title: Active gene repression by the Egr2.NAB complex during peripheral nerve myelination.
abstract: The Egr2/Krox20 transactivator is required for activation of many myelin-associated genes during peripheral nerve myelination by Schwann cells. However, recent work has indicated that Egr2 not only activates genes required for peripheral nerve myelination but may also be involved in gene repression. The NAB (NGFI-A/Egr-binding) corepressors interact with Egr2 and are required for proper coordination of myelin formation. Therefore, NAB proteins could mediate repression of some Egr2 target genes, although direct repression by Egr2 or NAB proteins during myelination has not been demonstrated. To define the physiological role of NAB corepression in gene repression by Egr2, we tested whether the Egr2.NAB complex directly repressed specific target genes. A screen for NAB-regulated genes identified several (including Id2, Id4, and Rad) that declined during the course of peripheral nerve myelination. In vivo chromatin immunoprecipitation analysis of the myelinating sciatic nerve was used to show developmental association of both Egr2 and NAB2 on the Id2, Id4, and Rad promoters as they were repressed during the myelination process. In addition, NAB2 represses transcription by interaction with the chromodomain helicase DNA-binding protein 4 (CHD4) subunit of the nucleosome remodeling and deacetylase chromatin remodeling complex, and we demonstrate that CHD4 occupies NAB-repressed promoters in a developmentally regulated manner in vivo. These results illustrate a novel aspect of genetic regulation of peripheral nerve myelination by showing that Egr2 directly represses genes during myelination in conjunction with NAB corepressors. Furthermore, repression of Id2 was found to augment activation of Mpz (myelin protein zero) expression.
authors.affiliation: Molecular and Cellular Pharmacology Training Program, Department of Comparative Biosciences, Graduate Program in Cellular and Molecular Biology, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Gennifer M
authors.initials: GM
authors.lastname: Mager
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Ward
authors.forename: Rajini
authors.initials: R
authors.lastname: Srinivasan
authors.forename: Sung-Wook
authors.initials: SW
authors.lastname: Jang
authors.forename: Lawrence
authors.initials: L
authors.lastname: Wrabetz
authors.forename: John
authors.initials: J
authors.lastname: Svaren
mesh_terms: D000818:Animals; D001324:Autoantigens / Q000737:chemistry; D002843:Chromatin / Q000378:metabolism; D004265:DNA Helicases / Q000737:chemistry; D051767:Early Growth Response Protein 2 / Q000378:metabolism*; D005786:Gene Expression Regulation; D051797:Inhibitor of Differentiation Protein 2 / Q000378:metabolism; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex; D051379:Mice; D009186:Myelin Sheath / Q000737:chemistry*; D010525:Peripheral Nerves / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D012097:Repressor Proteins / Q000378:metabolism*
chemical_list: D001324:Autoantigens; C115323:CHD4 protein, human; D002843:Chromatin; D051767:Early Growth Response Protein 2; C497327:Egr2 protein, mouse; C497328:Egr2 protein, rat; C497451:Id2 protein, rat; C497452:Idb2 protein, mouse; D051797:Inhibitor of Differentiation Protein 2; C490624:Nab1 protein, mouse; C490623:Nab1 protein, rat; D012097:Repressor Proteins; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex; D004265:DNA Helicases