Explore the vast range of titles available.

About the Authors: Didier Y. R. Stainier * E-mail: didier.stainier@mpi-bn.mpg.de (DYRS); cmoens@fredhutch.org (CBM) Affiliation: Department of Developmental Genetics, Max Planck Institute for Heart and Lung Research, Bad Nauheim, Germany ORCID http://orcid.org/0000-0002-0382-0026 Erez Raz Affiliation: Institute of Cell Biology, ZBME, University of Münster, Münster, Germany ORCID http://orcid.org/0000-0002-6347-3302 Nathan D. Lawson Affiliation: Department of Molecular, Cell, and Cancer Biology, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America Stephen C. Ekker Affiliation: Mayo Clinic, Rochester, Minnesota, United States of America Rebecca D. Burdine Affiliation: Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America Judith S. Eisen Affiliation: Institute of Neuroscience, University of Oregon, Eugene, Oregon, United States of America ORCID http://orcid.org/0000-0003-1229-1696 Philip W. Ingham Affiliations Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, The Living Systems Institute, University of Exeter, Exeter, United Kingdom Stefan Schulte-Merker Affiliation: Institute of Cardiovascular Organogenesis and Regeneration, WWU Münster, Faculty of Medicine, Münster, Germany Deborah Yelon Affiliation: Division of Biological Sciences, University of California, San Diego, La Jolla, California, United States of America Brant M. Weinstein Affiliation: Division of Developmental Biology, NICHD, NIH, Bethesda, Maryland, United States of America Mary C. Mullins Affiliation: Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America ORCID http://orcid.org/0000-0002-9979-1564 Stephen W. Wilson Affiliation: Department of Cell and Developmental Biology, University College London, London, United Kingdom ORCID http://orcid.org/0000-0002-8557-5940 Lalita Ramakrishnan Affiliation: Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom Sharon L. Amacher Affiliation: Departments of Molecular Genetics and Biological Chemistry and Pharmacology, Ohio State University, Columbus, Ohio, United States of America Stephan C. F. Neuhauss Affiliation: Institute of Molecular Life Sciences, University of Zurich, Zurich, Switzerland ORCID http://orcid.org/0000-0002-9615-480X Anming Meng Affiliation: School of Life Sciences, Tsinghua University, Beijing, China Naoki Mochizuki Affiliation: National Cerebral and Cardiovascular Center Research Institute, Osaka, Japan ORCID http://orcid.org/0000-0002-3938-9602 Pertti Panula Affiliation: Department of Anatomy and Neuroscience Center, University of Helsinki, Helsinki, Finland Cecilia B. Moens * E-mail: didier.stainier@mpi-bn.mpg.de (DYRS); cmoens@fredhutch.org (CBM) Affiliation: Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of AmericaCitation: Stainier DYR, Raz E, Lawson ND, Ekker SC, Burdine RD, Eisen JS, et al. Additionally, mutant alleles for many genes are now readily available through zebrafish community resource centers. [...]MOs should be used alongside mutant(s) for the corresponding gene. [...]a word of caution that previous publication of MOs is not a guarantee of their fidelity, particularly if a new phenotype is being described. [...]we hope that these brief and mostly conceptual guidelines will assist scientists working with zebrafish as well as those assessing manuscripts and grant proposals based on experiments using zebrafish.

