ADGRD1 and glioblastoma: To investigate which isoform is relevant in GBM, we performed qRT–PCR on five primary GBM cultures using two different Taqman probes: one against the full N-terminal ectodomain (detecting only the long isoform) and one against the C-terminal cytoplasmic domain of GPR133 (detecting all isoforms) (Supplementary Table 2a).