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Leyva-Díaz E, Masoudi N, Serrano-Saiz E, Glenwinkel L, Hobert O. Brn3/POU-IV-type POU homeobox genes-Paradigmatic regulators of neuronal identity across phylogeny. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2020; 9:e374. [PMID: 32012462 DOI: 10.1002/wdev.374] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2019] [Revised: 12/18/2019] [Accepted: 01/07/2020] [Indexed: 02/06/2023]
Abstract
One approach to understand the construction of complex systems is to investigate whether there are simple design principles that are commonly used in building such a system. In the context of nervous system development, one may ask whether the generation of its highly diverse sets of constituents, that is, distinct neuronal cell types, relies on genetic mechanisms that share specific common features. Specifically, are there common patterns in the function of regulatory genes across different neuron types and are those regulatory mechanisms not only used in different parts of one nervous system, but are they conserved across animal phylogeny? We address these questions here by focusing on one specific, highly conserved and well-studied regulatory factor, the POU homeodomain transcription factor UNC-86. Work over the last 30 years has revealed a common and paradigmatic theme of unc-86 function throughout most of the neuron types in which Caenorhabditis elegans unc-86 is expressed. Apart from its role in preventing lineage reiterations during development, UNC-86 operates in combination with distinct partner proteins to initiate and maintain terminal differentiation programs, by coregulating a vast array of functionally distinct identity determinants of specific neuron types. Mouse orthologs of unc-86, the Brn3 genes, have been shown to fulfill a similar function in initiating and maintaining neuronal identity in specific parts of the mouse brain and similar functions appear to be carried out by the sole Drosophila ortholog, Acj6. The terminal selector function of UNC-86 in many different neuron types provides a paradigm for neuronal identity regulation across phylogeny. This article is categorized under: Gene Expression and Transcriptional Hierarchies > Regulatory Mechanisms Invertebrate Organogenesis > Worms Nervous System Development > Vertebrates: Regional Development.
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Affiliation(s)
- Eduardo Leyva-Díaz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York
| | - Neda Masoudi
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York
| | | | - Lori Glenwinkel
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York
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2
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Jafari S, Alkhori L, Schleiffer A, Brochtrup A, Hummel T, Alenius M. Combinatorial activation and repression by seven transcription factors specify Drosophila odorant receptor expression. PLoS Biol 2012; 10:e1001280. [PMID: 22427741 PMCID: PMC3302810 DOI: 10.1371/journal.pbio.1001280] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Accepted: 01/26/2012] [Indexed: 01/22/2023] Open
Abstract
The mechanism that specifies olfactory sensory neurons to express only one odorant receptor (OR) from a large repertoire is critical for odor discrimination but poorly understood. Here, we describe the first comprehensive analysis of OR expression regulation in Drosophila. A systematic, RNAi-mediated knock down of most of the predicted transcription factors identified an essential function of acj6, E93, Fer1, onecut, sim, xbp1, and zf30c in the regulation of more than 30 ORs. These regulatory factors are differentially expressed in antennal sensory neuron classes and specifically required for the adult expression of ORs. A systematic analysis reveals not only that combinations of these seven factors are necessary for receptor gene expression but also a prominent role for transcriptional repression in preventing ectopic receptor expression. Such regulation is supported by bioinformatics and OR promoter analyses, which uncovered a common promoter structure with distal repressive and proximal activating regions. Thus, our data provide insight into how combinatorial activation and repression can allow a small number of transcription factors to specify a large repertoire of neuron classes in the olfactory system.
