Methylmercury alters Eph and ephrin expression during neuronal differentiation of P19 embryonal carcinoma cells

Developmental exposure to methylmercury (MeHg) induces a spectrum of neurological impairment characterized by cognitive disturbance, sensory/motor deficit, and diffuse structural abnormalities of the brain. These alterations may arise from neural path-finding errors during brain development, resulting from disturbances in the function of morphoregulatory guidance molecules. The Eph family of tyrosine kinase receptors and their ligands, the ephrins, guide neuronal migration and neurite pathfinding mainly via repulsive intercellular interactions. The present study examined the effects of MeHg on mRNA and protein expression profiles of Ephs and ephrins in the P19 embryonal carcinoma (EC) cell line and its neuronal derivatives. Undifferentiated control P19 cells displayed low- to undetectable levels of mRNA for ephrins or Ephs, with the sole exception of EphA2 which was highly expressed. Upon differentiation into neurons, the ephrin expression increased progressively through day 10. Similarly, expression of the Ephs, including EphsA3, -A4, -A8, -B2, -B3, -B4, and -B6, increased significantly. In contrast, EphA2 expression decreased in day 2, 6 and 10 control neurons. Treatment with MeHg did not affect the expression of mRNA for ephrins or Ephs in undifferentiated P19 cells. However, treatment of differentiating neurons with MeHg for 24 h caused consistent increases in ligand mRNA expression, particularly ephrin-A5, -A6, -B1, and -B2. Similarly, MeHg induced variable increases in mRNA expression of receptors EphA2, -A3, -B3, and -B6. A trend toward a concentration-response relationship was observed for the alterations in Eph receptor mRNA expression although increases at the low and mid concentrations did not reach statistical significance. Immunoblots for ligand and receptor proteins mirrored the increases in the mRNA levels at the 0.5 and 1.5 microM MeHg concentrations but showed decreased protein levels compared to controls at the 3.0 microM concentration. Alterations in the Eph/ephrin family of repulsion molecules may represent an important mechanism in developmental MeHg neurotoxicity.     

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.     

Expression of gangliosides in neuronal development of P19 embryonal carcinoma stem cells

Gangliosides are constituents of the cell membrane and are known to have important functions in neuronal differentiation. We employed an embryonal carcinoma stem cell line P19 as an in vitro model to investigate the expression of gangliosides during neuronal development. After treatment with retinoic acid, these cells differentiate synchronously into neuron-like cells by a series of well-defined events of development. We examined several aspects of ganglioside metabolism, including the changes of ganglioside pattern, the activities and gene expression of several enzymes at different stages of differentiation, and the distribution of gangliosides in differentiating neurons. Undifferentiated P19 cells express mainly GM3 and GD3. After P19 cells were committed to differentiation, the synthesis of complex gangliosides was elevated more than 20-fold, coinciding with the stage of neurite outgrowth. During the maturation of differentiated cells, the expression of c-series gangliosides was downregulated concomitantly with upregulation of the expression of a- and b-series gangliosides. We also examined the distribution of gangliosides in differentiating neurons by confocal and transmission electron microscopy after cholera toxin B subunit and sialidase treatment. Confocal microscopic studies showed that gangliosides were distributed on the growth cones and exhibited a punctate localization on neurites and soma. Electron microscopic studies indicated that they also are enriched on the plasma membranes of neurites and the filopodia as well as on the lamellipodia of growth cones during the early stage of neurite outgrowth. Our data demonstrate that the expression of gangliosides in P19 cells during RA-induced neuronal differentiation resembles that of the in vivo development of the vertebrate brain, and hence validates it as an in vitro model for investigating the function of gangliosides in neuronal development.     

