RNA Biology

Transfer RNAs carry a highly conserved, cloverleaf-like secondary structure, which is essential to fulfill their task as adaptor molecules in translation. However, in mitochondria of metazoans, tRNA molecules were identified that deviate from this consensus structure and lack either the D- or T-arm, or, in some extreme cases, even both arms. These deviations are predominantly found in nematodes and arachnids, where in many cases the entire set of 22 mt tRNA genes are predicted to encode for such aberrant tRNAs or where even the complete loss of tRNA genes is proposed. Due to this unusual composition, we analyzed and characterized the mt tRNA pool of one representative of both groups. We identified the whole set of mt tRNAs and reannotated several tRNAs that differ significantly from previous genome-based predictions. In some cases, the sequence reads indicate putative tRNA editing events, showing that predictions exclusively based on mitogenome data have only a limited reliability. Our data also provide first insights into the modification pattern of such hairpin-like tRNAs.

Transcriptional termination efficiency is considered an important parameter for fine tuning bacterial gene expression. Still, the design principles that determine transcription termination efficiency remain poorly understood. In this study, we aimed to investigate the impact of the 3' untranslated region (3'UTR) on gene expression in Escherichia coli and other bacteria. First, 3'UTR variant sequences were generated, with randomized 30 bp sequences inserted between the STOP-codon and an intrinsic terminator, consisting of a GC-rich hairpin and a downstream poly(U)-tail. Using three reporter genes, it was found that different 3'UTR sequences resulted in an up to five-fold difference in protein production, independent of the upstream coding sequence. The highest protein production was achieved when an adenosine was present directly upstream of the terminator hairpin. This was consolidated by systematic substitution of key nucleotides of the terminator and assessing their effect on mRNA and protein levels. Subsequently, we developed a predictive random forest machine learning model trained on the termination efficiency of different natural and synthetic terminator sequences, revealing an important role for the nucleotides directly upstream of the terminator hairpin. Altogether, this study showed that an additional adenosine nucleotide upstream of the terminator hairpin leads to improved protein production while reducing terminator read-through.

Bacterial small RNAs (sRNAs) regulate gene expression by base pairing with target mRNAs, yet transcriptome-wide interactome mapping has shown that many sRNA-mRNA interactions detected in vivo have modest or no regulatory effect using orthogonal reporter assays. The features that determine functional outcome remain poorly defined. Here, we integrated Hfq-CLASH interactome mapping with matched transcriptomic and proteomic profiling in Escherichia coli and developed an interpretable machine-learning framework to identify the determinants that distinguish functional from non-functional interactions. Using sequence, structural, thermodynamic, duplex and protein-occupancy features, transcriptomic and proteomic responses were predicted with above-chance performance, achieving AUCs of 0.78 and 0.74, respectively. Feature attribution revealed that physical pairing alone is insufficient for regulation; instead, regulatory outcome is shaped by a coordinated interplay between RNA secondary structure, thermodynamic accessibility and local protein-binding context. Target-side Hfq occupancy emerged as a positive predictor of functional regulation, whereas AR2-domain occupancy on the sRNA was associated with non-responsive interactions, suggesting that distinct ribonucleoprotein states may separate productive regulation from non-productive binding. These findings indicate that the regulatory fate of an sRNA-mRNA interaction is an emergent property of its biophysical context and protein-binding environment, rather than a direct consequence of physical pairing alone.

Transfer RNAs (tRNAs) are key molecules that deliver amino acids to the translating ribosome according to their cognate codon encoded in messenger RNA (mRNA). Due to the modified nature of tRNA nucleotides, accurate tRNA quantification can be tedious, especially when dealing with small sample inputs. Here, we took advantage of an RNA-dependent RNA amplification method using T7 polymerase to quantify tRNA abundance in low biological input. Our method, called T7 High-resolution original RNA (Thor)-tRNA-Seq, showed reproducible and quantitative measurement of low tRNA inputs. Thus, our Thor-tRNA-Seq is a robust and reliable approach for the quantification of tRNA in samples with small and precious biological material.

