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Bisch, P. M.

Publications and source records attributed to Bisch, P. M..

2 recordsLinked to original sources
bioRxiv2025

Extracellular vesicles from saxitoxin-producing strains of the cyanobacterium Raphidiopsis raciborskii and investigation of their potential allelopathic effect

Raphidiopsis raciborskii is a filamentous cyanobacterium with global distribution in tropical and temperate climates. Toxic strains isolated in Latin America produce saxitoxins (STXs), which are neurotoxins that block voltage-gated ion channels in cells. This cyanobacterium can exert allelopathic effects on other phytoplankton species in response to resource competition through the secretion of substances that impair the target-cell physiology. Extracellular vesicles (EVs) constitute a secretion system that can transport biologically active molecules to distant targets in a protected, concentrated and targeted way. However, the role of EVs in cyanobacterial biology is poorly understood. We aimed to characterize R. raciborskii EVs and test whether this extracellular fraction or other exudate fractions contribute to its allelopathic effect. Exudates from two STX-producing R. raciborskii strains (T3 and CY-10) were subjected to filtration and divided into vesicular fractions (VF, >100 kDa, with EVs), which were concentrated by ultracentrifugation, and dissolved fractions (DF, <100 kDa, no EVs). Characterization of the VF through nanoparticle tracking analysis and transmission electron microscopy revealed spheric structures with diameters of 100-200 nm. Ratios of the number of EVs/cell were estimated as 21.54 {+/-} 1.33 for T3 and 8.79 {+/-} 0.38 for CY-10. The STX content of exudate fractions was determined by ELISA. Total extracellular STX concentrations (STX + neosaxitoxin (neoSTX)) were 170.64 ({+/-}15.43) pg.mL-1 for T3 and 913.84 ({+/-}226.87) pg.mL-1 for CY-10 and these values were similar to those of the DF (<100 kDa fraction). In the VF, STX concentrations were approximately 103-10 times lower. The estimation of toxin quotas (per biovolume) resulted in values 20-40 times lower in EVs (0.27{+/-}0,09 ng.mm-3 for T3 and 1.81{+/-}0.49 ng.mm-3 for CY-10) than in cells (13.05 {+/-}2.16 ng.mm-3 for T3 and 33.65 {+/-}7.31 ng.mm-3 for CY-10). A shift in the predominant analog between compartments was observed, with neoSTX prevailing in cells and STX in EVs. The CY-10 strain exhibited higher toxin concentrations than T3 in the VF, DF, total extracellular fraction and cellular fraction. The allelopathic effect of R. raciborskii exudate fractions was tested on the green algae Monoraphidium capricornutum. The total extracellular fraction and the DF equally inhibited M. capricornutum growth and photosynthesis, but the VF had no effect. Thus, the effect can be attributed to dissolved allelopathic compounds <100 kDa. These results open new opportunities to further investigate the role of EVs in the ecophysiology of R. raciborskii. HighlightsO_LIExtracellular vesicles (EVs) from two toxic strains of R. raciborskii were characterized; C_LIO_LISaxitoxins can be released within EVs; C_LIO_LIExtracellular saxitoxins content includes dissolved and vesicular fractions; C_LIO_LIWhile cyanobacterial EVs had no allelopathic effect the dissolved extracellular fraction (<100 kDa) of R. raciborskii did. C_LI

microbiology↗
bioRxiv2020

A Reaction-Diffusion Network model predicts a dual role of Cactus/IκB to regulate Dorsal/NFκB nuclear translocation in Drosophila

Dorsal-ventral patterning of the Drosophila embryo depends on the NF{kappa}B superfamily transcription factor Dorsal (Dl). Toll receptor activation signals for degradation of the I{kappa}B inhibitor Cactus (Cact), leading to a ventral-to-dorsal nuclear Dl gradient. Cact is critical for Dl nuclear import, as it binds to and prevents Dl from entering the nuclei. Quantitative analysis of cact mutants revealed an additional Cact function to promote Dl nuclear translocation in ventral regions of the embryo. To investigate this dual Cact role, we developed a predictive model based on a reaction-diffusion regulatory network. This network considers non-uniform Toll activation as well as Toll-dependent Dl nuclear import and Cact degradation. In addition, it incorporates translational control of Cact levels by Dl, a Toll-independent pathway for Cact regulation and reversible nuclear-cytoplasmic Dl flow. Our model successfully reproduces wild-type data and emulates the Dl nuclear gradient in mutant dl and cact allelic combinations. Our results indicate that the dual role of Cact depends on targeting distinct Dl complexes along the dorsal-ventral axis: In the absence of Toll activation, free Dl-Cact trimers inhibit direct Dl nuclear entry; upon ventral-lateral Toll activation, Dl-Cact trimers are recruited into predominant signaling complexes and promote active Dl nuclear translocation. Simulations suggest that Toll-independent regulatory mechanisms that target Cact are fundamental to reproduce the full assortment of Cact effects. Considering the high evolutionary conservation of these pathways, our analysis should contribute to understand NF{kappa}B/c-Rel activation in other contexts such as in the vertebrate immune system and disease.

developmental biology↗