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William Thurston, Robert Mackin, Deborah L Stenkamp; Sexually Dimorphic Expression of Cone and Rod Opsins in the Zebrafish. Invest. Ophthalmol. Vis. Sci. 2017;58(8):346.
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© ARVO (1962-2015); The Authors (2016-present)
The zebrafish is an important model organism for vision science, particularly in studies of development, disease, and regeneration of its cone-rich retina. Studies supported by the NIH are now required to consider sex as a biological variable; however, there is no information regarding the existence of sexual dimorphisms in the zebrafish visual system. To begin to fill this knowledge gap, the purpose of this study was to determine whether expression of cone and/or rod opsins was sexually dimorphic in the zebrafish.
Using real-time polymerase chain reaction (qPCR), we analyzed expression of all 10 cone and rod opsin genes in eyes of sexually mature females and males (1.5 yrs), and in eyes of old females and males (3.25 yrs) (n=3 per condition).
1.5 yr females showed higher levels of expression of RH2-1 and RH2-4 (the first and last members of the tandemly-quadruplicated RH2 cone opsin array) than 1.5 yr males (p=7.29x10-8; p=0.021, respectively). All other cone and rod opsins showed no significant differences in expression in 1.5 yr females vs. 1.5 yr males (p>0.05). Old females exhibited lower expression levels of the following opsins than old males: RH2-1 (p=4.48x10-7), RH2-2 (p=3.58x10-6), RH2-3 (p=6.61x10-5), RH2-4 (p=1.17x10-10), LWS1 (p=1.91x10-8), LWS2 (p=3.72x10-6), and RHO (p=6.18x10-4). Expression levels of SWS1, SWS2, and RHO-L were not significantly different in old females vs. old males (p>0.05). In the case of RH2-1,we confirmed that sex differences in old fish were due to a large decline in RH2-1 expression in old females compared with 1.5 yr females (p=2.75x10-7), while there was no decline in males (p=0.441).
Expression levels of several photoreceptor opsins in zebrafish are regulated as a function of sex and/or age. The RH2-1 gene encodes the most blue-shifted (467 nm peak spectral sensitivity) of the RH2 cone opsins. The highly significant increases in RH2-1 expression in sexually mature females in comparison to all other conditions suggest a possible function related to mate identification/selection. Declines in expression of some opsins in old females (which at 3.25 yrs were likely reproductively senescent) further suggest the potential for sex hormones to influence expression of cone and rod opsins.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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