In vitro segregation of different cell lines with neuronal and glial properties from a stem cell line of rat neurotumor RT4

p66Shc activation promotes increased oxidative phosphorylation and renders CNS cells more vulnerable to amyloid beta toxicity

A key pathological feature of Alzheimer's disease (AD) is the accumulation of the neurotoxic amyloid beta (Aβ) peptide within the brains of affected individuals. Previous studies have shown that neuronal cells selected for resistance to Aβ toxicity display a metabolic shift from mitochondrial-dependent oxidative phosphorylation (OXPHOS) to aerobic glycolysis to meet their energy needs. The Src homology/collagen (Shc) adaptor protein p66Shc is a key regulator of mitochondrial function, ROS production and aging. Moreover, increased expression and activation of p66Shc promotes a shift in the cellular metabolic state from aerobic glycolysis to OXPHOS in cancer cells. Here we evaluated the hypothesis that activation of p66Shc in CNS cells promotes both increased OXPHOS and enhanced sensitivity to Aβ toxicity. The effect of altered p66Shc expression on metabolic activity was assessed in rodent HT22 and B12 cell lines of neuronal and glial origin respectively. Overexpression of p66Shc repressed glycolytic enzyme expression and increased both mitochondrial electron transport chain activity and ROS levels in HT22 cells. The opposite effect was observed when endogenous p66Shc expression was knocked down in B12 cells. Moreover, p66Shc activation in both cell lines increased their sensitivity to Aβ toxicity. Our findings indicate that expression and activation of p66Shc renders CNS cells more sensitive to Aβ toxicity by promoting mitochondrial OXPHOS and ROS production while repressing aerobic glycolysis. Thus, p66Shc may represent a potential therapeutically relevant target for the treatment of AD.

Activation of Ras requires the ERM-dependent link of actin to the plasma membrane

BACKGROUND

Receptor tyrosine kinases (RTKs) participate in a multitude of signaling pathways, some of them via the small G-protein Ras. An important component in the activation of Ras is Son of sevenless (SOS), which catalyzes the nucleotide exchange on Ras.

PRINCIPAL FINDINGS

We can now demonstrate that the activation of Ras requires, in addition, the essential participation of ezrin, radixin and/or moesin (ERM), a family of actin-binding proteins, and of actin. Disrupting either the interaction of the ERM proteins with co-receptors, down-regulation of ERM proteins by siRNA, expression of dominant-negative mutants of the ERM proteins or disruption of F-actin, abolishes growth factor-induced Ras activation. Ezrin/actin catalyzes the formation of a multiprotein complex consisting of RTK, co-receptor, Grb2, SOS and Ras. We also identify binding sites for both Ras and SOS on ezrin; mutations of these binding sites destroy the interactions and inhibit Ras activation. Finally, we show that the formation of the ezrin-dependent complex is necessary to enhance the catalytic activity of SOS and thereby Ras activation.

CONCLUSIONS

Taking these findings together, we propose that the ERM proteins are novel scaffolds at the level of SOS activity control, which is relevant for both normal Ras function and dysfunction known to occur in several human cancers.

Site-specific and developmental expression of pannexin1 in the mouse nervous system

Until recently, members of the connexin gene family were believed to comprise the sole molecular component forming gap junction channels in vertebrates. The recent discovery of the pannexin gene family has challenged this view, as these genes may encode for a putative second class of gap junction proteins in vertebrates. The expression of pannexin genes overlaps with those cellular networks known to exhibit a high degree of gap junctional coupling. We investigated the spatio-temporal mRNA distribution of one member of this gene family, pannexin1 (Panx1), in the brain and retina of mice using quantitative real-time polymerase chain reaction and a combination of in situ hybridization and immunohistochemistry for cellular resolution. Our results demonstrate a widespread expression of Panx1 in the brain, retina and other non-neuronal tissues. In the cortex, cerebellum and eye, Panx1 is expressed at early embryonic time points and peaks around embryonic day 18 followed by a decline towards adulthood. Most notably, Panx1 is detectable in neurons of many brain nuclei, which are known to be coupled by gap junctions as well as in previously unrecognized areas. Abundant expression was found in the adult hippocampal and neocortical pyramidal cells and interneurons, neurons of the reticular thalamus, the inferior olive, magnocellular hypothalamic neurons, midbrain and brain stem motoneurons, Purkinje cells and the retina.

