Overexpression of murine Pax3 increases NCAM polysialylation in a human medulloblastoma cell line

Pax3 induces target-specific reinnervation through axon collateral expression of PSA-NCAM

Damaged or dysfunctional neural circuits can be replaced after a lesion by axon sprouting and collateral growth from undamaged neurons. Unfortunately, these new connections are often disorganized and rarely produce clinical improvement. Here we investigate how to promote post-lesion axonal collateral growth, while retaining correct cellular targeting. In the mouse olivocerebellar path, brain-derived neurotrophic factor (BDNF) induces correctly-targeted post-lesion cerebellar reinnervation by remaining intact inferior olivary axons (climbing fibers). In this study we identified cellular processes through which BDNF induces this repair. BDNF injection into the denervated cerebellum upregulates the transcription factor Pax3 in inferior olivary neurons and induces rapid climbing fiber sprouting. Pax3 in turn increases polysialic acid-neural cell adhesion molecule (PSA-NCAM) in the sprouting climbing fiber path, facilitating collateral outgrowth and pathfinding to reinnervate the correct targets, cerebellar Purkinje cells. BDNF-induced reinnervation can be reproduced by olivary Pax3 overexpression, and abolished by olivary Pax3 knockdown, suggesting that Pax3 promotes axon growth and guidance through upregulating PSA-NCAM, probably on the axon's growth cone. These data indicate that restricting growth-promotion to potential reinnervating afferent neurons, as opposed to stimulating the whole circuit or the injury site, allows axon growth and appropriate guidance, thus accurately rebuilding a neural circuit.

Restoration of functional PAX3 transcriptional factor enhanced neuronal differentiation in PAX3b isoform-depleted neuroblastoma cells

Reexpressed PAX3 transcription factor is believed to be responsible for the differentiation defects observed in neuroblastoma. Although the importance of PAX3 in neuronal differentiation is documented how it is involved in the defective differentiation remains unexplored particularly with its isoforms. Here, first we have analyzed PAX3 expression, its functional status, and its correlation with the neuronal marker expression in SH-SY5Y and its parental SK-N-SH cells. We have found that SH-SY5Y cells which expressed more PAX3 showed increased expression of neuronal marker genes (TUBB, MAP2, NEFL, NEUROG2, SYP) and reported PAX3 target genes (MET, TGFA, and NCAM1) than the SK-N-SH cells that had low PAX3 level. Retinoic acid treatment is unable to induce neuronal differentiation in cells (SK-N-SH) with low PAX3 level/activity. Moreover, ectopic expression of PAX3 in SK-N-SH cells neither induces neuronal marker genes nor its target genes. PAX3 isoform expression analysis revealed the expression of PAX3b isoform that contains only paired domain in SK-N-SH cells, whereas in SH-SY5Y cells, we could also observe PAX3c isoform that contains all functional domains. Further, PAX3b depletion in SK-N-SH cells is not induced PAX3 target genes, and the cells remain poorly differentiated. Interestingly, ectopic PAX3 expression in PAX3b-depleted SK-N-SH cells enhanced neuronal outgrowth along with neuronal marker gene induction. Collectively, these results showed that the PAX3b isoform may be responsible for the differentiation defect observed in SK-N-SH cells and restoration of functional PAX3 in the absence of PAX3b can induce neurogenesis in these cells.

Investigating the molecular mechanisms of learning and memory using Caenorhabditis elegans

Learning is an essential biological process for survival since it facilitates behavioural plasticity in response to environmental changes. This process is mediated by a wide variety of genes, mostly expressed in the nervous system. Many studies have extensively explored the molecular and cellular mechanisms underlying learning and memory. This review will focus on the advances gained through the study of the nematode Caenorhabditis elegans. C. elegans provides an excellent system to study learning because of its genetic tractability, in addition to its invariant, compact nervous system (~300 neurons) that is well-characterised at the structural level. Importantly, despite its compact nature, the nematode nervous system possesses a high level of conservation with mammalian systems. These features allow the study of genes within specific sensory-, inter- and motor neurons, facilitating the interrogation of signalling pathways that mediate learning via defined neural circuits. This review will detail how learning and memory can be studied in C. elegans through behavioural paradigms that target distinct sensory modalities. We will also summarise recent studies describing mechanisms through which key molecular and cellular pathways are proposed to affect associative and non-associative forms of learning.

Construction and Validation of a 13-Gene Signature for Prognosis Prediction in Medulloblastoma

Background: Recent studies have identified several molecular subgroups of medulloblastoma associated with distinct clinical outcomes; however, no robust gene signature has been established for prognosis prediction. Our objective was to construct a robust gene signature-based model to predict the prognosis of patients with medulloblastoma.

