DDX21 and urinary bladder carcinoma: Alternative splicing–splicing factor regulatory network analysis has identified several splicing factors, including pre-mRNA processing factor 39 (PRPF39), LUC7-like 3 pre-mRNA splicing factor (LUC7L), heat shock protein family A member 8 (HSPA8), and DEAD-box helicase 21 (DDX21), as potential biomarkers for bladder cancer (113).