Comparative analysis of Schwann cell lines as model systems for myelin gene transcription studies

Primary and immortalized cultured Schwann cells are commonly utilized in analyses of myelin gene promoters, but few lines are well-characterized in terms of their endogenous expression of myelin genes. This is particularly significant in that cultured Schwann cells typically do not express myelin genes at levels comparable to those observed in vivo. In this study, the steady-state levels of mRNA and protein for five Schwann cell markers (PMP22, P0, MBP, MAG, and LNGF-R) were assessed in primary Schwann cells and six representative Schwann cell lines (RT4-D6P2T, JS-1, RSC96, R3, S16, and S16Y). RT4-D6P2T and S16 cells were the most similar to myelinating Schwann cells based on their comparatively high expression of PMP22 and P0 mRNA. Both RT4-D6P2T and S16 also expressed P0 protein. In addition, the previously reported P1-A positive regulatory region from the myelination-specific PMP22 promoter demonstrated significant activity in both these cell lines. However, nuclear proteins that interacted with P1-A were different in extracts prepared from RT4-D6P2T and S16 cells. Primary Schwann cells expressed myelin proteins at levels that were equal or less than those observed with the RT4-D6P2T and S16 lines, indicating that primary Schwann cells are not necessarily better than immortalized Schwann cells as model systems for the study of myelin gene regulation. The data presented here demonstrate that cultured Schwann cells used to study myelin gene promoters have to be carefully selected on the basis of the endogenous level of expression of the myelin gene under study.

Overexpression of activated neu/erbB2 initiates immortalization and malignant transformation of immature Schwann cells in vitro

The neu/erbB2 protooncogene is overexpressed in numerous human cancers and is mutationally activated in N-ethyl-N-nitrosourea (ENU)-induced rodent tumors of the Schwann cell lineage. We investigated whether expression of activated neu in Schwann cells is sufficient to initiate their immortalization and transformation. Clones of embryonic dorsal root ganglia cells infected with a retrovirus bearing activated neu (NID cells) were selected based on their expression of Schwann cell-specific markers. Compared to embryonic Schwann cells infected with a virus encoding empty vector, we found that NID cells have altered shapes and disorganized cytoskeletons, grow in the absence of growth factors required for normal Schwann cell survival and proliferation, and can be repeatedly passaged. Furthermore, NID cells are invasive in an in vitro matrix invasion assay and form metastatic tumors when injected into syngeneic animals. The neu-induced growth and invasive phenotypes could be reversed by drugs that inhibit Ras and Src activity. Interestingly, later stage Schwann cells infected with activated neu failed to become immortalized. These findings indicate that constitutive activation of erbB2 is sufficient to initiate the immortalization and transformation of immature Schwann cells, and support the notion that Schwann cells have particular developmental stages during which they are susceptible to immortalizing and transforming events.

POU domain genes are differentially expressed in the early stages after lineage commitment of the PNS-derived stem cell line, RT4-AC

RT4 is a family of cell lines derived from a rat peripheral neurotumor and consists of a multipotential stem cell which spontaneously gives rise to a glial derivative and two neuronal derivatives. To begin to understand the role(s) of transcription factors in neural differentiation, we examined the expression of ten transcription factor genes (MASH1, REST/NRSF, Oct-1, Oct-2, Tst-1/SCIP, Brn-1, Brn-2, Brn-3.0, Brn-4, Brn-5) in the RT4 cell lines. We report here that all of the RT4 cells express REST/NRSF, Oct-1 and Brn-5, but do not express MASH1, Brn-3.0 or Brn-4. Furthermore, Brn-2 and Tst-1/SCIP expression was restricted to the RT4 stem cell line and glial derivative, while Oct-2 was expressed predominantly by the RT4 stem cell line and neuronal derivatives. We propose that the lack of expression of MASH1 (which is expressed relatively early in autonomic neuron differentiation) and Brn-3.0 (which is expressed early in sensory neuron differentiation), in combination with the presence of REST/NRSF (a repressor of neuronal gene expression), in all of the RT4 cell lines, establishes the RT4 system as a unique model for examining very early events in neuronal versus glial cell fate determination.

