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W.S. Stark; Effects of Lutein and Zeaxanthin as Chromophore Precursors and in Regulating Opsin Gene Transcription in Drosophila . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2836.
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Since lutein and zeaxanthin were identified as human macular pigments (Bone et al., Vision Res., 25, 1531–1536, 1985), interest in these carotenoids has grown. Since the chromophore of the fly visual pigment is 3–hydroxyretinal (Vogt & Kirschfeld, Naturwissen. 71, S211, 1984), it seemed useful to revisit dietary supplementation with lutein and zeaxanthin. These studies are addressed to the six known opsins as well as the increase in opsin gene transcription induced by dietary retinoids.
Vitamin A deprived Drosophila were given "replacement therapy" with zeaxanthin, lutein and beta–carotene; also flies were reared from egg to adult on these carotenoids. Zeaxanthin (OPTISHARP(TM)) and lutein were gifts from DSM Nutritional Products Ltd., Kaiseraugst, Switzerland. Transgenic Drosophila and optical techniques assisted in the visualization of the six rhodopsins (Rh1 to Rh6) and in assaying opsin promoter activation via green fluorescent reporter (GFP) (Stark & Thomas, Mol. Vision, 2004; 10:943–955).
Opsin–promoter –– GFP–reporter analyses show that zeaxanthin and lutein activate transcription as effectively as beta carotene relative to vitamin A deprived flies. Optical density difference as rhodopsin–480 is converted to metarhodopsin–580 shows that zeaxanthin and lutein are effective precursors for Rh1. Transgenics in which other opsins replace Rh1 in R1–6 photoreceptors demonstrate that zeaxanthin and lutein can serve in the biosynthesis of these rhodopsins.
Although the gene induction was easily observed, visual pigment levels in zeaxanthin and lutein flies were sub–maximal. This may be because flies utilize (3S)–3–hydroxyretinal (Seki & Vogt Comp. Biochem. Physiol. 119B, 53–64, 1998); our zeaxanthin is 3R,3'R (and the lutein was purified from marigold extract). Our analyses fit with a growing literature in which Drosophila mutants have been used to dissect caroteinoid metabolism (Sarfare et al., J. Biol. Chem. 280, 11895–11901, 2005; von Lintig et al., PNAS, 98, 1130–1135, 2001; Wang & Montell, J. Neurosci, 25, 5187–5194, 2005).
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