Abstract
Purpose :
Calcium plays an important role in regulating the response sensitivity, kinetics and adaptation in photoreceptor cells. In zebrafish cones, this calcium feedback includes direct modulation of the transduction CNG channels by the calcium binding protein CNG-modulin. However, the possible role of its mammalian homolog, EML1 in modulating CNG channel conductance in mammalian photoreceptors has not been examined. Here, we investigated the effect of mutating the EML1 gene on the function of rod photoreceptors.
Methods :
NOR mice carrying homozygous EML1 mutation and littermate wild type controls maintained at 12/12 hours light/dark cycle were used in the experiments. The presence of EML1 in the mouse retina was determined by western blot and in situ hybridization using the RNAscope assay. Mutant mice were identified by genotyping. In order to assess the role of EML1 on rod function, ex-vivo transretinal ERG recordings were performed from control and EML1 mutant mice first in darkness and then in the presence of background light of increasing intensity. We measured the sensitivity and kinetics of the dim flash responses in each case.
Results :
Dark-adapted EML1 mutant mice exhibited about 50% reduction in the maximum rod response, which could be explained by the down-regulated rhodopsin expression (confirmed by western blotting) in these animals. We also found higher fractional sensitivity and corresponding lower intensity to produce half of the maximum response indicating an overall higher dark-adapted sensitivity in the mutants. The kinetics of the dim flash response were found to be faster in the EML1 mutants as compared to controls. Surprisingly, we did not see a notable difference in the sensitivity of EML1 mutants and controls during background light adaptation.
Conclusions :
The mutation in EML1 gene possibly causing loss of functional EML1 protein leads to elevated sensitivity and faster response kinetics in mouse rods. These results are consistent with the notion that EML1 is a calcium-dependent modulator of mammalian rod phototransduction.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.