TTX-sensitive and -resistant Na+ currents, and mRNA for the TTX-resistant rH1 channel, are expressed in B104 neuroblastoma cells

To examine the molecular basis for membrane excitability in a neuroblastoma cell line, we used whole cell patch-clamp methods and reverse transcription-polymerase chain reaction (RT-PCR) to study Na+ currents and channels in B104 cells. We distinguished Tetrodotoxin (TTX)-sensitive and -resistant Na+ currents and detected the mRNA for the cardiac rH1 channel in B104 cells. Na+ currents could be recorded in 65% of cells. In the absence of TTX, mean peak Na+ current density was 126 +/- 19 pA/pF, corresponding to a channel density of 2.7 +/- 0.4/micron 2 (mean +/- SE). Time-to-peak (t-peak), activation (tau m), and inactivation time constants (tau h) for Na+ currents in B104 cells were 1.0 +/- 0.04, 0.4 +/- 0.06, and 0.9 +/- 0.04 ms at -10 mV. The peak conductance-voltage relationship had a V 1/2 of -39.8 +/- 1.5 mV. V 1/2 for steady-state inactivation was -81.6 +/- 1.5 mV. TTX-sensitive and -resistant components of the Na current had half-maximal inhibitions (IC50), respectively, of 1.2 nM and, minimally, 575.5 nM. The TTX-sensitive and -resistant Na+ currents were kinetically distinct; time-to-peak, tau m, and tau h for TTX-sensitive currents were shorter than for TTX-resistant currents. Steady-state voltage dependence of the two currents was indistinguishable. The presence of TTX-sensitive and -resistant Na+ currents, which are pharmacologically and kinetically distinct, led us to search for mRNAs known to be associated with TTX-resistant channels, in addition to the alpha subunit mRNAs, which have previously been shown to be expressed in these cells. Using RT-PCR and restriction enzyme mapping, we were unable to detect alpha SNS, but detected mRNA for rH1, which is known to encode a TTX-resistant channel, in B104 cells. B104 neuroblastoma cells thus express TTX-sensitive and -resistant Na+ currents. These appear to be encoded by neuronal-type and cardiac Na+ channel mRNAs including the RH1 transcript. This cell line may be useful for studies on the rH1 channel, which is known to be mutated in the long-QT syndrome.

Regulation of the rat S100 beta gene expression: the role of the 2 kb 5'-upstream sequence in glial specific expression

We have studied the role of the 2047 bp 5'-upstream region and 232 bp first exon sequence of the rat S100 beta gene in glial specific expression. S100 beta luciferase expression vectors carrying serial deletions of the S100 beta 5' upstream sequence were constructed and transiently transfected into the peripheral nervous system (PNS) glial-type cell line RT4-D6, the PNS neuronal-type cell line RT4-E5, and the central nervous system (CNS) glial-type cell line C6. The hepatoma cell line HTC was also transfected as a nonneural control. From this functional analysis, we found a glial-specific positive regulatory sequence(s) mapped between -583 and -106 relative to the transcriptional start site. This region confers a significantly higher level of luciferase expression in the glial-type cell lines RT4-D6 and C6 than in the neuronal cell line RT4-E5 and the hepatoma cell line HTC. Also, a non-cell type specific positive regulatory element was identified in the first exon sequence between +78 and +232. Though non-cell type-specific, it was found to have a predominant effect in glial cells. From these observations, we have concluded that the 2047 bp 5'-upstream region and 232 bp of the first exon sequence confers the high levels of S100 beta expression in glial cells through these two positive elements.

Schwann cell tumors express characteristic patterns of CD44 splice variants

Members of the CD44 family of cell surface hyaluronate-binding proteins have been implicated in cell migration, cell-matrix interactions and tumor progression. To determine whether these proteins might play a role in the normal functions of Schwann cells and in their tumorigenesis, we examined the patterns of CD44 expression in Schwann cells from rat peripheral nerve, rat Schwann cell tumor lines, and human schwannomas. Normal rat spinal nerves and primary Schwann cell cultures expressed standard CD44 (CD44s) but not alternatively spliced variant isoforms. In contrast, rat Schwann cell tumor lines expressed both CD44s and a number of variants, including proteins containing sequences encoded by exon v6. Furthermore, we found that these cell lines bind hyaluronate, and that their cell surface hyaluronate binding correlates with CD44 expression. All of the human schwannomas also expressed CD44 variants, especially epitopes encoded by exon v5, the border between v7 and v8, and v9-10. These data indicate that Schwann cells normally express CD44s, that Schwann cell tumors express both CD44s and particular variants of CD44, and that CD44s and possibly variants of CD44 are involved in hyaluronate recognition by Schwann cell tumors.

