We found that there are many other genes that are dependent upon Crx. Those that are expressed at a lower level in the Crx-/- retina, such as rhodopsin and peripherin, comprise many that are either enriched or specific to photoreceptors in their expression [35]. They include enzymes that are important in lipid metabolism, protein folding and transport, as well as in other processes that one might envision would be important in building a structure such as the outer segment. In situ hybridization using probes from this collection of genes has revealed that some of them have their RNA localized to the inner segment, a finding typical for proteins targeted to the outer segment. Future analyses of the function of these genes might reveal their role in outer segment biogenesis.