Biology subjects

Morris, R.

Publications and source records attributed to Morris, R..

27 records · Page 2Linked to original sources

bioRxiv2021

Mechanisms underlying sequence-dependent DNA hybridisation rates in the absence of secondary structure

The kinetics of DNA hybridisation are fundamental to biological processes and DNA-based technologies. However, the precise physical mechanisms that determine why different DNA sequences hybridise at different rates are not well understood. Secondary structure is one predictable factor that influences hybridisation rates but is not sufficient on its own to fully explain the observed sequence-dependent variance. Consequently, to achieve a good correlation with experimental data, current prediction algorithms require many parameters that provide little mechanistic insight into DNA hybridisation. In this context, we measured hybridisation rates of 43 different DNA sequences that are not predicted to form secondary structure and present a parsimonious physically justified model to quantify their hybridisation rates. Accounting only for the combinatorics of complementary nucleating interactions and their sequence-dependent stability, the model achieves good correlation with experiment with only two free parameters, thus providing new insight into the physical factors underpinning DNA hybridisation rates.

biochemistry↗

bioRxiv2021

E2F/Dp inactivation in fat body cells triggers systemic metabolic changes

The E2F transcription factors play a critical role in controlling cell fate. In Drosophila, the inactivation of E2F in either muscle or fat body results in lethality, suggesting an essential function for E2F in these tissues. However, the cellular and organismal consequences of inactivating E2F in these tissues are not fully understood. Here, we show that the E2F loss exerts both tissue-intrinsic and systemic effects. The proteomic profiling of E2F-deficient muscle and fat body revealed that E2F regulates carbohydrate metabolism, a conclusion further supported by metabolomic profiling. Intriguingly, animals with E2F-deficient fat body had a lower level of circulating trehalose and reduced storage of fat. Strikingly, a sugar supplement was sufficient to restore both trehalose and fat levels, and subsequently, rescued animal lethality. Collectively, our data highlight the unexpected complexity of E2F mutant phenotype, which is a result of combining both tissue-specific and systemic changes that contribute to animal development.

developmental biology↗

bioRxiv2020

Multiplexed fractionated proteomics reveals synaptic factors associated with cognitive resilience in Alzheimer's Disease

Alzheimers disease (AD) is a complex neurodegenerative disease defined by the presence of amyloid-{beta} (A{beta}) plaques and tau neurofibrillary tangles, and driven by dysproteostatis, inflammation, metabolic dysfunction, and oxidative injury, eventually leading to synapse loss and cell death. Synapse loss correlates with cognitive impairment and may occur independently of the extent of AD pathology. To understand how synaptic composition is changed in relation to AD neuropathology and cognition, highly sensitive multiplexed liquid chromatography mass-spectrometry was used to quantify biochemically enriched synaptic proteins from the parietal association cortex of 100 subjects with contrasting AD pathology and cognitive performance. Functional analysis showed preservation of synaptic signaling, ion transport, and mitochondrial proteins in normal aged and "resilient" (cognitively unimpaired with AD pathology) individuals. Compared to these individuals, those with cognitive impairment showed significant metabolic differences and increased immune- and inflammatory-related proteins, establishing the synapse as a potential integration point for multiple AD pathophysiologies.

neuroscience↗

bioRxiv2020

Phylogenetic diversity of 200+ isolates of the ectomycorrhizal fungus Cenococcum geophilum associated with Populus trichocarpa soils in the Pacific Northwest, USA and comparison to globally distributed representatives

The ectomycorrhizal fungal symbiont Cenococcum geophilum is of great interest as it is globally distributed, associates with many plant species, and has resistance to multiple environmental stressors. C. geophilum is only known from asexual states but is often considered a cryptic species complex, since extreme phylogenetic divergence is often observed within morphologically identical strains. Alternatively, C. geophilum may represent a highly diverse single species, which would suggest cryptic but frequent recombination. Here we describe a new isolate collection of 229 C. geophilum isolates from soils under Populus trichocarpa at 123 collection sites spanning a ~283 mile north-south transect in Washington and Oregon, USA (PNW). To further understanding of the phylogenetic relationships within C. geophilum, we performed maximum likelihood phylogenetic analyses to assess divergence within the PNW isolate collection, as well as a global GAPDH phylogenetic analysis of 789 isolates with publicly available data from the United States, Europe, Japan, and other countries. Phylogenetic analyses of the PNW isolates revealed three distinct phylogenetic groups, with 15 clades that strongly resolved at >80% bootstrap support based on a GAPDH phylogeny and one clade segregating strongly in two principle component analyses. The abundance and representation of PNW isolate clades varied greatly across the North-South range, including a monophyletic group of isolates that spanned nearly the entire gradient at ~250 miles. A direct comparison between the GAPDH and ITS phylogenies combined with additional analyses revealed stark incongruence between the ITS and GAPDH gene regions, implicating probable intra-species recombination between PNW isolates. In the global isolate collection phylogeny, 34 clades were strongly resolved at >80% bootstrap support, with some clades having intra- and intercontinental distributions. These data are highly suggestive of divergence within multiple cryptic species, however additional analyses such as higher resolution genotype-by-sequencing approaches are needed to distinguish potential species boundaries and recombination patterns.