The tetrodotoxin-insensitive sodium current in rat dorsal root ganglia is unlikely to involve the expression of the tetrodotoxin-resistant sodium channel, SkM2

Tetrodotoxin-insensitive (TTX-I) sodium currents have been recorded from newborn and adult rat sensory neurons, but the sodium channel gene(s) responsible for the TTX-I current are unknown. Because SkM2, one of six voltage-sensitive sodium channel genes cloned from rat, encodes the only cloned channel that is relatively resistant to tetrodotoxin, we sought to test whether the TTX-I current in rat sensory neurons is due to the SkM2 channel. We hypothesized that the TTX-I current might be generated from (1) an RNA splicing variant of SkM2, (2) post-translational modification of the SkM2 protein, or (3) interaction with alternate additional channel subunits. SkM2 mRNA expression was examined in newborn rat dorsal root ganglia (DRG) by RNase protection assay. No SkM2 expression was detected. Therefore, we conclude that the TTX-I sodium current in DRG is unlikely to result from the expression of the SkM2 gene.

Glial-specific cAMP response of the glial fibrillary acidic protein gene cell lines

Expression of the rat glial fibrillary acidic protein (GFAP) gene is responsive to the intracellular level of cAMP. We have examined the sequence 5'-upstream of the transcription start site of the rat GFAP-encoding gene to determine the elements responsible for regulating the cAMP response. The RT4 cell lines consist of a neural stem-cell type RT4-AC and its three derivative cell types, one glial-cell type, RT4-D, and two neuronal-cell types, RT4-B and RT4-E. GFAP is expressed in the stem-cell type and the glial-cell type but is not expressed in the neuronal-cell types. Luciferase expression vectors containing various areas of the 10.8-kb region upstream of the transcription start site of the GFAP gene were transiently transfected into these RT4 cells. The effect of cAMP was examined by quantitating the transient expression of luciferase. We found that (i) the 5'-upstream region alone (up to 10.8 kb) allows expression of the GFAP gene in the stem-cell type, the glial-cell type, and a neuronal-cell type; (ii) there are negative and positive cAMP-responsive elements that are juxtaposed within the region between -240 bp and -110 bp upstream and are functional in the stem-cell and glial-cell types but are not functional in the neuronal-cell type RT4-E; (iii) there may be elements that respond to dibutyryl-cAMP in all three RT4 cell types within the region from 2 kb to 10.8 kb upstream of the transcription start site; and (iv) a regulatory luciferase plasmid pRLgfap-1, containing both the upstream and downstream regulatory regions of the GFAP gene, not only expresses luciferase but also responds to forskolin in the stem-cell type and the glial-cell type. This regulatory plasmid, however, does not express in the neuronal-cell type with or without the forskolin treatment.

Cell-type specific segregation of transcriptional expression of glial genes in the rat peripheral neurotumor RT4 cell lines

Four types of cells, RT4-AC (stem cell type), RT4-B and RT4-E (neuronal cell types), and RT4-D (glial cell type) were previously isolated from an ethylnitrosourea (ENU) induced rat peripheral neurotumor RT4. In a phenomenon termed cell-type conversion, RT4-AC spontaneously and permanently gives rise to the three other cell types in culture. In the RT4 system the expression of glial fibrillary acidic protein (GFAP) and S100 beta protein genes segregates in a cell-type specific manner. To further characterize the RT4 family, the expression of four myelin-forming glial genes--P0 glycoprotein, suppressed cAMP inducible POU (SCIP), 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), and myelin basic protein (MBP)--has been studied in the RT4 cell lines. In addition to these genes, the expression of the low-affinity nerve growth factor (LNGF) receptor (expressed in immature Schwann cells) has been examined. We have found the following results. 1) The stem cell type RT4-AC and the glial cell type RT4-D express mRNA transcripts of P0, SCIP, and CNP (the larger form, 2.8 kb), and the amount of mRNA of these genes was increased by forskolin. 2) RT4-AC and RT4-D also express a low level of MBP mRNA upon forskolin treatment. 3) The neuronal cell types RT4-B and RT4-E do not express any of these myelin-forming glial genes with or without forskolin treatment. 4) The LNGF receptor mRNA is expressed in RT4-AC and RT4-D and at a lower level in RT4-B; its expression is stimulated by forskolin.