Neuronal differentiation of P19 embryonal carcinoma cells in defined media

The P19 embryonal carcinoma cell line is a useful model system for analyzing the factors that regulate neuronal differentiation. In order to analyze the extrinsic factors that are involved in differentiation, it is necessary to carry out experiments in fully defined media. Here we have investigated the neuronal differentiation of P19 cells in two defined media. Cells that are propagated and induced with retinoic acid in standard serum-containing medium are capable of differentiating into neuron-like cells in N2 medium. Dividing fibroblast-like cells also appeared in these cultures. After about 10 days in culture in N2 medium, the great majority of neuron-like cells died. On the other hand, culturing induced cells in N2 medium for 5 days and then switching to a defined medium consisting of Neurobasal medium plus B27 supplement allowed the neuron-like cells to survive for prolonged periods of time. This defined medium thus provides a suitable system for analyzing extrinsic factors that affect the survival and differentiation of P19 neurons. P19 cells induced with retinoic acid and plated in N2 were exposed to bFGF and EGF, which are known to be mitogens for neuronal precursor cells. Both growth factors were mitogenic for a subpopulation of the induced cells. In separate experiments, cells cultured in N2 in the presence of RA were induced to differentiate into neuron-like cells. © 1995 Wiley-Liss, Inc.     

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 method for generating high-yield enriched neuronal cultures from P19 embryonal carcinoma cells

P19 embryonal carcinoma (EC) cells are an invaluable tool for approximating the mechanisms that govern neuronal differentiation but with an enormous degree of simplification and have primarily been used to model the early stages of neurogenesis. However, they are often cultured under conditions that promote unrestricted non-neuronal growth that compromises neuronal viability. In this study we report an improved method to differentiate P19 EC cells that gives rise to high yields of functionally and morphologically mature neurons while significantly reducing the over-growth of non-neuronal cells in the cultures. In this protocol, P19 EC cells are induced in Minimum Essential Medium alpha supplemented with all-trans retinoic acid (RA) and 2.5% serum, and cultured as a monolayer. After RA-induction, cells are cultured on Matrigel coated-plates using defined media comprised of Neurobasal-A medium temporally supplemented with N2 and then B-27 for the remaining culture period. By treating the culture with Cytosine β-d-arabinofuranoside and 2′-Deoxycytidine for five days, the cultures are reliably promoted toward the neuronal differentiation vs non-neuronal differentiation, this accounting for a progressive neuronal enrichment of the cultures reaching 56% after 20 days of culture. P19-derived neural progenitor cells progressively expressed neuronal markers such as NeuN, Calretinin, Calbindin and Synapsin I in close resemblance to that occurring in vivo in the central nervous system (CNS). Furthermore, RA-induced P19 EC cells progressively acquired functional neuronal traits and after approximately 3 weeks in culture revealed mature neurophysiological properties, characteristics of CNS neurons. This protocol allows for a more specific assessment of the neuronal differentiation processes in vitro.     

Regulation of alternative splicing in the amyloid precursor protein (APP) mRNA during neuronal and glial differentiation of P19 embryonal carcinoma cells

Cell-specific alteration in the splicing of exons 7, 8 and 15 of the amyloid precursor protein gene was investigated in differenting P19 EC cells into neuronal and glial cells. Exons 7 and 8 were skipped in the neuronal state and exon 15 was skipped in the glial state. Expression of U2AF, one of the essential factor for splicing in mammalian cells, was down-regulated during cellular differentiation. The skipping of exon 15 was suppressed in the glial cells transfected with U2AF. Thus, a reduction in U2AF is believed to play a crucial role in glial-specific splicing of the APP gene.     

NSSR1 promotes neuronal differentiation of mouse embryonic carcinoma P19 cells

We generated the small interference RNAs to specifically silence the expression of neural salient serine/arginine rich protein 1 (NSSR1) and showed that the inhibition of NSSR1 expression in mouse embryonic carcinoma cells (P19) reduces neuronal differentiation. By contrast, its over-expression promotes the differentiation. Neither inhibition nor over-expression shows distinct effect on cell proliferation. The over-expression increases the inclusion of NCAM L1 exon2 while the inhibition reduces the inclusion. The splicing of kinase insert free isoform of TrkC (TrkC-K1) is increased by the over-expression. The results demonstrate that NSSR1 promotes neuronal differentiation and the splicing of NCAML1 exon2 and TrkC-K1.     

