RDH12 Expression Relative to Other Short Chain Dehydrogenase/Reductase Isoforms Present in the Retina

Abstract

Purpose:: Although RDH12 is one of a number of short chain dehydrogenases/reductases present in the retina, the involvement of RDH12 mutations in severe childhood-onset retinal dystrophy indicates that its function is not redundant with that of other RDH isoforms. The purpose of this study is to characterize the expression of RDH12 in the retina to determine whether differences relative to other isoforms may contribute to the unique role of RDH12 in retinal physiology.

Methods:: Total RNA was isolated from whole retinas, as well as flow-sorted GFP+ photoreceptor cells from wild type and Nrl-/- mice (PNAS 2006;103:3890-5). RDH transcript levels were assayed using quantitative RT-PCR and by microarray expression profiling on Affymetrix Mouse Genome 430_2.0 arrays. Immunohistochemical analysis of mouse and human retinal cyrosections was performed using RDH isoform-specific antibodies.

Results:: Transcripts encoding RDH12 were the most abundant of the RDH isoforms present in adult mouse retina, followed by DHRS3(retSDR1), RDH10, RDH8(prRDH), RDH14, and RDH11. Levels of RDH12 and DHRS3 encoding transcripts significantly increased during differentiation of the retina, beginning at PN day 6 and coincident with rod outer segment genesis. RDH12 and DHRS3 expression was dramatically down-regulated in the ‘all-cone’ retinas of adult mice deficient for the transcription factor NRL. RDH12, RDH11, and DHRS3 localized primarily to photoreceptor inner segments in both human and mouse retinas.

Conclusions:: The high level expression of RDH12 in photoreceptor inner segments in human and mouse supports emerging evidence that RDH12 activity is not essential for visual cycle throughput (Mol Cell Biol doi:10.1128/MCB.01486-06), and raises the possibility that RDH12 plays a critical role in another key biosynthetic pathway. The expression pattern of RDH12 appears most similar to that of DHRS3 in terms of abundance, localization, and time of onset during development. Thus, differences in the functional roles of these two isoforms are likely to reflect differences relative to substrate specificity and/or other associations in the retina.The two first authors contributed equally to this study.

Keywords: retinal degenerations: hereditary • photoreceptors • proteins encoded by disease genes