Tissue-specific versus cell type-specific expression of the glial fibrillary acidic protein

Expression of the glial cell-specific gene encoding glial fibrillary acidic protein (GFAP) is regulated in a tissue-specific (neural tissue versus other tissues) as well as a cell type-specific (glial cell versus neuron) manner. Using a family of rat neurotumor RT4 cell lines in which neuronal/glial differentiation occurs in vitro, along with cell lines of different tissue origins, we identified by transient- and permanent-transfection assays two negative regulatory regions, GFAP downstream regulators 1 and 2 (GDR1 and GDR2). Both regions lie 3' of the transcription start site; GDR1 is in a 2.7-kb region extending from the first intron through the fifth exon, and GDR2 is within 1.7 kb 3' of the polyadenylylation site. GDR1 alone is responsible for tissue-specific expression (suppression in nonneural tissues), while both GDR1 and GDR2 are necessary for cell type-specific expression (suppression in neuronal cells).

Dibutyryl-cAMP increases functions of 5-hydroxytryptamine2 receptors, but not of beta 2-adrenergic receptors, in a clonal cell line of rat neurotumor RT4

A peripheral nervous system cell line RT4-B, established by Imada and Sueoka (Dev. Biol., 66:97-108, 1978), was shown to respond to serotonin [5-hydroxytryptamine (5-HT)] and catecholamines. 5-HT induced a small and transient increase in cytosolic free Ca2+ concentration ([Ca2+]i) in the RT4-B cells. The increase was effectively blocked by 5-HT2 receptor antagonists (spiperone, ritanserin and mianserin), but not by a 5-HT3 receptor antagonist (MDL72222), or a alpha 1-adrenergic receptor antagonist (prazosin), indicating that RT4-B cells express 5-HT2 receptors. On the other hand, catecholamines increased cyclic AMP production by RT4-B. The order of potency for stimulating cyclic AMP synthesis was isoproterenol greater than epinephrine much greater than norepinephrine much greater than dopamine, and the stimulation was effectively inhibited by the nonselective beta-adrenergic receptor antagonist propranolol, but not by the beta 1-adrenergic receptor antagonist atenolol, suggesting that RT4-B cells express beta 2-adrenergic receptors. The differentiating agent N6,2'-O-dibutyryladenosine 3',5'-monophosphate (dibutyryl-cAMP) enhanced the 5-HT-induced [Ca2+]i increase, but not the catecholamine-induced cyclic AMP production. The increase in the 5-HT response paralleled the increase in the density of 5-HT2 receptors. n-Butyric acid (2 mM) and 8-bromoadenosine 3',5'-monophosphate (1 mM) also increased the 5-HT response, and the sum of these increases was nearly equal to that induced by dibutyryl-cAMP. These results indicate that RT4-B is a novel model cell line for the study of 5-HT2 and beta 2-adrenergic receptors and their second messenger responses and for the analysis of the mechanisms how 5-HT2 receptor gene expression is controlled.

Two histospecific enzyme expressions in the same cleavage-arrested one-celled ascidian embryos

Fertilized eggs of the ascidian, Ciona intestinalis, were prevented from undergoing cytokinesis but not nuclear division by treatment with cytochalasin B. After appropriate times, such cleavage-arrested multinucleate zygotes developed acetylcholinesterase of larval tail muscle and an alkaline phosphatase ordinarily localized in the larval endoderm tissues. Separate histochemical reactions on one of a pair of samples taken from the eggs of single animals provided examples (6/34) in which the numbers of cytochalasin-treated embryos displaying the respective reaction product overlapped sufficiently (15-29%) to indicate that some of the zygotes had developed both enzymes in the same uncleaved single cell. With an actual dual-staining technique that can be applied to single cleavage-arrested zygotes, 62% of those developing a strong alkaline phosphatase reaction also had a strong acetylcholinesterase reaction. In other experiments, quantitative measurements of enzyme activity in homogenates of 114 single cleavage-arrested zygotes confirm directly that 18% of the zygotes produce both enzymes. There was no obligatory mutual exclusion of the potential for simultaneous expression of two tissue-specific characteristics that would ordinarily be segregated into different lineages during early cleavages. The cytoplasmic determinants believed responsible for these histotypic expressions can apparently function independently in the same cell.

