Genetics of sensory mechanotransduction

Unveiling salivary gland-specific gene expression of Piezo1 and Neuroendocrine in the leech, Helobdella austinensis

Mechanotransduction is a critical biological phenomenon in living organisms, with Piezo1 being one of the key mechanotransduction ion channel genes. Piezo1 is widely expressed across various tissues and organs, playing critical roles in numerous biological processes, including innate and adaptive immune activation. While most studies on Neuroendocrine and Piezo functions have focused on vertebrates and higher invertebrates (e.g., Drosophila), however research in lophotrochozoan animal models remains scarce. To address this gap, we utilized Helobdella austinensis (phylum: Annelida) to investigate the putative function of Piezo1 and uncovered evidence related to the neuroendocrine system through spatiotemporal characterization. Our findings represent the developmental contribution of Piezo1 from early to late embryonic stages by demonstrating its expression in a lophotrochozoan. Intriguingly, the expression of Hau-Piezo1 was specifically detected in salivary gland-related precursors and tissues during development. Additionally, Neuroendocrine expression was observed in a lophotrochozoan, suggesting the correlation between neuronal stimulation and immune cells along the salivary glands of leeches. Furthermore, the downregulation of Hau-Piezo1 following bacterial challenge suggests that Piezo1 plays a role in regulating inflammatory responses. Taken together, we characterized the spatiotemporal expression pattern of Hau-Piezo1 in leeches and demonstrated its conserved and diversified functions based on its phylogenetic relationship with other homologs. These results suggest that Piezo1 may serve as a salivary gland marker in leeches and provide evidence for the presence of immune cells along the salivary glands in lophotrochozoans.

An ultrastructural map of a spinal sensorimotor circuit reveals the potential of astroglial modulation

Information flow through circuits is dictated by the precise connectivity of neurons and glia. While a single astrocyte can contact many synapses, how glial-synaptic interactions are arranged within a single circuit to impact information flow remains understudied. Here, we use the local spinal sensorimotor circuit in zebrafish as a model to understand how neurons and astroglia are connected in a vertebrate circuit. With semi-automated cellular reconstructions and automated approaches to map all the synaptic connections, we identified the precise synaptic connections of the local sensorimotor circuit, from dorsal root ganglia neurons to spinal interneurons and finally to motor neurons. This revealed a complex network of interneurons that interact in the local sensorimotor circuit. We then mapped the glial processes within tripartite synapses in the circuit. We demonstrate that tripartite synapses are equally distributed across the circuit, supporting the idea that glia can modulate information flow through the circuit at different levels. We show that multiple astroglia, including bona fide astrocytes, contact synapses within a single sensory neuron's circuit and that each of these astroglia can contact multiple parts of the circuit. This detailed map reveals an extensive network of connected neurons and astroglia that process sensory stimuli in a vertebrate. We then utilized this ultrastructural map to model how synaptic thresholding and glial modulation could alter information flow in circuits. We validated this circuit map with GCaMP6s imaging of dorsal root ganglia, spinal neurons and astroglia. This work provides a foundational resource detailing the ultrastructural organization of neurons and glia in a vertebrate circuit, offering insights in how glia could influence information flow in complex neural networks.

A Neural Device Inspired by Neuronal Oscillatory Activity with Intrinsic Perception and Decision-Making

Bionic neural devices often feature complex structures with multiple interfaces, requiring extensive post-processing. In this paper, a neural device with intrinsic perception and decision-making (NDIPD), inspired by neuronal oscillatory activity is introduced. The device utilizes alternating signals generated by coupling the human body with the power-frequency electromagnetic field as both a signal source and energy source, mimicking neuronal oscillatory activity. The peaks and valleys of the alternating signal are differentially modulated to replicate the baseline shift process in neuronal oscillatory activity. By comparing the amplitude of the peaks and valleys in the NDIPD's electrical output signal, the device achieves intrinsic perception and decision-making regarding the location of mechanical stimulation. This is accomplished using a single interface, which reduces data transmission, simplifies functionality, and eliminates the need for an external power supply. The NDIPD demonstrates a low-pressure detection limit (<0.02 N), fast response time (<20 ms), and exceptional stability (>200 000 cycles). It shows great potential for applications such as game control, UAV navigation, and virtual vehicle driving. The innovative energy supply method and sensing mechanism are expected to open new avenues in the development of bionic neural devices.

Mechanosensitive Ion Channels: The Unending Riddle of Mechanotransduction

Sensation begins at the periphery, where distinct transducer proteins, activated by specific physical stimuli, initiate biological events to convert the stimulus into electrical activity. These evoked pulse trains encode various properties of the stimulus and travel to higher centers, enabling perception of the physical environment. Transduction is an essential process in all of the five senses described by Aristotle. A substantial amount of information is already available on how G-protein coupled receptor proteins transduce exposure to light, odors, and tastants. Functional studies have revealed the presence of mechanosensitive (MS) ion channels, which act as force transducers, in a wide range of organisms from archaea to mammals. However, the molecular basis of mechanosensitivity is incompletely understood. Recently, the structure of a few MS channels and the molecular mechanisms linking mechanical force to channel gating have been partially revealed. This article reviews recent developments focusing on the molecular basis of mechanosensitivity and emerging methods to investigate MS channels.

Integrating molecular and cellular components of endothelial shear stress mechanotransduction

The lining of blood vessels is constantly exposed to mechanical forces exerted by blood flow against the endothelium. Endothelial cells detect these tangential forces (i.e., shear stress), initiating a host of intracellular signaling cascades that regulate vascular physiology. Thus, vascular health is tethered to the endothelial cells' capacity to transduce shear stress. Indeed, the mechanotransduction of shear stress underlies a variety of cardiovascular benefits, including some of those associated with increased physical activity. However, endothelial mechanotransduction is impaired in aging and disease states such as obesity and type 2 diabetes, precipitating the development of vascular disease. Understanding endothelial mechanotransduction of shear stress, and the molecular and cellular mechanisms by which this process becomes defective, is critical for the identification and development of novel therapeutic targets against cardiovascular disease. In this review, we detail the primary mechanosensitive structures that have been implicated in detecting shear stress, including junctional proteins such as platelet endothelial cell adhesion molecule-1 (PECAM-1), the extracellular glycocalyx and its components, and ion channels such as piezo1. We delineate which molecules are truly mechanosensitive and which may simply be indispensable for the downstream transmission of force. Furthermore, we discuss how these mechanosensors interact with other cellular structures, such as the cytoskeleton and membrane lipid rafts, which are implicated in translating shear forces to biochemical signals. Based on findings to date, we also seek to integrate these cellular and molecular mechanisms with a view of deciphering endothelial mechanotransduction of shear stress, a tenet of vascular physiology.

