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1 Chapter 27 Transcription Factors in the Central Nervous System Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
2 FIGURE 27-1: Formation and regulation of the transcriptional complex. The transcribed region of a gene is indicated in black. Immediately to the right of this box, on the 5-side, is an orange helix, indicating the TATA box sequence. These are cis -regulatory sequences. The transcription complex binds to the TATA box and can initiate transcription when stimulated. Transcription can be regulated by the binding of various trans-acting factors to the enhancers (blue shapes) adjacent to the TATA box. The positioning of these sequences permits a direct interaction between trans-acting factors and the RNA polymerase II complex. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
3 FIGURE 27-2: Gene expression as a biological amplifier. Transcription is an amplification step, giving rise to thousands of mRNA molecules from a single gene. Translation is a second amplification process, producing hundreds of protein molecules from a single mRNA molecule. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
4 FIGURE 27-3: Epigenetic modifications. A. Histones (green) are wrapped with DNA (purple) to form a structure that resembles beads on a string. Histone tails (black) are available sites for modification. B. Acetylation (red) by HATs (histone acetyltransferases) generates a more open chromatin conformation. C. Histone deacetylation by HDACs (histone deacetylases) generates a more closed chromatin conformation. D. Methylation marks (yellow) are present on CpG sites on DNA (purple.) E. Denovo methyltransferases add methyl groups to sites on a single strand of DNA where the sites have no corresponding methylated marks on the complementary strand. F. Maintenance methyltransferases add methyl groups when methylation is present on the complimentary strand. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
5 FIGURE 27-4: Serotonergic signaling can modulate glucocorticoid receptor (GR) expression. ERK activation occurs through serotonin binding. MSK phosphorylates CREB. Phosphorylated CREB recruits CBP, which associates with the exon 1 7 promoter of GR gene. cAMP and PKA are released via adenylate cyclase coupled to the serotonin receptor, resulting in NGFI-A expression. NGFI-A binding to the glucocorticoid receptor gene is enhanced by the CBP binding, resulting in enhanced GR expression. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
6 FIGURE 27-5: Structure of transcription factors from different families. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
7 FIGURE 27-6: ChIP and microarray analysis of transcription. The chromatin immunoprecipitation assay is depicted on the left-hand portion of this figure. Each of the steps leading to characterization of the DNA sequence associated with selected transcription factors is illustrated for the CREB transcription factor. On the right-hand portion of this figure is a schematic of one method for selecting putative CREB responsive genes. Brain tissues from a normal mouse and a CREB knockout (KO) mouse are dissected, RNA is isolated and probes are made from each tissue with the CREB+probe giving rise to red fluorescence while the KO probe gives rise to green fluorescence. When simultaneously hybridized to an array containing thousands of immobilized clones, any RNA that is more abundant in CREB-containing tissue would be RED; any RNA that is less abundant in CREB containing tissue (knockout mouse) would be GREEN; and those RNAs that are present in nearly equal abundances appear as the YELLOW overlapped signal. The RED fluorescing clones correspond to candidate genes whose transcription is stimulated by CREB, while those that are GREEN represent candidate genes whose transcription is inhibited by CREB. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
8 FIGURE 27-7: Immunohistochemical localization of type I corticosteroid receptor (mineralocorticoid receptor) in the rat hippocampus. A: Mineralocorticoid immunoreactivity is concentrated in pyramidal cell fields of the cornu ammons (CA2). B: High-power photomicrograph shows that steroid-bound mineralocorticoid receptors are primarily localized to neuronal cell nuclei. (Photomicrographs courtesy of Dr. James P. Herman, Department of Anatomy and Neurobiology, University of Kentucky.) Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
9 FIGURE 27-8: Activation of glucocorticoid receptors. Glucocorticoids (red) ( )diffuse across the plasma membrane and bind to the glucocorticoid receptor (dark orange). Upon glucocorticoid receptor binding to the steroid, the receptor undergoes a conformational change, which permits it to dissociate from the chaperone heat shock proteins (light orange circles). The activated glucocorticoid receptor translocates across the nuclear membrane and binds as a homo- or heterodimer to glucocorticoid response element sequences to regulate gene transcription. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
10 Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved. FIGURE 27-9: Activation of cAMP-regulated genes. When agonists ( ) bind to G protein-coupled receptors that activate dissociation of G s from the G s complex, G s will interact with the enzyme adenylyl cyclase, resulting in synthesis and increase of intracellular cAMP. cAMP binds to the regulatory subunits (orange ovals) of protein kinase A (PKA). This binding facilitates the dissociation of the catalytic subunits (dark orange spheres) from the PKA complex. The catalytic subunits then translocate across the nuclear membrane and phosphorylate cAMP response element–binding protein (CREB) and CREB-related proteins. Phosphorylated CREB increases gene transcription (right arrow).
11 Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved. FIGURE 27-10: Immunohistochemical localization of cAMP response element binding protein (CREB) in rat hippocampal neurons. Using a polyclonal antibody that recognizes both CREB and phospho-CREB protein, it is apparent that CREB protein is enriched in the nucleus of pyramidal cells of the CA1 region of the hippocampus. Scale bar is 30μm. (Photomicrograph courtesy of Dr. Stephen Ginsberg, Department of Pathology, University of Pennsylvania.)
12 Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved. FIGURE 27-11: Mechanism for generation of activators and repressors of cAMP-stimulated transcription. The cAMP response element binding protein (CREB) and the cAMP response element modulator (CREM) genes can give rise to alternatively spliced mRNAs, which give rise to distinct protein products. While CREB and CREM can stimulate CRE-mediated gene expression, generation of the α, β or forms of CREM will produce proteins that can heterodimerize with activated CREB and CREM subunits inhibiting their stimulatory capacity. The symbols used to highlight functional regions of CREB and CREM protein are Q for the polyglutamine tract, which stimulates transcription; D for the DNAbinding region; and Z for the leucine-zipper region, which is involved in dimerization.
13 Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved. FIGURE 27-12: Sox2 activity is regulated by cell- or tissuespecific binding partners. The binding of cofactors or binding partners significantly augments transcriptional activation by Sox2. The binding partner dimerizes with Sox2 and both of them bind the DNA. Each partner binds a unique DNA sequence, while the sequence specificity for Sox2 remains the same regardless of the binding partner. In this way the specificity and dynamic range of Sox2 activity is increased, such that, in different tissues Sox2 may activate transcription of different genes, as shown in the cartoon. In ES cells, Sox2 may dimerize with Oct to drive expression of Nanog. In contrast, in early neural tissue, Sox2 may dimerize with Pou to drive expression of Sox2 itself, while in retinal tissue Sox2 may dimerize with Pax6 to drive expression of dCry.
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