The present embodiments provide for compositions and methods that regulate microRNA-binding protein-mediated miRNA biogenesis; for example Lin28-mediated biogenesis of let-7; and in particular Lin28A-recruited 3' terminal uridylyl transferase (TUTase) uridylation of pre-let-7. A particular embodiment provides compositions and methods for screening for agents that inhibit TUTase-dependent Lin28A-mediated repression of let-7 miRNA.