Central Channelopathies in Obesity

As obesity has raised heightening awareness, researchers have attempted to identify potential targets that can be treated for therapeutic intervention. Focusing on the central nervous system (CNS), the key organ in maintaining energy balance, a plethora of ion channels that are expressed in the CNS have been inspected and determined through manipulation in different hypothalamic neural subpopulations for their roles in fine-tuning neuronal activity on energy state alterations, possibly acting as metabolic sensors. However, a remaining gap persists between human clinical investigations and mouse studies. Despite having delineated the pathways and mechanisms of how the mouse study-identified ion channels modulate energy homeostasis, only a few targets overlap with the obesity-related risk genes extracted from human genome-wide association studies. Here, we present the most recently discovered CNS-specific metabolism-correlated ion channels using reverse and forward genetics approaches in mice and humans, respectively, in the hope of illuminating the prospects for future therapeutic development.

Endothelial discoidin domain receptor 1 senses flow to modulate YAP activation

Mechanotransduction in endothelial cells is critical to maintain vascular homeostasis and can contribute to disease development, yet the molecules responsible for sensing flow remain largely unknown. Here, we demonstrate that the discoidin domain receptor 1 (DDR1) tyrosine kinase is a direct mechanosensor and is essential for connecting the force imposed by shear to the endothelial responses. We identify the flow-induced activation of endothelial DDR1 to be atherogenic. Shear force likely causes conformational changes of DDR1 ectodomain by unfolding its DS-like domain to expose the buried cysteine-287, whose exposure facilitates force-induced receptor oligomerization and phase separation. Upon shearing, DDR1 forms liquid-like biomolecular condensates and co-condenses with YWHAE, leading to nuclear translocation of YAP. Our findings establish a previously uncharacterized role of DDR1 in directly sensing flow, propose a conceptual framework for understanding upstream regulation of the YAP signaling, and offer a mechanism by which endothelial activation of DDR1 promotes atherosclerosis.

Mechanisms of endothelial flow sensing

Fluid shear stress plays a key role in sculpting blood vessels during development, in adult vascular homeostasis and in vascular pathologies. During evolution, endothelial cells evolved several mechanosensors that convert physical forces into biochemical signals, a process termed mechanotransduction. This Review discusses our understanding of endothelial flow sensing and suggests important questions for future investigation.

TREK channels in Mechanotransduction: a Focus on the Cardiovascular System

Mechano-electric feedback is one of the most important subsystems operating in the cardiovascular system, but the underlying molecular mechanism remains rather unknown. Several proteins have been proposed to explain the molecular mechanism of mechano-transduction. Transient receptor potential (TRP) and Piezo channels appear to be the most important candidates to constitute the molecular mechanism behind of the inward current in response to a mechanical stimulus. However, the inhibitory/regulatory processes involving potassium channels that operate on the cardiac system are less well known. TWIK-Related potassium (TREK) channels have emerged as strong candidates due to their capacity for the regulation of the flow of potassium in response to mechanical stimuli. Current data strongly suggest that TREK channels play a role as mechano-transducers in different components of the cardiovascular system, not only at central (heart) but also at peripheral (vascular) level. In this context, this review summarizes and highlights the main existing evidence connecting this important subfamily of potassium channels with the cardiac mechano-transduction process, discussing molecular and biophysical aspects of such a connection.

Mechanosensitive membrane proteins: Usual and unusual suspects in mediating mechanotransduction

This Viewpoint, which accompanies a Special Issue focusing on membrane mechanosensors, discusses unifying and unique features of both established and emerging mechanosensitive (MS) membrane proteins, their distribution across protein families and phyla, and current and future challenges in the study of these important proteins and their partners. MS membrane proteins are essential for tissue development, cellular motion, osmotic homeostasis, and sensing external and self-generated mechanical cues like those responsible for touch and proprioception. Though researchers' attention and this Viewpoint focus on a few famous ion channels that are considered the usual suspects as MS mechanosensors, we also discuss some of the more unusual suspects, such as G-protein coupled receptors. As the field continues to grow, so too will the list of proteins suspected to function as mechanosensors and the diversity of known MS membrane proteins.

Developmental function of Piezo1 in mouse submandibular gland morphogenesis

Mechanically activated factors are important in organogenesis, especially in the formation of secretory organs, such as salivary glands. Piezo-type mechanosensitive ion channel component 1 (Piezo1), although previously studied as a physical modulator of the mechanotransduction, was firstly evaluated on its developmental function in this study. The detailed localization and expression pattern of Piezo1 during mouse submandibular gland (SMG) development were analyzed using immunohistochemistry and RT-qPCR, respectively. The specific expression pattern of Piezo1 was examined in acinar-forming epithelial cells at embryonic day 14 (E14) and E16, which are important developmental stages for acinar cell differentiation. To understand the precise function of Piezo1 in SMG development, siRNA against Piezo1 (siPiezo1) was employed as a loss-of-function approach, during in vitro organ cultivation of SMG at E14 for the designated period. Alterations in the histomorphology and expression patterns of related signaling molecules, including Bmp2, Fgf4, Fgf10, Gli1, Gli3, Ptch1, Shh, and Tgfβ-3, were examined in acinar-forming cells after 1 and 2 days of cultivation. Particularly, altered localization patterns of differentiation-related signaling molecules including Aquaporin5, E-cadherin, Vimentin, and cytokeratins would suggest that Piezo1 modulates the early differentiation of acinar cells in SMGs by modulating the Shh signaling pathway.

The release of osteoclast-stimulating factors on supraphysiological loading by osteoprogenitors coincides with expression of genes associated with inflammation and cytoskeletal arrangement

Supraphysiological loading induced by unstable orthopedic implants initiates osteoclast formation, which results in bone degradation. We aimed to investigate which mechanosensitive cells in the peri-implant environment produce osteoclast-stimulating factors and how the production of these factors is stimulated by supraphysiological loading. The release of osteoclast-stimulating factors by different types of isolated bone marrow-derived hematopoietic and mesenchymal stem cells from six osteoarthritic patients was analyzed after one hour of supraphysiological loading (3.0 ± 0.2 Pa, 1 Hz) by adding their conditioned medium to osteoclast precursors. Monocytes produced factors that enhanced osteoclastogenesis by 1.6 ± 0.07-fold and mesenchymal stem cells by 1.4 ± 0.07-fold. Medium from osteoprogenitors and pre-osteoblasts enhanced osteoclastogenesis by 1.3 ± 0.09-fold and 1.4 ± 0.03-fold, respectively, where medium from four patients elicited a response and two did not. Next generation sequencing analysis of osteoprogenitors revealed that genes encoding for inflammation-related pathways and cytoskeletal rearrangements were regulated differently between responders and non-responders. Our data suggest that released osteoclast-stimulating soluble factors by progenitor cells in the bone marrow after supraphysiological loading may be related to cytoskeletal arrangement in an inflammatory environment. This connection could be relevant to better understand the aseptic loosening process of orthopedic implants.