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Affiliation(s)
- Shadi Jafari
- Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
| | - Liza Alkhori
- Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
| | | | - Anna Brochtrup
- Department of Neurobiology, University of Vienna, Vienna, Austria
| | - Thomas Hummel
- Department of Neurobiology, University of Vienna, Vienna, Austria
| | - Mattias Alenius
- Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
- * E-mail:
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3
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Trieu M, Ma A, Eng SR, Fedtsova N, Turner EE. Direct autoregulation and gene dosage compensation by POU-domain transcription factor Brn3a. Development 2003; 130:111-21. [PMID: 12441296 DOI: 10.1242/dev.00194] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Brn3a is a POU-domain transcription factor expressed in peripheral sensory neurons and in specific interneurons of the caudal CNS. Sensory expression of Brn3a is regulated by a specific upstream enhancer, the activity of which is greatly increased in Brn3a knockout mice, implying that Brn3a negatively regulates its own expression. Brn3a binds to highly conserved sites within this enhancer, and alteration of these sites abolishes Brn3a regulation of reporter transgenes. Furthermore, endogenous Brn3a expression levels in the sensory ganglia of Brn3a(+/+) and Brn3a(+/-) mice are similar, demonstrating that autoregulation can compensate for the loss of one allele by increasing transcription of the remaining gene copy. Conversely, transgenic overexpression of Brn3a in the trigeminal ganglion suppresses the expression of the endogenous gene. These findings demonstrate that the Brn3a locus functions as a self-regulating unit to maintain a constant expression level of this key regulator of neural development.
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MESH Headings
- Animals
- Animals, Newborn
- Base Sequence
- Central Nervous System/cytology
- Central Nervous System/embryology
- Central Nervous System/metabolism
- Cloning, Molecular
- Conserved Sequence
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/metabolism
- Enhancer Elements, Genetic
- Ganglia, Sensory/cytology
- Ganglia, Sensory/embryology
- Ganglia, Sensory/metabolism
- Gene Dosage
- Gene Expression Regulation, Developmental
- Homeostasis
- Humans
- Mice
- Mice, Knockout
- Mice, Transgenic
- Molecular Sequence Data
- Neurons, Afferent/physiology
- Protein Structure, Tertiary
- Transcription Factor Brn-3
- Transcription Factor Brn-3A
- Transcription Factors/genetics
- Transcription Factors/metabolism
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Affiliation(s)
- May Trieu
- Department of Psychiatry, University of California, San Diego and San Diego VA Medical Center, La Jolla, CA 92093-0603, USA
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4
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Abnormal chemosensory jump 6 is a positive transcriptional regulator of the cholinergic gene locus in Drosophila olfactory neurons. J Neurosci 2002. [PMID: 12097480 DOI: 10.1523/jneurosci.22-13-05291.2002] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Cholinergic neurons acquire their neurotransmitter phenotype, in part, by expressing the cholinergic gene locus. Previous studies have indicated that the 5' flanking DNA of the locus contains both positive and negative regulatory elements important for expression in different subsets of cholinergic neurons in Drosophila and other animals. Approximately 300 bases of proximal 5' flanking DNA control expression in Drosophila CNS neurons essential for viability, whereas more distal regulatory elements are important for expression in PNS sensory neurons. In this study we identify the POU domain transcription factor abnormal chemosensory jump 6 (Acj6) as a necessary positive transcriptional regulator for cholinergic locus expression in primary olfactory neurons. Choline acetyltransferase enzyme activity, protein levels, mRNA, and a fluorescent cholinergic reporter gene are all decreased in olfactory neurons of acj6 mutants. Decreased cholinergic expression was observed in both adults and larvae. The presence of a specific Acj6 binding site has been identified in the cholinergic locus 5' flanking DNA, suggesting that Acj6 may play a direct role in specifying the cholinergic neurotransmitter phenotype of most olfactory neurons. Transgenic expression of two different isoforms of Acj6 restricted to olfactory neurons indicates that additional trans factors may be required for cholinergic locus expression. Transgenic expression in all cholinergic neurons, however, results in lethality when a POU IV box element is absent but is essentially benign when present, indicating the importance of this motif in specifying different functional roles for Acj6.
