Neonatal seizures induced by pentylenetetrazol or kainic acid disrupt primary cilia growth on developing mouse cortical neurons

Ex-vivo Imaging of Glial Energy Metabolism in the Neonatal Mouse Brain during Convulsive Seizures with Intranasal Radiotracer Administration

PURPOSE

In this study, we examined changes in glial energy metabolism in neonatal mouse brain images obtained under pathological conditions following intranasal administration of the radiotracer [2-14C]acetate.

PROCEDURES

[2-14C]acetate was administered via the mouse nasal cavity, after which autoradiograms of the brain of 7-day-old mice were obtained. Radio thin-layer chromatography was applied for metabolite analysis of brain radioactivity. We also compared brain uptake of [2-14C]acetate when administrated intranasally and intravenously in 3-week-old mice. To confirm selective uptake by glial cells, [2-14C]acetate was injected into the nasal cavity of mice injected with a glial toxin in the brain. Pentylenetetrazole (PTZ) was applied to induce seizures.

RESULTS

Intranasally administered [2-14C]acetate was rapidly incorporated into the brains of 7-day-old mice, reaching its highest uptake level 20 min after administration. After 20 min of intranasal [2-14C]acetate administration, glutamate and glutamine accounted for 32 ± 2.5% and 30 ± 3.4% of total brain radioactivity, respectively. There was no difference in the radioactivity distribution in the brain between intranasal and intravenous administration, except in the ventral olfactory bulb in 3-week-old mice. Microinjection of the glial-specific toxin fluorocitrate reduced the accumulation of radioactivity in the brain by 60% following intranasal administration in 3-week-old mice. The uptake of [2-14C]acetate in the brains of 7-day-old mice significantly decreased 30 min after systemic PTZ administration, suggesting a decrease in energy metabolism in glial cells during seizures.

CONCLUSIONS

Quantitative images of biological functions in the neonatal mouse brain can be obtained by intranasal administration. This technique allowed the observation of a decrease in acetate uptake associated with convulsive seizures. The results of this study could be applied to the imaging of biological brain functions and research on neurological disorders using labeled probes in neonatal mice.

An Epilepsy-Associated CILK1 Variant Compromises KATNIP Regulation and Impairs Primary Cilia and Hedgehog Signaling

Mutations in human CILK1 (ciliogenesis associated kinase 1) are linked to ciliopathies and epilepsy. Homozygous point and nonsense mutations that extinguish kinase activity impair primary cilia function, whereas mutations outside the kinase domain are not well understood. Here, we produced a knock-in mouse equivalent to the human CILK1 A615T variant identified in juvenile myoclonic epilepsy (JME). This residue is in the intrinsically disordered C-terminal region of CILK1 separate from the kinase domain. Mouse embryo fibroblasts (MEFs) with either heterozygous or homozygous A612T mutant alleles exhibited a higher ciliation rate, shorter individual cilia, and upregulation of ciliary Hedgehog signaling. Thus, a single A612T mutant allele was sufficient to impair primary cilia and ciliary signaling in MEFs. Gene expression profiles of wild-type versus mutant MEFs revealed profound changes in cilia-related molecular functions and biological processes. The CILK1 A615T mutant protein was not increased to the same level as the wild-type protein when co-expressed with scaffold protein KATNIP (katanin-interacting protein). Our data show that KATNIP regulation of a JME-associated single-residue variant of CILK1 is compromised, and this impairs the maintenance of primary cilia and Hedgehog signaling.

Analysis of clinical characteristics and histopathological transcription in 40 patients afflicted by epilepsy stemming from focal cortical dysplasia

OBJECTIVE

This study aims to comprehensively analyze the clinical characteristics and identify the differentially expressed genes associated with drug-resistant epilepsy (DRE) in patients with focal cortical dysplasia (FCD).

METHODS

A retrospective investigation was conducted from July 2019 to June 2022, involving 40 pediatric cases of DRE linked to FCD. Subsequent follow-ups were done to assess post-surgical outcomes. Transcriptomic sequencing and quantitative reverse transcription polymerase chain reaction (qRT-PCR) were used to examine differential gene expression between the FCD and control groups.

