in the human neuroblastoma BE(2)-C cells, with the genes located at the 3' end being activated generally earlier than those positioned more 5' within the cluster. Individual induction of HOXD8, HOXD9, HOXD10 or HOXD12 is sufficient to induce both growth arrest and neuronal differentiation, which is associated with downregulation of cell cycle-promoting genes and upregulation of neuronal differentiation genes. However, induction of other HOXD genes either has no effect (HOXD1) or has partial effects (HOXD3, HOXD4, HOXD11 and HOXD13) on BE(2)-C cell proliferation or differentiation. We further show that knockdown of HOXD8 expression, but not that of HOXD9 expression, significantly inhibits the differentiation-inducing activity of RA. HOXD8 directly activates the transcription of HOXC9, a key effector of RA action in neuroblastoma cells. These findings highlight the distinct functions of HOXD genes in RA induction of neuroblastoma cell differentiation.

Distinct roles for Wnt-4 and Wnt-11 during retinoic acid-induced neuronal differentiation

Retinoic acid and Wnt/β-catenin signals play important roles during neuronal differentiation but less is known about noncanonical Wnt signals in this context. We examined retinoic acid and Wnt signaling in two human embryonal carcinoma cell lines, NTERA-2 (clone D1), which undergoes neuronal differentiation in response to retinoic acid, and 2102Ep, which does not. Retinoic acid treatment inhibited β-catenin/Tcf activity in NTERA-2 cells but not in 2102Ep cells. Inhibition occurred downstream of β-catenin but did not involve competition between retinoic acid receptors and β-catenin for binding to p300 or Tcf-4. Ectopic expression of FZD1 partially restored inhibition in 2102Ep cells, suggesting the involvement of Wnt ligands. Retinoic acid treatment of NTERA-2 cells induced the expression of Wnt-4 and Wnt-11, both of which were able to inhibit β-catenin/Tcf activity. Wnt-4 and Wnt-11 were found at cell borders in islands of cells that expressed OCT4 and GFAP and were predominantly negative for Nestin, PAX6, and GATA6. Gene silencing of Wnt-4, but not Wnt-11, reduced retinoic acid downregulation of OCT4 and Nanog and upregulation of PAX6, ASCL1, HOXC5, and NEUROD1, suggesting that Wnt-4 promotes early neuronal differentiation. Gene expression analysis of NTERA-2 cells stably overexpressing Wnt-11 suggested that Wnt-11 potentiates retinoic acid induction of early neurogenesis. Consistent with this, overexpression of Wnt-11 maintained a population of proliferating progenitor cells in cultures treated with retinoic acid for several weeks. These observations highlight the distinct roles of two noncanonical Wnts during the early stages of retinoic acid-induced neuronal differentiation.

Regulation of HOXA2 gene expression by the ATP-dependent chromatin remodeling enzyme CHD8

Chromodomain, helicase, DNA-binding protein 8 (CHD8) is an ATP-dependent chromatin remodeling enzyme that has been demonstrated to exist within a large protein complex which includes WDR5, Ash2L, and RbBP5, members of the Mixed Lineage Leukemia (MLL) histone modifying complexes. Here we show that CHD8 relocalizes to the promoter of the MLL regulated gene HOXA2 upon gene activation. Depletion of CHD8 enhances HOXA2 expression under activating conditions. Furthermore, depletion of CHD8 results in a loss of the WDR5/Ash2L/RbBP5 subcomplex, and consequently H3K4 trimethylation, at the HOXA2 promoter. These studies suggest that CHD8 alters HOXA2 gene expression and regulates the recruitment of chromatin modifying enzymes.

Synthesis and evaluation of synthetic retinoid derivatives as inducers of stem cell differentiation

All-trans-retinoic acid (ATRA) and its associated analogues are important mediators of cell differentiation and function during the development of the nervous system. It is well known that ATRA can induce the differentiation of neural tissues from human pluripotent stem cells. However, it is not always appreciated that ATRA is highly susceptible to isomerisation when in solution, which can influence the effective concentration of ATRA and subsequently its biological activity. To address this source of variability, synthetic retinoid analogues have been designed and synthesised that retain stability during use and maintain biological function in comparison to ATRA. It is also shown that subtle modifications to the structure of the synthetic retinoid compound impacts significantly on biological activity, as when exposed to cultured human pluripotent stem cells, synthetic retinoid 4-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-ylethynyl)benzoic acid, 4a (para-isomer), induces neural differentiation similarly to ATRA. In contrast, stem cells exposed to synthetic retinoid 3-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-ylethynyl)benzoic acid, 4b (meta-isomer), produce very few neurons and large numbers of epithelial-like cells. This type of structure-activity-relationship information for such synthetic retinoid compounds will further the ability to design more targeted systems capable of mediating robust and reproducible tissue differentiation.

Differential expression of SOX17 and SOX2 in germ cells and stem cells has biological and clinical implications

Combined action of SOX and POU families of transcription factors plays major roles in embryonic development. In embryonic stem cells, the combination of SOX2 and POU5F1 (OCT3/4) is essential for maintaining the undifferentiated state by activating pluripotency-linked genes, and inhibition of genes involved in differentiation. Besides embryonic stem cells, POU5F1 is also present in early germ cells, primordial germ cells, and gonocytes, where it has a role in suppression of apoptosis. Here we demonstrate that SOX2 is absent in germ cells of human fetal gonads, and as expected carcinoma in situ (CIS), ie the precursor lesion of testicular germ cell tumours of adolescents and adults (TGCTs), and seminoma. Based on genome-wide expression profiling, SOX17 was found to be present, instead of SOX2, in early germ cells and their malignant counterparts, CIS and seminoma. Immunohistochemistry, western blot analysis, and quantitative RT-PCR showed that SOX17 is a suitable marker to distinguish seminoma from embryonal carcinoma, confirmed in representative cell lines. Aberrant SOX2 expression can be present in Sertoli cells when associated with CIS, which can be misdiagnosed as embryonal carcinoma. In conclusion, this study demonstrates the absence of SOX2 in human embryonic and malignant germ cells, which express SOX17 in conjunction with POU5F1. This finding has both diagnostic and developmental biological implications. It allows the identification of seminoma-like cells from embryonal carcinoma based on a positive marker and might be the explanation for the different function of POU5F1 in normal and malignant germ cells versus embryonic stem cells.

