Biology subjects

Miska, E. A.

Publications and source records attributed to Miska, E. A..

52 records · Page 3Linked to original sources

bioRxiv2019

Ancestral hybridisation facilitated species diversification in the Lake Malawi cichlid fish adaptive radiation

The adaptive radiation of cichlid fishes in East Afrian Lake Malawi encompasses over 500 species that are believed to have evolved within the last 800 thousand years from a common founder population. It has been proposed that hybridisation between ancestral lineages can provide the genetic raw material to fuel such exceptionally high diversification rates, and evidence for this has recently been presented for the Lake Victoria Region cichlid superflock. Here we report that Lake Malawi cichlid genomes also show evidence of hybridisation between two lineages that split 3-4 million years ago, today represented by Lake Victoria cichlids and the riverine Astatotilapia sp. ruaha blue. The two ancestries in Malawi cichlid genomes are present in large blocks of several kilobases, but there is little variation in this pattern between Malawi cichlid species, suggesting that the large-scale mosaic structure of the genomes was largely established prior to the radiation. Nevertheless, tens of thousands of polymorphic variants apparently derived from the hybridisation are interspersed in the genomes. These loci show a striking excess of differentiation across ecological subgroups in the Lake Malawi cichlid assemblage, and parental alleles sort differentially into benthic and pelagic Malawi cichlid lineages, consistent with strong differential selection on these loci during species divergence. Furthermore, these loci are enriched for genes involved in immune response and vision, including opsin genes previously identified as important for speciation. Our results reinforce the role of ancestral hybridisation in explosive diversification by demonstrating its significance in one of the largest recent vertebrate adaptive radiations.

evolutionary biology↗

bioRxiv2019

Alternative splicing modulation by G-quadruplexes

Alternative splicing is central to metazoan gene regulation but the regulatory mechanisms involved are only partially understood. Here, we show that G-quadruplex (G4) motifs are enriched ~3-fold both upstream and downstream of splice junctions. Analysis of in vitro G4-seq data corroborates their formation potential. G4s display the highest enrichment at weaker splice sites, which are frequently involved in alternative splicing events. The importance of G4s in RNA as supposed to DNA is emphasized by a higher enrichment for the non-template strand. To explore if G4s are involved in dynamic alternative splicing responses, we analyzed RNA-seq data from mouse and human neuronal cells treated with potassium chloride. We find that G4s are enriched at exons which were skipped following potassium ion treatment. We validate the formation of stable G4s for three candidate splice sites by circular dichroism spectroscopy, UV-melting and fluorescence measurements. Finally, we explore G4 motifs across eleven representative species, and we observe that strong enrichment at splice sites is restricted to mammals and birds.

genomics↗

bioRxiv2019

A genetic pathway encoding double-stranded RNA transporters and interactors regulates growth and plasticity in Caenorhabditis elegans

The environment and genes shape the development, physiology and behaviour of organisms. Many animal species can take-up double-stranded RNA (dsRNA) from the environment. Environmental dsRNA changes gene expression through RNA interference (RNAi). While environmental RNAi is used as a laboratory tool, e.g. in nematodes, planaria and insects, its biological role remains enigmatic. Here we characterise the environmental dsRNA receptor SID-2 to understand the biological function of dsRNA uptake in Caenorhabditis elegans. First we determine that SID-2 localises to the apical membrane and the trans-Golgi-network (TGN) in the intestine, implicating the TGN as a central cellular compartment for environmental dsRNA uptake. We demonstrate that SID-2 is irrelevant for nucleotide uptake from the environment as a nutritional (nitrogen) source. Instead RNA profiling and high-resolution live imaging revealed a new biological function for sid-2 in growth and phenotypic plasticity. Surprisingly, lack of the ability to uptake environmental RNA reduces plasticity of gene expression. Furthermore, using genetic analyses we show that the dsRNA pathway genes sid-2, sid-1 and rde-4 together regulate growth. This work suggest that environmental RNA affects morphology and plasticity through gene regulation.

molecular biology↗

bioRxiv2019

C. elegans transgenerationally adapts to bacterial infection by increasing the expression of cysteine synthases in progeny

Parental exposure to pathogens can prime offspring immunity in diverse organisms. The mechanisms by which this heritable priming occurs are largely unknown. Here we report that the soil bacteria Pseudomonas vranovensis is a natural pathogen of the nematode Caenorhabditis elegans and that parental exposure of animals to P. vranovensis promotes offspring resistance to infection. Furthermore, we demonstrate a transgenerational enhancement of progeny survival when three consecutive generations of animals are exposed to P. vranovensis. By investigating the mechanisms by which animals heritably adapt to P. vranovensis infection, we found that parental infection by P. vranovensis results in increased expression of the cysteine synthases CYSL-1 and CYSL-2 and the regulator of hypoxia inducible factor RHY-1 in progeny and that these three genes are required for adaptation to P. vranovensis. To our knowledge, these observations represent the largest heritable increase in offspring survival in response to a pathogen infection reported in any organism to date and establish a new CYSL-1, CYSL-2, and RHY-1 dependent mechanism by which animals adapt to infection.

genetics↗

bioRxiv2019

Silencing of SmAgo2 increases abundance of retrotransposons in the parasitic flatworm Schistosoma mansoni.

