Biology subjects

Hill, T.

Publications and source records attributed to Hill, T..

35 records · Page 2Linked to original sources

bioRxiv2023

Benchmarking and optimization of cell-free DNA deconvolution

Reference methylomes, used in deconvolution algorithms to determine cell-free DNA tissue sources, were based on driver CpGs from either microarray or sequencing platforms. Cross-validation of these algorithms is important to allow interpretation of data across studies, select optimal sequencing depth, and thus reduce costs of cf-DNA deconvolution assays. Towards this end, we assessed the performance of two reference-based deconvolution algorithms: cfDNAme, sequencing-based methylome signatures, and Meth-Atlas, a microarray-based methylome signatures using a cfDNA bisulfite sequencing. While both algorithms use NNLS model, cfDNAme uses CpG windows, while Meth-Atlas uses individual CpGs as cell or tissue signatures. We determined the optimal the number of informative CpGs signatures, and the best sequencing depths for precise deconvolution. We found that above 5-fold coverage, much lower coverage than what is frequently used, there is little difference between our two chosen algorithms, both identifying the correct tissue make-up with a high accuracy, suggesting that whole genome bisulfite sequencing for tissue of origin identification can be completed in a much more cost-effective manner than previously thought.

bioinformatics↗

bioRxiv2023

Brain cell-specific origin of circulating microRNA biomarkers in experimental temporal lobe epilepsy

The diagnosis of epilepsy is complex and challenging and would benefit from the availability of molecular biomarkers, ideally measurable in a biofluid such as blood. Experimental and human epilepsy are associated with altered brain and blood levels of various microRNAs (miRNAs). Evidence is lacking, however, as to whether any of the circulating pool of miRNAs originates from the brain. To explore the link between circulating miRNAs and the pathophysiology of epilepsy, we first sequenced argonaute 2 (Ago2)-bound miRNAs in plasma samples collected from mice subject to status epilepticus induced by intraamygdala microinjection of kainic acid. This identified time-dependent changes in plasma levels of miRNAs with known neuronal and microglial-cell origins. To explore whether the circulating miRNAs had originated from the brain, we generated mice expressing FLAG-Ago2 in neurons or microglia using tamoxifen-inducible Thy1 or Cx3cr1 promoters, respectively. FLAG immunoprecipitates from the plasma of these mice after seizures contained miRNAs, including let-7i-5p and miR-19b-3p. Taken together, these studies confirm that a portion of the circulating pool of miRNAs in experimental epilepsy originates from the brain, increasing support for miRNAs as mechanistic biomarkers of epilepsy.

neuroscience↗

bioRxiv2023

Molecular encoding of stimulus features in a single sensory neuron type enables neuronal and behavioral plasticity

Neurons modify their transcriptomes in response to an animals experience. How specific experiences are transduced to modulate gene expression and precisely tune neuronal functions are not fully defined. Here, we describe the molecular profile of a thermosensory neuron pair in C. elegans experiencing different temperature stimuli. We find that distinct salient features of the temperature stimulus including its duration, magnitude of change, and absolute value are encoded in the gene expression program in this single neuron, and identify a novel transmembrane protein and a transcription factor whose specific transcriptional dynamics are essential to drive neuronal, behavioral, and developmental plasticity. Expression changes are driven by broadly expressed activity-dependent transcription factors and corresponding cis-regulatory elements that nevertheless direct neuron- and stimulus-specific gene expression programs. Our results indicate that coupling of defined stimulus characteristics to the gene regulatory logic in individual specialized neuron types can customize neuronal properties to drive precise behavioral adaptation.

neuroscience↗

bioRxiv2021

Ecological correlates of gene family size: the draft genome of the redheaded pine sawfly Neodiprion lecontei

