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A more recent version of this article appeared on June 1, 2009
 (Investigative Ophthalmology and Visual Science. )
© 2009 by The Association for Research in Vision and Ophthalmology, Inc.
doi:10.1167/iovs.08-2713
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Article

Thyroid hormone induces a time-dependent opsin switch in the retina of salmonid fishes

Christiana L Cheng 1, Kathlyn J Gan 1, and Inigo Novales Flamarique 2*

1 Biological Sciences, Simon Fraser University, Burnaby, Canada
2 Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, V5A 1S6, Canada

* To whom correspondence should be addressed. E-mail: inigo{at}sfu.ca.


  Abstract

Purpose. To determine the role of thyroid hormone in inducing the UV (SWS1) to blue (SWS2) opsin switch in the retina of two salmonid fishes. Methods. Fish were treated with thyroid hormone (T4) or the vehicle solution (0.1 M NaOH, control), exogenously or by intraocular injection, at different life history stages. Microspectrophotometry and in-situ hybridization with riboprobes against the SWS1 and SWS2 opsins were used to reveal the dynamics of opsin expression in treated and control animals. To assess whether thyroid hormone induced differentiation of retinal progenitor cells into cones, treated and control fish were injected intraocularly with bromodeoxyuridine (BrdU) and the number of proliferating cells in the outer nuclear layer (ONL) determined. Results. Thyroid hormone induced a reversible UV-to-blue opsin switch in differentiated single cones of juvenile salmonids (alevin and parr stages), but failed to exert any effect in the retina of older fish (smolt stage). Thyroid hormone did not induce cone density changes or alterations in numbers of BrdU-labelled cells, which were the same in control and treated animals. Conclusions. Thyroid hormone induces a UV (SWS1) to blue (SWS2) opsin switch in the retina of young salmonid fishes that is identical to that occurring during natural development. The switch occurs in differentiated photoreceptors, is reversible (maintained by thyroid hormone exposure), and can only be induced prior to its natural onset. Thyroid hormone did not cause changes in the numbers of proliferating cells in the ONL. Our work establishes a role for thyroid hormone in triggering opsin switches in the vertebrate retina.

Key Words: cones, visual pigment, thyroid hormone, ultraviolet cone, blue cone, retina




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J. C. Raine, A. B. Coffin, and C. W. Hawryshyn
Systemic thyroid hormone is necessary and sufficient to induce ultraviolet-sensitive cone loss in the juvenile rainbow trout retina
J. Exp. Biol., February 1, 2010; 213(3): 493 - 501.
[Abstract] [Full Text] [PDF]


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