SID-1 is a dsRNA-selective dsRNA-gated channel

C. elegans transgenerational avoidance of P. fluorescens is mediated by the Pfs1 sRNA and vab-1

In its natural habitat, Caenorhabditis elegans must distinguish friend from foe. Pseudomonas are abundant in the worm's environment and can be nutritious or pathogenic. Previously, we found that worms learn to avoid Pseudomonas aeruginosa and Pseudomonas vranovensis through a small RNA (sRNA)-mediated pathway targeting the C. elegans gene maco-1, and this behavior is inherited for four generations. Here, we show that C. elegans learns to transgenerationally avoid another pathogenic bacteria Pseudomonas fluorescens 15 (PF15). The PF15 sRNA, Pfs1, targets the VAB-1 ephrin receptor through 16 nt of perfect match, suggesting the evolution of a distinct bacterial sRNA/C. elegans gene target pair. Knockdown of both maco-1 and vab-1 induce PF15 avoidance, and vab-1 loss reduces maco-1 expression, placing both genes in the sRNA-targeted pathogenic avoidance pathway. Thus, multiple genes in this avoidance pathway can act as targets for bacterial sRNAs, expanding the possibilities for evolution of trans-kingdom regulation of C. elegans behavior.

Reported transgenerational responses to Pseudomonas aeruginosa in Caenorhabditis elegans are not robust

We report our attempt to replicate reports of transgenerational epigenetic inheritance in Caenorhabditis elegans. Multiple laboratories report that C. elegans adults and their F1 embryos exposed to the pathogen Pseudomonas aeruginosa show pathogen aversion behavior and increased daf-7/TGFβ reporter gene expression. However, results from one group show persistence of both through the F4 generation. We failed to consistently detect either the avoidance response or elevated daf-7 expression beyond the F1 generation. We confirmed that the dsRNA transport proteins SID-1 and SID-2 are required for intergenerational (F1) inheritance of pathogen avoidance, but not for the F1 inheritance of elevated daf-7 expression. Reanalysis of RNA seq data provides additional evidence that this intergenerational inherited PA14 response may be mediated by small RNAs. The experimental methods are well-described, the source materials are readily available, including samples from the reporting laboratory, and we explored a variety of environmental conditions likely to account for lab-to-lab variability. None of these adjustments altered our results. We conclude that this example of transgenerational inheritance lacks robustness, confirm that the intergenerational avoidance response, but not the elevated daf-7p::gfp expression in F1 progeny, requires sid-1 and sid-2, and identify candidate siRNAs and target genes that may mediate this intergenerational response.

Multispanning membrane protein SIDT2 increases knockdown activity of gapmer antisense oligonucleotides

Recent advances in the clinical development of oligonucleotide therapeutics, such as antisense oligonucleotides (ASOs) and small interfering RNAs, have attracted attention as promising therapeutic modalities for genetic and intractable diseases. These oligonucleotide therapeutics exert their efficacy by binding to target RNAs present within cells; however, the mechanisms underlying their cellular uptake, especially their passage through membranes, remain largely unclear. In the nematode, Caenorhabditis elegans, the multi-pass transmembrane protein, SID-1, is involved in the cellular uptake of double-stranded RNAs. In mammals, SIDT1 and SIDT2 (SID-1 transmembrane family, members 1 and 2, respectively) are homologs of SID-1, yet their functional differences are not fully understood. In this study, we conducted a comparative analysis of the amino acid sequences of mammalian SIDT1 and SIDT2 to identify regions characteristic to each. By inducing SIDT1 or SIDT2 expression in human cell lines, we demonstrated that SIDT2 enhanced the knockdown activity of gapmer ASOs and potentially promoted their endosomal escape into the cytosol. Furthermore, by analyzing chimeric proteins of SIDT2 and SIDT1, we identified a region in SIDT2 that might be crucial for the enhancement of gapmer ASO activity. These findings elucidate the novel role of SIDT2 in the transport mechanism of gapmer ASOs and are expected to contribute to further development of oligonucleotide therapeutics.

Infectious myonecrosis virus (IMNV) induces upregulation of RNAi-related genes in white shrimp Penaeus vannamei

Infectious myonecrosis virus (IMNV) still causes significant economic and social losses in American and Asian shrimp farming. In this work, we investigated the transcription patterns of Sid-1, Dicer-2 and Argonaute-2 genes from the RNAi mechanism in Penaeus vannamei naturally infected with IMNV, and injected with inoculum containing 1.02 × 105, 1.02 × 104 or 1.02 × 103 IMNV copies‧μL-1. We observed that infection with increasing IMNV concentrations affected the transcription levels of these key genes. However, the viral load did not decrease during the experiment. We suggest that changes in Sid-1 mRNA expression could be used as marker of viral replication for evaluating sanitary status in P. vannamei farming.

Cross-kingdom regulation of plant microRNAs: potential application in crop improvement and human disease therapeutics

Plant microRNAs (miRNAs) are small non-coding RNA molecules that usually negatively regulate gene expression at the post-transcriptional level. Recent data reveal that plant miRNAs are not limited to individual plants but can transfer across different species, allowing for communication with the plant, animal, and microbial worlds in a cross-kingdom approach. This review discusses the differences in miRNA biosynthesis between plants and animals and summarizes the current research on the cross-species regulatory effects of plant miRNAs on nearby plants, pathogenic fungi, and insects, which can be applied to crop disease and pest resistance. In particular, this review highlights the latest findings regarding the function of plant miRNAs in the transboundary regulation of human gene expression, which may greatly expand the clinical applicability of plant miRNAs as intriguing tools in natural plant-based medicinal products in the future.

Efficient RNA interference method by feeding in Brachionus plicatilis (Rotifera)

Rotifers are small, ubiquitous invertebrate animals found throughout the world and have emerged as a promising model system for studying molecular mechanisms in the fields of experimental ecology, aquatic toxicology, and geroscience. However, the lack of efficient gene expression manipulation techniques has hindered the study of rotifers. In this study, we used the L4440 plasmid with two reverse-oriented T7 promoters, along with RNase-deficient E. coli HT115, to efficiently produce dsRNA and thereby present an efficient feeding-based RNAi method in Brachionus plicatilis. We targeted Bp-Ku70 & Ku80, key proteins in the DNA double-strand breaks repair pathway, and then subjected rotifers to UV radiation. We found that the mRNA expression, fecundity, as well as survival rate diminished significantly as a result of RNAi. Overall, our results demonstrate that the feeding-based RNAi method is a simple and efficient tool for gene knockdown in B. plicatilis, advancing their use as a model organism for biological research.