Zebrafish embryos injected with egfl7 morpholino exhibit severe vascular defects but egfl7 mutants do not show any obvious phenotypes, illustrating the power of comparing mutants and morphants to identify modifier genes. Mutant versus morphant phenotypes Antisense approaches to gene knockdown or interference, using agents such as siRNA and morpholino oligomers, have been criticized as being prone to off-target effects that can lead to phenotypes unrelated to the silencing of the target gene. Didier Stainer and colleagues contribute to this debate with a report that may cast doubt on the superiority of genetic inactivation versus knockdown. They show that 'morphant' zebrafish embryos in which the egfl7 gene is silenced using morpholinos, display severe vascular defects, whereas egfl7 mutant fish show very mild phenotypes. The discrepancy is a result of genetic compensation induced by deleterious mutations (upregulation of Emilins to counter the loss of Egfl7), but not by transcriptional or translational knockdown. This work illustrates the power of comparing mutants and morphants to identify modifier genes. Cells sense their environment and adapt to it by fine-tuning their transcriptome. Wired into this network of gene expression control are mechanisms to compensate for gene dosage. The increasing use of reverse genetics in zebrafish, and other model systems, has revealed profound differences between the phenotypes caused by genetic mutations and those caused by gene knockdowns at many loci 1 , 2 , 3 , an observation previously reported in mouse and Arabidopsis 4 , 5 , 6 , 7 . To identify the reasons underlying the phenotypic differences between mutants and knockdowns, we generated mutations in zebrafish egfl7 , an endothelial extracellular matrix gene of therapeutic interest, as well as in vegfaa . Here we show that egfl7 mutants do not show any obvious phenotypes while animals injected with egfl7 morpholino (morphants) exhibit severe vascular defects. We further observe that egfl7 mutants are less sensitive than their wild-type siblings to Egfl7 knockdown, arguing against residual protein function in the mutants or significant off-target effects of the morpholinos when used at a moderate dose. Comparing egfl7 mutant and morphant proteomes and transcriptomes, we identify a set of proteins and genes that are upregulated in mutants but not in morphants. Among them are extracellular matrix genes that can rescue egfl7 morphants, indicating that they could be compensating for the loss of Egfl7 function in the phenotypically wild-type egfl7 mutants. Moreover, egfl7 CRISPR interference, which obstructs transcript elongation and causes severe vascular defects, does not cause the upregulation of these genes. Similarly, vegfaa mutants but not morphants show an upregulation of vegfab . Taken together, these data reveal the activation of a compensatory network to buffer against deleterious mutations, which was not observed after translational or transcriptional knockdown.

Key Points All RNA-targeted therapeutic technologies exploit oligonucleotides that bind to target RNA, but they differ in their mechanism of action and produce different effects. Small interfering RNAs, antisense oligonucleotides and external guide sequences lead to enzyme-dependent degradation of targeted mRNA. Drugs involving these approaches are designed to reduce the level of harmful gene products such as viral or bacterial proteins or disease-promoting cellular proteins. They could be useful against cancer as well as viral and bacterial infections, or used to prevent the accumulation of high levels of cholesterol in the bloodstream. Steric-blocking oligonucleotides block the access of cellular machinery to pre-mRNA and mRNA without degrading RNA. Splice-switching oligonucleotides are discussed in detail in this Review; these oligonucleotides redirect alternative splicing, repair defective RNA or restore the production of proteins that are missing because of genetic defects. Splice-switching oligonucleotide-based drugs should be useful for the treatment of genetic diseases such as Duchenne muscular dystrophy, spinal muscular atrophy and β-thalassaemia. Compared to classical small-molecule drugs, it is much more difficult to achieve intracellular delivery with oligonucleotides; this is still a major issue for this class of drugs. The advantage of oligonucleotides is their high specificity, which results from sequence-specific base pairing to target RNA. The oligonucleotide-based drug fomivirsen was approved by the US Food and Drug Administration in 1998 for the treatment of viral retinitis in patients with AIDS. Oligonucleotide-based drugs are now in advanced clinical trials for the treatment of cancer and Duchenne muscular dystrophy as well as for lowering high cholesterol levels. Here, the authors highlight how RNA-blocking oligonucleotides can redirect alternative splicing, repair defective RNA, restore protein production or downregulate gene expression, and so may be useful for treating disorders such as Duchenne muscular dystrophy, spinal muscular atrophy and β-thalassaemia. Here, we discuss three RNA-based therapeutic technologies exploiting various oligonucleotides that bind to RNA by base pairing in a sequence-specific manner yet have different mechanisms of action and effects. RNA interference and antisense oligonucleotides downregulate gene expression by inducing enzyme-dependent degradation of targeted mRNA. Steric-blocking oligonucleotides block the access of cellular machinery to pre-mRNA and mRNA without degrading the RNA. Through this mechanism, steric-blocking oligonucleotides can redirect alternative splicing, repair defective RNA, restore protein production or downregulate gene expression. Moreover, they can be extensively chemically modified to acquire more drug-like properties. The ability of RNA-blocking oligonucleotides to restore gene function makes them best suited for the treatment of genetic disorders. Positive results from clinical trials for the treatment of Duchenne muscular dystrophy show that this technology is close to achieving its clinical potential.