Force From Filaments: The Role of the Cytoskeleton and Extracellular Matrix in the Gating of Mechanosensitive Channels

The senses of proprioception, touch, hearing, and blood pressure on mechanosensitive ion channels that transduce mechanical stimuli with high sensitivity and speed. This conversion process is usually called mechanotransduction. From nematode MEC-4/10 to mammalian PIEZO1/2, mechanosensitive ion channels have evolved into several protein families that use variant gating models to convert different forms of mechanical force into electrical signals. In addition to the model of channel gating by stretching from lipid bilayers, another potent model is the opening of channels by force tethering: a membrane-bound channel is elastically tethered directly or indirectly between the cytoskeleton and the extracellular molecules, and the tethering molecules convey force to change the channel structure into an activation form. In general, the mechanical stimulation forces the extracellular structure to move relative to the cytoskeleton, deforming the most compliant component in the system that serves as a gating spring. Here we review recent studies focusing on the ion channel mechanically activated by a tethering force, the mechanotransduction-involved cytoskeletal protein, and the extracellular matrix. The mechanosensitive channel PIEZO2, DEG/ENaC family proteins such as acid-sensing ion channels, and transient receptor potential family members such as NompC are discussed. State-of-the-art techniques, such as polydimethylsiloxane indentation, the pillar array, and micropipette-guided ultrasound stimulation, which are beneficial tools for exploring the tether model, are also discussed.

Translating the Force - mechano-sensing GPCRs

Incorporating mechanical cues into cellular responses allows us to experience our direct environment. Specialized cells can perceive and discriminate between different physical properties such as level of vibration, temperature, or pressure. Mechanical forces are abundant signals that also shape general cellular responses such as cytoskeletal rearrangement, differentiation, or migration and contribute to tissue development and function. The molecular structures that perceive and transduce mechanical forces are specialized cytoskeletal proteins, cell junction molecules, and membrane proteins such as ion channels and metabotropic receptors. G protein-coupled receptors (GPCRs) have attracted attention as metabotropic force receptors as they are among the most important drug targets. This review summarizes the function of mechano-sensitive GPCRs, specifically, the angiotensin II type 1 receptor and adrenergic, apelin, histamine, parathyroid hormone 1, and orphan receptors, focusing particularly on the advanced knowledge gained from adhesion-type GPCRs. We distinguish between shear stress and cell swelling/stretch as the two major types of mechano-activation of these receptors and contemplate the potential contribution of the force-from-lipid and force-from-tether models that have previously been suggested for ion channels.

E, Medha M. P, Michael D. C, Wendy F. L. Ion channel mediated mechanotransduction in immune cells

The immune system performs critical functions to defend against invading pathogens and maintain tissue homeostasis. Immune cells reside within or are recruited to a host of mechanically active tissues throughout the body and, as a result, are exposed to varying types and degrees of mechanical stimuli. Despite their abundance in such tissues, the role of mechanical stimuli in influencing immune cell function and the molecular mechanisms responsible for mechanics-mediated changes are still poorly understood. The recent emergence of mechanically-gated ion channels, particularly Piezo1, has provided an exciting avenue of research within the fields of mechanobiology and immunology. Numerous studies have identified roles for mechanically-gated ion channels in mechanotransduction within various different cell types, with a few recent studies in immune cells. These initial studies provide strong evidence that mechanically-gated ion channels play pivotal roles in regulating the immune system. In this review, we discuss characteristics of ion channel mediated force transduction, review the current techniques used to quantify and visualize ion channel activity in response to mechanical stimuli, and finally we provide an overview of recent studies examining the role of mechanically-gated ion channels in modulating immune cell function.

With an Ear Up against the Wall: An Update on Mechanoperception in Arabidopsis

Cells interpret mechanical signals and adjust their physiology or development appropriately. In plants, the interface with the outside world is the cell wall, a structure that forms a continuum with the plasma membrane and the cytoskeleton. Mechanical stress from cell wall damage or deformation is interpreted to elicit compensatory responses, hormone signalling, or immune responses. Our understanding of how this is achieved is still evolving; however, we can refer to examples from animals and yeast where more of the details have been worked out. Here, we provide an update on this changing story with a focus on candidate mechanosensitive channels and plasma membrane-localized receptors.

Flow-mediated vasodilation through mechanosensitive G protein-coupled receptors in endothelial cells

Currently, endothelium-dependent vasodilatation involves three main mechanisms: production of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS), synthesis of prostanoids by cyclooxygenase, and/or opening of calcium-sensitive potassium channels. Researchers have proposed multiple mechanosensors that may be involved in flow-mediated vasodilation (FMD), including G protein-coupled receptors (GPCRs), ion channels, and intercellular junction proteins, among others. However, GPCRs are considered the major mechanosensors that play a pivotal role in shear stress signal transduction. Among mechanosensitive GPCRs, G protein-coupled receptor 68, histamine H1 receptors, sphingosine-1-phosphate receptor 1, and bradykinin B2 receptors have been identified as endothelial sensors of flow shear stress regulating flow-mediated vasodilation. Thus, this review aims to expound on the mechanism whereby flow shear stress promotes vasodilation through the proposed mechanosensitive GPCRs in ECs.

Pharmacological profiling of stretch activated channels in proprioceptive neurons

Proprioception in mammals and invertebrates occurs through stretch activated ion channels (SACs) localized in sensory endings. In mammals, the primary organs for proprioception are the intrafusal muscle spindles embedded within extrafusal muscle. In invertebrates there are varied types of sensory organs, from chordotonal organs spanning joints to muscle receptor organs (MRO) which are analogous to the mammalian muscle spindles that monitor stretch of muscle fibers. A subset of SACs are the PIEZO channels. They are comprised of a distinct type of protein sequence and are similar among species, from mammals to invertebrates. We screened several new agents (YODA 1, JEDI 2, OB 1 and DOOKU) which have been identified to act on SACs of the PIEZO 1 subtype. JEDI 2 increased activity in the crayfish MRO but not the crab chordotonal organs. The SACs of the crustacean proprioceptors have not been satisfactorily pharmacologically classified, nor has their molecular makeup been identified. We screened these pharmacological agents on model sensory organs in crustaceans to learn more about their subtype classification and compare genomic profiles of related species.