Regulated galactolipid synthesis and cell surface expression in Schwann cell line D6P2T

Clonal cell line D6P2T, subcloned from an ethylnitrosourea-induced tumor line D6 of the rat peripheral nervous system, has been characterized with particular attention to galactolipid metabolism. Galactosylcerebroside and sulfatide synthesis and expression on the cell surface are highly regulated in D6P2T cells by mechanisms involving serum- and cyclic AMP-mediated pathways. These cells also express 2',3'-cyclic nucleotide 3'-phosphohydrolase (Wolfgram protein W1a) and laminin. In contrast, myelin basic protein and antigen HNK-1 were not detected. Line D6P2T appears to be a semi-differentiated Schwann cell model, which offers interesting possibilities for studies of galactolipid synthesis, transport, and sorting.

Induction and segregation of glial intermediate filament expression in the RT4 family of peripheral nervous system cell lines

We have found glial fibrillary acidic protein (GFAP), the major component of astrocyte intermediate filaments, to be expressed in cell lines of the RT4 peripheral neurotumor family. The RT4 family is a "stem-cell-like" cell line, RT4-AC, that spontaneously undergoes differentiation in culture to three derivative cell types. This process, termed cell-type conversion, results in a segregation among the derivative cell types of parental cell phenotypes that have been described as neuronal-like or glial-like. We have identified a 50-kDa GFAP-immunoreactive cytoskeletal protein and GFAP mRNA in continuous RT4-AC and RT4-D (glial-type derivative) cell lines, but not in two presumptive neuronal-type cell lines. This result suggests that GFAP gene expression is coordinately coupled with the expression of other glial properties during cell-type conversion. In addition, the RT4-AC and RT4-D sublines were found to significantly express GFAP only at high cell densities and not during logarithmic growth and to express GFAP precociously during morphological differentiation following treatment with 1 mM N6, O2'-dibutyryladenosine 3',5'-cyclic monophosphate. These observations closely reflect reports of glial filament expression in astrocyte cultures, suggesting that a common regulatory mechanism is employed by central and peripheral nervous system glia.

Cell-type-specific responses of RT4 neural cell lines to dibutyryl-cAMP: branch determination versus maturation

This report describes the induction of cell-type-specific maturation, by dibutyryl-cAMP and testololactone, of neuronal and glial properties in a family of cell lines derived from a rat peripheral neurotumor, RT4. This maturation allows further understanding of the process of determination because of the close lineage relationship between the cell types of the RT4 family. The RT4 family is characterized by the spontaneous conversion of one of the cell types, RT4-AC (stem-cell type), to any of three derivative cell types, RT4-B, RT4-D, or RT4-E, with a frequency of about 10(-5). The RT4-AC cells express some properties characteristic of both neuronal and glial cells. Of these neural properties expressed by RT4-AC cells, only the neuronal properties are expressed by the RT4-B and RT4-E cells, and only the glial properties are expressed by the RT4-D cells. This in vitro cell-type conversion of RT4-AC to three derivative cell types is a branch point for the coordinate regulation of several properties and seems to resemble determination in vivo. In our standard culture conditions, several other neuronal and glial properties are not expressed by these cell types. However, addition of dibutyryl-cAMP induces expression of additional properties, in a cell-type-specific manner: formation of long cellular processes in the RT4-B8 and RT4-E5 cell lines and expression of high-affinity uptake of gamma-aminobutyric acid, by a glial-cell-specific mechanism, in the RT4-D6-2 cell line. These new properties are maximally expressed 2-3 days after addition of dibutyryl-cAMP. This indicates that conversion of RT4-AC to the derivative cell types is also a branch point for the regulation of cell-type-specific properties whose expression is responsive to cAMP. Thus, the potential for maturation in response to increased cAMP is a property that segregates in a cell-type-specific manner and is activated at the determinational level in this system.

Ontogeny of electrically excitable cells in cultured olfactory epithelium

A primary system has been developed in which it is possible to study the production of electrically excitable neuron-like cells from a precursor population of olfactory epithelial cells. Rat nasal epithelium was dissociated and placed in culture. The initial surviving cells are flat and ciliated and contain glial fibrillary acidic protein (GFAP). After 3-5 days electrically excitable cells appear that contain neuron-specific enolase but not GFAP. These round cells originate by means of the differentiation of the GFAP-positive flat cell to a round cell, followed by the division of the round cell. Therefore, neuron-like cells can be derived from cells that synthesize GFAP.