Methods: Expression data of medulloblastomas were acquired from the Gene Expression Omnibus (GSE85217, n = 763; GSE37418, n = 76). To identify genes associated with overall survival (OS), we performed univariate survival analysis and least absolute shrinkage and selection operator (LASSO) Cox regression. A risk score model was constructed based on selected genes and was validated using multiple datasets. Differentially expressed genes (DEGs) between the risk groups were identified. Kyoto Encyclopedia of Genes and Genomes (KEGG), Gene Ontology (GO), and protein–protein interaction (PPI) analyses were performed. Network modules and hub genes were identified using Cytoscape. Furthermore, tumor microenvironment (TME) was evaluated using ESTIMATE algorithm. Tumor-infiltrating immune cells (TIICs) were inferred using CIBERSORTx.

Results: A 13-gene model was constructed and validated. Patients classified as high-risk group had significantly worse OS than those as low-risk group (Training set: p < 0.0001; Validation set 1: p < 0.0001; Validation set 2: p = 0.00052). The area under the curve (AUC) of the receiver operating characteristic (ROC) analysis indicated a good performance in predicting 1-, 3-, and 5-year OS in all datasets. Multivariate analysis integrating clinical factors demonstrated that the risk score was an independent predictor for the OS (validation set 1: p = 0.001, validation set 2: p = 0.004). We then identified 265 DEGs between risk groups and PPI analysis predicted modules that were highly related to central nervous system and embryonic development. The risk score was significantly correlated with programmed death-ligand 1 (PD-L1) expression (p < 0.001), as well as immune score (p = 0.035), stromal score (p = 0.010), and tumor purity (p = 0.010) in Group 4 medulloblastomas. Correlations between the 13-gene signature and the TIICs in Sonic hedgehog and Group 4 medulloblastomas were revealed.

Conclusion: Our study constructed and validated a robust 13-gene signature model estimating the prognosis of medulloblastoma patients. We also revealed genes and pathways that may be related to the development and prognosis of medulloblastoma, which might provide candidate targets for future investigation.

Mental disorders and an acidic glycan-from the perspective of polysialic acid (PSA/polySia) and the synthesizing enzyme, ST8SIA2

Mental disorders, such as schizophrenia, bipolar disorder, and autism spectrum disorder, are challenging to manage, worldwide. Understanding the molecular mechanisms underlying these disorders is essential and required. Studies investigating such molecular mechanisms are well performed and important findings are accumulating apace. Based on the fact that these disorders are due in part to the accumulation of genetic and environmental risk factors, consideration of multi-molecular and/or multi-system dependent phenomena might be important. Acidic glycans are an attractive family of molecules for understanding these disorders, because impairment of the fine-tuned glycan system affects a large number of molecules that are deeply involved in normal brain function. One of the candidates of this important family of glycan epitopes in the brain is polysialic acid (PSA/polySia). PSA is a well-known molecule because of its role as an oncodevelopmental antigen and is also widely used as a marker of adult neurogenesis. Recently, several reports have suggested that PSA and PSA-related genes are associated with multiple mental disorders. The relationships among PSA, PSA-related genes, and mental disorders are reviewed here.

In vitro Magnetic Stimulation: A Simple Stimulation Device to Deliver Defined Low Intensity Electromagnetic Fields

Non-invasive brain stimulation (NIBS) by electromagnetic fields appears to benefit human neurological and psychiatric conditions, although the optimal stimulation parameters and underlying mechanisms remain unclear. Although, in vitro studies have begun to elucidate cellular mechanisms, stimulation is delivered by a range of coils (from commercially available human stimulation coils to laboratory-built circuits) so that the electromagnetic fields induced within the tissue to produce the reported effects are ill-defined. Here, we develop a simple in vitro stimulation device with plug-and-play features that allow delivery of a range of stimulation parameters. We chose to test low intensity repetitive magnetic stimulation (LI-rMS) delivered at three frequencies to hindbrain explant cultures containing the olivocerebellar pathway. We used computational modeling to define the parameters of a stimulation circuit and coil that deliver a unidirectional homogeneous magnetic field of known intensity and direction, and therefore a predictable electric field, to the target. We built the coil to be compatible with culture requirements: stimulation within an incubator; a flat surface allowing consistent position and magnetic field direction; location outside the culture plate to maintain sterility and no heating or vibration. Measurements at the explant confirmed the induced magnetic field was homogenous and matched the simulation results. To validate our system we investigated biological effects following LI-rMS at 1 Hz, 10 Hz and biomimetic high frequency, which we have previously shown induces neural circuit reorganization. We found that gene expression was modified by LI-rMS in a frequency-related manner. Four hours after a single 10-min stimulation session, the number of c-fos positive cells increased, indicating that our stimulation activated the tissue. Also, after 14 days of LI-rMS, the expression of genes normally present in the tissue was differentially modified according to the stimulation delivered. Thus we describe a simple magnetic stimulation device that delivers defined stimulation parameters to different neural systems in vitro. Such devices are essential to further understanding of the fundamental effects of magnetic stimulation on biological tissue and optimize therapeutic application of human NIBS.

