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Abstract
This review compares the biological and physiological function of Sigma receptors [σRs] and their potential therapeutic roles. Sigma receptors are widespread in the central nervous system and across multiple peripheral tissues. σRs consist of sigma receptor one (σ1R) and sigma receptor two (σ2R) and are expressed in numerous regions of the brain. The sigma receptor was originally proposed as a subtype of opioid receptors and was suggested to contribute to the delusions and psychoses induced by benzomorphans such as SKF-10047 and pentazocine. Later studies confirmed that σRs are non-opioid receptors (not an µ opioid receptor) and play a more diverse role in intracellular signaling, apoptosis and metabolic regulation. σ1Rs are intracellular receptors acting as chaperone proteins that modulate Ca2+ signaling through the IP3 receptor. They dynamically translocate inside cells, hence are transmembrane proteins. The σ1R receptor, at the mitochondrial-associated endoplasmic reticulum membrane, is responsible for mitochondrial metabolic regulation and promotes mitochondrial energy depletion and apoptosis. Studies have demonstrated that they play a role as a modulator of ion channels (K+ channels; N-methyl-d-aspartate receptors [NMDAR]; inositol 1,3,5 triphosphate receptors) and regulate lipid transport and metabolism, neuritogenesis, cellular differentiation and myelination in the brain. σ1R modulation of Ca2+ release, modulation of cardiac myocyte contractility and may have links to G-proteins. It has been proposed that σ1Rs are intracellular signal transduction amplifiers. This review of the literature examines the mechanism of action of the σRs, their interaction with neurotransmitters, pharmacology, location and adverse effects mediated through them.
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Affiliation(s)
- Colin G Rousseaux
- a Department of Pathology and Laboratory Medicine , University of Ottawa , Ottawa , ON , Canada and
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Abstract
Glu (glutamate), the excitatory transmitter at the main signalling pathway in the retina, is critically involved in changes in the protein repertoire through the activation of signalling cascades, which regulate protein synthesis at transcriptional and translational levels. Activity-dependent differential gene expression by Glu is related to the activation of ionotropic and metabotropic Glu receptors; however, recent findings suggest the involvement of Na+-dependent Glu transporters in this process. Within the retina, Glu uptake is aimed at the replenishment of the releasable pool, and for the prevention of excitotoxicity and is carried mainly by the GLAST/EAAT-1 (Na+-dependent glutamate/aspartate transporter/excitatory amino acids transporter-1) located in Müller radial glia. Based on the previous work showing the alteration of GLAST expression induced by Glu, the present work investigates the involvement of GLAST signalling in the regulation of protein synthesis in Müller cells. To this end, we explored the effect of D-Asp (D-aspartate) on Ser-2448 mTOR (mammalian target of rapamycin) phosphorylation in primary cultures of chick Müller glia. The results showed that D-Asp transport induces the time- and dose-dependent phosphorylation of mTOR, mimicked by the transportable GLAST inhibitor THA (threo-β-hydroxyaspartate). Signalling leading to mTOR phosphorylation includes Ca2+ influx, the activation of p60src, phosphatidylinositol 3-kinase, protein kinase B, mTOR and p70S6K. Interestingly, GLAST activity promoted AP-1 (activator protein-1) binding to DNA, supporting a function for transporter signalling in retinal long-term responses. These results add a novel receptor-independent pathway for Glu signalling in Müller glia, and further strengthen the critical involvement of these cells in the regulation of glutamatergic transmission in the retina.
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Kiyota T, Kato A, Altmann CR, Kato Y. The POU homeobox protein Oct-1 regulates radial glia formation downstream of Notch signaling. Dev Biol 2008; 315:579-92. [PMID: 18241856 DOI: 10.1016/j.ydbio.2007.12.013] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2007] [Revised: 12/11/2007] [Accepted: 12/14/2007] [Indexed: 12/31/2022]
Abstract
Radial glia cells function as guide cells for neuronal migration and a source of neural progenitor cells, and play a crucial role for the development of the central nervous system. To date, several signals have been demonstrated to promote the formation of radial glia cells and Notch signaling is one such signal. However, the mechanism of the signaling hierarchy of radial glia developmental cascade promoted by Notch signaling still remains incomplete. Here we show that Notch signaling promotes Xenopus radial glia formation and that the Notch activation is sufficient for radial glia formation prior to neural tube closure. Moreover, we have identified Oct-1 (POU2f1), a POU transcription factor, as a downstream target of Notch signaling by microarray based screen. We demonstrate that the expression of Oct-1 in the brain is regulated by Notch signaling and that Oct-1 is sufficient and necessary for radial glia formation. Together, Oct-1 is a downstream effector of Notch signaling during radial glia formation.
