ATXN1 and retinal degeneration: Expression of the human mutant ATXN1 gene in Drosophila’s neurons leads to retinal degeneration and loss of axonal projections of the interneurons in the ventral nerve cord of the brains (Fernandez-Funez et al., 2000), expression of the pathogenic form of SCA1 or SCA3 in Drosophila larval dendritic neurons reduced their arborization with disruption of F-actin dendritic structures, defect that is partially rescued by Rac-PAK signaling activation (Lee et al., 2011).