Transposable elements (TEs) are mobile parts of the genome that can jump or self-replicate, posing a threat to the stability and integrity of the host genome. TEs are prevented from causing damage to the host genome by defense mechanisms such as nuclear silencing, where TE transcripts are targeted for degradation in an RNAi-like fashion. These pathways are well characterised in model organisms but very little is known about them in other species. Parasitic flatworms present an opportunity to investigate evolutionary novelties in TE control because they lack canonical pathways identified in model organisms (such as the piRNA pathways) but have conserved central players such as Dicer and Ago (argonaute) enzymes. Notably, parasitic flatworm Ago proteins are phylogenetically distinct from classical Ago, raising the question of whether they play special roles in these organisms. In this report, we investigate the role of Ago proteins in the parasitic flatworm Schistosoma mansoni. We show that transcript abundance of two retrotransposable elements increases upon silencing of S. mansoni Ago genes. We further demonstrate that SmAgo2 protein is primarily localised in the germ line of adult worms and its sub-cellular localisation is both nuclear and cytoplasmic. These findings provide further evidence of active TE control under a yet not fully unveiled pathway.

molecular biology↗

bioRxiv2019

A novel mode of communication between blood and the germline for the inheritance of paternal experiences

In many species, environmental stimuli can affect the germline and contribute to phenotypic changes in the offspring, without altering the genetic code1-5. So far, little is known about which biological signals can link exposure to germ cells. Using a mouse model of postnatal trauma with transgenerational effects, we show that exposure alters lipid-based metabolites in blood of males and their non-exposed offspring. Comparable alterations are validated in serum and saliva of orphan children exposed to trauma. Peroxisome proliferator-activated receptor (PPAR) is identified as mediating the effects of metabolites alterations. Mimicking PPAR activation with a dual PPAR/{gamma} agonist in vivo induces changes in the sperm transcriptome similarly to trauma, and reproduces metabolic phenotypes in the offspring. Injecting serum collected from adult males exposed to postnatal trauma into controls recapitulates metabolic phenotypes in the offspring. These results suggest conserved effects of early life adversity on blood metabolites, and causally involve paternal blood factors and PPAR nuclear receptor in phenotype heritability.

molecular biology↗

bioRxiv2019

NSUN2 introduces 5-methylcytosines in mammalian mitochondrial tRNAs

Maintenance and expression of mitochondrial DNA is indispensable for proper function of the oxidative phosphorylation machinery. Post-transcriptional modification of mitochondrial RNA has emerged as one of the key regulatory steps of human mitochondrial gene expression. Mammalian NOP2/Sun RNA Methyltransferase Family Member 2 (NSUN2) has been characterised as an RNA methyltransferase that introduces 5-methylcytosine (m5C) in nuclear-encoded tRNAs, mRNAs, microRNA and noncoding RNAs. In these roles, NSUN2 has been associated with cell proliferation and differentiation. Pathogenic variants in NSUN2 have been linked with neurodevelopmental disorders. Here we employ spatially restricted proximity labelling and immunodetection to demonstrate that NSUN2 is imported into the matrix of mammalian mitochondria. Using three genetic models for NSUN2 inactivation - knockout mice, patient-derived fibroblasts and CRISPR/Cas9 knockout in human cells - we show that NSUN2 in necessary for the generation of m5C at positions 48, 49 and 50 of several mammalian mitochondrial tRNAs. Finally, we show that inactivation of NSUN2 does not have a profound effect on mitochondrial tRNA stability and oxidative phosphorylation in differentiated cells. We discuss the importance of the newly discovered function of NSUN2 in the context of human disease.

biochemistry↗

bioRxiv2019

Direct interaction of PIWI and DEPS-1 is essential for piRNA function and condensate ultrastructure in Caenorhabditis elegans

