title: Developmental and daily expression of the Pax4 and Pax6 homeobox genes in the rat retina: localization of Pax4 in photoreceptor cells.
abstract: Pax4 is a homeobox gene encoding Pax4, a transcription factor that is essential for embryonic development of the endocrine pancreas. In the pancreas, Pax4 counters the effects of the related transcription factor, Pax6, which is known to be essential for eye morphogenesis. In this study, we have discovered that Pax4 is strongly expressed in retinal photoreceptors of the rat. Pax4 expression is not detectable in the foetal eye; however, postnatal Pax4 transcript levels rapidly increase. In contrast, Pax6 exhibits an inverse developmental pattern of expression being more strongly expressed in the foetal eye. Histological analysis revealed that Pax4 mRNA is exclusively expressed in the retinal photoreceptors, whereas Pax6 mRNA and protein are present in the inner nuclear layer and in the ganglion cell layer of the mature retina. In the adult retina, Pax4 transcripts exhibit a diurnal rhythm with maximal levels occurring during the light period, whereas retinal Pax6 transcript levels do not change throughout the day. The daily changes in Pax4 expression may contribute to daily changes in function in the differentiated retinal photoreceptor.
authors.affiliation: Department of Neuroscience and Pharmacology, Panum Institute, University of Copenhagen, Copenhagen, Denmark. mrath@sund.ku.dk
authors.forename: Martin F
authors.initials: MF
authors.lastname: Rath
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Bailey
authors.forename: Jong-So
authors.initials: JS
authors.lastname: Kim
authors.forename: Steven L
authors.initials: SL
authors.lastname: Coon
authors.forename: David C
authors.initials: DC
authors.lastname: Klein
authors.forename: Morten
authors.initials: M
authors.lastname: Møller
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002940:Circadian Rhythm / Q000502:physiology*; D004622:Embryo, Mammalian; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D008297:Male; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism*; D010786:Photoreceptor Cells / Q000378:metabolism*; D011247:Pregnancy; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000033:anatomy & histology / Q000196:embryology / Q000254:growth & development / Q000378:metabolism
chemical_list: D005136:Eye Proteins; D018398:Homeodomain Proteins; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; C110218:Pax4 protein, mouse; C000605732:Pax6 protein, mouse; C000605733:Pax6 protein, rat; D012333:RNA, Messenger; D012097:Repressor Proteins