A central goal in evolutionary biology is to determine the predictability of adaptive genetic changes. Despite many documented cases of convergent evolution at individual loci, little is known about the repeatability of gene family expansions and contractions. To address this void, we examined gene family evolution in the redheaded pine sawfly Neodiprion lecontei, a non-eusocial hymenopteran and exemplar of a pine-specialized lineage evolved from angiosperm-feeding ancestors. After assembling and annotating a draft genome, we manually annotated multiple gene families with chemosensory, detoxification, or immunity functions and characterized their genomic distributions and evolutionary history. Our results suggest that expansions of bitter gustatory receptor (GR), clan 3 cytochrome P450 (CYP3), and antimicrobial peptide (AMP) subfamilies may have contributed to pine adaptation. By contrast, there was no evidence of recent gene family contraction via pseudogenization. Next, we compared the number of genes in these same families across insect taxa that vary in diet, dietary specialization, and social behavior. In Hymenoptera, herbivory was associated with small GR and olfactory receptor (OR) families, eusociality was associated with large OR and small AMP families, and--unlike investigations in more closely related taxa--ecological specialization was not related to gene family size. Overall, our results suggest that gene families that mediate ecological interactions may expand and contract predictably in response to particular selection pressures, however, the ecological drivers and temporal pace of gene gain and loss likely varies considerably across gene families.

evolutionary biology↗

bioRxiv2020

Rapid evolution and horizontal gene transfer in the genome of a male-killing Wolbachia

Wolbachia are widespread bacterial endosymbionts that infect a large proportion of insect species. While some strains of this bacteria do not cause observable host phenotypes, many strains of Wolbachia have some striking effects on their hosts. In some cases, these symbionts manipulate host reproduction to increase the fitness of infected, transmitting females. Here we examine the genome and population genomics of a male-killing Wolbachia strain, wInn, that infects Drosophila innubila mushroom-feeding flies. We compared wInn to other closely-related Wolbachia genomes to understand the evolutionary dynamics of specific genes. The wInn genome is similar in overall gene content to wMel, but also contains many unique genes and repetitive elements that indicate distinct gene transfers between wInn and non-Drosophila hosts. We also find that genes in the Wolbachia prophage and Octomom regions are particularly rapidly evolving, including those putatively or empirically confirmed to be involved in host pathogenicity. Of the genes that rapidly evolve, many also show evidence of recent horizontal transfer among Wolbachia symbiont genomes, suggesting frequent movement of rapidly evolving regions among individuals. These dynamics of rapid evolution and horizontal gene transfer across the genomes of several Wolbachia strains and divergent host species may be important underlying factors in Wolbachias global success as a symbiont.

genomics↗

bioRxiv2020

Rapid divergence of the copulation proteins in the Drosophila dunni group is associated with hybrid post-mating-prezygotic incompatibilities

Proteins involved in post-copulatory interactions between males and females are among the fastest evolving genes in many species and this has been attributed to reproductive conflict. Likely as a result, these proteins are frequently involved in cases of post-mating-prezygotic isolation between species. The Drosophila dunni subgroup consists of a dozen recently diverged species found across the Caribbean islands with varying levels of hybrid incompatibility. We sought to examine how post-mating-prezygotic factors are involved in isolation among members of this species group. We performed experimental crosses between species in the dunni group and find evidence of hybrid inviability. We also find an insemination reaction-like response preventing egg laying and leading to reduced female survival post-mating. To identify that genes may be involved in these incompatibilities, we sequenced and assembled the genomes of four species in the dunni subgroup and looked for signals of rapid evolution between species. Despite low levels of divergence, we found evidence of rapid evolution and divergence of some reproductive proteins, specifically the seminal fluid proteins. This suggests post-mating-prezygotic isolation as a barrier for gene flow between even the most closely related species in this group and seminal fluid proteins as a possible culprit.

evolutionary biology↗

bioRxiv2020

Selection and demography shape genomic variation in a Sky Island species

Over time, populations of species can expand, contract, fragment and become isolated, creating subpopulations that must adapt to local conditions. Understanding how species maintain variation after divergence as well as adapt to these changes in the face of gene flow, is of great interest, especially as the current climate crisis has caused range shifts and frequent migrations for many species. Here, we characterize how a mycophageous fly species, Drosophila innubila, came to inhabit and adapt to its current range which includes mountain forests in southwestern USA separated by large expanses of desert. Using population genomic data from more than 300 wild-caught individuals, we examine four populations to determine their population history in these mountain forests, looking for signatures of local adaptation. We find D. innubila spread northwards during the previous glaciation period (30-100 KYA), and has recently expanded even further (0.2-2 KYA). D. innubila shows little evidence of population structure, consistent with a recent establishment and genetic variation maintained since before geographic stratification. We also find some signatures of recent selective sweeps in chorion proteins and population differentiation in antifungal immune genes suggesting differences in the environments to which flies are adapting. However, we find little support for long-term recurrent selection in these genes. In contrast, we find evidence of long-term recurrent positive selection in immune pathways such as the Toll-signaling system and the Toll-regulated antimicrobial peptides.

