Biology subjects

Spealman, P.

Publications and source records attributed to Spealman, P..

11 recordsLinked to original sources

bioRxiv2026

TEscape: Defining the human transposable element transcriptome using multiplatform long-read sequencing

Transposable elements (TEs) not only account for half of the human genome sequence but also generate transcripts that contribute to transcriptomic diversity. Yet, their repetitive nature has hindered accurate quantification of the full TE-derived transcriptome, a challenge that long-read sequencing can overcome. Here, we combined multiplexed arrays isoform sequencing (MAS-ISO-seq) with a dedicated computational framework (TEscape) to perform an in-depth annotation of the human TE transcriptome. To capture the breadth of human transcriptome diversity, we profiled six representative cell types spanning three distinct biological contexts, including metabolism with, primary patient-derived adipogenic cells at two differentiation stages, and iPSC derived hepatic progenitor cells; the nervous system with iPSC-derived neurons, neural progenitor cells (NPCs), and pluripotency using induced pluripotent stem cells (iPSCs). Together, these datasets yielded over 235 million full-length long reads. First, to assess data coverage and transcriptome depth, we quantified protein-coding gene expression, detecting 14,312 genes (73.6% of all annotated protein-coding genes), which is a level consistent with deep and comprehensive transcriptome representation. Second, focusing on TE-derived transcripts, we identified >83,000 previously unannotated isoforms, the vast majority (84%) originating from a complex combination of multi-TEs. We also identified solo TEs, which are predominantly from LINE1 (14%). We confirmed that TE-transcripts are able to be exemplified by signatures detected in Liver Hepatocellular Carcinoma (LICH). Together, MAS-ISO-seq and TEscape establish the first long-read-based, high-resolution atlas of transcribed human TEs, providing a foundational resource for integrative transcriptome analyses and for investigating TE expression and regulation in health and disease. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/737305v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@18158aeorg.highwire.dtl.DTLVardef@e51fdforg.highwire.dtl.DTLVardef@8f9504org.highwire.dtl.DTLVardef@804113_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG

bioinformatics↗

bioRxiv2026

Finding the Goldilocks zone: Modulating glycoprotein cleavage and fusogenicity optimizes the efficacy of a candidate Crimean-Congo hemorrhagic fever virus vaccine

Crimean-Congo hemorrhagic fever virus (CCHFV) is the etiologic agent of a lethal hemorrhagic disease spread by ticks throughout Europe, the Middle East, Africa and Asia. The lack of approved medical countermeasures and fundamental understanding of molecular mechanisms of viral assembly and egress have thus far curtailed disease prevention. Here, we identify and characterize key residues within the viral glycoprotein through forward and reverse genetics for vesicular stomatitis virus (VSV)-based vaccine candidates that are highly protective in animal models. These residues are broadly applicable across divergent CCHFV strains and lead to greater protection in vivo against heterologous challenge. We further characterize the essential role of proteolytic processing in the maintenance of a stable fusogenic state required for effective VSV-based CCHFV vaccines. This study establishes a toolkit for better understanding orthonairovirus glycoprotein processing and vaccine development.

microbiology↗

bioRxiv2025

Tight translation regulation of the canonical C9ORF72 through a multi-component system

C9ORF72 is involved in multiple neuronal functions and a major factor in Amyotrophic Lateral Sclerosis, a fatal neurodegenerative disease. Pathogenicity is implemented through an intronic repeat expansion in the genes mRNA leader that produces long, repetitive RNA and dipeptides when translated through a non-canonical mechanism. In contrast, despite the presence of ribosome-occupied, regulatory elements in the mRNA leader, nothing is known about C9ORF72 translation regulation under normal conditions. Surprisingly, when analyzing a series of mutants of the C9ORF72 mRNA leader, we found that translation of C9ORF72 is tightly regulated through a multi-layer system. First, non-canonical, multi-initiation upstream open reading frames (nc-uORFs) in all three frames, a start-stop element in frame 2, and a canonical uORF in frame 1work together to keep baseline C9ORF72 translation very low. Second, a strong secondary structure enhances these repressive elements, mainly the two nc-uORFs in frames 0 and 2. Finally, as initiation at the nc-uORFs reduces initiation at the downstream start-stop, the nc-uORFs effectively dampen the start-stops repressive function, forming a feedforward loop. We hypothesize that this buffered repressor system has likely evolved to ensure reliable, noise-insensitive expression of this critical regulator of neuronal function.

molecular biology↗

bioRxiv2025

Investigating the distribution of antibiotic resistance genes in relation to bacterial, fungal, and functional diversity in a hay field.