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Liu W, Khare SL, Liang X, Peters MA, Liu X, Cepko CL, Xiang M. All Brn3 genes can promote retinal ganglion cell differentiation in the chick. Development 2000; 127:3237-47. [PMID: 10887080 DOI: 10.1242/dev.127.15.3237] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Targeted gene disruption studies in the mouse have demonstrated crucial roles for the Brn3 POU domain transcription factor genes, Brn3a, Brn3b, Brn3c (now called Pou4f1, Pou4f2, Pou4f3, respectively) in sensorineural development and survival. During mouse retinogenesis, the Brn3b gene is expressed in a large set of postmitotic ganglion cell precursors and is required for their early and terminal differentiation. In contrast, the Brn3a and Brn3c genes, which are expressed later in ganglion cells, appear to be dispensable for ganglion cell development. To understand the mechanism that causes the functional differences of Brn3 genes in retinal development, we employed a gain-of-function approach in the chick embryo. We find that Brn3b(l) and Brn3b(s), the two isoforms encoded by the Brn3b gene, as well as Brn3a and Brn3c all have similar DNA-binding and transactivating activities. We further find that the POU domain is minimally required for these activities. Consequently, we show that all these Brn3 proteins have a similar ability to promote development of ganglion cells when ectopically expressed in retinal progenitors. During chick retinogenesis, cBrn3c instead of cBrn3b exhibits a spatial and temporal expression pattern characteristic of ganglion cell genesis and its misexpression can also increase ganglion cell production. Based on these data, we propose that all Brn3 factors are capable of promoting retinal ganglion cell development, and that this potential may be limited by the order of expression in vivo.
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Affiliation(s)
- W Liu
- Graduate Program in Molecular Genetics and Microbiology, Center for Advanced Biotechnology and Medicine, UMDNJ-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
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6
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Certel SJ, Clyne PJ, Carlson JR, Johnson WA. Regulation of central neuron synaptic targeting by the Drosophila POU protein, Acj6. Development 2000; 127:2395-405. [PMID: 10804181 DOI: 10.1242/dev.127.11.2395] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Mutations in the Drosophila class IV POU domain gene, abnormal chemosensory jump 6 (acj6), have previously been shown to cause physiological deficits in odor sensitivity. However, loss of Acj6 function also has a severe detrimental effect upon coordinated larval and adult movement that cannot be explained by the simple loss in odorant detection. In addition to olfactory sensory neurons, Acj6 is expressed in a distinct subset of postmitotic interneurons in the central nervous system from late embryonic to adult stages. In the larval and adult brain, Acj6 is highly expressed in central brain, optic and antennal lobe neurons. Loss of Acj6 function in larval optic lobe neurons results in disorganized retinal axon targeting and synapse selection. Furthermore, the lamina neurons themselves exhibit disorganized synaptic arbors in the medulla of acj6 mutant pupal brains, suggesting that Acj6 may play a role in regulating synaptic connections or structure. To further test this hypothesis, we misexpressed two Acj6 isoforms in motor neurons where they are not normally found. The two Acj6 isoforms are produced from alternatively spliced acj6 transcripts, resulting in significant structural differences in the amino-terminal POU IV box. Acj6 misexpression caused marked alterations at the neuromuscular junction, with contrasting effects upon nerve terminal branching and synapse formation associated with specific Acj6 isoforms. Our results suggest that the class IV POU domain factor, Acj6, may play an important role in regulating synaptic target selection by central neurons and that the amino-terminal POU IV box is important for regulation of Acj6 activity.
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Affiliation(s)
- S J Certel
- Department of Physiology and Biophysics, University of Iowa, Iowa City, IA, USA
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Zelzer E, Shilo BZ. Interaction between the bHLH-PAS protein Trachealess and the POU-domain protein Drifter, specifies tracheal cell fates. Mech Dev 2000; 91:163-73. [PMID: 10704841 DOI: 10.1016/s0925-4773(99)00295-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
bHLH-PAS proteins represent a class of transcription factors involved in diverse biological activities. Previous experiments demonstrated that the PAS domain confers target specificity (Zelzer et al., 1997. Genes Dev. 11, 2079-2089). This suggested an association between the PAS domain and additional DNA-binding proteins, which is essential for the induction of specific target genes. A candidate for interaction with Trh is Drifter/Ventral veinless, a POU-domain protein. A dual requirement for Trh and Drifter was identified for the autoregulation of Trh and Drifter expression. Furthermore, ectopic expression of both Trh and Dfr (but not each one alone) triggered trh autoregulation in several embryonic tissues. A direct interaction between Drifter and Trh proteins, mediated by the PAS domain of Trh and the POU domain of Drifter, was demonstrated.
