| Retinoblastoma is a retinal cancer, resulting from RB1 mutations. Coding aberrations are implicated in 90% of probands, while 4% have promoter mutations. For the remainder, no mutation has been identified. Although transcriptional regulatory sequences reside mainly within the promoter, control regions have been discovered within introns. We hypothesize that probands lacking identified RB1 mutations have aberrations within intronic regions that regulate RB1 expression. Using phylogenetic footprinting three intron 1 regions conserved between human, mouse, and rat, ranging in length from 18 to 27 bp, were found to contain several potential transcription factor binding sites. All three regions were GC-biased, and did not represent snoRNAs, microRNAs, or genomic repeats. Electromobility shift assays suggested that proteins interact specifically with conserved regions 1 and 3. No intron 1 mutations were identified in 50 probands tested suggesting that the frequency of retinoblastoma-causing mutations within these regions is less than 1/553. |