RESULTS

Among the 40 patients included in the study, focal to bilateral tonic-clonic seizures (13/40, 32.50%) and epileptic spasms (9/40, 22.50%) were the predominant seizure types. Magnetic resonance imaging (MRI) showed frequent involvement of the frontal (22/40, 55%) and temporal lobes (12/40, 30%). In cases with negative MRI results (13/13, 100%), positron emission tomography/computed tomography (PET-CT) scans revealed hypometabolic lesions. Fused MRI/PET-CT images demonstrated lesion reduction in 40.74% (11/27) of cases compared with PET-CT alone, while 59.26% (16/27) yielded results consistent with PET-CT findings. FCD type II was identified in 26 cases, and FCD type I in 13 cases. At the last follow-up, 38 patients were prescribed an average of 1.27 ± 1.05 anti-seizure medications (ASMs), with two patients discontinuing treatment. After a postoperative follow-up period of 23.50 months, 75% (30/40) of patients achieved Engel class I outcome. Transcriptomic sequencing and qRT-PCR analysis identified several genes primarily associated with cilia, including CFAP47, CFAP126, JHY, RSPH4A, and SPAG1.

SIGNIFICANCE

This study highlights focal to bilateral tonic-clonic seizures as the most common seizure type in patients with DRE due to FCD. Surgical intervention primarily targeted lesions in the frontal and temporal lobes. Patients with FCD-related DRE showed a promising prognosis for seizure control post-surgery. The identified genes, including CFAP47, CFAP126, JHY, RSPH4A, and SPAG1, could serve as potential biomarkers for FCD.

PLAIN LANGUAGE SUMMARY

This study aimed to comprehensively evaluate the clinical data of individuals affected by focal cortical dysplasia and analyze transcriptomic data from brain tissues. We found that focal to bilateral tonic-clonic seizures were the most prevalent seizure type in patients with drug-resistant epilepsy. In cases treated surgically, the frontal and temporal lobes were the primary sites of the lesions. Moreover, patients with focal cortical dysplasia-induced drug-resistant epilepsy exhibited a favorable prognosis for seizure control after surgery. CFAP47, CFAP126, JHY, RSPH4A, and SPAG1 have emerged as potential pathogenic genes for the development of focal cortical dysplasia.

An epilepsy-associated CILK1 variant compromises KATNIP regulation and impairs primary cilia and Hedgehog signaling

Mutations in human CILK1 (ciliogenesis associated kinase 1) are linked to ciliopathies and epilepsy. Homozygous point and nonsense mutations that extinguish kinase activity impair primary cilia function, whereas mutations outside the kinase domain are not well understood. Here, we produced a knock-in mouse equivalent of the human CILK1 A615T variant identified in juvenile myoclonic epilepsy (JME). This residue is in the C-terminal region of CILK1 separate from the kinase domain. Mouse embryo fibroblasts (MEF) with either heterozygous or homozygous A612T mutant alleles exhibited a higher ciliation rate, shorter individual cilia and up-regulation of ciliary Hedgehog signaling. Thus, a single A612T mutant allele was sufficient to impair primary cilia and ciliary signaling in MEFs. Gene expression profiles of wild type versus mutant MEFs revealed profound changes in cilia-related molecular functions and biological processes. CILK1 A615T mutant protein was not increased to the same level as the wild type protein when co-expressed with scaffold protein KATNIP (katanin-interacting protein). Our data show that KATNIP regulation of a JME-associated single residue variant of CILK1 is compromised and this impairs the maintenance of primary cilia and Hedgehog signaling.

Primary cilia in the postnatal brain: Subcellular compartments for organizing neuromodulatory signaling

Primary cilia have well characterized roles in early brain development, relaying signals critical for neurogenesis and brain formation during embryonic stages. Less understood are the contributions of cilia-mediated signaling to postnatal brain function. Several cilia-localized receptors that bind neuropeptides and neurotransmitters endogenous to the brain have been identified in adult neurons, but the functional significance of signaling through these cilia-localized receptors is largely unexplored. Ciliopathic disorders in humans often manifest with neurodevelopmental abnormalities and cognitive deficits. Intriguingly, recent research has also linked several neuropsychiatric disorders and neurodegenerative diseases to ciliary dysfunction. This review summarizes recent evidence suggesting that cilia signaling may dynamically regulate postnatal neuronal physiology and connectivity, and highlights possible links among cilia, neuronal circuitry, neuron survival, and neurological disorders.

