Alternative polyadenylation couples to transcription initiation: Insights from ELAV-mediated 3' UTR extension

Transcription initiation and mRNA maturation were long considered co-occurring but separately regulated events of gene control. In the past decade, gene promoters, the platforms of transcription initiation, have been assigned additional functions such as the regulation of splicing and 3' end processing. In a recent study, Oktaba and Zhang and al. reveal that neural 3' UTR extension is dependent on promoter sequences. In Drosophila neurons, promoter regions of a subset of genes recruit the RNA-binding protein ELAV, which is required for subsequent ELAV-mediated alternative polyadenylation. Intriguingly, RNA Polymerase II pausing at promoters seems to facilitate ELAV recruitment. How transcription initiation and alternative polyadenylation, processes separated by an entire gene length, are functionally linked, remains unsolved. In this article, I summarize recent findings and discuss possible mechanisms

ELAV mediates 3' UTR extension in the Drosophila nervous system

Post-transcriptional gene regulation is prevalent in the nervous system, where multiple tiers of regulatory complexity contributeto the development and function of highly specialized cell types. Whole-genome studies in Drosophila have identified several hundred genes containing long 3′ extensions in neural tissues. We show that ELAV (embryonic-lethalabnormal visual system) is a key mediator of these neural-specific extensions. Misexpression of ELAV results in the ectopicsynthesis of long messenger RNAs (mRNAs) in transgenic embryos. RNA immunoprecipitation assays suggest that ELAV directlybinds the proximal polyadenylation signals of many target mRNAs. Finally, ELAV is sufficient to suppress 3′ end formationat a strong polyadenylation signal when tethered to a synthetic RNA. We propose that this mechanism for coordinating 3′ UTRextension may be generally used in a variety of cellular processes

Regulation of neuronal RNA signatures by ELAV/Hu proteins

The RNA-binding proteins encoded by the highly conserved elav/Hu gene family, found in all metazoans, regulate the expression of a wide range of genes, at both the co-transcriptional and posttranscriptional level. Nervous-system-specific ELAV/Hu proteins are prominent for their essential role in neuron differentiation, and mutations have been associated with human neurodevelopmental and neurodegenerative diseases. Drosophila ELAV, the founding member of the protein family, mediates the synthesis of neuronal RNA signatures by promoting alternative splicing and alternative polyadenylation of hundreds of genes. The recent identification of ELAV's direct RNA targets revealed the protein's central role in shaping the neuronal transcriptome, and highlighted the importance of neuronal transcript signatures for neuron maintenance and organism survival. Animals have evolved multiple cellular mechanisms to ensure robustness of ELAV/Hu function. In Drosophila, elav autoregulates in a 3′UTR-dependent manner to maintain optimal protein levels. A complete absence of ELAV causes the activation and nuclear localization of the normally cytoplasmic paralogue FNE, in a process termed EXon-Activated functional Rescue (EXAR). Other species, including mammals, seem to utilize different strategies, such as protein redundancy, to maintain ELAV protein function and effectively safeguard the identity of the neuronal transcriptome

The PSI-U1 snRNP interaction regulates male mating behavior in Drosophila

Alternative pre-mRNA splicing (AS) is a critical regulatory mechanism that operates extensively in the nervous system to produce diverse protein isoforms. Fruitless AS isoforms have been shown to influence male courtship behavior, but the underlying mechanisms are unknown. Using genome-wide approaches and quantitative behavioral assays, we show that the P-element somatic inhibitor (PSI) and its interaction with the U1 small nuclear ribonucleoprotein complex (snRNP) control male courtship behavior. PSI mutants lacking the U1 snRNP-interacting domain (PSIΔAB mutant) exhibit extended but futile mating attempts. The PSIΔAB mutant results in significant changes in the AS patterns of ∼1,200 genes in the Drosophila brain, many of which have been implicated in the regulation of male courtship behavior. PSI directly regulates the AS of at least one-third of these transcripts, suggesting that PSI-U1 snRNP interactions coordinate the behavioral network underlying courtship behavior. Importantly, one of these direct targets is fruitless, the master regulator of courtship. Thus, PSI imposes a specific mode of regulatory control within the neuronal circuit controlling courtship, even though it is broadly expressed in the fly nervous system. This study reinforces the importance of AS in the control of gene activity in neurons and integrated neuronal circuits, and provides a surprising link between a pleiotropic pre-mRNA splicing pathway and the precise control of successful male mating behavior

A critical developmental window for ELAV/Hu-dependent mRNA signatures at the onset of neuronal differentiation