Decrease in SHP-1 enhances myometrium remodeling via FAK activation leading to labor

Preterm birth is one of the most common complications during human pregnancy and is associated with a dramatic switch within the uterus from quiescence to contractility. However, the mechanisms underlying uterine remodeling are largely unknown. Protein kinases and phosphatases play critical roles in regulating the phosphorylation of proteins involved in the smooth muscle cell functions. In the present study, we found that Src-homology phosphatase type-1 (SHP-1, PTPN6) was significantly decreased in human myometrium in labor compared with that not in labor. Timed-pregnant mice injected intraperitoneally with the specific SHP-1 inhibitor protein tyrosine phosphatase inhibitor I (PTPI-1) manifested significantly preterm labor, with enriched plasmalemmal dense plaques between myometrial cells and increased phosphorylation at Tyr397 and Tyr576/577 sites of focal adhesion kinase (FAK) in myometrial cells, which remained to the time of labor, whereas the phosphorylation levels of ERK1/2 and phosphatidylinositol 3 kinase (PI3K) showed a rapid increase upon PTPI-1 injection but fell back to normal at the time of labor. The Tyr576/577 in FAK played an important role in the interaction between FAK and SHP-1. Knockdown of SHP-1 dramatically increased the spontaneous contraction of human uterine smooth muscle cells (HUSMCs), which was reversed by coinfection of a FAK-knockdown lentivirus. PGF2α downregulated SHP-1 via PLCβ-PKC-NF-κB or PI3K-NF-κB pathways, suggesting the regenerative downregulation of SHP-1 enhances the uterine remodeling and plasticity by activating FAK and subsequent focal adhesion pathway, which eventually facilitates myometrium contraction and leads to labor. The study sheds new light on understanding of mechanisms that underlie the initiation of labor, and interventions for modulation of SHP-1 may provide a potential strategy for preventing preterm birth.

Ciliary Genes in Renal Cystic Diseases

Cilia are microtubule-based organelles, protruding from the apical cell surface and anchoring to the cytoskeleton. Primary (nonmotile) cilia of the kidney act as mechanosensors of nephron cells, responding to fluid movements by triggering signal transduction. The impaired functioning of primary cilia leads to formation of cysts which in turn contribute to development of diverse renal diseases, including kidney ciliopathies and renal cancer. Here, we review current knowledge on the role of ciliary genes in kidney ciliopathies and renal cell carcinoma (RCC). Special focus is given on the impact of mutations and altered expression of ciliary genes (e.g., encoding polycystins, nephrocystins, Bardet-Biedl syndrome (BBS) proteins, ALS1, Oral-facial-digital syndrome 1 (OFD1) and others) in polycystic kidney disease and nephronophthisis, as well as rare genetic disorders, including syndromes of Joubert, Meckel-Gruber, Bardet-Biedl, Senior-Loken, Alström, Orofaciodigital syndrome type I and cranioectodermal dysplasia. We also show that RCC and classic kidney ciliopathies share commonly disturbed genes affecting cilia function, including VHL (von Hippel-Lindau tumor suppressor), PKD1 (polycystin 1, transient receptor potential channel interacting) and PKD2 (polycystin 2, transient receptor potential cation channel). Finally, we discuss the significance of ciliary genes as diagnostic and prognostic markers, as well as therapeutic targets in ciliopathies and cancer.

Mechanotransduction and Uterine Blood Flow in Preeclampsia: The Role of Mechanosensing Piezo 1 Ion Channels

There is a large increase in uterine arterial blood flow during normal pregnancy. Structural and cellular adjustments occur in the uterine vasculature during pregnancy to accommodate this increased blood flow through a complex adaptive process that is dependent on multiple coordinated and interactive influences and this process is known as "vascular remodeling." The etiology of preeclampsia involves aberrant placentation and vascular remodeling leading to reduced uteroplacental perfusion. The placental ischemia leads to development of hypertension and proteinuria in the mother, intrauterine growth restriction, and perinatal death in the fetus. However, the underlying source of the deficient vascular remodeling and the subsequent development of preeclampsia remain to be fully understood. Mechanoreceptors in the vascular system convert mechanical force (shear stress) to biochemical signals and feedback mechanisms. This review focuses on the Piezo 1 channel, a mechanosensitive channel that is sensitive to shear stress in the endothelium; it induces Ca2+ entry which is linked to endothelial nitric oxide synthase (eNOS) activation as the mechanoreceptor responsible for uterine vascular dilatation during pregnancy. Here we describe the downstream signaling pathways involved in this process and the possibility of a deficiency in expression of Piezo 1 in preeclampsia leading to the abnormal vascular dysfunction responsible for the pathophysiology of the disease. The Piezo 1 ion channel is expressed in the endothelium and vascular smooth muscle cells (VSMCs) of small-diameter arteries. It plays a role in the structural remodeling of arteries and is involved in mechanotransduction of hemodynamic shear stress by endothelial cells (ECs).

Coordination of WNT signaling and ciliogenesis during odontogenesis by piezo type mechanosensitive ion channel component 1

Signal transmission from the mechanical forces to the various intracellular activities is a fundamental process during tissue development. Despite their critical role, the mechanism of mechanical forces in the biological process is poorly understood. In this study, we demonstrated that in the response to hydrostatic pressure (HP), the piezo type mechanosensitive ion channel component 1 (PIEZO1) is a primary mechanosensing receptor for odontoblast differentiation through coordination of the WNT expression and ciliogenesis. In stem cells from human exfoliated deciduous teeth (SHED), HP significantly promoted calcium deposition as well as the expression of odontogenic marker genes, PANX3 and DSPP, and WNT related-genes including WNT5b and WNT16, whereas HP inhibited cell proliferation and enhanced primary cilia expression. WNT signaling inhibitor XAV939 and primary cilia inhibitor chloral hydrate blocked the HP-induced calcium deposition. The PIEZO1 activator Yoda1 inhibited cell proliferation but induced ciliogenesis and WNT16 expression. Interestingly, HP and Yoda1 promoted nuclear translocation of RUNX2, whereas siRNA-mediated silencing of PIEZO1 decreased HP-induced nuclear translocation of RUNX2. Taken together, these results suggest that PIEZO1 functions as a mechanotransducer that connects HP signal to the intracellular signalings during odontoblast differentiation.

The role of anthrax toxin protein receptor 1 as a new mechanosensor molecule and its mechanotransduction in BMSCs under hydrostatic pressure

Anthrax toxin protein receptor (ANTXR) 1 has many similarities to integrin and is regarded in some respects as a single-stranded integrin protein. However, it is not clear whether ANTXR1 responds to mechanical signals secondary to the activation of integrins or whether it is a completely new, independent and previously undiscovered mechanosensor that responds to an undefined subset of mechanical signaling molecules. Our study demonstrates that ANTXR1 is a novel mechanosensor on the cell membrane, acting independently from the classical mechanoreceptor molecule integrinβ1. We show that bone marrow stromal cells (BMSCs) respond to the hydrostatic pressure towards chondrogenic differentiation partly through the glycogen synthase kinase (GSK) 3β/β-Catenin signaling pathway, which can be partly regulated by ANTXR1 and might be related to the direct binding between ANTXR1 and low-density lipoprotein receptor-related protein (LRP) 5/6. In addition, ANTXR1 specifically activates Smad2 and upregulates Smad4 expression to facilitate the transport of activated Smad2 to the nucleus to regulate chondrogenesis, which might be related to the direct binding between ANTXR1 and Actin/Fascin1. We also demonstrate that ANTXR1 binds to some extent with integrinβ1, but this interaction does not affect the expression and function of either protein under pressure. Thus, we conclude that ANTXR1 plays a crucial role in BMSC mechanotransduction and controls specific signaling pathways that are distinct from those of integrin to influence the chondrogenic responses of BMSCs under hydrostatic pressure.

