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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.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.

The conventionally clear distinction between exons and introns in eukaryotic genes is actually blurred. To illustrate this point, consider sequences that are retained in mature mRNAs about 50% of the time: how should they be classified? Moreover, although it is clear that RNA splicing influences gene expression levels and is an integral part of interdependent cellular networks, introns continue to be regarded as accidental insertions; exogenous sequences whose evolutionary origin is independent of mRNA-associated processes and somewhat still elusive. Here, we present evidence that aids to resolve this disconnect between conventional views about introns and current knowledge about the role of RNA splicing in the eukaryotic cell. We first show that coding sequences flanked by cryptic splice sites are negatively selected on a genome-wide scale in Paramecium. Then, we exploit selection intensity to infer splicing-related evolutionary dynamics. Our analyses suggest that intron gain begins as a splicing error, involves a transient phase of alternative splicing, and is preferentially completed at the 5’ end of genes, which through intron gain can become highly expressed. We conclude that relaxed selective constraints may promote biological complexity in Paramecium and that the relationship between exons and introns is fluid on an evolutionary scale.

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.

Nucleosomal modifications have been implicated in fundamental epigenetic regulation, but the roles of nucleosome occupancy in shaping changes through evolution remain to be addressed. Here we present high-resolution nucleosome occupancy profiles for multiple tissues derived from human, macaque, tree shrew, mouse, and pig. Genome-wide comparison reveals conserved nucleosome occupancy profiles across both different species and tissue types. Notably, we found significantly higher levels of nucleosome occupancy in exons than in introns, a pattern correlated with the different exon–intron GC content. We then determined whether this biased occupancy may play roles in the origination of new exons through evolution, rather than being a downstream effect of exonization, through a comparative approach to sequentially trace the order of the exonization and biased nucleosome binding. By identifying recently evolved exons in human but not in macaque using matched RNA sequencing, we found that higher exonic nucleosome occupancy also existed in macaque regions orthologous to these exons. Presumably, such biased nucleosome occupancy facilitates the origination of new exons by increasing the splice strength of the ancestral nonexonic regions through driving a local difference in GC content. These data thus support a model that sites bound by nucleosomes are more likely to evolve into exons, which we term the “nucleosome-first” model.

Background The long introns of mammals are pools of evolutionary potential due to the multiplicity of sequences that permit the acquisition of novel exons. However, the permissibility of genes to this type of acquisition and its influence on the evolution of cell regulation is poorly understood. Results Here, we observe that human genes are highly permissive to the inclusion of novel exonic regions permitting the emergence of novel regulatory features. Our analysis reveals the potential for novel exon acquisition to occur in over 30% of evaluated human genes. Regulatory processes including the rate of splicing efficiency and RNA polymerase II (RNAPII) elongation control this process by modulating the “window of opportunity” for spliceosomal recognition. DNA damage alters this window promoting the inclusion of repeat-derived novel exons that reduce the ribosomal engagement of cell cycle genes. Finally, we demonstrate that the inclusion of novel exons is suppressed in hematological cancer samples and can be reversed by drugs modulating the rate of RNAPII elongation. Conclusion Our work demonstrates that the inclusion of repeat-associated novel intronic regions is a tightly controlled process capable of expanding the regulatory capacity of cells.

The human genome is under constant invasion by retrotransposable elements. The most successful of these are the Alu elements; with a copy number of over a million, they occupy about 10 % of the entire genome. Interestingly, the vast majority of these Alu insertions are located in gene-rich regions, and one-third of all human genes contains an Alu insertion. Alu sequences are often embedded in gene sequence encoding pre-mRNAs and mature mRNAs, usually as part of their intron or UTRs. Once transcribed, they can regulate gene expression as well as increase the number of RNA isoforms expressed in a tissue or a species. They also regulate the function of other RNAs, like microRNAs, circular RNAs, and potentially long non-coding RNAs. Mechanistically, Alu elements exert their effects by influencing diverse processes, such as RNA editing, exonization, and RNA processing. In so doing, they have undoubtedly had a profound effect on human evolution.

Background Alternative splicing (AS) generates various transcripts from a single gene and thus plays a significant role in transcriptomic diversity and proteomic complexity. Alu elements are primate-specific transposable elements (TEs) and can provide a donor or acceptor site for AS. In a study on TE-mediated AS, we recently identified a novel AluSz6-exonized ACTR8 transcript of the crab-eating monkey (Macaca fascicularis). In the present study, we sought to determine the molecular mechanism of AluSz6 exonization of the ACTR8 gene and investigate its evolutionary and functional consequences in the crab-eating monkey. Results We performed RT-PCR and genomic PCR to analyze AluSz6 exonization in the ACTR8 gene and the expression of the AluSz6-exonized transcript in nine primate samples, including prosimians, New world monkeys, Old world monkeys, and hominoids. AluSz6 integration was estimated to have occurred before the divergence of simians and prosimians. The Alu-exonized transcript obtained by AS was lineage-specific and expressed only in Old world monkeys and apes, and humans. This lineage-specific expression was caused by a single G duplication in AluSz6, which provides a new canonical 5′ splicing site. We further identified other alternative transcripts that were unaffected by the AluSz6 insertion. Finally, we observed that the alternative transcripts were transcribed into new isoforms with C-terminus deletion, and in silico analysis showed that these isoforms do not have a destructive function. Conclusions The single G duplication in the TE sequence is the source of TE exonization and AS, and this mutation may suffer a different fate of ACTR8 gene expression during primate evolution.