Cloning of DNA corresponding to rare transcripts of rat brain: evidence of transcriptional and post-transcriptional control and of the existence of nonpolyadenylated transcripts

To examine the expression of genes encoding rare transcripts in the rat brain, we have characterized genomic DNA clones corresponding to this class. In brain cells, as in all cell types, rare transcripts constitute the majority of different sequences transcribed. Moreover, when compared with other tissues or cultured cells, brain tissue may be expected to have an even larger set of rare transcripts, some of which could be restricted to subpopulations of neural cells. We have identified seven clones whose transcripts are nonabundant, averaging less than three copies per cell. Clone rg13 (rat genomic 13) RNA was detected only in the brain, whereas RNA of a second clone, rg40, was also detected in the brain and in a melanoma. Transcripts of rg13 were found in cerebellum, cerebral cortex, and regions underlying the cortex, whereas rg40 transcripts were not detected in the cerebellum. Transcripts of both rg13 and rg40 were found in pelleted polysomal RNA. RNA of another clone, rg34, was found in the brain, liver, and kidney but was found in pelleted polysomal RNA only in the brain, suggesting that its expression may be post-transcriptionally controlled. The remaining four clones represent rare transcripts that are common to the brain, liver, and kidney; rg18 RNA is restricted to the nucleus, whereas rg3, rg26, and rg36 transcripts are found in the cytoplasm of all three tissues. Transcripts of the brain-specific clone, rg13, and the commonly expressed clone, rg3, are nonpolyadenylated, presumably belonging to the high-complexity, nonpolyadenylated class of transcripts in the mammalian brain.

Cloning of DNA corresponding to rare transcripts of rat brain: evidence of transcriptional and post-transcriptional control and of the existence of nonpolyadenylated transcripts

To examine the expression of genes encoding rare transcripts in the rat brain, we have characterized genomic DNA clones corresponding to this class. In brain cells, as in all cell types, rare transcripts constitute the majority of different sequences transcribed. Moreover, when compared with other tissues or cultured cells, brain tissue may be expected to have an even larger set of rare transcripts, some of which could be restricted to subpopulations of neural cells. We have identified seven clones whose transcripts are nonabundant, averaging less than three copies per cell. Clone rg13 (rat genomic 13) RNA was detected only in the brain, whereas RNA of a second clone, rg40, was also detected in the brain and in a melanoma. Transcripts of rg13 were found in cerebellum, cerebral cortex, and regions underlying the cortex, whereas rg40 transcripts were not detected in the cerebellum. Transcripts of both rg13 and rg40 were found in pelleted polysomal RNA. RNA of another clone, rg34, was found in the brain, liver, and kidney but was found in pelleted polysomal RNA only in the brain, suggesting that its expression may be post-transcriptionally controlled. The remaining four clones represent rare transcripts that are common to the brain, liver, and kidney; rg18 RNA is restricted to the nucleus, whereas rg3, rg26, and rg36 transcripts are found in the cytoplasm of all three tissues. Transcripts of the brain-specific clone, rg13, and the commonly expressed clone, rg3, are nonpolyadenylated, presumably belonging to the high-complexity, nonpolyadenylated class of transcripts in the mammalian brain.

Modulation of cell-associated plasminogen activator activity by cocultivation of a stem cell and its tumorigenic descendant

The effect of the presence of one cell type on the plasminogen activator activity of another cell type was studied. The cell types, AC and D, were isolated from a rat neuroblastoma (I. Imada and N. Sueoka, Dev. Biol. 66:97-108, 1978). AC cells are stem cells capable of multipotential differentiation in vitro and have little or no cell-associated plasminogen activator activity. D cells are tumorigenic and have high levels of cell-associated plasminogen activator activity. When AC cells were cocultivated with D cells, the plasminogen activator activity of the D cells was dramatically inhibited. The presence of as few as 1,250 AC cells inhibited 70% of the plasminogen activator activity of 20,000 D cells, as determined by a highly quantitative assay. The amount of inhibition by AC cells was proportional to the number of AC cells present. At increasing numbers of AC cells and a constant number of D cells, the Vmax for the activation of plasminogen proportionately decreased and the Km remained constant, implying that AC cells did not alter the structure or concentration of plasminogen. Inhibition was not mediated by a soluble inhibitor secreted by AC cells. Rather, attachment of AC cells adjacent to D cells, i.e., cell-to-cell contact, seemed to be required for inhibition. The substratum-attached material of AC cells, that which remained on the microwell surface after removal of AC cells with EDTA, inhibited D cell plasminogen activator activity. If plasminogen activator activity is involved in metastasis, then regulation of the plasminogen activator activity of one cell type by another cell type may be involved in determining which cells in a tumor can metastasize and where secondary tumors can arise.