Recent advances in drug development have seen numerous successful clinical translations using synthetic antisense oligonucleotides (ASOs). However, major obstacles, such as challenging large-scale production, toxicity, localization of oligonucleotides in specific cellular compartments or tissues, and the high cost of treatment, need to be addressed. Thiomorpholino oligonucleotides (TMOs) are a recently developed novel nucleic acid analog that may potentially address these issues. TMOs are composed of a morpholino nucleoside joined by thiophosphoramidate internucleotide linkages. Unlike phosphorodiamidate morpholino oligomers (PMOs) that are currently used in various splice-switching ASO drugs, TMOs can be synthesized using solid-phase oligonucleotide synthesis methodologies. In this study, we synthesized various TMOs and evaluated their efficacy to induce exon skipping in a Duchenne muscular dystrophy (DMD) in vitro model using H2K mdx mouse myotubes. Our experiments demonstrated that TMOs can efficiently internalize and induce excellent exon 23 skipping potency compared with a conventional PMO control and other widely used nucleotide analogs, such as 2’-O-methyl and 2’-O-methoxyethyl ASOs. Notably, TMOs performed well at low concentrations (5−20 nM). Therefore, the dosages can be minimized, which may improve the drug safety profile. Based on the present study, we propose that TMOs represent a new, promising class of nucleic acid analogs for future oligonucleotide therapeutic development.

Duchenne muscular dystrophy (DMD), the most common lethal genetic disorder, is caused by mutations in the dystrophin (DMD) gene. Exon skipping is a therapeutic approach that uses antisense oligonucleotides (AOs) to modulate splicing and restore the reading frame, leading to truncated, yet functional protein expression. In 2016, the US Food and Drug Administration (FDA) conditionally approved the first phosphorodiamidate morpholino oligomer (morpholino)-based AO drug, eteplirsen, developed for DMD exon 51 skipping. Eteplirsen remains controversial with insufficient evidence of its therapeutic effect in patients. We recently developed an in silico tool to design antisense morpholino sequences for exon skipping. Here, we designed morpholino AOs targeting DMD exon 51 using the in silico tool and quantitatively evaluated the effects in immortalized DMD muscle cells in vitro. To our surprise, most of the newly designed morpholinos induced exon 51 skipping more efficiently compared with the eteplirsen sequence. The efficacy of exon 51 skipping and rescue of dystrophin protein expression were increased by up to more than 12-fold and 7-fold, respectively, compared with the eteplirsen sequence. Significant in vivo efficacy of the most effective morpholino, determined in vitro, was confirmed in mice carrying the human DMD gene. These findings underscore the importance of AO sequence optimization for exon skipping. Exon skipping is a promising approach to treating Duchenne muscular dystrophy; however, the clinical benefit of treatment has not been demonstrated, and the recent FDA approval remains controversial. Echigoya et al. develop a screening method to identify efficacious oligonucleotides, showing that exon skipping efficacy dramatically improves with sequence optimization.

Mycobacterium abscessus is the most frequently isolated rapidly growing mycobacterium in human disease and recently has emerged as responsible for severe pulmonary infections in cystic fibrosis patients. However, little is known about the virulence mechanisms of this human pathogen. We adapted the zebrafish embryo as a tractable infection model to study, at a spatiotemporal level, the physiopathology of M. abscessus infection. We describe the high propensity of virulent rough variant M. abscessus to produce serpentine cords in vivo , which are not observed with the less virulent smooth variant. We demonstrate that extracellular cording allows the bacterium to withstand phagocytosis, leading to uncontrolled growth and establishment of an acute and lethal infection, thus constituting a determinant of virulence. Mycobacterium abscessus is a rapidly growing Mycobacterium causing a wide spectrum of clinical syndromes. It now is recognized as a pulmonary pathogen to which cystic fibrosis patients have a particular susceptibility. The M. abscessus rough (R) variant, devoid of cell-surface glycopeptidolipids (GPLs), causes more severe clinical disease than the smooth (S) variant, but the underlying mechanisms of R-variant virulence remain obscure. Exploiting the optical transparency of zebrafish embryos, we observed that the increased virulence of the M. abscessus R variant compared with the S variant correlated with the loss of GPL production. The virulence of the R variant involved the massive production of serpentine cords, absent during S-variant infection, and the cords initiated abscess formation leading to rapid larval death. Cording occurred within the vasculature and was highly pronounced in the central nervous system (CNS). It appears that M. abscessus is transported to the CNS within macrophages. The release of M. abscessus from apoptotic macrophages initiated the formation of cords that grew too large to be phagocytized by macrophages or neutrophils. This study is a description of the crucial role of cording in the in vivo physiopathology of M. abscessus infection and emphasizes cording as a mechanism of immune evasion.

