Biology subjects

Parker, M. T.

Publications and source records attributed to Parker, M. T..

11 recordsLinked to original sources

bioRxiv2026

Developing a Standard Definition for Sequences of Concern

Readily available nucleic acid synthesis is both critical for the bioeconomy and an increasingly pressing security concern due to the potential for accidental or deliberate misuse. While biosecurity experts broadly agree that nucleic acid providers should screen orders for potential "sequences of concern," there has previously been no agreed standard for how to define and recognize such sequences. To address this gap, we first organized a test set of 1.1 million sequences from pathogens and toxins on the Australia Group Common Control Lists and their non-controlled relatives, along with model organisms and synthetic constructs. An initial categorization of sequences as to whether or not they were sequence of concern was produced by comparing the results of four biosecurity screening systems for each of these sequences, finding that these systems already agreed on the categorization of more than 80% of sequences. We then refined these results through a science-based stakeholder review process to define a rubric for determining whether a sequence should be flagged as a potential sequence of concern, then applied this rubric to improve the categorization of test sets. The result is a rubric that identifies sequences of concern with respect to human pandemic-potential viruses, key classes of low-risk genes, and controlled toxins. Applying this rubric to the test set collection has reduced the number of test sequences with disputed categorization by 44.3% for controlled viruses and 10.7% across the test set as a whole. Together, these results provide a concrete "sequence of concern" definition that can be used as a foundation for development of biosecurity screening standards and policy.

bioinformatics↗

bioRxiv2026

coelsch: Platform-agnostic single-cell analysis of meiotic recombination events

BackgroundMeiotic recombination creates genetic diversity through reciprocal exchange of haplotypes between homologous chromosomes. Scalable and robust methods for mapping recombination breakpoints are essential for understanding meiosis and for genetic mapping. Single cell sequencing of gametes offers a direct approach to recombination mapping, yet the effect of technical differences between single-cell sequencing methods for crossover detection remains unclear. ResultsWe benchmark single cell methods for droplet-based chromatin accessibility and RNA sequencing and plate-based whole-genome amplification for mapping meiotic recombination in Arabidopsis thaliana. For this purpose we introduce two novel open-source tools coelsch_mapping_pipeline and coelsch for haplotype-aware alignment and per-cell crossover detection, using them to recover known recombination frequencies and quantify the effects of coverage sparsity. We subsequently apply our approach to a panel of 40 recombinant F hybrids derived from crosses of 22 diverse natural accessions, successfully recovering genetic maps for 34 F1s in a single dataset. This analysis reveals substantial variation in recombination rate and identifies a [~]10 Mb pericentric inversion in the accession Zin-9, the largest natural inversion reported in A. thaliana to date. ConclusionsThese results demonstrate the applicability and scalability of single-cell gamete sequencing for high-throughput mapping of meiotic recombination, and highlight the strengths and limitations of different single-cell modalities. The accompanying open-source tools provide a framework for haplotyping and crossover detection analysis using sparse single-cell sequencing data. Our methodology enables parallel analysis of large numbers of hybrids in a single dataset, removing a major technical barrier to large-scale studies of natural variation in recombination rate.

bioinformatics↗

bioRxiv2024

Expression quantitative trait locus mapping in recombinant gametes using single nucleus RNA sequencing

Phenotypic differences between individuals of a species are often caused by differences in gene expression, which are in turn caused by genetic variation. Expression quantitative trait locus (eQTL) analysis is a methodology by which we can identify such causal variants. Scaling eQTL analysis is costly due to the expense of generating mapping populations, and the collection of matched transcriptomic and genomic information. We developed a rapid eQTL analysis approach using single-cell/nucleus RNA sequencing of gametes from a small number of heterozygous individuals. Patterns of inherited polymorphisms are used to infer the recombinant genomes of thousands of individual gametes and identify how different haplotypes correlate with variation in gene expression. Applied to Arabidopsis pollen nuclei, our approach uncovers both cis- and trans-eQTLs, ultimately mapping variation in a master regulator of sperm cell development that affects the expression of hundreds of genes. This establishes snRNA-sequencing as a powerful, cost-effective method for the mapping of meiotic recombination, addressing the scalability challenges of eQTL analysis and enabling eQTL mapping in specific cell-types.