Reported transgenerational responses to Pseudomonas aeruginosa in C. elegans are not robust

Here we report our attempt to replicate reports of transgenerational epigenetic inheritance in Caenorhabditis elegans. Published results from multiple laboratories show that C. elegans adults and their F1 embryos exposed to the pathogen Pseudomonas aeruginosa show pathogen aversion behavior and a pathogen exposure-dependent increase in daf-7/TGFβ reporter gene expression. However, results from one group show persistence of the aversion behavior and elevated daf-7 expression in the F2, F3, and F4 generations. In contrast, we failed to consistently detect either the pathogen avoidance response or elevated daf-7 expression beyond the F1 generation. We did confirm that the dsRNA transport proteins SID-1 and SID-2 are required for the intergenerational (F1) inheritance of pathogen avoidance, but not for the F1 inheritance of elevated daf-7 expression. Furthermore, our reanalysis of RNA seq data provides additional evidence that this intergenerational inherited PA14 response may be mediated by small RNAs. The experimental methods are well-described, the source materials are readily available, including samples from the reporting laboratory, and we explored a variety of environmental conditions likely to account for lab-to-lab variability. None of these adjustments altered our results. We conclude that this example of transgenerational inheritance lacks robustness, confirm that the intergenerational avoidance response, but not the elevated daf-7p::gfp expression in F1 progeny, requires sid-1 and sid-2, and identify candidate siRNAs and target genes that may mediate this intergenerational response.

RNA Interference Applied to Crustacean Aquaculture

RNA interference (RNAi) is a powerful tool that can be used to specifically knock-down gene expression using double-stranded RNA (dsRNA) effector molecules. This approach can be used in aquaculture as an investigation instrument and to improve the immune responses against viral pathogens, among other applications. Although this method was first described in shrimp in the mid-2000s, at present, no practical approach has been developed for the use of dsRNA in shrimp farms, as the limiting factor for farm-scale usage in the aquaculture sector is the lack of cost-effective and simple dsRNA synthesis and administration procedures. Despite these limitations, different RNAi-based approaches have been successfully tested at the laboratory level, with a particular focus on shrimp. The use of RNAi technology is particularly attractive for the shrimp industry because crustaceans do not have an adaptive immune system, making traditional vaccination methods unfeasible. This review summarizes recent studies and the state-of-the-art on the mechanism of action, design, use, and administration methods of dsRNA, as applied to shrimp. In addition, potential constraints that may hinder the deployment of RNAi-based methods in the crustacean aquaculture sector are considered.

Efficient siRNA delivery to murine melanoma cells via a novel genipin-based nano-polymer

Small-interfering RNAs (siRNAs) are therapeutic nucleic acids, often delivered via cationic polymers, liposomes, or extracellular vesicles, each method with its limitations. Genipin, a natural crosslinker for primary amines, was explored for siRNA delivery scaffolds. Spermine/genipin-based GxS5 polymers were synthesized, showing slightly positive ζ potential at neutral pH and intrinsic fluorescence. We then tuned their polymerization adding glycine to the reaction batch, from 1 to 10 molar ratio with genipin, therefore conferring them a "zwitterionic" character. GxS5 efficiently internalized into B16F10 murine melanoma cells, and exhibited strong siRNA-complexing ability and they were able to elicit up to 60% of gene knock-down without any toxicity. This highlights GxS5's potential as a safe, replicable, and tunable platform for therapeutic nucleic acid delivery, suggesting broader applications. This innovative approach not only sheds light on the intricate genipin reaction mechanism but also underscores the importance of fine-tuning nanoparticle properties for effective siRNA delivery. GxS5's success in mitigating cytotoxicity while maintaining delivery efficacy signifies a promising step towards safer and more efficient nucleic acid therapeutics.

Recent advances in understanding of the mechanisms of RNA interference in insects

We highlight the recent 5 years of research that contributed to our understanding of the mechanisms of RNA interference (RNAi) in insects. Since its first discovery, RNAi has contributed enormously as a reverse genetic tool for functional genomic studies. RNAi is also being used in therapeutics, as well as agricultural crop and livestock production and protection. Yet, for the wider application of RNAi, improvement of its potency and delivery technologies is needed. A mechanistic understanding of every step of RNAi, from cellular uptake of RNAi trigger molecules to targeted mRNA degradation, is key for developing an efficient strategy to improve RNAi technology. Insects provide an excellent model for studying the mechanism of RNAi due to species-specific variations in RNAi efficiency. This allows us to perform comparative studies in insect species with different RNAi sensitivity. Understanding the mechanisms of RNAi in different insects can lead to the development of better strategies to improve RNAi and its application to manage agriculturally and medically important insects.

Structural insights into double-stranded RNA recognition and transport by SID-1

RNA uptake by cells is critical for RNA-mediated gene interference (RNAi) and RNA-based therapeutics. In Caenorhabditis elegans, RNAi is systemic as a result of SID-1-mediated double-stranded RNA (dsRNA) across cells. Despite the functional importance, the underlying mechanisms of dsRNA internalization by SID-1 remain elusive. Here we describe cryogenic electron microscopy structures of SID-1, SID-1-dsRNA complex and human SID-1 homologs SIDT1 and SIDT2, elucidating the structural basis of dsRNA recognition and import by SID-1. The homodimeric SID-1 homologs share conserved architecture, but only SID-1 possesses the molecular determinants within its extracellular domains for distinguishing dsRNA from single-stranded RNA and DNA. We show that the removal of the long intracellular loop between transmembrane helix 1 and 2 attenuates dsRNA uptake and systemic RNAi in vivo, suggesting a possible endocytic mechanism of SID-1-mediated dsRNA internalization. Our study provides mechanistic insights into dsRNA internalization by SID-1, which may facilitate the development of dsRNA applications based on SID-1.

Structural basis for double-stranded RNA recognition by SID1

The nucleic acid transport properties of the systemic RNAi-defective (SID) 1 family make them attractive targets for developing RNA-based therapeutics and drugs. However, the molecular basis for double-stranded (ds) RNA recognition by SID1 family remains elusive. Here, we report the cryo-EM structures of Caenorhabditis elegans (c) SID1 alone and in complex with dsRNA, both at a resolution of 2.2 Å. The dimeric cSID1 interacts with two dsRNA molecules simultaneously. The dsRNA is located at the interface between β-strand rich domain (BRD)1 and BRD2 and nearly parallel to the membrane plane. In addition to extensive ionic interactions between basic residues and phosphate backbone, several hydrogen bonds are formed between 2'-hydroxyl group of dsRNA and the contact residues. Additionally, the electrostatic potential surface shows three basic regions are fitted perfectly into three major grooves of dsRNA. These structural characteristics enable cSID1 to bind dsRNA in a sequence-independent manner and to distinguish between DNA and RNA. The cSID1 exhibits no conformational changes upon binding dsRNA, with the exception of a few binding surfaces. Structural mapping of dozens of loss-of-function mutations allows potential interpretation of their diverse functional mechanisms. Our study marks an important step toward mechanistic understanding of the SID1 family-mediated dsRNA uptake.