ecology↗

bioRxiv2019

A map of transcriptional heterogeneity and regulatory variation in human microglia

Microglia, the tissue resident macrophages of the CNS, are implicated in a broad range of neurological pathologies, from acute brain injury to dementia. Here, we profiled gene expression variation in primary human microglia isolated from 141 patients undergoing neurosurgery. Using single cell and bulk RNA sequencing, we defined distinct cellular populations of acutely in vivo-activated microglia, and characterised a dramatic switch in microglial population composition in patients suffering from acute brain injury. We mapped expression quantitative trait loci (eQTLs) in human microglia and show that many disease-associated eQTLs in microglia replicate well in a human induced pluripotent stem cell (hIPSC) derived macrophage model system. Using ATAC-seq from 95 individuals in this hIPSC model we fine-map candidate causal variants at risk loci for Alzheimers disease, the most prevalent neurodegenerative condition in acute brain injury patients. Our study provides the first population-scale transcriptional map of a critically important cell for neurodegenerative disorders.

genomics↗

bioRxiv2018

Integrated accounts of behavioral and neuroimaging data using flexible recurrent neural network models

Neuroscience studies of human decision-making abilities commonly involve sub-jects completing a decision-making task while BOLD signals are recorded using fMRI. Hypotheses are tested about which brain regions mediate the effect of past experience, such as rewards, on future actions. One standard approach to this is model-based fMRI data analysis, in which a model is fitted to the behavioral data, i.e., a subjects choices, and then the neural data are parsed to find brain regions whose BOLD signals are related to the models internal signals. However, the internal mechanics of such purely behavioral models are not constrained by the neural data, and therefore might miss or mischaracterize aspects of the brain. To address this limitation, we introduce a new method using recurrent neural network models that are flexible enough to be jointly fitted to the behavioral and neural data. We trained a model so that its internal states were suitably related to neural activity during the task, while at the same time its output predicted the next action a subject would execute. We then used the fitted model to create a novel visualization of the relationship between the activity in brain regions at different times following a reward and the choices the subject subsequently made. Finally, we validated our method using a previously published dataset. We found that the model was able to recover the underlying neural substrates that were discovered by explicit model engineering in the previous work, and also derived new results regarding the temporal pattern of brain activity.

neuroscience↗

bioRxiv2018

Transcriptional variation and divergence of host-finding behaviour in Steinernema carpocapsae infective juveniles