Differential effects of Pax3 on expression of polysialyltransferases STX and PST in TGF-β-treated normal murine mammary gland cells

Glycosylation of certain proteins at the mammalian cell surface is an essential event in carcinogenesis. Sialylation, one type of glycosylation, can act on multiple cell-behaviors, such as migration, growth, and malignant invasion. Two polysialyltransferases, ST8Sia II (STX) and ST8Sia IV (PST), are responsible for synthesis of polysialic acid on neural cell adhesion molecule. We showed previously that STX and PST are oppositely expressed in normal murine mammary gland cells undergoing transforming growth factor-β-induced epithelial-mesenchymal transition. The molecular basis for regulation of STX and PST remained unclear. In the present study, we observed that transcription factor Pax3 upregulates STX expression, downregulates PST expression, and modulates upregulated expression of PSA, which attaches primarily to neural cell adhesion molecule to form PSA-NCAM. Overexpression of Pax3 in normal murine mammary gland cells transformed the expression of epithelial-mesenchymal transition markers E-cadherin and N-cadherin, and significantly promoted cell migration, but had no effect on cell proliferation.

On the trail of the glycan codes stored in cancer-related cell adhesion proteins

Changes in the profile of protein glycosylation are a hallmark of ongoing neoplastic transformation. A unique set of tumor-associated carbohydrate antigens expressed on the surface of malignant cells may serve as powerful diagnostic and therapeutic targets. Cell-surface proteins with altered glycosylation affect the growth, proliferation and survival of those cells, and contribute to their acquisition of the ability to migrate and invade. They may also facilitate tumor-induced immunosuppression and the formation of distant metastases. Deciphering the information encoded in these particular glycan portions of glycoconjugates may shed light on the mechanisms of cancer progression and metastasis. A majority of the related review papers have focused on overall changes in the patterns of cell-surface glycans in various cancers, without pinpointing the molecular carriers of these glycan structures. The present review highlights the ways in which particular tumor-associated glycan(s) coupled with a given membrane-bound protein influence neoplastic cell behavior during the development and progression of cancer. We focus on altered glycosylated cell-adhesion molecules belonging to the cadherin, integrin and immunoglobulin-like superfamilies, examined in the context of molecular interactions.

Molecular Basis of the Receptor Interactions of Polysialic Acid (polySia), polySia Mimetics, and Sulfated Polysaccharides

Polysialic acid (polySia) and polySia glycomimetic molecules support nerve cell regeneration, differentiation, and neuronal plasticity. With a combination of biophysical and biochemical methods, as well as data mining and molecular modeling techniques, it is possible to correlate specific ligand-receptor interactions with biochemical processes and in vivo studies that focus on the potential therapeutic impact of polySia, polySia glycomimetics, and sulfated polysaccharides in neuronal diseases. With this strategy, the receptor interactions of polySia and polySia mimetics can be understood on a submolecular level. As the HNK-1 glycan also enhances neuronal functions, we tested whether similar sulfated oligo- and polysaccharides from seaweed could be suitable, in addition to polySia, for finding potential new routes into patient care focusing on an improved cure for various neuronal diseases. The knowledge obtained here on the structural interplay between polySia or sulfated polysaccharides and their receptors can be exploited to develop new drugs and application routes for the treatment of neurological diseases and dysfunctions.

Pharmacological inhibition of polysialyltransferase ST8SiaII modulates tumour cell migration

Polysialic acid (polySia), an α-2,8-glycosidically linked polymer of sialic acid, is a developmentally regulated post-translational modification predominantly found on NCAM (neuronal cell adhesion molecule). Whilst high levels are expressed during development, peripheral adult organs do not express polySia-NCAM. However, tumours of neural crest-origin re-express polySia-NCAM: its occurrence correlates with aggressive and invasive disease and poor clinical prognosis in different cancer types, notably including small cell lung cancer (SCLC), pancreatic cancer and neuroblastoma. In neuronal development, polySia-NCAM biosynthesis is catalysed by two polysialyltransferases, ST8SiaII and ST8SiaIV, but it is ST8SiaII that is the prominent enzyme in tumours. The aim of this study was to determine the effect of ST8SiaII inhibition by a small molecule on tumour cell migration, utilising cytidine monophosphate (CMP) as a tool compound. Using immunoblotting we showed that CMP reduced ST8iaII-mediated polysialylation of NCAM. Utilizing a novel HPLC-based assay to quantify polysialylation of a fluorescent acceptor (DMB-DP3), we demonstrated that CMP is a competitive inhibitor of ST8SiaII (K i = 10 µM). Importantly, we have shown that CMP causes a concentration-dependent reduction in tumour cell-surface polySia expression, with an absence of toxicity. When ST8SiaII-expressing tumour cells (SH-SY5Y and C6-STX) were evaluated in 2D cell migration assays, ST8SiaII inhibition led to significant reductions in migration, while CMP had no effect on cells not expressing ST8SiaII (DLD-1 and C6-WT). The study demonstrates for the first time that a polysialyltransferase inhibitor can modulate migration in ST8SiaII-expressing tumour cells. We conclude that ST8SiaII can be considered a druggable target with the potential for interfering with a critical mechanism in tumour cell dissemination in metastatic cancers.