This study proposes a novel therapeutic strategy to suppress cancer growth by modulating the MDM2-p53 axis via Alternative Polyadenylation (APA). MDM2 normally promotes tumorigenesis by ubiquitinating and degrading the tumor suppressor p53. In cancer cells, preferential use of proximal polyadenylation signals (PAS) results in shortened 3'UTRs, allowing oncogenic transcripts like MDM2 to evade nuclear sequestration mediated by Inverted Alu (IRAlu) double-stranded RNA structures. We hypothesized that forcing distal PAS usage would elongate the MDM2 mRNA, promoting its nuclear retention and reducing protein translation, thereby restoring p53 activity. Using CRISPR-Cas9, we targeted and deleted the most frequent proximal PAS in the MDM2 3'UTR of A549 cells. Successful genome editing was confirmed via PCR. As expected, Western blot analysis showed a significant reduction in MDM2 expression in PAS-edited cells. However, experimental outcomes contradicted our initial hypothesis: edited cells exhibited higher viability under doxorubicin treatment compared to wild-type cells. Furthermore, despite decreased MDM2 levels, a concurrent reduction in phosphorylated p53 (p-p53) was observed. These unexpected results suggest that MDM2 3'UTR elongation may trigger a non-canonical regulatory mechanism that bypasses the traditional MDM2-p53 interaction. This study highlights the complexity of post-transcriptional regulation and suggests that APA-mediated gene modulation can induce unforeseen compensatory survival pathways in cancer cells, necessitating further investigation into the broader functional landscape of elongated 3'UTRs.

MicroRNAs (miRNAs) act as key regulators of gene expression across diverse cellular processes, and their precise quantification can provide unique insight into disease pathogenesis. High-throughput sequencing allows for comprehensive small RNA profiling; however, standard commercial library preparation workflows are challenged by issues of low sensitivity and representational bias, limiting reliable profiling, especially in scenarios where samples are scarce. Several structural studies have shown that this bias primarily arises due to sequence and secondary structure variations between miRNAs and adapters during enzyme-catalyzed biochemical reactions. In this work, we propose a new approach to ligation adapter engineering using a bioinformatic analysis of the human miRNome to rationally design structure-forcing 5 adapters, that physically override localized, unpredictable structural variations during the intermediate ligation state. We show that this approach combined with a practical fluorescence-guided workflow, utilizing a fluorescently-labeled 3 adapter and novel Fluorescent Ligation Rulers (FLRs) to guide precise band excision, can minimize representational bias and increase the sensitivity of small RNA sequencing from low-input biological matrices. In comprehensive benchmarks using a synthetic panel, this method significantly reduced bias and outperformed alternative commercial protocols. Finally, we demonstrate that this workflow enhances biomarker detection and library quality in challenging clinical matrices, especially in cerebrospinal fluid. Overall, this protocol enables highly accurate miRNome characterization and is well-suited for biomarker discovery in challenging sample types.

Small regulatory RNAs (sRNAs) are key players in bacterial adaptation to stress. They often occupy central positions in regulatory networks and control the expression of multiple targets. In a striking example of this, the enterobacterial OmrA and OmrB paralogous sRNAs are known to regulate about ten different targets, with extensive data suggesting the regulon is in fact much larger. Here we performed transcriptome and proteome analyses and identified more than fifteen new targets of Escherichia coli OmrA and OmrB. We validated several, including genes involved in central carbon metabolism and fatty acid synthesis, among which ppc, actP and fabA. Consistent with a role in carbon metabolism, overproducing OmrA or OmrB inhibited growth on glucose minimal medium. The analysis of suppressor mutants shows that this is due to a decreased carbon flux through the TCA cycle. Incorporating other datasets such as RIL-seq, we generated a multi-omics-based prediction of target candidates. Together, our results show that OmrA/B base-pair to various regions of their mRNA targets, and therefore likely act through diverse regulatory mechanisms. Hence, this work extends the OmrA and OmrB regulons, establishes an unsuspected connection with carbon usage, and shows the benefits of combining global analyses to investigate sRNA regulons.

