The metabolic pathways that produce 11-cis retinal are important for vision because this retinoid is the chromophore residing in rhodopsin (180380) and the cone opsins. The all-trans retinal that is generated after cone and rod photopigments absorb photons of light is recycled back to 11-cis retinal by the retinal pigment epithelium and Muller cells of the retina. Several of the enzymes involved have been purified and cloned at the molecular level. The RDH5 microsomal enzyme is abundant in the retinal pigment epithelium, where it has been proposed to catalyze the conversion of 11-cis retinol to 11-cis retinal.
General function
Enzyme
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Cellular localization
Cytoplasmic
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Ovarian function
Follicle development
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Expression regulated by
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Ovarian localization
Theca
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Wood JR, et al reported the molecular phenotype of polycystic ovary syndrome (PCOS) Theca cells and new candidate PCOS genes defined by microarray analysis.
Polycystic ovary syndrome (PCOS) affects 5 percent of reproductive aged women and is the leading cause of anovulatory infertility. A hallmark of PCOS is excessive theca cell androgen secretion, which is directly linked to the symptoms of PCOS. However, the genes responsible for ovarian hyperandrogenemia of PCOS have not been identified. In this present study, the authors carried out microarray analysis to define the gene networks involved in excess androgen synthesis by the PCOS theca cells in order to identify candidate PCOS genes. PCOS theca cells have a gene expression profile that is distinct from normal theca cells. Included in the cohort of genes with increased mRNA abundance in PCOS theca cells were aldehyde dehydrogenase 6 and retinol dehydrogenase 2, which play a role in all-trans retinoic acid biosynthesis and the transcription factor GATA6. The authors demonstrated that retinoic acid and GATA6 increased the expression of 17a-hydroxylase providing a functional link between altered gene expression and intrinsic abnormalities in PCOS theca cells. Thus, the analyses have (1) defined a stable molecular phenotype of PCOS theca cells; (2) suggested new mechanisms for excess androgen synthesis by PCOS theca cells; and (3) identified new candidate genes that may be involved in the genetic etiology of PCOS.