Olfactory Sensory Neurons Axons Research Articles

The Molecular Basis of Olfactory Dysfunction in COVID-19 and Long COVID.

Olfactory dysfunction (OD) is not uncommon following viral infection. Herein, we explore the interplay of host genetics with viral correlates in coronavirus disease 2019 (COVID-19)- and long COVID-related OD, and its diagnosis and treatment that remain challenging. Two genes associated with olfaction, UGT2A1 and UGT2A2, appear to be involved in COVID-19-related anosmia, a hallmark symptom of acute infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), particularly in the early stages of the pandemic. SARS-CoV-2 infects olfactory support cells, sustentacular and Bowman gland cells, that surround olfactory sensory neurons (OSNs) in the olfactory epithelium (OE) where the initial step of odor detection takes place. Anosmia primarily arises from the infection of support cells of the OE, followed by the deciliation and disruption of OE integrity, typically without OSN infection. Through the projected axons of OSNs, the virus could theoretically reach the olfactory bulb and brain, but current evidence points against this route. Intriguingly, SARS-CoV-2 infection of support cells leads to profound alterations in the nuclear architecture of OSNs, leading to the downregulation of odorant receptor-related genes, e.g., of Adcy3. Viral factors associated with the development of OD include spike protein aminoacidic changes, e.g., D614G, the first substitution that was selected early during SARS-CoV-2 evolution. More recent variants of the Omicron family are less likely to cause OD compared to Delta or Alpha, although OD has been associated with a milder disease course. OD is one of the most prevalent post-acute neurologic symptoms of SARS-CoV-2 infection. The tens of millions of people worldwide who have lingering problems with OD wait eagerly for effective new treatments that will restore their sense of smell which adds value to their quality of life.

WAPL functions as a rheostat of Protocadherin isoform diversity that controls neural wiring.

Neural type-specific expression of clustered Protocadherin (Pcdh) proteins is essential for the establishment of connectivity patterns during brain development. In mammals, deterministic expression of the same Pcdh isoform promotes minimal overlap of tiled projections of serotonergic neuron axons throughout the brain, while stochastic expression of Pcdh genes allows for convergence of tightly packed, overlapping olfactory sensory neuron axons into targeted structures. How can the same gene locus generate opposite transcriptional programs that orchestrate distinct spatial arrangements of axonal patterns? Here, we reveal that cell type-specific Pcdh expression and axonal behavior depend on the activity of cohesin and its unloader, WAPL (wings apart-like protein homolog). While cohesin erases genomic-distance biases in Pcdh choice, WAPL functions as a rheostat of cohesin processivity that determines Pcdh isoform diversity.

Axonal mRNA binding of hnRNP A/B is crucial for axon targeting and maturation of olfactory sensory neurons

Spatiotemporal control of gene expression is important for neural development and function. Here, we show that heterogeneous nuclear ribonucleoprotein (hnRNP) A/B is highly expressed in developing olfactory sensory neurons (OSNs), and its knockout results in reduction in mature OSNs and aberrant targeting of OSN axons to the olfactory bulb. RNA immunoprecipitation analysis reveals that hnRNP A/B binds to a group of mRNAs that are highly related to axon projections and synapse assembly. Approximately 11% of the identified hnRNP A/B targets, including Pcdha and Ncam2, encode cell adhesion molecules. In Hnrnpab knockout mice, PCDHA and NCAM2 levels are significantly reduced at the axon terminals of OSNs. Furthermore, deletion of the hnRNP A/B-recognition motif in the 3' UTR of Pcdha leads to impaired PCDHA expression at the OSN axon terminals. Therefore, we propose that hnRNP A/B facilitates OSN maturation and axon projection by regulating the local expression of its target genes at axon terminals.

Role of serotonin in modulating the development and function of adult-born neurons in the olfactory bulb.

Role of serotonin in modulating the development and function of adult-born neurons in the olfactory bulb.

Molecular and structural basis of olfactory sensory neuron axon coalescence by Kirrel receptors.

SUMMARYProjections from sensory neurons of olfactory systems coalesce into glomeruli in the brain. The Kirrel receptors are believed to homodimerize via their ectodomains and help separate sensory neuron axons into Kirrel2- or Kirrel3-expressing glomeruli. Here, we present the crystal structures of homodimeric Kirrel receptors and show that the closely related Kirrel2 and Kirrel3 have evolved specific sets of polar and hydrophobic interactions, respectively, disallowing heterodimerization while preserving homodimerization, likely resulting in proper segregation and coalescence of Kirrel-expressing axons into glomeruli. We show that the dimerization interface at the N-terminal immunoglobulin (IG) domains is necessary and sufficient to create homodimers and fail to find evidence for a secondary interaction site in Kirrel ectodomains. Furthermore, we show that abolishing dimerization of Kirrel3 in vivo leads to improper formation of glomeruli in the mouse accessory olfactory bulb as observed in Kirrel3−/− animals. Our results provide evidence for Kirrel3 homodimerization controlling axonal coalescence.

Novel factor in olfactory ensheathing cell-astrocyte crosstalk: Anti-inflammatory protein α-crystallin B.