Genes, chromosomes and the development of testicular germ cell tumors of adolescents and adults

Testicular germ cell tumors (TGCTs) of adults and adolescents are thought to be derived from primordial germ cells or gonocytes. TGCTs develop postpuberty from precursor lesions known as intratubular germ cell neoplasia undifferentiated. The tumors can be divided into two groups based on their histology and clinical behavior; seminomas resemble primordial germ cells or gonocytes and nonseminomas resemble embryonic or extraembryonic tissues at various stages of differentiation. The most undifferentiated form of nonseminoma, embryonal carcinoma, resembles embryonic stem cells in terms of morphology and expression profiling, both mRNAs and microRNAs. Evidence supports both environmental factors and genetic predisposition underlying the development of TGCTs. Various models of development have been proposed and are discussed. In TGCTs, gain of material from the short arm of chromosome 12 is invariable: genes from this region include the proto-oncogene KRAS, which has activating mutations in approximately 10% of tumors or is frequently overexpressed. A number of different approaches to increase the understanding of the development and progression of TGCTs have highlighted the involvement of KIT, RAS/RAF/MAPK, STAT, and PI3K/AKT signaling. We review the role of these signaling pathways in this process and the potential influence of environmental factors in the development of TGCTs.

Epigenetic marking prepares the human HOXA cluster for activation during differentiation of pluripotent cells

Activation of Hox gene clusters is an early event in embryonic development since individual members play important roles in patterning of the body axis. Their functions require precise control of spatiotemporal expression to provide positional information for the cells of the developing embryo, and the manner by which this control is achieved has generated considerable interest. The situation is different in pluripotent cells, where HOX genes are not expressed but are held in potentio as bivalent chromatin domains, which are resolved upon differentiation to permit HOX cluster activation. In this study we have used differentiation of the pluripotent embryonal carcinoma cell line NTera2SP12 and the human embryonic stem cell line H9 to examine epigenetic changes that accompany activation of the HOXA cluster and show that specific genomic loci are marked by lysine methylation of histone H3 (H3K4 tri- and dimethyl, H3K9 trimethyl) and acetylation of histone H4 even in the undifferentiated cells. The precise locations of such modified histones may be involved in controlling the colinear expression of genes from the cluster.

Polymorphisms in the homeobox gene OTX2 may be a risk factor for bipolar disorder

We investigated the possible involvement of OTX2, a homeobox gene crucial for forebrain development, in the pathogenesis of schizophrenia and bipolar disorder. The disruption of this gene results in cortical malformations and causes serotonergic and dopaminergic cells in the midbrain to be expressed in aberrant locations. Resequencing of DNA from OTX2 exons and surrounding introns from 60 individuals (15 schizophrenia, 15 bipolar disorder, 15 depression, and 15 control) revealed two intronic polymorphisms, rs2277499 (C/T) and rs28757218 (G/T), but no other variations. The minor allele of rs2277499 (T) did not associate with clinical diagnosis. However, using a Taqman genotyping assay, we found the rs28757218 minor allele (T) in 30 out of 720 (4.2%) individuals with bipolar disorder but only in 6 out of 526 (1.1%) control individuals (odds ratio 3.5, 95% confidence interval 1.4-10.4, P = 0.003). On the other hand, the rs28757218 minor allele was only found in 6 out of 458 (1.3%) individuals with schizophrenia. All individuals with the rs28757218 polymorphism were heterozygous for the allele. Based on this positive case-control association finding, we conclude that variations in OTX2 might confer risk for the development of bipolar disorder.

Qualification of embryonal carcinoma 2102Ep as a reference for human embryonic stem cell research

As the number of human embryonic stem cell (hESC) lines increases, so does the need for systematic evaluation of each line's characteristics and potential. Comparisons between lines are complicated by variations in culture conditions, feeders, spontaneous differentiation, and the absence of standardized assays. These difficulties, combined with the inability of most labs to maintain more than a few lines simultaneously, compel the development of reference standards to which hESC lines can be compared. The use of a stable cell line as a reference standard offers many advantages. A line with a relatively unchanging hESC-like gene and protein expression pattern could be a positive control for developing assays. It can be used as a reference for genomics or proteomics studies, especially for normalizing results obtained in separate laboratories. Such a cell line should be widely available without intellectual property restraints, easily cultured without feeders, and resistant to spontaneous changes in phenotype. We propose that the embryonal carcinoma (EC) line 2102Ep meets these requirements. We compared the protein, gene, and microRNA expression of this cell line with those of hESC lines and alternative reference lines such as the EC line NTERA-2 and the karyotypically abnormal hESC line BG01V. The overall expression profiles of all these lines were similar, with exceptions reflecting the germ cell origins of EC. On the basis of global gene and microRNA expression, 2102Ep is somewhat less similar to hESC than the alternatives; however, 2102Ep expresses more hESC-associated microRNAs than NTERA-2 does, and fewer markers of differentiated fates.