Impact of structural aberrancy of polysialic acid and its synthetic enzyme ST8SIA2 in schizophrenia

Psychiatric disorders are a group of human diseases that impair higher cognitive functions. Whole-genomic analyses have recently identified susceptibility genes for several psychiatric disorders, including schizophrenia. Among the genes reported to be involved in psychiatric disorders, a gene encoding a polysialyltransferase involved in the biosynthesis of polysialic acid (polySia or PSA) on cell surfaces has attracted attention for its potential role in emotion, learning, memory, circadian rhythm, and behaviors. PolySia is a unique polymer that spatio-temporally modifies neural cell adhesion molecule (NCAM) and is predominantly found in embryonic brains, although it persists in areas of the adult brain where neural plasticity, remodeling of neural connections, or neural generation is ongoing, such as the hippocampus, subventricular zone (SVZ), thalamus, prefrontal cortex, and amygdala. PolySia is thought to be involved in the regulation of cell-cell interactions; however, recent evidence suggests that it is also involved in the functional regulation of ion channels and neurologically active molecules, such as Brain-derived neurotrophic factor (BDNF), FGF2, and dopamine (DA) that are deeply involved in psychiatric disorders. In this review, the possible involvement of polysialyltransferase (ST8SIA2/ST8SiaII/STX/Siat8B) and its enzymatic product, polySia, in schizophrenia is discussed.

Role of Pax3 acetylation in the regulation of Hes1 and Neurog2

Pax3 plays a role in regulating Hes1 and Neurog2 activity and thereby stem cell maintenance and neurogenesis. A mechanism for Pax3 regulation of these two opposing events, during caudal neural tube development, is examined in this study. Pax3 acetylation on C-terminal lysine residues K437 and K475 may be critical for proper regulation of Hes1 and Neurog2. Removal of these lysine residues increased Hes1 but decreased Neurog2 promoter activity. SIRT1 deacetylase may be a key component in regulating Pax3 acetylation. Chromatin immunoprecipitation assays showed that SIRT1 is associated with Hes1 and Neurog2 promoters during murine embryonic caudal neural tube development at E9.5, but not at E12.5. Overexpression of SIRT1 decreased Pax3 acetylation, Neurog2 and Brn3a positive staining. Conversely, siRNA-mediated silencing of SIRT1 increased these factors. These studies suggest that Pax3 acetylation results in decreased Hes1 and increased Neurog2 activity, thereby promoting sensory neuron differentiation.

Pax2 coordinates epithelial morphogenesis and cell fate in the inner ear

Crucial components of the vertebrate eye, ear and nose develop from discrete patches of surface epithelium, called placodes, which fold into spheroids and undergo complex morphogenesis. Little is known about how the changes in cell and tissue shapes are coordinated with the acquisition of cell fates. Here we explore whether these processes are regulated by common transcriptional mechanisms in the developing ear. After specification, inner ear precursors elongate to form the placode, which invaginates and is transformed into the complex structure of the adult ear. We show that the transcription factor Pax2 plays a key role in coordinating otic fate and placode morphogenesis, but appears to regulate each process independently. In the absence of Pax2, otic progenitors not only lose otic marker expression, but also fail to elongate due to the loss of apically localised N-cadherin and N-CAM. In the absence of either N-cadherin or N-CAM otic cells lose apical cell-cell contact and their epithelial shape. While misexpression of Pax2 leads to ectopic activation of both adhesion molecules, it is not sufficient to confer otic identity. These observations suggest that Pax2 controls cell shape independently from cell identity and thus acts as coordinator for these processes.

PAX3 across the spectrum: from melanoblast to melanoma

The PAX3 transcription factor is critical for the proper development of neural crest lineages including melanocytes. These cells show continued PAX3 expression from formation to differentiation. While many expression, misexpression and mutation studies clarify the importance of PAX3 in melanocyte development, less well understood, and more perplexing, is the continued PAX3 expression in the adult skin. In this article we explore the multiple roles of PAX3 in melanocyte genesis, and draw on evidence from expression in developing melanoblasts, adult melanocytes and melanocyte stem cells. From this, we present a more encompassing theory that PAX3 is a key regulator of the myriad steps in melanocytic cell determination. These roles may be accomplished by differential association with cofactors, via alternate transcripts or posttranslational protein modification(s). In light of the plethora of information gleaned from development we then consider its roles in melanoma and provide here a comprehensive consideration of the significance of PAX3 expression in melanoma. PAX3 and Pax3 indicate human and mouse transcription factors respectively.

