Expression of Cone-Photoreceptor–Specific Antigens in a Cell Line Derived from Retinal Tumors in Transgenic Mice

Retinal cell culture has been a useful tool for ocular research. Although it does not replace the intact eye, retinal cell cultures provide convenient experimental systems for the assessment of numerous retinal processes. As with any in vitro systems, cell culture offers great advantages, but not without potential limitations. Advantages include controllable conditions that allow for the assessment of isolated cellular functions, a more affordable system when compared with the more costly animal research, and time course flexibility. Potential limitations include loss of native tissue architecture, lack of functional feedback from other retinal cell types, and a questionable correlation between in vitro and in vivo findings. However, for a great number of research applications, the advantages offered by in vitro systems outweigh the limitations. Retinal cell culture can be routinely used to determine the cell specificity of promoter sequences,1 the effect of mutations on the structure and function of retinal proteins,2 or the role of multiple domains on the function of retinal proteins.3 Furthermore, retinal cell culture has been applied in studies of cell growth, death, differentiation, and cytotoxicity (for review, see Ref. 4). Photoreceptor cells are terminally differentiated, specialized neuronal cells with a limited capacity for cell division. Therefore, to establish a line of photoreceptor cells, it is essential to transform them, possibly with a virus. Immortalized cell lines of several ocular cell types currently exist, including Muller,5 ganglion,6 corneal endothelial,7 and RPE cells.8 A cell line expressing retina-specific genes, including interphotoreceptor retinol-binding protein (IRBP) and cone transducin, has been isolated from a mouse ocular tumor.9 In addition, Y-7910 and WERI-Rb11 are immortalized human retinoblastoma cell lines available for the study of photoreceptors. Initially, it was thought that the Y-79 cells were of cone cell origin,12 but more recently these cells have been shown to express rod-specific antigens, such as opsin, transducin, phosphodiesterase, and recoverin.13,14 Primary retinal cultures have been created from several vertebrate retinas, including those of humans.15 These types of cultures, in addition to being tedious to prepare, are not adequate for some types of studies, because of their heterogeneity, limited cell division, and special conditions for growth as monolayers. Thus, there is a need for additional photoreceptor cell models that are homogeneous, passageable, and easily grown as a monolayer by using standard tissue culture techniques. Herein, we describe a mouse photoreceptor-derived cell line (661W) immortalized by the expression of simian virus (SV)40 T antigen (T-ag) under control of the human IRBP promoter.16 Cellular, and molecular analyses show that these cells express cone but not rod photoreceptor markers, which suggests that the cells arise from a cone photoreceptor lineage. For this reason, the 661W cell line should contribute significantly to the study of cone photoreceptor cell function and of diseases affecting cone photoreceptor cells, including mechanisms of photoreceptor cell death in various retinal dystrophies.