Moving average filtering with deconvolution (MAD) for hidden Markov model with filtering and correlated noise

Ion channel data recorded using the patch clamp technique are low-pass filtered to remove high-frequency noise. Almanjahie et al. (Eur Biophys J 44:545-556, 2015) based statistical analysis of such data on a hidden Markov model (HMM) with a moving average adjustment for the filter but without correlated noise, and used the EM algorithm for parameter estimation. In this paper, we extend their model to include correlated noise, using signal processing methods and deconvolution to pre-whiten the noise. The resulting data can be modelled as a standard HMM and parameter estimates are again obtained using the EM algorithm. We evaluate this approach using simulated data and also apply it to real data obtained from the mechanosensitive channel of large conductance (MscL) in Escherichia coli. Estimates of mean conductances are comparable to literature values. The key advantages of this method are that it is much simpler and computationally considerably more efficient than currently used HMM methods that include filtering and correlated noise.

GPR68 Senses Flow and Is Essential for Vascular Physiology

Mechanotransduction plays a crucial role in vascular biology. One example of this is the local regulation of vascular resistance via flow-mediated dilation (FMD). Impairment of this process is a hallmark of endothelial dysfunction and a precursor to a wide array of vascular diseases, such as hypertension and atherosclerosis. Yet the molecules responsible for sensing flow (shear stress) within endothelial cells remain largely unknown. We designed a 384-well screening system that applies shear stress on cultured cells. We identified a mechanosensitive cell line that exhibits shear stress-activated calcium transients, screened a focused RNAi library, and identified GPR68 as necessary and sufficient for shear stress responses. GPR68 is expressed in endothelial cells of small-diameter (resistance) arteries. Importantly, Gpr68-deficient mice display markedly impaired acute FMD and chronic flow-mediated outward remodeling in mesenteric arterioles. Therefore, GPR68 is an essential flow sensor in arteriolar endothelium and is a critical signaling component in cardiovascular pathophysiology.

Association Between Acid-Sensing Ion Channel 3 Gene Variants and Balance Impairment in People With Mild Traumatic Brain Injury

Introduction: Dizziness and balance impairment are common symptoms of mild traumatic brain injury (mTBI). Acid-sensing ion channel 3 (ASIC3) is expressed in the vestibular and proprioceptive systems and associated with balance functions. However, whether the genetic variants of ASIC3 are associated with people who suffer dizziness and balance impairment after mTBI remained unknown. Materials and methods: A total of 200 people with mTBI and 109 non-mTBI controls were recruited. Dizziness, balance functions, and the ability to perform daily activities were assessed by Dizziness Handicap Inventory (DHI), and objective balance functions were investigated by the postural stability test. Three diseases-related genetic variants of ASIC3 were determined through polymerase chain reaction and followed by restriction fragment length polymorphism. The Student's t-test and Mann-Whitney U-test were used for normal and abnormal distributed data, respectively. The regression was applied to adjust gender and age. The normality of continuous data was evaluated by Shapiro-Wilk test. Results: In the mTBI people, the rs2288645-A allele carriers exhibited a significantly worse physical domain DHI score (A-allele carriers: 11.39 ± 8.42, non-A carriers: 8.76 ± 7.87, p = 0.03). The rs4148855-GTC deletion carriers an exhibited significantly worse overall postural stability (GTC deletion carriers: 0.53 ± 0.33, non-carriers: 0.46 ± 0.20, p = 0.03). In the controls, rs2288646-A allele carriers were significant worse in the medial-to-lateral postural stability (A-allele carriers: 0.31 ± 0.17, non-A carriers: 0.21 ± 0.10, p = 0.01). Conclusion: The present study demonstrated that ASIC3 genetic variants were associated with certain aspects of balance functions and dizziness questionnaires in people of mTBI and non-mTBI. It provides a possible evidence that ASIC3 could be a new target for the management of the balancing disorders. However, further investigations are warranted to elucidate the underlying mechanisms and clinical significance.

Quantitative and functional posttranslational modification proteomics reveals that TREPH1 plays a role in plant touch-delayed bolting

Environmental mechanical forces, such as wind and touch, trigger gene-expression regulation and developmental changes, called "thigmomorphogenesis," in plants, demonstrating the ability of plants to perceive such stimuli. In Arabidopsis, a major thigmomorphogenetic response is delayed bolting, i.e., emergence of the flowering stem. The signaling components responsible for mechanotransduction of the touch response are largely unknown. Here, we performed a high-throughput SILIA (stable isotope labeling in Arabidopsis)-based quantitative phosphoproteomics analysis to profile changes in protein phosphorylation resulting from 40 seconds of force stimulation in Arabidopsis thaliana Of the 24 touch-responsive phosphopeptides identified, many were derived from kinases, phosphatases, cytoskeleton proteins, membrane proteins, and ion transporters. In addition, the previously uncharacterized protein TOUCH-REGULATED PHOSPHOPROTEIN1 (TREPH1) became rapidly phosphorylated in touch-stimulated plants, as confirmed by immunoblots. TREPH1 fractionates as a soluble protein and is shown to be required for the touch-induced delay of bolting and gene-expression changes. Furthermore, a nonphosphorylatable site-specific isoform of TREPH1 (S625A) failed to restore touch-induced flowering delay of treph1-1, indicating the necessity of S625 for TREPH1 function and providing evidence consistent with the possible functional relevance of the touch-regulated TREPH1 phosphorylation. Taken together, these findings identify a phosphoprotein player in Arabidopsis thigmomorphogenesis regulation and provide evidence that TREPH1 and its touch-induced phosphorylation may play a role in touch-induced bolting delay, a major component of thigmomorphogenesis.

Cell Mechanotransduction With Piconewton Forces Applied by Optical Tweezers

Mechanical stresses are always present in the cellular environment and mechanotransduction occurs in all cells. Although many experimental approaches have been developed to investigate mechanotransduction, the physical properties of the mechanical stimulus have yet to be accurately characterized. Here, we propose a mechanical stimulation method employing an oscillatory optical trap to apply piconewton forces perpendicularly to the cell membrane, for short instants. We show that this stimulation produces membrane indentation and induces cellular calcium transients in mouse neuroblastoma NG108-15 cells dependent of the stimulus strength and the number of force pulses.

