RHO and retinoblastoma: Using DNMTi and HDACi in terminally differentiated retinoblastoma cells (Y79 and WERI) and immortalized cells of non-retinal origin (HEK 293), we found upregulation of opsins by drug treatment in both expressing (i.e., OPN1LW in WEI and Y79) and non-expressing (i.e., RHO and OPN1LW in HEK 293) cell lines, consistent with previous studies [31,32,33,34].