Steinernema carpocapsae is an entomopathogenic nematode that employs nictation and jumping behaviours to find host insects. We aimed to investigate the transcriptional basis of variant host-finding behaviours in the infective juvenile (IJ) stage of three S. carpocapsae strains (ALL, Breton and UK1). RNA-seq analysis revealed that whilst up to 28% of the S. carpocapsae transcriptome was differentially expressed (P<0.0001) between strains, remarkably few of the most highly differentially expressed genes (>2 log2 fold change, P<0.0001) were from neuronal gene families. S. carpocapsae Breton displays increased chemotaxis toward the laboratory host Galleria mellonella, relative to the other strains. This correlates with the up-regulation of four srsx chemosensory GPCR genes, and a sodium transporter gene, asic-2, relative to both ALL and UK1 strains. The UK1 strain exhibits a decreased nictation phenotype relative to ALL and Breton strains, which correlates with co-ordinate up-regulation of neuropeptide like protein 36 (nlp-36), and down-regulation of an srt family GPCR gene, and a distinct asic-2-like sodium channel paralogue. To further investigate the link between transcriptional regulation and behavioural variation, we sequenced microRNAs across IJs of each strain. We have identified 283 high confidence microRNA genes, yielding 321 isomiR variants in S. carpocapsae, and find that up to 36% of microRNAs are differentially expressed (P<0.0001) between strains. Many of the most highly differentially expressed microRNAs (>2 log2 fold, P<0.0001) are predicted to regulate a variety of neuronal genes that may contribute to variant host-finding behaviours. We have also found evidence for differential gene isoform usage between strains, which alters predicted microRNA interactions, and could contribute to the diversification of behaviour. These data provide deeper insight to the transcriptional landscape of behavioural variation in S. carpocapsae, underpinning efforts to functionally dissect the parasite host-finding apparatus.\n\nAuthor summarySteinernema carpocapsae is a lethal parasite of insects. In order to find and invade a host insect, the S. carpocapsae infective juvenile will typically stand upright, waving its anterior in the air as it searches for host-specific cues. When the infective juvenile senses insect volatile compounds and movement (both signals are required), it will attempt to jump towards the source of those stimuli. Whilst the jumping behaviour is unique to Steinernema species nematodes, nictation is a host-finding behaviour shared with other important parasites of medical and veterinary importance. We have found that different strains of S. carpocpsae use modified host-finding strategies, and that these behavioural differences correlate with gene expression patterns, identifying genes that may be crucial in regulating aspects of host-finding. We also assessed the complement of microRNAs, which are small non-coding RNAs that regulate target gene expression. We found a surprising difference in the abundance of shared microRNAs between strains of S. carpocapsae; these differences also reveal expression differences that correlate with behavioural variation. Predicted microRNA target genes suggest that microRNA variation could significantly influence the behaviour of nematodes. Broadly, this study provides insight to the relationship between gene expression and behaviour, paving the way for detailed studies on gene function.

animal behavior and cognition↗

bioRxiv2017

Formation of functional, non-amyloidogenic fibres by recombinant Bacillus subtilis TasA

Bacterial biofilms are communities of microbial cells encased within a self-produced polymeric matrix. In the Bacillus subtilis biofilm matrix the extracellular fibres of TasA are essential. Here a recombinant expression system allows interrogation of TasA, revealing that monomeric and fibre forms of TasA have identical secondary structure, suggesting that fibrous TasA is a linear assembly of globular units. Recombinant TasA fibres form spontaneously, and share the biological activity of TasA fibres extracted from B. subtilis, whereas a TasA variant restricted to a monomeric form is inactive and subjected to extracellular proteolysis. The biophysical properties of both native and recombinant TasA fibres indicate that they are not functional amyloid-like fibres. A gel formed by TasA fibres can recover after physical shear force, suggesting that the biofilm matrix is not static and that these properties may enable B. subtilis to remodel its local environment in response to external cues. Using recombinant fibres formed by TasA orthologues we uncover species variability in the ability of heterologous fibres to cross-complement the B. subtilis tasA deletion. These findings are indicative of specificity in the biophysical requirements of the TasA fibres across different species and/or reflect the precise molecular interactions needed for biofilm matrix assembly.\n\nContributionsConceived and designed the experiments: CE, EE, RG, CEM, RJM, MS, NSW; Performed the experiments: KB, LC, CE, EE, PKF, RG, CEM, RJM, MS, TS; Contributed new analytical tools: CE, EE, RG, TS; Analysed the data: CE, EE, CEM, RJM, MS, LCS, NSW; Wrote the paper: EE, RJM, CEM, MS, NSW.

microbiology↗

bioRxiv2017

Regulatory divergence of flowering time genes in the allopolyploid Brassica napus

Polyploidy is a recurrent feature of eukaryotic evolution and has been linked to increases in complexity, adaptive radiation and speciation. Within angiosperms, such events occur repeatedly in many plant lineages. We investigated the role of duplicated genes in the regulation of flowering in Brassica napus. This relatively young allotetraploid represents a snapshot of evolution and artificial selection in progress. In line with the gene balance hypothesis, we find preferential retention of expressed flowering time genes relative to the whole genome. Furthermore, gene expression dynamics across development reveal diverged regulation of many flowering time gene copies. This finding supports the concept of responsive backup circuits being key for the retention of duplicated genes. A case study of BnaTFL1 reveals differences in cis-regulatory elements downstream of these genes that could explain this divergence. Such differences in the regulatory dynamics of duplicated genes highlight the challenges for translating gene networks from model to more complex polyploid crop species.

plant biology↗