Biology subjects

Six, C.

Publications and source records attributed to Six, C..

3 recordsLinked to original sources

bioRxiv2025

The phosphate exporter XPR1 regulates a gasdermin D-independent mature IL-1β secretion pathway in LPS-stimulated human monocytic cells

The inflammatory cytokine interleukin (IL)-1{beta} is a leaderless protein that is not secreted via the classical endoplasmic reticulum-Golgi pathway but instead is secreted during pyroptosis, a form of caspase-dependent inflammatory cell death mediated by gasdermin D (GSDMD) cleavage and pore formation at the plasma membrane. However, human monocytes can secrete IL-1{beta} in the absence of cell death, and the contribution of GSDMD in this secretory pathway is not established. Here, we identify two mechanisms of mature IL-1{beta} secretion by living human monocytic cells: a rapid, GSDMD-dependent pathway and a slower, GSDMD-independent pathway. Using a CRISPR-Cas9 loss-of-function screen, we identified XPR1 (Xenotropic and Polytropic retrovirus Receptor 1) as a key regulator of the GSDMD-independent pathway. XPR1 is the only phosphate exporter identified in metazoans and has no previously described function in cytokine secretion. XPR1 invalidation in GSDMD-/- monocytic cells impaired IL-1{beta} secretion. We further show that this regulatory function requires cell-surface expression of XPR1 and is linked to its phosphate export activity. Our results reveal a previously undescribed mechanism of IL-1{beta} secretion by living human monocytic cells, independent of GSDMD and unexpectedly linked to phosphate homeostasis. Deciphering this pathway could lead to new therapeutic modalities for IL-1{beta}-driven inflammatory diseases.

immunology↗

bioRxiv2022

Global phylogeography of marine Synechococcus in coastal areas reveals strikingly different communities than in the open ocean

Marine Synechococcus comprise a numerically and ecologically prominent phytoplankton group, playing a major role in both carbon cycling and trophic networks in all oceanic regions except in the polar oceans. Despite their high abundance in coastal areas, our knowledge of Synechococcus communities in these environments is based on only a few local studies. Here, we use the global metagenome dataset of the Ocean Sampling Day (June 21st 2014) to get a snapshot of the taxonomic composition of coastal Synechococcus communities worldwide, by recruitment on a reference database of 141 picocyanobacterial genomes, representative of the whole Prochlorococcus, Synechococcus and Cyanobium diversity. This allowed us to unravel drastic community shifts over small to medium scale gradients of environmental factors, in particular along European coasts. The combined analysis of the phylogeography of natural populations and the thermophysiological characterization of eight strains, representative of the four major Synechococcus lineages (clades I to IV), also brought novel insights about the differential niche partitioning of clades I and IV, which most often co-dominate the Synechococcus community in cold and temperate coastal areas. Altogether, this study tackles the main differences between open-ocean and coastal communities worldwide.

microbiology↗

bioRxiv2018

Chloroplasts of symbiotic microalgae remain active during bleaching induced by thermal stress in Collodaria (Radiolaria)

Collodaria (Radiolaria) are important contributors to planktonic communities and biogeochemical processes (e.g. the biologic pump) in oligotrophic oceans. Similarly to corals, Collodaria live in symbiosis with dinoflagellate algae, a relationship that is thought to explain partly their ecological success. In the context of global change, the robustness of the symbiotic interaction and potential subsequent bleaching events are worth consideration. In the present study, we compared the ultrastructure morphology, symbiont density, photosynthetic capacities and respiration rates of colonial Collodaria exposed to a range of temperatures corresponding to natural conditions (21{degrees}C), moderate (25{degrees}C) and high (28{degrees}C) thermal stress. We showed that symbiont density immediately decreased when temperature rises to 25{degrees}C and the collodaria holobiont metabolic activity increased. When temperature reached 28{degrees}C, the collodarian host arrived at a tolerance threshold with a respiration nearly stopped and largely damaged morphological structures. Over the course of the experiment the photosynthetic capacities of remaining symbionts were stable, chloroplasts being the last degraded organelles from the microalgae. These results contribute to a better characterization and understanding of temperature-induced bleaching processes in planktonic photosymbiosis.

physiology↗