Fas-independent apoptosis of photoreceptor cells in C3H mice.

The morphogenesis of the photoreceptor cells in the retinas of C3H mice carrying the rd gene and C57BL mice carrying the normal gene was compared, and retinas of the C3H mutants (C3H-lpr/lpr, -lprcg/lprcg, and -lpr/lpr-gld/gld) defective in apoptosis through the Fas system were examined. In the C57BL retina, the inner and outer nuclear layers were separated at 8 days of age, and the photoreceptor inner and outer segments began to grow between 8-11 days after birth with their most rapid growth occurring between 14-17 days of age. In the C3H retina, the development was comparable to that of the C57BL retina at 8 days of age but the reduction in thickness of the outer nuclear and photoreceptor layers was noted at 11 days of age, and the outer nuclear layer became reduced to only a few nuclei in thickness at 14 days, being completely missing or reduced to a single row of cells at 20 days. The degeneration was by an apoptotic mechanism as confirmed morphologically and by the TUNEL method. In all the C3H mutant retinas examined over 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 seen. The rd gene action is therefore independent of Fas/Fas ligand-medicated apoptosis.