Cryo-EM analysis reveals human SID-1 transmembrane family member 1 dynamics underlying lipid hydrolytic activity

Two mammalian homologs of systemic RNA interference defective protein 1 (SID-1) (SIDT1/2) are suggested to function as double-stranded RNA (dsRNA) transporters for extracellular dsRNA uptake or for release of incorporated dsRNA from lysosome to cytoplasm. SIDT1/2 is also suggested to be involved in cholesterol transport and lipid metabolism. Here, we determine the cryo-electron microscopy structures of human SIDT1, homodimer in a side-by-side arrangement, with two distinct conformations, the cholesterol-bound form and the unbound form. Our structures reveal that the membrane-spanning region of SIDT1 harbors conserved histidine and aspartate residues coordinating to putative zinc ion, in a structurally similar manner to alkaline ceramidases or adiponectin receptors that require zinc for ceramidase activity. We identify that SIDT1 has a ceramidase activity that is attenuated by cholesterol binding. Observations from two structures suggest that cholesterol molecules serve as allosteric regulator that binds the transmembrane region of SIDT1 and induces the conformation change and the reorientation of the catalytic residues. This study represents a contribution to the elucidation of the cholesterol-mediated mechanisms of lipid hydrolytic activity and RNA transport in the SID-1 family proteins.

Optimized protocols for RNA interference in Macrostomum lignano

Macrostomum lignano, a marine free-living flatworm, has emerged as a potent invertebrate model in developmental biology for studying stem cells, germline, and regeneration processes. In recent years, many tools have been developed to manipulate this worm and to facilitate genetic modification. RNA interference is currently the most accessible and direct technique to investigate gene functions. It is obtained by soaking worms in artificial seawater containing dsRNA targeting the gene of interest. Although easy to perform, the original protocol calls for daily exchange of dsRNA solutions, usually until phenotypes are observed, which is both time- and cost-consuming. In this work, we have evaluated alternative dsRNA delivery techniques, such as electroporation and osmotic shock, to facilitate the experiments with improved time and cost efficiency. During our investigation to optimize RNAi, we demonstrated that, in the absence of diatoms, regular single soaking in artificial seawater containing dsRNA directly produced in bacteria or synthesized in vitro is, in most cases, sufficient to induce a potent gene knockdown for several days with a single soaking step. Therefore, this new and highly simplified method allows a very significant reduction of dsRNA consumption and lab work. In addition, it enables performing experiments on a larger number of worms at minimal cost.

Enhancing plant biotechnology by nanoparticle delivery of nucleic acids

Plant biotechnology plays a crucial role in developing modern agriculture and plant science research. However, the delivery of exogenous genetic material into plants has been a long-standing obstacle. Nanoparticle-based delivery systems are being established to address this limitation and are proving to be a feasible, versatile, and efficient approach to facilitate the internalization of functional RNA and DNA by plants. The nanoparticle-based delivery systems can also be designed for subcellular delivery and controlled release of the biomolecular cargo. In this review, we provide a concise overview of the recent advances in nanocarriers for the delivery of biomolecules into plants, with a specific focus on applications to enhance RNA interference, foreign gene transfer, and genome editing in plants.

Mitochondrial stress in GABAergic neurons non-cell autonomously regulates organismal health and aging

Mitochondrial stress within the nervous system can trigger non-cell autonomous responses in peripheral tissues. However, the specific neurons involved and their impact on organismal aging and health have remained incompletely understood. Here, we demonstrate that mitochondrial stress in γ-aminobutyric acid-producing (GABAergic) neurons in Caenorhabditis elegans ( C. elegans ) is sufficient to significantly alter organismal lifespan, stress tolerance, and reproductive capabilities. This mitochondrial stress also leads to significant changes in mitochondrial mass, energy production, and levels of reactive oxygen species (ROS). DAF-16/FoxO activity is enhanced by GABAergic neuronal mitochondrial stress and mediates the induction of these non-cell-autonomous effects. Moreover, our findings indicate that GABA signaling operates within the same pathway as mitochondrial stress in GABAergic neurons, resulting in non-cell-autonomous alterations in organismal stress tolerance and longevity. In summary, these data suggest the crucial role of GABAergic neurons in detecting mitochondrial stress and orchestrating non-cell-autonomous changes throughout the organism.

Optimization of RNAi efficiency in PVD neuron of C. elegans

PVD neuron of C. elegans has become an attractive model for the study of dendrite development and regeneration due to its elaborate and stereotype dendrite morphology. RNA interference (RNAi) by feeding E. coli expressing dsRNA has been the basis of several genome wide screens performed using C. elegans. However, the feeding method often fails when it comes to knocking down genes in nervous system. In order to optimize the RNAi conditions for PVD neuron, we fed the worm strains with E. coli HT115 bacteria expressing dsRNA against mec-3, hpo-30, and tiam-1, whose loss of function are known to show dendrite morphology defects in PVD neuron. We found that RNAi of these genes in the available sensitive backgrounds including the one expresses sid-1 under unc-119 promoter, although resulted in reduction of dendrite branching, the phenotypes were significantly modest compared to the respective loss of function mutants. In order to enhance RNAi in PVD neurons, we generated a strain that expressed sid-1 under the promoter mec-3, which exhibits strong expression in PVD. When Pmec-3::sid-1 is expressed in either nre-1(-)lin-15b(-) or lin-15b(-) backgrounds, the higher order branching phenotype after RNAi of mec-3, hpo-30, and tiam-1 was significantly enhanced as compared to the genetic background alone. Moreover, knockdown of genes playing role in dendrite regeneration in the nre-1(-)lin-15b(-), Pmec-3-sid-1[+] background resulted in significant reduction in dendrite regeneration following laser injury. The extent of dendrite regrowth due to the RNAi of aff-1 or ced-10 in our optimized strain was comparable to that of aff-1 and ced-10 mutants. Essentially, our strain expressing sid-1 in PVD neuron, provides an RNAi optimized platform for high throughput screening of genes involved in PVD development, maintenance and regeneration.

Tissue-specific overexpression of systemic RNA interference components limits lifespan in C. elegans

Intertissue RNA transport recently emerged as a novel signaling mechanism. In mammals, mounting evidence suggests that small RNA transfer between cells is widespread and used in various physiological contexts. In the nematode C. elegans, a similar mechanism is conferred by the systemic RNAi pathway. Members of the Systemic RNA Interference Defective (SID) family act at different steps of cellular RNA uptake and export. The limiting step in systemic RNA interference (RNAi) is the import of extracellular RNAs via the conserved double-stranded (dsRNA)-gated dsRNA channel SID-1. To better understand the role of RNAs as intertissue signaling molecules, we modified the function of SID-1 in specific tissues of C. elegans. We observed that sid-1 loss-of-function mutants are as healthy as wild-type worms. Conversely, overexpression of sid-1 in C. elegans intestine, muscle, or neurons rendered worms short-lived. The effects of intestinal sid-1 overexpression were attenuated by silencing the components of systemic RNAi sid-1, sid-2 and sid-5, implicating systemic RNA signaling in the lifespan reduction. Accordingly, tissue-specific overexpression of sid-2 and sid-5 also reduced worm lifespan. Additionally, an RNAi screen for components of several non-coding RNA pathways revealed that silencing the miRNA biogenesis proteins PASH-1 and DCR-1 rendered the lifespan of worms with intestinal sid-1 overexpression similar to controls. Collectively, our data support the notion that systemic RNA signaling must be tightly regulated, and unbalancing that process provokes a reduction in lifespan. We termed this phenomenon Intercellular/Extracellular Systemic RNA imbalance (InExS).

