Induction and repression of mammalian achaete-scute homologue (MASH) gene expression during neuronal differentiation of P19 embryonal carcinoma cells

Olfactory Neuroblastoma: Morphological Reappraisal and Molecular Insights with Quantum Leap in Clinical Perspectives

PURPOSE OF REVIEW

The purpose of review is to provide a comprehensive review of the literature focusing on the recent advances in the diagnosis, molecular underpinning, and targeted therapy of olfactory neuroblastoma (ONB).

RECENT FINDINGS

Studies focused on the molecular fingerprinting of ONB are critical to engage new promising treatment strategies. Molecular-based subtype classifications have been proposed (basal-like ONB and neural-like ONB) but are not widely used. The rationale for implementation of DNA methylation analysis and IDH2 sequencing in routine work-up for ONB is gaining recognition. Expression of somatostatin receptors (SSTR) in ONB open new avenues for both, diagnostic (especially metastatic disease) and new treatment protocols with somatostatin analogs. Olfactory carcinoma is proposed as a unifying diagnostic terminology pertinent to epithelial divergent differentiation in olfactory neuroblastoma. Molecular (genetic and epigenetic) efforts on olfactory neuroblastoma are promising; however further refinement is needed for employment of these biomarkers as clinical standard of care. Ongoing and future multi-institutional collaborative studies will contribute to further understanding of ONB biology and aid the development of targeted treatments for this disease.

Human bone marrow-derived MSCs spontaneously express specific Schwann cell markers

In peripheral nerve injuries, Schwann cells (SC) play pivotal roles in regenerating damaged nerve. However, the use of SC in clinical cell-based therapy is hampered due to its limited availability. In this study, we aim to evaluate the effectiveness of using an established induction protocol for human bone marrow derived-MSC (hBM-MSCs) transdifferentiation into a SC lineage. A relatively homogenous culture of hBM-MSCs was first established after serial passaging (P3), with profiles conforming to the minimal criteria set by International Society for Cellular Therapy (ISCT). The cultures (n = 3) were then subjected to a series of induction media containing β-mercaptoethanol, retinoic acid, and growth factors. Quantitative RT-PCR, flow cytometry, and immunocytochemistry analyses were performed to quantify the expression of specific SC markers, that is, S100, GFAP, MPZ and p75 NGFR, in both undifferentiated and transdifferentiated hBM-MSCs. Based on these analyses, all markers were expressed in undifferentiated hBM-MSCs and MPZ expression (mRNA transcripts) was consistently detected before and after transdifferentiation across all samples. There was upregulation at the transcript level of more than twofolds for NGF, MPB, GDNF, p75 NGFR post-transdifferentiation. This study highlights the existence of spontaneous expression of specific SC markers in cultured hBM-MSCs, inter-donor variability and that MSC transdifferentiation is a heterogenous process. These findings strongly oppose the use of a single marker to indicate SC fate. The heterogenous nature of MSC may influence the efficiency of SC transdifferentiation protocols. Therefore, there is an urgent need to re-define the MSC subpopulations and revise the minimal criteria for MSC identification.

Retinoic Acid-Signaling Regulates the Proliferative and Neurogenic Capacity of Müller Glia-Derived Progenitor Cells in the Avian Retina

In the retina, Müller glia have the potential to become progenitor cells with the ability to proliferate and regenerate neurons. However, the ability of Müller glia-derived progenitor cells (MGPCs) to proliferate and produce neurons is limited in higher vertebrates. Using the chick model system, we investigate how retinoic acid (RA)-signaling influences the proliferation and the formation of MGPCs. We observed an upregulation of cellular RA binding proteins (CRABP) in the Müller glia of damaged retinas where the formation of MGPCs is known to occur. Activation of RA-signaling was stimulated, whereas inhibition suppressed the proliferation of MGPCs in damaged retinas and in fibroblast growth factor 2-treated undamaged retinas. Furthermore, inhibition of RA-degradation stimulated the proliferation of MGPCs. Levels of Pax6, Klf4, and cFos were upregulated in MGPCs by RA agonists and downregulated in MGPCs by RA antagonists. Activation of RA-signaling following MGPC proliferation increased the percentage of progeny that differentiated as neurons. Similarly, the combination of RA and insulin-like growth factor 1 (IGF1) significantly increased neurogenesis from retinal progenitors in the circumferential marginal zone (CMZ). In summary, RA-signaling stimulates the formation of proliferating MGPCs and enhances the neurogenic potential of MGPCs and stem cells in the CMZ. Stem Cells 2018;36:392-405.

Retinoid acid and taurine promote NeuroD1-induced differentiation of induced pluripotent stem cells into retinal ganglion cells

Induced pluripotent stem cells (iPSCs) possess the capacity to differentiate into multiple cell types including retinal neurons. Despite substantial progress in the transcriptional regulation of iPSC differentiation process, the efficiency of generation of retinal neurons from iPSCs is still low. In this study, we investigated the role of transcription factor NeuroD1 in the differentiation of iPSCs into retinal neurons. We observed that retrovirus-mediated NeuroD1 overexpression in iPSCs increased the efficiency of neuronal differentiation. Immunostaining analysis showed that NeuroD1 overexpression increased the expression of retina ganglion cell markers including Islet-1, Math5, Brn3b, and Thy1.2. Retinoid acid (RA) and taurine further improved the differentiation efficiency of iPSCs overexpressing NeuroD1. However, RA and taurine did not promote differentiation in the absence of NeuroD1 overexpression. Together, our study provides new evidence in transcription factor-regulated stem cell differentiation in vitro.

Model for studying Clostridium botulinum neurotoxin using differentiated motor neuron-like NG108-15 cells

Cancerous cell lines have traditionally shown low sensitivity to laboratory or pharmaceutical preparations of botulinum neurotoxin. The work presented here demonstrates that the mouse neuroblastoma/rat glioma hybrid cell line NG108-15 is capable of more sensitively detecting BoNT/A1 than any cell line previously described. This cell line has previously been described to have motor neuron like characteristics, therefore making it a good model to study BoNTs. Differentiation of NG108-15 cells in serum-free medium containing retinoic acid and purmorphamine dramatically increased sensitivity of the neurons to BoNT/A (EC(50) = ~16 LD(50) U). Additional pre-treatment with triasialoganglioside GT1B prior to toxin exposure reduced the EC(50) further to ~11 LD(50) U. Co-culture of the neurons with C2C12 myotubes also significantly increased BoNT/A sensitivity of NG108-15 cells (EC(50) = 26 U) in the absence of differentiation factors.

Coupling hippocampal neurogenesis to brain pH through proneurogenic small molecules that regulate proton sensing G protein-coupled receptors

Acidosis, a critical aspect of central nervous system (CNS) pathophysiology and a metabolic corollary of the hypoxic stem cell niche, could be an expedient trigger for hippocampal neurogenesis and brain repair. We recently tracked the function of our isoxazole stem cell-modulator small molecules (Isx) through a chemical biology-target discovery strategy to GPR68, a proton (pH) sensing G protein-coupled receptor with no known function in brain. Isx and GPR68 coregulated neuronal target genes such as Bex1 (brain-enriched X-linked protein-1) in hippocampal neural progenitors (HCN cells), which further amplified GPR68 signaling by producing metabolic acid in response to Isx. To evaluate this proneurogenic small molecule/proton signaling circuit in vivo, we explored GPR68 and BEX1 expression in brain and probed brain function with Isx. We localized proton-sensing GPR68 to radial processes of hippocampal type 1 neural stem cells (NSCs) and, conversely, localized BEX1 to neurons. At the transcriptome level, Isx demonstrated unrivaled proneurogenic activity in primary hippocampal NSC cultures. In vivo, Isx pharmacologically targeted type 1 NSCs, promoting neurogenesis in young mice, depleting the progenitor pool without adversely affecting hippocampal learning and memory function. After traumatic brain injury, cerebral cortical astrocytes abundantly expressed GPR68, suggesting an additional role for proton-GPCR signaling in reactive astrogliosis. Thus, probing a novel proneurogenic synthetic small molecule's mechanism-of-action, candidate target, and pharmacological activity, we identified a new GPR68 regulatory pathway for integrating neural stem and astroglial cell functions with brain pH.