Tumor Treating Fields Suppression of Ciliogenesis Enhances Temozolomide Toxicity

Tumor Treating Fields (TTFields) are low-intensity, alternating intermediate-frequency (200 kHz) electrical fields that extend survival of glioblastoma patients receiving maintenance temozolomide (TMZ) chemotherapy. How TTFields exert efficacy on cancer over normal cells or interact with TMZ is unclear. Primary cilia are microtubule-based organelles triggered by extracellular ligands, mechanical and electrical field stimulation and are capable of promoting cancer growth and TMZ chemoresistance. We found in both low- and high-grade patient glioma cell lines that TTFields ablated cilia within 24 h. Halting TTFields treatment led to recovered frequencies of elongated cilia. Cilia on normal primary astrocytes, neurons, and multiciliated/ependymal cells were less affected by TTFields. The TTFields-mediated loss of glioma cilia was partially rescued by chloroquine pretreatment, suggesting the effect is in part due to autophagy activation. We also observed death of ciliated cells during TTFields by live imaging. Notably, TMZ and TTFields have opposing effects on glioma ciliogenesis. TMZ-induced stimulation of ciliogenesis in both adherent cells and gliomaspheres was blocked by TTFields. Surprisingly, the inhibitory effects of TTFields and TMZ on tumor cell recurrence are linked to the relative timing of TMZ exposure to TTFields and ARL13B⁺ cilia. Finally, TTFields disrupted cilia in patient tumors treated ex vivo. Our findings suggest that the efficacy of TTFields may depend on the degree of tumor ciliogenesis and relative timing of TMZ treatment.

Targeted Ablation of Primary Cilia in Differentiated Dopaminergic Neurons Reduces Striatal Dopamine and Responsiveness to Metabolic Stress

Primary cilia (PC) are microtubule-based protrusions of the cell membrane transducing molecular signals during brain development. Here, we report that PC are required for maintenance of Substantia nigra (SN) dopaminergic (DA) neurons highly vulnerable in Parkinson's disease (PD). Targeted blockage of ciliogenesis in differentiated DA neurons impaired striato-nigral integrity in adult mice. The relative number of SN DA neurons displaying a typical auto-inhibition of spontaneous activity in response to dopamine was elevated under control metabolic conditions, but not under metabolic stress. Strikingly, in the absence of PC, the remaining SN DA neurons were less vulnerable to the PD neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP). Our data indicate conserved PC-dependent neuroadaptive responses to DA lesions in the striatum. Moreover, PC control the integrity and dopamine response of a subtype of SN DA neurons. These results reinforce the critical role of PC as sensors of metabolic stress in PD and other disorders of the dopamine system.

HDAC6 Signaling at Primary Cilia Promotes Proliferation and Restricts Differentiation of Glioma Cells

Simple Summary

Glioblastoma is the most common and lethal brain tumor in adults because it becomes resistant to virtually every treatment. Histone deacetylase 6 (HDAC6), which is located primarily in the cytoplasm, has a unique role in promoting the disassembly of cells’ primary cilium, a non-motile “antenna” that must be broken down before cells can progress through the cell cycle. The role of HDAC6 and its function in gliomas have not been investigated with respect to tumor cell cilia. We have found that inhibitors of HDAC6 cause rapid and specific changes inside glioma cilia, reducing tumor cell proliferative capacity and promoting cell differentiation. Importantly, the HDAC6 inhibitors did not affect the proliferation or differentiation of glioma cells that we genetically modified unable to grow cilia. Our findings reveal a conserved and critical role for HDAC6 in glioma growth that is dependent on cilia.

