Intrauterine infusion of platelet-rich plasma improves fibrosis by transforming growth factor beta 1/Smad pathway in a rat intrauterine adhesion model.

This study aims to elucidate the effects of Platelet-rich plasma (PRP) in fibrosis development in intrauterine adhesion (IUA), and the associated underlying mechanisms are also explored, which are expected to be a potential therapeutic scheme for IUA. In this research, PRP was obtained and prepared from the peripheral venous blood of rats. A rat model was induced by mechanical injury. Further, PRP was directly injected into the uterus for treatment. The appearance and shape of the uterus were assessed based on the tissues harvested. The fibrosis biomarker levels were analyzed. The transforming growth factor beta 1 (TGF-ß1) and Mothers against decapentaplegic homolog 7 (Smad7) levels, the phosphorylation of Smad2 (p-Smad2), and the phosphorylation of Smad3 (p-Smad3) were analyzed, and the molecular mechanism was investigated by rescue experiments. It was found that PRP improved the appearance and shape of the uterus in IUA and increased endometrial thickness and gland numbers. The administration of PRP resulted in a decrease in the expressions of fibrosis markers including collagen I, α-SMA, and fibronectin. Furthermore, PRP increased Smad7 levels and decreased TGF-ß1 levels, p-Smad2, and p-Smad3. Meanwhile, administration of TGF-ß1 activator reversed the therapeutic effects of PRP in IUA. Collectively, the intrauterine infusion of PRP can promote endometrial damage recovery and improve endometrial fibrosis via the TGF-ß1/Smad pathway. Hence, PRP can be a potential therapeutic strategy for IUA.

Sensory neurons promote immune homeostasis in the lung.

Cytokines employ downstream Janus kinases (JAKs) to promote chronic inflammatory diseases. JAK1-dependent type 2 cytokines drive allergic inflammation, and patients with JAK1 gain-of-function (GoF) variants develop atopic dermatitis (AD) and asthma. To explore tissue-specific functions, we inserted a human JAK1 GoF variant (JAK1GoF) into mice and observed the development of spontaneous AD-like skin disease but unexpected resistance to lung inflammation when JAK1GoF expression was restricted to the stroma. We identified a previously unrecognized role for JAK1 in vagal sensory neurons in suppressing airway inflammation. Additionally, expression of Calcb/CGRPß was dependent on JAK1 in the vagus nerve, and CGRPß suppressed group 2 innate lymphoid cell function and allergic airway inflammation. Our findings reveal evolutionarily conserved but distinct functions of JAK1 in sensory neurons across tissues. This biology raises the possibility that therapeutic JAK inhibitors may be further optimized for tissue-specific efficacy to enhance precision medicine in the future.

Transient Receptor Potential Vanilloid 4-Dependent Microglial Function in Myelin Injury and Repair.

Microglia are found pathologically at all stages of multiple sclerosis (MS) lesion development and are hypothesized to contribute to both inflammatory injury and neuroprotection in the MS brain. Transient receptor potential vanilloid 4 (TRPV4) channels are widely expressed, play an important role as environmental sensors, and are involved in calcium homeostasis for a variety of cells. TRPV4 modulates myeloid cell phagocytosis in the periphery and microglial motility in the central nervous system. We hypothesized that TRPV4 deletion would alter microglia phagocytosis in vitro and lessen disease activity and demyelination in experimental autoimmune encephalitis (EAE) and cuprizone-induced demyelination. We found that genetic deletion of TRPV4 led to increased microglial phagocytosis in vitro but did not alter the degree of demyelination or remyelination in the cuprizone mouse model of MS. We also found no difference in disease in EAE following global or microglia-specific deletion of Trpv4. Additionally, lesioned and normal appearing white matter from MS brains exhibited similar TRPV4 expression compared to healthy brain tissue. Taken together, these findings indicate that TRPV4 modulates microglial activity but does not impact disease activity in mouse models of MS, suggesting a muted and/or redundant role in MS pathogenesis.

Structural and functional analysis of human pannexin 2 channel.