Glial-guided neuronal migration in P19 embryonal carcinoma stem cell aggregates

During development of the nervous system, neuronal precursors that originated in proliferative regions migrate along radial glial fibers to reach their final destination. P19 embryonal carcinoma (EC) stem cells exposed to retinoic acid (RA) differentiate into neurons, glia, and fibroblast-like cells. In this work, we induced P19 aggregates for 4 days with RA and plated them onto tissue culture dishes coated with poly-L-lysine. Several cells migrated out of and/or extended processes from the aggregates after 24 hr. Some cell processes were morphologically similar to radial glial fibers and stained for glial fibrillar acidic protein (GFAP) and nestin. Large numbers of migrating cells showed characteristics similar to those of bipolar migrating neurons and expressed the neuronal marker microtubule-associated protein 2. Furthermore, scanning electron microscopy analysis revealed an intimate association between the radial fibers and the migrating cells. Therefore, the migration of neuron-like cells on radial glia fibers in differentiated P19 aggregates resembled some of the migration models used thus far to study gliophilic neuronal migration. In addition, HPTLC analysis in this system showed the expression of 9-O-acetyl GD3, a ganglioside that has been associated with neuronal migration. Antibody perturbation assays showed that immunoblockage of 9-O-acetyl GD3 arrested neuronal migration in a reversible manner. In summary, we have characterized a new cell culture model for investigation of glial-guided neuronal migration and have shown that 9-O-acetyl GD3 ganglioside has an important role in this phenomenon.     

Targeted disruption of GAP-43 in P19 embryonal carcinoma cells inhibits neuronal differentiation. As well as acquisition of the morphological phenotype

GAP-43 is expressed in proliferating neuroblasts in vivo and in vitro, but its role during early neurogenesis has not been investigated. Here we show that neuroectodermal differentiation stimulated by retinoic acid (RA) in the embryonal carcinoma (EC) line P19 is accompanied by upregulation of GAP-43 expression in neuroepithelial precursor cells. In contrast, when upregulation of GAP-43 expression was prevented in 3 independent P19 lines because of a targeted insertion into the gene, generation of neuroepithelial precursors was inhibited. Consequently, neuronal number was significantly decreased, neuronal morphology was abnormal and fewer than 20% of all neurons were able to initiate neuritogenesis. Extracellular matrix (ECM) was unable to rescue initiation of neuritogenesis in the mutant cells, however those neurites that were extended responded normally to ECM-stimulated neurite outgrowth-promoting signals. These data suggest that GAP-43 function is required for commitment to a neuronal phenotype as well as initiation of neurite extension. However, stimulation of neurite outgrowth by ECM in P19s occurs independently of GAP-43.     

Pharmacological properties of purinergic receptors and their effects on proliferation and induction of neuronal differentiation of P19 embryonal carcinoma cells

We have used P19 embryonal carcinoma cells as in vitro model for early neurogenesis to study ionotropic P2X and metabotropic P2Y receptor-induced Ca²⁺ transients and their participation in induction of proliferation and differentiation. In embryonic P19 cells, P2Y₁, P2Y₂ and P2X₄ receptors or P2X-heteromultimers with similar P2X₄ pharmacology were responsible for ATP and ATP analogue-induced Ca²⁺ transients. In neuronal-differentiated cells, P2Y_2, P2Y₆, P2X₂ and possibly P2X₂/P2X₆ heteromeric receptors were the major mediators of the elevations in intracellular free calcium concentration [Ca²⁺]_i. We have collected evidence for the involvement of metabotropic purinergic receptors in proliferation induction of undifferentiated and neural progenitor cells by using a BrdU-incorporation assay. ATP-, UTP-, ADP-, 2-MeS-ATP- and ADP-βS-induced proliferation in P19 cells was mediated by P2Y₁ and P2Y₂ receptors as judged from pharmacological profiles of receptor responses. ATP-provoked acceleration of neuronal differentiation, determined by analysis of nestin and neuron-specific enolase gene and protein expression, also resulted from P2Y₁ and P2Y₂ receptor activation. Proliferation- and differentiation-induction involved the activation of inositol-trisphosphate sensitive intracellular Ca²⁺ stores.     