Piezo channels and GsMTx4: Two milestones in our understanding of excitatory mechanosensitive channels and their role in pathology

Discovery of Piezo channels and the reporting of their sensitivity to the inhibitor GsMTx4 were important milestones in the study of non-selective cationic mechanosensitive channels (MSCs) in normal physiology and pathogenesis. GsMTx4 had been used for years to investigate the functional role of cationic MSCs, especially in muscle tissue, but with little understanding of its target or inhibitory mechanism. The sensitivity of Piezo channels to bilayer stress and its robust mechanosensitivity when expressed in heterologous systems were keys to determining GsMTx4's mechanism of action. However, questions remain regarding Piezo's role in muscle function due to the non-selective nature of GsMTx4 inhibition toward membrane mechanoenzymes and the implication of MCS channel types by genetic knockdown. Evidence supporting Piezo like activity, at least in the developmental stages of muscle, is presented. While the MSC targets of GsMTx4 in muscle pathology are unclear, its muscle protective effects are clearly demonstrated in two recent in situ studies on normal cardiomyocytes and dystrophic skeletal muscle. The muscle protective function may be due to the combined effect of GsMTx4's inhibitory action on cationic MSCs like Piezo and TRP, and its potentiation of repolarizing K⁺ selective MSCs like K2P and SAKCa. Paradoxically, the potent in vitro action of GsMTx4 on many physiological functions seems to conflict with its lack of in situ side-effects on normal animal physiology. Future investigations into cytoskeletal control of sarcolemma mechanics and the suspected inclusion of MSCs in membrane micro/nano sized domains with distinct mechanical properties will aide our understanding of this dichotomy.

Transition between synaptic branch formation and synaptogenesis is regulated by the lin-4 microRNA

Axonal branch formation and synaptogenesis are sequential events that are required for the establishment of neuronal connectivity. However, little is known about how the transition between these two events is regulated. Here, we report that the lin-4 microRNA can regulate the transition between branch formation and synaptogenesis in the PLM axon of C. elegans. The PLM axon grows a collateral branch during the early L1 stage and undergoes synaptogenesis during the late L1 stage. Loss of the lin-4 microRNA disrupts synaptogenesis during the late L1 stage, suggesting that lin-4 promotes synaptogenesis. Conversely, the target of lin-4, the LIN-14 transcription factor, promotes PLM branch formation and inhibits synaptogenesis during the early L1 stage. Moreover, we present genetic evidence suggesting that synaptic vesicle transport is required for PLM branch formation and that the role of LIN-14 is to promote transport of synaptic vesicles to the region of future branch growth. These observations provide a novel mechanism whereby lin-4 promotes the transition from branch formation to synaptogenesis by repressing the branch-promoting and synaptogenesis-inhibiting activities of LIN-14.

Touch, Tension, and Transduction - The Function and Regulation of Piezo Ion Channels

In 2010, two proteins, Piezo1 and Piezo2, were identified as the long-sought molecular carriers of an excitatory mechanically activated current found in many cells. This discovery has opened the floodgates for studying a vast number of mechanotransduction processes. Over the past 6 years, groundbreaking research has identified Piezos as ion channels that sense light touch, proprioception, and vascular blood flow, ruled out roles for Piezos in several other mechanotransduction processes, and revealed the basic structural and functional properties of the channel. Here, we review these findings and discuss the many aspects of Piezo function that remain mysterious, including how Piezos convert a variety of mechanical stimuli into channel activation and subsequent inactivation, and what molecules and mechanisms modulate Piezo function.

Feeling force: physical and physiological principles enabling sensory mechanotransduction

Organisms as diverse as microbes, roundworms, insects, and mammals detect and respond to applied force. In animals, this ability depends on ionotropic force receptors, known as mechanoelectrical transduction (MeT) channels, that are expressed by specialized mechanoreceptor cells embedded in diverse tissues and distributed throughout the body. These cells mediate hearing, touch, and proprioception and play a crucial role in regulating organ function. Here, we attempt to integrate knowledge about the architecture of mechanoreceptor cells and their sensory organs with principles of cell mechanics, and we consider how engulfing tissues contribute to mechanical filtering. We address progress in the quest to identify the proteins that form MeT channels and to understand how these channels are gated. For clarity and convenience, we focus on sensory mechanobiology in nematodes, fruit flies, and mice. These themes are emphasized: asymmetric responses to applied forces, which may reflect anisotropy of the structure and mechanics of sensory mechanoreceptor cells, and proteins that function as MeT channels, which appear to have emerged many times through evolution.

Native Piezo2 Interactomics Identifies Pericentrin as a Novel Regulator of Piezo2 in Somatosensory Neurons

The ability of somatosensory neurons to perceive mechanical stimuli relies on specialized mechanotransducing proteins and their molecular environment. Only recently has the identity of a major transducer of mechanical forces in vertebrates been revealed by the discovery of Piezo2. Further work has established its pivotal role for innocuous touch in mice. Therefore, Piezo2 offers a unique platform for the molecular investigation of somatosensory mechanosensation. We performed a mass spectrometry-based interactomics screen on native Piezo2 in somatosensory neurons of mouse dorsal root ganglia (DRG). Stringent and quantitative data analysis yielded the identity of 36 novel binding partners of Piezo2. The biological significance of this data set is reflected by functional experiments demonstrating a role for Pericentrin in modulating Piezo2 activity and membrane expression in somatosensory neurons. Collectively, our findings provide a framework for understanding Piezo2 physiology and serve as a rich resource for the molecular dissection of mouse somatosensation.

Signaling mechanisms implicated in cranial sutures pathophysiology: Craniosynostosis

Normal extension and skull expansion is a synchronized process that prevails along the osteogenic intersections of the cranial sutures. Cranial sutures operate as bone growth sites allowing swift bone generation at the edges of the bone fronts while they remain patent. Premature fusion of one or more cranial sutures can trigger craniosynostosis, a birth defect characterized by dramatic manifestations in appearance and functional impairment. Up until today, surgical correction is the only restorative measure for craniosynostosis associated with considerable mortality. Clinical studies have identified several genes implicated in the pathogenesis of craniosynostosis syndromes with useful insights into the underlying molecular signaling events that determine suture fate. In this review, we exploit the intracellular signal transduction pathways implicated in suture pathobiology, in an attempt to identify key signaling molecules for therapeutic targeting.

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Cranial sutures operate as bone growth sites.

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Premature fusion of one or more cranial sutures can trigger craniosynostosis.

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Several genes are involved in the pathogenesis of craniosynostosis syndromes.

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An array of molecular signaling events determine suture fate.

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Herein, the signal transduction pathways implicated in suture pathobiology are discussed.

Regulation of Gap Junction Dynamics by UNC-44/ankyrin and UNC-33/CRMP through VAB-8 in C. elegans Neurons

Gap junctions are present in both vertebrates and invertebrates from nematodes to mammals. Although the importance of gap junctions has been documented in many biological processes, the molecular mechanisms underlying gap junction dynamics remain unclear. Here, using the C. elegans PLM neurons as a model, we show that UNC-44/ankyrin acts upstream of UNC-33/CRMP in regulation of a potential kinesin VAB-8 to control gap junction dynamics, and loss-of-function in the UNC-44/UNC-33/VAB-8 pathway suppresses the turnover of gap junction channels. Therefore, we first show a signal pathway including ankyrin, CRMP, and kinesin in regulating gap junctions.