Key basic helix-loop-helix transcription factor genes Hes1 and Ngn2 are regulated by Pax3 during mouse embryonic development

Pax3 is expressed early during embryonic development in spatially restricted domains including limb muscle, neural crest, and neural tube. Pax3 functions at the nodal point in melanocyte stem cell differentiation, cardiogenesis and neurogenesis. Additionally Pax3 has been implicated in migration and differentiation of precursor cell populations. Currently there are questions about how Pax3 regulates these diverse functions. In this study we found that in the absence of functional Pax3, as in Splotch embryos, the neural crest cells undergo premature neurogenesis, as evidenced by increased Brn3a positive staining in neural tube explants, in comparison with wild-type. Premature neurogenesis in the absence of functional Pax3 may be due to a change in the regulation of basic helix-loop-helix transcription factors implicated in proliferation and differentiation. Using promoter-luciferase activity measurements in transient co-transfection experiments and electro-mobility shift assays, we show that Pax3 regulates Hairy and enhancer of split homolog-1 (Hes1) and Neurogenin2 (Ngn2) by directly binding to their promoters. Chromatin immunoprecipitation assays confirmed that Pax3 bound to cis-regulatory elements within Hes1 and Ngn2 promoters. These observations suggest that Pax3 regulates Hes1 and Ngn2 and imply that it may couple migration with neural stem cell maintenance and neurogenesis.

PSA-NCAM in the developing and mature thalamus

The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) is involved in several morphogenetic processes of the central nervous system. In the present study the expression of PSA-NCAM has been investigated in the rat thalamus during embryonic and postnatal development using light and electron microscopic immunocytochemical techniques. At all the examined ages, PSA-NCAM staining in the thalamus was mainly observed along neuronal plasmatic membranes and absent in astrocytes identified by labelling with cytoskeletal (vimentin and glial fibrillary acidic protein) and membrane (GABA transporter-3) markers. At embryonic day 14 the immunoreactivity was restricted to the dorsal thalamic mantle and to the region of reticular thalamic migration and subsequently it extended throughout the whole thalamic primordium. PSA-NCAM labelling remained intense and homogeneously distributed along perinatal period, but from P4 it began to decrease selectively, persisting throughout adulthood only in the reticular nucleus, ventral lateral geniculate nucleus and midline and intralaminar nuclei. The expression of this adhesion molecule differed in areas characterized by the presence of neurons containing distinct calcium binding proteins, as PSA-NCAM labelling was intense around calretinin-positive neurons, whereas it decreased in some calbindin-immunoreactive regions. These findings show evidence of a selective neuronal expression of PSA-NCAM in developing thalamus, supporting its suggested role in cell migration and synaptogenesis as it occurs in the cerebral cortex. In adulthood PSA-NCAM could instead be a marker of thalamic nuclei that retain a potential for synaptic plasticity.

Functional Analysis of Alternative Isoforms of the Transcription Factor PAX3 in MelanocytesIn vitro

Transcription factor PAX3 has seven isoforms of which PAX3c has been studied extensively whereas the functions of the other isoforms are less well known. Here, we found that PAX3 isoforms in a stable transfection system have different biological functions in mouse melanocytes in vitro. PAX3a and PAX3b had negative effects on melanocyte proliferation but had no discernable effect on melanocyte growth in soft agar. PAX3a did not affect cell migration and apoptosis but PAX3b reduced migration and accelerated apoptosis. PAX3c and PAX3d promoted cell proliferation, migration, transformation, and survival. PAX3e reduced melanocyte growth; transformation and migration were unchanged and apoptosis was increased in vitro. PAX3g did not influence cell proliferation or apoptosis. Cells expressing PAX3g were able to grow in soft agar but migration was reduced. PAX3h increased cell proliferation, migration, survival, and transformation. These functional studies have advanced our understanding of the effects of PAX3 isoforms in melanocytes and their potential contribution in tumorigenesis.

Regulation of murine TGFbeta2 by Pax3 during early embryonic development

Previously our laboratory identified TGFbeta2 as a potential downstream target of Pax3 by utilizing microarray analysis and promoter data base mining (Mayanil, C. S. K., George, D., Freilich, L., Miljan, E. J., Mania-Farnell, B. J., McLone, D. G., and Bremer, E. G. (2001) J. Biol. Chem. 276, 49299-49309). Here we report that Pax3 directly regulates TGFbeta2 transcription by binding to cis-regulatory elements within its promoter. Chromatin immunoprecipitation revealed that Pax3 bound to the cis-regulatory elements on the TGFbeta2 promoter (GenBanktrade mark accession number AF118263). Both TGFbeta2 promoter-luciferase activity measurements in transient cotransfection experiments and electromobility shift assays supported the idea that Pax3 regulates TGFbeta2 by directly binding to its cis-regulatory regions. Additionally, by using a combination of co-immunoprecipitation and chromatin immunoprecipitation, we show that the TGFbeta2 cis-regulatory elements between bp 741-940 and bp 1012-1212 bind acetylated Pax3 and are associated with p300/CBP and histone deacetylases. The cis-regulatory elements between bp 741 and 940 in addition to associating with acetylated Pax3 and HDAC1 also associated with SIRT1. Whole mount in situ hybridization and quantitative real time reverse transcription-PCR showed diminished levels of TGFbeta2 transcripts in Pax3(-/-) mouse embryos (whose phenotype is characterized by neural tube defects) as compared with Pax3(+/+) littermates (embryonic day 10.0; 30 somite stage), suggesting that Pax3 regulation of TGFbeta2 may play a pivotal role during early embryonic development.

