Biology subjects

MacMillan, H.

Publications and source records attributed to MacMillan, H..

6 recordsLinked to original sources

bioRxiv2025

Engineered spermidine-secreting Saccharomyces boulardii enhances olfactory memory in Drosophila melanogaster

The polyamines putrescine, spermidine and spermine are ubiquitous metabolites synthesized in all cells. The intracellular levels of polyamines, especially spermidine, decrease in aging. Oral spermidine supplementation has been reported to alleviate aspects of age-related disease in animal models, including decline in learning and memory. The diverse health benefits of spermidine supplementation, often at doses that do not significantly alter spermidine levels of target organs, suggests that exogenous spermidine may have a common site of action, the gastrointestinal (GI) tract. To directly deliver spermidine to the GI tract with minimum impact on the global spermidine levels, we engineered the probiotic yeast Sacchromyces boulardii (Sb) to overproduce and secrete spermidine. We tested the effects of a spermidine-producing yeast strain (Sb576) on age-associated learning and memory decline in an olfactory classical conditioning in Drosophila melanogaster. Feeding of newly emerged adult flies [w1118(isoCJ1)] for 30 days with food supplemented with live Sb576, but not live wild-type Sb (SbWT) or free spermidine, reduced age-associated short-term memory (STM) decline. Notably, Sb576 supplementation, but not SbWT or spermidine supplementation, of either young flies or old flies for only three days also enhanced STM without affecting locomotive ability. Transcriptome analysis of the gut revealed relatively few (30) differentially overexpressed genes in the Sb576 group compared to the SbWT group including the gene coding neuropeptide Dh31, which has been implicated in memory in the flies. These results demonstrate that in situ production of spermidine by a synthetic biotic yeast in the GI tract can enhance STM, and further suggest a mechanism involving the gut-brain axis.

synthetic biology↗

bioRxiv2025

The disadvantage of having a big mouth: the relationship between insect body size and microplastic ingestion

Plastic pollution is ubiquitous, and animals are exposed to diverse plastic shapes and sizes. When plastics enter natural environments, they break down into microplastics (MPs; <5 mm) and likely become more accessible to smaller animals. Insects play critical environmental and economic roles, ingest plastics in the wild, and can physically degrade ingested MPs into smaller and more harmful nanoplastics. While particle size and body size undoubtedly impact plastic ingestion, we have no predictive understanding of how these factors interact to influence which plastics are a threat to which animals. To uncover these potential interactions, we studied how a model cricket species (Gryllodes sigillatus) interacts with plastics of differing sizes throughout a twentyfold change in body size during growth and development. We fed crickets a range of MP sizes of 38 to 500 {micro}m with clearly defined particle size thresholds. We investigated whether crickets would avoid MPs when given a choice and found that they do not; instead they gradually began to consume more of the plastic diet over time. We then studied how MP ingestion is influenced by body size and mouth size, and the extent of breakdown that occurs once MPs are ingested. We found that crickets would only consume whole beads when their mouth size was larger than the MP. While small MPs were more likely to be excreted whole, larger MPs were more extensively broken down as crickets grew. We conclude that crickets do not exhibit avoidance behaviour towards plastic and ingest it once a particle can be consumed whole. These effects of insect behaviour and body size on the likelihood of plastic ingestion and the degree to which MPs are degraded have important implications for regulating the size classes of plastic particles entering natural environments and how plastics move through those environments once discarded.

physiology↗

bioRxiv2022

Persistent serum protein signatures define an inflammatory subset of long COVID

Long COVID or post-acute sequelae of SARS-CoV-2 (PASC) is a clinical syndrome featuring diverse symptoms that can persist for months after acute SARS-CoV-2 infection. The etiologies are unknown but may include persistent inflammation, unresolved tissue damage, or delayed clearance of viral protein or RNA. Attempts to classify subsets of PASC by symptoms alone have been unsuccessful. To molecularly define PASC, we evaluated the serum proteome in longitudinal samples from 55 PASC individuals with symptoms lasting [≥]60 days after onset of acute infection and compared this to symptomatically recovered SARS-CoV-2 infected and uninfected individuals. We identified subsets of PASC with distinct signatures of persistent inflammation. Type II interferon signaling and canonical NF-{kappa}B signaling (particularly associated with TNF), were the most differentially enriched pathways. These findings help to resolve the heterogeneity of PASC, identify patients with molecular evidence of persistent inflammation, and highlight dominant pathways that may have diagnostic or therapeutic relevance. One Sentence SummarySerum proteome profiling identifies subsets of long COVID patients with evidence of persistent inflammation including key immune signaling pathways that may be amenable to therapeutic intervention.