Cell surface RNAs control neutrophil recruitment

RNAs localizing to the outer cell surface have been recently identified in mammalian cells, including RNAs with glycan modifications known as glycoRNAs. However, the functional significance of cell surface RNAs and their production are poorly known. We report that cell surface RNAs are critical for neutrophil recruitment and that the mammalian homologs of the sid-1 RNA transporter are required for glycoRNA expression. Cell surface RNAs can be readily detected in murine neutrophils, the elimination of which substantially impairs neutrophil recruitment to inflammatory sites in vivo and reduces neutrophils' adhesion to and migration through endothelial cells. Neutrophil glycoRNAs are predominantly on cell surface, important for neutrophil-endothelial interactions, and can be recognized by P-selectin (Selp). Knockdown of the murine Sidt genes abolishes neutrophil glycoRNAs and functionally mimics the loss of cell surface RNAs. Our data demonstrate the biological importance of cell surface glycoRNAs and highlight a noncanonical dimension of RNA-mediated cellular functions.

Characterization of N-glycosylation and its functional role in SIDT1-Mediated RNA uptake

The mammalian SID-1 transmembrane family members, SIDT1 and SIDT2, are multipass transmembrane proteins that mediate the cellular uptake and intracellular trafficking of nucleic acids, playing important roles in the immune response and tumorigenesis. Previous work has suggested that human SIDT1 and SIDT2 are N-glycosylated, but the precise site-specific N-glycosylation information and its functional contribution remain unclear. In this study, we use high-resolution liquid chromatography tandem mass spectrometry to comprehensively map the N-glycosites and quantify the N-glycosylation profiles of SIDT1 and SIDT2. Further molecular mechanistic probing elucidates the essential role of N-linked glycans in regulating cell surface expression, RNA binding, protein stability, and RNA uptake of SIDT1. Our results provide crucial information about the potential functional impact of N-glycosylation in the regulation of SIDT1-mediated RNA uptake and provide insights into the molecular mechanisms of this promising nucleic acid delivery system with potential implications for therapeutic applications.

Invasion by exogenous RNA: cellular defense strategies and implications for RNA inference

Exogenous RNA poses a continuous threat to genome stability and integrity across various organisms. Accumulating evidence reveals complex mechanisms underlying the cellular response to exogenous RNA, including endo-lysosomal degradation, RNA-dependent repression and innate immune clearance. Across a variety of mechanisms, the natural anti-sense RNA-dependent defensive strategy has been utilized both as a powerful gene manipulation tool and gene therapy strategy named RNA-interference (RNAi). To optimize the efficiency of RNAi silencing, a comprehensive understanding of the whole life cycle of exogenous RNA, from cellular entry to its decay, is vital. In this paper, we review recent progress in comprehending the recognition and elimination of foreign RNA by cells, focusing on cellular entrance, intracellular transportation, and immune-inflammatory responses. By leveraging these insights, we highlight the potential implications of these insights for advancing RNA interference efficiency, underscore the need for future studies to elucidate the pathways and fates of various exogenous RNA forms, and provide foundational information for more efficient RNA delivery methods in both genetic manipulation and therapy in different organisms.

The functions of SID1 transmembrane family, member 2 (Sidt2)

The SID1 transmembrane family, member 2, namely, Sidt2, is a highly glycosylated multichannel lysosomal transmembrane protein, but its specific physiological function remains unknown. Lysosomal membrane proteins are very important for the executive functioning of lysosomes. As an important part of the lysosomal membrane, Sidt2 can maintain the normal morphology of lysosomes and help stabilize them from the acidic pH environment within. As a receptor/transporter, it binds and transports nucleic acids and mediates the uptake and degradation of RNA and DNA by the lysosome. During glucose metabolism, deletion of Sidt2 can cause an increase in fasting blood glucose and the impairment of grape tolerance, which is closely related to the secretion of insulin. During lipid metabolism, the loss of Sidt2 can cause hepatic steatosis and lipid metabolism disorders and can also play a role in signal regulation and transport. Here, we review the function of the lysosomal membrane protein Sidt2, and focus on its role in glucose and lipid metabolism, autophagy and nucleotide (DNA/RNA) transport.

RNA Crossing Membranes: Systems and Mechanisms Contextualizing Extracellular RNA and Cell Surface GlycoRNAs

The subcellular localization of a biopolymer often informs its function. RNA is traditionally confined to the cytosolic and nuclear spaces, where it plays critical and conserved roles across nearly all biochemical processes. Our recent observation of cell surface glycoRNAs may further explain the extracellular role of RNA. While cellular membranes are efficient gatekeepers of charged polymers such as RNAs, a large body of research has demonstrated the accumulation of specific RNA species outside of the cell, termed extracellular RNAs (exRNAs). Across various species and forms of life, protein pores have evolved to transport RNA across membranes, thus providing a mechanistic path for exRNAs to achieve their extracellular topology. Here, we review types of exRNAs and the pores capable of RNA transport to provide a logical and testable path toward understanding the biogenesis and regulation of cell surface glycoRNAs.

Structural insight into the human SID1 transmembrane family member 2 reveals its lipid hydrolytic activity

The systemic RNAi-defective (SID) transmembrane family member 2 (SIDT2) is a putative nucleic acid channel or transporter that plays essential roles in nucleic acid transport and lipid metabolism. Here, we report the cryo-electron microscopy (EM) structures of human SIDT2, which forms a tightly packed dimer with extensive interactions mediated by two previously uncharacterized extracellular/luminal β-strand-rich domains and the unique transmembrane domain (TMD). The TMD of each SIDT2 protomer contains eleven transmembrane helices (TMs), and no discernible nucleic acid conduction pathway has been identified within the TMD, suggesting that it may act as a transporter. Intriguingly, TM3-6 and TM9-11 form a large cavity with a putative catalytic zinc atom coordinated by three conserved histidine residues and one aspartate residue lying approximately 6 Å from the extracellular/luminal surface of the membrane. Notably, SIDT2 can hydrolyze C18 ceramide into sphingosine and fatty acid with a slow rate. The information presented advances the understanding of the structure-function relationships in the SID1 family proteins.

Attenuation of Dopaminergic Neurodegeneration in a C. elegans Parkinson's Model through Regulation of Xanthine Dehydrogenase (XDH-1) Expression by the RNA Editase, ADR-2

Differential RNA editing by adenosine deaminases that act on RNA (ADARs) has been implicated in several neurological disorders, including Parkinson's disease (PD). Here, we report results of a RNAi screen of genes differentially regulated in adr-2 mutants, normally encoding the only catalytically active ADAR in Caenorhabditis elegans, ADR-2. Subsequent analysis of candidate genes that alter the misfolding of human α-synuclein (α-syn) and dopaminergic neurodegeneration, two PD pathologies, reveal that reduced expression of xdh-1, the ortholog of human xanthine dehydrogenase (XDH), is protective against α-synuclein-induced dopaminergic neurodegeneration. Further, RNAi experiments show that WHT-2, the worm ortholog of the human ABCG2 transporter and a predicted interactor of XDH-1, is the rate-limiting factor in the ADR-2, XDH-1, WHT-2 system for dopaminergic neuroprotection. In silico structural modeling of WHT-2 indicates that the editing of one nucleotide in the wht-2 mRNA leads to the substitution of threonine with alanine at residue 124 in the WHT-2 protein, changing hydrogen bonds in this region. Thus, we propose a model where wht-2 is edited by ADR-2, which promotes optimal export of uric acid, a known substrate of WHT-2 and a product of XDH-1 activity. In the absence of editing, uric acid export is limited, provoking a reduction in xdh-1 transcription to limit uric acid production and maintain cellular homeostasis. As a result, elevation of uric acid is protective against dopaminergic neuronal cell death. In turn, increased levels of uric acid are associated with a decrease in ROS production. Further, downregulation of xdh-1 is protective against PD pathologies because decreased levels of XDH-1 correlate to a concomitant reduction in xanthine oxidase (XO), the form of the protein whose by-product is superoxide anion. These data indicate that modifying specific targets of RNA editing may represent a promising therapeutic strategy for PD.