The pannexin 2 channel (PANX2) participates in multiple physiological processes including skin homeostasis, neuronal development, and ischemia-induced brain injury. However, the molecular basis of PANX2 channel function remains largely unknown. Here, we present a cryo-electron microscopy structure of human PANX2, which reveals pore properties contrasting with those of the intensely studied paralog PANX1. The extracellular selectivity filter, defined by a ring of basic residues, more closely resembles that of the distantly related volume-regulated anion channel (VRAC) LRRC8A, rather than PANX1. Furthermore, we show that PANX2 displays a similar anion permeability sequence as VRAC, and that PANX2 channel activity is inhibited by a commonly used VRAC inhibitor, DCPIB. Thus, the shared channel properties between PANX2 and VRAC may complicate dissection of their cellular functions through pharmacological manipulation. Collectively, our structural and functional analysis provides a framework for development of PANX2-specific reagents that are needed for better understanding of channel physiology and pathophysiology.

MrgprA3-expressing pruriceptors drive pruritogen-induced alloknesis through mechanosensitive Piezo2 channel.

Although touch and itch are coded by distinct neuronal populations, light touch also provokes itch in the presence of exogenous pruritogens, resulting in a phenomenon called alloknesis. However, the cellular and molecular mechanisms underlying the initiation of pruritogen-induced mechanical itch sensitization are poorly understood. Here, we show that intradermal injections of histamine or chloroquine (CQ) provoke alloknesis through activation of TRPV1- and MrgprA3-expressing prurioceptors, and functional ablation of these neurons reverses pruritogen-induced alloknesis. Moreover, genetic ablation of mechanosensitive Piezo2 channel function from MrgprA3-expressing prurioceptors also dampens pruritogen-induced alloknesis. Mechanistically, histamine and CQ sensitize Piezo2 channel function, at least in part, through activation of the phospholipase C (PLC) and protein kinase C-δ (PKCδ) signaling. Collectively, our data find a TRPV1+/MrgprA3+ prurioceptor-Piezo2 signaling axis in the initiation of pruritogen-induced mechanical itch sensitization in the skin.

Yi-Shen-Hua-Shi granule ameliorates diabetic kidney disease by the "gut-kidney axis".

ETHNOPHARMACOLOGICAL RELEVANCE: Yi-Shen-Hua-Shi (YSHS) granule is an effective prescription widely used in traditional Chinese medicine to treat diabetic kidney disease (DKD), its exact efficacy in treating DKD has been confirmed but the underlying regulatory mechanism has not been fully elucidated. AIM OF THE STUDY: To explore the mechanism by which YSHS granule regulates intestinal flora and serum metabolites and then regulates renal mRNA expression through the "gut-kidney axis", so as to improve DKD. MATERIALS AND METHODS: 40 rats were divided into five groups: Normal group (N) (normal saline), model group (M) (STZ + normal saline), YSHS granule low-dose group (YL) (STZ + 2.27 g kg-1 d-1), YSHS granule high-dose group (YH) (STZ + 5.54g kg-1 d-1) and valsartan group (V) (STZ + 7.38mg kg-1 d-1). After 6 weeks, changes in blood glucose, blood lipids, and renal function related indexes were observed, as well as pathological changes in the kidney and colon. Intestinal microbiota was sequenced by 16S rDNA, serum differential metabolites were identified by LC-MS/MS, and renal differences in mRNA expression were observed by RNA-seq. Further, through the association analysis of intestinal differential microbiota, serum differential metabolites and kidney differential mRNAs, the target flora, target metabolites and target genes of YSHS granule were screened and verified, and the "gut-metabolism-transcription" co-expression network was constructed. RESULTS: In group M, blood glucose, blood lipid and proteinuria were increased, inflammation, oxidative stress and renal function were aggravated, with the proliferation of mesangial matrix, vacuolar degeneration of renal tubules, accumulation of collagen and lipid, and increased intestinal permeability, and YSHS granule and valsartan improved these disorders to varying degrees. High dose of YSHS granule improved the diversity and abundance of flora, decreased the F/B value, greatly increased the abundance of Lactobacillus and Lactobacillus_murinus, and decreased the abundance of Prevoella UCG_001. 14 target metabolites of YSHS granule were identified, which were mainly enriched in 20 KEGG pathways, such as Glycerophospholipid metabolism, Sphingolipid metabolism and Phenylalanine, tyrosine and tryptophan biosynthesis. 96 target mRNAs of YSHS granule were also identified. The enriched top 20 pathways were closely related to glucose and lipid metabolism, of which a total of 21 differential mRNAs were expressed. Further correlation analysis revealed that Lactobacillus, Lactobacillus_murinus and Prevotella UCG_001 were highly correlated with Glycerophospholipid metabolism, Sphingolipid metabolism and Phenylalanine, tyrosine and tryptophan biosynthesis pathways. At the same time, 6 pathways including Glycerophospholipid metabolism, Arachidonic acid metabolism, Purine metabolism, Primary bile acid biosynthesis, Ascorbate and aldarate metabolism and Galactose metabolism were co-enriched by the target metabolites and the target mRNAs of YSHS granule, including 7 differential metabolites such as phosphatidylethanolamine and 7 differential genes such as Adcy3. The 7 differential metabolites had high predictive value of AUC, and the validation of 7 differential genes were highly consistent with the sequencing results. CONCLUSION: YSHS granule could improve DKD through the "gut-kidney axis". Lactobacillus and Lactobacillus_murinus were the main driving forces. 6 pathways related to glucose and lipid metabolism, especially Glycerophospholipid metabolism, may be an important follow-up response and regulatory mechanism.

