Purpose: To characterize CLUL1, a cone photoreceptor-specific gene.
Methods: A comparative genomics approach was used to analyze the gene organization and protein sequence of a retinal clusterin-like protein and to identify conserved elements between human and dog. Its expression was studied by Northern and Western analyses and its localization by in situ hybridization and immunocytochemistry.
Results: The CLUL1 sequences of the human and dog share 85% and 73% identity, respectively, at the nucleotide and deduced amino acid level. The gene is organized into nine exons and shows strong homology, not only in exonic but also in some intronic sequences between the species. The polypeptide homology of CLUL1 to CLU, a molecular chaperone, indicates structural similarity of the two proteins. However, these data demonstrated that they present different expression profiles in the tissues, in retinal development, and in retinal diseases. Finally, CLUL1 was localized to retinal cone photoreceptor cells and a different immunolabeling in light- and dark-adapted retinas was shown.
Conclusions: CLUL1 represents a potentially important gene and a candidate locus for retinal disease, particularly those diseases that affect cones.