YAP regulates neuronal differentiation through Sonic hedgehog signaling pathway

Tight regulation of cell numbers by controlling cell proliferation and apoptosis is important during development. Recently, the Hippo pathway has been shown to regulate tissue growth and organ size in Drosophila. In mammalian cells, it also affects cell proliferation and differentiation in various tissues, including the nervous system. Interplay of several signaling cascades, such as Notch, Wnt, and Sonic Hedgehog (Shh) pathways, control cell proliferation during neuronal differentiation. However, it remains unclear whether the Hippo pathway coordinates with other signaling cascades in regulating neuronal differentiation. Here, we used P19 cells, a mouse embryonic carcinoma cell line, as a model to study roles of YAP, a core component of the Hippo pathway, in neuronal differentiation. P19 cells can be induced to differentiate into neurons by expressing a neural bHLH transcription factor gene Ascl1. Our results showed that YAP promoted cell proliferation and inhibited neuronal differentiation. Expression of Yap activated Shh but not Wnt or Notch signaling activity during neuronal differentiation. Furthermore, expression of Yap increased the expression of Patched homolog 1 (Ptch1), a downstream target of the Shh signaling. Knockdown of Gli2, a transcription factor of the Shh pathway, promoted neuronal differentiation even when Yap was over-expressed. We further demonstrated that over-expression of Yap inhibited neuronal differentiation in primary mouse cortical progenitors and Gli2 knockdown rescued the differentiation defect in Yap over-expressing cells. In conclusion, our study reveals that Shh signaling acts downstream of YAP in regulating neuronal differentiation.

Lectins as a tool for detecting neural stem/progenitor cells in the adult mouse brain

Glycoconjugates are biopolymers that are broadly distributed in the central nervous system, including the cell surface of neural stem cells or neural precursor cells (NSCs/NPCs). Glycoconjugates can be recognized by carbohydrate-binding proteins, lectins. Two lectins, Phaseolus vulgaris lectin agglutinin E-form (PHA-E4) and wheat germ agglutinin (WGA) have been reported to be useful in isolating NSCs/NPCs by fluorescence-activated cell sorting (FACS) or immunopanning methods. In this study, we analyzed the lectin-binding properties of NSCs/NPCs in two neurogenic regions of the adult mouse brain to determine whether PHA-E4 and WGA exhibit specific binding patterns on sections and whether there are other lectins presenting the binding pattern similar to those of PHA-E4 and WGA in lectin histochemistry. Among nine types of lectins, peanut agglutinin was localized to the white matter and four lectins bound to cells within the subventricular zone (SVZ) of the lateral ventricle. Lectin histochemistry combined with immunohistochemistry demonstrated that one lectin, Ricinus communis agglutinin, specifically detected type A neuronal precursors and that the remaining three lectins, Agaricus bisporus agglutinin (ABA), PHA-E4, and WGA, recognized type B NSCs and type C transient amplifying cells in the SVZ. These three lectins also recognized type 1 quiescent neural progenitors and type 2a amplifying neural progenitors in the subgranular layer of the dentate gyrus. Lectin histochemistry of the neurosphere culture also yielded similar results. These observations suggest that, in addition to PHA-E4 and WGA, ABA lectin may also be applicable in FACS or immunopanning for the isolation of NSCs/NPCs.

Differentiation of neural stem cells into Schwann-like cells in vitro

Neural stem cells (NSCs) are multipotent stem cells that have the potential to differentiate into different cells of the neural lineage like neurons, astrocytes and oligodendrocytes. In the current work, we explored whether NSCs could be differentiated into functional Schwann-like cells, which has not been investigated up to date. NSCs were harvested from the hippocampus of rats and identified by single cell cloning and immunofluorescence staining. Then NSCs were treated with DMEM/F12 supplemented with forskolin, heregulin, bFGF, PDGF-AA and retinoic acid (RA). Differentiated NSCs (dNSCs) exhibited a spindle-like morphology similar to Schwann cells and expressed the glial markers p75 and S100. We also found that dNSCs could enhance neurite outgrowth when co-cultured with NG108-15 cells. These results indicated that NSCs, derived from hippocampus of rats, could differentiate into Schwann-like cells with morphological, phenotypic and functional similarities.

Human umbilical cord-derived mesenchymal stromal cells differentiate into functional Schwann cells that sustain peripheral nerve regeneration

Human umbilical cord-derived mesenchymal stromal cells (UC-MSCs) that are available from cell banks can be induced to differentiate into various cell types, thereby making them practical potential sources for cell-based therapies. In injured peripheral nerves, Schwann cells (SCs) contribute to functional recovery by supporting axonal regeneration and myelin reconstruction. Here, we first demonstrate a system to induce UC-MSCs to differentiate into cells with SC properties (UC-SCs) by treatment with β-mercaptoethanol followed by retinoic acid and a set of specific cytokines. The UC-SCs are morphologically similar to SCs and express SC markers, including P0, as assessed by immunocytochemistry and reverse transcription polymerase chain reaction. Transplantation of UC-SCs into transected sciatic nerves in adult rats enhanced nerve regeneration. The effectiveness of UC-SCs for axonal regeneration was comparable to that of authentic human SCs based on histological criteria and functional recovery. Immunohistochemistry and immunoelectron microscopy also demonstrated myelination of regenerated axons by UC-SCs. These findings indicate that cells with SC properties and with the ability to support axonal regeneration and reconstruct myelin can be successfully induced from UC-MSCs to promote functional recovery after peripheral nerve injury. This system may be applicable for the development of cell-based therapies.

Direct transcriptional induction of Gadd45gamma by Ascl1 during neuronal differentiation

The basic helix-loop-helix transcription factor Ascl1 plays a critical role in the intrinsic genetic program responsible for neuronal differentiation. Here, we describe a novel model system of P19 embryonic carcinoma cells with doxycycline-inducible expression of Ascl1. Microarray hybridization and real-time PCR showed that these cells demonstrated increased expression of many neuronal proteins in a time- and concentration-dependent manner. Interestingly, the gene encoding the cell cycle regulator Gadd45gamma was increased earliest and to the greatest extent following Ascl1 induction. Here, we provide the first evidence identifying Gadd45gamma as a direct transcriptional target of Ascl1. Transactivation and chromatin immunoprecipitation assays identified two E-box consensus sites within the Gadd45gamma promoter necessary for Ascl1 regulation, and demonstrated that Ascl1 is bound to this region within the Gadd45gamma promoter. Furthermore, we found that overexpression of Gadd45gamma itself is sufficient to initiate some aspects of neuronal differentiation independent of Ascl1.

Interaction of MTG family proteins with NEUROG2 and ASCL1 in the developing nervous system

During neural development, members of MTG family of transcriptional repressors are induced by proneural basic helix-loop-helix (bHLH) transcription factors and in turn inhibit the activity of the bHLH proteins, forming a negative feedback loop that regulates the normal progression of neurogenesis. Three MTG genes, MTG8, MTG16 and MTGR1, are expressed in distinct patterns in the developing nervous system. Various bHLH proteins are also expressed in distinct patterns. We asked whether there is a functional relationship between specific MTG and bHLH proteins in developing chick spinal cord. First, we examined if each MTG gene is induced by specific bHLH proteins. Although expression of NEUROG2, ASCL1 and MTG genes overlapped, the boundaries of gene expression did not match. Ectopic expression analysis showed that MTGR1 and NEUROD4, which show similar expression patterns, are regulated differently by NEUROG2 and ASCL1. Thus, our results show that expression of MTG genes is not regulated by a single upstream bHLH protein, but represents an integration of the activity of multiple regulators. Next, we asked if each MTG protein inhibits specific bHLH proteins. Transcription assay showed that NEUROG2 and ASCL1 are inhibited by MTGR1 and MTG16, and less efficiently by MTG8. Deletion mapping of MTGR1 showed that MTGR1 binds NEUROG2 and ASCL1 using multiple interaction surfaces, and all conserved domains are required for its repressor activity. These results support the model that MTG proteins form a higher-order repressor complex and modulate transcriptional activity of bHLH proteins during neurogenesis.

Effect of dioxins on regulation of tyrosine hydroxylase gene expression by aryl hydrocarbon receptor: a neurotoxicology study

BACKGROUND

Dioxins and related compounds are suspected of causing neurological disruption. Epidemiological studies indicated that exposure to these compounds caused neurodevelopmental disturbances such as learning disability and attention deficit hyperactivity disorder, which are thought to be closely related to dopaminergic dysfunction. Although the molecular mechanism of their actions has not been fully investigated, a major participant in the process is aryl hydrocarbon receptor (AhR). This study focused on the effect of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on the regulation of TH, a rate-limiting enzyme of dopamine synthesis, gene expression by AhR.

