Cooperative evolution of two different TEs results in lineage-specific novel transcripts in the BLOC1S2 gene

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.

Sense-oriented AluYRa1 elements provide a lineage-specific transcription environment for polyadenylation

Transposable elements cause alternative splicing (AS) in different ways, contributing to transcript diversification. Alternative polyadenylation (APA), one of the AS events, is related to the generation of mRNA isoforms in 70% of human genes. In this study, we tried to investigate AluYRa1s located at the terminal region of cynomolgus monkey genes, utilizing both computational analysis and molecular experimentation. We found that ten genes had AluYRa1 at their 3' end, and nine of these AluYRa1s were sense-oriented. Furthermore, in seven genes, AluYRa1s were expected to have a similar consensus sequence for polyadenylation cleavage. Additional computational analysis using the annotation files from the UCSC database showed that AluYRa1 was more involved in polyadenylation than in open reading frame exon splicing. To examine the extent of AluYRa1 involvement in polyadenylation, RNA-seq data from 30 normal cynomolgus monkeys were analyzed using TAPAS, a recently devised software that detects all the promising polyadenylation sites including APA sites. We observed that approximately 74% of possible polyadenylation sites in the analyzed genes were provided by sense-oriented AluYRa1. In conclusion, AluYRa1 is an Old-World monkey-specific TE, and its sense-oriented insertion at the 3'UTR region tends to provide a favorable environment for polyadenylation, diversifying gene transcripts.