GO enrichment analysis

One model organism per taxa was selected to perform the GO enrichment analyses: Drosophila melanogaster, Danio rerio, Gallus gallus and Homo sapiens. All proteins from the set of orthologs from these four species were retrieved, and their Ensembl protein ID were mapped to either UniProt accession numbers using the ID mapping resource provided by UniProt [33] (D. rerio, G. gallus and H. sapiens) or to FlyBase gene ID using the Convert ID tool provided by the FlyBase database version FB2019_04 [34] (D. melanogaster). The mapped IDs were distributed in independent files depending on the category of the polyQ they contain (or at least one of their orthologs). These ID lists were used to perform the GO enrichment analyses in DAVID v6.8 [33] per organism and per category. Number of IDs successfully mapped to DAVID IDs per polyQ category (1–3) were: 115, 785, and 1267 for D. melanogaster; 978, 562, and 890 for D. rerio; 562, 137, and 163 for G. gallus; and 1369, 264, and 488 for H. sapiens. Selected annotations were UP_KEYWORDS, GOTERM_BP_DIRECT, GOTERM_CC_DIRECT and GOTERM_MF_DIRECT. Duplicated enriched GO terms (e.g. “GP:0005737 ~ cytoplasm” and “Cytoplasm”) were manually simplified to keep only one result. Only the top-10 enriched GO terms per species and categories were taken into account, for simplification purposes; all of them with p-values < 0.05.