BackgroundMicroRNAs (miRNAs) play key roles in modulating gene expression. Upon transcription, primary miRNA transcripts (pri-miRNAs or MIRNAs) fold into stem-loop structures. Endonucleolytic cleavage releases a miRNA/miRNA* duplex from the stem, which is subsequently matured. In higher plants, the pri-miRNA hairpins vary widely in length and structure. Pri-miRNA processing is extensively regulated by RNA-binding proteins (RBPs) and the range of underlying mechanisms continues to expand. ResultsHere, we performed an unbiased screen to identify Arabidopisis thaliana RBPs that interact with pri-miRNAs, using pri-miRNA159a and pri-miRNA398b as paradigms. Nucleoplasmic proteins were significantly enriched in pulldowns with bead-immobilized in vitro transcripts of the stem-loop regions of these pri-miRNAs compared with pulldowns using empty beads. The enriched proteins included several members of the family of the serine/arginine-rich (SR) splicing factor family, including RS31 and SR34a. Mutant analysis indicated that selected candidate interactors affect pri-miRNA and/or mature miRNA accumulation. To validate interactions with pri-miRNAs in vivo, we performed individual-nucleotide resolution crosslinking and immunoprecipitation (iCLIP). Whereas our conventional plant iCLIP procedure detected only a few crosslink sites on pri-miRNAs, likely because of the low abundance of these transcripts, our improved plant iCLIP2 protocol enabled the identification of binding sites on numerous pri-miRNAs. RS31 and SR34a bound overlapping sets of pri-miRNAs and contacted both stem-loop regions and flanking regions upstream and downstream of the stem-loop. RS31 and SR34 bound both overlapping and distinct regions of pri-miRNAs. ConclusionIn vitro pulldowns of nucleoplasmic proteins identified RBPs associated with pri-miRNA stem-loops, and the improved plant iCLIP2 protocol revealed in vivo binding of RS31 and SR34a to a subset of pri-miRNAs. Together, these findings expand the repertoire of RBPs implicated in plant miRNA biogenesis and support a role for SR proteins as candidate regulators of pri-miRNA processing.

O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=79 SRC="FIGDIR/small/745202v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@52e3edorg.highwire.dtl.DTLVardef@1f21637org.highwire.dtl.DTLVardef@909ee8org.highwire.dtl.DTLVardef@b0c907_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGRAPHICAL ABSTRACTC_FLOATNO C_FIG Crosslinking and immunoprecipitation followed by sequencing (CLIP-seq) is widely used to identify the RNA targets of RNA-binding proteins (RBPs). However, its application to non-canonical RBPs lacking canonical RNA-binding domains and frequently displaying low or transient RNA occupancy, is limited by low signal-to-noise ratios, high input requirements and error-prone ligation steps during library preparation. To overcome these limitations, we developed soniCLIP, a streamlined CLIP-seq workflow that replaces RNase-mediated RNA fragmentation with sonication and uses a ligation-free strategy for library construction. soniCLIP is optimized for reproducible identification of enriched RBP-associated RNA regions from limited starting material. We benchmarked soniCLIP against the widespread eCLIP approach and observed reproducible recovery of known RBP-associated regions and target recovery comparable to ENCODE eCLIP, while requiring only 10% (500 {micro}g) of protein input. We further applied soniCLIP to the glycolytic enzyme and non-canonical RBP pyruvate kinase M2 (PKM2). We identified 197 significantly enriched RNA regions and validated selected targets by RIP-qRT-PCR and in vitro binding assays. By combining reduced input requirements, high reproducibility, a shortened 3.5-day workflow and the elimination of gel-based purification, soniCLIP provides an efficient and robust approach for the identification of RNA targets of canonical and non-canonical RBPs.