METHODS

N2a-Rbeta cells were established by transfecting murine neuroblastoma Neuro2a with the rat AhR cDNA. TH expression induced by TCDD was assessed by RT-PCR and Western blotting. Participation of AhR in TCDD-induced TH gene expression was confirmed by suppressing AhR expression using the siRNA method. Catecholamines including dopamine were measured by high-performance liquid chromatography. A reporter gene assay was used to identify regulatory motifs in the promoter region of TH gene. Binding of AhR with the regulatory motif was confirmed by an electrophoretic mobility shift assay (EMSA).

RESULTS

Induction of TH by TCDD through AhR activation was detected at mRNA and protein levels. Induced TH protein was functional and its expression increased dopamine synthesis. The reporter gene assay and EMSA indicated that AhR directly regulated TH gene expression. Regulatory sequence called aryl hydrocarbon receptor responsive element III (AHRE-III) was identified upstream of the TH gene from -285 bp to -167 bp. Under TCDD exposure, an AhR complex was bound to AHRE-III as well as the xenobiotic response element (XRE), though AHRE-III was not identical to XRE, the conventional AhR-binding motif.

CONCLUSION

Our results suggest TCDD directly regulate the dopamine system by TH gene transactivation via an AhR-AHRE-III-mediated pathway. The AhR- mediated pathway could have a particular AhR-mediated genomic control pathway transmitting the effects of TCDD action to target cells in the development of dopaminergic disabilities.

Suppression of chondrogenesis by Id helix-loop-helix proteins in murine embryonic orofacial tissue

Inhibitors of differentiation (Id) proteins are helix-loop-helix (HLH) transcription factors lacking a DNA-binding domain. Id proteins modulate cell proliferation, apoptosis and differentiation in embryonic/fetal tissue. Perturbation of any of these processes in cells of the developing orofacial region results in orofacial anomalies. Chondrogenesis, a process integral to normal orofacial ontogenesis, is known to be modulated, in part, by Id proteins. In the present study, the mRNA and protein expression patterns of Id1, Id2, Id3 and Id4 were examined in developing murine orofacial tissue in vivo, as well as in murine embryonic maxillary mesenchymal cells in vitro. The functional role of Ids during chondrogenesis was also explored in vitro. Results reveal that cells derived from developing murine orofacial tissue (1) express Id1, Id2, Id3 and Id4 mRNAs and proteins on each of gestational days 12-14, (2) express all four Id proteins in a developmentally regulated manner, (3) undergo chondrogenesis and express genes encoding various chondrogenic marker proteins (e.g. Runx2, Type X collagen, Sox9) when cultured under micromass conditions and (4) can have their chondrogenic potential regulated via alteration of Id protein function through overexpression of a basic HLH factor. In summary, results from the current report reveal for the first time the expression of all four Id proteins in cells derived from developing murine orofacial tissue, and demonstrate a functional role for the Ids in regulating the ability of these cells to undergo chondrogenesis.

Neurotrophin-3 improves retinoic acid-induced neural differentiation of skin-derived precursors through a p75NTR-dependent signaling pathway

Skin-derived precursors (SKPs) are derived from mesoblast and can differentiate into smooth muscle cells, adipocytes, and less neuronal phenotypes. This study demonstrates that retinoic acid (RA) improves SKPs exit from self-proliferation to neural differentiation through up-regulating of NeuroD and cell-cycle regulatory protein p21, meanwhile RA also induces p75 neurotrophin receptor (p75NTR) up-regulation and apoptosis of SKPs. When treated sequentially with neurotrophin-3 (NT-3) after RA induction, the survival and neural differentiation of SKPs were enhanced significantly, and cell apoptosis induced by RA was decreased. These effects could be reversed by p75NTR inhibitor Pep5 instead of Trk receptor inhibitor K252a. The results indicate that NT-3 improves the neural differentiation of SKPs induced by RA through a p75NTR-dependent signaling pathway.

Regulatory expression of Brachyury and Goosecoid in P19 embryonal carcinoma cells

Mouse P19 embryonal carcinoma cells can differentiate into various cell types depending on culture conditions. Here we show that the expression of the mesodermal genes Brachyury (Bra) and Goosecoid (Gsc) are under regulatory control in P19 cells. When P19 cells were cultured in a tissue culture dish in the presence of serum, Bra and Gsc were unexpectedly expressed. Expression of Bra and Gsc was greatly reduced with culture time, and expression levels at 144 h of culture were below 25% those at 48 h of culture. Members of the Tgf-beta family such as Activin and Nodal have been known to up-regulate expression of mesodermal genes. Treatment with SB431542, an Alk4/5/7 inhibitor, decreased Bra and Gsc in a dose-dependent manner, whereas it induced the expression of the neuroectodermal genes Mash-1 and Pax-6. Quantitative RT-PCR and dsRNAi transfection indicated Nodal as a possible ligand responsible for the regulation of Bra and Gsc. In addition, exogenous Nodal increased expression of Bra and Gsc in a dose-dependent manner. Serum concentration in culture medium positively related to expression of Nodal, Bra, Gsc, and Cripto, which encodes a membrane-tethered protein required for Nodal signaling. Addition of the culture supernatant of P19 cells at 144 h of culture to medium decreased expression of these genes. The present study reveals that stimulation and inhibition of the Nodal pathway increases mesodermal genes and neuroectodermal genes, respectively, indicating the importance of control of Nodal and Cripto expression for mesodermal formation and neurogenesis.

Neuronal differentiation of synovial sarcoma and its therapeutic application

Synovial sarcoma is a rare sarcoma of unknown histologic origin. We previously reported the gene expression profile of synovial sarcoma was closely related to that of malignant peripheral nerve sheath tumors, and the fibroblast growth factor (FGF) signal was one of the main growth signals in synovial sarcoma. Here we further demonstrate the neural origin of synovial sarcoma using primary tumors and cell lines. The expression of neural tissue-related genes was confirmed in synovial sarcoma tumor tissues, but the expression of some genes was absent in synovial sarcoma cell lines. Treatment of synovial sarcoma cell lines with BMP4 or FGF2 enhanced or restored the expression of neural tissue-related genes and induced a neuron-like morphology with positive Tuj-1 expression. Treatment with all-trans-retinoic acid also induced the expression of neural tissue-related genes in association with growth inhibition, which was not observed in other cell lines except a malignant peripheral nerve sheath tumor cell line. A growth-inhibitory effect of all-trans-retinoic acid was also observed for xenografted tumors in athymic mice. The simultaneous treatment with FGF signal inhibitors enhanced the growth-inhibitory effect of all-trans-retinoic acid, suggesting the combination of growth signaling inhibition and differentiation induction could be a potential molecular target for treating synovial sarcoma.

SoxB1 transcription factors and Notch signaling use distinct mechanisms to regulate proneural gene function and neural progenitor differentiation

The preservation of a pool of neural precursors is a prerequisite for proper establishment and maintenance of a functional central nervous system(CNS). Both Notch signaling and SoxB1 transcription factors have been ascribed key roles during this process, but whether these factors use common or distinct mechanisms to control progenitor maintenance is unsettled. Here, we report that the capacity of Notch to maintain neural cells in an undifferentiated state requires the activity of SoxB1 proteins, whereas the mechanism by which SoxB1 block neurogenesis is independent of Notch signaling. A common feature of Notch signaling and SoxB1 proteins is their ability to inhibit the activity of proneural bHLH proteins. Notch represses the transcription of proneural bHLH genes, while SoxB1 proteins block their neurogenic capacity. Moreover, E-proteins act as functional partners of proneural proteins and the suppression of E-protein expression is an important mechanism by which Notch counteracts neurogenesis. Interestingly, in contrast to the Hes-dependent repression of proneural genes, suppression of E-protein occurs in a Hes-independent fashion. Together, these data reveal that Notch signaling and SoxB1 transcription factors use distinct regulatory mechanisms to control proneural protein function and to preserve neural cells as undifferentiated precursors.

