title: Developmental dynamics of cone photoreceptors in the eel.
abstract: BACKGROUND
  Many fish alter their expressed visual pigments during development. The number of retinal opsins expressed and their type is normally related to the environment in which they live. Eels are known to change the expression of their rod opsins as they mature, but might they also change the expression of their cone opsins?
  
  
  RESULTS
  The Rh2 and Sws2 opsin sequences from the European Eel were isolated, sequenced and expressed in vitro for an accurate measurement of their lambdamax values. In situ hybridisation revealed that glass eels express only rh2 opsin in their cone photoreceptors, while larger yellow eels continue to express rh2 opsin in the majority of their cones, but also have <5% of cones which express sws2 opsin. Silver eels showed the same expression pattern as the larger yellow eels. This observation was confirmed by qPCR (quantitative polymerase chain reaction).
  
  
  CONCLUSIONS
  Larger yellow and silver European eels express two different cone opsins, rh2 and sws2. This work demonstrates that only the Rh2 cone opsin is present in younger fish (smaller yellow and glass), the sws2 opsin being expressed additionally only by older fish and only in <5% of cone cells.
authors.affiliation: UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL, UK. p.cottrill@ucl.ac.uk
authors.forename: Phillippa B
authors.initials: PB
authors.lastname: Cottrill
authors.forename: Wayne L
authors.initials: WL
authors.lastname: Davies
authors.forename: Ma'ayan
authors.initials: M
authors.lastname: Semo
authors.forename: James K
authors.initials: JK
authors.lastname: Bowmaker
authors.forename: David M
authors.initials: DM
authors.lastname: Hunt
authors.forename: Glen
authors.initials: G
authors.lastname: Jeffery
mesh_terms: D000818:Animals; D055358:Cone Opsins / Q000235:genetics / Q000378:metabolism*; D004524:Eels / Q000196:embryology* / Q000235:genetics; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D020419:Photoreceptor Cells, Vertebrate; D010802:Phylogeny; D012160:Retina / Q000196:embryology*; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D012168:Retinal Pigments / Q000378:metabolism
chemical_list: D055358:Cone Opsins; D029941:Fish Proteins; D012168:Retinal Pigments