Polycystins and mechanotransduction: From physiology to disease

Polycystins are key mechanosensor proteins able to respond to mechanical forces of external or internal origin. They are widely expressed in primary cilium and plasma membrane of several cell types including kidney, vascular endothelial and smooth muscle cells, osteoblasts and cardiac myocytes modulating their physiology. Interaction of polycystins with diverse ion channels, cell-cell and cell-extracellular matrix junctional proteins implicates them in the regulation of cell structure, mechanical force transmission and mechanotransduction. Their intracellular localization in endoplasmic reticulum further regulates subcellular trafficking and calcium homeostasis, finely-tuning overall cellular mechanosensitivity. Aberrant expression or genetic alterations of polycystins lead to severe structural and mechanosensing abnormalities including cyst formation, deregulated flow sensing, aneurysms, defective bone development and cancer progression, highlighting their vital role in human physiology.

The vesicle protein SAM-4 regulates the processivity of synaptic vesicle transport

Axonal transport of synaptic vesicles (SVs) is a KIF1A/UNC-104 mediated process critical for synapse development and maintenance yet little is known of how SV transport is regulated. Using C. elegans as an in vivo model, we identified SAM-4 as a novel conserved vesicular component regulating SV transport. Processivity, but not velocity, of SV transport was reduced in sam-4 mutants. sam-4 displayed strong genetic interactions with mutations in the cargo binding but not the motor domain of unc-104. Gain-of-function mutations in the unc-104 motor domain, identified in this study, suppress the sam-4 defects by increasing processivity of the SV transport. Genetic analyses suggest that SAM-4, SYD-2/liprin-α and the KIF1A/UNC-104 motor function in the same pathway to regulate SV transport. Our data support a model in which the SV protein SAM-4 regulates the processivity of SV transport.

Most cellular components of neurons are synthesized in the cell body and must be transported great distances to form synapses at the ends of axons and dendrites. Neurons use a specialized axonal transport system consisting of microtubule cytoskeletal tracks and numerous molecular motors to shuttle specific cargo to specific destinations in the cell. Disruption of this transport system has severe consequences to human health. Disruption of specific neuronal motors are linked to hereditary neurodegenerative conditions including forms of Charcot Marie Tooth disease, several types of hereditary spastic paraplegia, and certain forms of amyotrophic lateral sclerosis motor neuron disease. Despite recent progress in defining the cargo of many of kinesin family motors in neurons, little is known about how the activity of these transport systems is regulated. Here, using a simple invertebrate model we identify and characterize a novel protein that regulates the efficacy of the KIF1A motor that mediates transport of synaptic vesicles. These studies define a new pathway regulating SV transport with potential links to human neurological disease.

Low intensity pulsed ultrasound enhanced mesenchymal stem cell recruitment through stromal derived factor-1 signaling in fracture healing

Low intensity pulsed ultrasound (LIPUS) has been proven effective in promoting fracture healing but the underlying mechanisms are not fully depicted. We examined the effect of LIPUS on the recruitment of mesenchymal stem cells (MSCs) and the pivotal role of stromal cell-derived factor-1/C-X-C chemokine receptor type 4 (SDF-1/CXCR4) pathway in response to LIPUS stimulation, which are essential factors in bone fracture healing. For in vitro study, isolated rat MSCs were divided into control or LIPUS group. LIPUS treatment was given 20 minutes/day at 37 °C for 3 days. Control group received sham LIPUS treatment. After treatment, intracellular CXCR4 mRNA, SDF-1 mRNA and secreted SDF-1 protein levels were quantified, and MSCs migration was evaluated with or without blocking SDF-1/CXCR4 pathway by AMD3100. For in vivo study, fractured 8-week-old young rats received intracardiac administration of MSCs were assigned to LIPUS treatment, LIPUS+AMD3100 treatment or vehicle control group. The migration of transplanted MSC to the fracture site was investigated by ex vivo fluorescent imaging. SDF-1 protein levels at fracture site and in serum were examined. Fracture healing parameters, including callus morphology, micro-architecture of the callus and biomechanical properties of the healing bone were investigated. The in vitro results showed that LIPUS upregulated SDF-1 and CXCR4 expressions in MSCs, and elevated SDF-1 protein level in the conditioned medium. MSCs migration was promoted by LIPUS and partially inhibited by AMD3100. In vivo study demonstrated that LIPUS promoted MSCs migration to the fracture site, which was associated with an increase of local and serum SDF-1 level, the changes in callus formation, and the improvement of callus microarchitecture and mechanical properties; whereas the blockade of SDF-1/CXCR4 signaling attenuated the LIPUS effects on the fractured bones. These results suggested SDF-1 mediated MSCs migration might be one of the crucial mechanisms through which LIPUS exerted influence on fracture healing.

Mechanosensory molecules and circuits in C. elegans

Mechanosensory neurons, whose activity is controlled by mechanical force, underlie the senses of touch, hearing, and proprioception, yet despite their importance, the molecular basis of mechanotransduction is poorly understood. Genetic studies in Caenorhabditis elegans have provided a useful approach for identifying potential components of mechanotransduction complexes that might be conserved in more complex organisms. This review describes the mechanosensory systems of C. elegans, including the sensory neurons and circuitry involved in body touch, nose touch, and proprioception. In addition, the roles of genes encoding known and potential mechanosensory receptors, including members of the broadly conserved transient receptor potential (TRP) and degerin/epithelial Na⁺ channel (DEG/ENaC) channel families, are discussed.

Sensory mechanotransduction at membrane-matrix interfaces

Sensory cells specialized to detect extremely small mechanical changes are common to the auditory and somatosensory systems. It is widely accepted that mechanosensitive channels form the core of the mechanoelectrical transduction in hair cells as well as the somatic sensory neurons that underlie the sense of touch and mechanical pain. Here, we will review how the activation of such channels can be measured in a meaningful physiological context. In particular, we will discuss the idea that mechanosensitive channels normally occur in transmembrane complexes that are anchored to extracellular matrix components (ECM) both in vitro and in vivo. One component of such complexes in sensory neurons is the integral membrane scaffold protein STOML3 which is a robust physiological regulator of native mechanosensitive currents. In order to better characterize such channels in transmembrane complexes, we developed a new electrophysiological method that enables the quantification of mechanosensitive current amplitude and kinetics when activated by a defined matrix movement in cultured cells. The results of such studies strongly support the idea that ion channels in transmembrane complexes are highly tuned to detect movement of the cell membrane in relation to the ECM.