Genome-wide analysis of aging and learning-related genes in the hippocampal dentate gyrus

We have previously described the transcriptional changes that occur in the hippocampal CA1 field of aged rats following a Morris Water Maze (MWM) training paradigm. In this report we proceed with the analysis of the dentate region from the same animals. Animals were first identified as age learning-impaired or age-superior learners when compared to young rats based on their performance in the MWM. Messenger RNA was isolated from the dentate gyrus of each animal to interrogate Affymetrix RAE 230A rat genome microarrays. Microarray profiling identified 1129 genes that were differentially expressed between aged and young rats as a result of aging, and independent of their behavioral training (p<0.005). We applied Ingenuity Pathway Analysis (IPA) algorithms to identify the significant biological processes underlying age-related changes in the dentate gyrus. The most significant functions, as calculated by IPA, included cell movement, cell growth and proliferation, nervous system development and function, cellular assembly and organization, cell morphology and cell death. These significant processes are consistent with age-related changes in neurogenesis, and the neurogenic markers were generally found to be downregulated in senescent animals. In addition, statistical analysis of the different experimental groups of aged animals recognized 85 genes (p<0.005) that were different in the dentate gyrus of aged rats that had learned the MWM when compared to learning impaired and a number of controls for stress, exercise and non-spatial learning. The list of learning-related genes expressed in the dentate adds to the set of genes we previously described in the CA1 region. This long list of genes constitutes a starting tool to elucidating the molecular pathways involved in learning and memory formation.

Hand2 determines the noradrenergic phenotype in the mouse sympathetic nervous system

The basic helix-loop-helix (bHLH) transcription factor Hand2 has been shown to play a role in the development of the mammalian sympathetic nervous system (SNS); however, its precise role could not be uncovered because Hand2 is required for early embryonic survival. We therefore generated a conditional Hand2 knockout mouse line by excising Hand2 in Wnt1-Cre-expressing neural crest-derived cells. These mice die at 12.5 dpc with embryos showing severe cardiovascular and facial defects. Crest-derived cells, however, populate sites of SNS development and proliferate normally. Sympathetic precursors differentiate into neurons and express the pan-neuronal markers, beta3-tubulin (Tuj1) and Hu showing that Hand2 is not essential for SNS neuronal differentiation. To determine whether Hand2 regulates noradrenergic differentiation, the levels of the norepinephrine biosynthetic enzymes, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) was examined. Both enzymes were dramatically reduced in mutant embryos suggesting that the primary role of Hand2 in the SNS is determination of neuronal phenotype. Loss of Hand2 did not affect the expression of other members of the transcriptional circuit regulating SNS development, including Phox2a/b, Mash1 and Gata2/3; however, Hand2 was required for Hand1 expression. Our data suggest that the major role of Hand2 during SNS development is to permit sympathetic neurons to acquire a catecholaminergic phenotype.

Role of retinoic acid in the differentiation of embryonal carcinoma and embryonic stem cells

Retinoic acid (RA), the most potent natural form of vitamin A, plays an important role in many diverse biological processes such as embryogenesis and cellular differentiation. This chapter is a review of the mechanism of action of RA and the role of specific RA-regulated genes during the cellular differentiation of embryonal carcinoma (EC) and embryonic stem (ES) cells. RA acts by binding to its nuclear receptors and inducing transcription of specific target genes. The most studied mouse EC cell lines include F9 cells, which can be induced by RA to differentiate into primitive, parietal, and visceral endodermal cells; and P19 cells, which can differentiate to endodermal and neuronal cells upon RA treatment. ES cells can be induced to differentiate into a number of different cell types; many of which require RA treatment. Over the years, many RA-regulated genes have been discovered in EC and ES cells using a diverse set of techniques. Current research focuses on the elucidation how these genes affect differentiation in EC and ES cells using a variety of molecular biology approaches. However, the exact molecule events that lead from a pluripotent stem cell to a fully differentiated cell following RA treatment are yet to be determined.

Genetic analysis of anterior posterior expression gradients in the developing mammalian forebrain

Intrinsic regulatory factors play critical roles in early cortical patterning, including the development of the anteroposterior (A-P) axis. To identify genes that are differentially expressed along the A-P axis of the developing cerebral cortex, we analyzed gene expression in presumptive frontal, parietal, and occipital cerebral walls of E12.5 mouse using complementary DNA microarrays. We identified 106 genes, including expressed sequence tags (ESTs), expressed in an A-P gradient in the embryonic brain and screened 88 by in situ hybridization for confirmation. Central nervous system (CNS) expression patterns of many of these genes were previously unknown. Others, such as Sfrp1, CoupTF1, and FABP7, were expressed in a manner consistent with previous studies, providing independent confirmation. Two related transcription factors, previously not implicated in CNS development, Fhl1 and Fhl2, were observed to be enriched in posterior and anterior telencephalon, respectively. We studied patterning gradients in Fhl1 knockout mice but observed no changes in gene expression related to A-P regionalization in the Fhl1 knockout mice. These data provide an important set of new candidates for studies of cortical patterning and maturation.

Transcription Factor IIA tau is associated with undifferentiated cells and its gene expression is repressed in primary neurons at the chromatin level in vivo

The levels of General Transcription Factor (TF) IIA were examined during mammalian brain development and in rat embryo fibroblasts and transformed cell lines. The large TFIIA subunit paralogues alphabeta and tau are largely produced in unsynchronized cell lines, yet only TFIIA alphabeta is observed in a number of differentiated tissue extracts. Steady-state protein levels of the TFIIA tau, alphabeta, and gamma subunits were significantly reduced when human embryonal (ec) and hepatic carcinoma cell lines were stimulated to differentiate with either all-trans-retinoic acid (ATRA) or sodium butyrate. ATRA-treated NT2-ec cells required replating to induce a neuronal phenotype and loss of detectable TFIIA tau and gamma proteins. High levels of TFIIA tau, alphabeta, and gamma and Sp factors were identified in extracts from human fetal and rat embryonic day-18 brains, but not in human and rat adult brain extracts. A high histone H3 Lys9/Lys4 methylation ratio was observed in the TFIIA tau promoter of primary hippocampal neurons from day-18 rat embryos, suggesting that repressive epigenetic marks of chromatin prevent TFIIA tau from being transcribed in neurons. We conclude that TFIIA tau is associated with undifferentiated cells during development, yet is down-regulated at the chromatin level upon cellular differentiation.

Involvement of the mouse Prp19 gene in neuronal/astroglial cell fate decisions

The molecular mechanisms involved in neuronal/astroglial cell fate decisions during the development of the mammalian central nervous system are poorly understood. Here, we report that PRP19beta, a splice variant of mouse PRP19alpha corresponding to the yeast PRP19 protein, can function as a neuron-astroglial switch during the retinoic acid-primed neural differentiation of P19 cells. The beta-variant possesses an additional 19 amino acid residues in-frame in the N-terminal region of the alpha-variant. The forced expression of the alpha-variant RNA caused the down-regulation of oct-3/4 and nanog mRNA expression during the 12-48 h of the late-early stages of neural differentiation and was sufficient to convert P19 cells into neurons (but not glial cells) when the cells were cultured in aggregated form without retinoic acid. In contrast, the forced expression of the beta-variant RNA suppressed neuronal differentiation and conversely stimulated astroglial cell differentiation in retinoic acid-primed P19 cells. Based on yeast two-hybrid screening, cyclophilin A was identified as a specific binding partner of the beta-variant. Luciferase reporter assay mediated by the oct-3/4 promoter revealed that cyclophilin A could act as a transcriptional activator and that its activity was suppressed by the beta-variant, suggesting that cyclophilin A takes part in the induction of oct-3/4 gene expression, which might lead to neuroectodermal otx2 expression within 12 h of the immediate-early stages of retinoic acid-primed neural differentiation. These results show that the alpha-variant gene plays a pivotal role in neural differentiation and that the beta-variant participates in neuronal/astroglial cell fate decisions.

Transplantation of GABAergic neurons into adult mouse neocortex

GABAergic neurons in the neocortex contribute to various brain functions by regulating cortical pyramidal neurons. A deficiency of GABAergic neurons in the neocortex leads to the dysregulation of cortical neuronal circuits, but this can be overcome by cell transplantation, which provides a practical approach to repair damaged neuronal circuits. Here, we focused on the transplantation of committed neuronal progenitor cells. Because neuronal differentiation is considerably suppressed in the adult neocortex, we transfected proneural bHLH transcription factors into neural precursor cells to commit them to a neuronal lineage prior to the cell transplantation. We show that ventral neural stem cells transfected with Ngn1 are integrated as GABAergic neurons within a few days of transplantation into the adult mouse neocortex. These results demonstrate that the transplantation of committed neuronal progenitor cells is an effective method for brain repair.