Temporally regulated neural crest transcription factors distinguish neuroectodermal tumors of varying malignancy and differentiation

Neuroectodermal tumor cells, like neural crest (NC) cells, are pluripotent, proliferative, and migratory. We tested the hypothesis that genetic programs essential to NC development are activated in neuroectodermal tumors. We examined the expression of transcription factors PAX3, PAX7, AP-2alpha, and SOX10 in human embryos and neuroectodermal tumors: neurofibroma, schwannoma, neuroblastoma, malignant nerve sheath tumor, melanoma, medulloblastoma, supratentorial primitive neuroectodermal tumor, and Ewing's sarcoma. We also examined the expression of P0, ERBB3, and STX, targets of SOX10, AP-2alpha, and PAX3, respectively. PAX3, AP-2alpha, and SOX10 were expressed sequentially in human NC development, whereas PAX7 was restricted to mesoderm. Tumors expressed PAX3, AP-2alpha, SOX10, and PAX7 in specific combinations. SOX10 and AP-2alpha were expressed in relatively differentiated neoplasms. The early NC marker, PAX3, and its homologue, PAX7, were detected in poorly differentiated tumors and tumors with malignant potential. Expression of NC transcription factors and target genes correlated. Transcription factors essential to NC development are thus present in neuroectodermal tumors. Correlation of specific NC transcription factors with phenotype, and with expression of specific downstream genes, provides evidence that these transcription factors actively influence gene expression and tumor behavior. These findings suggest that PAX3, PAX7, AP-2alpha, and SOX10 are potential markers of prognosis and targets for therapeutic intervention.

High-purity lineage selection of embryonic stem cell-derived neurons

The derivation of somatic cell types from pluripotent and self-renewing embryonic stem (ES) cells offers attractive prospects for basic research, compound development, and regenerative medicine. A key prerequisite for biomedical applications of ES cells is the ability to differentiate and isolate defined somatic cell populations at high purity. In this study, we explore the potential of the Talpha1- enhanced green fluorescent protein (EGFP) transgene and polysialic acid (PSA)-neural cell adhesion molecule (NCAM) as lineage selection markers for the derivation of ES cell-derived neurons. Upon controlled in vitro differentiation, ES cells engineered to express EGFP under control of the Talpha1-tubulin promoter exhibited exclusive transgene expression in neurons. Similarly, PSA-NCAM expression during the early stages of ES cell differentiation was restricted to neuronal progeny. Talpha1- EGFP- and PSA-NCAM-positive neurons comprised both inhibitory and excitatory phenotypes. Compared to Talpha1-EGFP, the expression of PSA-NCAM was initiated at slightly earlier stages of neural differentiation. FACSorting of Talpha1-EGFP-positive cells and immunopanning of PSA-NCAMexpressing cells yielded neuronal populations at purities up to 99.6% and 96.9%, respectively. These findings depict Talpha1-EGFP and PSA-NCAM as suitable markers for high-purity selection of early ES cell-derived neurons.

Human neural tube defects: developmental biology, epidemiology, and genetics

Birth defects (congenital anomalies) are the leading cause of death in babies under 1 year of age. Neural tube defects (NTD), with a birth incidence of approximately 1/1000 in American Caucasians, are the second most common type of birth defect after congenital heart defects. The most common presentations of NTD are spina bifida and anencephaly. The etiologies of NTDs are complex, with both genetic and environmental factors implicated. In this manuscript, we review the evidence for genetic etiology and for environmental influences, and we present current views on the developmental processes involved in human neural tube closure.

Cell-type-specific regulation of distinct sets of gene targets by Pax3 and Pax3/FKHR

The oncogenic fusion protein, Pax3/FKHR, is a more potent transcription factor relative to its normal counterpart, Pax3. Since Pax3 induced a mesenchymal to epithelial transition (MET) in human SaOS-2 osteosarcomas, we hypothesized that Pax3/FKHR would also induce a morphological change in SaOS-2 cells. We demonstrate here that Pax3/FKHR more potently induces a MET in SaOS-2 cells than Pax3. This greater potency was further evident where Pax3/FKHR, but not Pax3, induced a morphological alteration in U2-OS osteosarcoma cells. By microarray analysis, we determined that Pax3/FKHR altered the expression of gene targets in a manner quantitatively and qualitatively distinct from Pax3. Three classes of genes were identified: (i) genes induced or repressed by Pax3 and Pax3/FKHR, (ii) genes induced or repressed by Pax3/FKHR but not Pax3 and (iii) genes induced by Pax3/FKHR but repressed by Pax3. Chromatin immunoprecipitations confirmed the direct binding of Pax3/FKHR to the promoter region of several factors including cannabinoid receptor-1, EPHA2 and EPHA4. Verification of the microarray data also revealed coordinate alteration in the expression of factors involved in BMP4 signalling. Regulation of gene expression by Pax3 and Pax3/FKHR is, however, cell-type specific. BMP4 expression, for example, was repressed by both Pax3 and Pax3/FKHR in SaOS-2 cells, while in the rhabdomyosarcoma, RD, Pax3/FKHR, but not Pax3, induced BMP4 expression. Thus, our data reveal that Pax3/FKHR regulates a distinct but overlapping set of genes relative to Pax3 and that the global set of Pax3 and Pax3/FKHR gene targets is cell-type specific.

