In search for a mechanism that might allow PTBP1 to function as a bona fide splicing activator we examined cassette exons consistently up- and down-regulated upon knocking down this RBP alone (siPtbp1) or together with its functionally similar paralog PTBP2 (27) (siPtbp1/2) in the mouse neuroblastoma cell line CAD (Supplementary Tables S1 and S2; see Materials and Methods). This evidence concerns the gene PTBP1 and neuroblastoma.