HighlightsO_LIIdentified hundreds of potential chromatin-associated circRNAs in HEK293 cells, H9, and HeLa cells C_LIO_LIThe first report suggesting global interaction of circular RNAs with chromatin C_LIO_LIChromatin-associated circular RNAs interact with various RBPs involved in RNA splicing or processing C_LI Circular RNAs (circRNAs) have emerged as novel regulators of gene expression by interacting with various proteins and RNAs in a spatiotemporal manner. CircRNAs localized in the cytoplasm regulate mRNA translation or stability by binding to microRNAs and RNA-binding proteins (RBPs), while circRNAs in the nucleus regulate transcription and pre-mRNA splicing by associating with transcription factors and splicing factors. In this study, we sought to explore the interaction between circRNAs and chromatin. Analyzing published RNA-seq data from chromatin fractions identified hundreds of chromatin-associated circRNAs (cacRNAs) in various human cells. We validated the enrichment of a subset of circRNAs in the chromatin fraction and established the direct interaction of circDYNC1H1 and circKIF2C with chromatin in HEK293T cells. Furthermore, cacRNAs were found to interact with RBPs. Together, our research demonstrates the global association of hundreds of circRNAs with chromatin and expands our understanding of novel functional aspects of the circRNAs. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=186 SRC="FIGDIR/small/739476v1_ufig1.gif" ALT="Figure 1"> View larger version (69K): org.highwire.dtl.DTLVardef@1fc8831org.highwire.dtl.DTLVardef@516cdcorg.highwire.dtl.DTLVardef@1c20395org.highwire.dtl.DTLVardef@79313a_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstractC_FLOATNO C_FIG

Transfer RNA (tRNA) modifications are essential for translational accuracy and cellular adaptation to environmental changes. While short-term modification dynamics are well documented, the impact of prolonged stress exposure on the global tRNA landscape remains largely unexplored. This study provides the first systematic profiling of tRNA modifications in Saccharomyces cerevisiae following long-term exposure to distinct stress types: heat, suboptimal pH, oxidative stress (paraquat and diamide), osmotic stress (NaCl and KCl), and genotoxic stress (MMS). To this end, we used a broad-range UPLC-MS protocol to quantify global changes in tRNA modification and identify stress-specific signatures. The results revealed that long-term stress triggers a global reprogramming of the tRNA epitranscriptome in a stress-specific and time-dependent manner. Importantly, while our findings confirm the previously reported temperature-sensitivity of wobble uridine thiolation, we also identified a complete or partial loss of 5-methoxycarbonylmethyl-2-thiouridine (mcm5s2U34) modification upon exposure to paraquat and pH stress. Furthermore, this loss of thiolation is accompanied by an accumulation of the non-thiolated 5-methoxycarbonylmethyl (mcm5U) precursor, suggesting a stress-dependent impairment of the thiolation pathway. Next, we applied MarathonRT-based tRNA sequencing and showed that these modification changes occur independently of tRNA isoacceptor abundance. To further integrate these results, we devised a modification deviation (MDm) index, which indicates that the observed reprogramming is primarily linked to events that are independent from changes in tRNA abundance. Together, this study provides a comprehensive atlas of tRNA modification dynamics under prolonged stress, addressing a critical gap in our understanding of RNA-based translational control and establishes the MDm index as a robust quantitative framework to decouple the influence of tRNA abundance from global modification signals, providing a necessary metric for the field to interpret epitranscriptomic reprogramming. TABLE OF CONTENTS GRAPHIC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=108 SRC="FIGDIR/small/745200v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@2cf571org.highwire.dtl.DTLVardef@1a5f3c2org.highwire.dtl.DTLVardef@266d61org.highwire.dtl.DTLVardef@d7214f_HPS_FORMAT_FIGEXP M_FIG C_FIG

SARS-CoV-2 nonstructural protein 1 (Nsp1) binds to 40S ribosomal subunits and induces host protein synthesis shut off by inhibiting translation initiation and triggering endonucleolytic cleavage of cellular mRNAs. Irrespective of the mode of initiation, Nsp1-mediated cleavage is induced by the cooperative action of the N-terminal domain of Nsp1, the RRM domain of eIF3g and 40S subunits. Using in vitro reconstitution, we determined that cleavage occurs by transesterification following intramolecular nucleophilic attack of the 2’OH of the ribose on the adjacent phosphodiester bond yielding 5’OH and 2’,3‘-cyclic phosphate termini. Cleavage requires a guanosine ∼10-22 nucleotides from the 5’ end of mRNA, occurs within a narrow window upstream of this G, is most efficient between nucleotides at positions -6/-7 and -7/-8 relative to G, and shows a preference for Pu at positions -7 or -8 which provides the 2’OH for the nucleophilic attack. Zero-length UV cross-linking of Nsp1 to nucleotides at positions -1 and -2 suggests that the critical guanosine may be recognized by Nsp1. Resistance to Nsp1-mediated cleavage of SARS-CoV-2 mRNA was ensured both by the relatively long distance between its G 23 G 24 and the 5’end and by the preceding oligoPy stretch lacking purines at positions -7 or -8 upstream of G 23 G 24 .