Sox6 overexpression causes cellular aggregation and the neuronal differentiation of P19 embryonic carcinoma cells in the absence of retinoic acid

The Sox6 gene is a member of the Sox gene family that encodes transcription factors. Previous studies have suggested that Sox6 plays an important role in the development of the central nervous system. Aggregation of embryonic carcinoma P19 cells with retinoic acid (RA) results in the development of neurons, glia and fibroblast-like cells. In this report, we have shown that Sox6 mRNA increased rapidly in P19 cells during RA induction and then decreased during the differentiation of P19 into neuronal cells. To explore the possible roles of Sox6 during this process, stably Sox6-overexpressing P19 cell lines (P19[Sox6]) were established. These P19[Sox6] had acquired both characteristics of the wild-type P19 induced by RA. First, P19[Sox6] cells showed a marked cellular aggregation in the absence of RA. Second, P19[Sox6] could differentiate into microtubule-associated protein 2 (MAP2)-expressing neuronal cells in the absence of RA. Sox6 expression could cause the activation of endogenous genes including the neuronal transcription factor Mash-1, the neuronal development-related gene Wnt-1, the neuron-specific cell adhesion molecule N-cadherin, and the neuron-specific protein MAP2, resulting in neurogenesis. Moreover, E-cadherin, a major cell adhesion molecule of wild-type P19, was strongly induced by Sox6, resulting in cellular aggregation without RA. Thus Sox6 may play a critical role in cellular aggregation and neuronal differentiation of P19 cells.

hASH1 expression is closely correlated with endocrine phenotype and differentiation extent in pulmonary neuroendocrine tumors

The human homolog 1 of the Drosophila neurogenic achaete-scute genes, hASH1, is specifically expressed in fetal pulmonary neuroendocrine cells and in some neuroendocrine tumor cell lines. However, no data have been gathered regarding its in vivo expression in tumors. hASH1 mRNA expression was investigated by in situ hybridization in 238 surgically resected lung carcinomas, and the correlations between hASH1 expression status and immunostaining results of neuroendocrine markers chromogranin A, neural cell adhesion molecule, gastrin-releasing peptide and calcitonin, and clinical outcome were analyzed. hASH1 expression was detected in 2/20 (10%) adenocarcinomas, 4/30 (13.3%) typical carcinoids, 11/13 (84.6%) atypical carcinoids, 38/67 (56.7%) large-cell neuroendocrine carcinomas and 56/78 (71.8%) small-cell carcinomas, respectively, but not in any squamous cell carcinoma (0/21) or large-cell carcinoma (0/9). The 2 hASH1+ adenocarcinomas also expressed multiple neuroendocrine markers. Thus, hASH1 expression was restricted to lung cancers with neuroendocrine phenotypes. However, not all neuroendocrine tumors expressed hASH1. Within the entities of large-cell neuroendocrine carcinoma and small-cell carcinoma, hASH1 expression correlated very closely with chromogranin A, gastrin-releasing peptide and calcitonin expression (P<0.0001, r=0.852), but was not related to neural cell adhesion molecule expression (P=0.8892), suggesting that hASH1 expression, at least in lung cancer, is associated with endocrine phenotype expression other than 'neuroendocrine differentiation' in a broad sense. The fact that hASH1 was virtually absent in almost fully differentiated typical carcinoids, but was expressed in most, if not all, less differentiated atypical carcinoids as well as large-cell neuroendocrine carcinomas and small-cell carcinomas, suggests that hASH1 expression in lung cancer imitates its early and transient expression in fetal development, and that hASH1 is instrumental in the establishment, but not in the maintenance, of a cellular endocrine phenotype. Finally, hASH1 expression correlated with a significantly shortened survival in small-cell carcinoma patients (P=0.041).

Retinoic acid-mediated induction of neurons and glial cells from human umbilical cord-derived hematopoietic stem cells

Recent studies reporting trans-differentiation of mononucleated cells derived from human umbilical cord blood into neuronal cells aroused interest among investigators for their clinical implication and significance in regenerative medicine. In the present study, purified populations of hematopoietic stem cells were isolated via magnetic bead sorting and fluorescence-activated cell sorter (FACS) using a specific CD133 antibody, a cell type-specific marker for hematopoietic stem cells, and grown in culture in the presence of retinoic acid (RA). CD133+ hematopoietic stem cells expressed neuronal and glial phenotypes after RA treatment. RT-PCR analysis indicated that the RA treated CD133+ cells expressed mRNA transcripts for ATP-binding cassettes transporter ABCG2 (a universal stem cell marker), nestin (a specific cell type marker for neural stem cells), Musashi1 (a specific marker for neural stem cells) and RA receptors (RAR) including RAR-alpha, RAR-beta, and retinoid X receptor (RXR)-gamma. RA-treated CD133+ cells expressed mRNA transcripts for neuron-specific markers neurofilament proteins (NF-L, -M, -H) and synaptophysin as determined by RT-PCR, structural proteins characteristic of neurons including tubulin beta III and neuron specific enolase (NSE) by Western blot, and neuron-specific markers NeuN and microtubule-associated protein-2 (MAP2) by immunocytochemistry. RA-treated CD133+ cells also expressed the astrocyte-specific marker glial fibrillary acidic protein (GFAP), as demonstrated by RT-PCR, Western blot, and immunocytochemistry. In addition, RA-treated CD133+ cells expressed cell type-specific markers for oligodendrocytes including myelin basic protein (MBP) as shown by RT-PCR, proteolipid protein (PLP) by Western blot analysis, and cyclic nucleotide phosphodiesterase (CNPase) by immunostaining. Upregulated expression of several basic helix-loop-helix (bHLH) transcription factors important for early neurogenesis, including Otx2, Pax6, Wnt1, Olig2, Hash1 and NeuroD1, was also demonstrated in CD133+ cells after RA treatment. These results indicate that human cord blood-derived CD133+ hematopoietic stem cells could trans-differentiate into neural cell types of neuron-like cells, astrocytes, and oligodendrocytes by RA treatment.

Promoter-specific function of the TATA element in undifferentiated P19 cells

P19 embryonal carcinoma cells differentiate into neuronal cells when treated with retinoic acid (RA). To explore the importance of core promoter structures in the regulation of gene expression during neuronal differentiation, the activities of three classes of modified or unmodified model promoters (Spec2a, OtxE, and Ars) were compared in P19 cells before and after RA treatment. The Spec2a promoter was activated in undifferentiated cells specifically when the E-box was located at a proximal position, whereas the OtxE promoter was activated when the E-box was in a distal position. The Ars promoter was only slightly activated by this element. In addition, the TATA element reduced the level of activation provided by the E-box, but only when it was located in the Spec2a core promoter. These results indicate that the core promoter structure may govern, at least in part, the stage-specific expression of endogenous genes involved in the neuronal differentiation of P19 cells.

