ARTICLES 10 VOLUME 18 | NUMBER 1 | JANUARY 2015 NATURE NEUROSCIENCE Mechanotransduction, the conversion of mechanical force into electrochemical signals, is the basis for several sensory phenomena, including hearing, balance and touch sensation. Touch receptors are highly specialized sensory neurons that innervate the skin and con- fer the capacity to discriminate shape and fine texture of objects 1 . In vivo, touch receptors, also referred to as low-threshold mechano- receptors (LTMRs), are intermingled with sensory neurons finely tuned to detect a variety of other thermal and chemical stimuli 2 . Unlike LTMRs, nociceptors are transducers of high-threshold noxious and painful stimuli and thus constitute a separate category of sensory neurons. These functional differences correlate with the expression of different molecular markers 3 . The heterogeneity of sensory ganglia and very low abundance of modality-specific sensory neuron subtypes in vivo have hampered efforts to isolate and characterize them. Both human nociceptors and LTMRs are inaccessible for functional characterization. Recent studies describe the generation of nociceptors from hES cells by use of small-molecule inhibitors 4,5 , opening up new possi- bilities for studying nociceptor function and deriving new cellular disease models relevant for pain therapy. However, no in vitro model of human LTMRs has been described, and neuronal mechanisms that mediate rapid transduction of small mechanical stimuli have remained largely elusive. Two molecules implicated in sensing mechanical force in differ- ent cellular contexts are the large transmembrane proteins Piezo1 and Piezo2 (refs. 6–9). Piezo2 is expressed in both nociceptors and LTMRs and is also found in epidermal Merkel cells that are part of terminal touch-receptive specializations 6,8–10 . Indeed, Merkel cells modulate and tune touch responses of LTMRs in a Piezo2- dependent manner, as shown by specific and restricted Merkel cell knockout and knockdown studies 8–10 . These studies clearly show that Piezo2 conveys mechanical sensitivity to epidermal Merkel cells, but touch responses are not abolished in these mouse models, and it is currently not known whether Piezo2 is a transducer of mechanical stimuli in LTMRs, nociceptors or both. To examine human touch receptor function, we recapitulated sensory neuron development in vitro and established a multistep differentiation protocol to generate LTMRs via the intermediate production of hES cell–derived neural crest (NC) cells, the sensory neuron progenitors 3,11 . The resulting neurons express a highly distinct set of LTMR-specific genes. They also convert mechanical stimuli into electrical signals, their most salient characteristic in vivo. The differentiation procedure is not only effective in hES cells but also facilitates the conversion of hiPS cells into LTMRs. Additionally, we find that viral delivery of NGN2, a key transcription factor in sensory neuron development, promotes differentiation and directs a larger fraction of progenitor cells to adopt LTMR fate. Finally, we demonstrate that Piezo2 expression is required for mechanotransduction of hES cell–derived LTMRs. RESULTS hES cell–derived NC cells generate sensory neurons in vitro In vivo, peripheral sensory neurons derive from multipotent NC cells. During development, NC cells delaminate from the neural tube and generate functionally distinct subpopulations of dorsal root ganglion (DRG) neurons in consecutive waves 11,12 . Inducing hES cells to form neuroectodermal spheres mimics key aspects of neural tube formation 1 Department of Pharmacology, University of Heidelberg, Heidelberg, Germany. 2 Max Delbrück Center for Molecular Medicine, Berlin, Germany. 3 Skin Cancer Unit, German Cancer Research Center (DKFZ), Heidelberg and University Medical Center Mannheim, Mannheim, Germany. Correspondence should be addressed to J.S. (jan.siemens@pharma.uni-heidelberg.de). Received 6 October; accepted 13 November; published online 3 December 2014; doi:10.1038/nn.3894 PIEZO2 is required for mechanotransduction in human stem cell–derived touch receptors Katrin Schrenk-Siemens 1 , Hagen Wende 1 , Vincenzo Prato 1 , Kun Song 1 , Charlotte Rostock 1 , Alexander Loewer 2 , Jochen Utikal 3 , Gary R Lewin 2 , Stefan G Lechner 1 & Jan Siemens 1 Human sensory neurons are inaccessible for functional examination, and thus little is known about the mechanisms mediating touch sensation in humans. Here we demonstrate that the mechanosensitivity of human embryonic stem (hES) cell–derived touch receptors depends on PIEZO2. To recapitulate sensory neuron development in vitro, we established a multistep differentiation protocol and generated sensory neurons via the intermediate production of neural crest cells derived from hES cells or human induced pluripotent stem (hiPS) cells. The generated neurons express a distinct set of touch receptor–specific genes and convert mechanical stimuli into electrical signals, their most salient characteristic in vivo. Strikingly, mechanosensitivity is lost after CRISPR/Cas9-mediated PIEZO2 gene deletion. Our work establishes a model system that resembles human touch receptors, which may facilitate mechanistic analysis of other sensory subtypes and provide insight into developmental programs underlying sensory neuron diversity. npg © 2015 Nature America, Inc. All rights reserved.