Molecular cloning, characterization and mapping of the canine glucocorticoid receptor DNA binding factor 1 (GRLF1)

Progressive rod-cone degeneration (prcd) is an autosomal recessive retinal degeneration of dogs that maps to chromosome 9 (CFA9). Positional cloning and candidate gene approaches are presently used to identify the disease-causing gene. To complement these strategies and identify novel candidate genes, we have used a subtraction approach to detect modified gene expression caused by prcd that may be causally associated with the disease, or, alternatively, be involved in the molecular mechanisms leading to the disease phenotype. With this technique we characterized a 4503 nucleotide open reading frame (ORF) within a 5.6 kb cDNA that predicts a protein of 1500 amino acids. The gene shows about 90% homology to the human and rat glucocorticoid receptor DNA binding factor 1 (GRLF1) gene, also known as p190-A. The transcript was detected in several tissues, including retina, and the protein was localized to the photoreceptor cell layer. The canine GRLF1 maps near the telomere of CFA1 close to CRX, a region synteny to human chromosome 19q13 (HSA19q13). Based on its chromosomal location, GRLF1 has been excluded as a candidate gene for prcd. Northern blot analysis also failed to prove down-regulation of the gene in early stages of disease in six different non-allelic canine retinal degenerations. However, we were able to show that in advanced stages of prcd, GRLF1 is expressed in remaining photoreceptor cells, thus, providing a challenging task to uncover the gene's exact function in the retina and degenerative processes.