The zebra mussel (Dreissena polymorpha) is an invasive species that causes extensive economic and ecological damage. Here, we identify and characterize the key components of the small RNA (sRNA) and RNA interference (RNAi) pathways in zebra mussels. Like other mollusks, zebra mussels have extensive microRNA (miRNA) and Piwi-interacting RNA (piRNA) machinery but lack or have modified canonical factors needed to produce small interfering RNA (siRNA). Specifically, the zebra mussel Dicer sequence displays substitutions in the conserved DEAD box motif that is required for substrate processivity, and this organism also lacks some attendant accessory factors such as R2D2. We sequenced the small RNA found in both isolated somatic tissue (adductor muscle) and whole animals (including germline), and identified both conserved and novel miRNA and diverse piRNA sequences, but few endogenous siRNAs. To determine whether their remaining sRNA machinery could still be co-opted to initiate gene silencing, we injected dsRNA targeting several genes into zebra mussel adductor muscle. The injected rpn8-targeting dsRNA reduced rpn8 mRNA levels and was processed into sRNA that resemble endogenous miRNAs and piRNAs. The levels of both sRNA types correlated with mRNA knockdown, suggesting that they may act together to initiate RNAi as seen elsewhere. dsRNA targeting other genes produced variable results suggesting that particular criteria may be needed to trigger an RNAi response in this assay. Our results characterize endogenous sRNA pathways in zebra mussels, establish that dsRNA can induce RNAi, and lay the groundwork for further optimizations to establish RNAi-based genetic manipulation tools for this damaging invasive species.

Bacterial small non-coding RNAs (sRNAs) are central post-transcriptional regulators, yet their computational identification suffers from high false-positive rates due to transcriptional noise and the absence of canonical coding features. We developed a three-stage pipeline integrating sRNA prediction (sRNA-Detect), transcription start site mapping (TSSAR, dRNA-seq), and Rho-independent terminator detection (RNIE), applied across nine phylogenetically diverse bacterial species spanning six phyla. Sequential filtering achieved 1.4 to 33 fold precision improvements across nine species, reducing candidate sets by up to 99.6% while recovering known sRNAs at rates reflecting reference database depth (6% recall in S. aureus, 33-34% in E. coli and S. enterica) TSS and RIT constraints constitute universal, genome-size-independent biological filters that substantially enrich sRNA predictions across bacterial diversity. Precision variation across species reflects database incompleteness rather than pipeline failure, with unmatched predictions in poorly annotated organisms representing candidate novel sRNAs rather than false positives. RNA-seq coverage depth provides a reliable secondary indicator of biological relevance, though its interpretation requires accounting for sequencing depth variation across datasets.

Various methods have detected miRNA-target interactions via immunoprecipitation of UV-crosslinked Argonaute ribonucleoprotein complexes, followed by intermolecular ligation of bound miRNAs to target strands, forming chimeric RNAs. To date, these methods have relied on conventional viral reverse transcriptases (RTs) to generate cDNAs for sequencing. However, crosslinked RNAs often retain adducts after purification, which can make them poor templates for viral RTs. Here, we adapted OTTR (Ordered Two-Template Relay) techniques to generate cDNAs from Ago2-bound RNAs. OTTR makes use of a modified retroelement-encoded RT, which is strongly processive even on templates with modifications or adducts. We show that this "OTTR-CLASH" method increases the frequency of generating chimeric RNAs compared to previous methods. We also developed an improved bioinformatic pipeline for analysis of these data, and we use this to catalog miRNA-target interactions not previously described in the literature. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=147 HEIGHT=200 SRC="FIGDIR/small/738487v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@13bc276org.highwire.dtl.DTLVardef@5beb41org.highwire.dtl.DTLVardef@b204e5org.highwire.dtl.DTLVardef@15f747d_HPS_FORMAT_FIGEXP M_FIG C_FIG