Valproic acid modulates NCAM polysialylation and polysialyltransferase mRNA expression in human tumor cells

Polysialic acid (PSA) is a dynamically regulated carbohydrate modification of the neural cell adhesion molecule NCAM, which has been linked to cancer development and dissemination. Two enzymes, the polysialyltransferases ST8SiaIV and ST8SiaII, are known to be involved in the polysialylation of NCAM. The antiepileptic drug valproic acid (VPA) is associated with anti-cancer activity. In this study, VPA blocked the adhesion of several neuroectodermal tumor cell lines to human umbilical vein endothelial cells. Furthermore, VPA induced intracellular PSA accumulation and enhanced expression of PSA-NCAM on the cell surface. Using a semiquantitative RT-PCR strategy, VPA was shown to up-regulate ST8SiaIV mRNA, whereas ST8SiaII mRNA was down-regulated by this compound. Our data indicate that increased expression of ST8SiaIV enables accelerated polysialylation of NCAM, which might be coupled to a loss of adhesive functions of tumor cells.

Differential regulation of polysialyltransferase expression during hippocampus development: Implications for neuronal survival

Polysialyltransferases ST8SiaII/STX and ST8SiaIV/PST add polysialic acid (PSA) to the neural cell adhesion molecule (NCAM). Surface-located PSA is involved in cell-cell interactions participating in structural and functional plasticity of neuronal circuits. This study was undertaken to investigate the polysialyltransferase regulation pattern during hippocampal development. Polysialyltransferase expression levels analyzed by real-time RT-PCR indicated that ST8SiaII/STX mRNA is markedly down-regulated in vivo, decreasing abruptly at about the first week of postnatal development. ST8SiaII/STX mRNA is also down-regulated in hippocampal cells in culture, accompanying the morphological differentiation of neuronal interconnectivity. In contrast, ST8SiaIV/PST levels remain comparatively low during hippocampus ontogeny. Immunolabeling of primary hippocampal culture assays demonstrated that PSA expression parallels ST8SiaII/STX mRNA levels. In comparison, polysialyltransferase mRNA levels are not regulated in neuroblastoma cells during their proliferation. Sequence analysis of the 3'-untranslated region of ST8SiaII/STX cDNA indicated putative regulatory motifs. This information and the observed changes in mRNA half-life during development suggest that ST8SiaII/STX might be also regulated at the posttranscriptional level. To understand the reasons for the tight control of ST8SiaII/STX expression during development, we overexpressed the enzyme in hippocampal primary cultures by transfection. Overexpression of ST8SiaII/STX wild type as well as of a mutant lacking enzymatic activity affected neuronal viability, leading to cell death. However, this phenomenon was abolished by a double mutation in the ST8SiaII/STX that prevents formation of its three-dimentional structure. Interestingly, the overexpressed polysialyltransferase accumulates not only in the perinuclear region but also in the plasma membrane. Thus, overexpression of an ST8SiaII/STX that conserves its structure leads to abnormal accumulation of the protein, probably on the neuronal surface, affecting cell viability. This result explains the importance of an accurate regulation of polysialyltransferase expression during development.

Differential expression of DNA-methyltransferases in drug resistant murine neuroblastoma cells

Neuroblastoma tumors frequently become drug resistant during the process of chemotherapy resulting in unfavorable clinical outcomes. Development of sustained drug resistance in neuroblastoma is a major problem in successful treatment. To explore the role of DNA-methyltransferases (Dnmt) in acquired drug resistance of neuroblastoma, the present investigation was carried out to study the expression of Dnmtl, Dnmt3a, and Dnmt3b in drug resistant murine neuroblastoma cells, in an in vitro model system. We have analyzed the expression of Dnmtl, Dnmt3a, and Dnmt3b methyltransferases in wild type and drug resistant murine neuroblastoma cells by using Western blot, immunofluorescence microscopy, semiquantitative and quantitative real time RT-PCR analyses. The present investigation demonstrates that total Dnmt enzymatic activity was increased two-fold (P < 0.001) with a 33% increase in global DNA methylation rate in drug resistant cells. Results of the Western blot, immunofluorescence microscopy, RT-PCR, and quantitative real time RT-PCR analysis demonstrated that Dnmt1 and Dnmt3b expression increased significantly (P < 0.001) in drug resistant cells when compared with wild type cells. Dnmt3a expression did not reveal any change between wild type and drug resistant cells. These findings suggest that Dnmtases are differentially expressed in drug resistant murine neuroblastoma cells and overexpression of Dnmtl and Dnmt3b may contribute towards loss of function of the growth regulatory or tumor suppressor genes by methylation of their 'CpG' region and subsequently silencing of their expression. The products of these methylated genes may, thus, confer a high level of drug resistant phenotype in drug resistant neuroblastoma cells.