A TRPV4-dependent neuroimmune axis in the spinal cord promotes neuropathic pain.

Microglia, resident macrophages of the CNS, are essential to brain development, homeostasis, and disease. Microglial activation and proliferation are hallmarks of many CNS diseases, including neuropathic pain. However, molecular mechanisms that govern the spinal neuroimmune axis in the setting of neuropathic pain remain incompletely understood. Here, we show that genetic ablation or pharmacological blockade of transient receptor potential vanilloid type 4 (TRPV4) markedly attenuated neuropathic pain-like behaviors in a mouse model of spared nerve injury. Mechanistically, microglia-expressed TRPV4 mediated microglial activation and proliferation and promoted functional and structural plasticity of excitatory spinal neurons through release of lipocalin-2. Our results suggest that microglial TRPV4 channels reside at the center of the neuroimmune axis in the spinal cord, which transforms peripheral nerve injury into central sensitization and neuropathic pain, thereby identifying TRPV4 as a potential new target for the treatment of chronic pain.

Piezo2 channels expressed by colon-innervating TRPV1-lineage neurons mediate visceral mechanical hypersensitivity.

Inflammatory and functional gastrointestinal disorders such as irritable bowel syndrome (IBS) and obstructive bowel disorder (OBD) underlie the most prevalent forms of visceral pain. Although visceral pain can be generally provoked by mechanical distension/stretch, the mechanisms that underlie visceral mechanosensitivity in colon-innervating visceral afferents remain elusive. Here, we show that virally mediated ablation of colon-innervating TRPV1-expressing nociceptors markedly reduces colorectal distention (CRD)-evoked visceromotor response (VMR) in mice. Selective ablation of the stretch-activated Piezo2 channels from TRPV1 lineage neurons substantially reduces mechanically evoked visceral afferent action potential firing and CRD-induced VMR under physiological conditions, as well as in mouse models of zymosan-induced IBS and partial colon obstruction (PCO). Collectively, our results demonstrate that mechanosensitive Piezo2 channels expressed by TRPV1-lineage nociceptors powerfully contribute to visceral mechanosensitivity and nociception under physiological conditions and visceral hypersensitivity under pathological conditions in mice, uncovering potential therapeutic targets for the treatment of visceral pain.

Ion channel regulation of gut immunity.

Mounting evidence indicates that gastrointestinal (GI) homeostasis hinges on communications among many cellular networks including the intestinal epithelium, the immune system, and both intrinsic and extrinsic nerves innervating the gut. The GI tract, especially the colon, is the home base for gut microbiome which dynamically regulates immune function. The gut's immune system also provides an effective defense against harmful pathogens entering the GI tract while maintaining immune homeostasis to avoid exaggerated immune reaction to innocuous food and commensal antigens which are important causes of inflammatory disorders such as coeliac disease and inflammatory bowel diseases (IBD). Various ion channels have been detected in multiple cell types throughout the GI tract. By regulating membrane properties and intracellular biochemical signaling, ion channels play a critical role in synchronized signaling among diverse cellular components in the gut that orchestrates the GI immune response. This work focuses on the role of ion channels in immune cells, non-immune resident cells, and neuroimmune interactions in the gut at the steady state and pathological conditions. Understanding the cellular and molecular basis of ion channel signaling in these immune-related pathways and initial testing of pharmacological intervention will facilitate the development of ion channel-based therapeutic approaches for the treatment of intestinal inflammation.