In mammalian reproduction, sperm and oocytes fuse to generate embryos. In contrast to maternally inherited small RNAs, sperm-borne small RNAs have been implicated in embryo viability but remain incompletely understood. Unanswered questions about molecular forces shaping small RNA content in sperm and sources of reporting discrepancies hinder a deeper understanding of their post-fertilization roles. Here, we investigate the dynamics and protein association of small RNAs in C57BL/6 mice during spermiogenesis and sperm capacitation. Using unique molecular identifiers and spike-ins to minimize technical biases in low-input sequencing, we demonstrate a selective sperm small RNA repertoire derived from a subset of spermatogenic small RNAs that remains malleable during capacitation. Retained PIWI-interacting RNAs persist despite widespread RNA decay and are insensitive to capacitation, which may be partly attributed to their association with MIWI proteins. Our data reveal RNA species susceptible to PCR duplicate-related abundance overestimation and uncover biological and technical factors shaping experimentally observed sperm small RNA profiles. These findings refine our understanding of sperm-borne RNAs and inform future functional studies and medically assisted reproduction.

Viruses alter host gene expression to create a proviral environment while the host simultaneously regulates gene expression to restrict the virus spread. Owing to RNA virus complete reliance on the host translational machinery, it is important to assess the translational control during virus infection. Therefore, we used ribosome profiling (ribo-seq) paired with RNAseq to observe how red clover necrotic mosaic virus (RCNMV) infection of Arabidopsis plants alters cellular gene expression at the levels of mRNA abundance and translation efficiency. We determined that at 5 days post-inoculation (dpi), the translational response to RCNMV infection is enriched in genes of the innate immune system. Expression of a tumor necrosis factor receptor-associated factor (TRAF)-like protein, a regulator of development and immune response, was translationally but not transcriptionally upregulated early in systemic infection. By 8 dpi, many pathways were regulated/dysregulated, and unfolded protein response (UPR) genes were transcriptionally upregulated but with reduced translation efficiency. Ribosome profiling of RCNMV RNAs revealed (i) -1 programmed ribosomal frameshifting at 7.5-8.0%, the first direct measurement of frameshift efficiency in infected cells for any plant virus; (ii) that coat protein is translated at extremely high efficiency, while the RNA-dependent RNA polymerase is translated least efficiently, and (iii) an unexpected extremely strong ribosomal pause site in the open reading frame that encodes the movement protein. To our knowledge, this is the first genome-wide study that assesses the translational control of gene expression in plants infected with a virus from the large and diverse Tombusviridae family. ImportancePositive strand RNA viruses usurp the hosts translation machinery to synthesize viral proteins. Moreover, translation of host mRNAs is altered by virus infection, both as part of the host immune response and by the virus to inhibit host defenses. To assess all these changes globally, we used ribosome profiling of plants infected with a member of the large and ubiquitous Tombusviridae family. We identified key host genes and pathways that were differentially altered in translation efficiency, giving us an understanding of host responses not detectable by conventional RNA sequencing. Moreover, ribosome profiling revealed (i) the most accurate calculation of efficiency of ribosomal frameshifting during infection for any plant virus, (ii) the extremely high level of translation of viral coat protein, and (iii) an unexpected strong ribosomal pause site in the movement protein gene. This work provides understanding of a new dimension of gene expression control in plant-virus interactions.

