Diversification of human plasmacytoid predendritic cells in response to a single stimulus.

Innate immune cells adjust to microbial and inflammatory stimuli through a process termed environmental plasticity, which links a given individual stimulus to a unique activated state. Here, we report that activation of human plasmacytoid predendritic cells (pDCs) with a single microbial or cytokine stimulus triggers cell diversification into three stable subpopulations (P1-P3). P1-pDCs (PD-L1+CD80-) displayed a plasmacytoid morphology and specialization for type I interferon production. P3-pDCs (PD-L1-CD80+) adopted a dendritic morphology and adaptive immune functions. P2-pDCs (PD-L1+CD80+) displayed both innate and adaptive functions. Each subpopulation expressed a specific coding- and long-noncoding-RNA signature and was stable after secondary stimulation. P1-pDCs were detected in samples from patients with lupus or psoriasis. pDC diversification was independent of cell divisions or preexisting heterogeneity within steady-state pDCs but was controlled by a TNF autocrine and/or paracrine communication loop. Our findings reveal a novel mechanism for diversity and division of labor in innate immune cells.

Pinching the cortex of live cells reveals thickness instabilities caused by myosin II motors.

The cell cortex is a contractile actin meshwork, which determines cell shape and is essential for cell mechanics, migration, and division. Because its thickness is below optical resolution, there is a tendency to consider the cortex as a thin uniform two-dimensional layer. Using two mutually attracted magnetic beads, one inside the cell and the other in the extracellular medium, we pinch the cortex of dendritic cells and provide an accurate and time-resolved measure of its thickness. Our observations draw a new picture of the cell cortex as a highly dynamic layer, harboring large fluctuations in its third dimension because of actomyosin contractility. We propose that the cortex dynamics might be responsible for the fast shape-changing capacity of highly contractile cells that use amoeboid-like migration.

Interplay between Rab5 and PtdIns(4,5)P2 controls early endocytosis in the Drosophila germline.

Phosphoinositides have emerged as key regulators of membrane traffic through their control of the localization and activity of several effector proteins. Both Rab5 and phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P(2)] are involved in the early steps of the clathrin-dependent endocytic pathway, but little is known about how their functions are coordinated. We have studied the role of PtdIns(4,5)P(2) and Rab5 in the Drosophila germline during oogenesis. We found that Rab5 is required for the maturation of early endocytic vesicles. We show that PtdIns(4,5)P(2) is required for endocytic-vesicle formation, for Rab5 recruitment to endosomes and, consistently, for endocytosis. Furthermore, we reveal a previously undescribed role of Rab5 in releasing PtdIns(4,5)P(2), PtdIns(4,5)P(2)-binding budding factors and F-actin from early endocytic vesicles. Finally, we show that overexpressing the PtdIns(4,5)P(2)-synthesizing enzyme Skittles leads to an endocytic defect that is similar to that seen in rab5 loss-of-function mutants. Hence, our results argue strongly in favor of the hypothesis that the Rab5-dependant release of PtdIns(4,5)P(2) from endosomes that we discovered in this study is crucial for endocytosis to proceed.