Mammalian antiviral systems directed by small RNA

There are strong incentives for human populations to develop antiviral systems. Similarly, genomes that encode antiviral systems have had strong selective advantages. Protein-guided immune systems, which have been well studied in mammals, are necessary for survival in our virus-laden environments. Small RNA–directed antiviral immune systems suppress invasion of cells by non-self genetic material via complementary base pairing with target sequences. These RNA silencing-dependent systems operate in diverse organisms. In mammals, there is strong evidence that microRNAs (miRNAs) regulate endogenous genes important for antiviral immunity, and emerging evidence that virus-derived nucleic acids can be directly targeted by small interfering RNAs (siRNAs), PIWI-interacting RNAs (piRNAs), and transfer RNAs (tRNAs) for protection in some contexts. In this review, we summarize current knowledge of the antiviral functions of each of these small RNA types and consider their conceptual and mechanistic overlap with innate and adaptive protein-guided immunity, including mammalian antiviral cytokines, as well as the prokaryotic RNA-guided immune system, CRISPR. In light of recent successes in delivery of RNA for antiviral purposes, most notably for vaccination, we discuss the potential for development of small noncoding RNA–directed antiviral therapeutics and prophylactics.

Are Argonaute-Associated Tiny RNAs Junk, Inferior miRNAs, or a New Type of Functional RNAs?

The biosynthesis pathways of microRNAs (miRNAs) have been well characterized with the identification of the required components. miRNAs are synthesized from the transcripts of miRNA genes and other RNAs, such as introns, transfer RNAs, ribosomal RNAs, small nucleolar RNAs, and even viral miRNAs. These small RNAs are loaded into Argonaute (AGO) proteins and recruit the effector complexes to target mRNAs, repressing their gene expression post-transcriptionally. While mature miRNAs were defined as 19–23 nucleotides (nt), tiny RNAs (tyRNAs) shorter than 19 nt have been found to bind AGOs as equivalent or lesser miRNAs compared to their full-length mature miRNAs. In contrast, my recent study revealed that when human AGO3 loads 14 nt cleavage-inducing tyRNAs (cityRNAs), comprised of the first 14 nt of their corresponding mature miRNA, it can become a comparable slicer to AGO2. This observation raises the possibility that tyRNAs play distinct roles from their mature form. This minireview focuses on human AGO-associated tyRNAs shorter than 19 nt and discusses their possible biosynthesis pathways and physiological benefits, including how tyRNAs could avoid target-directed miRNA degradation accompanied by AGO polyubiquitination.

Accuracy mechanism of eukaryotic ribosome translocation

Translation of the genetic code into proteins is realized through repetitions of synchronous translocation of messenger RNA (mRNA) and transfer RNAs (tRNA) through the ribosome. In eukaryotes translocation is ensured by elongation factor 2 (eEF2), which catalyses the process and actively contributes to its accuracy1. Although numerous studies point to critical roles for both the conserved eukaryotic posttranslational modification diphthamide in eEF2 and tRNA modifications in supporting the accuracy of translocation, detailed molecular mechanisms describing their specific functions are poorly understood. Here we report a high-resolution X-ray structure of the eukaryotic 80S ribosome in a translocation-intermediate state containing mRNA, naturally modified eEF2 and tRNAs. The crystal structure reveals a network of stabilization of codon–anticodon interactions involving diphthamide1 and the hypermodified nucleoside wybutosine at position 37 of phenylalanine tRNA, which is also known to enhance translation accuracy2. The model demonstrates how the decoding centre releases a codon–anticodon duplex, allowing its movement on the ribosome, and emphasizes the function of eEF2 as a ‘pawl’ defining the directionality of translocation3. This model suggests how eukaryote-specific elements of the 80S ribosome, eEF2 and tRNAs undergo large-scale molecular reorganizations to ensure maintenance of the mRNA reading frame during the complex process of translocation.

Potential Biomarkers for Therapeutic Monitoring and Clinical Outcome in Breast Cancer

Non-coding RNAs are a species of RNA that are not translated to proteins. These include transfer RNAs and ribosomal RNAs, microRNAs, transfer RNA-derived fragments, and long non-coding RNA. It is known that expression levels of some non-coding RNAs included microRNAs are altered in cancer cells or tumor tissues. Moreover, expression profiles of such non-coding RNAs correlate between tissues and body fluids. Therefore, several non-coding RNAs are being used as diagnostic/prognosis biomarkers or therapeutic targets in cancer. In this chapter, we review about representative non-coding RNAs and introduce especially microRNA as diagnosis/prognosis biomarkers and therapeutic targets.

