Biology subjects

Polak, M.

Publications and source records attributed to Polak, M..

7 recordsLinked to original sources

bioRxiv2025

Dehydrating microhabitats increase mite activity and intensify ectoparasitism of Drosophila

Parasites interact with their host in variable environments that are often subject to water scarcity and dehydration. Drosophila fruit flies and associated ectoparasitic mites interact across a range of microhabitats, typically in decaying organic matter, such as fallen fruit and cactus tissue, that dries out and deteriorates over periods ranging from days to months. Here, we report that mite parasitism of Drosophila increases with exposure to increasingly dry conditions for two fly-mite systems (D. nigrospiracula-Macrocheles and D. melanogaster-Gamasodes). In D. melanogaster, artificial selection for behavioral resistance did not eliminate this effect, as previously selected lines remained relatively more resistant than non-selected controls even under dry conditions. Water balance assays confirmed that mites became dehydrated when held under dry conditions, which was also associated with increased mite activity. Exposure of D. melanogaster to mites dehydrated by exposure to low relative humidity increased parasitism, further supporting that mite infestation intensifies under dry conditions. The results indicate that ectoparasitism in this system is affected by the water content of the mites. The increased motivation of mites to parasitise flies under dry conditions may serve to replenish mite water stores and facilitate dispersal to more favorable microhabitats.

physiology↗

bioRxiv2025

Single-Cell Atlas of CD4+ T-Helper 2 Cells Reveals Distinct Cytokine Functions Across Diseases

Despite the prevalence of autoimmune diseases, treatment options for specific conditions remain limited. These diseases are driven by three types of inflammatory pathways, each orchestrated by different T-helper cell subsets; however, a comprehensive atlas capturing their diverse functions across conditions and tissues is lacking. One of these subsets, CD4+ T-helper type 2 (Th2) cells, is a relatively infrequent immune cell population that plays a central role in orchestrating type 2 inflammation. In this study, we developed the first comprehensive CD4+Th2 single-cell atlas by analyzing the BioTuring database, which has data from over 300 million cells. This atlas integrates data from 52 studies, comprising a total of 39,243 cells derived from 9 major tissues, representing over 30 distinct diseases. Leveraging this atlas, we confirmed a rarely recognized CD4+Th2 cell population co-expressing IL22 and IL13 observed exclusively in atopic dermatitis and not in other allergic conditions. By integrating single-cell data with other "omics" technologies, our analysis suggests distinct downstream effects of IL22 and IL13, highlighting the potential for combination therapy to enhance treatment outcomes for AD patients. Additionally, by utilizing data derived from the wide range of diseases, tissues, and time points included in this atlas, we re-confirmed the unique connection between IL9 expression and conditions related to allergen exposure. Pseudotime analysis detailed CD4+Th2 cytokine dynamics upon allergen stimulation, showing a shift from early IL2 and IL4 expression to later IL9 and IL5, with IL13 consistently expressed, and further revealed that IL9 production was transient. Collectively, these findings reveal distinct, context-dependent CD4+Th2 cytokine functions, opening the potential for identifying novel therapeutic strategies for allergic and inflammatory diseases.

immunology↗

bioRxiv2025

Antagonistic insulin mimetics lock the insulin receptor in an alternative apo-state

Despite significant advancements in high-resolution structural analysis of activated human insulin receptor (IR), the molecular mechanisms underlying its conformational plasticity that govern the transition from the apo state to the activated state are still not well understood. This leaves critical aspects of IR regulation unclear. Here, we reveal the mechanism by which the insulin mimetics Ada, Trim, and S661 fully inhibit the insulin receptor. The receptor is stabilized in a yet structurally un-described {cap}-shaped conformation which is induced by antagonist binding between the L1 and FnIII-1 domains. In contrast to insulin-bound IR structures, the -CT helix is not observable in the {cap} conformation, and the membrane-proximal regions of the FnIII-3 domains are >10 nm apart, which prohibits transmembrane signal transduction and kinase domain activation. Analysis of apo-IR electron cryo-microscopy data indicates that the {cap}-shaped state is one of several metastable apo-IR conformations. These findings underscore the intrinsic conformational dynamics of apo-IR and its role in integrating insulin binding and receptor activation.

molecular biology↗

bioRxiv2024

Post-proline cleaving enzymes also show specificity to reduced cysteine.

