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First published online November 28, 2008
Journal of Experimental Biology 211, 3879-3888 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.020289
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Ontogenetic changes in photoreceptor opsin gene expression in coho salmon (Oncorhynchus kisutch, Walbaum)

S. E. Temple1, K. M. Veldhoen1, J. T. Phelan1, N. J. Veldhoen2 and C. W. Hawryshyn1,3,*

1 Department of Biology, University of Victoria, Victoria, British Columbia, Canada
2 Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada
3 Department of Biology, Queen's University, Kingston, Ontario, Canada


Figure 1
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  		Fig. 1. Mean {lambda}max ±2 s.e.m. for rods, middle wavelength-sensitive (MWS) cones and long wavelength-sensitive (LWS) cones from alevin (A), parr (P), ocean smolt (O) and TH-treated alevin (TH) coho (Oncorhynchus kisutch, Walbaum). The mean values for each group were calculated from the means of all individual fish in each group (N-values below the error bars). The means for each fish were based on the {lambda}max values obtained for that receptor class (see text for details).

 

Figure 2
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  		Fig. 2. Frequency histograms of {lambda}max values of individual MWS cones from coho salmon (Oncorhynchus kisutch, Walbaum): (A) all groups combined, (B) alevins, (C) TH-treated alevins, (D) parr, (E) ocean smolts and (F) an individual alevin. Bin size=1 nm. The {lambda}max values were obtained by microspectrophotometry (MSP) of individual MWS cones from the dorsal retina of coho salmon obtained from Target Marine Products in April–May, 2005. There are progressively fewer MWS cones with {lambda}max values below 500 nm as the coho increase in size from alevin (B) to parr (D) and ocean smolt (E). Treatment with exogenous TH (C) resulted in a significant increase in the {lambda}max of MWS cones, mostly as a result of a conversion from predominantly A1- to A2-based chromophores.

 

Figure 3
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  		Fig. 3. Frequency histograms of {lambda}max values of individual LWS cones from coho salmon (Oncorhynchus kisutch, Walbaum): (A) all groups combined, (B) alevins, (C) TH-treated alevins, (D) parr and (E) ocean smolts. Bin size=2 nm. The {lambda}max values were obtained by MSP of individual LWS cones from the dorsal retina of coho salmon obtained from Target Marine Products in April–May, 2005. Treatment with exogenous TH resulted in a significant increase in the {lambda}max of LWS cones, mostly as a result of a conversion from predominantly A1- to A2-based chromophores.

 

Figure 4
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  		Fig. 4. Scatter plot showing {lambda}max values for MWS and LWS outer segments of individual double cones measured in coho salmon (Oncorhynchus kisutch, Walbaum). Vertical dotted lines predict the range of {lambda}max values for the MWS cones at the short wavelength range of the data set. Taking the lower value of 4901 nm as the A1 observed value, we used the Whitmore and Bowmaker model (Whitmore and Bowmaker, 1989Go) to calculate that the same opsin would have a {lambda}max of 5162 nm if combined with an A2 chromophore. Vertical dashed lines indicate the range for the longer of the two opsins, with a pigment pair that would have a range of 5121 to 5482 nm. The horizontal dotted lines predict the range for the shorter of the two proposed LWS cone opsins, having a pigment pair that extends from 5451 to 6002 nm based on Harosi's model (Harosi, 1994Go). Likewise, the horizontal dashed lines indicate the range for the longer of the two proposed LWS opsins, with a pigment pair that has a range of 5631 to 6332 nm. All data points fit between these vertical and horizontal limits within the measurement error of the MSP device (±3 nm), except those in the lower range of the LWS data set (see text).

 

Figure 5
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  		Fig. 5. RH2 opsin subtype expression in dorsal retinas of alevin, parr and TH-treated alevin coho salmon (Oncorhynchus kisutch, Walbaum) measured using real-time quantitative RT-PCR. Expression levels are the mean of three replicates per fish (N-values above error bars represent the number of fish) and were normalized to the β-actin gene. Error bars represent 2 s.e.m.

 

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© The Company of Biologists Ltd 2008