Regulation of expression of sulfoglucuronyl carbohydrate (HNK-1), Amphoterin and RAGE in retinoic acid-differentiated P19 embryonal carcinoma cells

HNK-1 antibody reactive sulfoglucuronyl carbohydrate (SGC) and SSEA-1 antibody reactive Lewis X (Lex) epitope are expressed on several glycolipids, glycoproteins, and proteoglycans of the nervous system and have been implicated in cell-cell recognition, neurite outgrowth, and/or neuronal migration during development. Interaction of SGC with its binding protein Amphoterin and interaction of Amphoterin with a cell-signaling molecule, receptor for advance glycation end product (RAGE) have been suggested to regulate neurite outgrowth and neuronal migration. The regulation of expression of SGC, Lex, Amphoterin, and RAGE was studied in embryonal carcinoma P19 cells after treatment with retinoic acid (RA). The untreated proliferating P19 cells strongly expressed the Lex epitope, which was mostly due to Lex-glycoproteins. P19 cells, when differentiated into neuron-like cells by RA, did not express the Lex epitope, but expressed increasing levels of SGC, with time in culture. Quantitative biochemical analyses showed that in the P19 cells after RA treatment, the amount of SGC-glycoproteins increased at a significantly higher level than sulfoglucuronyl glycolipid-1 (SGGL-1). The increase in the levels of SGGL-1 was due to 16-fold upregulation in the activity of lactosylceramide: N-acetylglucosaminyl-transferase (Lc3 synthase), which synthesizes the key intermediate lactotriosylceramide (Lc3Cer), for lacto- and neolacto-glycolipids. The large increase in the activity of Lc3 synthase appeared to regulate the levels of other neolacto glycolipids, such as Lc3Cer, nLc4Cer, nLc6Cer, disialosyl-nLc4Cer (LD1), and Lex-glycolipids. Strong upregulation of glucuronyl-transferase and modest twofold enhancement in the activity of the glucuronyl-sulfotransferase, which catalyze the final steps in the SGC synthesis, also would account for the large increase in the synthesis SGC-glycoproteins. RA also upregulated the synthesis of Amphoterin and RAGE in P19 cells. SGC, RAGE, and Amphoterin were co-localized in the RA-differentiated neurons. The initiation of neurite outgrowth along with co-ordinated upregulation of Amphoterin, RAGE, SGC-glycoproteins, and SGGLs in RA-treated P19 cells support the hypothesis that these molecules are involved in the neuronal process formation.

The role of transcriptional corepressor Nif3l1 in early stage of neural differentiation via cooperation with Trip15/CSN2

Mouse Nif3l1 gene is highly conserved from bacteria to human. Even though this gene is expressed throughout embryonic development, its biological function is still obscure. Here, we show that Nif3l1 participates in retinoic acid-primed neural differentiation of P19 embryonic carcinoma cells through cooperation with Trip15/CSN2, a transcriptional corepressor/component of COP9 signalosome. We isolated Nif3l1 cDNA from P19 cell cDNA library by a yeast two-hybrid screening using Trip15/CSN2 as a bait. This interaction was confirmed by a pull-down assay and an epitope-tagged coimmunoprecipitation. Although Nif3l1 was mainly detected in the cytoplasm, the translocation of Nif3l1 into the nuclei was observed in retinoic acid-primed neural differentiation of P19 cells and enhanced by the enforced expression of Trip15/CSN2. Furthermore, enforced expression of sense Nif3l1 RNA, but not antisense RNA, enhanced the neural differentiation of P19 cells accompanying the intense down-regulation of Oct-3/4 mRNA expression and the rapid induction of Mash-1 mRNA expression. Luciferase reporter assay showed that Nif3l1 could act as a transcriptional repressor and synergized the transcriptional repression by Trip15/CSN2. These results indicate that Nif3l1 implicates in neural differentiation through the cooperation with Trip15/CSN2.

Vitamin A deficiency leads to increased cell proliferation in olfactory epithelium of mature rats

We have shown previously that vitamin A deficiency (VAD) leads to the decreased expression of gene products that are specifically synthesized by mature neurons in the olfactory epithelium (OE) of adult rats. These results support the hypothesis that retinoic acid, a derivative of vitamin A, is required for neurogenesis and neuron replacement in vivo. VAD does not cause gross degeneration of the OE, raising the question: what types of cells continue to populate VAD OE? In this study, we compared the cell densities of VAD and VA-sufficient (VAS) OE and investigated whether cell proliferation is upregulated in VAD OE. The results show that (1) total cell number in VAD and VAS OE are comparable; (2) localized areas of hyperplasia are present in the basal regions of VAD, but not VAS, OE; (3) there is a substantial increase in the number of PCNA (proliferating cell nuclear antigen) positive cells in the basal region of VAD OE relative to VAS OE; and (4) there is a relative increase in the levels of mRNA encoding the transcription factor, MASH I, in VAD OE. We conclude that reduced availability of vitamin A derivatives, such as retinoic acid, leads to a loss of control over proliferation, hyperplasia, and increased numbers of pro-neural cells in vivo.

Induction of neural differentiation by electrically stimulated gene expression of NeuroD2

Regulation of cell differentiation is an important assignment for cellular engineering. One of the techniques for regulation is gene transfection into undifferentiated cells. Transient expression of NeuroD2, one of neural bHLH transcription factors, converted mouse N1E-115 neuroblastoma cells into differentiated neurons. The regulation of neural bHLH expression should be a novel strategy for cell differentiation. In this study, we tried to regulate neural differentiation by NeuroD2 gene inserted under the control of heat shock protein-70 (HSP) promoter, which can be activated by electrical stimulation. Mouse neuroblastoma cell line, N1E-115, was stably transfected with expression vector containing mouse NeuroD2 cDNA under HSP promoter. Transfected cells were cultured on the electrode surface and applied electrical stimulation. After stimulation, NeuroD2 expression was induced, and transfected cells adopt a neuronal morphology at 3 days after stimulation. These results suggest that neural differentiation can be induced by electrically stimulated gene expression of NeuroD2.

EphA family gene expression in the developing mouse neocortex: regional patterns reveal intrinsic programs and extrinsic influence

Parcellation of the mammalian cerebral cortex into distinct areas is essential for proper cortical function; however, the developmental program that results in the genesis of distinct areas is not fully understood. We examined the expression of members of the EphA family-the EphA receptor tyrosine kinases and the ephrin-A ligands-within the developing mouse cerebral cortex, with the aim of characterizing this component of the molecular landscape during cortical parcellation. We found that specific embryonic zones, such as the ventricular, subventricular, intermediate, subplate, and marginal zones, as well as the cortical plate, were positive for particular EphA genes early in corticogenesis (E12-E15). Along with this zone-selective expression, several genes (EphA3, EphA4, EphA5) were evenly expressed along the axes of the developing cortex, whereas one family member (EphA7) was expressed in a distinct anteroposterior pattern. Later in corticogenesis (E16-E18), other EphA family members became selectively expressed, but only within the cortical plate: EphA6 was present posteriorly, and ephrin-A5 was expressed within a middle region. At birth, patterning of EphA gene expression was striking. Thus, we found that the expression of a single EphA gene or a combination of family members can define distinct embryonic zones and anteroposterior regions of the neocortex during development. To examine whether cellular context affects the patterning of EphA expression, we examined gene expression in embryonic cortical cells grown in vitro, such that all cellular contacts are lacking, and in Mash-1 mutant mice, in which thalamocortical connections do not form. We found that the expression patterns of most EphA family members remained stable in these scenarios, whereas the pattern of ephrin-A5 was altered. Taken together, this work provides a comprehensive picture of EphA family expression during mouse corticogenesis and demonstrates that most EphA expression profiles are cell intrinsically based, whereas ephrin-A5 is plastically regulated.

Cloning and characterization of GRIPE, a novel interacting partner of the transcription factor E12 in developing mouse forebrain

The helix-loop-helix (HLH) family of transcription factors are key contributors to a wide array of developmental processes, including neurogenesis and hematopoiesis. These factors are thought to exert their regulatory influences by binding to cognate promoter-DNA sequences as dimers. Although studies in mice have convincingly demonstrated that neurogenic HLH proteins such as NeuroD are intimately involved in neuronal fate determination, the role of the ubiquitously expressed HLH protein, E12, in mammalian neurogenesis remains ambiguous. To address this, a yeast two-hybrid interaction screen was employed to identify dimerization partners to E12. Screening of an embryonic day 11.5 forebrain library resulted in the cloning of GRIPE, a novel GAP-related interacting protein to E12. GRIPE binds to the HLH region of E12 and may require E12 for nuclear import. Furthermore, GRIPE may negatively regulate E12-dependent target gene transcription. High levels of GRIPE and E12 mRNA were coincidentally detected during embryogenesis, but only GRIPE mRNA levels remained high in adult brain, particularly in neurons of the cortex and hippocampus. These observations were recapitulated through an in vitro model of neurogenesis. Taken together, these results indicate that GRIPE is a novel protein dimerization of which with E12 has important consequences for cells undergoing neuronal differentiation.

