Developmental dynamics of cone photoreceptors in the eel

Phillippa B Cottrill,James K Bowmaker,Ma'Ayan Semo,David M Hunt,Wayne L Davies,Glen Jeffery

doi:10.1186/1471-213x-9-71

Phillippa B Cottrill, James K Bowmaker + Show 4 more

Open Access

https://doi.org/10.1186/1471-213x-9-71

Copy DOI

Abstract

BackgroundMany 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?ResultsThe Rh2 and Sws2 opsin sequences from the European Eel were isolated, sequenced and expressed in vitro for an accurate measurement of their λmax 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).ConclusionsLarger 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.

Highlights

Many fish alter their expressed visual pigments during development
The former was found at all three developmental stages but showed a variable λmax that arose from changes in the proportions of the A1 pigment rhodopsin and the A2 pigment porphyropsin that were present
We have demonstrated here that the European eel (Anguilla anguilla) changes opsin gene expression more times during its lifetime than had previously been reported

Summary

Introduction

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. Leptocephali travel the ~6000 km to the European continental shelf with its more green coastal water, where they metamorphose into glass eels, one of two juvenile forms. As elvers (pigmented glass eels) and as yellow eels (the larger juvenile form), they travel up European rivers and spend 6-20 years in a yellow/brown stained fresh water environment, where they grow and mature as a freshwater species. Mature eels must cross the Atlantic Ocean to return to the Sargasso Sea to spawn. Both just prior to and during this migration they undergo 'silvering', usually described as a second metamorphosis but which is more correctly a pubertal event [4], when they become sexually mature adult fish.

Methods

Results

Discussion

Conclusion