FAS-INDEPENDENT APOPTOSIS OF PHOTORECEPTOR CELLS IN C3H MICE

The morphogenesis of the photoreceptor cells in the retinas of C3H mic e carrying the rd gene and G(57)BL mice carrying the normal gene was c ompared, and retinas of the C3H mutants (C3H-Ipr/Ipr, -Ipr(cg)/Ip(cg), and -lpr/lpr . gld/gld) defective in apoptosis through the Fas system were examined. In the C(57)BL retina, the inner and outer nuclear lay ers were separated at 8 days of age, and the photoreceptor inner and o uter segments began to grow between 8-11 days after birth with their m ost rapid growth occurring between 14-17 days of age. In the C3H retin a, the development was comparable to that of the C(57)BL retina at 8 d ays of age but the reduction in thickness of the outer nuclear and pho toreceptor layers was noted at II days of age, and the outer nuclear l ayer became reduced to only a few nuclei in thickness at 14 days, bein g completely missing or reduced to a single row of cells at 20 days. T he degeneration was by an apoptotic mechanism as confirmed morphologic ally and by the TUNEL method. In all the C3H mutant retinas examined o ver 24 days of age, the complete depletion of the outer nuclear layer or reduction to a single row comparable to 20-day-old C3H mice was see n. The rd gene action is therefore independent of Fas/Fas ligand-medic ated apoptosis.