The spread of antibiotic resistance in pathogenic bacteria is one of the most pressing public health threats of the 21st century, with at least 5 million deaths currently associated with it. While recent work has shown the importance of environmental reservoirs in the emergence of antibiotic resistance genes (ARGs), it is unclear which features of microbial diversity relate to ARGs of clinical relevance. Here, we investigate the role of bacterial, fungal, and functional diversity on the distribution of clinical and environmental ARGs along a single transect located in an aging hay field on an otherwise active farm. This transect spans a length of several hundred meters, increasing in distance from an agricultural access road and stream. We use 16S rRNA and ITS amplicon sequencing to measure bacterial and fungal diversity respectively, in combination with whole-genome sequencing (WGS) to characterize functional and ARG diversity. We find increasing bacterial and functional diversity along the transect, as well as distinct community structures for both bacteria and fungi. While we find that the diversity of environmental ARGs is significantly correlated with both bacterial and fungal diversity, clinical ARG diversity only significantly decreased as fungal diversity increased. Our results suggest that while microbial diversity increases with distance from the road and stream; and this diversity tends to determine the diversity of the majority of ARGs; this trend is not observed for ARGs of clinical relevance, which appear to be largely driven by the variety of fungal groups in the environment.

ecology↗

bioRxiv2025

Segmental copy number amplifications are stable in the absence of selection

Copy number variants (CNVs) are DNA duplications and deletions that cause genetic variation, underlying rapid adaptive evolution. CNVs often confer selective advantages, but can also incur fitness costs. Evolution of Saccharomyces cerevisiae in nutrient-limited chemostats recurrently selects for amplifications of nutrient transporter genes. However, their fate upon return to a non-selective environment remains unknown. To investigate CNV fitness and stability upon removing the original selection pressure, we studied 15 CNV lineages (11 segmental, 4 whole-chromosomal amplifications) selected in nitrogen-limited chemostats. CNV stability was monitored using fluorescent reporters during propagation in nutrient-rich batch cultures for 110-220 generations. All aneuploid lineages showed rapid CNV loss and reversion to a single-copy genotype, whereas segmental amplifications were remarkably stable- one of 11 strains reverted. Pairwise fitness competitions in rich media revealed strong fitness defects associated solely with CNVs that reverted; reversion led to increased fitness. Using simulation-based inference to estimate reversion rates and fitness effects, we determined negative selection as the primary driver of CNV loss. Whole-genome sequencing revealed that reversion of aneuploids and a segmental amplification left no evidence of prior CNV existence, rendering revertant genomes indistinguishable from the single-copy ancestor. Detailed characterization of a partial revertant identified chromosomal translocation, suggesting that extant CNVs can undergo structural diversification. Our findings provide novel evidence that most segmental CNVs adapted to nitrogen limitation are stable upon removal of selection, but costly gene amplifications are readily reversible. Together, these highlight the importance of CNVs in both long-term genome evolution and rapid, reversible adaptation to transient selection.

evolutionary biology↗

bioRxiv2023

Post-transcriptional mechanisms modulate the consequences of adaptive copy number variation

