title: High opsin diversity in a non-visual infaunal brittle star.
abstract: BACKGROUND
  In metazoans, opsins are photosensitive proteins involved in both vision and non-visual photoreception. Echinoderms have no well-defined eyes but several opsin genes were found in the purple sea urchin (Strongylocentrotus purpuratus) genome. Molecular data are lacking for other echinoderm classes although many species are known to be light sensitive.
  
  
  RESULTS
  In this study focused on the European brittle star Amphiura filiformis, we first highlighted a blue-green light sensitivity using a behavioural approach. We then identified 13 new putative opsin genes against eight bona fide opsin genes in the genome of S. purpuratus. Six opsins were included in the rhabdomeric opsin group (r-opsins). In addition, one putative ciliary opsin (c-opsin), showing high similarity with the c-opsin of S. purpuratus (Sp-opsin 1), one Go opsin similar to Sp-opsins 3.1 and 3.2, two basal-branch opsins similar to Sp-opsins 2 and 5, and two neuropsins similar to Sp-opsin 8, were identified. Finally, two sequences from one putative RGR opsin similar to Sp-opsin 7 were also detected. Adult arm transcriptome analysis pinpointed opsin mRNAs corresponding to one r-opsin, one neuropsin and the homologue of Sp-opsin 2. Opsin phylogeny was determined by maximum likelihood and Bayesian analyses. Using antibodies designed against c- and r-opsins from S. purpuratus, we detected putative photoreceptor cells mainly in spines and tube feet of A. filiformis, respectively. The r-opsin expression pattern is similar to the one reported in S. purpuratus with cells labelled at the tip and at the base of the tube feet. In addition, r-opsin positive cells were also identified in the radial nerve of the arm. C-opsins positive cells, expressed in pedicellariae, spines, tube feet and epidermis in S. purpuratus were observed at the level of the spine stroma in the brittle star.
  
  
  CONCLUSIONS
  Light perception in A. filiformis seems to be mediated by opsins (c- and r-) in, at least, spines, tube feet and in the radial nerve cord. Other non-visual opsin types could participate to the light perception process indicating a complex expression pattern of opsins in this infaunal brittle star.
authors.affiliation: Biology of Marine Organisms and Biomimetics, Research Institute for Biosciences, University of Mons, Avenue du Champs de Mars 6, 7000 Mons, Belgium. jerome.delroisse@umons.ac.be.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Delroisse
authors.forename: Esther
authors.initials: E
authors.lastname: Ullrich-Lüter
authors.forename: Olga
authors.initials: O
authors.lastname: Ortega-Martinez
authors.forename: Sam
authors.initials: S
authors.lastname: Dupont
authors.forename: Maria-Ina
authors.initials: MI
authors.lastname: Arnone
authors.forename: Jérôme
authors.initials: J
authors.lastname: Mallefet
authors.forename: Patrick
authors.initials: P
authors.lastname: Flammang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001522:Behavior, Animal; D015870:Gene Expression; D014644:Genetic Variation; D023281:Genomics; D008969:Molecular Sequence Data; D055355:Opsins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny
chemical_list: D055355:Opsins