evolutionary biology↗

bioRxiv2020

Recurrent evolution of two competing haplotypes in an insect DNA virus

Hosts and viruses are constantly evolving in response to each other: as hosts attempt to suppress the virus, the virus attempts to evade and suppress the hosts immune system. This arms race results in the evolution of novel pathways in both the host and virus to gain the upper hand. Here we describe the coevolution between Drosophila species and a common and virulent DNA virus. We identify two distinct viral types that differ 100-fold in viral titer in infected individuals, with similar effects across multiple species. Our analysis suggests that one of the viral types appears to have recurrently evolved at least 4 times in the past [~]30,000 years, including in another geographically distinct species, due to the high effective mutation rate which increases with titer. The higher titer viral type is associated with suppression of the host immune system and an increased transmission rate compared to the low viral titer type. Both types are maintained in all populations, likely due to an increased virulence in the high titer type creating a trade-off between effective transmission and virulence and resulting in nearly equal reproduction rates (R0) in both types. Together these results suggest that the reciprocal selective pressures caused by the co-evolution between host and virus has resulted in this recurrently evolving relationship.

evolutionary biology↗

bioRxiv2020

Multi-proxy evidence for the impact of the Storegga Slide Tsunami on the early Holocene landscapes of the southern North Sea

Doggerland was a land mass occupying an area currently covered by the North Sea until marine inundation took place during the mid-Holocene, ultimately separating the British land mass from the rest of Europe. The Storegga Slide, which triggered a tsunami reflected in sediment deposits in the Northern North Sea, North East coastlines of the British Isles and across the North Atlantic, was a major event during this transgressive phase. The spatial extent of the Storegga tsunami however remains unconfirmed because to date no direct evidence for the event has been recovered from the southern North Sea. We present evidence that Storegga associated deposits occur in the southern North Sea. Palaeo-river systems have been identified using seismic survey in the southwestern North Sea and sedimentary cores extracted to track the Mid Holocene inundation. At the head of one palaeo-river system near the Outer Dowsing Deep, the Southern River, we observed an abrupt and catastrophic inundation stratum. Based on lithostratigraphic, macro and microfossils and sedimentary ancient DNA (sedaDNA) evidence, supported by optical stimulation luminescence (OSL) and radiocarbon dating, we conclude these deposits were a result of the Storegga event. Seismic identification of this stratum to adjacent cores indicated diminished traces of the tsunami, largely removed by subsequent erosional processes. Our results demonstrate the catastrophic impact of Storegga within this area of the Southern North Sea, but indicate that these effects were temporary and likely localized and mitigated by the dense woodland and topography of the area. We conclude clear physical remnants of the wave are likely to be restricted to inland basins and incised river valley systems.

paleontology↗

bioRxiv2020

AVP-induced counter-regulatory glucagon is diminished in type 1 diabetes

Insulin-induced hypoglycemia is a major barrier to the treatment of type-1 diabetes (T1D). Accordingly, it is important that we understand the mechanisms regulating the circulating levels of glucagon - the bodys principal blood glucose-elevating hormone which is secreted from alpha-cells of the pancreatic islets. Varying glucose over the range of concentrations that occur physiologically between the fed and fuel-deprived states (from 8 to 4 mM) has no significant effect on glucagon secretion in isolated islets (in vitro) and yet associates with dramatic changes in plasma glucagon in vivo. The identity of the systemic factor(s) that stimulates glucagon secretion remains unknown. Here, we show that arginine-vasopressin (AVP), secreted from the posterior pituitary, stimulates glucagon secretion. Glucagon-secreting alpha-cells express high levels of the vasopressin 1b receptor gene (Avpr1b). Activation of AVP neurons in vivo increased circulating copeptin (the C-terminal segment of the AVP precursor peptide, a stable surrogate marker of AVP) and increased blood glucose; effects blocked by pharmacological antagonism of either the glucagon receptor or vasopressin 1b receptor. AVP also mediates the stimulatory effects of hypoglycemia produced by exogenous insulin and 2-deoxy-D-glucose on glucagon secretion. We show that the A1/C1 neurons of the medulla oblongata drive AVP neuron activation in response to insulin-induced hypoglycemia. Exogenous injection of AVP in vivo increased cytoplasmic Ca2+ in alpha-cells (implanted into the anterior chamber of the eye) and glucagon release. Hypoglycemia also increases circulating levels of AVP in humans and this hormone stimulates glucagon secretion from isolated human islets. In patients with T1D, hypoglycemia failed to increase both plasma copeptin and glucagon levels. These findings suggest that AVP is a physiological systemic regulator of glucagon secretion and that this mechanism becomes impaired in T1D.

