title: Opsin co-expression in Limulus photoreceptors: differential regulation by light and a circadian clock.
abstract: A long-standing concept in vision science has held that a single photoreceptor expresses a single type of opsin, the protein component of visual pigment. However, the number of examples in the literature of photoreceptors from vertebrates and invertebrates that break this rule is increasing. Here, we describe a newly discovered Limulus opsin, Limulus opsin5, which is significantly different from previously characterized Limulus opsins, opsins1 and 2. We show that opsin5 is co-expressed with opsins1 and 2 in Limulus lateral and ventral eye photoreceptors and provide the first evidence that the expression of co-expressed opsins can be differentially regulated. We show that the relative levels of opsin5 and opsin1 and 2 in the rhabdom change with a diurnal rhythm and that their relative levels are also influenced by the animal's central circadian clock. An analysis of the sequence of opsin5 suggests it is sensitive to visible light (400-700 nm) but that its spectral properties may be different from that of opsins1 and 2. Changes in the relative levels of these opsins may underlie some of the dramatic day-night changes in Limulus photoreceptor function and may produce a diurnal change in their spectral sensitivity.
authors.affiliation: Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St Augustine, FL 32080, USA.
authors.forename: C
authors.initials: C
authors.lastname: Katti
authors.forename: K
authors.initials: K
authors.lastname: Kempler
authors.forename: M L
authors.initials: ML
authors.lastname: Porter
authors.forename: A
authors.initials: A
authors.lastname: Legg
authors.forename: R
authors.initials: R
authors.lastname: Gonzalez
authors.forename: E
authors.initials: E
authors.lastname: Garcia-Rivera
authors.forename: D
authors.initials: D
authors.lastname: Dugger
authors.forename: B-A
authors.initials: BA
authors.lastname: Battelle
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D001683:Biological Clocks / Q000235:genetics / Q000528:radiation effects*; D002462:Cell Membrane / Q000378:metabolism / Q000528:radiation effects; D002940:Circadian Rhythm / Q000235:genetics / Q000528:radiation effects*; D004996:Ethidium / Q000378:metabolism; D005453:Fluorescence; D005629:Frozen Sections; D005786:Gene Expression Regulation / Q000528:radiation effects; D006737:Horseshoe Crabs / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects*; D008027:Light; D008163:Luminescent Measurements; D008969:Molecular Sequence Data; D055355:Opsins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D017956:Photoreceptor Cells, Invertebrate / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects; D010802:Phylogeny; D034443:RNA Transport / Q000528:radiation effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000528:radiation effects
chemical_list: D000906:Antibodies; D055355:Opsins; D012333:RNA, Messenger; D004996:Ethidium