The use of alternative promoters, splicing, and cleavage and polyadenylation (APA) generates mRNA isoforms that expand the diversity and complexity of the transcriptome. Here, we uncovered thousands of previously undescribed 5\' uncapped and polyadenylated transcripts (5\' UPTs). We show that these transcripts resist exonucleases due to a highly structured RNA and N6-methyladenosine modification at their 5\' termini. 5\' UPTs appear downstream of APA sites within their host genes and are induced upon APA activation. Strong enrichment in polysomal RNA fractions indicates 5\' UPT translational potential. Indeed, APA promotes downstream translation initiation, non-canonical protein output, and consistent changes to peptide presentation at the cell surface. Lastly, we demonstrate the biological importance of 5\' UPTs using Bcl2, a prominent anti-apoptotic gene whose entire coding sequence is a 5\' UPT generated from 5\' UTR-embedded APA sites. Thus, APA is not only accountable for terminating transcripts, but also for generating downstream uncapped RNAs with translation potential and biological impact.

Most human genes have diverse transcript isoforms, which mainly arise from alternative cleavage and polyadenylation (APA) at 3\' ends. N7-methylguanosine (m7 G) is also an essential epigenetic modification at the 5\' end. However, the contribution of these two RNA modifications to the development, prognosis, regulation mechanisms, and drug sensitivity of gastric cancer (GC) is unclear.
The expression data of 2412 patients were extracted from 12 cohorts and the RNA modification patterns of 20 marker genes were systematically identified into phenotypic clusters using the unsupervised clustering approach. Following that, we developed an RNA modification model (RMscore) to quantify each GC patient\'s RNA modification index. Finally, we examined the correlation between RMscore and clinical features such as survival outcomes, molecular subtypes identified by the Asian Cancer Research Group (ACRG), posttranscriptional regulation, and chemotherapeutic sensitivity in GC.
The samples were categorized into two groups on the basis of their RMscore: high and low. The group with a low RMscore had a bad prognosis. Moreover, the low RMscore was associated with KRAS, Hedgehog, EMT, and TGF-β signaling, whereas a high RMscore was related to abnormal cell cycle signaling pathway activation. The findings also revealed that the RMscore contributes to the regulation of the miRNA-mRNA network. Drug sensitivity analysis revealed that RMscore is associated with the response to some anticancer drugs.
The RMscore model has the potential to be a useful tool for prognosis prediction in patients with GC. A comprehensive investigation of APA-RNA and m7 G-RNA modifications may reveal novel insights into the epigenetics of GC and aid in the development of more effective treatment strategies.

Pseudouridine is a modified nucleotide that is prevalent in human mRNAs and is dynamically regulated. Here, we investigate when in their life cycle mRNAs become pseudouridylated to illuminate the potential regulatory functions of endogenous mRNA pseudouridylation. Using single-nucleotide resolution pseudouridine profiling on chromatin-associated RNA from human cells, we identified pseudouridines in nascent pre-mRNA at locations associated with alternatively spliced regions, enriched near splice sites, and overlapping hundreds of binding sites for RNA-binding proteins. In vitro splicing assays establish a direct effect of individual endogenous pre-mRNA pseudouridines on splicing efficiency. We validate hundreds of pre-mRNA sites as direct targets of distinct pseudouridine synthases and show that PUS1, PUS7, and RPUSD4-three pre-mRNA-modifying pseudouridine synthases with tissue-specific expression-control widespread changes in alternative pre-mRNA splicing and 3\' end processing. Our results establish a vast potential for cotranscriptional pre-mRNA pseudouridylation to regulate human gene expression via alternative pre-mRNA processing.

Alternative cleavage and polyadenylation (APA) is pervasive, occurring for more than 70% of human and mouse genes. Distal poly(A) site selection to generate longer 3\' UTR mRNA isoforms is prevalent in the nervous system, affecting thousands of genes. Here, we establish mouse embryonic stem cell (mESC)-derived neurons (mES-neurons) as a suitable system to study long 3\' UTR isoforms. RNA-seq analysis revealed that mES-neurons show widespread 3\' UTR lengthening that closely resembles APA patterns found in mouse cortex. mESCs are highly amenable to genetic manipulation. We present a method to eliminate long 3\' UTR isoform expression using CRISPR/Cas9 editing. This approach can lead to clones with the desired deletion within several weeks. We demonstrate this strategy on the Mprip gene as a proof-of-principle. To confirm loss of long 3\' UTR expression and the absence of cryptic poly(A) site usage stemming from the CRISPR deletion, we present a simple and cost-efficient targeted long-read RNA-sequencing strategy using the Oxford Nanopore Technologies platform. Using this method, we confirmed specific loss of the Mprip long 3\' UTR isoform. CRISPR gene editing of mESCs thus serves as a highly relevant platform for studying the molecular and cellular functions of long 3\' UTR mRNA isoforms.

In the messenger RNA (mRNA) maturation process, the 3\'-end of pre-mRNA is cleaved and a poly(A) sequence is added, this is an important determinant of mRNA stability and its cellular functions. More than 60%-70% of human genes have three or more polyadenylation (APA) sites and can be cleaved at different sites, generating mRNA transcripts of varying lengths. This phenomenon is termed as alternative cleavage and polyadenylation (APA) and it plays role in key biological processes like gene regulation, cell proliferation, senescence, and also in various human diseases. Loss of regulatory microRNA binding sites and interactions with RNA-binding proteins leading to APA are largely investigated in human diseases. However, the functions of the core APA machinery and related factors during disease conditions remain largely unknown. In this review, we discuss the roles of polyadenylation machinery in relation to brain disease, cardiac failure, pulmonary fibrosis, cancer, infectious conditions, and other human diseases. Collectively, we believe this review will be a useful avenue for understanding the emerging role of APA in the pathobiology of various human diseases.

