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Rizwan A. Bhatti, Shirley Yu, Ana Boulanger, Robert N. Fariss, Yan Guo, Steven L. Bernstein, Susan Gentleman, T. Michael Redmond; Expression of β-Carotene 15,15′ Monooxygenase in Retina and RPE-Choroid. Invest. Ophthalmol. Vis. Sci. 2003;44(1):44-49. doi: https://doi.org/10.1167/iovs.02-0167.
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purpose. β-Carotene 15,15′ monooxygenase (β-CM) catalyzes the central cleavage of β-carotene to all-trans-retinal, the first step in vitamin A synthesis. This study was conducted to determine the expression of β-CM in the mammalian retina and RPE, to assess its relevance in carotenoid-retinoid metabolism in the retina and RPE.
methods. RT-PCR was used to detect expression of β-CM mRNA in the retina and RPE-choroid of the mouse, cow, human, and monkey and in RPE cells and other cell lines. Immunofluorescence microscopy was used to localize β-CM in mouse and monkey retina with an anti-peptide antibody specific for β-CM.
results. By RT-PCR, β-CM mRNA was detected at a low level in mouse and monkey retina and in the RPE-choroid of the monkey but not of the mouse. Conversely, β-CM mRNA was expressed at a low level in both human and bovine RPE-choroid, but not in the retina of either. RPE primary cultured cells of the monkey also showed β-CM mRNA expression, although the three human lines did not. In addition, of nine other cell lines tested, only COS-7 was positive for β-CM. Immunofluorescence microscopy showed weak immunoreactivity in the inner retina in both the mouse and monkey. β-CM immunoreactivity was not detectable in RPE of the mouse. Use of a long-wavelength exciting and emitting secondary probe to mitigate lipofuscin autofluorescence, facilitated the detection of a low level of β-CM immunoreactivity in monkey RPE.
conclusions. β-CM mRNA and protein are expressed at low levels in the mammalian retina and RPE-choroid. Given the low and variable expression of β-CM in the retina and RPE, it can be concluded that β-CM is not necessary for a conserved retina or RPE-specific function, but may be necessary for a species-specific function.
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