Abstract

Histone deacetylase 6 (HDAC6) is an emerging therapeutic target that is overexpressed in glioblastoma when compared to other HDACs. HDAC6 catalyzes the deacetylation of alpha-tubulin and mediates the disassembly of primary cilia, a process required for cell cycle progression. HDAC6 inhibition disrupts glioma proliferation, but whether this effect is dependent on tumor cell primary cilia is unknown. We found that HDAC6 inhibitors ACY-1215 (1215) and ACY-738 (738) inhibited the proliferation of multiple patient-derived and mouse glioma cells. While both inhibitors triggered rapid increases in acetylated alpha-tubulin (aaTub) in the cytosol and led to increased frequencies of primary cilia, they unexpectedly reduced the levels of aaTub in the cilia. To test whether the antiproliferative effects of HDAC6 inhibitors are dependent on tumor cell cilia, we generated patient-derived glioma lines devoid of cilia through depletion of ciliogenesis genes ARL13B or KIF3A. At low concentrations, 1215 or 738 did not decrease the proliferation of cilia-depleted cells. Moreover, the differentiation of glioma cells that was induced by HDAC6 inhibition did not occur after the inhibition of cilia formation. These data suggest HDAC6 signaling at primary cilia promotes the proliferation of glioma cells by restricting their ability to differentiate. Surprisingly, overexpressing HDAC6 did not reduce cilia length or the frequency of ciliated glioma cells, suggesting other factors are required to control HDAC6-mediated cilia disassembly in glioma cells. Collectively, our findings suggest that HDAC6 promotes the proliferation of glioma cells through primary cilia.

Analysis of ciliary status via G-protein-coupled receptors localized on primary cilia

G-protein-coupled receptors (GPCRs) comprise the largest and most diverse cell surface receptor family, with more than 800 known GPCRs identified in the human genome. Binding of an extracellular cue to a GPCR results in intracellular G protein activation, after which a sequence of events, can be amplified and optimized by selective binding partners and downstream effectors in spatially discrete cellular environments. Because GPCRs are widely expressed in the body, they help to regulate an incredible range of physiological processes from sensation to growth to hormone responses. Indeed, it is estimated that ∼ 30% of all clinically approved drugs act by binding to GPCRs. The primary cilium is a sensory organelle composed of a microtubule axoneme that extends from the basal body. The ciliary membrane is highly enriched in specific signaling components, allowing the primary cilium to efficiently convey signaling cascades in a highly ordered microenvironment. Recent data demonstrated that a limited number of non-olfactory GPCRs, including somatostatin receptor 3 and melanin-concentrating hormone receptor 1 (MCHR1), are selectively localized to cilia on several mammalian cell types including neuronal cells. Utilizing cilia-specific cell biological and molecular biological approaches, evidence has accumulated to support the biological importance of ciliary GPCR signaling followed by cilia structural changes. Thus, cilia are now considered a unique sensory platform for integration of GPCR signaling toward juxtaposed cytoplasmic structures. Herein, we review ciliary GPCRs and focus on a novel role of MCHR1 in ciliary length control that will impact ciliary signaling capacity and neuronal function.

Neonatal Seizures and Purinergic Signalling

Neonatal seizures are one of the most common comorbidities of neonatal encephalopathy, with seizures aggravating acute injury and clinical outcomes. Current treatment can control early life seizures; however, a high level of pharmacoresistance remains among infants, with increasing evidence suggesting current anti-seizure medication potentiating brain damage. This emphasises the need to develop safer therapeutic strategies with a different mechanism of action. The purinergic system, characterised by the use of adenosine triphosphate and its metabolites as signalling molecules, consists of the membrane-bound P1 and P2 purinoreceptors and proteins to modulate extracellular purine nucleotides and nucleoside levels. Targeting this system is proving successful at treating many disorders and diseases of the central nervous system, including epilepsy. Mounting evidence demonstrates that drugs targeting the purinergic system provide both convulsive and anticonvulsive effects. With components of the purinergic signalling system being widely expressed during brain development, emerging evidence suggests that purinergic signalling contributes to neonatal seizures. In this review, we first provide an overview on neonatal seizure pathology and purinergic signalling during brain development. We then describe in detail recent evidence demonstrating a role for purinergic signalling during neonatal seizures and discuss possible purine-based avenues for seizure suppression in neonates.

Targeted Depletion of Primary Cilia in Dopaminoceptive Neurons in a Preclinical Mouse Model of Huntington's Disease

