Dynamic Variations of 3'UTR Length Reprogram the mRNA Regulatory Landscape

This paper concerns 3'-untranslated regions (3'UTRs) of mRNAs, which are non-coding regulatory platforms that control stability, fate and the correct spatiotemporal translation of mRNAs. Many mRNAs have polymorphic 3'UTR regions. Controlling 3'UTR length and sequence facilitates the regulation of the accessibility of functional effectors (RNA binding proteins, miRNAs or other ncRNAs) to 3'UTR functional boxes and motifs and the establishment of different regulatory landscapes for mRNA function. In this context, shortening of 3'UTRs would loosen miRNA or protein-based mechanisms of mRNA degradation, while 3'UTR lengthening would strengthen accessibility to these effectors. Alterations in the mechanisms regulating 3'UTR length would result in widespread deregulation of gene expression that could eventually lead to diseases likely linked to the loss (or acquisition) of specific miRNA binding sites. Here, we will review the mechanisms that control 3'UTR length dynamics and their alterations in human disorders. We will discuss, from a mechanistic point of view centered on the molecular machineries involved, the generation of 3'UTR variability by the use of alternative polyadenylation and cleavage sites, of mutually exclusive terminal alternative exons (exon skipping) as well as by the process of exonization of Alu cassettes to generate new 3'UTRs with differential functional features.