title: Diurnal rhythm of the chromatin protein Hmgb1 in rat photoreceptors is under circadian regulation.
abstract: Hmgb1 belongs to a family of structure-specific DNA binding proteins with DNA chaperone-like properties that mediate chromatin remodeling in a wide range of nuclear processes including regulation of transcription, DNA repair, genome stability, and stress response. A diurnal oscillation of Hmgb1 at the protein level occurs in rat retinal photoreceptor cells and to a lesser extent in bipolar neurons. Expression of Hmgb1 was least at night at Zeitgeber time (ZT) 18 and maximal in the middle of the lights-on period (ZT6). Since rhythmic expression of Hmgb1 protein in photoreceptors continued in complete darkness, it is likely under control of a circadian clock. Within photoreceptor nuclei, Hmgb1 colocalized with acetylated histone H3, a marker of euchromatin. Outside the nucleus a distinct smaller-sized isoform of Hmgb1 was present in photoreceptor inner segments and bound to a membrane fraction with characteristics of endoplasmic reticulum membranes. The rhythmic expression of Hmgb1 protein may underlie the circadian change in chromatin remodeling in addition to histone acetylation.
authors.affiliation: Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA. hoppeg@ccf.org
authors.forename: George
authors.initials: G
authors.lastname: Hoppe
authors.forename: Mary E
authors.initials: ME
authors.lastname: Rayborn
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Sears
mesh_terms: D000368:Aged; D000818:Animals; D002940:Circadian Rhythm; D022041:Euchromatin / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D024243:HMGB1 Protein / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008875:Middle Aged; D010786:Photoreceptor Cells / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D020318:Rats, Long-Evans; D012160:Retina / Q000166:cytology
chemical_list: D022041:Euchromatin; D024243:HMGB1 Protein