The CDK inhibitor p27 enhances neural differentiation in pluripotent NTERA2 human EC cells, but does not permit differentiation of 2102Ep nullipotent human EC cells

Embryonal carcinoma (EC) cells, the stem cells of teratocarcinomas, are the malignant counterparts of pluripotent embryonic stem (ES) cells, but commonly exhibit a reduced ability to differentiate, presumably because of continual selection for genetic changes that alter the balance between self-renewal, differentiation and apoptosis in favour of self-renewal. To explore the nature of the genetic changes that promote nullipotency, we have compared two human EC cell lines, a 'nullipotent' line, 2102Ep, and a 'pluripotent' line, NTERA2. A hybrid derived by fusion of these cells differentiates in response to retinoic acid but, unlike the parental NTERA2 line, does not form terminally differentiated neurons. This implies that the nullipotent EC cell line, 2102Ep, differs in expression of at least two functions in comparison with the NTERA2 pluripotent line, one affecting commitment to differentiation, and one affecting terminal neural differentiation. We have now investigated the possible role of the CDK inhibitor, p27kip1 (p27) in commitment and terminal differentiation. In NTERA2, but not in 2102Ep cells, retinoic acid induces up-regulation of p27 expression, suggesting that 2102Ep cells lack this capacity. However, constitutive expression of a p27 transgene does not overcome the block to differentiation in the 2102Ep parental cells; commitment to differentiation must be blocked elsewhere. On the other hand, constitutive over-expression of p27 from a transgene enhances the neural differentiation of NTERA2 cells. Our results suggest that p27 plays a role in terminal neuronal differentiation of human EC cells, but not in their initial commitment to differentiation, and that other factors, possibly Cyclin D2, specifically limit its ability to promote neural differentiation.

Developmental gene expression profiling of mammalian, fetal orofacial tissue

BACKGROUND

The embryonic orofacial region is an excellent developmental paradigm that has revealed the centrality of numerous genes encoding proteins with diverse and important biological functions in embryonic growth and morphogenesis. DNA microarray technology presents an efficient means of acquiring novel and valuable information regarding the expression, regulation, and function of a panoply of genes involved in mammalian orofacial development.

METHODS

To identify differentially expressed genes during mammalian orofacial ontogenesis, the transcript profiles of GD-12, GD-13, and GD-14 murine orofacial tissue were compared utilizing GeneChip arrays from Affymetrix. Changes in gene expression were verified by TaqMan quantitative real-time PCR. Cluster analysis of the microarray data was done with the GeneCluster 2.0 Data Mining Tool and the GeneSpring software.

RESULTS

Expression of >50% of the approximately 12,000 genes and expressed sequence tags examined in this study was detected in GD-12, GD-13, and GD-14 murine orofacial tissues and the expression of several hundred genes was up- and downregulated in the developing orofacial tissue from GD-12 to GD-13, as well as from GD-13 to GD-14. Such differential gene expression represents changes in the expression of genes encoding growth factors and signaling molecules; transcription factors; and proteins involved in epithelial-mesenchymal interactions, extracellular matrix synthesis, cell adhesion, proliferation, differentiation, and apoptosis. Following cluster analysis of the microarray data, eight distinct patterns of gene expression during murine orofacial ontogenesis were selected for graphic presentation of gene expression patterns.

CONCLUSIONS

This gene expression profiling study identifies a number of potentially unique developmental participants and serves as a valuable aid in deciphering the complex molecular mechanisms crucial for mammalian orofacial development.

All-trans retinoic acid-responsive genes identified in the human SH-SY5Y neuroblastoma cell line and their regulated expression in the nervous system of early embryos

The vitamin A metabolite, all-trans retinoic acid (atRA), is required for embryonic development. atRA binds to the nuclear retinoic acid receptors and regulates the transcription of specific target genes. In order to identify atRA-induced genes that play a role in neural development, a subtractive library was created from SH-SY5Y neuroblastoma cells, a human cell line that exhibits changes in cell adhesion and neurite outgrowth after exposure to the vitamin A acid. We report here the identification of 14 genes that are rapidly induced by atRA (retinoic acid induced in neuroblastoma or RAINB), eight of which were previously not known to be atRA responsive (BTBD11, calmin, cyclin M2, ephrin B2, HOXD10, NEDD9, RAINB6 and tenascin R). mRNA regulation by atRA was confirmed in SH-SY5Y cells by Northern blotting, and gene regulation was studied in additional human cell lines using the quantitative polymerase chain reaction. The majority of the atRA-responsive clones revealed in this screen are highly expressed in the nervous system of developing rat embryos. Further, the expression of several of these genes is perturbed in developing rat embryos exposed to excess atRA or conversely, deprived of sufficient retinoid during early development. We propose that a subset of these genes lie downstream of atRA and its receptors in the regulation of neurite outgrowth and cell adhesion in both neural and non-neural tissues within the developing embryo.

Malformations of the axial skeleton inMuseum Vrolik I: Homeotic transformations and numerical anomalies

The Museum Vrolik collection of anatomical specimens in Amsterdam, The Netherlands, comprises over 5,000 specimens of human and animal anatomy, embryology, pathology, and congenital anomalies. Recently, we rediagnosed a subset of the collection comprising dried human trunk skeletons and cranial base preparations presenting with homeotic transformations (vertebral phenotypic shifts) and numerical vertebral anomalies. We identified 11 trunk skeletons with either anterior or posterior homeotic transformations (AHT or PHT), 5 trunk skeletons with either less or more than the normal number of vertebrae, and well over a hundred cranial base preparations with either AHT (atlas-assimilation) or PHT (occipital vertebra). We found that, although homeotic transformations and numerical anomalies are distinct conditions, both can be described in terms of mismatch between homeotic patterning and morphological segmentation of the paraxial mesoderm. Therefore these two processes are perhaps not as tightly linked as they may seem on the basis of recent molecular studies. In homeotic transformations there is a constant mismatch between homeotic patterning and morphological segmentation throughout the affected region of the vertebral column. In numerical anomalies there is a variable mismatch between homeotic patterning and morphological segmentation, either because of stretching or squeezing of the homeotic pattern or because of oligo- or polysegmentation of the presomitic mesoderm (PSM). Homeotic transformations of the axial skeleton have an incidence of about 1%-5%, apart from their occurrence in malformation syndromes. Of the various etiological possibilities, explaining their frequent but mostly sporadic occurrence, maternal hyperthermia seems an attractive candidate.