Radiosynthesis and Evaluation of a C-11 Radiotracer for Transient Receptor Potential Canonical 5 in the Brain.

PURPOSE: TRPC5 belongs to the mammalian superfamily of transient receptor potential (TRP) Ca2+-permeable cationic channels and it has been implicated in various CNS disorders. As part of our ongoing interest in the development of a PET radiotracer for imaging TRPC5, herein, we explored the radiosynthesis, and in vitro and in vivo evaluation of a new C-11 radiotracer [11C]HC070 in rodents and nonhuman primates. PROCEDURES: [11C]HC070 was radiolabeled utilizing the corresponding precursor and [11C]CH3I via N-methylation protocol. Ex vivo biodistribution study of [11C]HC070 was performed in Sprague-Dawley rats. In vitro autoradiography study was conducted for the rat brain sections to characterize the radiotracer distribution in the brain regionals. MicroPET brain imaging studies of [11C]HC070 were done for 129S1/SvImJ wild-type mice and 129S1/SvImJ TRPC5 knockout mice for 0-60-min dynamic data acquisition after intravenous administration of the radiotracer. Dynamic PET scans (0-120 min) for the brain of cynomolgus male macaques were performed after the radiotracer injection. RESULTS: [11C]HC070 was efficiently prepared with good radiochemical yield (45 ± 5%, n = 15), high chemical and radiochemical purity (> 99%), and high molar activity (320.6 ± 7.4 GBq/µmol, 8.6 ± 0.2 Ci/µmol) at the end of bombardment (EOB). Radiotracer [11C]HC070 has good solubility in the aqueous dose solution. The ex vivo biodistribution study showed that [11C]HC070 had a quick rat brain clearance. Autoradiography demonstrated that [11C]HC070 specifically binds to TRPC5-enriched regions in rat brain. MicroPET study showed the peak brain uptake (SUV value) was 0.63 in 129S1/SvImJ TRPC5 knockout mice compared to 1.13 in 129S1/SvImJ wild-type mice. PET study showed that [11C]HC070 has good brain uptake with maximum SUV of ~ 2.2 in the macaque brain, followed by rapid clearance. CONCLUSIONS: Our data showed that [11C]HC070 is a TRPC5-specific radiotracer with high brain uptake and good brain washout pharmacokinetics in both rodents and nonhuman primates. The radiotracer is worth further investigating of its suitability to be a PET radiotracer for imaging TRPC5 in animals and human subjects in vivo.

Gut-innervating nociceptors regulate the intestinal microbiota to promote tissue protection.

Nociceptive pain is a hallmark of many chronic inflammatory conditions including inflammatory bowel diseases (IBDs); however, whether pain-sensing neurons influence intestinal inflammation remains poorly defined. Employing chemogenetic silencing, adenoviral-mediated colon-specific silencing, and pharmacological ablation of TRPV1+ nociceptors, we observed more severe inflammation and defective tissue-protective reparative processes in a murine model of intestinal damage and inflammation. Disrupted nociception led to significant alterations in the intestinal microbiota and a transmissible dysbiosis, while mono-colonization of germ-free mice with Gram+Clostridium spp. promoted intestinal tissue protection through a nociceptor-dependent pathway. Mechanistically, disruption of nociception resulted in decreased levels of substance P, and therapeutic delivery of substance P promoted tissue-protective effects exerted by TRPV1+ nociceptors in a microbiota-dependent manner. Finally, dysregulated nociceptor gene expression was observed in intestinal biopsies from IBD patients. Collectively, these findings indicate an evolutionarily conserved functional link between nociception, the intestinal microbiota, and the restoration of intestinal homeostasis.

Quantification of CGRP-immunoreactive myenteric neurons in mouse colon.