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Affiliation(s)
- Tomomi Kiyota
- Department of Biomedical Science, Florida State University College of Medicine, 1115 W. Call St., Tallahassee, FL 32306, USA
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Rousseaux CG. A Review of Glutamate Receptors II: Pathophysiology and Pathology. J Toxicol Pathol 2008. [DOI: 10.1293/tox.21.133] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Affiliation(s)
- Colin G. Rousseaux
- Department of Pathology and Laboratory Medicine, Faculty of Medicine, University of Ottawa
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Hadley D, Murphy T, Valladares O, Hannenhalli S, Ungar L, Kim J, Bućan M. Patterns of sequence conservation in presynaptic neural genes. Genome Biol 2007; 7:R105. [PMID: 17096848 PMCID: PMC1794582 DOI: 10.1186/gb-2006-7-11-r105] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2006] [Revised: 09/25/2006] [Accepted: 11/10/2006] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The neuronal synapse is a fundamental functional unit in the central nervous system of animals. Because synaptic function is evolutionarily conserved, we reasoned that functional sequences of genes and related genomic elements known to play important roles in neurotransmitter release would also be conserved. RESULTS Evolutionary rate analysis revealed that presynaptic proteins evolve slowly, although some members of large gene families exhibit accelerated evolutionary rates relative to other family members. Comparative sequence analysis of 46 megabases spanning 150 presynaptic genes identified more than 26,000 elements that are highly conserved in eight vertebrate species, as well as a small subset of sequences (6%) that are shared among unrelated presynaptic genes. Analysis of large gene families revealed that upstream and intronic regions of closely related family members are extremely divergent. We also identified 504 exceptionally long conserved elements (> or =360 base pairs, > or =80% pair-wise identity between human and other mammals) in intergenic and intronic regions of presynaptic genes. Many of these elements form a highly stable stem-loop RNA structure and consequently are candidates for novel regulatory elements, whereas some conserved noncoding elements are shown to correlate with specific gene expression profiles. The SynapseDB online database integrates these findings and other functional genomic resources for synaptic genes. CONCLUSION Highly conserved elements in nonprotein coding regions of 150 presynaptic genes represent sequences that may be involved in the transcriptional or post-transcriptional regulation of these genes. Furthermore, comparative sequence analysis will facilitate selection of genes and noncoding sequences for future functional studies and analysis of variation studies in neurodevelopmental and psychiatric disorders.
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Affiliation(s)
- Dexter Hadley
- Penn Center for Bioinformatics, 423 Guardian Drive, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Genomics and Computational Biology Graduate Group, 423 Guardian Drive, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Tara Murphy
- Department of Genetics in the School of Medicine, University of Pennsylvania, 415 Curie Boulevard Philadelphia, Pennsylvania 19104, USA
- UCLA Neuroscience Graduate Office, 695 Young Drive South, Los Angeles, California 90095, USA
| | - Otto Valladares
- Department of Genetics in the School of Medicine, University of Pennsylvania, 415 Curie Boulevard Philadelphia, Pennsylvania 19104, USA
| | - Sridhar Hannenhalli
- Penn Center for Bioinformatics, 423 Guardian Drive, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Genomics and Computational Biology Graduate Group, 423 Guardian Drive, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Lyle Ungar
- Penn Center for Bioinformatics, 423 Guardian Drive, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Department of Computer & Information Sciences in School of Engineering and Applied Sciences, 3330 Walnut Street, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Junhyong Kim
- Penn Center for Bioinformatics, 423 Guardian Drive, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Department of Computer & Information Sciences in School of Engineering and Applied Sciences, 3330 Walnut Street, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Department of Biology in the School of Arts and Sciences, 433 S University Avenue, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Maja Bućan
- Penn Center for Bioinformatics, 423 Guardian Drive, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Department of Genetics in the School of Medicine, University of Pennsylvania, 415 Curie Boulevard Philadelphia, Pennsylvania 19104, USA
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