Biology subjects

Harding, T.

Publications and source records attributed to Harding, T..

3 recordsLinked to original sources

bioRxiv2021

Comparative transcriptomics reveals the molecular toolkit used by an algivorous protist for cell wall perforation

Microbial eukaryotes display a stunning diversity of feeding strategies, ranging from generalist predators to highly specialised parasites. The unicellular "protoplast feeders" represent a fascinating mechanistic intermediate, as they penetrate other eukaryotic cells (algae, fungi) like some parasites, but then devour their cell contents by phagocytosis. Besides prey recognition and attachment, this complex behaviour involves the local, pre-phagocytotic dissolution of the prey cell wall, which results in well-defined perforations of species-specific size and structure. Yet, the molecular processes that enable protoplast feeders to overcome cell walls of diverse biochemical composition remain unknown. We used the flagellate Orciraptor agilis (Viridiraptoridae, Rhizaria) as a model protoplast feeder, and applied differential gene expression analysis to examine its penetration of green algal cell walls. Besides distinct expression changes that reflect major cellular processes (e.g. locomotion, cell division), we found lytic carbohydrate-active enzymes that are highly expressed and upregulated during the attack on the alga. A putative endocellulase (family GH5_5) with a secretion signal is most prominent, and a potential key factor for cell wall dissolution. Other candidate enzymes (e.g. lytic polysaccharide monooxygenases) belong to families that are largely uncharacterised, emphasising the potential of non-fungal micro-eukaryotes for enzyme exploration. Unexpectedly, we discovered various chitin-related factors that point to an unknown chitin metabolism in Orciraptor, potentially also involved in the feeding process. Our findings provide first molecular insights into an important microbial feeding behaviour, and new directions for cell biology research on non-model eukaryotes.

microbiology↗

bioRxiv2021

The effective family size of immigrant founders predicts their long-term demographic outcome: from Quebec settlers to their 20th-century descendants

Human evolution involves population splits, size fluctuations, founder effects, and admixture. Population history reconstruction based on genetic diversity data routinely relies on simple demographic models while projecting the past. No specific demographic assumptions are needed to understand the genetic structure of the founder population of Quebec. Because genealogy and genetics are intimately related, we used descending genealogies of this population to pursue the fate of its founder lineages. Maternal and paternal lines reflect the transmission of mtDNA and the Y-chromosome, respectively. We followed their transmission in real-time, from the 17th century down to its 20th-century population. We counted the number of married children of immigrants (i.e., their effective family size, EFS), estimated the proportion of successful immigrants in terms of their survival ratio, and assessed net growth rates and extinction. Likewise, we evaluated the same parameters for their Quebec-born descendants. The survival ratio of the first immigrants was the highest and declined over time in association with the decreasing immigrants EFS. Parents with high EFS left plentiful married progeny, putting EFS as the most important variable determining the parental demographic success throughout time for generations ahead. The 17th and 18th-century immigrants bear the most remarkable demographic and genetic impact on the 20th-century population of Quebec. Lessons learned from Quebec genealogies can teach us about the consequences of founder effects and migrations through real peoples history. The effective family size of immigrant founders predicts their long-term demographic outcome.

evolutionary biology↗

bioRxiv2020

GardeninA confers neuroprotection against environmental toxin in a Drosophila model of Parkinson's disease

Parkinson’s disease (PD) is an age-associated neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons from the midbrain. Epidemiological studies have implicated exposures to environmental toxins like the herbicide, paraquat (PQ) as major contributors to PD etiology in both mammalian and invertebrate models. We have employed a PQ-induced PD model in Drosophila as an inexpensive in vivo platform to screen therapeutics from natural products. We have identified the polymethoxyflavonoid, GardeninA, with neuroprotective potential against PQ-induced parkinsonian symptoms involving reduced survival, mobility defects, and loss of dopaminergic neurons. GardeninA-mediated neuroprotection is not solely dependent on its antioxidant activities but also involves modulation of the neuroinflammatory and cellular death responses. Furthermore, we have successfully detected GardeninA bioavailability in the fly heads after oral administration using ultra-performance liquid chromatography and mass spectrometry. Our findings reveal a molecular mechanistic insight into GardeninA-mediated neuroprotection against environmental toxin-induced PD pathogenesis for novel therapeutic intervention.Competing Interest StatementThe authors have declared no competing interest.View Full Text

pharmacology and toxicology↗