Adenomatous polyposis coli control of retinoic acid biosynthesis is critical for zebrafish intestinal development and differentiation

Mutations in the APC (adenomatous polyposis coli) tumor suppressor gene cause uncontrolled proliferation and impaired differentiation of intestinal epithelial cells. Recent studies indicate that human colon adenomas and carcinomas lack retinol dehydrogenases (RDHs) and that APC regulates the expression of human RDHL. These data suggest a model wherein APC controls enterocyte differentiation by controlling retinoic acid production. However, the importance of APC and retinoic acid in mediating control of normal enterocyte development and differentiation remains unclear. To examine the relationship between APC and retinoic acid biosynthesis in normal enterocytes, we have identified two novel zebrafish retinol dehydrogenases, termed zRDHA and zRDHB, that show strong expression within the gut of developing zebrafish embryos. Morpholino knockdown of either APC or zRDHB in zebrafish embryos resulted in defects in structures known to require retinoic acid. These defects included cardiac abnormalities, pericardial edema, failed jaw and pectoral fin development, and the absence of differentiated endocrine and exocrine pancreas. In addition, APC or zRDHB morphant fish developed intestines that lacked columnar epithelial cells and failed to express the differentiation marker intestinal fatty acid-binding protein. Treatment of either APC or zRDHB morphant embryos with retinoic acid rescued the defective phenotypes. Downstream of retinoic acid production, we identified hoxc8 as a retinoic acid-induced gene that, when ectopically expressed, rescued phenotypes of APC- and zRDHB-deficient zebrafish. Our data establish a genetic link supporting a critical role for retinoic acid downstream of APC and confirm the importance of retinoic acid in enterocyte differentiation.

Neural Differentiation from Embryonic Stem Cells: Which Way?

Embryonic stem (ES) cells can in theory produce all cell types of a living organism while renewing themselves with a stable genetic background. These unique features make ES cells a favorable tool for biomedical researches as well as a potential source for therapeutic application. A first step for approaching to ES cells is the directed differentiation to cells of interest, such as the neural cell lineage. Here, we summarize the up and down sides of each category of neural differentiation protocols that have so far been used in mouse and human ES cells, and introduce an efficient and plausible method used in our laboratory for derivation of neuroectodermal cells from human ES cells. This synthesis has led to our suggestions on issues for future design of neural differentiation protocols.

Transcriptional profiling of neuronal differentiation by human embryonal carcinoma stem cells in vitro

Pluripotent stem cell lines can be induced to differentiate into a range of somatic cell types in response to various stimuli. Such cell-based systems provide powerful tools for the investigation of molecules that modulate cellular development. For instance, the formation of the nervous system is a highly regulated process, controlled by molecular pathways that determine the expression of specific proteins involved in cell differentiation. To begin to decipher this mechanism in humans, we used oligonucleotide microarrays to profile the complex patterns of gene expression during the differentiation of neurons from pluripotent human stem cells. Samples of mRNA were isolated from cultured NTERA2 human embryonal carcinoma stem cells and their retinoic-acid-induced derivatives and were prepared for hybridization on custom microarrays designed to detect the expression of genes primarily associated with the neural lineage. In response to retinoic acid, human NTERA2 cells coordinately regulate the expression of large numbers of neural transcripts simultaneously. Transcriptional profiles of many individual genes aligned closely with expression patterns previously recorded by developing neural cells in vitro and in vivo, demonstrating that cultured human pluripotent stem cells appear to form neurons in a conserved manner. These experiments have produced many new expression data concerning neuronal differentiation from human stem cells in vitro. Of particular interest was the regulated expression of Pax6 and Nkx6.1 mRNA and the absence of Pax7 transcription, indicating that neurons derived from NTERA2 pluripotent stem cells are characteristic of neuroectodermal cells of the ventral phenotype.

Global down-regulation of HOX gene expression in PML-RARalpha + acute promyelocytic leukemia identified by small-array real-time PCR

Acute promyelocytic leukemia (APL) is associated with a reciprocal and balanced translocation involving the retinoic acid receptor-alpha (RARalpha). All-trans retinoic acid (ATRA) is used to treat APL and is a potent morphogen that regulates HOX gene expression in embryogenesis and organogenesis. HOX genes are also involved in hematopoiesis and leukemogenesis. Thirty-nine mammalian HOX genes have been identified and classified into 13 paralogous groups clustered on 4 chromosomes. They encode a complex network of transcription regulatory proteins whose precise targets remain poorly understood. The overall function of the network appears to be dictated by gene dosage. To investigate the mechanisms involved in HOX gene regulation in hematopoiesis and leukemogenesis by precise measurement of individual HOX genes, a small-array real-time HOX (SMART-HOX) quantitative polymerase chain reaction (PCR) platform was designed and validated. Application of SMART-HOX to 16 APL bone marrow samples revealed a global down-regulation of 26 HOX genes compared with normal controls. HOX gene expression was also altered during differentiation induced by ATRA in the PML-RARalpha(+) NB4 cell line. PML-RARalpha fusion proteins have been reported to act as part of a repressor complex during myeloid cell differentiation, and a model linking HOX gene expression to this PML-RARalpha repressor complex is now proposed.