cell biology↗

bioRxiv2019

A Simple Deep Learning Approach for Detecting Duplications and Deletions in Next-Generation Sequencing Data

Copy number variants (CNV) are associated with phenotypic variation in several species. However, properly detecting changes in copy numbers of sequences remains a difficult problem, especially in lower quality or lower coverage next-generation sequencing data. Here, inspired by recent applications of machine learning in genomics, we describe a method to detect duplications and deletions in short-read sequencing data. In low coverage data, machine learning appears to be more powerful in the detection of CNVs than the gold-standard methods or coverage estimation alone, and of equal power in high coverage data. We also demonstrate how replicating training sets allows a more precise detection of CNVs, even identifying novel CNVs in two genomes previously surveyed thoroughly for CNVs using long read data.\n\nAvailable at: https://github.com/tomh1lll/dudeml

bioinformatics↗

bioRxiv2019

Transposable element dynamics are consistent across the Drosophila phylogeny, despite drastically differing content

BackgroundThe evolutionary dynamics of transposable elements (TEs) vary across the tree of life and even between closely related species with similar ecologies. In Drosophila, most of the focus on TE dynamics has been completed in Drosophila melanogaster and the overall pattern indicates that TEs show an excess of low frequency insertions, consistent with their frequent turn over and high fitness cost in the genome. Outside of D. melanogaster, insertions in the species Drosophila algonquin, suggests that this situation may not be universal, even within Drosophila. Here we test whether the pattern observed in D. melanogaster is similar across five Drosophila species that share a common ancestor more than fifty million years ago.\n\nResultsFor the most part, TE family and order insertion frequency patterns are broadly conserved between species, supporting the idea that TEs have invaded species recently, are mostly costly and dynamics are conserved in orthologous regions of the host genome\n\nConclusionsMost TEs retain similar activities and fitness costs across the Drosophila phylogeny, suggesting little evidence of drift in the dynamics of TEs across the phylogeny, and that most TEs have invaded species recently.

genomics↗

bioRxiv2018

Antiviral genes are not rapidly evolving in Drosophila innubila

Viruses make up a considerable proportion of the pathogens infecting animals. They can spread rapidly between hosts, and sicken or even kill their hosts to promote their own proliferation. Due to this strong selective pressure, antiviral immune genes are some of the fastest evolving genes across metazoans, as highlighted in mammals and insects. While Drosophila melanogaster are frequently exposed to pathogenic RNA viruses, little is known about D. melanogasters ecology in terms of viral exposure, or if they are representative of other Drosophila species. Here, we sequence and assemble the genome of a highly diverged, mushroom-feeding Drosophila species, Drosophila innubila, a species frequently exposed to a highly pathogenic DNA virus. We investigate the evolution of the immune system and find little evidence for rapid evolution of the antiviral RNAi genes, though we do find rapid evolution of several other pathways, suggesting alternate means of viral resistance. This contrasts with D. melanogaster, and suggests that evolution of resistance to DNA viruses differs greatly from that of RNA viruses.

genomics↗

bioRxiv2018

Balancing selection drives maintenance of geneticvariation in Drosophila antimicrobial peptides

