Disclosed herein are methods, compositions, polynucleic acid polymers, assays, and kits for inducing processing of a partially processed mRNA transcript to remove a retained intron to produce a fully processed mRNA transcript that encodes a full-length functional form of a protein. Also described herein are methods and compositions for treating a disease or condition characterized by impaired production of a full-length functional form of a protein or for treating a disease or condition characterized by a defective splicing in a subject.