Lineage study of degenerating photoreceptor cells in the rd mouse retina

Purpose. A retroviral marker was used to label daughter cells arising from individual neuroblasts in the rd mouse retina, in order to investigate the hypothesis that a clonal relationship exists among degenerating photoreceptor cells. Methods. On the day of birth, a single injection of retrovirus with a lac Z (beta-galactosidase) reporter construct was injected into the retina in the vicinity of the subretinal space. Descendants of single neuroblasts were identified histochemically by examining the retinas at P14 (postnatal day 14). Light and electron microscopic studies were used to identify the retrovirally-induced marker beta-D-galactosidase using Blue-gal dye. Double-labeling of degenerating cone cells was accomplished by taking 100 mu m vibratome sections of retrovirally-injected eyes and using either FITC-PNA or HRP-PNA to visualize clusters of degenerating cones as well as Blue-gal labeled clones of photoreceptor cells on the same tissue section. Results. A relatively large number of clones of primarily photoreceptor cells were observed in the peripheral retinas of both normal and rd mice. In a few cases in the rd, photoreceptor cells in a given clone consisted of both PNA- and Blue-gal-labeled cells as well as of only Blue-gal-labeled cells. Conclusion. These results suggest that during the period of intense cell death in the rd retina, a single dying photoreceptor cell can be surrounded by photoreceptors (either rods or cones) from the same clone that appear morphologically normal with out evidence of degeneration.