bioinformatics↗

bioRxiv2023

U6 snRNA m6A modification is required for accurate and efficient cis- and trans-splicing of C. elegans mRNAs

pre-mRNA splicing is a critical feature of eukaryotic gene expression. Many eukaryotes use cis-splicing to remove intronic sequences from pre-mRNAs. In addition to cis-splicing, many organisms use trans-splicing to replace the 5' ends of mRNAs with a non-coding spliced-leader RNA. Both cis- and trans-splicing rely on accurately recognising splice site sequences by spliceosomal U snRNAs and associated proteins. Spliceosomal snRNAs carry multiple RNA modifications with the potential to affect different stages of pre-mRNA splicing. Here, we show that m6A modification of U6 snRNA A43 by the RNA methyltransferase METT-10 is required for accurate and efficient cis- and trans-splicing of C. elegans pre-mRNAs. The absence of U6 snRNA m6A modification primarily leads to alternative splicing at 5' splice sites. Furthermore, weaker 5' splice site recognition by the unmodified U6 snRNA A43 affects splicing at 3' splice sites. U6 snRNA m6A43 and the splicing factor SNRNP27K function to recognise an overlapping set of 5' splice sites with an adenosine at +4 position. Finally, we show that U6 snRNA m6A43 is required for efficient SL trans-splicing at weak 3' trans-splice sites. We conclude that the U6 snRNA m6A modification is important for accurate and efficient cis- and trans-splicing in C. elegans.

molecular biology↗

bioRxiv2023

The evolution of splice site sequence preference is linked to the U6 snRNA m6A methyltransferase METTL16

Eukaryotic genes are interrupted by introns that are removed from transcribed RNAs by splicing. The extent of alternative splicing is the best genomic predictor of developmental complexity, yet it is unclear what mediates change in patterns of splicing complexity between species. Here we show that variation in 5 splice site sequence preferences correlate with the presence of the U6 snRNA methyltransferase METTL16 and the splicing factor SNRNP27K. We used inter-species association mapping with Saccharomycotina species to correlate splicing phenotypes with the presence or absence of splicing factors. The greatest variation in 5 splice site sequence occurred at the +4 position and involved a preference switch between adenosine and uridine. Loss of METTL16 and SNRNP27K orthologs, or a single SNRNP27K methionine residue, was associated with a preference for +4U. These findings are consistent with splicing analyses of mutants defective in either METTL16 or SNRNP27K orthologs and models derived from spliceosome structures, demonstrating that inter-species association mapping is a powerful orthogonal approach to molecular studies. We conclude that variation in concerted processes of 5 splice site selection by U6 snRNA is crucial to evolutionary change in splicing complexity.

bioinformatics↗

bioRxiv2022

m6A modification of U6 snRNA modulates usage of two major classes of pre-mRNA 5' splice site

Alternative splicing of messenger RNAs is associated with the evolution of developmentally complex eukaryotes. Splicing is mediated by the spliceosome, and docking of the pre-mRNA 5 splice site into the spliceosome active site depends upon pairing with the conserved ACAGA sequence of U6 snRNA. In some species, including humans, the central adenosine of the ACAGA box is modified by N6 methylation, but the role of this m6A modification is poorly understood. Here we show that m6A modified U6 snRNA determines the accuracy and efficiency of splicing. We reveal that the conserved methyltransferase, FIO1, is required for Arabidopsis U6 snRNA m6A modification. Arabidopsis fio1 mutants show disrupted patterns of splicing that can be explained by the sequence composition of 5 splice sites and cooperative roles for U5 and U6 snRNA in splice site selection. U6 snRNA m6A influences 3 splice site usage and reinforces splicing fidelity at elevated temperature. We generalise these findings to reveal two major classes of 5 splice site in diverse eukaryotes, which display anti-correlated interaction potential with U5 snRNA loop 1 and the U6 snRNA ACAGA box. We conclude that U6 snRNA m6A modification contributes to the selection of degenerate 5 splice sites crucial to alternative splicing.

molecular biology↗

bioRxiv2021

Yanocomp: robust prediction of m6A modifications in individual nanopore direct RNA reads.

Yanocomp is a tool for predicting the positions and stoichiometries of RNA modifications in Nanopore direct RNA sequencing data. It uses general mixture models to identify differentially modified sites between two conditions, with good support for replicates. Yanocomp models across adjacent kmers and uses a uniform component to account for outliers, improving the accuracy of single molecule predictions. Consequently, Yanocomp can be used to measure modification stoichiometry, and correlate modifications with other RNA processing events. AvailabilityYanocomp is available under an MIT license at www.github.com/bartongroup/yanocomp.

bioinformatics↗

bioRxiv2020

Widespread premature transcription termination of Arabidopsis thaliana NLR genes by the spen protein FPA