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Affiliation(s)
- E Zelzer
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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Rhee JM, Gruber CA, Brodie TB, Trieu M, Turner EE. Highly cooperative homodimerization is a conserved property of neural POU proteins. J Biol Chem 1998; 273:34196-205. [PMID: 9852081 DOI: 10.1074/jbc.273.51.34196] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
POU-domain proteins have been shown to play important roles in the development of the nervous, endocrine, and immune systems. However, the distinctive DNA recognition properties of the six major POU subclasses have not been well defined. Here, we have used random oligonucleotide selection and competitive binding assays to determine the optimal DNA recognition elements for the POU-III and POU-VI protein classes, represented by Brn-2 and Brn-5, respectively. The optimal Brn-5 consensus binding sequence GCATAA(T/A)TTAT strongly resembles that previously determined for the POU-IV (Brn-3) class, whereas Brn-2 exhibits highest affinity for non-octamer sites of the form ATG(A/C)AT(A/T)0-2ATTNAT and for octamer sites that contain a full associated heptamer sequence. Brn-2, Brn-3.0, and their invertebrate homologues all exhibit highly cooperative homodimerization on the Brn-2 consensus sequence, demonstrating that cooperative dimerization is a general property of these neural POU proteins. However, modified sites to which Brn-2 binds only as a monomer mediate the transcriptional effects of Brn-2 better than the consensus sequence, demonstrating that dimerization on these sites diminishes the transactivation ability of the protein. Together with the findings of our prior studies these data greatly facilitate the identification of functional POU recognition elements in the regulatory regions of neural genes.
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Affiliation(s)
- J M Rhee
- Department of Psychiatry, University of California, San Diego, La Jolla, California 92093-0603, USA
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9
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Muñoz-Mármol AM, Casali A, Miralles A, Bueno D, Bayascas JR, Romero R, Saló E. Characterization of platyhelminth POU domain genes: ubiquitous and specific anterior nerve cell expression of different epitopes of GtPOU-1. Mech Dev 1998; 76:127-40. [PMID: 9767147 DOI: 10.1016/s0925-4773(98)00113-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
POU domain proteins are a large family of transcription factors that have been identified in a variety of metazoans, from freshwater sponges, planarians and nematodes to arthropods, echinoderms and vertebrates. Many of these proteins are implicated in the development and establishment of the nervous system. In this paper we describe the identification of the planarian genes GtPOU-1, GtPOU-3 and GtPOU-4, which belong to the subclasses III and IV of POU-domain genes. Their similarity with other members of the POU family is restricted to the POU and homeo domains, plus some peptide sequences scattered in the linker and flanking regions. As with other subclass III POU genes, GtPOU-1 is devoid of introns. Axial transcript distribution by RT-PCR and immunohistochemical assays, performed with a polyclonal antibody raised against the GtPOU-1 fusion protein, indicate that both the GtPOU-1 transcript and protein are continuously expressed along the antero-posterior axis. A monoclonal antibody raised against the same fusion protein indicates that a GtPOU-1-specific epitope, probably obtained by post-translational modification, is present in neural cells from both the central and peripheral nerve systems of the adult planarian's anterior third. Moreover, the GtPOU-1-specific epitope shows a dynamic expression pattern during regeneration, always marking the most anterior region of the planarian nervous system. Both the rapid and general GtPOU-1-specific epitope modification, during posterior regeneration, indicate that regeneration is a global process involving all planarian regions, including those that are far from the wound, by a combination of morphallactic and epimorphic mechanisms.
