title: Activation of rhodopsin gene transcription in cultured retinal precursors of chicken embryo: role of Ca(2+) signaling and hyperpolarization-activated cation channels.
abstract: This study reports that the spontaneous 50-fold activation of rhodopsin gene transcription, observed in cultured retinal precursors from 13-day chicken embryo, relies on a Ca(2+)-dependent mechanism. Activation of a transiently transfected rhodopsin promoter (luciferase reporter) in these cells was inhibited (60%) by cotransfection of a dominant-negative form of the cAMP-responsive element-binding protein. Both rhodopsin promoter activity and rhodopsin mRNA accumulation were blocked by Ca(2+)/calmodulin-dependent kinase II inhibitors, but not by protein kinase A inhibitors, suggesting a role of Ca(2+) rather than cAMP. This was confirmed by the inhibitory effect of general and T-type selective Ca(2+) channel blockers. Oscillations in Ca(2+) fluorescence (Fluo8) could be observed in 1/10 cells that activated the rhodopsin promoter (DsRed reporter). A robust and reversible inhibition of rhodopsin gene transcription by ZD7288 indicated a role of hyperpolarization-activated channels (HCN). Cellular localization and developmental expression of HCN1 were compatible with a role in the onset of rhodopsin gene transcription. Together, the data suggest that the spontaneous activation of rhodopsin gene transcription in cultured retinal precursors results from a signaling cascade that involves the pacemaker activity of HCN channels, the opening of voltage-gated Ca(2+)-channels, activation of Ca(2+)/calmodulin-dependent kinase II and phosphorylation of cAMP-responsive element-binding protein. Rhodopsin gene expression in cultured retinal precursors from chicken embryo relies on a Ca2+-dependent mechanism whereby hyperpolarization-activated cyclic nucleotide-gated channels (HCN) activate T-type voltage-dependent Ca2+ channels (VDCC) through membrane depolarization, causing calmodulin-dependent kinase II (CaMKII) to phosphorylate the cAMP-responsive element-binding protein (CREB) and leading to activation of rhodopsin gene transcription. Photoreceptor localization and development of HCN1 channels suggest similar role in vivo.
authors.affiliation: Université de Poitiers, CNRS, Poitiers, France.
authors.forename: Marianne
authors.initials: M
authors.lastname: Bernard
authors.forename: Camille
authors.initials: C
authors.lastname: Dejos
authors.forename: Thierry
authors.initials: T
authors.lastname: Bergès
authors.forename: Matthieu
authors.initials: M
authors.lastname: Régnacq
authors.forename: Pierre
authors.initials: P
authors.lastname: Voisin
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels / Q000502:physiology*; D012160:Retina / Q000166:cytology / Q000196:embryology* / Q000378:metabolism*; D012243:Rhodopsin / Q000096:biosynthesis* / Q000235:genetics; D013234:Stem Cells / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology
chemical_list: D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D012243:Rhodopsin
keywords: calcium channels; hyperpolarization‐activated channels; photoreceptor; retina; rhodopsin; transcription