Quantitative data of biological systems provide valuable baseline information for understanding pathology, experimental perturbations, and computational modeling. In mouse colon, calcitonin gene-related peptide (CGRP) is expressed by myenteric neurons with multiaxonal (Dogiel type II) morphology, characteristic of intrinsic primary afferent neurons (IPANs). Analogous neurons in other species and gut regions represent 5-35% of myenteric neurons. We aimed to quantify proportions of CGRP-immunopositive (CGRP+) myenteric neurons. Colchicine-treated wholemount preparations of proximal, mid, and distal colon were labeled for HuC/D, CGRP, nitric oxide synthase (NOS), and peripherin (Per). The pan-neuronal markers (Hu+/Per+) co-labeled 94% of neurons. Hu+/Per- neurons comprised ∼6%, but Hu-/Per+ cells were rare. Thus, quantification was based on Hu+ myenteric neurons (8576 total; 1225 ± 239 per animal, n = 7). CGRP+ cell bodies were significantly larger than the average of all Hu+ neurons (329 ± 13 vs. 261 ± 12 µm2 , p < .0001). CGRP+ neurons comprised 19% ± 3% of myenteric neurons without significant regional variation. NOS+ neurons comprised 42% ± 2% of myenteric neurons overall, representing a lower proportion in proximal colon, compared to mid and distal colon (38% ± 2%, 44% ± 2%, and 44% ± 3%, respectively). Peripherin immunolabeling revealed cell body and axonal morphology in some myenteric neurons. Whether all CGRP+ neurons were multiaxonal could not be addressed using peripherin immunolabeling. However, of 118 putatively multiaxonal neurons first identified based on peripherin immunoreactivity, all were CGRP+ (n = 4). In conclusion, CGRP+ myenteric neurons in mouse colon were comprehensively quantified, occurring within a range expected of a putative IPAN marker. All Per+ multiaxonal neurons, characteristic of Dogiel type II/IPAN morphology, were CGRP+.

Miswiring of Merkel cell and pruriceptive C fiber drives the itch-scratch cycle.

Itch sensation provokes the scratch reflex to protect us from harmful stimuli in the skin. Although scratching transiently relieves acute itch through activation of mechanoreceptors, it propagates the vicious itch-scratch cycle in chronic itch by further aggravating itch over time. Although well recognized clinically, the peripheral mechanisms underlying the itch-scratch cycle remain poorly understood. Here, we show that mechanical stimulation of the skin results in activation of the Piezo2 channels on Merkel cells that pathologically promotes spontaneous itch in experimental dry skin. Three-dimensional reconstruction and immunoelectron microscopy revealed structural alteration of MRGPRA3+ pruriceptor nerve endings directed toward Merkel cells in the setting of dry skin. Our results uncover a functional miswiring mechanism under pathologic conditions, resulting in touch receptors triggering the firing of pruriceptors in the skin to drive the itch-scratch cycle.

Estrogen metabolites increase nociceptor hyperactivity in a mouse model of uterine pain.

Pain emanating from the female reproductive tract is notoriously difficult to treat, and the prevalence of transient pelvic pain has been placed as high as 70%-80% in women surveyed. Although sex hormones, especially estrogen, are thought to underlie enhanced pain perception in females, the underlying molecular and cellular mechanisms are not completely understood. Here, we showed that the pain-initiating TRPA1 channel was required for pain-related behaviors in a mouse model of estrogen-induced uterine pain in ovariectomized female mice. Surprisingly, 2- and 4-hydroxylated estrogen metabolites (2- and 4-HEMs) in the estrogen hydroxylation pathway, but not estrone, estradiol, or 16-HEMs, directly increased nociceptor hyperactivity through TRPA1 and TRPV1 channels, and picomolar concentrations of 2- and 4-hydroxylation estrone (2- or 4-OHE1) could sensitize TRPA1 channel function. Moreover, both TRPA1 and TRPV1 were expressed in uterine-innervating primary nociceptors, and their expression was increased in the estrogen-induced uterine pain model. Importantly, pretreatment with 2- or 4-OHE1 recapitulated estrogen-induced uterine pain-like behaviors, and intraplantar injections of 2- and 4-OHE1 directly produced a TRPA1-dependent mechanical hypersensitivity. Our findings demonstrated that TRPA1 is critically involved in estrogen-induced uterine pain-like behaviors, which may provide a potential drug target for treating female reproductive tract pain.

Modification of Neurogenic Colonic Motor Behaviours by Chemogenetic Ablation of Calretinin Neurons.