Membraneless organelles are platforms for many aspects of RNA biology including small non-coding RNA (ncRNA) mediated gene silencing. How small ncRNAs utilise phase separated environments for their function is unclear. To address this question, we investigated how the PIWI-interacting RNA (piRNA) pathway engages with the membraneless organelle P granule in Caenorhabditis elegans. Proteomic analysis of the PIWI protein PRG-1 revealed an interaction with the constitutive P granule protein DEPS-1. Furthermore we identified a novel motif on DEPS-1, PBS, which interacts directly with the Piwi domain of PRG-1. This protein complex forms intertwining ultrastructures to build elongated condensates in vivo. These sub-organelle ultrastructures depend on the Piwi-interacting motif of DEPS-1 and mediate piRNA function. Additionally, we identify a novel interactor of DEPS-1, EDG-1, which is required for DEPS-1 condensates to form correctly. We show that DEPS-1 is not required for piRNA biogenesis but piRNA function: deps-1 mutants fail to produce the secondary endo-siRNAs required for the silencing of piRNA targets. Our study reveals how specific protein-protein interactions drive the spatial organisation and function of small RNA pathways within membraneless organelles.

cell biology↗

bioRxiv2019

Mature sperm small RNA profile in the sparrow: implications for transgenerational effects of age on fitness

Mammalian sperm RNA has recently received a lot of interest due to its involvement in epigenetic germline inheritance. Studies of epigenetic germline inheritance have shown that environmental exposures can induce effects in the offspring without altering the DNA sequence of germ cells. Most mechanistic studies were conducted in laboratory rodents and C.elegans while observational studies confirm the phenotypic phenomenon in wild populations of humans and other species including birds. Prominently, paternal age in house sparrows affects offspring fitness, yet the mechanism is unknown. This study provides a first reference of house sparrow sperm small RNA as an attempt to uncover their role in the transmission of the effects of paternal age on the offspring. In this small scale pilot, we found no statistically significant differences between miRNA and tRNA fragments in aged and prime sparrow sperm. These results indicate a role of other epigenetic information carriers, such as distinct RNA classes, RNA modifications, DNA methylation and retained histones, and a clear necessity of future studies in wild populations.

developmental biology↗

bioRxiv2018

Identification of functional long non-coding RNAs in C. elegans

BackgroundFunctional characterisation of the compact genome of the model organism Caenorhabditis elegans remains incomplete despite its sequencing twenty years ago. The last decade of research has seen a tremendous increase in the number of non-coding RNAs identified in various organisms. While we have mechanistic understandings of small non-coding RNA pathways, long non-coding RNAs represent a diverse class of active transcripts whose function remains less well characterised.\n\nResultsBy analysing hundreds of published transcriptome datasets, we annotated 3,397 potential lncRNAs including 146 multi-exonic loci that showed increased nucleotide conservation and GC content relative to other non-coding regions. Using CRISPR / Cas9 genome editing we generated deletion mutants for ten long non-coding RNA loci. Using automated microscopy for in-depth phenotyping, we show that six of the long non-coding RNA loci are required for normal development and fertility. Using RNA interference mediated gene knock-down, we provide evidence that for two of the long non-coding RNA loci, the observed phenotypes are dependent on the corresponding RNA transcripts.\n\nConclusionsOur results highlight that a large section of the non-coding regions of the C. elegans genome remain unexplored. Based on our in vivo analysis of a selection of high-confidence lncRNA loci, we expect that a significant proportion of these high-confidence regions is likely to have biological function at either the genomic or the transcript level.

genetics↗

bioRxiv2017

SLAM-ITseq: Sequencing cell type-specific transcriptomes without cell sorting

Cell type-specific transcriptome analysis is an essential tool in understanding biological processes but can be challenging due to the limits of microdissection or fluorescence-activated cell sorting (FACS). Here, we report a novel in vivo sequencing method, which captures the transcriptome of a specific type of cells in a tissue without prior cellular or molecular sorting. SLAM-ITseq provides an accurate snapshot of the transcriptional state in vivo.

molecular biology↗

bioRxiv2017

Terminal uridylyltransferases target RNA viruses as part of the innate immune system in animals

RNA viruses are a major threat to animals and plants. RNA interference (RNAi) and the interferon response provide innate antiviral defense against RNA viruses. Here we performed a large-scale screen using C. elegans and its natural pathogen, the Orsay virus (OrV), and identified cde-1 as important for antiviral defense. CDE-1 is a homologue of the mammalian TUT4/7 terminal uridylyltransferases; its catalytic activity is required for its antiviral function. CDE-1 uridylates the 3' end of the OrV RNA genome and promotes its degradation, independently of the RNAi pathway. Likewise, TUT4/7 uridylate influenza A virus (IAV) mRNAs in mammalian cells. Deletion of TUT4/7 leads to increased IAV mRNA and protein levels. We have defined 3' terminal uridylation of viral RNAs as a conserved antiviral defense mechanism.

