PDE6B and retinal degeneration: To identify potential miRNAs associated with PR degeneration, we used the four following canine models: X-linked progressive retinal atrophy 2 (xlpra2), rod cone dysplasia 1 (rcd1), early retina degeneration (erd), and progressive rod-cone degeneration (prcd) that have mutations in RPGR, PDE6B, STK38L, and PRCD, respectively.