RNAi Technology: A New Path for the Research and Management of Obligate Biotrophic Phytopathogenic Fungi

Powdery mildew and rust fungi are major agricultural problems affecting many economically important crops and causing significant yield losses. These fungi are obligate biotrophic parasites that are completely dependent on their hosts for growth and reproduction. Biotrophy in these fungi is determined by the presence of haustoria, specialized fungal cells that are responsible for nutrient uptake and molecular dialogue with the host, a fact that undoubtedly complicates their study under laboratory conditions, especially in terms of genetic manipulation. RNA interference (RNAi) is the biological process of suppressing the expression of a target gene through double-stranded RNA that induces mRNA degradation. RNAi technology has revolutionized the study of these obligate biotrophic fungi by enabling the analysis of gene function in these fungal. More importantly, RNAi technology has opened new perspectives for the management of powdery mildew and rust diseases, first through the stable expression of RNAi constructs in transgenic plants and, more recently, through the non-transgenic approach called spray-induced gene silencing (SIGS). In this review, the impact of RNAi technology on the research and management of powdery mildew and rust fungi will be addressed.

The third barrier to transgenerational inheritance in animals: somatic epigenetic resetting

After early controversy, it is now increasingly clear that acquired responses to environmental factors may perpetuate across multiple generations-a phenomenon termed transgenerational epigenetic inheritance (TEI). Experiments with Caenorhabditis elegans, which exhibits robust heritable epigenetic effects, demonstrated small RNAs as key factors of TEI. Here, we discuss three major barriers to TEI in animals, two of which, the "Weismann barrier" and germline epigenetic reprogramming, have been known for decades. These are thought to effectively prevent TEI in mammals but not to the same extent in C. elegans. We argue that a third barrier-that we termed "somatic epigenetic resetting"-may further inhibit TEI and, unlike the other two, restricts TEI in C. elegans as well. While epigenetic information can overcome the Weismann barrier and transmit from the soma to the germline, it usually cannot "travel back" directly from the germline to the soma in subsequent generations. Nevertheless, heritable germline memory may still influence the animal's physiology by indirectly modifying gene expression in somatic tissues.

Integrated regulation of dopaminergic and epigenetic effectors of neuroprotection in Parkinson's disease models

Whole-exome sequencing of Parkinson's disease (PD) patient DNA identified single-nucleotide polymorphisms (SNPs) in the tyrosine nonreceptor kinase-2 (TNK2) gene. Although this kinase had a previously demonstrated activity in preventing the endocytosis of the dopamine reuptake transporter (DAT), a causal role for TNK2-associated dysfunction in PD remains unresolved. We postulated the dopaminergic neurodegeneration resulting from patient-associated variants in TNK2 were a consequence of aberrant or prolonged TNK2 overactivity, the latter being a failure in TNK2 degradation by an E3 ubiquitin ligase, neuronal precursor cell-expressed developmentally down-regulated-4 (NEDD4). Interestingly, systemic RNA interference protein-3 (SID-3) is the sole TNK2 ortholog in the nematode Caenorhabditis elegans, where it is an established effector of epigenetic gene silencing mediated through the dsRNA-transporter, SID-1. We hypothesized that TNK2/SID-3 represents a node of integrated dopaminergic and epigenetic signaling essential to neuronal homeostasis. Use of a TNK2 inhibitor (AIM-100) or a NEDD4 activator [N-aryl benzimidazole 2 (NAB2)] in bioassays for either dopamine- or dsRNA-uptake into worm dopaminergic neurons revealed that sid-3 mutants displayed robust neuroprotection from 6-hydroxydopamine (6-OHDA) exposures, as did AIM-100 or NAB2-treated wild-type animals. Furthermore, NEDD4 activation by NAB2 in rat primary neurons correlated to a reduction in TNK2 levels and the attenuation of 6-OHDA neurotoxicity. CRISPR-edited nematodes engineered to endogenously express SID-3 variants analogous to TNK2 PD-associated SNPs exhibited enhanced susceptibility to dopaminergic neurodegeneration and circumvented the RNAi resistance characteristic of SID-3 dysfunction. This research exemplifies a molecular etiology for PD whereby dopaminergic and epigenetic signaling are coordinately regulated to confer susceptibility or resilience to neurodegeneration.

A Tale of Two Lobsters—Transcriptomic Analysis Reveals a Potential Gap in the RNA Interference Pathway in the Tropical Rock Lobster Panulirus ornatus

RNA interference (RNAi) has been widely utilised in many invertebrate models since its discovery, and in a majority of instances presents as a highly efficient and potent gene silencing mechanism. This is emphasized in crustaceans with almost all taxa having the capacity to trigger effective silencing, with a notable exception in the spiny lobsters where repeated attempts at dsRNA induced RNAi have demonstrated extremely ineffective gene knockdown. A comparison of the core RNAi machinery in transcriptomic data from spiny lobsters (Panulirus ornatus) and the closely related slipper lobsters (Thenus australiensis, where silencing is highly effective) revealed that both lobsters possess all proteins involved in the small interfering and microRNA pathways, and that there was little difference at both the sequence and domain architecture level. Comparing the expression of these genes however demonstrated that T. australiensis had significantly higher expression in the transcripts encoding proteins which directly interact with dsRNA when compared to P. ornatus, validated via qPCR. These results suggest that low expression of the core RNAi genes may be hindering the silencing response in P. ornatus, and suggest that it may be critical to enhance the expression of these genes to induce efficient silencing in spiny lobsters.

SID-4/NCK-1 is important for dsRNA import in Caenorhabditis elegans

RNA interference is sequence-specific gene silencing triggered by double-stranded RNA. Systemic RNA interference is where double-stranded RNA, expressed or introduced into 1 cell, is transported to and initiates RNA interference in other cells. Systemic RNA interference is very efficient in Caenorhabditis elegans and genetic screens for systemic RNA interference-defective mutants have identified RNA transporters (SID-1, SID-2, and SID-5) and a signaling protein (SID-3). Here, we report that SID-4 is nck-1, a C. elegans NCK-like adaptor protein. sid-4 null mutations cause a weak, dose-sensitive, systemic RNA interference defect and can be effectively rescued by SID-4 expression in target tissues only, implying a role in double-stranded RNA import. SID-4 and SID-3 (ACK-1 kinase) homologs interact in mammals and insects, suggesting that they may function in a common signaling pathway; however, a sid-3; sid-4 double mutants showed additive resistance to RNA interference, suggesting that these proteins likely interact with other signaling pathways as well. A bioinformatic screen coupled to RNA interference sensitivity tests identified 23 additional signaling components with weak RNA interference-defective phenotypes. These observations suggest that environmental conditions may modulate systemic RNA interference efficacy, and indeed, sid-3 and sid-4 are required for growth temperature effects on systemic RNA interference silencing efficiency.