N-twist, an evolutionarily conserved bHLH protein expressed in the developing CNS, functions as a transcriptional inhibitor

Members of the basic helix-loop-helix (bHLH) transcription factor family play an essential role in multiple developmental processes. During neurogenesis, positive and negative regulation by bHLH proteins is essential for proper development. Here we report the identification and initial characterization of the bHLH gene, Neuronal twist (N-twist), named for its neural expression pattern and high sequence homology and physical linkage to the mesodermal inhibitor, M-twist. N-twist is expressed in the developing mouse central nervous system in the midbrain, hindbrain, and neural tube. This neural expression is conserved in invertebrates, as expression of the Drosophila ortholog of N-twist is also restricted to the central nervous system. Like other bHLH family members, N-Twist heterodimerizes with E protein and binds DNA at a consensus bHLH-binding site, the E box. We show that N-Twist inhibits MASH1-dependent transcriptional activation by sequestering E protein in a dominant negative fashion. Thus, these studies support the notion that N-Twist represents a novel negative regulator of neurogenesis.

REN: a novel, developmentally regulated gene that promotes neural cell differentiation

Expansion and fate choice of pluripotent stem cells along the neuroectodermal lineage is regulated by a number of signals, including EGF, retinoic acid, and NGF, which also control the proliferation and differentiation of central nervous system (CNS) and peripheral nervous system (PNS) neural progenitor cells. We report here the identification of a novel gene, REN, upregulated by neurogenic signals (retinoic acid, EGF, and NGF) in pluripotent embryonal stem (ES) cells and neural progenitor cell lines in association with neurotypic differentiation. Consistent with a role in neural promotion, REN overexpression induced neuronal differentiation as well as growth arrest and p27Kip1 expression in CNS and PNS neural progenitor cell lines, and its inhibition impaired retinoic acid induction of neurogenin-1 and NeuroD expression. REN expression is developmentally regulated, initially detected in the neural fold epithelium of the mouse embryo during gastrulation, and subsequently throughout the ventral neural tube, the outer layer of the ventricular encephalic neuroepithelium and in neural crest derivatives including dorsal root ganglia. We propose that REN represents a novel component of the neurogenic signaling cascade induced by retinoic acid, EGF, and NGF, and is both a marker and a regulator of neuronal differentiation.

Role and distribution of retinoic acid during CNS development

Retinoic acid (RA), the biologically active derivative of vitamin A, induces a variety of embryonal carcinoma and neuroblastoma cell lines to differentiate into neurons. The molecular events underlying this process are reviewed with a view to determining whether these data can lead to a better understanding of the normal process of neuronal differentiation during development. Several transcription factors, intracellular signaling molecules, cytoplasmic proteins, and extracellular molecules are shown to be necessary and sufficient for RA-induced differentiation. The evidence that RA is an endogenous component of the developing central nervous system (CNS) is then reviewed, data which include high-pressure liquid chromotography (HPLC) measurements, reporter systems and the distribution of the enzymes that synthesize RA. The latter is particularly relevant to whether RA signals in a paracrine fashion on adjacent tissues or whether it acts in an autocrine manner on cells that synthesize it. It seems that a paracrine system may operate to begin early patterning events within the developing CNS from adjacent somites and later within the CNS itself to induce subsets of neurons. The distribution of retinoid-binding proteins, retinoid receptors, and RA-synthesizing enzymes is described as well as the effects of knockouts of these genes. Finally, the effects of a deficiency and an excess of RA on the developing CNS are described from the point of view of patterning the CNS, where it seems that the hindbrain is the most susceptible part of the CNS to altered levels of RA or RA receptors and also from the point of view of neuronal differentiation where, as in the case of embryonal carcinoma (EC) cells, RA promotes neuronal differentiation. The crucial roles played by certain genes, particularly the Hox genes in RA-induced patterning processes, are also emphasized.

Identification of neuronal cell lineage-specific molecules in the neuronal differentiation of P19 EC cells and mouse central nervous system

P19 embryonic carcinoma (EC) cells are one of the simplest systems for analyzing the neuronal differentiation. To identify the membrane-associated molecules on the neuronal cells involved in the early neuronal differentiation in mice, we generated two monoclonal antibodies, SKY-1 and SKY-2, by immunizing rats with a membrane fraction of the neuronally committed P19 EC cells as an antigen. SKY-1 and SKY-2 recognized the carbohydrate moiety of a 90 kDa protein (RANDAM-1) and the polypeptide core of a 40 kDa protein (RANDAM-2), respectively. In the P19 EC cells, the expression of RANDAM-1 was colocalized to a part of Nestin-positive cells, whereas that of RANDAM-2 was observed in most Nestin-positive cells as well as beta-III-tubulin positive neurons. In the embryonic and adult brain of mice, RANDAM-1 was expressed at embryonic day 8.5 (E8.5), and the localization of antigen was restricted on the neuroepithelium and choroid plexus. The RANDAM-2 expression commenced at E6.0, and the antigen was distributed not only on the neuroepithelium of embryonic brain but on the neurons of adult brain. Collectively, it was concluded that RANDAM-1 is a stage specific antigen to express on the neural stem cells, and RANDAM-2 is constitutively expressed on both the neural stem cells and differentiated neuronal cells in mouse central nervous system (CNS).

Sciatic nerve regeneration in rats induced by transplantation of in vitro differentiated bone-marrow stromal cells

Bone marrow stromal cells (MSCs) are multipotent stem cells that have the potential to differentiate into bone, cartilage, fat and muscle. We now demonstrate that MSCs can be induced to differentiate into cells with Schwann cell characteristics, capable of eliciting peripheral nervous system regeneration in adult rats. MSCs treated with beta-mercaptoethanol followed by retinoic acid and cultured in the presence of forskolin, basic-FGF, PDGF and heregulin, changed morphologically into cells resembling primary cultured Schwann cells and expressing p75, S-100, GFAP and O4. The MSCs were genetically engineered by transduction with retrovirus encoding green fluorescent protein (GFP), and then differentiated by treatment with factors described above. They were transplanted into the cut ends of sciatic nerves, which then responded with vigorous nerve fibre regeneration within 3 weeks of the operation. Myelination of regenerated fibers by GFP-expressing MSCs was recognized using confocal and immunoelectron microscopy. The results suggest that MSCs are able to differentiate into myelinating cells, capable of supporting nerve fibre re-growth, and they can therefore be applied to induce nerve regeneration.

Isolation of neuronal precursors from differentiating P19 embryonal carcinoma cells by neuronal T alpha 1-promoter-driven GFP

The induction of pluripotent P19 embryonal carcinoma (EC) cells with retinoic acid results in their differentiation into cells that resemble neurons, glia, and fibroblasts. To isolate and enrich the developing neurons from heterogeneously differentiating P19 EC cells, we used a recently introduced protocol combining the expression of green fluorescent protein (GFP) driven by a tissue-specific promoter and fluorescence-activated cell sorting. Cells were transfected with the gene for GFP, which is under the control of the neuronal T alpha 1 tubulin promoter. After four days of retinoic acid treatment, GFP was specifically detected in cells undergoing neuronal differentiation. Sorting of fluorescent differentiating P19 EC transfectants yielded populations highly enriched in neuronal precursors and neurons. Immunoreactivity for nestin and neurofilament was observed in 80 and 25% of the sorted cell population, respectively. These results demonstrate that differentiated neuronal precursor cells can be efficiently isolated from differentiating pluripotent embryonic cells in vitro, suggesting that this method can reproducibly provide homogeneous materials for further studies on neurogenesis.

A murine homologue of the Drosophila brainiac gene shows homology to glycosyltransferases and is required for preimplantation development of the mouse

The neurogenic gene brainiac was first isolated in Drosophila melanogaster, where it interacts genetically with members of the Notch signaling cascade. We have isolated a murine homologue of the Drosophila brainiac gene and delineated its highly specific expression pattern during development and adult life. We find particularly strong expression in the developing central nervous system, in the developing retina, and in the adult hippocampus. Targeted deletion of mouse Brainiac 1 expression leads to embryonic lethality prior to implantation. Null embryos can be recovered as blastocysts but do not appear to implant, indicating that mouse Brainiac 1, likely a glycosyltransferase, is crucial for very early development of the mouse embryo.

A role of N-cadherin in neuronal differentiation of embryonic carcinoma P19 cells

N-cadherin is one of the important molecules for cell to cell interaction in the development of the central nervous system (CNS). In this report, we have shown that N-cadherin mRNA and protein were increased rapidly in retinoic acid (RA)-induced neuronal differentiation of embryonic carcinoma P19 cells. To explore possible roles for N-cadherin during this process, N-cadherin-overexpressing P19 cell lines were established. These transfected cells could differentiate into neurofilament-expressing neurons in the absence of RA. RT-PCR revealed that the expression patterns of development-related genes, such as Oct-3/4, nestin, Notch-1, and Mash-1 were similar between the transfected P19 cells and the RA-induced wild-type P19 cells during their neuronal differentiation. On the contrary, the Wnt-1 gene was up-regulated in the N-cadherin-overexpressing P19 cells, but could not be detected in the wild-type P19 cells. These results suggest N-cadherin may play a role in neuronal differentiation of P19 cells, possibly through the Wnt-1 signaling pathway.