Cell-type-specific gene regulatory programs are essential for cell differentiation and function. In animal neurons, the highly conserved ELAV/Hu family of proteins promotes alternative splicing and polyadenylation of mRNA precursors to create unique neuronal transcript isoforms. Here, we assess transcriptome profiles and neurogenesis success in Drosophila models engineered to express differing levels of ELAV activity in the course of development. We show that the ELAV-mediated establishment of a subset of neuronal mRNA isoforms at the onset of neuron differentiation constitutes a developmental bottleneck that cannot be overcome later by the nuclear activation of the paralog found in neurons (FNE). Loss of ELAV function outside of that critical time window results in neurological defects. We find that FNE, when activated early enough, can restore ELAV-dependent neuronal mRNA isoforms and fully rescue development. Our findings demonstrate the essential role of robust cellular strategies to maintain ELAV activity and intact neuronal signatures in neurogenesis and neuronal function

ELAV links paused Pol II to alternative polyadenylation in the Drosophila nervious system

Alternative polyadenylation (APA) has been implicated in a variety of developmental and disease processes. A particularly dramatic form of APA occurs in the developing nervous system of flies and mammals, whereby various developmental genes undergo coordinate 3' UTR extension. In Drosophila, the RNA-binding protein ELAV inhibits RNA processing at proximal polyadenylation sites, thereby fostering the formation of exceptionally long 3' UTRs. Here, we present evidence that paused Pol II promotes recruitment of ELAV to extended genes. Replacing promoters of extended genes with heterologous promoters blocks normal 3' extension in the nervous system, while extension-associated promoters can induce 3' extension in ectopic tissues expressing ELAV. Computational analyses suggest that promoter regions of extended genes tend to contain paused Pol II and associated cis-regulatory elements such as GAGA. ChIP-seq assays identify ELAV in the promoter regions of extended genes. Our study provides evidence for a regulatory link between promoter-proximal pausing and APA

Integration of a smoking cessation program in the treatment protocol for patients with head and neck and lung cancer

Smoking is the main causative factor for development of head and neck and lung cancer. In addition, other malignancies such as bladder, stomach, colorectal, kidney and pancreatic cancer have a causative relation with smoking. Continued smoking after having been diagnosed with cancer has many negative consequences: effectiveness of radiotherapy is diminished, survival time is shortened and risks of recurrence, second primary malignancies and treatment complications are increased. In view of the significant health consequences of continued smoking, therefore, additional support for patients to stop smoking seems a logical extension of the present treatment protocols for smoking-related cancers. For prospectively examining the effect of nursing-delivered smoking cessation programme for patients with head and neck or lung cancer, 145 patients with head and neck or lung cancer enrolled into this programme over a 2-year period. Information on smoking behaviour, using a structured, programme specific questionnaire, was collected at baseline, and after 6 and 12 months. At 6 months, 58 patients (40%) had stopped smoking and at 12 months, 48 patients (33%) still had refrained from smoking. There were no differences in smoking cessation results between patients with head and neck and lung cancer. The only significant factor predicting success was whether the patient had made earlier attempts to quit smoking. A nurse-managed smoking cessation programme for patients with head and neck or lung cancer shows favourable long-term success rates. It seems logical, therefore, to integrate such a programme in treatment protocols for smoking-related cancers

Repression of the Hox gene abd-A by ELAV-mediated Transcriptional Interference

Intergenic transcription is a common feature of eukaryotic genomes and performs important and diverse cellular functions. Here, we investigate the iab-8 ncRNA from the Drosophila Bithorax Complex and show that this RNA is able to repress the transcription of genes located at its 3’ end by a sequence-independent, transcriptional interference mechanism. Although this RNA is expressed in the early epidermis and CNS, we find that its repressive activity is limited to the CNS, where, in wild-type embryos, it acts on the Hox gene, abd-A, located immediately downstream of it. The CNS specificity is achieved through a 3’ extension of the transcript, mediated by the neuronal-specific, RNA-binding protein, ELAV. Loss of ELAV activity eliminates the 3’ extension and results in the ectopic activation of abd-A. Thus, a tissue-specific change in the length of a ncRNA is used to generate a precise pattern of gene expression in a higher eukaryote

Simulations of the solar orbiter spacecraft interactions with the solar wind: effects on RPW and SWA/EAS measurements

International audienceWe present numerical simulations of the future Solar Orbiter spacecraft/plasma interactions performed with the Spacecraft Plasma Interaction System (SPIS) software. This spacecraft, to be launched in October 2018, is dedicated to the Sun observation with in-situ and remote sensing instruments, brought as close as 0.28 A.U. from our star. In this hot and dense environment, the entire satellite will be submitted to high radiations and temperatures (up to 10 Solar constants). Material responses to environment constraints (heat, U.V. flux, photoemission, secondary electron emission under electron impact – SEEE – or under proton impact - SEEP) might bias the scientific instrument measurements. Our interest is focused on two instruments: the Radio and Plasma Waves (RPW) and the Electron Analyzer System (EAS)