Papers In Press, published online ahead of print October 18, 2005
J. Biol. Chem, 10.1074/jbc.M509470200
Submitted on August 26, 2005
Revised on October 13, 2005
Accepted on October 18, 2005
Chx10 targets a subset of photoreceptor genes
Kimberley M. Dorval, Brian P. Bobechko, Hiroki Fujieda, Shiming Chen, Don J. Zack, and Rod Bremner
Cellular and Molecular Division, Toronto Western Research Institute, Toronto, Ontario M5T 2S8
Corresponding Author: rbremner{at}uhnres.utoronto.ca
The homeobox gene CHX10 is required for retinal progenitor cell proliferation early in retinogenesis and subsequently for bipolar neuron differentiation. To clarify the molecular mechanisms employed by CHX10 we sought to identify its target genes. In a yeast 1-hybrid assay CHX10 interacted with the Ret1 site of the photoreceptor-specific gene rhodopsin. Gel shift assays using in vitro translated protein confirmed that CHX10 binds to Ret1, but not to the similar rhodopsin sites Ret4 and BAT-1. Using retinal nuclear lysates, we observed interactions between CHX10 and additional photoreceptor-specific elements including the PCE-1 (rod arrestin/S-antigen) and the opsin locus control region (red/green cone opsin). However, chromatin immunoprecipitation assays revealed that in vivo, CHX10 bound sites upstream of the arrestin and interphotoreceptor retinoid binding protein genes but not rhodopsin or cone opsin. Thus, in a chromatin context, CHX10 associates with a specific subset of elements that it binds with comparable apparent affinity in vitro. Our data suggest that CHX10 may target these motifs to inhibit rod photoreceptor gene expression in bipolar cells.