immunology↗

bioRxiv2017

Pan-arthropod analysis reveals somatic piRNAs as an ancestral TE defence

In animals, small RNA molecules termed PIWI-interacting RNAs (piRNAs) silence transposable elements (TEs), protecting the germline from genomic instability and mutation. piRNAs have been detected in the soma in a few animals, but these are believed to be specific adaptations of individual species. Here, we report that somatic piRNAs were likely present in the ancestral arthropod more than 500 million years ago. Analysis of 20 species across the arthropod phylum suggests that somatic piRNAs targeting TEs and mRNAs are common among arthropods. The presence of an RNA-dependent RNA polymerase in chelicerates (horseshoe crabs, spiders, scorpions) suggests that arthropods originally used a plant-like RNA interference mechanism to silence TEs. Our results call into question the view that the ancestral role of the piRNA pathway was to protect the germline and demonstrate that small RNA silencing pathways have been repurposed for both somatic and germline functions throughout arthropod evolution.

evolutionary biology↗

bioRxiv2017

Whole Genome Sequences Of Malawi Cichlids Reveal Multiple Radiations Interconnected By Gene Flow

The hundreds of cichlid fish species in Lake Malawi constitute the most extensive recent vertebrate adaptive radiation. Here we characterize its genomic diversity by sequencing 134 individuals covering 73 species across all major lineages. Average sequence divergence between species pairs is only 0.1-0.25%. These divergence values overlap diversity within species, with 82% of heterozygosity shared between species. Phylogenetic analyses suggest that diversification initially proceeded by serial branching from a generalist Astatotilapia-like ancestor. However, no single species tree adequately represents all species relationships, with evidence for substantial gene flow at multiple times. Common signatures of selection on visual and oxygen transport genes shared by distantly related deep water species point to both adaptive introgression and independent selection. These findings enhance our understanding of genomic processes underlying rapid species diversification, and provide a platform for future genetic analysis of the Malawi radiation.\n\nOne Sentence Summary: The genomes of 73 cichlid fish species from Lake Malawi uncover evolutionary processes underlying a large adaptive evolutionary radiation.

evolutionary biology↗

bioRxiv2017

An alternative STAT signaling pathway acts in antiviral immunity in Caenorhabditis elegans

Across metazoans, innate immunity is vital in defending organisms against viral infection. In mammals, antiviral innate immunity is orchestrated by interferon signaling, activating the STAT transcription factors downstream of the JAK kinases to induce expression of antiviral effector genes. In the nematode C. elegans, which lacks the interferon system, the major antiviral response so far described is RNA interference but whether additional gene expression responses are employed is not known. Here we show that, despite the absence of both interferon and JAK, the C. elegans STAT homologue STA-1 orchestrates antiviral immunity. Intriguingly, mutants lacking STA-1 show increased resistance to antiviral infection. Using gene expression analysis and chromatin immunoprecipitation we show that, in contrast to the mammalian pathway, STA-1 acts as a transcriptional repressor. Thus STA-1 might act to suppress a constitutive antiviral response in the absence of infection. Using a reverse genetic screen we identify the SID-3 as a kinase upstream of STA-1 in the response to infection. Together, our work identifies a novel STAT regulatory cascade controlling its activity in antiviral resistance, illustrating the complex evolutionary trajectory displayed by innate immune signaling pathways across metazoan organisms.

immunology↗

bioRxiv2016

The Aquarius/EMB-4 helicase licenses co-transcriptional gene silencing

Small RNAs (sRNAs) play an ancient role in genome defence against transposable elements. In animals, plants and fungi small RNAs guide Argonaute proteins to nascent RNA transcripts to induce co-transcriptional gene silencing. In animals the link between small RNA pathways and the transcriptional machinery remains unclear. Here we show that the Caenorhabditis elegans germline Argonaute HRDE-1 physically interacts with the conserved RNA helicase Aquarius/EMB-4. We demonstrate that the Aquarius/EMB-4 helicase activity is required to initiate small RNA-induced co-transcriptional gene silencing. HRDE-1 and Aquarius/EMB-4 are required to silence the transcription of overlapping sets of transposable elements. Surprisingly, removal of introns from a small RNA pathway target abolishes the requirement for Aquarius/EMB-4, but not HRDE-1, for gene silencing. We conclude that the Aquarius/EMB-4 helicase activity allows HRDE-1/sRNA complexes to efficiently engage nascent RNA transcripts - in competition with the general RNA processing machinery. We postulate that Aquarius/EMB-4 facilitates the surveillance of the nascent transcriptome to detect and silence transposable elements through small RNA pathways.

molecular biology↗