Mobile plant microRNAs allow communication within and between organisms

Plant microRNAs (miRNAs) are small regulatory RNAs that are encoded by endogenous miRNA genes and regulate gene expression through gene silencing, by inducing degradation of their target messenger RNA or by inhibiting its translation. Some miRNAs are mobile molecules inside the plant, and increasing experimental evidence has demonstrated that miRNAs represent molecules that are exchanged between plants, their pathogens, and parasitic plants. It has also been shown that miRNAs are secreted into the external growing medium and that these miRNAs regulate gene expression and the phenotype of nearby receiving plants, thus defining a new concept in plant communication. However, the mechanism of miRNA secretion and uptake by plant cells still needs to be elucidated.

Small RNAs couple embryonic developmental programs to gut microbes

Embryogenesis has long been known for its robustness to environmental factors. Although developmental tuning of embryogenesis to the environment experienced by the parent may be beneficial, little is understood on whether and how developmental patterns proactively change. Here, we show that Caenorhabditis elegans undergoes alternative embryogenesis in response to maternal gut microbes. Harmful microbes result in altered endodermal cell divisions; morphological changes, including left-right asymmetric development; double association between intestinal and primordial germ cells; and partial rescue of fecundity. The miR-35 microRNA family, which is controlled by systemic endogenous RNA interference and targets the β-transducin repeat-containing protein/cell division cycle 25 (CDC25) pathway, transmits intergenerational information to regulate cell divisions and reproduction. Our findings challenge the widespread assumption that C. elegans has an invariant cell lineage that consists of a fixed cell number and provide insights into how organisms optimize embryogenesis to adapt to environmental changes through epigenetic control.

The transcription factor ZIP-1 promotes resistance to intracellular infection in Caenorhabditis elegans

Defense against intracellular infection has been extensively studied in vertebrate hosts, but less is known about invertebrate hosts; specifically, the transcription factors that induce defense against intracellular intestinal infection in the model nematode Caenorhabditis elegans remain understudied. Two different types of intracellular pathogens that naturally infect the C. elegans intestine are the Orsay virus, which is an RNA virus, and microsporidia, which comprise a phylum of fungal pathogens. Despite their molecular differences, these pathogens induce a common host transcriptional response called the intracellular pathogen response (IPR). Here we show that zip-1 is an IPR regulator that functions downstream of all known IPR-activating and regulatory pathways. zip-1 encodes a putative bZIP transcription factor, and we show that zip-1 controls induction of a subset of genes upon IPR activation. ZIP-1 protein is expressed in the nuclei of intestinal cells, and is at least partially required in the intestine to upregulate IPR gene expression. Importantly, zip-1 promotes resistance to infection by the Orsay virus and by microsporidia in intestinal cells. Altogether, our results indicate that zip-1 represents a central hub for triggers of the IPR, and that this transcription factor has a protective function against intracellular pathogen infection in C. elegans.

Intestinal immune responses to intracellular infection of Caenorhabditis elegans and other Invertebrate hosts are not well understood. Here the authors show a key role for the transcription factor ZIP-1 during intestinal intracellular infection.

RNAi for Western Corn Rootworm Management: Lessons Learned, Challenges, and Future Directions

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is considered one of the most economically important pests of maize (Zea mays L.) in the United States (U.S.) Corn Belt with costs of management and yield losses exceeding USD ~1-2 billion annually. WCR management has proven challenging given the ability of this insect to evolve resistance to multiple management strategies including synthetic insecticides, cultural practices, and plant-incorporated protectants, generating a constant need to develop new management tools. One of the most recent developments is maize expressing double-stranded hairpin RNA structures targeting housekeeping genes, which triggers an RNA interference (RNAi) response and eventually leads to insect death. Following the first description of in planta RNAi in 2007, traits targeting multiple genes have been explored. In June 2017, the U.S. Environmental Protection Agency approved the first in planta RNAi product against insects for commercial use. This product expresses a dsRNA targeting the WCR snf7 gene in combination with Bt proteins (Cry3Bb1 and Cry34Ab1/Cry35Ab1) to improve trait durability and will be introduced for commercial use in 2022.

Establishing RNAi for basic research and pest control and identification of the most efficient target genes for pest control: a brief guide

RNA interference (RNAi) has emerged as a powerful tool for knocking-down gene function in diverse taxa including arthropods for both basic biological research and application in pest control. The conservation of the RNAi mechanism in eukaryotes suggested that it should-in principle-be applicable to most arthropods. However, practical hurdles have been limiting the application in many taxa. For instance, species differ considerably with respect to efficiency of dsRNA uptake from the hemolymph or the gut. Here, we review some of the most frequently encountered technical obstacles when establishing RNAi and suggest a robust procedure for establishing this technique in insect species with special reference to pests. Finally, we present an approach to identify the most effective target genes for the potential control of agricultural and public health pests by RNAi.

Small RNAs Worm Up Transgenerational Epigenetics Research

DNA is central to the propagation and evolution of most living organisms due to the essential process of its self-replication. Yet it also encodes factors that permit epigenetic (not included in DNA sequence) flow of information from parents to their offspring and beyond. The known mechanisms of epigenetic inheritance include chemical modifications of DNA and chromatin, as well as regulatory RNAs. All these factors can modulate gene expression programs in the ensuing generations. The nematode Caenorhabditis elegans is recognized as a pioneer organism in transgenerational epigenetic inheritance research. Recent advances in C. elegans epigenetics include the discoveries of control mechanisms that limit the duration of RNA-based epigenetic inheritance, periodic DNA motifs that counteract epigenetic silencing establishment, new mechanistic insights into epigenetic inheritance carried by sperm, and the tantalizing examples of inheritance of sensory experiences. This review aims to highlight new findings in epigenetics research in C. elegans with the main focus on transgenerational epigenetic phenomena dependent on small RNAs.

Perturbing the Normal Level of SIDT1 Suppresses the Naked ASO Effect

Although antisense oligonucleotide (ASO) therapeutics can be taken up by living cells without carrier molecules, a large part of incorporated ASOs are trapped in the endosomes and do not exert therapeutic effects. To improve their therapeutic effects, it would be important to elucidate the mechanism of cellular uptake and intracellular trafficking of ASOs. In this study, we investigated how SIDT1 affects cellular uptake and intracellular trafficking of ASOs. Fluorescence microscopic analysis suggested that most of naked ASOs are trafficked to the lysosomes via the endosomes. The data obtained from flow cytometry and fluorescence microscopy together showed that although the SIDT1 level barely affects the total cellular uptake of ASOs, it appears to affect the intracellular trafficking of ASOs. We also showed that SIDT1 exists mainly in the endoplasmic reticulum and that perturbing the normal level of SIDT1 suppresses the antisense effect of the naked ASO targeting miR-16.