In proteomics, post-proline cleaving enzymes (PPCEs) like Aspergillus niger prolyl endopeptidase and neprosin complement proteolytic tools because proline is a stop site for many proteases. However, our systematic analysis of cleavage preferences showed that both PPCEs also display specificity to reduced cysteine. Post-cysteine cleavage was blocked by Cys alkylation, explaining why this activity has remained undetected. Our findings redefine their applicability and how we study and interpret their cleavage mechanism.

biochemistry↗

bioRxiv2023

Shifted levels of sleep and activity under darkness as mechanisms underlying ectoparasite resistance

Parasites harm host fitness and are pervasive agents of natural selection capable of driving the evolution of host resistance traits. Indeed, host resistance in natural populations typically shows ample genetic variation, which may be maintained when parasite resistance imposes fitness costs on the host in the absence of parasites. Previously we demonstrated significant evolutionary responses to artificial selection for increasing behavioral immunity to Gamasodes queenslandicus mites in replicate lines of Drosophila melanogaster. Here, we report transcriptional shifts in metabolic processes between selected and control fly lines based on RNA-seq analyses. We also show decreased starvation resistance and increased use of nutrient reserves in flies from mite-resistant lines. Additionally, resistant lines exhibited increased behavioral activity, reduced sleep, and elevated oxygen consumption under conditions of darkness. Using an independent panel of D. melanogaster genetic lines exhibiting variable sleep durations, we found a positive correlation between mite resistance and reduced sleep, providing additional support for a link between resistance and sleep. Experimentally restraining the activity of artificially selected mite-resistant flies during exposure to parasites under dark conditions reduced their resistance advantage relative to control flies. The results suggest that ectoparasite resistance in this system involves increased dark-condition activity and metabolic gene expression at the expense of nutrient reserves and starvation resistance. Significance statementParasites are potent agents of selection, yet resistance may often be constrained evolutionarily because of trade-offs involving other fitness-related traits. Using artificial selection, we show that resistance to ectoparasites directly increases metabolism and decreases starvation resistance, predominantly through altered sleep and activity patterns at night. These studies highlight that active-resting patterns of the host are a significant driving force in ectoparasite resistance, but may have a negative impact on fitness during periods of low food availability. Our strongly integrative work suggests that parasite pressure may influence the evolution of host sleep and activity patterns.

evolutionary biology↗

bioRxiv2022

Heritability and pre-adult survivorship costs of ectoparasite resistance in the naturally occurring Drosophila-Gamasodes mite system

Our understanding of the evolutionary significance of ectoparasites in natural communities is limited by a paucity of information concerning the mechanisms and heritability of resistance to this ubiquitous and diverse assemblage of organisms. Here, we report the results of artificial selection for increasing ectoparasite resistance in replicate lines of Drosophila melanogaster derived from a field-fresh population. Resistance, as ability to avoid infestation by naturally occurring Gamasodes queenslandicus mites, increased significantly in response to selection, and realized heritability (s.e.) was estimated to be 0.11 (0.0090). Ability to deploy energetically expensive bursts of flight from the substrate was a main mechanism of resistance that responded to selection, aligning with previously documented metabolic costs of fly behavioral defenses. Host body size, which affects parasitism rate in some fly-mite systems, was not shifted by selection. In contrast, resistant lines expressed significant reductions in larva-to-adult survivorship with increasing toxic (ammonia) stress, identifying an environmentally modulated pre-adult cost of resistance. Flies resistant to G. queenslandicus were also more resistant to a different mite, Macrocheles subbadius, suggesting that we documented genetic variation and a pleiotropic cost of broad-spectrum behavioral immunity against ectoparasites. This study demonstrates significant evolutionary potential of an ecologically important trait.

evolutionary biology↗

bioRxiv2021

Refutation of traumatic insemination in the Drosophila bipectinata species complex: Hypothesis fails critical tests

Traumatic insemination (TI) is a rare reproductive behaviour characterized by the transfer of sperm to the female via puncture wounds inflicted across her body wall. Here, we challenge the claim made by Kamimura (2007) that males of species of the Drosophila bipectinata complex utilize a pair of claw-like processes ("claws") to traumatically inseminate females: the claws are purported to puncture the female body wall and genital tract, and to inject sperm through the wounds into the genital tract, bypassing the vaginal opening, the route of sperm transfer occurring in other Drosophila. This supposed case of TI is widely cited and featured in prominent subject reviews. We examined high-resolution scanning electron micrographs of the claws and failed to discover any obvious "groove" for sperm transport. We demonstrated that sperm occurred in the female reproductive tract as a single integrated unit when mating flies were experimentally separated, inconsistent with the claim that sperm are injected via paired processes. The aedeagus in the bipectinata complex was imaged, and shown to deliver sperm through the vaginal opening. Laser ablation of the sharp terminal ends of the claws failed to inhibit insemination. The results refute the claim of TI in the Drosophila bipectinata species complex.

evolutionary biology↗