Altered hox gene expression and cellular pathogenesis of 5-aza-2'-deoxycytidine-induced murine hindlimb dysmorphogenesis

The DNA demethylating agent, 5-aza-2'-deoxycytidine (d-AZA), elicits temporally related morphological defects and altered gene expression in mouse hindlimbs. Segmental formation of limb regions (stylopod, zeugopod. and autopod) is partially dependent on Hox gene activation. The objective of this study was to understand the role of altered expression of key hox genes in the early pathogenesis of d-AZA-induced hindlimb defects in mice. Semiquantitative RT-PCR was used to analyze hox gene expression (Hox C-11 and Hox A and D homologs, paralogs 9-13). Untreated and treated fore and hindlimb buds were collected 12 and 24 hours after IP injection (1 mg/kg) of d-AZA at 9 am on gestational (GD) 10 and processed for RT-PCR. Additional pregnant mice were treated similarly and whole embryos collected 12 and 24 hours posttreatment and processed for histopathological analysis. No changes in hox gene expression were detected in the forelimb tissue. There was a 2-fold down-regulation of hoxA-11 and C-11 in the 12-hour hindlimb bud tissue. No changes in the HoxD series were detected in the hindlimb bud tissue. The 12- and 24-hour untreated mice exhibited some of the morphological features consistent with physiological apoptosis. Most tissues of the treated mice exhibited cellular changes consistent with cell death associated with the cytotoxicity of the compound. The data reported supports the hypothesis that altered gene expression and not cytotoxicity alone is associated with d-AZA-induced hindlimb dysmorphogenesis.

Hybrids of pluripotent and nullipotent human embryonal carcinoma cells: partial retention of a pluripotent phenotype

To investigate whether the failure of human EC cells that do not differentiate is due to the loss of key differentiation-permissive functions or the acquisition of specific inhibitory functions, we tested the ability to differentiate of 2 hybrids produced between a relatively nullipotent human EC cell line, 2102Ep, and a pluripotent human EC cell line NTERA2. Both hybrids, which exhibited an EC phenotype, were able to differentiate readily in response to retinoic acid. Furthermore, 1 hybrid produced a well-differentiated xenograft tumor, which contained, like the NTERA2 tumors, glandular structures, loose mesenchymal tissues and nodules of cartilage, after injection into a SCID mouse. Thus, the failure of 2102Ep EC cells to differentiate is recessive and due to the loss of a key gene function or functions. Nevertheless, the hybrids differed from the pluripotent NTERA2 line by failing to differentiate in neurons, indicating that 2102Ep cells also had acquired a specific, dominantly-acting, inhibitory mutation specific to the neural lineage. Furthermore, the expression of collagen II by one hybrid before and after induction with retinoic suggested a propensity for spontaneous differentiation not evident in the parental NTERA2 cells. Thus, the mechanisms that restrict the differentiation capacity of the nullipotent 2102Ep line are complex and include both recessive and dominant acting factors.

Retinoic acid down-regulates the expression of EmH-3 homeobox-containing gene in the freshwater sponge Ephydatia muelleri

The effects of retinoic acid (RA), a common morphogen and gene expression regulator in vertebrates, were studied in the freshwater sponge Ephydatia muelleri, both on morphogenesis and on the expression of EmH-3 homeobox-containing gene. At 0.3 microM, RA had no noticeable influence on sponge development, slightly up-regulating EmH-3 expression. In contrast, in sponges reared in 10, 8 microM and to a lesser extent 2 microM RA, there was a strong down-regulation of EmH-3 expression after hatching. This induced modifications in cell composition and morphology, greatly disturbing normal development. Archaeocytes kept the features found in newly hatched sponges while choanocytes and a functional aquiferous system were completely absent. The inhibition of morphogenesis and down-regulation of EmH-3 expression were reversible when sponges were no longer subjected to RA. After RA removal, EmH-3 expression returned to the high values found in untreated sponges, archaeocytes differentiated into choanocytes and sponges achieved a normal development. These results clearly show that, in freshwater sponges, the most primitive metazoan, RA may also act as a morphogen, regulating the expression of a homeobox-containing gene. They demonstrate that the expression of EmH-3 is necessary for the differentiation of archaeocytes into choanocytes and hence for the formation of a complete functional aquiferous system.

Reconciling different models of forebrain induction and patterning: a dual role for the hypoblast

Several models have been proposed for the generation of the rostral nervous system. Among them, Nieuwkoop's activation/transformation hypothesis and Spemann's idea of separate head and trunk/tail organizers have been particularly favoured recently. In the mouse, the finding that the visceral endoderm (VE) is required for forebrain development has been interpreted as support for the latter model. Here we argue that the chick hypoblast is equivalent to the mouse VE, based on fate, expression of molecular markers and characteristic anterior movements around the time of gastrulation. We show that the hypoblast does not fit the criteria for a head organizer because it does not induce neural tissue from naive epiblast, nor can it change the regional identity of neural tissue. However, the hypoblast does induce transient expression of the early markers Sox3 and Otx2. The spreading of the hypoblast also directs cell movements in the adjacent epiblast, such that the prospective forebrain is kept at a distance from the organizer at the tip of the primitive streak. We propose that this movement is important to protect the forebrain from the caudalizing influence of the organizer. This dual role of the hypoblast is more consistent with the Nieuwkoop model than with the notion of separate organizers, and accommodates the available data from mouse and other vertebrates.

