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Ralph F Nelson, Annika Balraj, Tara Suresh, Meaghan Torvund, Sara Stokes Patterson; A computational method for determining opsin peak absorbance wavelengths from zebrafish PIII ERG responses. Invest. Ophthalmol. Vis. Sci. 2018;59(9):600.
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© ARVO (1962-2015); The Authors (2016-present)
To determine, using electroretinography, which of 8 cone opsin types (Chinen et al, 2003) are expressed in the red, green, blue and UV cone types of zebrafish over the course of eye development.
Microelectrodes are inserted into perfused, in vitro, roy/roy zebrafish eyes. Eyes are perfused with oxygenated MEM containing Na Aspartate to saturate post-synaptic glutamatergic receptors and to isolate cone PIII responses, evoked at 9 wavelengths (330-650nm) with either infrared (IR), red (627nm) or blue (418nm) backgrounds. Spectra were fit by a ‘sum of Hill functions’ model (Nelson & Singla, 2009), where each cone is represented by a Hill function whose semi-saturation parameter is adjusted with wavelength according to a spectral nomogram function for zebrafish cone opsins (Hughes et al, 1998; Palacios et al, 1996). Peak opsin absorbance of individual cone signals is a calculated fit parameter. For each age and background treatment, large datasets of over 1000 PIII spectral signals were compiled from 6-13 eyes, and fit as a group to the spectral function.
The mean larval (5, 6, 7, and 12 dpf) LWS opsin peak was 555.9±1.5 nm. The peak was little affected by chromatic backgrounds. The mean adult LWS opsin peak was 573.5±2.1 nm for IR, 418nm and white backgrounds. For red backgrounds, the adult LWS peak was 564.7±0.1 nm. The mean larval RH2 (green cone) opsin peak was 465.6 ±3.0 nm, tending towards shorter wavelengths with 418nm backgrounds, and longer wavelengths with 627nm backgrounds. The mean adult RH2 peak (all backgrounds) was 475.1±3.7 nm.
Adult LWS and RH2 opsin peaks are like published measurements with microspectrophotometric or microelectrode recording of single cones. The larval RH2 peak (465.6nm) is like the 467nm value for RH2-1 of Chinen et al. RH2-1 is expressed in larvae, but adults express additional longer wavelength RH2’s (Takechi and Kawamura, 2005), consistent with a slightly longer wavelength RH2 peak (475.1nm) found in adults. Both the larval (555.9nm) and adult (573.5nm) peaks are longer than those of Chinen (LWS-2, 548nm; LWS-1, 558nm). Invariance of the larval LWS peak with selective chromatic adaptation suggests a single LWS opsin. The shortening of the adult LWS peak by red backgrounds suggests mixed LWS-1, LWS-2 expression in adults (Takechi and Kawamura, 2005).
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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