Comparative study of time-dependent effects of 4 and 8 Hz mechanical vibration at infrasound frequency on E. coli K-12 cells proliferation

The aim of the present work is to study the time-dependent effects of mechanical vibration (MV) at infrasound (IS) frequency at 4 and 8 Hz on E. coli K-12 growth by investigating the cell proliferation, using radioactive [(3)H]-thymidine assay. In our previous work it was suggested that the aqua medium can serve as a target through which the biological effect of MV on microbes could be realized. At the same time it was shown that microbes have mechanosensors on the surface of the cells and can sense small changes of the external environment. The obtained results were shown that the time-dependent effects of MV at 4 and 8 Hz frequency could either stimulate or inhibit the growth of microbes depending from exposure time. It more particularly, the invention relates to a method for controlling biological functions through the application of mechanical vibration, thus making it possible to artificially control the functions of bacterial cells, which will allow us to develop method that can be used in agriculture, industry, medicine, biotechnology to control microbial growth.

Polycystins and partners: proposed role in mechanosensitivity

Mutations of the two polycystins, PC1 and PC2, lead to polycystic kidney disease. Polycystins are able to form complexes with numerous families of proteins that have been suggested to participate in mechanical sensing. The proposed role of polycystins and their partners in the kidney primary cilium is to sense urine flow. A role for polycystins in mechanosensing has also been shown in other cell types such as vascular smooth muscle cells and cardiac myocytes. At the plasma membrane, polycystins interact with diverse ion channels of the TRP family and with stretch-activated channels (Piezos, TREKs). The actin cytoskeleton and its interacting proteins, such as filamin A, have been shown to be essential for these interactions. Numerous proteins involved in cell-cell and cell-extracellular matrix junctions interact with PC1 and/or PC2. These multimeric protein complexes are important for cell structure integrity, the transmission of force, as well as for mechanosensing and mechanotransduction. A group of polycystin partners are also involved in subcellular trafficking mechanisms. Finally, PC1 and especially PC2 interact with elements of the endoplasmic reticulum and are essential components of calcium homeostasis. In conclusion, we propose that both PC1 and PC2 act as conductors to tune the overall cellular mechanosensitivity.

A force-controlled robotic micromanipulation system for mechanotransduction studies of Drosophila larvae

This paper presents an automated robotic micromanipulation system capable of force-controlled mechanical stimulation and fluorescence imaging of Drosophila larvae, for mechanotransduction studies of Drosophila neural circuitry. An elastomeric microdevice is developed for efficient immobilization of an array of larvae for subsequent force-controlled touching. A microelectromechanical systems (MEMS) based force sensor is integrated into the system for closed-loop force control of larva touching at a resolution of 50 μN. Two microrobots are coordinately servoed using orchestrated position and force control laws for automatic operations. The system performs simultaneous force-controlled larva touching and fluorescence imaging at a speed of 4 larvae per minute, with a success rate of 92.5%. This robotic system will greatly facilitate the dissection of mechanotransduction mechanisms of Drosophila larvae at both the molecular and cellular levels.

Regulation of ASIC channels by a stomatin/STOML3 complex located in a mobile vesicle pool in sensory neurons

A complex of stomatin-family proteins and acid-sensing (proton-gated) ion channel (ASIC) family members participate in sensory transduction in invertebrates and vertebrates. Here, we have examined the role of the stomatin-family protein stomatin-like protein-3 (STOML3) in this process. We demonstrate that STOML3 interacts with stomatin and ASIC subunits and that this occurs in a highly mobile vesicle pool in dorsal root ganglia (DRG) neurons and Chinese hamster ovary cells. We identify a hydrophobic region in the N-terminus of STOML3 that is required for vesicular localization of STOML3 and regulates physical and functional interaction with ASICs. We further characterize STOML3-containing vesicles in DRG neurons and show that they are Rab11-positive, but not part of the early-endosomal, lysosomal or Rab14-dependent biosynthetic compartment. Moreover, uncoupling of vesicles from microtubules leads to incorporation of STOML3 into the plasma membrane and increased acid-gated currents. Thus, STOML3 defines a vesicle pool in which it associates with molecules that have critical roles in sensory transduction. We suggest that the molecular features of this vesicular pool may be characteristic of a ‘transducosome’ in sensory neurons.

The LIM homeobox gene ceh-14 is required for phasmid function and neurite outgrowth

Transcription factors play key roles in cell fate specification and cell differentiation. Previously, we showed that the LIM homeodomain factor CEH-14 is expressed in the AFD neurons where it is required for thermotaxis behavior in Caenorhabditis elegans. Here, we show that ceh-14 is expressed in the phasmid sensory neurons, PHA and PHB, a number of neurons in the tail, i.e., PHC, DVC, PVC, PVN, PVQ, PVT, PVW and PVR, as well as the touch neurons. Analysis of the promoter region shows that important regulatory elements for the expression in most neurons reside from -4kb to -1.65kb upstream of the start codon. Further, within the first introns are elements for expression in the hypodermis. Phylogenetic footprinting revealed numerous conserved motifs in these regions. In addition to the existing deletion mutation ceh-14(ch3), we isolated a new allele, ceh-14(ch2), in which only one LIM domain is disrupted. The latter mutant allele is partially defective for thermosensation. Analysis of both mutant alleles showed that they are defective in phasmid dye-filling. However, the cell body, dendritic outgrowth and ciliated endings of PHA and PHB appear normal, indicating that ceh-14 is not required for growth. The loss of a LIM domain in the ceh-14(ch2) allele causes a partial loss-of-function phenotype. Examination of the neurites of ALA and tail neurons using a ceh-14::GFP reporter shows abnormal axonal outgrowth and pathfinding.

Rearrangement of microtubule network under biochemical and mechanical stimulations

Cells are constantly under the influence of various external forces in their physiological environment. These forces are countered by the viscoelastic properties of the cytoskeleton. To understand the response of the cytoskeleton to biochemical and mechanical stimuli, GFP-tubulin expressing CHO cells were investigated using scanning laser confocal microscopy. Cells treated with nocodazole revealed disruption in the microtubule network within minutes of treatment while keeping the cell shape intact. By contrast, trypsin, a proteolytic agent, altered the shape of CHO cells by breaking the peptide bonds at adhesion sites. CHO cells were also stimulated mechanically by applying an indentation force with an atomic force microscope (AFM) and by shear stress in a parallel plate flow chamber. Mechanical stimulation applied using AFM showed two distinct cytoskeletal responses to the applied force: an immediate response that resulted in the depolymerization and displacement of the microtubules out of the contact zone, and a slower response characterized by tubulin polymerization at the periphery of the indented area. Flow chamber experiments revealed that shear force did not induce formation of new microtubules in CHO cells and that detachment of adherent cells from the substrate occurred independent from the flow direction. Overall, the experimental system described here allows real-time characterization of dynamic changes in cell cytoskeleton in response to the mechano-chemical stimuli and, therefore, provides better understanding of the biophysical and functional properties of cells.