P19胚胎癌细胞体外定向心肌细胞分化模型的构建*★○

目的：如何在体外将胚胎干细胞培育转化为大量的心肌细胞并进行移植，使之成为具有成熟心肌细胞功能？实验采用不同诱导剂对P19胚胎干细胞进行诱导，拟构建体外定向心肌细胞分化模型。 方法：实验于2006-09/2007-03在日本东京工业大学生体分子机能工学研究室完成。①材料：P19细胞由日本东北大学加龄医学研究所提供。钙粘素融合蛋白N-cad-Fc由本研究室合成。②实验方法：P19细胞按1×107 L-1密度接种进行悬浮培养，分别以终浓度1，5，10，50，100 nmol/L视黄酸及0.5%、0.75%、1%、1.25%、1.5%二甲基亚砜各自诱导4 d，将形成的细胞聚集体分别接种于预铺有0.1%明胶、2.5mg/L N-cad-Fc、10 mg/L N-cad-Fc基质的24孔板中培养10 d。③实验评估：观察不同诱导条件及不同基质上的细胞跳动情况，免疫荧光染色检测心肌特异性蛋白Troponin T的表达，RT-PCR法检测心肌细胞标志性基因cardiac actin、gata-4的表达。 结果：①P19细胞经1，5，10 nmol/L视黄酸或0.5%、0.75%、1%二甲基亚砜诱导后，均出现可自主节律跳动的细胞。P19细胞聚集体悬浮培养至20d，预铺有0.1%明胶、2.5 mg/L N-cad-Fc及10 mg/L N-cad-Fc基质的培养板上节律跳动细胞团的出现率分别为44.6%、71.3%和70.1%。②药物诱导后，P19细胞心肌特异性蛋白Troponin T呈阳性表达。③与传统预铺有明胶的培养板比较，在预铺有N-cad-Fc的培养板上心肌标志性基因cardiac actin、gata-4的表达均明显升高，但10 mg/L N-cad-Fc的表达量略低于2.5 mg/L N-cad-Fc。④分别在上述不同基质上单层培养的P19细胞，二甲基亚砜诱导14 d后均仍呈上皮样细胞形态，未见跳动细胞出现，RT-PCR检测无心肌标志性基因表达。 结论：①使用0.5%~1%二甲基亚砜或1~10 nmol/L视黄酸可成功诱导P19细胞心肌分化，心肌特异性蛋白Troponin T 的表达早于心肌跳动的出现。②作为一种基质模型来模拟细胞间黏附，2.5 mg/L N-cad-Fc是较适宜P19细胞心肌分化的条件。③P19细胞心肌分化有赖于药物诱导和细胞成团的共同作用，细胞间黏附分子对其分化有促进作用。     

Expression and role of p27(kip1) in neuronal differentiation of embryonal carcinoma cells

We examined the expression and the regulation of p21(waf1) and p27(kip1) cdk inhibitors in P19 mouse embryonal carcinoma (EC) cells following treatment with all-trans retinoic acid (ATRA) to induce neuronal differentiation. The levels of p27 mRNA and protein increased within 24 h of treatment with ATRA, reaching a plateau 4-5 days later prior to neurite formation. In contrast, levels of p21 expression remained low until after neurites were extensively formed. Induction of muscle differentiation from P19 cells by treatment with dimethyl sulfoxide caused only transient increases in p27 levels. In a mutant P19 cell line, RAC65, treatment with ATRA induced neither p27 accumulation nor neuronal differentiation, but p21 mRNA expression increased markedly. In contrast, treatment of RAC65 cells with 9-cis retinoic acid induced both p27 expression and neuronal differentiation. Correlation between p27 expression and neuronal differentiation was also observed in NT2/D1 human EC cells. Luciferase reporter assays showed that p27 promoter activity increased in ATRA-treated cells, consistent with the elevation of p27 mRNA levels. Arrest of neuronal differentiation of P19 cells by okadaic acid resulted in inhibition of p27 expression, whereas p21 mRNA expression was greatly enhanced. Conversely, inhibition of p27 expression by antisense p27 oligonucleotides resulted in blockade of neuronal differentiation. Taken together, these results strongly suggest that the expression of p27 is indispensable for neuronal differentiation of EC cells.     