Hindbrain respecification in the retinoid-deficient quail

We report here the development and rescue of the truncated hindbrain of retinoid-deprived quail embryos. The embryo is completely rescued by an injection of retinol into the egg; this confirms retinol, or a related retinoid, as a required molecule in hindbrain development. Staging the retinoid replacement enabled us to determine that the 3-4 somite stage is the period when retinoids are required for normal development. Analysis of the development of the retinoid-deprived hindbrain phenotype through somitogenesis has revealed a pathway of retinoid action in early hindbrain regionalization. The hindbrain of the retinoid-deprived embryo is normal in size, during early somitogenesis, but has a respecified pattern of Krox-20 expression. From the earliest expression of Krox-20, at the 5 somite stage, the rhombomere 3 stripe fills the caudal third of the developing hindbrain to the level of the first somite. Morphologically only 2, instead of the normal 5, rhombomere bulges form. These 2 bulges express genes and, later, develop morphology characteristic of rhombomeres 1 and 2 and rhombomere 3. Posterior hindbrain specific genes, Hoxb-1, Fgf3, MafB, and the rhombomere 5 stripe of Krox-20 are never expressed in the head neuroepithelium of these embryos. From the initial formation of the neural plate, there is no evidence of rhombomere 4-7 specific characteristics. These results indicate the specification of the posterior hindbrain is lost and its cells participate in the formation of an enlarged anterior hindbrain. In our previous study, we reported the absence of the posterior hindbrain in retinoid-deprived quails (Maden, M., Gale, E., Kostetskii, I., Zile, M., 1996. Vitamin A-deficient quail embryos have half a hindbrain and other neural defects. Curr. Biol. 6, 417-426). Here, we show this phenotype to be the result of respecification of the hindbrain cells. This provides evidence for a region specific response to a single stimulus, retinol, which suggests a pre-rhombomeric regionalization of the hindbrain.

Induction of lactoferrin expression in murine ES cells by retinoic acid and estrogen

Lactoferrin is an iron-binding glycoprotein present in high concentrations in milk and exocrine fluids such as bile and tears. Many functions have been attributed to lactoferrin, including antimicrobial and antiviral activities, immunomodulation, and cell growth regulation. Lactoferrin expression is controlled by different regulators, including retinoic acid and estrogen. However, the expression pattern of lactoferrin in mammalian early development has not yet been reported. Murine embryonic stem cells are pluripotent cells that can contribute to all tissues and were used for this study. We show here that while no lactoferrin protein or mRNA was detected in untreated murine embryonic stem cells, retinoic acid and estrogen can induce high levels lactoferrin expression in these cells. Expression, demonstrated by reverse transcription-polymerase chain reaction, Western blot, immunofluorescence, and ELISA assay, was dose and time dependent. Our study provides an in vitro model for examining lactoferrin expression in early development and differentiation.

All-trans retinol, vitamin D and other hydrophobic compounds bind in the axial pore of the five-stranded coiled-coil domain of cartilage oligomeric matrix protein

The potential storage and delivery function of cartilage oligomeric matrix protein (COMP) for cell signaling molecules was explored by binding hydrophobic compounds to the recombinant five-stranded coiled-coil domain of COMP. Complex formation with benzene, cyclohexane, vitamin D3 and elaidic acid was demonstrated through increases in denaturation temperatures of 2-10 degreesC. For all-trans retinol and all-trans retinoic acid, an equilibrium dissociation constant KD = 0.6 microM was evaluated by fluorescence titration. Binding of benzene and all-trans retinol into the hydrophobic axial pore of the COMP coiled-coil domain was proven by the X-ray crystal structures of the corresponding complexes at 0.25 and 0.27 nm resolution, respectively. Benzene binds with its plane perpendicular to the pore axis. The binding site is between the two internal rings formed by Leu37 and Thr40 pointing into the pore of the COMP coiled-coil domain. The retinol beta-ionone ring is positioned in a hydrophobic environment near Thr40, and the 1.1 nm long isoprene tail follows a completely hydrophobic region of the pore. Its terminal hydroxyl group complexes with a ring of the five side chains of Gln54. A mutant in which Gln54 is replaced by Ile binds all-trans retinol with affinity similar to the wild-type, demonstrating that hydrophobic interactions are predominant.

Inducible expression of N-methyl-D-aspartate receptor, and delta and mu opioid receptor messenger RNAs and protein in the NT2-N human cell line

Retinoic acid treatment of NT-era2/cl.D1 (NT2) cells, a human teratocarcinoma cell line, yields 95% pure cultures of terminally differentiated neuronal cells. Concomitant with their terminal differentiation into neurons, NT2 cells are induced by retinoic acid to express neuronal N-methyl-D-aspartate receptor channels, which are fully functional. We determined the effects of retinoic acid-induced differentiation of NT2 cells on the levels of N-methyl-D-aspartate, delta opioid and mu opioid receptor messenger RNAs. RNA levels were measured using quantitative solution hybridization assays. The riboprobes were complementary to major portions of the coding regions of the N-methyl-D-aspartate, delta opioid and mu opioid receptor complementary DNAs. After four weeks of exposure to 10 microM retinoic acid, followed by four weeks of treatment with mitotic inhibitors (1 microM of cytosine arabinoside, 10 microM of fluorodeoxyuridine and 10 microM of uridine) the levels of N-methyl-D-aspartate receptor messenger RNA in differentiated NT2-N cells increased 10-fold, delta opioid receptor messenger RNA increased three-fold, and mu opioid receptor messenger RNA increased four-fold. Northern blot analysis revealed two transcripts for the N-methyl-D-aspartate receptor messenger RNA (4.2 and 4.4 kb) and two transcripts for delta opioid receptor messenger RNA (7.0 and 11.0 kb). To determine whether the increases in messenger RNAs were accompanied by an increased synthesis of the respective proteins, we examined the immunoperoxidase localization of N-methyl-D-aspartate receptor and delta opioid receptor antisera. N-Methyl-D-aspartate receptor-like immunoreactivity was seen within the cell bodies as well as on the processes of the retinoic acid-differentiated cells. Although delta opioid receptor-like immunoreactivity was detected within the soma of isolated cells prior to retinoic acid treatment, the apparent number of these labelled cells and their ramified processes were markedly enhanced following retinoic acid differentiation. These results demonstrate parallels between the inducible expression of the N-methyl-D-aspartate and opioid receptor messenger RNAs and proteins during the acquisition of the fully differentiated neuronal phenotype in cultured NT2 cells. Retinoic acid-differentiated NT2 cells express increased levels for the N-methyl-D-aspartate, delta opioid and mu opioid receptor messenger RNAs, providing the opportunity to study the interactions among these receptor systems in human terminally differentiated neuronal cells in culture.