Multiple pathomechanisms triggered by mutant Huntingtin (mHTT) underlie progressive degeneration of dopaminoceptive striatal neurons in Huntington’s disease (HD). The primary cilium is a membrane compartment that functions as a hub for various pathways that are dysregulated in HD, for example, dopamine (DA) receptor transmission and the mechanistic target of rapamycin (mTOR) pathway. The roles of primary cilia (PC) for the maintenance of striatal neurons and in HD progression remain unknown. Here, we investigated PC defects in vulnerable striatal neurons in a progressive model of HD, the mHTT-expressing knock-in zQ175 mice. We found that PC length is affected in striatal but not in cortical neurons, in association with the accumulation of mHTT. To explore the role of PC, we generated conditional mutant mice lacking IFT88, a component of the anterograde intraflagellar transport-B complex lacking PC in dopaminoceptive neurons. This mutation preserved the expression of the dopamine 1 receptor (D1R), and the survival of striatal neurons, but resulted in a mild increase of DA metabolites in the striatum, suggesting an imbalance of ciliary DA receptor transmission. Conditional loss of PC in zQ175 mice did not trigger astrogliosis, however, mTOR signaling was more active and resulted in a more pronounced accumulation of nuclear inclusions containing mHTT. Further studies will be required of aged mice to determine the role of aberrant ciliary function in more advanced stages of HD.

Effectiveness of low dose of rapamycin in preventing seizure-induced anxiety-like behaviour, cognitive impairment, and defects in neurogenesis in developing rats

Aims: Previous studies have demonstrated that rapamycin prevents seizure-induced anxiety-like behaviors. However, rapamycin had been used at a higher dose of 3 mg/kg and resulted in side effects in immature animals. This work was designed to explore whether a lower dose of rapamycin has similar efficacy but has milder side effects.Methods: Acute seizures were induced by injection of pilocarpine at postnatal 10-day Sprague-Dawley rats. Western blot analysis was used to detect changes in mammalian target of rapamycin (mTOR) pathway after seizure. Immunofluorescent intensity of doublecortin (DCX) was conducted to evaluate the development of neurons in hippocampus. Morris water maze and Y-maze test were used to assess cognitive functions and open-field test and elevated plus maze were used to detect anxiety-like behaviors 4 weeks after seizure onset.Results: mTOR pathway was abnormally activated with two peaks after pilocarpine-induced seizures, and no difference of DCX-positive cells and body weight were noticed between control and pilocarpine-induced seizure rats. Pilocarpine-induced seizure in postnatal 10 days rats did not exert impairment on cognitive functions, but resulted in obvious anxiety-like behaviors. Low dose of rapamycin at 0.3 mg/kg significantly reversed seizure-induced increase of p-S6 levels as well as abnormal anxiety-like behaviors. In addition, rapamycin at the dose of 0.3mg/kg did not affect normal development and cognitive functions.Conclusion: lower doses of rapamycin should be used in infants compared with older children or adults.

Fibroblast Primary Cilia Are Required for Cardiac Fibrosis

BACKGROUND

The primary cilium is a singular cellular structure that extends from the surface of many cell types and plays crucial roles in vertebrate development, including that of the heart. Whereas ciliated cells have been described in developing heart, a role for primary cilia in adult heart has not been reported. This, coupled with the fact that mutations in genes coding for multiple ciliary proteins underlie polycystic kidney disease, a disorder with numerous cardiovascular manifestations, prompted us to identify cells in adult heart harboring a primary cilium and to determine whether primary cilia play a role in disease-related remodeling.

METHODS

Histological analysis of cardiac tissues from C57BL/6 mouse embryos, neonatal mice, and adult mice was performed to evaluate for primary cilia. Three injury models (apical resection, ischemia/reperfusion, and myocardial infarction) were used to identify the location and cell type of ciliated cells with the use of antibodies specific for cilia (acetylated tubulin, γ-tubulin, polycystin [PC] 1, PC2, and KIF3A), fibroblasts (vimentin, α-smooth muscle actin, and fibroblast-specific protein-1), and cardiomyocytes (α-actinin and troponin I). A similar approach was used to assess for primary cilia in infarcted human myocardial tissue. We studied mice silenced exclusively in myofibroblasts for PC1 and evaluated the role of PC1 in fibrogenesis in adult rat fibroblasts and myofibroblasts.

RESULTS

We identified primary cilia in mouse, rat, and human heart, specifically and exclusively in cardiac fibroblasts. Ciliated fibroblasts are enriched in areas of myocardial injury. Transforming growth factor β-1 signaling and SMAD3 activation were impaired in fibroblasts depleted of the primary cilium. Extracellular matrix protein levels and contractile function were also impaired. In vivo, depletion of PC1 in activated fibroblasts after myocardial infarction impaired the remodeling response.