Alu elements contribute considerably to gene regulation and genome evolution in primates. The generation of new exons from Alu elements has been found in various human genes, and the regulatory function of the Alu exon has been investigated in many studies. However, the functionalization of Alu elements in protein coding regions remains unknown. Here, we reported that an Alu-J element exonized in the glycoprotein hormone alpha (GPHA) gene and encoded an additional N-terminal peptide (Alu-J encoding peptide) of the mature GPHA peptide, leading to a splicing variant of Alu-GPHA in anthropoid primates ∼35 Ma. Interestingly, adaptive evolution of the Alu-J exon occurred in the human and ape lineages during anthropoid evolution. The Alu-J encoding peptide is found to be a new biomarker in human early pregnancy and prolongs the serum half-life of human chorionic gonadotropin (HCG) circulation. Moreover, Alu-J encoding peptide enhances the bioactivity of HCG protein, both in vivo and in vitro. Our study reveals the first example of an Alu element functioning as the encoding peptide to increase the whole protein stability and provides insight into the potential multi-functionalization of the Alu exon in the protein coding regions. Furthermore, with the chorionic gonadotropin linking with hemochorial placentation, the exonization and functionalization of the Alu-J exon in GPHA gene represent a novel mechanism to the evolution of hemochorial placentation in primates.

Key message Here, we show that Au SINE elements have strong associations with protein-coding genes in wheat. Most importantly Au SINE insertion within introns causes allelic variation and might induce intron retention . The impact of transposable elements (TEs) on genome structure and function is intensively studied in eukaryotes, especially in plants where TEs can reach up to 90% of the genome in some cases, such as in wheat. Here, we have performed a genome-wide in-silico analysis using the updated publicly available genome draft of bread wheat ( T. aestivum ), in addition to the updated genome drafts of the diploid donor species, T. urartu and Ae. tauschii , to retrieve and analyze a non-LTR retrotransposon family, termed Au SINE, which was found to be widespread in plant species. Then, we have performed site-specific PCR and realtime RT-PCR analyses to assess the possible impact of Au SINE on gene structure and function. To this end, we retrieved 133, 180 and 1886 intact Au SINE insertions from T. urartu, Ae. tauschii and T. aestivum genome drafts, respectively. The 1886 Au SINE insertions were distributed in the seven homoeologous chromosomes of T. aestivum , while ~ 67% of the insertions were associated with genes. Detailed analysis of 40 genes harboring Au SINE revealed allelic variation of those genes in the Triticum–Aegilops genus. In addition, expression analysis revealed that both regular transcripts and alternative Au SINE-containing transcripts were simultaneously amplified in the same tissue, indicating retention of Au SINE-containing introns. Analysis of the wheat transcriptome revealed that hundreds of protein-coding genes harbor Au SINE in at least one of their mature splice variants. Au SINE might play a prominent role in speciation by creating transcriptome variation.

Evolution is change over time. Although neutral changes promoted by drift effects are most reliable for phylogenetic reconstructions, selection-relevant changes are of only limited use to reconstruct phylogenies. On the other hand, comparative analyses of neutral and selected changes of protein-coding DNA sequences (CDS) retrospectively tell us about episodic constrained, relaxed, and adaptive incidences. The ratio of sites with nonsynonymous (amino acid altering) versus synonymous (not altering) mutations directly measures selection pressure and can be analysed by using the Phylogenetic Analysis by Maximum Likelihood (PAML) software package. We developed a CDS extractor for compiling protein-coding sequences (CDS-extractor) and parallel PAML (paPAML) to simplify, amplify, and accelerate selection analyses via parallel processing, including detection of negatively selected sites. paPAML compiles results of site, branch-site, and branch models and detects site-specific negative selection with the output of a codon list labelling significance values. The tool simplifies selection analyses for casual and inexperienced users and accelerates computing speeds up to the number of allocated computer threads. We then applied paPAML to examine the evolutionary impact on a new GINS Complex Subunit 3 exon, and neutrophil-associated as well as lysin and apolipoprotein genes. Compared with codeml (PAML version 4.9j) and HyPhy (HyPhy FEL version 2.5.26), all paPAML test runs performed with 10 computing threads led to identical selection pressure results, whereas the total selection analysis via paPAML, including all model comparisons, was about 3 to 5 times faster than the longest running codeml model and about 7 to 15 times faster than the entire processing time of these codeml runs.