immunology↗

bioRxiv2021

Longitudinal immune dynamics of mild COVID-19 define signatures of recovery and persistence

SARS-CoV-2 has infected over 200 million and caused more than 4 million deaths to date. Most individuals (>80%) have mild symptoms and recover in the outpatient setting, but detailed studies of immune responses have focused primarily on moderate to severe COVID-19. We deeply profiled the longitudinal immune response in individuals with mild COVID-19 beginning with early time points post-infection (1-15 days) and proceeding through convalescence to >100 days after symptom onset. We correlated data from single cell analyses of peripheral blood cells, serum proteomics, virus-specific cellular and humoral immune responses, and clinical metadata. Acute infection was characterized by vigorous coordinated innate and adaptive immune activation that differed in character by age (young vs. old). We then characterized signals associated with recovery and convalescence to define and validate a new signature of inflammatory cytokines, gene expression, and chromatin accessibility that persists in individuals with post-acute sequelae of SARS-CoV-2 infection (PASC).

immunology↗

bioRxiv2021

Mechanotaxis directs Pseudomonas aeruginosa twitching motility.

The opportunistic pathogen Pseudomonas aeruginosa explores surfaces using twitching motility powered by retractile extracellular filaments called type IV pili. Single cells twitch by successive pili extension, attachment and retraction. However, whether and how single cells control twitching migration remains unclear. We discovered that P. aeruginosa actively directs twitching in the direction of mechanical input from type IV pili, in a process we call mechanotaxis. The Chp chemotaxis-like system controls the balance of forward and reverse twitching migration of single cells in response to the mechanical signal. On surfaces, Chp senses type IV pili attachment at one pole thereby sensing a spatially-resolved signal. As a result, the Chp response regulators PilG and PilH control the polarization of the extension motor PilB. PilG stimulates polarization favoring forward migration, while PilH inhibits polarization inducing reversal. Subcellular segregation of PilG and PilH efficiently orchestrates their antagonistic functions, ultimately enabling rapid reversals upon perturbations. This distinct localization of response regulators establishes a signaling landscape known as local-excitation, global-inhibition in higher order organisms, identifying a conserved strategy to transduce spatially-resolved signals. Our discovery finally resolves the function of the Chp system and expands our view of the signals regulating motility.

microbiology↗

bioRxiv2019

Chilling induces unidirectional solute leak through the locust gut epithelia

Chill-susceptible insects, like the migratory locust, often die when exposed to low temperatures from an accumulation of tissue damage that is unrelated to freezing (chilling injuries). Chilling injury is consistently associated with ion imbalance across the gut epithelia. It has recently been suggested that this imbalance is at least partly caused by a cold-induced disruption of epithelial barrier function. Here, we aim to test this hypothesis in the migratory locust (L. migratoria). First, chill tolerance was quantified by exposing locusts to -2{degrees}C for various durations and monitored for chill coma recovery time and survival 24h post-cold exposure. Longer exposure times significantly increased recovery time and caused injury and death. Ion-selective microelectrodes were also used to determine the presence of cold-induced ion imbalance. We found a significant increase and decrease of hemolymph K+ and Na+ concentrations over time, respectively. Next, barrier failure along the gut was tested by monitoring the movement of an epithelial barrier marker (FITC-dextran) across the gut epithelia during exposure to -2{degrees}C. We found minimal marker movement across the epithelia in the serosal to mucosal direction, suggesting that locust gut barrier function remains generally conserved during chilling. However, when tested in the mucosal to serosal direction, we saw significant increases of FITC-dextran with chilling. This instead suggests that while cold-induced barrier disruption is present, it is likely unidirectional. It is important to note that these data reveal only the phenomenon itself. The location of this leak as well as the underlying mechanisms remain unclear and require further investigation.\n\nSummary statementIn this study, we provide the first evidence for the presence of cold-induced paracellular leak along the gut of the migratory locust, and that this leak is strongest in the mucosal to serosal direction.

physiology↗