CONCLUSIONS

Fibroblasts in the neonatal and adult heart harbor a primary cilium. This organelle and its requisite signaling protein, PC1, are required for critical elements of fibrogenesis, including transforming growth factor β-1-SMAD3 activation, production of extracellular matrix proteins, and cell contractility. Together, these findings point to a pivotal role of this organelle, and PC1, in disease-related pathological cardiac remodeling and suggest that some of the cardiovascular manifestations of autosomal dominant polycystic kidney disease derive directly from myocardium-autonomous abnormalities.

Quantitative Comparison of Primary Cilia Marker Expression and Length in the Mouse Brain

Primary cilia are small, special cellular organelles that provide important sensory and signaling functions during the development of mammalian organs and coordination of postnatal cellular processes. Dysfunction of primary cilia are thought to be the main cause of ciliopathies, a group of genetic disorders characterized by overlapping developmental defects and prominent neurodevelopmental features. Although, disrupted cilia-linked signaling pathways have been implicated in the regulation of numerous neuronal functions, the precise role of primary cilia in the brain are still unknown. Importantly, studies of recent years have highlighted that different functions of primary cilia are reflected by their diverse morphology and unique signaling components localized in the ciliary membrane. In the present study, we conducted a comparative analysis of the expression pattern, distribution and length of adenylyl cyclase 3, somatostatin receptor 3, and ADP-ribosylation factor-like protein 13B expressing primary cilia in the mouse brain. We show that cilia of neurons and astrocytes display a well characterized distribution and ciliary marker arrangements. Moreover, quantitative comparison of their length, density and occurrence rate revealed that primary cilia exhibit region-specific alternations. In summary, our study provides a comprehensive overview of the cellular organization and morphological traits of primary cilia in regions of the physiological adult mouse brain.

The radial organization of neuronal primary cilia is acutely disrupted by seizure and ischemic brain injury

BACKGROUND

Neuronal primary cilia are sensory organelles that are critically involved in the proper growth, development, and function of the central nervous system (CNS). Recent work also suggests that they signal in the context of CNS injury, and that abnormal ciliary signaling may be implicated in neurological diseases.

METHODS

We quantified the distribution of neuronal primary cilia alignment throughout the normal adult mouse brain by immunohistochemical staining for the primary cilia marker adenylyl cyclase III (ACIII) and measuring the angles of primary cilia with respect to global and local coordinate planes. We then introduced two different models of acute brain insult-temporal lobe seizure and cerebral ischemia, and re-examined neuronal primary cilia distribution, as well as ciliary lengths and the proportion of neurons harboring cilia.

RESULTS

Under basal conditions, cortical cilia align themselves radially with respect to the cortical surface, while cilia in the dentate gyrus align themselves radially with respect to the granule cell layer. Cilia of neurons in the striatum and thalamus, by contrast, exhibit a wide distribution of ciliary arrangements. In both cases of acute brain insult, primary cilia alignment was significantly disrupted in a region-specific manner, with areas affected by the insult preferentially disrupted. Further, the two models promoted differential effects on ciliary lengths, while only the ischemia model decreased the proportion of ciliated cells.

CONCLUSIONS

These findings provide evidence for the regional anatomical organization of neuronal primary cilia in the adult brain and suggest that various brain insults may disrupt this organization.

Primary cilia as a novel horizon between neuron and environment

The primary cilium, a hair-like sensory organelle found on most mammalian cells, has gained recent attention within the field of neuroscience. Although neural primary cilia have been known to play a role in embryonic central nervous system patterning, we are just beginning to appreciate their importance in the mature organism. After several decades of investigation and controversy, the neural primary cilium is emerging as an important regulator of neuroplasticity in the healthy adult central nervous system. Further, primary cilia have recently been implicated in disease states such as cancer and epilepsy. Intriguingly, while primary cilia are expressed throughout the central nervous system, their structure, receptors, and signaling pathways vary by anatomical region and neural cell type. These differences likely bear relevance to both their homeostatic and neuropathological functions, although much remains to be uncovered. In this review, we provide a brief historical overview of neural primary cilia and highlight several key advances in the field over the past few decades. We then set forth a proposed research agenda to fill in the gaps in our knowledge regarding how the primary cilium functions and malfunctions in nervous tissue, with the ultimate goal of targeting this sensory structure for neural repair following injury.