title: Circadian dynamics of the cone-rod homeobox (CRX) transcription factor in the rat pineal gland and its role in regulation of arylalkylamine N-acetyltransferase (AANAT).
abstract: The cone-rod homeobox (Crx) gene encodes a transcription factor in the retina and pineal gland. Crx deficiency influences the pineal transcriptome, including a reduced expression of arylalkylamine N-acetyltransferase (Aanat), a key enzyme in nocturnal pineal melatonin production. However, previous functional studies on pineal Crx have been performed in melatonin-deficient mice. In this study, we have investigated the role of Crx in the melatonin-proficient rat pineal gland. The current study shows that pineal Crx transcript levels exhibit a circadian rhythm with a peak in the middle of the night, which is transferred into daily changes in CRX protein. The study further shows that the sympathetic innervation of the pineal gland controls the Crx rhythm. By use of adenovirus-mediated short hairpin RNA gene knockdown targeting Crx mRNA in primary rat pinealocyte cell culture, we here show that intact levels of Crx mRNA are required to obtain high levels of Aanat expression, whereas overexpression of Crx induces Aanat transcription in vitro. This regulatory function of Crx is further supported by circadian analysis of Aanat in the pineal gland of the Crx-knockout mouse. Our data indicate that the rhythmic nature of pineal CRX protein may directly modulate the daily profile of Aanat expression by inducing nighttime expression of this enzyme, thus facilitating nocturnal melatonin synthesis in addition to its role in ensuring a correct tissue distribution of Aanat expression.
authors.affiliation: Department of Neuroscience and Pharmacology (K.R., L.R., M.M., M.F.R.), Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; and Department of Physiology (K.R., A.K.H.), Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
authors.forename: Kristian
authors.initials: K
authors.lastname: Rohde
authors.forename: Louise
authors.initials: L
authors.lastname: Rovsing
authors.forename: Anthony K
authors.initials: AK
authors.lastname: Ho
authors.forename: Morten
authors.initials: M
authors.lastname: Møller
authors.forename: Martin F
authors.initials: MF
authors.lastname: Rath
mesh_terms: D000818:Animals; D047068:Arylalkylamine N-Acetyltransferase / Q000378:metabolism*; D002478:Cells, Cultured; D002940:Circadian Rhythm; D018398:Homeodomain Proteins / Q000378:metabolism*; D008297:Male; D008550:Melatonin / Q000096:biosynthesis; D051379:Mice; D018345:Mice, Knockout; D051857:Otx Transcription Factors / Q000378:metabolism; D010870:Pineal Gland / Q000201:enzymology / Q000294:innervation / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015534:Trans-Activators / Q000378:metabolism*
chemical_list: D018398:Homeodomain Proteins; D051857:Otx Transcription Factors; D015534:Trans-Activators; C109288:cone rod homeobox protein; C520223:Aanat protein, rat; D047068:Arylalkylamine N-Acetyltransferase; D008550:Melatonin