Required for pre-mRNA splicing and for exon-junction complex (EJC) assembly. Hinders EIF4A3 from non-specifically binding RNA and escorts it to the splicing machinery to promote EJC assembly on mature mRNAs. Through its role in EJC assembly, required for nonsense-mediated mRNA decay (By similarity). Plays a role in the nuclear retention of unspliced mRNAs (PubMed:23149939). Plays a role in sex determination (PubMed:23149939). Required for early embryogenesis and tissue differentiation. Expressed in germ cells, oocytes, and sperm cells. Expressed ubiquitously throughout development. RNAi-mediated knockdown results in germline masculinization and the accumulation of unspliced mRNAs in the cytoplasm. Belongs to the CWC22 family.