Intestinal GCN2 controls Drosophila systemic growth upon AA imbalance in response to Lactiplantibacillus plantarum symbiotic cues encoded by r/tRNA operons

Symbiotic bacteria support host growth upon malnutrition. How bacteria achieve this remains partly elusive. Here, we took advantage of the mutualism between Drosophila and Lactiplantibacillus plantarum (Lp) to investigate such mechanisms. Using chemically-defined holidic diets, we found that association with Lp improves the growth of larvae fed amino acid-imbalanced diets. We show that in this context Lp supports its host's growth through a molecular dialog that requires functional operons encoding ribosomal and transfer RNAs (r/tRNAs) in Lp and the GCN2 kinase in Drosophila's enterocytes. Our data indicate that Lp's r/tRNAs loci products activate GCN2 in a subset of larval enterocytes, a mechanism necessary for the host's adaptation to amino acid imbalance that ultimately supports growth. Our findings unravel a novel beneficial molecular dialog between hosts and microbes, which relies on a non-canonical role of GCN2 as a mediator of non-nutritional symbiotic cues encoded by r/tRNA operons.

Complete mitochondrial genome of Cultellus attenuatus and its phylogenetic implications

The complete mitochondrial genome of Cultellus attenuates, a new aquaculture species, was sequenced and compared with mitogenomes from seven species of Heterodonta bivalve mollusk in GenBank. The mitochondrial genome of C. attenuatus is 16888 bp in length and contains 36 genes, including 12 protein-coding genes, 2 ribosomal RNAs and 22 transfer RNAs, and all genes are encoded on the same strand. In comparison with C. attenuates, the mitochondrial genes of Sinonovacula constricta from the same family were not rearranged, but those of six other species from different families were rearranged to different degrees. The largest noncoding region of C. attenuatus is 1173 bp in length and has an A + T content of 68.24%, located between nad2 and trnK. The results of phylogenetic analysis show that C. attenuates and S. constricta belonging to Cultellidae cluster into one branch while two species of Solenidae (Solen grandis and Solen strictus) cluster as their sister taxa. In conclusion, we used the mitochondrial genome data to demonstrate the closest relationship between C. attenuatus and S. constricta in Heterodonta. These data not only contribute to the understanding of the phylogenetic relationship of Heterodonta but also serve as a resource for the development of genetic markers in aquaculture.

tRNA Metabolism and Lung Cancer: Beyond Translation

Lung cancer, one of the most malignant tumors, has extremely high morbidity and mortality, posing a serious threat to global health. It is an urgent need to fully understand the pathogenesis of lung cancer and provide new ideas for its treatment. Interestingly, accumulating evidence has identified that transfer RNAs (tRNAs) and tRNA metabolism–associated enzymes not only participate in the protein translation but also play an important role in the occurrence and development of lung cancer. In this review, we summarize the different aspects of tRNA metabolism in lung cancer, such as tRNA transcription and mutation, tRNA molecules and derivatives, tRNA-modifying enzymes, and aminoacyl-tRNA synthetases (ARSs), aiming at a better understanding of the pathogenesis of lung cancer and providing new therapeutic strategies for it.

The complete chloroplast genome sequence of Korean Neolitsea sericea (Lauraceae)

The complete chloroplast (cp) genome sequence of Neolitsea sericea was determined by Illumina sequencing. The complete cp genome was 152,446bp in length, containing a large single-copy region of 93,796 bp and a small single-copy region of 18,506bp, which were separated by a pair of 20,072bp inverted repeats. A total of 112 unique genes were annotated, including 78 protein-coding genes (PCGs), 30 transfer RNAs, and four ribosomal RNAs. Among the PCGs, 18 genes contained one or two introns. A very low level of sequence variation between two cp genomes of N. sericea was found with seven insertions or deletions and only one single nucleotide polymorphism. An analysis using the maximum likelihood method showed that N. sericea was closely related to Actinodaphne trichocarpa.

miRNATissueAtlas2: an update to the human miRNA tissue atlas

Small non-coding RNAs (sncRNAs) are pervasive regulators of physiological and pathological processes. We previously developed the human miRNA Tissue Atlas, detailing the expression of miRNAs across organs in the human body. Here, we present an updated resource containing sequencing data of 188 tissue samples comprising 21 organ types retrieved from six humans. Sampling the organs from the same bodies minimizes intra-individual variability and facilitates the making of a precise high-resolution body map of the non-coding transcriptome. The data allow shedding light on the organ- and organ system-specificity of piwi-interacting RNAs (piRNAs), transfer RNAs (tRNAs), microRNAs (miRNAs) and other non-coding RNAs. As use case of our resource, we describe the identification of highly specific ncRNAs in different organs. The update also contains 58 samples from six tissues of the Tabula Muris collection, allowing to check if the tissue specificity is evolutionary conserved between Homo sapiens and Mus musculus. The updated resource of 87 252 non-coding RNAs from nine non-coding RNA classes for all organs and organ systems is available online without any restrictions (https://www.ccb.uni-saarland.de/tissueatlas2).