Identification of NKL, a novel Gli-Kruppel zinc-finger protein that promotes neuronal differentiation

The proneural basic helix-loop-helix proteins play a crucial role in promoting the differentiation of postmitotic neurons from neural precursors. However, recent evidence from flies and frogs indicates that additional factors act together with the proneural bHLH proteins to promote neurogenesis. We have identified a novel zinc finger protein, neuronal Kruppel-like protein (NKL), that positively regulates neurogenesis in vertebrates. NKL is expressed in Xenopus primary neurons and in differentiating neuronal precursors in the intermediate zone of the mouse and chick neural tube. In frog embryos, NKL is induced by overexpression of Neurogenin (Ngn), arguing that NKL is downstream of the proneural determination genes. Our results show that NKL and a NKL/VP16 fusion protein promote differentiation of neuronal precursors in the embryonic chick spinal cord. Following in ovo misexpression of NKL, neuroepithelial cells exit the cell cycle and differentiate into neurons. Similarly, NKL/VP16 induces extra primary neurons in frogs and upregulates expression of the neural differentiation factors, Xath3 and MyT1, as well as the neuronal markers, N-tubulin and elrC. Our findings establish NKL as a novel positive regulator of neuronal differentiation and provide further evidence that non-bHLH transcription factors function in the neuronal differentiation pathway activated by the vertebrate neuronal determination genes.

Multiple roles of mouse Numb in tuning developmental cell fates

BACKGROUND

Notch signaling regulates multiple differentiation processes and cell fate decisions during both invertebrate and vertebrate development. Numb encodes an intracellular protein that was shown in Drosophila to antagonize Notch signaling at binary cell fate decisions of certain cell lineages. Although overexpression experiments suggested that Numb might also antagonize some Notch activity in vertebrates, the developmental processes in which Numb is involved remained elusive.

RESULTS

We generated mice with a homozygous inactivation of Numb. These mice died before embryonic day E11.5, probably because of defects in angiogenic remodeling and placental dysfunction. Mutant embryos had an open anterior neural tube and impaired neuronal differentiation within the developing cranial central nervous system (CNS). In the developing spinal cord, the number of differentiated motoneurons was reduced. Within the peripheral nervous system (PNS), ganglia of cranial sensory neurons were formed. Trunk neural crest cells migrated and differentiated into sympathetic neurons. In contrast, a selective differentiation anomaly was observed in dorsal root ganglia, where neural crest--derived progenitor cells had migrated normally to form ganglionic structures, but failed to differentiate into sensory neurons.

CONCLUSIONS

Mouse Numb is involved in multiple developmental processes and required for cell fate tuning in a variety of lineages. In the nervous system, Numb is required for the generation of a large subset of neuronal lineages. The restricted requirement of Numb during neural development in the mouse suggests that in some neuronal lineages, Notch signaling may be regulated independently of Numb.

Developmental regulation of neurogenesis in the pluripotent human embryonal carcinoma cell line NTERA-2

Embryonal carcinoma (EC) cells provide a caricature of pluripotent embryonic stem (ES) cells and may be used as surrogates for investigating the mechanisms that regulate cell differentiation during embryonic development. NTERA-2 is a human EC cell line that differentiates in response to retinoic acid yielding cells that include terminally differentiated neurons. The expression of genes known to be involved in the formation of the vertebrate nervous system was examined during retinoic acid-induced NTERA-2 differentiation. Differentiation of these human EC cells into neurons could be divided into three sequential phases. During phase 1, in the first week of differentiation, hath1 mRNA showed a small transient increase that correlated with the rapid accumulation of nestin message, a marker of neuroprogenitors. Transcripts of nestin were quickly downregulated during phase 2 as expression of neuroD1, characteristic of neuroprogenitors exiting the cell cycle, was induced. A neural cell surface antigen, detected by the monoclonal antibody A2B5, was expressed by cells exiting the cell cycle, correlating with the expression of neuroD1 as the cells became post-mitotic. Markers of mature neural cells (e.g. synaptophysin and neuron-specific enolase) were subsequently increased during phase 3 and were maintained. This regulated pattern of gene expression and commitment to the neural lineage indicates that differentiation of NTERA-2 neurons in vitro follows a similar pathway to that observed by neural ectodermal precursors during vertebrate neurogenesis in vivo.

HASH-1 and E2-2 are expressed in human neuroblastoma cells and form a functional complex

The basic helix-loop-helix (bHLH) transcription factor mammalian achaete-scute homolog-1 (MASH-1 in mouse and HASH-1 in human) is essential for proper development of olfactory and most peripheral autonomic neurons, and for the formation of distinct neuronal circuits within the central nervous system. We have previously shown that HASH-1 is expressed in neuroblastoma tumors and cell lines, and in this study we have used the yeast two-hybrid system to isolate HASH-1 interacting proteins from a human neuroblastoma cDNA library. Two of the isolated clones contained cDNA from the E2-2 gene (also known as ITF2/SEF2-1). We show that E2-2 interacts with HASH-1 in both yeast and mammalian cells. The HASH-1/E2-2 complex binds an E-box (CACCTG) in vitro, and transactivates an E-box containing reporter construct in vivo. Furthermore, E2-2 seems to be one of the major HASH-1 interacting proteins in extracts from neuroblastoma cells. In conclusion, E2-2 forms a functional complex with HASH-1, and might therefore be involved in the development of specific parts of the central and peripheral nervous systems.

Myocyte enhancer factor 2C upregulates MASH-1 expression and induces neurogenesis in P19 cells

MEF2C is a transcription factor expressed in neural lineages. After transient transfection, the MEF2 family of factors can act synergistically with the neural-specific transcription factor, MASH-1, and activate exogenous neural-specific promoters. To determine whether MEF2C is capable of modulating endogenous gene expression, P19 cell lines were analyzed that overexpressed MEF2C, termed P19[MEF2C] cells. Here we show that P19[MEF2C] cells differentiate into neurons when aggregated with ME(2)SO. MEF2C-induced neurons expressed neurofilament protein, the nuclear antigen NeuN, as well as MASH-1. Our results indicate that MEF2C can directly or indirectly activate the expression of MASH-1, leading to neurogenesis.

Early expression of the BM88 antigen during neuronal differentiation of P19 embryonal carcinoma cells

Previous studies have shown that the BM88 antigen, a neuron-specific molecule, promotes the differentiation of mouse neuroblastoma cells [23] (Mamalaki A., Boutou E., Hurel C., Patsavoudi E., Tzartos S. and Matsas R. (1995) The BM88 antigen, a novel neuron-specific molecule, enhances the differentiation of mouse neuroblastoma cells. J. Biol. Chem. 270, 14201-14208). In particular, stably transfected with the BM88 cDNA, Neuro 2a cells over-expressing the BM88 antigen are morphologically distinct from their non-transfected counterparts; they exhibit enhanced process outgrowth and a slower rate of division. Moreover, they respond differentially to growth factors [10] (Gomez J., Boutou E., Hurel C., Mamalaki A., Kentroti S. , Vernadakis A. and Matsas R. (1998) Overexpression of the neuron-specific molecule BM88 in mouse neuroblastoma cells: Altered responsiveness to growth factors. J. Neurosci. Res. 51, 119-128). In order to further elucidate the role of the BM88 antigen in the differentiation of developing neurons we used the in vitro system of differentiating P19 cells which closely resembles early murine development in vivo. In this study, P19 cells were driven to the neuronal pathway with retinoic acid. We examined by immunofluorescence studies the expression of the BM88 antigen in these cells and we found that it correlates well with the expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) which characterizes early differentiating post-mitotic neurons. In contrast, very few of the BM88 antigen-positive/PSA-NCAM-positive cells expressed neurofilament protein, a marker of more mature neurons. Our findings, in accordance with previously reported data, strongly suggest that the BM88 antigen is involved in the early stages of differentiation of neuronal cells.