title: Opsin Repertoire and Expression Patterns in Horseshoe Crabs: Evidence from the Genome of Limulus polyphemus (Arthropoda: Chelicerata).
abstract: Horseshoe crabs are xiphosuran chelicerates, the sister group to arachnids. As such, they are important for understanding the most recent common ancestor of Euchelicerata and the evolution and diversification of Arthropoda. Limulus polyphemus is the most investigated of the four extant species of horseshoe crabs, and the structure and function of its visual system have long been a major focus of studies critical for understanding the evolution of visual systems in arthropods. Likewise, studies of genes encoding Limulus opsins, the protein component of the visual pigments, are critical for understanding opsin evolution and diversification among chelicerates, where knowledge of opsins is limited, and more broadly among arthropods. In the present study, we sequenced and assembled a high quality nuclear genomic sequence of L. polyphemus and used these data to annotate the full repertoire of Limulus opsins. We conducted a detailed phylogenetic analysis of Limulus opsins, including using gene structure and synteny information to identify relationships among different opsin classes. We used our phylogeny to identify significant genomic events that shaped opsin evolution and therefore the visual system of Limulus We also describe the tissue expression patterns of the 18 opsins identified and show that transcripts encoding a number, including a peropsin, are present throughout the central nervous system. In addition to significantly extending our understanding of photosensitivity in Limulus and providing critical insight into the genomic evolution of horseshoe crab opsins, this work provides a valuable genomic resource for addressing myriad questions related to xiphosuran physiology and arthropod evolution.
authors.affiliation: Whitney Laboratory for Marine Bioscience, Departments of Neuroscience and Biology, University of Florida battelle@whitney.ufl.edu.
authors.forename: Barbara-Anne
authors.initials: BA
authors.lastname: Battelle
authors.affiliation: Whitney Laboratory for Marine Bioscience, Department of Biology, University of Florida.
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Ryan
authors.affiliation: Whitney Laboratory for Marine Bioscience, Departments of Neuroscience and Biology, University of Florida.
authors.forename: Karen E
authors.initials: KE
authors.lastname: Kempler
authors.affiliation: Whitney Laboratory for Marine Bioscience, Departments of Neuroscience and Biology, University of Florida Present address: School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY.
authors.forename: Spencer R
authors.initials: SR
authors.lastname: Saraf
authors.affiliation: Whitney Laboratory for Marine Bioscience, Departments of Neuroscience and Biology, University of Florida Present address: Department of Molecular Genetics and Microbiology, College of Medicine, University of Florida, Gainesville, FL.
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Marten
authors.affiliation: McDonnell Genome Institute, Washington University School of Medicine in St. Louis.
authors.forename: Wesley C
authors.initials: WC
authors.lastname: Warren
authors.affiliation: McDonnell Genome Institute, Washington University School of Medicine in St. Louis.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Minx
authors.affiliation: McDonnell Genome Institute, Washington University School of Medicine in St. Louis.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Montague
authors.affiliation: Department of Plant and Soil Sciences, School of Marine Science and Policy, Delaware Biotechnology Institute, University of Delaware.
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: Green
authors.affiliation: Department of Plant and Soil Sciences, School of Marine Science and Policy, Delaware Biotechnology Institute, University of Delaware.
authors.forename: Skye A
authors.initials: SA
authors.lastname: Schmidt
authors.affiliation: McDonnell Genome Institute, Washington University School of Medicine in St. Louis.
authors.forename: Lucinda
authors.initials: L
authors.lastname: Fulton
authors.affiliation: Department of Molecular Cell Biology, Center for Integrative Genomics, University of California, Berkley.
authors.forename: Nipam H
authors.initials: NH
authors.lastname: Patel
authors.affiliation: Department of Molecular Cell Biology, Center for Integrative Genomics, University of California, Berkley Present address: Department of Natural Sciences and Mathematics, Dominican University of California, San Rafael, CA.
authors.forename: Meredith E
authors.initials: ME
authors.lastname: Protas
authors.affiliation: McDonnell Genome Institute, Washington University School of Medicine in St. Louis.
authors.forename: Richard K
authors.initials: RK
authors.lastname: Wilson
authors.affiliation: Department of Biology, University of Hawaii, Manoa.
authors.forename: Megan L
authors.initials: ML
authors.lastname: Porter
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019143:Evolution, Molecular; D005123:Eye / Q000378:metabolism; D016678:Genome; D006737:Horseshoe Crabs / Q000235:genetics*; D005810:Multigene Family / Q000235:genetics; D055355:Opsins / Q000145:classification / Q000235:genetics*; D010802:Phylogeny
chemical_list: D055355:Opsins
keywords: Limulus polyphemus; evolution; opsin; photoreceptors; xiphosuran