We developed an efficient, robust, and broadly applicable system for light-induced protein translation to control the production of proteins of interest and study their function. The method is based on the displacement of a single type of antisense morpholino from RNA by the uncaged guanidinium-linked morpholino (GMO)-phosphorodiamidate morpholino oligonucleotide (PMO) chimera upon UV irradiation. The GMO-PMO chimera designed here is cell-permeable and the GMO part can be produced employing a mercury-free approach compatible with the synthesis on solid support. We demonstrate the function of this optochemical approach in live embryos by inducing, at desired times and locations, the expression of proteins that label specific cells, ablate tissue regions, and affect embryonic development. Together, our results demonstrate that the cell-permeable GMO-PMO chimera offers a strategy for controlling the function of mRNAs of interest. This method allows for the production of proteins at specific times and positions within live organisms, facilitating numerous applications in biomedical research and therapy. Tools enabling mechanistic studies of protein function are important for furthering developmental and cell biology research. Here, Tarbashevich et al. develop molecules that are activated by light to allow spatial and temporal control over RNA translation in live embryos.

Derepression of DUX4 in skeletal muscle has emerged as a likely cause of pathology in facioscapulohumeral muscular dystrophy (FSHD). Here we report on the use of antisense phosphorodiamidate morpholino oligonucleotides to suppress DUX4 expression and function in FSHD myotubes and xenografts. The most effective was phosphorodiamidate morpholino oligonucleotide FM10, which targets the polyadenylation signal of DUX4. FM10 had no significant cell toxicity, and RNA-seq analyses of FSHD and control myotubes revealed that FM10 down-regulated many transcriptional targets of DUX4, without overt off-target effects. Electroporation of FM10 into FSHD patient muscle xenografts in mice also down-regulated DUX4 and DUX4 targets. These findings demonstrate the potential of antisense phosphorodiamidate morpholino oligonucleotides as an FSHD therapeutic option.

Genetic switches that allow for precise control over transgene expression timing or levels may improve the safety and expand the use of adeno-associated viral (AAV) vector-based gene therapy technologies. We previously engineered an efficient RNA switch system that comprises a novel self-cleaving ribozyme (T3H38) and an octaguanidine dendrimer-conjugated morpholino oligonucleotide (v-M8) complementary to the ribozyme. This switch system can be used to efficiently regulate AAV-delivered transgenes with an up to 200-fold regulatory range in mice. However, this switch system has a relatively short induction half-life and only works well when v-M8 was locally but not systemically administered, representing two key limitations of the system. To address these issues, here, we tested replacing the octa-guanidine dendrimer in the v-M8 morpholino oligo with a cell-penetrating peptide (CPP). Two CPP-conjugated morpholino oligos (B-M8 and B-MSP-M8) were synthesized and compared with v-M8 for the induction of T3H38-regulated AAV-luciferase in mice. One of the CPP-conjugated oligos (B-MSP-M8) not only showed significantly improved induction half-life over that of v-M8, but also enabled efficient induction of AAV transgene expression when the oligo was systemically administered. This study improves in vivo performance and broadens the utility of the T3H38 ribozyme-based RNA switch system in gene therapy applications.

In organisms from insects to vertebrates, Toll-like receptors (TLRs) are primary pathogen detectors that activate downstream pathways, specifically those that direct expression of innate immune effector genes. TLRs also have roles in development in many species. The sea anemone Nematostella vectensis is a useful cnidarian model to study the origins of TLR signaling because its genome encodes a single TLR and homologs of many downstream signaling components, including the NF-κB pathway. We have characterized the single N. vectensis TLR (Nv-TLR) and demonstrated that it can activate canonical NF-κB signaling in human cells. Furthermore, we show that the intracellular Toll/IL-1 receptor (TIR) domain of Nv-TLR can interact with the human TLR adapter proteins MAL and MYD88. We demonstrate that the coral pathogen Vibrio coralliilyticus causes a rapidly lethal disease in N. vectensis and that heat-inactivated V. coralliilyticus and bacterial flagellin can activate a reconstituted Nv-TLR–to–NF-κB pathway in human cells. By immunostaining of anemones, we show that Nv-TLR is expressed in a subset of cnidocytes and that many of these Nv-TLR–expressing cells also express Nv-NF-κB. Additionally, the nematosome, which is a Nematostella-specific multicellular structure, expresses Nv-TLR and many innate immune pathway homologs and can engulf V. coralliilyticus. Morpholino knockdown indicates that Nv-TLR also has an essential role during early embryonic development. Our characterization of this primitive TLR and identification of a bacterial pathogen for N. vectensis reveal ancient TLR functions and provide a model for studying the molecular basis of cnidarian disease and immunity.