Reduction of connexin43 expression and dye-coupling during neuronal differentiation of human NTera2/clone D1 cells

Gap junctions are plasma membrane specializations that allow direct communication among adjoining cells. We used a human pluripotential teratocarcinoma cell line, NTera-2/clone D1 (NT2/D1), as a model to study gap junctions in CNS neurons and their neuronal precursors. These cells were differentiated following retinoic acid (RA) treatment for 4 weeks and antiproliferative agents for 3 weeks, respectively, to yield post-mitotic CNS neuronal (NT2-N) cells. The cytoplasmic RNA was isolated from NT2/D1 cells both before and during RA treatment and from differentiated neurons (NT2-N cells). These RNA samples were examined using Northern blot analysis with cDNA probes specific for connexin26, -32, and -43. Connexin26 and -32 mRNAs were absent in NT2/D1 and NT2-N cells. Connexin43 mRNA was expressed at high levels in NT2/D1 cells before RA treatment, but it decreased significantly during RA induction. There was no detectable connexin43 mRNA in NT2-N cells. Western blot analysis confirmed the expression of connexin43 protein in NT2/D1 cells before and during RA treatment. The protein profile detected in Western blot analysis indicated two bands representing different phosphorylation states of connexin43. Our immunocytochemistry results did not show connexin26 and -32 immunoreactivity in NT2/D1 and NT2-N cells. However, we detected connexin43 immunoreactivity in NT2/D1 cells with a decreasing pattern upon RA induction. Both Western blotting and immunocytochemistry confirmed the absence of connexin43 protein in NT2-N cells. NT2/D1 cells passed calcein readily to an average of 18 cells, confirming the functionality of gap junctions in these cells. The extent of dye-coupling decreased about 78% when NT2/D1 cells were RA treated for 4 weeks. NT2-N differentiated neurons did not pass dye to the adjacent cells. We conclude that both connexin43 expression and dye coupling capacity decrease during neuronal differentiation of NT2/D1 cells.

The Pbx family of proteins is strongly upregulated by a post-transcriptional mechanism during retinoic acid-induced differentiation of P19 embryonal carcinoma cells

Retinoic acid (RA) induces expression of genes encoding the Hox family of transcription factors, whose differential expression orchestrates developmental programs specifying anterior-posterior structures during embryogenesis. Hox proteins bind DNA as monomers and heterodimers with Pbx proteins. Here we show that RA upregulates Pbx protein abundance coincident with transcriptional activation of Hox genes in P19 embryonal carcinoma cells undergoing neuronal differentiation. However, in contrast to Hox induction, Pbx upregulation is predominantly a result of post-transcriptional mechanisms. Interestingly, Pbx1, Pbx2, and Pbx3 exhibit different profiles of upregulation, suggesting possible functional divergence. The parallel upregulation of Pbx and Hox proteins in this model suggests an important role for transcriptional control by Pbx-Hox heterodimers during neurogenesis, and argues for precise control by RA.

Functional interaction between a RARE and an AP-2 binding site in the regulation of the human HOX A4 gene promoter

HOX A genes are induced in a temporal fashion after retinoic acid (RA) treatment in non-N-ras-transformed PA-1 human teratcarcinoma cells. However, In N-ras-transformed PA-1 cells, RA-Induced expression of HOX A genes is delayed. The mRNA for the transcriptional activator AP-2 is overexpressed in these ras-transformed cells, but AP-2 transcriptional activity is inhibited relative to non ras-transformed PA-1 cells. Constitutive expression of AP-2 mimics the effect of ras by transforming cells and inhibiting differentiation in culture. We analyzed 4 kb of the human HOX A4 gene promoter and identified seven putative AP-2-binding sites in the DNA sequence. Transcription assays with variably sized HOX A4 promoter reporter constructs revealed that a 365 bp region of the promoter, -2950 to -3315 relative to the mRNA start, controls RA responsiveness and ras-mediated inhibition of HOX A4 activity. This region contains an AP-2 binding site and a RARE. Elimination of the AP-2 site by site-directed mutagenesis demonstrated that the AP-2 site is involved in RA-mediated transcriptional activation of the human HOX A4 promoter in combination with the RA receptor response element (RARE). In N-ras-transformed cells, low HOX A4 promoter activity results from ras inhibition of AP-2 transactivation.