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Affiliation(s)
- A M Muñoz-Mármol
- Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08071, Barcelona, Spain
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10
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Xiang M, Gan L, Li D, Chen ZY, Zhou L, O'Malley BW, Klein W, Nathans J. Essential role of POU-domain factor Brn-3c in auditory and vestibular hair cell development. Proc Natl Acad Sci U S A 1997; 94:9445-50. [PMID: 9256502 PMCID: PMC23217 DOI: 10.1073/pnas.94.17.9445] [Citation(s) in RCA: 251] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The Brn-3 subfamily of POU-domain transcription factor genes consists of three highly homologous members-Brn-3a, Brn-3b, and Brn-3c-that are expressed in sensory neurons and in a small number of brainstem nuclei. This paper describes the role of Brn-3c in auditory and vestibular system development. In the inner ear, the Brn-3c protein is found only in auditory and vestibular hair cells, and the Brn-3a and Brn-3b proteins are found only in subsets of spiral and vestibular ganglion neurons. Mice carrying a targeted deletion of the Brn-3c gene are deaf and have impaired balance. These defects reflect a complete loss of auditory and vestibular hair cells during the late embryonic and early postnatal period and a secondary loss of spiral and vestibular ganglion neurons. Together with earlier work demonstrating a loss of trigeminal ganglion neurons and retinal ganglion cells in mice carrying targeted disruptions in the Brn-3a and Brn-3b genes, respectively, the Brn-3c phenotype reported here demonstrates that each of the Brn-3 genes plays distinctive roles in the somatosensory, visual, and auditory/vestibular systems.
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Affiliation(s)
- M Xiang
- Center for Advanced Biotechnology and Medicine, Department of Pediatrics, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
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Terunuma A, Shiba K, Noda T. A novel genetic system to isolate a dominant negative effector on DNA-binding activity of Oct-2. Nucleic Acids Res 1997; 25:1984-90. [PMID: 9115366 PMCID: PMC146677 DOI: 10.1093/nar/25.10.1984] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Recent studies have revealed that interactions between transcription factors play an important role in regulation of gene expression in eukaryotic cells. To isolate cDNA clones that dominantly inhibit the DNA-binding activity of Oct-2, chosen as a representative factor, we have developed a novel screening system. This employs an Escherichia coli tester strain carrying a modified lac operon as a reporter gene, with the lac operator sequence replaced by an octamer sequence. Oct-2 expressed in this tester strain represses the expression of the reporter gene and changes the phenotype of the cell from Lac+to Lac-. Introduction of a cDNA expression library prepared from a human T-cell line into the Oct-2-harboring tester strain allowed selection of three Lac+clones out of 1 x 10(5) transformants. One of them, hT86, encoding a putative zinc finger protein was found to derepress beta-galactosidase activity in the Oct-2-harboring tester strain at the transcriptional level. In gel mobility shift assays, hT86 attenuated the intensity of the retarded band composed of the octamer probe and Oct-2, suggesting a dominant negative effect on the DNA-binding activity of Oct-2. The strategy described here provides a new approach for studying protein-protein interactions that govern the complex regulation of gene expression.
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Affiliation(s)
- A Terunuma
- Department of Cell Biology, The Cancer Institute, Japanese Foundation for Cancer Research, Kami-Ikebukuro, Toshima-ku, Tokyo 170, Japan
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Gruber CA, Rhee JM, Gleiberman A, Turner EE. POU domain factors of the Brn-3 class recognize functional DNA elements which are distinctive, symmetrical, and highly conserved in evolution. Mol Cell Biol 1997; 17:2391-400. [PMID: 9111308 PMCID: PMC232088 DOI: 10.1128/mcb.17.5.2391] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
To better understand the diversity of function within the POU domain class of transcriptional regulators, we have determined the optimal DNA recognition site of several proteins of the POU-IV (Brn-3) subclass by random oligonucleotide selection. The consensus recognition element derived in this study, ATAATTAAT, is clearly distinct from octamer sites described for the POU factor Oct-1. The optimal POU-IV site determined here also binds Brn-3.0 with significantly higher affinity than consensus recognition sites previously proposed for this POU subclass. The binding affinity of Brn-3.0 on its optimal site, several variants of this site, and several naturally occurring POU recognition elements is highly correlated with the activation of reporter gene expression by Brn-3.0 in transfection assays. The preferred DNA recognition site of Brn-3.0 resembles strongly the optimal sites of another mammalian POU-IV class protein, Brn-3.2, and of the Caenorhabditis elegans Brn-3.0 homolog Unc-86, demonstrating that the site-specific DNA recognition properties of these factors are highly conserved between widely divergent species.
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Affiliation(s)
- C A Gruber
- Department of Psychiatry, University of California, San Diego, La Jolla, USA
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