RNA Interference-Based Forest Protection Products (FPPs) Against Wood-Boring Coleopterans: Hope or Hype?

Forest insects are emerging in large extension in response to ongoing climatic changes, penetrating geographic barriers, utilizing novel hosts, and influencing many hectares of conifer forests worldwide. Current management strategies have been unable to keep pace with forest insect population outbreaks, and therefore novel and aggressive management strategies are urgently required to manage forest insects. RNA interference (RNAi), a Noble Prize-winning discovery, is an emerging approach that can be used for forest protection. The RNAi pathway is triggered by dsRNA molecules, which, in turn, silences genes and disrupts protein function, ultimately causing the death of the targeted insect. RNAi is very effective against pest insects; however, its proficiency varies significantly among insect species, tissues, and genes. The coleopteran forest insects are susceptible to RNAi and can be the initial target, but we lack practical means of delivery, particularly in systems with long-lived, endophagous insects such as the Emerald ash borer, Asian longhorn beetles, and bark beetles. The widespread use of RNAi in forest pest management has major challenges, including its efficiency, target gene selection, dsRNA design, lack of reliable dsRNA delivery methods, non-target and off-target effects, and potential resistance development in wood-boring pest populations. This review focuses on recent innovations in RNAi delivery that can be deployed against forest pests, such as cationic liposome-assisted (lipids), nanoparticle-enabled (polymers or peptides), symbiont-mediated (fungi, bacteria, and viruses), and plant-mediated deliveries (trunk injection, root absorption). Our findings guide future risk analysis of dsRNA-based forest protection products (FPPs) and risk assessment frameworks incorporating sequence complementarity-based analysis for off-target predictions. This review also points out barriers to further developing RNAi for forest pest management and suggests future directions of research that will build the future use of RNAi against wood-boring coleopterans.

Population scale nucleic acid delivery to Caenorhabditis elegans via electroporation

The free-living nematode Caenorhabditis elegans remains one of the most robust and flexible genetic systems for interrogating the complexities of animal biology. Targeted genetic manipulations, such as RNA interference (RNAi), CRISPR/Cas9- or array-based transgenesis, all depend on initial delivery of nucleic acids. Delivery of dsRNA by feeding can be effective, but the expression in Escherichia coli is not conducive to experiments intended to remain sterile or with defined microbial communities. Soaking-based delivery requires prolonged exposure of animals to high-material concentrations without a food source and is of limited throughput. Last, microinjection of individual animals can precisely deliver materials to animals' germlines, but is limited by the need to target and inject each animal one-by-one. Thus, we sought to address some of these challenges in nucleic acid delivery by developing a population-scale delivery method. We demonstrate efficient electroporation-mediated delivery of dsRNA throughout the worm and effective RNAi-based silencing, including in the germline. Finally, we show that guide RNA delivered by electroporation can be utilized by transgenic Cas9 expressing worms for population-scale genetic targeting. Together, these methods expand the scale and scope of genetic methodologies that can be applied to the C. elegans system.

Transcriptome analysis unravels RNAi pathways genes and putative expansion of CYP450 gene family in cotton leafhopper Amrasca biguttula (Ishida)

Cotton Leafhopper, Amrasca biguttula is an important pest of cotton and okra in the Indian subcontinent. Presently limited genomic/transcriptomic information is available for this insect in any of open source databases. The present study reports the first assembled and annotated de novo transcriptome of cotton leafhopper. Out of 75,551 transcripts, 39,613 CDS (Coding Sequence) were predicted with 35,282 showing positive blast hits with NCBI nr database. The Gene ontology (GO) analysis annotated 7431 CDS  with KEGG pathway categorizing these CDS into 22 different functional groups. The majority of CDS were annotated in signal transduction and transport catabolism pathways. The sequence data was screened for RNAi pathway genes and presence of 37 transcripts associated with this process confirmed the existence of robust RNAi machinery. The role of core RNAi machinery genes (Dicer-2, Ago-2, Piwi and Staufen) has been validated through dsRNA feeding studies. The data resource has also been used to identify potential RNAi targets and genes associated with insecticide detoxification specifically CYP 450 family. The current study provides a useful sequence resource which can be used to initiate molecular studies in this insect with emphasis on insecticide resistance, RNAi and functional genomics.

SID-2 negatively regulates development likely independent of nutritional dsRNA uptake

RNA interference (RNAi) is a gene regulatory mechanism based on RNA-RNA interaction conserved through eukaryotes. Surprisingly, many animals can take-up human-made double stranded RNA (dsRNA) from the environment to initiate RNAi suggesting a mechanism for dsRNA-based information exchange between organisms and their environment. However, no naturally occurring example has been identified since the discovery of the phenomenon 22 years ago. Therefore it remains enigmatic why animals are able to take up dsRNA. Here, we explore other possible functions by performing phenotypic studies of dsRNA uptake deficient sid-2 mutants in Caenorhabditis elegans. We find that SID-2 does not have a nutritional role in feeding experiments using genetic sensitized mutants. Furthermore, we use robot assisted imaging to show that sid-2 mutants accelerate growth rate and, by maternal contribution, body length at hatching. Finally, we perform transcriptome and lipidome analysis showing that sid-2 has no effect on energy storage lipids, but affects signalling lipids and the embryo transcriptome. Overall, these results suggest that sid-2 has mild effects on development and is unlikely functioning in the nutritional uptake of dsRNA. These findings broaden our understanding of the biological role of SID-2 and motivate studies identifying the role of environmental dsRNA uptake.

The Heritability of Behaviors Associated With the Host Gut Microbiota

What defines whether the interaction between environment and organism creates a genetic memory able to be transferred to subsequent generations? Bacteria and the products of their metabolism are the most ubiquitous biotic environments to which every living organism is exposed. Both microbiota and host establish a framework where environmental and genetic factors are integrated to produce adaptive life traits, some of which can be inherited. Thus, the interplay between host and microbe is a powerful model to study how phenotypic plasticity is inherited. Communication between host and microbe can occur through diverse molecules such as small RNAs (sRNAs) and the RNA interference machinery, which have emerged as mediators and carriers of heritable environmentally induced responses. Notwithstanding, it is still unclear how the organism integrates sRNA signaling between different tissues to orchestrate a systemic bacterially induced response that can be inherited. Here we discuss current evidence of heritability produced by the intestinal microbiota from several species. Neurons and gut are the sensing systems involved in transmitting changes through transcriptional and post-transcriptional modifications to the gonads. Germ cells express inflammatory receptors, and their development and function are regulated by host and bacterial metabolites and sRNAs thus suggesting that the dynamic interplay between host and microbe underlies the host's capacity to transmit heritable behaviors. We discuss how the host detects changes in the microbiota that can modulate germ cells genomic functions. We also explore the nature of the interactions that leave permanent or long-term memory in the host and propose mechanisms by which the microbiota can regulate the development and epigenetic reprogramming of germ cells, thus influencing the inheritance of the host. We highlight the vast contribution of the bacterivore nematode C. elegans and its commensal and pathogenic bacteria to the understanding on how behavioral adaptations can be inter and transgenerational inherited.