Modulation of cell-associated plasminogen activator activity by cocultivation of a stem cell and its tumorigenic descendant

The effect of the presence of one cell type on the plasminogen activator activity of another cell type was studied. The cell types, AC and D, were isolated from a rat neuroblastoma (I. Imada and N. Sueoka, Dev. Biol. 66:97-108, 1978). AC cells are stem cells capable of multipotential differentiation in vitro and have little or no cell-associated plasminogen activator activity. D cells are tumorigenic and have high levels of cell-associated plasminogen activator activity. When AC cells were cocultivated with D cells, the plasminogen activator activity of the D cells was dramatically inhibited. The presence of as few as 1,250 AC cells inhibited 70% of the plasminogen activator activity of 20,000 D cells, as determined by a highly quantitative assay. The amount of inhibition by AC cells was proportional to the number of AC cells present. At increasing numbers of AC cells and a constant number of D cells, the Vmax for the activation of plasminogen proportionately decreased and the Km remained constant, implying that AC cells did not alter the structure or concentration of plasminogen. Inhibition was not mediated by a soluble inhibitor secreted by AC cells. Rather, attachment of AC cells adjacent to D cells, i.e., cell-to-cell contact, seemed to be required for inhibition. The substratum-attached material of AC cells, that which remained on the microwell surface after removal of AC cells with EDTA, inhibited D cell plasminogen activator activity. If plasminogen activator activity is involved in metastasis, then regulation of the plasminogen activator activity of one cell type by another cell type may be involved in determining which cells in a tumor can metastasize and where secondary tumors can arise.

Cell type conversion in a mouse melanoma cell clone

A melanoma cell clone was isolated from cultured B16 mouse melanoma cells. This clone, conv, which was characterized by rounded and spindle-shaped cell morphology, was not highly melanotic under the usual culture condition but had high tyrosinase (dopa oxidase) activity. When the cells were seeded to form colonies on a plastic culture dish in Eagle's minimum essential medium supplemented with 10% bovine calf serum, two kinds of cell types always appeared. One was cytochemically dopa-positive and spindle-shaped (S type cell) with the same phenotypes as those of the parental cells. The other was dopa-negative and fibroblastlike (F type cell) containing no melanosomes. It was observed that the conversion from S type to F type occurred with a high frequency. The conversion from F type to S type also occurred but with a low frequency.

Renin, angiotensins, and angiotensin-converting enzyme in neuroblastoma cells: evidence for intracellular formation of angiotensins

The mechanism of formation of various peptide hormones in neuronal cells in the brain is not clear. The question of whether brain angiotensin II is formed by an extracellular mechanism as in the peripheral system or by an intracellular mechanism can be answered by using cloned cells in culture. We have screened several neuroblastoma cell lines of rat and mouse origin and found at least three cell lines that contain renin (EC 3.4.99.19), angiotensin-converting enzyme (dipeptidyl carboxypeptidase; peptidyldipeptide hydrolase, EC 3.4.15.1), and angiotensins I and II. This finding was interpreted to indicate that in these cells angiotensin formation takes place by an intracellular mechanism, in contrast to the extracellular mechanism well known to occur in plasma. This study also demonstrates the existence of viable and cloned cell lines that produce renin.

Tetrodotoxin-sensitive sodium channels in normal human fibroblasts and normal human glia-like cells

Tetrodotoxin-sensitive sodium channels are detectable in normal human fibroblasts and in "glia-like" cells at appreciable levels when compared to what is observed in established neuronal cell lines in culture. Two- to 3-fold stimulations of sodium influx are observed in the presence of 0.2 mM veratridine and scorpion venom at 0.1 mg/ml. Tetrodotoxin (2 microM) inhibits the observed stimulation of sodium influx. Previous work has indicated that these neurotoxins act on the voltage-sensitive sodium ionophore of excitable cells, and the presence of such channels in cells generally considered nonexcitable raises questions regarding both the uniqueness of this ionophore as a property of excitable cells and the origin of the cells generally described as fibroblasts.