Background: The aim of the present study was to define the rhodopsin promoter elements of various mammalian species by evaluating the effect of these promoters on transgene specificity and expression in human cell lines. Additional characterization of these promoters was performed in the presence or absence of a human inter-photoreceptor retinoid-binding protein (IRBP) enhancer element.
Methods: Truncated murine, bovine and human rhodopsin promoter fragments containing 1.4 kb of the 5' upstream regulatory sequence were subcloned into pEGFP-N1 expression vector to drive the expression of the green fluorescence protein (GFP). Fluorescence-activated cell sorter analysis was used to determine the strength and specificity of GFP expression in three human cell lines, in the presence or absence of an IRBP enhancer element at the 5' end of the promoters.
Results: It was found that the truncated murine rhodopsin promoter was the strongest in Y-79 retinoblastoma cells but it was less specific than the truncated human rhodopsin promoter. It is surmised that transcription factors located at the 5' proximal region of the rhodopsin promoter fragments were responsible for the expression patterns seen in the present study.
Conclusions: These results indicate that the rhodopsin promoter of choice for in vivo work should be from the same species if specificity is to be maximal and the addition of the IRBP enhancer element could increase transgene expression in photoreceptor cells without deleterious effects on specificity.