NR2E3-Linked Retinal Degenerations

Abstract

NR2E3 (nuclear receptor, class 2, subfamily E, member 3), previously known as PNR (photoreceptor-specific nuclear receptor), is a member of the nuclear hormone receptor superfamily of ligand-modulated transcription factors.1 These transcription factors are characterized by a modular protein structure, with functionally independent DNA-binding and ligand-binding domains.2 The DNA-binding domain mediates the binding to specific DNA sequences located in the promoters and regulatory regions of target genes. Therefore, nuclear receptors contribute in an essential manner to the establishment of a cell-type-specific gene expression profile. The transcriptional activity of nuclear receptors is modulated in response to binding of lipophilic molecules, such as steroid hormones, thyroid hormones, cholesterol, bile acids, fatty acids, retinoids, and heme, to the ligand-binding domain.3 Unlike many nuclear receptors that have a more ubiquitous tissue expression, NR2E3 expression is restricted to the retina in mammals,3,4 and transcripts are detected in putative immature human rods on the foveal edge as early as fetal week 11.7.5 Together with the transcription factors CRX (cone-rod homeobox) and NRL (neural leucine zipper), NR2E3 is implicated in the transcriptional network regulating photoreceptor development and maintenance.6,7 Proposed physiologic functions of NR2E3 include the suppression of the cone generation program in late mitotic retinal progenitor cells and the suppression of cone-specific gene expression in mature rods.8,9,10,11,12