effects of NGF and dibutyryl cAMP on neuronal differentiation of embryonal carcinoma cells

The P19S18O1A1 embryonal carcinoma cell line is capable of neuronal differentiation and is therefore useful in studying neuronal development and the influence of growth modulators on neuronal differentiation. We report here on the effects of nerve growth factor (NGF) and dibutyryl cyclic adenosine monophosphate (db cAMP), individually and combined, on differentiation of P19S18O1A1 cells. NGF alone did not induce any significant neuron-like changes in cultures exposed to NGF for as long as 12 days. Treatment with db cAMP resulted in changes in a significant population of the cells, including development of a neuron-like morphology, seen at both the light and electron microscopic level, loss of stage-specific embryonic antigen expression and the appearance of two neuronal markers, neurofilament protein and neuron-specific enolase. These changes were similar to changes seen when embryonal carcinoma (EC) cells are treated with retinoic acid. NGF in combination with dibutyryl cyclic adenosine monophosphate brought about similar changes as dibutyryl cyclic adenosine monophosphate alone, and was therefore not synergistic for induction of neuronal properties. In retinoic acid-treated cultures, the neuron-like cells had ultrastructural features very similar to neurons in non-tumorous, normal tissue, with typical organelles, such as one nucleolus, neurotubules and neurofilaments, while db cAMP-treated EC cells showed similar findings at the electronmicroscopic level. The results suggest that db cAMP can induce the neuronal phenotype in EC cells alone without pre-treatment with retinoic acid.     

Tyrosine phosphorylated proteins decrease during differentiation of neuronal and glial cells.

Tyrosine kinases have been implicated in the development of the nervous system. To investigate their role, immunoblotting with phosphotyrosine antibodies was used to identify substrates of tyrosine kinases during glial and neuronal differentiation in the rat and mouse. Fourteen prominent phosphotyrosine-containing proteins were detected in oligodendrocyte-type 2 astrocyte (O2A) progenitor cells. When O2A cells differentiated into type 2 astrocytes, a phosphotyrosine-modified protein of 74 kilodaltons (kDa) decreased 15-fold in abundance, and phosphotyrosine-containing proteins of 36-40 kDa declined. When O2A cells differentiated into oligodendrocytes, a prominent 71-kDa phosphotyrosine-modified protein became undetectable. During retinoic acid-induced neuronal differentiation of the mouse embryonal carcinoma cell line P19S101A1 (P19), an 80-kDa phosphotyrosine-containing protein decreased from high levels in the undifferentiated state to undetectable levels after 96 h in aggregation. Retinoic acid treatment also caused a rapid decrease in levels of a 96-kDa phosphotyrosine-containing protein. Cell-cell contact occurring as a result of aggregation resulted in decreases in 130- and 90-kDa phosphotyrosine-containing proteins in both retinoic acid-induced and control cultures. Cultured rat central nervous system cerebral cortical neurons and peripheral nervous system dorsal root ganglion neurons exhibited prominent phosphotyrosine-modified proteins of 90 and 46 kDa the same sizes as those in P19 neurons. The phosphotyrosine-containing proteins involved in the retinoic acid-induced differentiation of P19 cells to neurons were different from those altered in the glial differentiation of O2A cells to astrocytes or oligodendrocytes, indicating that the tyrosine kinase substrates modified during nervous system differentiation may be cell-type-specific.     

Isolation of neuronal precursors from differentiating P19 embryonal carcinoma cells by neuronal Tα1-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 Tα1 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.