PROS1 and neurodegenerative disease: Expression of aggregation prone proteins associated with neurodegenerative diseases in the photoreceptors of Drosophila typically cause a characteristic ‘rough eye’ phenotype in which the normal linear array of ommatidia and sensory bristles become disordered, and in addition the eye loses its natural pigmentation to varying degrees that depend on the toxicity of the proteins expressed [20]; this phenotype can be visualised both by optical and scanning electron microscopy.