Determining the Effect of MRP4 Knockout on Pigment Granule Position in Mouse RPE

Abstract

In the retinal pigment epithelium (RPE), pigment granules of wild type mice aggregate in darkness and disperse in light. In fish, pigment aggregation involves transport of cAMP into the RPE in vitro. We speculate that multidrug resistance protein 4 (MRP4) is responsible in vivo for the export of cAMP from the photoreceptors into the sub‐retinal space, making it available for uptake into the RPE in both fish and mice. We hypothesize if the MRP4 gene is knocked out in mice, we will not see a significant difference in pigment position between light and dark adapted mice. To test the hypothesis, we have quantified pigment position in RPE from wild type mice and knockout mice by estimating pigment granule density in the basal part of the cells examined by TEM. Bruch's membrane was used as a marker to determine the location of the base of the RPE. To measure pigment position, 2 μm × 2 μm boxes were aligned along Bruch's membrane, the pigment granules within each box were counted, and the average pigment density was calculated. The average pigment granule density for light adapted wildtype (LAWT; n = 3 mice) was 0.7 pigment granules/μm2 (± 0.2 pigment granules/μm2) and for dark adapted wildtype (DAWT; n = 3 mice) was 1.4 pigment granules/μm2 (± 0.3 pigment granules/μm2); pigment density was statistically significantly different (P < 0.02) between LAWT and DAWT. Preliminary data suggests the average pigment granule density for dark adapted MRP4 knockout is 0.57 pigment granules/μm2 (DAKO; n = 2). Our results with WT indicate basal pigment density increases in the dark, consistent with pigment aggregation and suggests dark adaptive pigment aggregation may be impaired in knockout mice.Support or Funding InformationThis project was supported by an Undergraduate Research Fellowship to AP and funds from the Office of the Provost awarded to DG in recognition of her service as Presidential Fellow. DEI received salary support from HSI STEM Program (84.031c) Award #P031C160035.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.