C9orf72 and amyotrophic lateral sclerosis: To identify interactors, biotin-GFP-tagged (bioGFP) constructs were generated for ATXN2, C9orf72, FUS, OPTN, TDP-43, and UBQLN2 as well as for a common ALS-associated mutant variant of each of these proteins (ATXN2 31Q, 39Q, FUS R521C, OPTN E478G, TDP-43 M337V and UBQLN2 P497H) (Fig. 1a).