During the maturation of pre-mRNAs and some lncRNAs, their 3\'ends are cleaved and polyadenylated. The cleavage and polyadenylation (C/P) require the presence of a polyadenylation signal (PAS) at the RNA 3?end. Most eukaryotic genes have multiple PASs, resulting in alternative cleavage and polyadenylation (APA). APA leads to transcript isoforms with different coding potentials and/or variable 3?UTRs. The 3\'UTR affects mRNA stability, translation, transportation, and cellular localization. Therefore, APA is an important mechanism of posttranscriptional gene regulation in eukaryotes. In recent years, whole genome sequencing of animals, plants and yeast has revealed that APA is pervasive in eukaryotes, and the functional consequences and regulation of APA have been studied. To date, many cis-acting regulatory elements and trans-acting factors for APA regulation have been identified. In this review, we summarize the recent advances in the functional consequences and regulation of APA and discuss the future directions, aiming to provide clues and references for future APA study.
真核生物基因的前体mRNA (pre-mRNA)及一些lncRNA在成熟过程中其3\'端会发生剪切和多聚腺苷酸化反应(cleavage and polyadenylation, C/P),C/P的发生需要多聚腺苷酸化信号(polyadenylation signal, PAS)的存在。选择性多聚腺苷酸化(alternative cleavage and polyadenylation, APA)是指具有多个PAS的基因,在其mRNA 3?端成熟过程中,由于选择不同的PAS,导致产生出多个3\'UTR长度和序列组成不同的转录异构体。3?UTR长度和序列的不同会影响mRNA的稳定性、翻译效率、运输和细胞定位等,因此APA是真核生物的一个重要转录后调控方式。近年来,对大量动物、植物及酵母的基因组测序分析发现,APA在真核生物广泛存在,针对APA的生物学效应和调控机制开展了一系列研究。目前已鉴定出许多APA调控的顺式调控元件和反式作用因子。本文重点介绍了APA生物学效应和调控机制的最新研究进展,并探讨了未来APA调控的研究方向。.

Dysregulation of DNA methylation and mRNA alternative cleavage and polyadenylation (APA) are both prevalent in cancer and have been studied as independent processes. We discovered a DNA methylation-regulated APA mechanism when we compared genome-wide DNA methylation and polyadenylation site usage between DNA methylation-competent and DNA methylation-deficient cells. Here, we show that removal of DNA methylation enables CTCF binding and recruitment of the cohesin complex, which, in turn, form chromatin loops that promote proximal polyadenylation site usage. In this DNA demethylated context, either deletion of the CTCF binding site or depletion of RAD21 cohesin complex protein can recover distal polyadenylation site usage. Using data from The Cancer Genome Atlas, we authenticated the relationship between DNA methylation and mRNA polyadenylation isoform expression in vivo. This DNA methylation-regulated APA mechanism demonstrates how aberrant DNA methylation impacts transcriptome diversity and highlights the potential sequelae of global DNA methylation inhibition as a cancer treatment.

Many metazoan genes express alternative long 3\' UTR isoforms in the nervous system, but their functions remain largely unclear. In Drosophila melanogaster, the Dscam1 gene generates short and long (Dscam1-L) 3\' UTR isoforms because of alternative polyadenylation (APA). Here, we found that the RNA-binding protein Embryonic Lethal Abnormal Visual System (Elav) impacts Dscam1 biogenesis at two levels, including regulation of long 3\' UTR biogenesis and skipping of an upstream exon (exon 19). MinION long-read sequencing confirmed the connectivity of this alternative splicing event to the long 3\' UTR. Knockdown or CRISPR deletion of Dscam1-L impaired axon outgrowth in Drosophila. The Dscam1 long 3\' UTR was found to be required for correct Elav-mediated skipping of exon 19. Elav thus co-regulates APA and alternative splicing to generate specific Dscam1 transcripts that are essential for neural development. This coupling of APA to alternative splicing might represent a new class of regulated RNA processing.

Deep sequencing of the 3\' end region of poly(A)+ RNA identifies the cleavage and polyadenylation site (PAS) and measures transcript abundance. However, mispriming at internal A-rich regions by the oligo-dT oligo in reverse transcription can lead to falsely identified PASs. This problem can be resolved by direct ligation of an adapter to the 3\' end of RNA. However, ligation-based methods are often inefficient. Here, we describe 3\'READS+, an accurate and sensitive method for deep sequencing of the 3\' end of poly(A)+ RNA. Through partial digestion by RNase H of the poly(A) tail bound to a locked nucleic acid (LNA)/DNA hybrid oligo, this method sequences an optimal number of terminal A\'s, which balances sequencing quality and accurate identification of PAS in A-rich regions. With efficient ligation steps, 3\'READS+ is amenable to small amounts of input RNA. 3\'READS+ can also be readily used as a cost-effective method for gene expression analysis.

Cleavage and polyadenylation (pA) is a fundamental step that is required for the maturation of primary protein encoding transcripts into functional mRNAs that can be exported from the nucleus and translated in the cytoplasm. 3\'end processing is dependent on the assembly of a multiprotein processing complex on the pA signals that reside in the pre-mRNAs. Most eukaryotic genes have multiple pA signals, resulting in alternative cleavage and polyadenylation (APA), a widespread phenomenon that is important to establish cell state and cell type specific transcriptomes. Here, we review how pA sites are recognized and comprehensively summarize how APA is regulated and creates mRNA isoform profiles that are characteristic for cell types, tissues, cellular states and disease.