Genes involved in disease resistance are some of the fastest evolving and most diverse components of genomes. Large numbers of nucleotide-binding, leucine-rich repeat receptor (NLR) genes are found in plant genomes and are required for disease resistance. However, NLRs can trigger autoimmunity, disrupt beneficial microbiota or reduce fitness. It is therefore crucial to understand how NLRs are controlled. Here we show that the RNA-binding protein FPA mediates widespread premature cleavage and polyadenylation of NLR transcripts, thereby controlling their functional expression and impacting immunity. Using long-read Nanopore direct RNA sequencing, we resolved the complexity of NLR transcript processing and gene annotation. Our results uncover a co-transcriptional layer of NLR control with implications for understanding the regulatory and evolutionary dynamics of NLRs in the immune responses of plants.

molecular biology↗

bioRxiv2020

Two-pass alignment using machine-learning-filtered splice junctions increases the accuracy of intron detection in long-read RNA sequencing

Transcription of eukaryotic genomes involves complex alternative processing of RNAs. Sequencing of full-length RNAs using long reads reveals the true complexity of processing. However, the relatively high error rates of long-read sequencing technologies can reduce the accuracy of intron identification. Here we apply alignment metrics and machine-learning-derived sequence information to filter spurious splice junctions from long read alignments and use the remaining junctions to guide realignment in a two-pass approach. This method, available in the software package 2passtools (https://github.com/bartongroup/2passtools), improves the accuracy of spliced alignment and transcriptome assembly for species both with and without existing high-quality annotations.

bioinformatics↗

bioRxiv2019

Nanopore direct RNA sequencing maps an Arabidopsis N6 methyladenosine epitranscriptome

Understanding genome organization and gene regulation requires insight into RNA transcription, processing and modification. We adapted nanopore direct RNA sequencing to examine RNA from a wild-type accession of the model plant Arabidopsis thaliana and a mutant defective in mRNA methylation (m6A). Here we show that m6A can be mapped in full-length mRNAs transcriptome-wide and reveal the combinatorial diversity of cap-associated transcription start sites, splicing events, poly(A) site choice and poly(A) tail length. Loss of m6A from 3 untranslated regions is associated with decreased relative transcript abundance and defective RNA 3' end formation. A functional consequence of disrupted m6A is a lengthening of the circadian period. We conclude that nanopore direct RNA sequencing can reveal the complexity of mRNA processing and modification in full-length single molecule reads. These findings can refine Arabidopsis genome annotation. Further, applying this approach to less well-studied species could transform our understanding of what their genomes encode.

molecular biology↗

bioRxiv2018

Innate Immune Priming by cGAS as a Preparatory Countermeasure Against RNA Virus Infection

The detection of nucleic acids by pattern recognition receptors is an ancient and conserved component of the innate immune system. Notably, RNA virus genomes are sensed by mammalian cytosolic RIG-I-like receptors, thereby activating interferon-stimulated gene (ISG) expression to restrict viral replication. However, recent evidence indicates that the cGAS-STING DNA sensing pathway also protects against RNA viruses. So far, the mechanisms responsible for DNA sensing of RNA viruses, which replicate without known DNA intermediates, remain unclear. By using cGAS gene knockout and reconstitution in human and mouse cell cultures, we discovered that DNA sensing and cGAMP synthase activities are required for cGAS-mediated restriction of vesicular stomatitis virus and Sindbis virus. The level of cGAMP produced in response to RNA virus infection was below the threshold of detection, suggesting that only transient and/or low levels of cGAMP are produced during RNA virus infections. To clarify the DNA ligands that activate cGAS activity, we confirmed that cGAS binds mitochondrial DNA in the cytosol of both uninfected and infected cells; however, the amount of cGAS-associated mitochondrial DNA did not change in response to virus infection. Rather, a variety of pre-existing cytosolic DNAs, including mitochondrial DNA and endogenous cDNAs, may serve as stimuli for basal cGAS activation. Importantly, cGAS knockout and reconstitution experiments demonstrated that cGAS drives low-level ISG expression at steady state. We propose that cGAS-STING restricts RNA viruses by promoting a preparatory immune activation state within cells, likely primed by endogenous cellular DNA ligands.\n\nImportanceMany medically important RNA viruses are restricted by the cGAS-STING DNA-sensing pathway of innate immune activation. Since these viruses replicate without DNA intermediates, it is unclear what DNA ligand(s) are responsible for triggering this pathway. We show here that cGASs DNA binding and signaling activities are required for RNA virus restriction, similar to the mechanisms by which it restricts DNA viruses. Furthermore, we confirmed that cGAS continuously binds host DNA, which was unaffected by RNA virus infection. Finally, cGAS expression correlated with the low-level expression of interferon-stimulated genes in uninfected cells, both in vitro and in vivo. We propose that cGAS-mediated sensing of endogenous DNA ligands contributes to RNA virus restriction by establishing a baseline of innate immune activation.

immunology↗