Biology subjects

Yuecel, R.

Publications and source records attributed to Yuecel, R..

6 recordsLinked to original sources

bioRxiv2025

Clec7a-mediated regulation of Killer-like Lectin Receptor expression controls T cell immunity

Clec7a is a C-type lectin receptor (CLR) originally defined for its non-redundant role in anti-fungal immunity. Subsequent work has broadened this view, implicating Clec7a in host defense against diverse pathogens and in the pathogenesis of cancer, autoimmunity, neuroinflammation, and developmental disorders. How a single innate receptor orchestrates such wide-ranging outcomes remains unresolved. We previously demonstrated that dendritic cell (DC)-expressed Clec7a is required for protective anti-fungal immunity in the gastrointestinal tract through regulation of fungus-specific CD4 T cell responses. Here, we show that Clec7a controls the expression of multiple C-type lectins in DCs, including a cluster of killer lectin-like receptors (KLRs). Notably, we reveal that these KLRs directly regulate DC function and control CD4 T cell responses. These findings define a novel Clec7a-KLR axis that integrates innate and adaptive immunity, highlighting a regulatory pathway with broad relevance for immune homeostasis, inflammation, and host defense.

immunology↗

bioRxiv2024

Heterogeneous efflux pump expression underpins phenotypic resistance to antimicrobial peptides

Antimicrobial resistance threatens the viability of modern medical interventions. There is a dire need of developing novel approaches to counter resistance mechanisms employed by starved or slow-growing pathogens that are refractory to conventional antimicrobial therapies. Antimicrobial peptides have been advocated as potential therapeutic solutions due to low levels of genetic resistance observed in bacteria against these compounds. However, here we show that subpopulations of stationary phase Escherichia coli and Pseudomonas aeruginosa survive tachyplesin treatment without genetic mutations. These phenotypic variants display enhanced efflux activity to limit intracellular peptide accumulation. Differential regulation of genes involved in outer membrane vesicle section, membrane modification, and protease activity were also found between phenotypically resistant and susceptible cells. We discovered that formation of these phenotypic variants could be prevented by administering tachyplesin in combination with sertraline, a clinically used antidepressant, suggesting a novel approach for combatting antimicrobial-refractory stationary phase bacteria.

microbiology↗

bioRxiv2023

Characterising phagocytes and measuring phagocytosis from live Galleria mellonella larvae

Over the last 20 years, the larva of the greater waxmoth, Galleria mellonella, has rapidly increased in popularity as an in vivo mammalian replacement model organism for the study of human pathogens. Despite this, experimental readouts of response to infection are generally limited to observing the melanisation cascade - where the organism turns black as part of the systemic immune response - and quantifying larval death over time. As an invertebrate, Galleria harbour an innate immune system comprised of both humoral components and a repertoire of innate immune cells - termed hemocytes. Though information on subtypes of hemocytes exist, there are conflicting reports on their exact number and function. Flow cytometry has previously been used to assay Galleria hemocytes, but protocols include both centrifugation and fixation - physical methods which have the potential to affect hemocyte morphology prior to analysis. Here, we present a method for live hemocyte analysis by flow cytometry, revealing that Galleria hemocytes constitute only a single resolvable population, based on relative size or internal complexity. Using fluorescent zymosan particles, we extend our method to show that up to 80% of the Galleria hemocyte population display phagocytic capability. Finally, we demonstrate that the developed assay reliably replicates in vitro data, showing that cell wall {beta}-1,3-glucan masking by Candida albicans subverts phagocytic responses. As such, our method provides a new tool with which to rapidly assess phagocytosis and understand live infection dynamics in Galleria.

cell biology↗

bioRxiv2023

Human Plasma-Like Medium (HPLM) induces Cryptococcus neoformans in vivo cell morphologies

The fungal pathogen Cryptococcus neoformans (C. neoformans) forms yeast cells of different sizes and morphological characteristics during infection. These features are usually not seen in standard laboratory in vitro conditions. Here, we describe in vivo cell morphologies when C. neoformans is grown in human plasma-like medium at 37{degrees}C-5% CO2. We observed mixed-size populations of cells less than 1 m up to 16.8 m cell diameter, increased capsule size, high chitin and DNA content in larger cells. Our findings show serum is not required for HPLM-induced C. neoformans cellular heterogeneity. Thus, this new method offers an opportunity to investigate factors of C. neoformans that mediate pathogenesis or host-pathogen interactions in a physiologically relevant setting. IMPORTANCEDescription of new in vitro culture condition using the human plasma-like medium that supports the formation of the full range of in vivo cell morphologies of C. neoformans.

