Neural stem cells are multipotent cells with the ability to differentiate into neurons, astrocytes, and oligodendrocytes. Lineage specification is strongly sensitive to the mechanical properties of the cellular environment. However, molecular pathways transducing matrix mechanical cues to intracellular signaling pathways linked to lineage specification remain unclear. We found that the mechanically gated ion channel Piezo1 is expressed by brainderived human neural stem/progenitor cells and is responsible for a mechanically induced ionic current. Piezo1 activity triggered by traction forces elicited influx of Ca 2+ , a known modulator of differentiation, in a substrate-stiffness-dependent manner. Inhibition of channel activity by the pharmacological inhibitor GsMTx-4 or by siRNA-mediated Piezo1 knockdown suppressed neurogenesis and enhanced astrogenesis. Piezo1 knockdown also reduced the nuclear localization of the mechanoreactive transcriptional coactivator Yes-associated protein. We propose that the mechanically gated ion channel Piezo1 is an important determinant of mechanosensitive lineage choice in neural stem cells and may play similar roles in other multipotent stem cells. (5) and that the mechanical properties of the culturing environment before transplantation can influence the outcome of in vivo stem cell transplants (6). Hence, a molecular and mechanistic understanding of how stem cells process mechanical cues and how this processing results in downstream signaling events and ultimately in fate decisions is needed for greater control over the fate of transplanted cells.Studies in mesenchymal and neural stem cells have revealed the involvement of focal adhesion zones and cytoskeletal proteins, such as integrins, nonmuscle myosin II (7), Rho GTPases (8-10), and vinculin (11), that participate in the generation of cellular traction forces. Recent work also has identified the nucleoskeletal protein lamin-A (12) and the transcriptional coactivators Yap (Yesassociated protein) and Taz (transcriptional coactivator with PDZbinding motif) (13) in mechanotransduction in mesenchymal stem cells. However, the mechanisms by which mechanical cues detected by cellular traction forces are transduced to downstream intracellular pathways of differentiation remain unclear.Ion channels are involved, directly or indirectly, in the transduction of all forms of physical stimuli-including sound, light, temperature, mechanical force, and even gravity-into intracellular signaling pathways. Hence, we wondered whether ion channels could be involved in transducing matrix mechanical cues to intracellular signaling pathways linked to lineage specification. In particular, we focused here on cationic stretch-activated channels (SACs) because they are known to detect mechanical forces with high sensitivity and broad dynamic range and because they are permeable to Ca 2+ , an important second messenger implicated in cell fate (14,15). We examined the role of SACs in neural stem cells, for which mechanical cues influence specification alo...

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Membrane depolarization causes voltage-gated ion channels to transition from a resting/closed conformation to an activated/open conformation. We used voltage-clamp fluorometry to measure protein motion at specific regions of the Shaker Kv channel. This enabled us to construct new structural models of the resting/closed and activated/open states based on the Kv1.2 crystal structure using the Rosetta-Membrane method and molecular dynamics simulations. Our models account for the measured gating charge displacement and suggest a molecular mechanism of activation in which the primary voltage sensors, S4s, rotate by approximately 180 degrees as they move "outward" by 6-8 A. A subsequent tilting motion of the S4s and the pore domain helices, S5s, of all four subunits induces a concerted movement of the channel's S4-S5 linkers and S6 helices, allowing ion conduction. Our models are compatible with a wide body of data and resolve apparent contradictions that previously led to several distinct models of voltage sensing.

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Voltage-gated ion channels sense voltage by shuttling arginine residues located in the S4 segment across the membrane electric field. The molecular pathway for this arginine permeation is not understood, nor is the filtering mechanism that permits passage of charged arginines but excludes solution ions. We find that substituting the first S4 arginine with smaller amino acids opens a high-conductance pathway for solution cations in the Shaker K(+) channel at rest. The cationic current does not flow through the central K(+) pore and is influenced by mutation of a conserved residue in S2, suggesting that it flows through a protein pathway within the voltage-sensing domain. The current can be carried by guanidinium ions, suggesting that this is the pathway for transmembrane arginine permeation. We propose that when S4 moves it ratchets between conformations in which one arginine after another occupies and occludes to ions the narrowest part of this pathway.