How the enteric nervous system determines the pacing and propagation direction of neurogenic contractions along the colon remains largely unknown. We used a chemogenetic strategy to ablate enteric neurons expressing calretinin (CAL). Mice expressing human diphtheria toxin receptor (DTR) in CAL neurons were generated by crossing CAL-ires-Cre mice with Cre-dependent ROSA26-DTR mice. Immunohistochemical analysis revealed treatment with diphtheria toxin incurred a 42% reduction in counts of Hu-expressing colonic myenteric neurons (P = 0.036), and 57% loss of CAL neurons (comprising ∼25% of all Hu neurons; P = 0.004) compared to control. As proportions of Hu-expressing neurons, CAL neurons that contained nitric oxide synthase (NOS) were relatively spared (control: 15 ± 2%, CAL-DTR: 13 ± 1%; P = 0.145), while calretinin neurons lacking NOS were significantly reduced (control: 26 ± 2%, CAL-DTR: 18 ± 5%; P = 0.010). Colonic length and pellet sizes were significantly reduced without overt inflammation or changes in ganglionic density. Interestingly, colonic motor complexes (CMCs) persisted with increased frequency (mid-colon interval 111 ± 19 vs. 189 ± 24 s, CAL-DTR vs. control, respectively, P < 0.001), decreased contraction size (mid-colon AUC 26 ± 24 vs. 59 ± 13 gram/seconds, CAL-DTR vs. control, respectively, P < 0.001), and lacked preferential anterograde migration (P < 0.001). The functional effects of modest calretinin neuron ablation, particularly increased neurogenic motor activity frequencies, differ from models that incur general enteric neuron loss, and suggest calretinin neurons may contribute to pacing, force, and polarity of CMCs in the large bowel.

How should we define a nociceptor in the gut-brain axis?

In the past few years, there has been extraordinary interest in how the gut communicates with the brain. This is because substantial and gathering data has emerged to suggest that sensory nerve pathways between the gut and brain may contribute much more widely in heath and disease, than was originally presumed. In the skin, the different types of sensory nerve endings have been thoroughly characterized, including the morphology of different nerve endings and the sensory modalities they encode. This knowledge is lacking for most types of visceral afferents, particularly spinal afferents that innervate abdominal organs, like the gut. In fact, only recently have the nerve endings of spinal afferents in any visceral organ been identified. What is clear is that spinal afferents play the major role in pain perception from the gut to the brain. Perhaps surprisingly, the majority of spinal afferent nerve endings in the gut express the ion channel TRPV1, which is often considered to be a marker of "nociceptive" neurons. And, a majority of gut-projecting spinal afferent neurons expressing TRPV1 are activated at low thresholds, in the "normal" physiological range, well below the normal threshold for detection of painful sensations. This introduces a major conundrum regarding visceral nociception. How should we define a "nociceptor" in the gut? We discuss the notion that nociception from the gut wall maybe a process encrypted into multiple different morphological types of spinal afferent nerve ending, rather than a single class of sensory ending, like free-endings, suggested to underlie nociception in skin.

Transmembrane protein TMEM184B is necessary for interleukin-31-induced itch.

ABSTRACT: Nociceptive and pruriceptive neurons in the dorsal root ganglia (DRG) convey sensations of pain and itch to the spinal cord, respectively. One subtype of mature DRG neurons, comprising 6% to 8% of neurons in the ganglia, is responsible for sensing mediators of acute itch and atopic dermatitis, including the cytokine IL-31. How itch-sensitive (pruriceptive) neurons are specified is unclear. Here, we show that transmembrane protein 184B (TMEM184B), a protein with roles in axon degeneration and nerve terminal maintenance, is required for the expression of a large cohort of itch receptors, including those for interleukin 31 (IL-31), leukotriene C4, and histamine. Male and female mice lacking TMEM184B show reduced responses to IL-31 but maintain normal responses to pain and mechanical force, indicating a specific behavioral defect in IL-31-induced pruriception. Calcium imaging experiments indicate that a reduction in IL-31-induced calcium entry is a likely contributor to this phenotype. We identified an early failure of proper Wnt-dependent transcriptional signatures and signaling components in Tmem184b mutant mice that may explain the improper DRG neuronal subtype specification. Accordingly, lentiviral re-expression of TMEM184B in mutant embryonic neurons restores Wnt signatures. Together, these data demonstrate that TMEM184B promotes adult somatosensation through developmental Wnt signaling and promotion of proper pruriceptive gene expression. Our data illuminate a new key regulatory step in the processes controlling the establishment of diversity in the somatosensory system.