microbiology↗

bioRxiv2018

Immediate visualization of recombination events and chromosome segregation defects in fission yeast meiosis

Schizosaccharomyces pombe, also known as fission yeast, is an established model for studying chromosome biological processes. Over the years research employing fission yeast has made important contributions to our knowledge about chromosome segregation during meiosis, as well as meiotic recombination and its regulation. Quantification of meiotic recombination frequency is not a straightforward undertaking, either requiring viable progeny for a genetic plating assay, or relying on laborious Southern blot analysis of recombination intermediates. Neither of these methods lends itself to high-throughput screens to identify novel meiotic factors. Here, we establish visual assays novel to Sz. pombe for characterizing chromosome segregation and meiotic recombination phenotypes. Genes expressing red, yellow, and/or cyan fluorophores from spore-autonomous promoters have been integrated into the fission yeast genomes, either close to the centromere of chromosome I to monitor chromosome segregation, or on the arm of chromosome III to form a genetic interval at which recombination frequency can be determined. The visual recombination assay allows straightforward and immediate assessment of the genetic outcome of a single meiosis by epi-fluorescence microscopy without requiring tetrad dissection. We also demonstrate that the recombination frequency analysis can be automatized by utilizing imaging flow cytometry to enable high-throughput screens. These assays have several advantages over traditional methods for analysing meiotic phenotypes.

genetics↗

bioRxiv2017

The Cryptococcus neoformans Titan cell is an inducible and regulated morphotype underlying pathogenesis

Fungi undergo changes in cell shape in response to environmental stimuli that drive pathogenesis and niche adaptation, such as the yeast-to-hyphal transition of dimorphic fungi in response to changing temperature. The basidiomycete Cryptococcus neoformans undergoes an unusual morphogenetic transition in the host lung from haploid yeast to large, highly polyploid cells termed Titan cells. Titan cells influence fungal interaction with host cells, including through increased drug resistance, altered cell size, and altered Pathogen Associated Molecular Pattern exposure. Despite the important role these cells play in pathogenesis, understanding the environmental stimuli that drive the morphological transition, and the molecular mechanisms underlying their unique biology, has been hampered by the lack of a reproducible in vitro induction system. Here we demonstrate reproducible in vitro Titan cell induction in response to environmental stimuli consistent with the host lung. In vitro Titan cells exhibit all the properties of in vivo generated Titan cells, the current gold standard, including altered capsule, cell wall, size, high mother cell ploidy, and aneuploid progeny. We identify bacterial peptidoglycan as a serum compound associated with shift in cell size and ploidy, and demonstrate the capacity of bronchial lavage fluid and E. coli co-culture to induce Titanisation. Additionally, we demonstrate the capacity of our assay to identify established and previously undescribed regulators of Titanisation in vitro and investigate the Titanisation capacity of clinical isolates and their impact on disease outcome. Together, these findings provide new insight into the environmental stimuli and molecular mechanisms underlying the yeast-to-titan transition and establish an essential in vitro model for the future characterization of this important morphotype.\n\nAuthor SummaryChanges in cell shape underlie fungal pathogenesis by allowing immune evasion and dissemination. Aspergillus and Candida albicans hyphae drive tissue penetration. Histoplasma capsulatum and C. albicans yeast growth allows evasion and dissemination. As major virulence determinates, morphogenic transitions are extensively studied in animal models and in vitro. The pathogenic fungus Cryptococcus neoformans is a budding yeast that, in the host lung, switches to an unusual morphotype termed the Titan cell. Titans are large, polyploid, have altered cell wall and capsule, and produce haploid daughters. Their size prevents engulfment by phagocytes, yet they are linked to dissemination and altered immune response. Despite their important influence on disease, replicating the yeast-to-Titan switch in vitro has proved challenging. Here we show that Titans are induced by host-relevant stimuli, including serum and bronchio-alveolar lavage fluid. We identify bacterial peptidoglycan as a relevant inducing compound and predict an in vivo Titan defect for a clinical isolate. Genes regulating in vivo Titanisation also influence in vitro formation. Titanisation is a conserved morphogenic switch across the C. neoformans species complex. Together, we show that Titan cells are a regulated morphotype analogous to the yeast-to-hyphal transition and establish new ways to study Titans outside the host lung.

microbiology↗