Genes involved in immune defense against pathogens provide some of the most well-known examples of both directional and balancing selection. Antimicrobial peptides (AMPs) are innate immune effector genes, playing a key role in pathogen clearance in many species, including Drosophila. Conflicting lines of evidence have suggested AMPs may be under directional, balancing or purifying selection. Here, we use a case-control gene approach to show that balancing selection is an important force shaping AMP diversity in two species of Drosophila. In D. melanogaster, this is most clearly observed in ancestral African populations. Furthermore, the signature of balancing selection is even clearer once background selection has been accounted for. Balancing selection also acts on AMPs in D. mauritiana, an isolated island endemic separated from D. melanogaster by about 4 million years of evolution. This suggests that balancing selection may be acting to maintain adaptive diversity in AMPs in insects as it does in other taxa.

evolutionary biology↗

bioRxiv2018

Extensive horizontal exchange of transposable elements in the Drosophila pseudoobscura group

While the horizontal transfer of a parasitic element can be a potentially catastrophic, it is increasingly recognized as a common occurrence. The horizontal exchange, or lack of exchange, of TE content between species results in different levels of divergence among a species group in the mobile component of their genomes. Here, we examine differences in the TE content of the Drosophila pseudoobscura species group. We identify several putative horizontal transfer events, and examine the role that horizontal transfer plays in the spread of TE families to new species and the homogenization of TE content in these species. Despite rampant exchange of TE families between species, we find that both TE content differs hugely across the group, likely due to differing activity of each TE family and differing suppression of TEs due to divergence in Y chromosome size, and its resulting effects of TE regulation. Overall, we show that TE content is highly dynamic in this species group, and that it plays a large role in shaping the differences seen between species.\n\nData availabilityAll data used in this study (summarized in table S1) is freely available online through the NCBI short read archive (NCBI SRA: ERR127385, SRR330416, SRR330418, SRR1925723, SRR330426, SRR330420, SRR330423, SRR617430-74). All genomes used are either available through Flybase.org or Popoolation.at.

genomics↗

bioRxiv2017

The dynamic evolution of Drosophila innubila Nudivirus

Viruses coevolve with their hosts to overcome host resistance and gain the upper hand in the evolutionary arms race. Drosophila innubila nudivirus (DiNV) is a double stranded DNA virus, closely related to Oryctes rhinoceros nudivirus (OrNV) and Kallithea virus. DiNV is the first DNA virus found to naturally infect Drosophila and therefore has the potential to be developed as a model for DNA virus immune defense and host/virus coevolution within its well-studied host system. Here we sequence and annotate the genome of DiNV and identify signatures of adaptation, revealing clues for genes involved in host-parasite coevolution. The genome is 155555bp long and contains 107 coding open reading frames (ORFs) and a wealth of AT-rich simple sequence repeats. While synteny is highly conserved between DiNV and Kallithea virus, it drops off rapidly as sequences become more divergent, consistent with rampant rearrangements across nudiviruses. Overall, we show that evolution of DiNV is likely due to adaptation of few genes coupled with high gene turnover.\n\nHighlightsO_LIWe sequence the genome of DiNV.\nC_LIO_LIFew genes are rapidly evolving between nudiviruses.\nC_LIO_LIWe find high gene turnover between DiNV and its closest relatives.\nC_LIO_LIHelicase and ODV-E56 show consistent signatures of adaptation.\nC_LI

genomics↗

bioRxiv2017

Persistent homology demarcates a leaf morphospace

Current morphometric methods that comprehensively measure shape cannot compare the disparate leaf shapes found in seed plants and are sensitive to processing artifacts. We explore the use of persistent homology, a topological method applied across the scales of a function, to overcome these limitations. The described method isolates subsets of shape features and measures the spatial relationship of neighboring pixel densities in a shape. We apply the method to the analysis of 182,707 leaves, both published and unpublished, representing 141 plant families collected from 75 sites throughout the world. By measuring leaves from throughout the seed plants using persistent homology, a defined morphospace comparing all leaves is demarcated. Clear differences in shape between major phylogenetic groups are detected and estimates of leaf shape diversity within plant families are made. This approach does not only predict plant family, but also the collection site, confirming phylogenetically invariant morphological features that characterize leaves from specific locations. The application of a persistent homology method to measure leaf shape allows for a unified morphometric framework to measure plant form, including shape and branching architectures.

plant biology↗