PHOTORECEPTOR DIFFERENTIATION ANALYZED BY THE NOVEL MONOCLONAL-ANTIBODY 1G1

vertebrates, photoreceptor development has become a key model system t o study mechanisms of cell differentiation. A still unresolved questio n 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 no cel monoclonal antibody 1G1 wh ich binds to outer photoreceptor segments of adult retinae of various species including chicken and rat. In the developing chicken retina pr esumptive photoreceptor cells were labeled by MAb 1G1 at embryonic day 10 (E10). Retinal cell cultures revealed that the corresponding antig en is expressed on tile cell surface of rods and tones likewise. Metab olic labeling with bromodeoxyuridine in vitro indicated that 1G1 antig en expression is restricted to postmitotic cells, Comparison of single cell cultures starting from different developmental stages showed tha t antigen expression can be induced prematurely, if cells are released from their native tissue environment. In order to analyze potential r egulatory cell interactions, retinal cells were cultured on cryosectio ns of the eye (cryoculture). The percentage of 1G1(+) cells which cont acted the pigment epithelium, was significantly lower in comparison to cells located on retinal tissue, The data are consistent with the not ion that the pigment epithelial cells which contact retinal photorecep tors in vivo, could be partially inhibitory and consequently delay pho toreceptor differentiation.