The maternal-to-zygotic transition (MZT) is a major developmental event during which inherited transcripts are remodeled and zygotic transcription is established. Although parentally inherited long noncoding RNAs (lncRNAs) are present in early embryos, they have been thought to be dispensable. We have identified more than 2000 inherited lncRNAs in zebrafish embryos, but how these RNAs participate in regulatory programs during early development has remained unexplored. Here, the inheritance of selected zebrafish lncRNAs spanning a broad expression range were confirmed at the pre-MZT stage and full-length sequences were captured by Direct RNA nanopore sequencing. We show that 30% inherited intergenic lncRNAs are preferentially associated with active enhancers, annotated as such in DANIO CODE, whereas non-inherited intergenic lncRNAs rarely overlap with enhancers. Perturbation of five inherited intergenic lncRNAs, individually, using antisense oligonucleotides reduced the expression of their respective neighboring genes at 2.5, 4.3, and/or 6 hours post fertilization, indicating that these RNAs act as positive local regulators during MZT. Together, these findings identify inherited intergenic lncRNAs as enhancer-associated regulators with elncRNA-like properties during early embryogenesis.

Interleukin 27 (IL-27) is an anti-HIV cytokine that induces 14 novel microRNAs (miRNAs) in T cells. We previously reported that transfection of two of these miRNA mimics, miRTC10 and miRTC14, differentially induced interferons (IFN)A2, A8, A13, and L1 expression in human primary macrophages. However, the mechanism underlying this activation remains unclear. Here, we show that miRTC14 does not directly target IFN-regulatory genes but instead engages cytosolic RNA-sensing proteins. Using miRNA pull-down coupled with mass spectrometry and immunoblotting, we identified a metabolic enzyme, pyruvate carboxylase (PC) and laboratory of genetics and physiology 2 (LGP2/DHX58) as direct binding partners of miRTC14. Functional analyses revealed that miRTC14 induces IFN expression by more than100-fold (p < 0.001), whereas PC and LGP2 depletion markedly attenuated this response (50-100 fold reduction, p < 0.01). Reconstitution of PC and LGP2 in deficient HEK293 cells restored miRTC14-driven IFN induction. We found that miRTC14-induced IFN activation depends on sequence features at the duplex termini and is unlikely to arise from canonical miRNA-mediated gene silencing. These findings establish PC as a novel miRNA-binding protein and define a previously unrecognized RNA-sensing mechanism by which miRTC14 drives IFN production, linking metabolic enzymes to RNA sequence-dependent innate immunity.

The majority of eukaryotes encode some intron-containing pre-tRNAs. Splicing of these pre-tRNAs requires a dedicated tRNA splicing machinery. The fungal and trypanosome tRNA ligase, Trl1, and the human RNA ligase, RTCB, catalyze an essential step in tRNA splicing. However, Trl1 and RTCB are nonhomologous and biochemically and structurally distinct from each other. Therefore, Trl1 could serve as a broad-spectrum antifungal and anti-trypanosomal target. While the functions and requirements of the three catalytic Trl1 domains have been extensively characterized in the model yeast Saccharomyces cerevisiae, the roles of Trl1 orthologs in pathogenic fungi remain unexplored. Here, we validate Trl1 as one of the few promising novel drug targets for the development of antifungal therapeutics. Functional analyses of the three Trl1 domains show that only the "sealing" domain is essential for growth and viability in Candida albicans and Aspergillus fumigatus. In contrast, the two "healing" domains are dispensable in these pathogenic fungi, suggesting the presence of redundant healing enzymes, unlike in S. cerevisiae. These findings indicate that only the sealing domain is a good drug target. Our analysis also shows that the Mucor enzyme, which only contains the sealing domain, is essential. Using a Caenorhabditis elegans infection model of C. albicans, we further demonstrated that inhibiting Trl1 expression protects worms during an established infection. In contrast to these fungal pathogens, we show that all three domains of Trl1 are essential in Trypanosoma brucei. Our findings show that the essentiality of the Trl1 sealing is conserved in important human pathogens and provides an impetus for future drug development. SIGNIFICANCEFungal infections are an important cause of human disease and death and difficult to treat and there is an urgent need to develop additional drugs. Based on studies in yeast, one promising target for antifungal drug development is the tRNA splicing pathway. Human tRNA ligase is fundamentally distinct from the fungal one. To investigate the possibility of developing tRNA ligase-targeting drugs, we investigated the function of the catalytic domains of fungal tRNA ligase in different fungal pathogens. Surprisingly, only the first domain is essential in these pathogens and yeast is not a good model fungus. In contrast, all three domains of Trypanosome tRNA ligase are essential. These findings provide an impetus for future drug development.