Microarray analysis detects novel Pax3 downstream target genes

Pax3 is a transcription factor that is required for the development of embryonic neural tube, neural crest, and somatic derivatives. Our previous study (Mayanil, C. S. K., George, D., Mania-Farnell, B., Bremer, C. L., McLone, D. G., and Bremer, E. G. (2000) J. Biol. Chem. 275, 23259-23266) reveals that overexpression of Pax3 in a human medulloblastoma cell line, DAOY, resulted in an up-regulation in alpha-2,8-polysialyltransferase (STX) gene expression and an increase in polysialic acid on neural cell adhesion molecule. This finding suggests that STX might be a previously undescribed downstream target of Pax3. Because Pax3 is important in diverse cellular functions during development, we are interested in the identification of additional downstream targets of Pax3. We utilized oligonucleotide arrays and RNA isolated from stable Pax3 transfectants to identify potential target genes. A total of 270 genes were altered in the Pax3 transfectants as compared with the vector control and parental cell line. An independent analysis by cDNA expression array and real-time quantitative polymerase chain reaction of several genes confirmed the changes observed by the oligonucleotide microarray data. Of the genes that displayed significant changes in expression, several contain paired and homeodomain binding motifs of Pax3 in their promoter regions. Using promoter-luciferase reporter transfection assays and electromobility shift assays, we showed at least one previously undescribed downstream target, STX, to be a biological downstream target of Pax3. Thus we report several previously undescribed candidate genes to be potential downstream targets of Pax3.

Sialyltransferases in cancer

It has long been known that cancer cells often express more heavily sialylated glycans on their surface and that this feature sometimes correlates with invasion. It is now well established that specific sialylated structures, such as the Thomsen-Friedenreich-related antigens, the sialyl Lewis antigens, the sialyl alpha2-6 lactosaminyl structure, the polysialic acid or some gangliosides, can mediate cellular interactions and are altered in cancer cells. This review summarizes the current knowledge on the cancer-associated alterations in sialyltransferase expression which are often at the basis of the deranged expression of sialylated structures.

Effect of polysialic acid on the tumor xenografts implanted into nude mice

Polysialic acid (PSA), which is abundantly expressed in the embryonic brain, plays important roles in neural development and plasticity. PSA is also expressed in tumors of neural crest origin such as neuroblastoma. However, the biologic significance of PSA in these tumors has not been elucidated. In this study, we examined the expression of PSA as well as 2 polysialyltransferases, PST and STX, in various tumor cell lines. PST and STX were simultaneously expressed in all the tumor cells positive for PSA. However, even in the tumor cells negative for PSA, they expressed PSA after transfection of neural cell adhesion molecule (NCAM) cDNA when these cells expressed PST, suggesting that the presence of NCAM was critical for PSA expression. To determine the role of PSA in tumor growth and development, we established tumor sublines expressing or lacking PSA from PC-14 or NCI-H146 cells. Although significant differences of growth rates between the PSA-positive and -negative tumor cells were not detected in vitro, the PSA-positive tumor cells hardly produced detectable tumors when injected into nude mice subcutaneously or intravenously. In addition, the PSA-positive tumor cells adhered less to a basement membrane matrix Matrigel than did the PSA-negative tumor cells. These results altogether suggested that PSA significantly reduced tumor formation in the transplanted xenografts through attenuation of cell-cell or cell-matrix interactions by its large, negatively charged glycans in this particular animal model system.

Roles, regulation, and mechanism of polysialic acid function during neural development

The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) appeared during the evolution of vertebrates as a new mechanism for regulation of cell interactions. This large and abundant glycoprotein can exert steric effects at the cell surface that lead to the attenuation of cell-cell bonds mediated not only by NCAM but also a variety of other adhesion receptors. PSA-NCAM expression changes both as a result of developmental programs and physiological inputs. This global modulation of cell-cell attachment has been shown to facilitate cell migration, axon pathfinding and targeting, and plastic changes in the embryonic and adult nervous system.

A nude mice model of human rhabdomyosarcoma lung metastases for evaluating the role of polysialic acids in the metastatic process

PSA is an oncodevelopmental antigen usually expressed in human tumors with high metastatic potential. Here we set up a metastatic model in nude mice by using TE671 cells, which strongly express PSA-NCAM. We observed the formation of lung metastases when TE671 cells were injected intravenously, intramuscularly, and intraperitoneally, but not subcutaneously. Intraperitoneal injections also induced peritoneal carcinosis, ascites, and liver metastases. To evaluate the putative role of PSA in the metastatic process we used a specific cleavage of PSA on NCAM by endoneuraminidase-N on intraperitoneal primary tumors. Mice with primary intramuscular tumors were taken as control. Repeated injections of endoneuraminidase-N led to a decrease in PSA expression in primary intraperitoneal nodules and ascites but not in intramuscular primary tumors. Endoneuraminidase-N also increased the delay in ascitic formation and decreased the number of lung or liver metastases in the case of intraperitoneal tumors but not in the case of intramuscular tumors. When metastases occurred in endoneuraminidase-N injected animals, they strongly expressed PSA-NCAM. Therefore, we established a relationship between PSA expression on the surface of primary tumor cells and the metastatic process.