Photoreceptor differentiation analyzed by the novel monoclonal antibody 1G1

In vertebrates, photoreceptor development has become a key model system to study mechanisms of cell differentiation. A still unresolved question is why photoreceptor maturation is retarded over an extended period of embryogenesis though photoreceptors are among the first cells born in the retina. We have generated the novel monoclonal antibody 1G1 which binds to outer photoreceptor segments of adult retinae of various species including chicken and rat. In the developing chicken retina presumptive photoreceptor cells were labeled by MAb 1G1 at embryonic day 10 (E10). Retinal cell cultures revealed that the corresponding antigen is expressed on the cell surface of rods and cones likewise. Metabolic labeling with bromodeoxyuridine in vitro indicated that 1G1 antigen expression is restricted to postmitotic cells. Comparison of single cell cultures starting from different developmental stages showed that antigen expression can be induced prematurely, if cells are released from their native tissue environment. In order to analyze potential regulatory cell interactions, retinal cells were cultured on cryosections of the eye (cryoculture). The percentage of 1G1+ cells which contacted the pigment epithelium, was significantly lower in comparison to cells located on retinal tissue. The data are consistent with the notion that the pigment epithelial cells which contact retinal photoreceptors in vivo, could be partially inhibitory and consequently delay photoreceptor differentiation.