Copy-number variants (CNVs) are an important class of recurrent variants that mediate adaptive evolution. While CNVs can increase the relative fitness of the organism, they can also incur a cost. We previously evolved populations of Saccharomyces cerevisiae over hundreds of generations in glutamine-limited (Gln-) chemostats and observed the recurrent evolution of CNVs at the GAP1 locus. To understand the role that expression plays in adaptation, both in relation to the adaptation of the organism to the selective condition, and as a consequence of the CNV, we measured the transcriptome, translatome, and proteome of 4 strains of evolved yeast, each with a unique CNV, and their ancestor in Gln-conditions. We find CNV-amplified genes correlate with higher RNA abundance; however, this effect is reduced at the level of the proteome, consistent with post-transcriptional dosage compensation. By normalizing each level of expression by the abundance of the preceding step we were able to identify widespread divergence in the efficiency of each step in the gene in the efficiency of each step in gene expression. Genes with significantly different translational efficiency were enriched for potential regulatory mechanisms including either upstream open reading frames, RNA binding sites for SSD1, or both. Genes with lower protein expression efficiency were enriched for genes encoding proteins in protein complexes. Taken together, our study reveals widespread changes in gene expression at multiple regulatory levels in lineages containing adaptive CNVs highlighting the diverse ways in which adaptive evolution shapes gene expression.

genomics↗

bioRxiv2023

Bacterial and molecular contamination of a small freshwater effluent used for drinking water

Sewage contamination of freshwater occurs in the form of raw waste or as effluent (at varying levels of treatment) from wastewater treatment plants. Global management of this contamination has focused on detection of live sewage-indicating bacteria in freshwater, drinking water, and irrigation systems. While raw waste (animal and human) and underfunctioning WWTPs can introduce live enteric bacteria to freshwater systems, most WWTPs, even when operating correctly, do not remove bacterial genetic material from treated waste, resulting in the addition of concentrated enteric bacterial DNA (molecular contamination), including antibiotic resistance genes, into water columns and sediment of freshwater systems. In freshwater systems with both raw and treated waste inputs, then, there will be increased interaction between live sewage-associated bacteria (untreated sewage) and molecular contamination (from both untreated and treated wastewater effluent), with the potential of increasing antibiotic resistance in the live bacterial populations. To evaluate this understudied interaction between molecular and bacterial contamination in the freshwater environment, we conducted a three-month field-based study of sewage-associated bacteria and genetic material in water and sediment in a freshwater tributary of the Hudson River (NY, USA) that supplies drinking water and receives treated and untreated wastewater discharges from several municipalities. Using both molecular and culture-based bacterial analyses, we demonstrate both treated and untreated sewage influences on water and sediment bacterial communities in this tributary, and water-sediment exchanges of enteric bacteria and associated genetic material with rain events. Furthermore, treated sewage effluent on this waterway serves as a concentrated source of int1 (antibiotic resistance) genes, which appear to collect in the sediments below the outfall along with fecal indicating bacteria, serving as a possible genetic exchange substrate and a source for future molecular and bacterial water contamination. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=144 SRC="FIGDIR/small/530486v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@1abdb61org.highwire.dtl.DTLVardef@1cfc550org.highwire.dtl.DTLVardef@1a33647org.highwire.dtl.DTLVardef@40829e_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIIn a model freshwater system used both as drinking water and wastewater disposal, C_LIO_LIBacterial and genetic material differ between water and sediment compartments C_LIO_LILive bacteria C_LI

microbiology↗

bioRxiv2022

Copy number variants alter local and global mutational tolerance

Copy number variants (CNVs), duplications and deletions of genomic content, contribute to evolutionary adaptation, but can also confer deleterious effects, and cause disease. Whereas the effects of amplifying individual genes or whole chromosomes (i.e., aneuploidy) have been studied extensively, much less is known about the genetic and functional effects of CNVs of differing sizes and structures. Here, we investigated Saccharomyces cerevisiae (yeast) strains that have CNVs of variable structures but with multiple copies of the gene GAP1. Although beneficial in glutamine-limited chemostats, CNVs result in decreased fitness compared with the euploid ancestor in rich media. We used transposon mutagenesis to investigate mutational tolerance and genetic interactions with CNVs. We find that CNVs confer novel mutational tolerance in amplified essential genes and novel genetic interactions. We validated a novel genetic interaction with BMH1. CNV strains have increased mutational tolerance in genes related to translation, and reduced mutational tolerance in genes related to mitochondrial function. We performed RNAseq and found that transcriptional dosage compensation does not affect the majority of genes amplified by CNVs. Furthermore, we do not find that CNV strains exhibit previously described transcriptional signatures of aneuploidy. Instead, CNV strains exhibit downregulation of genes involved in cellular respiration, nucleoside biosynthetic processes, and small molecule metabolism, and upregulation of genes involved in transposition, nucleic acid metabolic processes, and siderophore transport. Our study reveals the extent to which local and global mutational tolerance is modified by CNVs with implications for genome evolution and CNV associated diseases, such as cancer.