Retinoic acid-induced increase in delta-opioid receptor and N-methyl-D-aspartate receptor mRNA levels in neuroblastoma x glioma (NG108-15) cells

We determined the effects of all-trans retinoic acid (RA) on the levels of delta opioid receptor (DOR) mRNA and N-Methyl-D-Aspartate receptor (NMDAR1) mRNA in neuroblastoma x glioma hybrid cells (NG108-15) by use of quantitative solution hybridization assays. The assays utilized riboprobes complementary to major portions of the coding region of the DOR and NMDAR1 cDNAs. At 10 microM RA a 3-fold increase in DOR mRNA at 48 h, and later (144 h) alterations were observed in NMDAR1 mRNA levels. Northern blot analysis revealed six transcripts for DOR mRNA ranging in size from 8.7 to 2.0 Kb, and three transcripts for NMDAR1 mRNA ranging in size from 4.1 to 3.5 Kb. Neither the size nor the fractional band intensity was affected by RA treatment. The delayed induction of DOR mRNA suggests an indirect mechanism by which RA acts on transcription of this gene. A surprising induction of DOR mRNA by the protein synthesis inhibitor cycloheximide (CHX) suggests that either a repressor molecule or degrading enzymes/proteases may regulate basal levels of this mRNA. Treatment with RA resulted in a concentration- and time-dependent morphological differentiation characterized by increased size of the cell body and the appearance of numerous short and long processes.

Sonic hedgehog and Fgf-4 act through a signaling cascade and feedback loop to integrate growth and patterning of the developing limb bud

Proper limb growth and patterning requires signals from the zone of polarizing activity in the posterior mesoderm and from the overlying apical ectodermal ridge (AER). Sonic hedgehog and Fgf-4, respectively, have recently been identified as candidates for these signals. We have dissected the roles of these secreted proteins in early limb development by ectopically regulating their activities in a number of surgical contexts. Our results indicate that Sonic hedgehog initiates expression of secondary signaling molecules, including Bmp-2 in the mesoderm and Fgf-4 in the ectoderm. The mesoderm requires ectodermally derived competence factors, which include Fgf-4, to activate target gene expression in response to Sonic hedgehog. The expression of Sonic hedgehog and Fgf-4 is coordinately regulated by a positive feedback loop operating between the posterior mesoderm and the overlying AER. Taken together, these data provide a basis for understanding the integration of growth and patterning in the developing limb.

Gene regulation during neuronal and non-neuronal differentiation of NTERA2 human teratocarcinoma-derived stem cells

We constructed cDNA libraries from a clonal human teratocarcinoma-derived cell line and two retinoic acid-induced derivatives: a homogeneous population of neurons and a FACS-isolated, non-neuronal population. These libraries are large and representative of the cells from which they were derived, as determined by colony hybridization. PCR analysis indicates that the transcripts encoding P- and E-cadherin are down-regulated whereas the the prion protein (PrP) transcript is up-regulated in neurons. These cells offer a promising system for investigations of human prion infection and the cDNA libraries provide a source of neuron-specific genes.

DNA-binding proteins that interact with the 19-base pair (CRE-like) element from the HCMV major immediate early promoter in differentiating human embryonal carcinoma cells

The pluripotent human embryonal carcinoma (EC) cell line NTERA-2 provides a useful tool for investigating cell differentiation in a way that is pertinent to the development of the early human embryo. The major immediate early (MIE) gene of human cytomegalovirus (HCMV), which is not transcribed in undifferentiated NTERA-2 EC cells but is transcribed in their differentiated derivatives, offers a model with which to study the developmental regulation of gene activity during the differentiation of these cells. We have investigated the regulatory activity of the cAMP response elements (CRE) and the activation protein (AP1) site found within several repeated 19-base-pair (bp) elements from the HCMV MIE promoter, and the developmental regulation of nuclear DNA-binding factors that interact with these sites. The 19-bp CRE but not the AP1 site is responsive to cAMP in undifferentiated NTERA-2 EC and its activity is enhanced upon differentiation. Nuclear proteins of the CREB, Fos, and Jun families bind to these sites, but, surprisingly, their levels only show limited regulation during NTERA-2 differentiation. This contrasts with results obtained with murine EC cells. However, additional and apparently novel proteins with molecular weights between 80,000 and 90,000, and binding specificities for both CRE and AP1 sites, were detected in undifferentiated EC cells. The activity of these proteins decreased markedly after differentiation, indicating their involvement in negative regulation of the CRE/AP1-like site in undifferentiated EC cells. This suggests novel members able to interact via leucine zippers with other members of the Jun-Fos-CREB family of DNA binding proteins that are also involved in this regulation.

Expression of retinoic acid receptor genes in fetal and newborn rat lung

Lung differentiation and development are affected by vitamin A and its metabolites. One mechanism through which retinoids might exert their effects is through nuclear retinoic acid receptors (RAR). The gene expression profile of the RAR family (alpha, beta, gamma) has previously been determined in both the developing mouse embryo to 14.5 days gestation, and in the adult lung. The purpose of this study was to determine the expression of the RAR genes during the period of gestation that results in the formation of the saccular lung stage. Total RNA was extracted from fetal lungs of Sprague-Dawley rats at gestational days 17, 19, 20, 21, and 22, and from 12-hour-old newborns for Northern hybridization. Two transcripts of RAR alpha mRNA (3.7 and 2.7 kb) were found at each time point. At day 17, the 2.7 kb RAR alpha mRNA was increased two-fold or more than at any other time studied. At days 19-22 the levels of the 3.7 kb RAR alpha species were also lower than day 17 and newborn levels. One RAR beta mRNA transcript (3.4 kb), present at all time points, was significantly higher in the newborn than on days 17-22. Expression of RAR gamma mRNA could only be demonstrated by reverse transcriptase-polymerase chain reaction. We speculate that the higher RAR alpha species at day 17 indicates a role for RAR alpha in the maintenance of the columnar epithelial cells of the glandular phase of lung development.(ABSTRACT TRUNCATED AT 250 WORDS)