title: A null mutation in guanylate cyclase-1 alters the temporal dynamics and light entrainment properties of the iodopsin rhythm in cone photoreceptor cells.
abstract: Guanylate cyclase-1 (GC1) plays a critical role in visual phototransduction and its absence severely compromises the ability of the photoreceptor cells to transduce light for vision. In this study we sought to determine if the absence of GC1 has any effect on light entrainment of the circadian oscillators located in these cells. We compared the rhythmic changes in transcript levels of iodopsin, a photoreceptor-specific gene whose expression is regulated by circadian oscillators, in retinas of normal chickens and GUCY1*B (*B) chickens that carry a null mutation in GC1. Our results show that iodopsin rhythms are present in *B retinas and that they can be entrained to light; however, the rise and fall of iodopsin transcript levels in *B retina under cyclic light conditions is significantly more rapid than that observed in normal retina, and under constant dark conditions, the phase of the iodopsin rhythm in *B retina is advanced by 6 h relative to that observed in normal retina. In addition, the rate of entrainment of the iodopsin rhythm in *B retina to a reversal of the light cycle is significantly slower than normal. The results of our study show that a functioning visual phototransduction cascade is not essential for light entrainment of the oscillators that drive the iodopsin rhythm in photoreceptor cells. We propose that the abnormal synthesis of cGMP in *B photoreceptors underlies the irregular iodopsin rhythms observed in post-hatch *B retina.
authors.affiliation: Department of Neuroscience, McKnight Brain Institute, University of Florida, 100 S. Newell Dr., Gainesville, FL 32610-0244, USA.
authors.forename: P
authors.initials: P
authors.lastname: Larkin
authors.forename: S L
authors.initials: SL
authors.lastname: Semple-Rowland
mesh_terms: D000818:Animals; D002645:Chickens; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D006152:Cyclic GMP / Q000502:physiology; D003624:Darkness; D005136:Eye Proteins / Q000235:genetics* / Q000502:physiology; D005786:Gene Expression Regulation / Q000528:radiation effects*; D006162:Guanylate Cyclase / Q000235:genetics* / Q000502:physiology; D008027:Light; D009154:Mutation; D011956:Receptors, Cell Surface; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D012168:Retinal Pigments / Q000096:biosynthesis* / Q000235:genetics; D017299:Rod Opsins; D014158:Transcription, Genetic
chemical_list: D005136:Eye Proteins; D011956:Receptors, Cell Surface; D012168:Retinal Pigments; D017299:Rod Opsins; C110715:guanylate cyclase 1; C034941:iodopsin; D006162:Guanylate Cyclase; D006152:Cyclic GMP