The visual process depends upon the normal expression of a large number of genes and upon the normal functioning of the protein gene products. If these mechanisms fail, hereditary diseases of the retina such as retinitis pigmentosa and retinoblastoma can result. We have found that expression of the important photoreceptor protein, interphotoreceptor retinoid-binding protein (IRBP), is controlled by at least two mechanisms in normal development, first, hypomethylation; secondly, specific nuclear factors that bind in the promoter region. We have also found that the extracellular matrix protein laminin switches retinoblastoma cell differentiation from a photoreceptor-like pathway to a neuronal-like pathway via a low-affinity differentiative binding activity. This switch could have a major effect on early retinal cell development.
