Ivan, D. | bioRxiv Science

bioRxiv2021

Fission yeast polycystin Pkd2p promotes transition to cell growth during cytokinesis

Polycystins are conserved mechanosensitive channels whose mutations lead to the common human renal disorder ADPKD. Previously we discovered that the plasma membrane-localized fission yeast homologue Pkd2p is an essential protein required for cytokinesis, but the mechanism remains unclear. Here, we isolated a novel temperature-sensitive mutant pkd2-B42. Among its strong growth defects, the most unique was that many mutant cells often lost significant portion of their volume in just 5 minutes followed by a gradual recovery, a process that we termed Deflation. Unlike cell lysis, deflation did not result in the plasma membrane rupture and it occurred independently from the cell cycle progression. The tip extension of pkd2-B42 cells was 80% slower than the wild type and their turgor pressure was 50% lower. Both pkd2-B42 and the other mutant pkd2-81KD partially rescued the mutants of the yeast Hippo signaling pathway Septation Initiation Network, by preventing cell lysis, enhancing septum formation, and doubling the number of Sid2/Mob1 molecules at the spindle pole bodies. We conclude that Pkd2p promotes cell size expansion during interphase by regulating turgor pressure and antagonizes SIN during cytokinesis. Summary statementMutations of polycystins lead to human genetic disorder ADPKD. We discovered that the fission yeast homologue Pkd2p promotes the cell expansion during interphase growth and antagonizes the Hippo pathway SIN during cytokinesis.

cell biology↗

bioRxiv2020

Monocyte recruitment to the inflamed central nervous system: migration pathways and distinct functional polarization

The central nervous system (CNS) parenchyma is enclosed by anatomical interfaces including multilayered meninges, the blood-brain barrier (BBB), the choroid plexuses within ventricles and the glia limitans. These border areas hold distinct functional specializations which control the trafficking of monocyte-derived cells toward the CNS parenchyma, altogether maintaining CNS homeostasis. By crossing activated endothelial, epithelial and glial borders, circulating leukocytes gain however access to the CNS parenchyma in several inflammatory diseases including multiple sclerosis. Studies in animal models of neuroinflammation have helped describing the phenotypic specifications of these invading monocyte-derived cells, able to exert detrimental or beneficial functions depending on the local environment. In this context, in vivo visualization of iNOS+ pro-inflammatory and arginase-1+ anti-inflammatory macrophages has recently revealed that these distinct cell phenotypes are highly compartmentalized by CNS borders. While arginase-1+ macrophages densely populate the leptomeninges, iNOS+ macrophages rather accumulate in perivascular spaces and at the pia mater-CNS parenchymal interface. How and where these macrophages acquire their functional commitment, and whether differentially-activated monocyte-derived cells infiltrate the CNS through distinct gateways, remains however unclear. In this study, we have investigated the interaction of monocyte-derived macrophages with endothelial (BBB) and epithelial (choroid plexus) barriers of the CNS, both in vitro and in vivo. By using primary mouse brain microvascular endothelial cells as in vitro model of the BBB, we observed that, compared to unpolarized primary macrophages, adhesion of functionally-committed macrophages to endothelial cells was drastically reduced, literally abrogating their diapedesis across the BBB. Conversely, when interacting with an activated choroid plexus epithelium, both pro- and anti-inflammatory macrophages displayed substantial adhesive and migratory properties. Accordingly, in vivo analysis of choroid plexuses revealed increased macrophage trafficking and a scattered presence of polarized cells upon induction of anti-CNS inflammation. Altogether, we show that acquisition of distinct macrophage polarizations significantly alters the adhesive and migratory properties of these cells in a barrier-specific fashion. While monocytes trafficking at the level of the BBB seem to acquire their signature phenotype only following diapedesis, other anatomical interfaces can be the entry site for functionally activated monocyte-derived cells. Our study highlights the choroid plexus as a key access gateway for macrophages during neuroinflammation, and its stroma as a potential priming site for their functional polarization.

immunology↗