Engineering pest tolerance through plant-mediated RNA interference

Expression of insect-targeted RNA interference (RNAi) constructs in transgenic plants is a promising approach for agricultural pest control. Compared to conventional chemical insecticides, RNAi target specificity is high and the potential for negative environmental effects is low. However, although numerous laboratory studies show insect growth inhibition by double stranded RNA or artificial microRNA, few of these constructs have been moved into commercial application as genetically engineered plants. Variation in RNA degradation, uptake, processing, and systemic transport in insects can influence interspecific and intraspecific differences in RNAi efficacy and the development of resistance to RNAi in agricultural settings. Further research is needed, both to identify optimal gene targets for efficient RNAi in pest species and to reduce the potential for off-target effects in beneficial species.

What Is Lost in the Weismann Barrier?

The Weismann barrier has long been regarded as a basic tenet of biology. However, upon close examination of its historical origins and August Weismann's own writings, questions arise as to whether such a status is warranted. As scientific research has advanced, the persistence of the concept of the barrier has left us with the same dichotomies Weismann contended with over 100 years ago: germ or soma, gene or environment, hard or soft inheritance. These dichotomies distract from the more important questions we need to address going forward. In this review, we will examine the theories that have shaped Weismann's thinking, how the concept of the Weismann barrier emerged, and the limitations that it carries. We will contrast the principles underlying the barrier with recent and less recent findings in developmental biology and transgenerational epigenetic inheritance that have profoundly eroded the oppositional view of germline vs. soma. Discarding the barrier allows us to examine the interactive processes and their response to environmental context that generate germ cells in the first place, determine the entirety of what is inherited through them, and set the trajectory for the health status of the progeny they bear.

An ATP synthase beta subunit is required for internalization of dsRNA into shrimp cells

Extracellular double-stranded RNA (dsRNA) is an important modulator in innate immunity in both vertebrates and invertebrates. In shrimp, extracellular dsRNA can trigger RNAi pathway and serves as antiviral defense mechanism. However, the mechanism of dsRNA internalization into the cells has not yet known in shrimp cells. This study identified candidate cell surface proteins from shrimp hepatopancreatic cells that could interact with dsRNA by a ligand blot assay. Among the candidate proteins, a cell-surface beta subunit of ATP synthase was shown to be capable of internalizing dsRNA into shrimp hepatopancreatic cells that could rapidly occur in just 1 min upon dsRNA challenge. Colocalization between dsRNA and ATP synthase beta subunit implied correlation between dsRNA and ATP synthase beta subunit during dsRNA internalization. Furthermore, dsRNA showed colocalization with Ras-related endocytic proteins, Rab5 and Rab7 indicating that dsRNA was internalized via the receptor-mediated endocytosis. For the above evidences as well as the reduction of dsRNA internalization by angiostatin and antibodies against ATP synthase beta subunit, we propose that dsRNA interacts with ATP synthase via a nucleotide binding site in the beta subunit prior to internalize dsRNA into cells.

Cytosolic domain of SIDT2 carries an arginine-rich motif that binds to RNA/DNA and is important for the direct transport of nucleic acids into lysosomes

RNautophagy and DNautophagy (RDA) are unconventional autophagic pathways where nucleic acids are directly transported through the lysosomal membrane, then degraded inside lysosomes. We have previously shown that bitopic protein LAMP2C and putative RNA transporter SIDT2, both lysosomal membrane proteins, mediate the direct transport of nucleic acids into lysosomes and that LAMP2C interacts with the nucleic acids and functions as a receptor during RDA. Because SIDT2-mediated RDA occurs in isolated lysosomes that lack LAMP2C, in this study, we tested the hypothesis that SIDT2 itself could also interact with the nucleic acids. Our results show that SIDT2 directly binds RNA and DNA through an arginine-rich motif (ARM) located within its main cytosolic domain, and disruption of this motif dramatically impairs SIDT2-mediated RNautophagic activity. We also found that SIDT2 interacts with exon 1 of HTT (huntingtin) transcript through the ARM in a CAG-dependent manner. Moreover, overexpression of SIDT2 promoted degradation of HTT mRNA and reduced the levels of polyglutamine-expanded HTT aggregates, hallmarks of Huntington disease. In addition, a comparative analysis of LAMP2C and SIDT2 functions at the cellular level revealed that the two proteins exert a synergistic effect on RNautophagic activity and that the ARMs which mediate the interactions of SIDT2 and LAMP2C with RNA are essential for the synergy. Together, our results point out the importance of nucleic acid-binding capacity of SIDT2 for its function in translocating nucleic acids through the lipid bilayer and suggests a potential application of RNautophagy activation to reduce the expression levels of disease-causing toxic proteins. Abbreviations: ACTB/β-actin: actin beta; ARM: arginine-rich motif; CBB: Coomassie Brilliant Blue; CD: cytosolic domain; COX4I1/COX4: cytochrome c oxidase subunit 4I1; E. coli: Escherichia coli; EGFP: enhanced green fluorescent protein; EtBr: ethidium bromide; FITC: fluorescein isothiocyanate; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GOLGA2/GM130: golgin A2; GST: glutathione S-transferase; HRP: horseradish peroxidase; HSPA5/GRP78: heat shock protein family A (Hsp70) member 5; HTT: huntingtin; HTTex1: exon 1 of the HTT gene; LAMP2: lysosomal associated membrane protein 2; LMNA: lamin A/C; PAGE: polyacrylamide gel electrophoresis; PBS: phosphate-buffered saline; PEI: polyethyleneimine; polyQ: polyglutamine; qPCR: quantitative PCR; RAB5A: RAB5A, member RAS oncogene family; RDA: RNautophagy and DNautophagy; SCARB2/LIMP2: scavenger receptor class B member 2; SDS: sodium dodecyl sulfate; SID-1: systemic RNA interference deficient-1; SIDT2: SID1 transmembrane family member 2; WT: wild type.

Roles of Regulatory RNAs in Nutritional Control

Small RNAs (sRNAs), including microRNAs (miRNAs), are noncoding RNA (ncRNA) molecules involved in gene regulation. sRNAs play important roles in development; however, their significance in nutritional control and as metabolic modulators is still emerging. The mechanisms by which diet impacts metabolic genes through miRNAs remain an important area of inquiry. Recent work has established how miRNAs are transported in body fluids often within exosomes, which are small cell-derived vesicles that function in intercellular communication. The abundance of other recently identified ncRNAs and new insights regarding ncRNAs as dietary bioactive compounds could remodel our understanding about how foods impact gene expression. Although controversial, some groups have shown that dietary RNAs from plants and animals (i.e., milk) are functional in consumers. In the future, regulating sRNAs either directly through dietary delivery or indirectly by altered expression of endogenous sRNA may be part of nutritional interventions for regulating metabolism.