genetics↗

bioRxiv2019

Nanopore sequencing undergoes catastrophic sequence failure at inverted duplicated DNA sequences

Inverted duplicated sequences are a common feature of structural variants (SVs) and copy number variants (CNVs). Analysis of CNVs containing inverted duplicated sequences using nanopore sequencing identified recurrent aberrant behavior characterized by incorrect and low confidence base calls that result from a systematic elevation in the current recorded by the sequencing pore. The coincidence of inverted duplicated sequences with catastrophic sequence failure suggests that secondary DNA structures may impair transit through the nanopore.

genomics↗

bioRxiv2019

Microbial community structure and ecology in sediments of a pristine mangrove forest

Mangrove forests are coastal intertidal ecosystems, characterized by mangrove trees growing in slow moving saline waters, that constitute a large portion of the coastline in the tropical and subtropical regions. The dynamic water regime created by the tides results in different microhabitats in which microbial communities play an essential role in the functioning and maintenance of the mangrove ecosystem. However, little is known about the diversity of taxa within these micro-habitats and their functional roles, as only a small fraction of these organisms can be cultured in the laboratory. In this study, we characterized the microbial community present in three distinct regions of mangrove sediments from the Serinhaem estuary, part of the Atlantic Forest biome within the Environmental Protection Area of Pratigi. We sampled sediments from regions below the tidal waterline (submerged), intertidal regions (intertidal), and regions above the tidal waterline (seco). More than 85% of all the sequences in the samples belonged to 6 of 42 identified phyla: Proteobacteria (30.6%), Firmicutes (30%), Chloroflexi (8.7%), Planctomycetes (5.7%), Crenarchaeota (5.4%) and Actinobacteria (5.3%). Diversity indices show that the submerged regions of the mangrove forest exhibit the greatest diversity and richness relative to the other regions. Notably, the intertidal region has the least diversity, suggesting that the dynamics of environmental variables in this region has an important influence on microbial diversity. Furthermore, distance metrics indicate that submerged sediments are more homogeneous while the seco region exhibits greater variability between locations. Finally, we found that the most abundant microbial families in the sediments are associated with nutrient cycling consistent with the essential role of the microbiome in maintaining the health of the mangrove ecology.

microbiology↗

bioRxiv2018

Single-cell copy number variant detection reveals the dynamics and diversity of adaptation

Copy number variants (CNVs) are a pervasive, but understudied source of genetic variation and evolutionary potential. Long-term evolution experiments in chemostats provide an ideal system for studying the molecular processes underlying CNV formation and the temporal dynamics of de novo CNVs. Here, we developed a fluorescent reporter to monitor gene amplifications and deletions at a specific locus with single-cell resolution. Using a CNV reporter in nitrogen-limited chemostats, we find that GAP1 CNVs are repeatedly generated and selected during the early stages of adaptive evolution resulting in predictable dynamics of CNV selection. However, subsequent diversification of populations defines a second phase of evolutionary dynamics that cannot be predicted. Using whole genome sequencing, we identified a variety of GAP1 CNVs that vary in size and copy number. Despite GAP1s proximity to tandem repeats that facilitate intrachromosomal recombination, we find that non-allelic homologous recombination (NAHR) between flanking tandem repeats occurs infrequently. Rather, breakpoint characterization revealed that for at least 50% of GAP1 CNVs, origin-dependent inverted-repeat amplification (ODIRA), a DNA replication mediated process, is the likely mechanism. We also find evidence that ODIRA generates DUR3 CNVs, indicating that it may be a common mechanism of gene amplification. We combined the CNV reporter with barcode lineage tracking and found that 103-104 independent CNV-containing lineages initially compete within populations, which results in extreme clonal interference. Our study introduces a novel means of studying CNVs in heterogeneous cell populations and provides insight into the underlying dynamics of CNVs in evolution.

evolutionary biology↗