RHO and retinal degeneration: Combined together, these double mutant analyses suggest that intracellular rhodopsin aggregation triggers unregulated cell death in norpAP24, rdgC306, and trp1 photoreceptors, and that Osi21 is a key regulator in the formation of rhodopsin aggregation, wherein the loss of Osi21 function suppresses retinal degeneration in these mutant photoreceptor cells.