Astrocytes are key players in CNS neuroinflammation and neuroregeneration that may help or hinder recovery, depending on the context of the injury. Although pro-inflammatory factors that promote astrocyte-mediated neurotoxicity have been shown to be secreted by reactive microglia, anti-inflammatory factors that suppress astrocyte activation are not well-characterized. Olfactory ensheathing cells (OECs), glial cells that wrap axons of olfactory sensory neurons, have been shown to moderate astrocyte reactivity, creating an environment conducive to regeneration. Similarly, astrocytes cultured in medium conditioned by cultured OECs (OEC-CM) show reduced nuclear translocation of nuclear factor kappa-B (NFκB), a pro-inflammatory protein that induces neurotoxic reactivity in astrocytes. In this study, we screened primary and immortalized OEC lines to identify these factors and discovered that Alpha B-crystallin (CryAB), an anti-inflammatory protein, is secreted by OECs via exosomes, coordinating an intercellular immune response. Our results showed that: (a) OEC exosomes block nuclear NFκB translocation in astrocytes while exosomes from CryAB-null OECs could not; (b) OEC exosomes could be taken up by astrocytes, and (c) CryAB treatment suppressed neurotoxicity-associated astrocyte transcripts. Our results indicate CryAB, as well as other factors secreted by OECs, are potential agents that can ameliorate, or even reverse, the growth-inhibitory environment created by neurotoxic reactive astrocytes following CNS injuries.

Antagonistic odor interactions in olfactory sensory neurons are widespread in freely breathing mice

Odor landscapes contain complex blends of molecules that each activate unique, overlapping populations of olfactory sensory neurons (OSNs). Despite the presence of hundreds of OSN subtypes in many animals, the overlapping nature of odor inputs may lead to saturation of neural responses at the early stages of stimulus encoding. Information loss due to saturation could be mitigated by normalizing mechanisms such as antagonism at the level of receptor-ligand interactions, whose existence and prevalence remains uncertain. By imaging OSN axon terminals in olfactory bulb glomeruli as well as OSN cell bodies within the olfactory epithelium in freely breathing mice, we find widespread antagonistic interactions in binary odor mixtures. In complex mixtures of up to 12 odorants, antagonistic interactions are stronger and more prevalent with increasing mixture complexity. Therefore, antagonism is a common feature of odor mixture encoding in OSNs and helps in normalizing activity to reduce saturation and increase information transfer.

Functional morphology of the primary olfactory centers in the brain of the hermit crab Coenobita clypeatus (Anomala, Coenobitidae)

Terrestrial hermit crabs of the genus Coenobita display strong behavioral responses to volatile odors and are attracted by chemical cues of various potential food sources. Several aspects of their sense of aerial olfaction have been explored in recent years including behavioral aspects and structure of their peripheral and central olfactory pathway. Here, we use classical histological methods and immunohistochemistry against the neuropeptides orcokinin and allatostatin as well as synaptic proteins and serotonin to provide insights into the functional organization of their primary olfactory centers in the brain, the paired olfactory lobes. Our results show that orcokinin is present in the axons of olfactory sensory neurons, which target the olfactory lobe. Orcokinin is also present in a population of local olfactory interneurons, which may relay lateral inhibition across the array of olfactory glomeruli within the lobes. Extensive lateral connections of the glomeruli were also visualized using the histological silver impregnation method according to Holmes-Blest. This technique also revealed the structural organization of the output pathway of the olfactory system, the olfactory projection neurons, the axons of which target the lateral protocerebrum. Within the lobes, the course of their axons seems to be reorganized in an axon-sorting zone before they exit the system. Together with previous results, we combine our findings into a model on the functional organization of the olfactory system in these animals.

Zebrafish Astroglial Morphology in the Olfactory Bulb Is Altered With Repetitive Peripheral Damage.

Zebrafish do not possess the typical astrocytes that are found in mammalian systems. In some brain areas, this teleost has radial glia that appears to perform astrocyte-like functions, but these cells have not been described in the zebrafish olfactory bulb. Mammalian astrocytes facilitate neuroplasticity and undergo astrogliosis after insult. The role of these cells in the zebrafish olfactory system after the damage has been poorly explored. This is important to examine because zebrafish have a high degree of neuroplasticity and the olfactory bulb is a brain area renowned for plasticity. The goal of this study was to explore the potential role of zebrafish astrocytes in the olfactory bulb damage response, with a goal to exploit the high level of regeneration in this system. We found that anti-glial fibrillary acidic protein (GFAP) labels numerous processes in the zebrafish olfactory bulb that are concentrated in the nerve and glomerular layers (GL) and do not show radial glial-like morphology. We propose to term this astroglia, since their location and response to damage suggests that they are similar in function to the mammalian astrocyte. To induce repetitive peripheral damage to the olfactory organ, a wax plug was inserted into the nasal cavity of adult zebrafish every 12 h for up to 7 days; this crushes the olfactory organ and leads to degradation of olfactory sensory neuron axons that project to the olfactory bulb. After 1 day, we found a significant increase in astroglial labeling in the affected bulb when compared to the internal control bulb and astroglial branches appeared to increase in number and size. By the third day of plug insertions there was no significant difference in astroglial labeling between the affected bulb and the internal control bulb. These data lead us to believe that astrogliosis does occur in the presence of peripheral damage, but this process attenuates within 1 week and no glial scar is evident upon recovery from the damage. Further exploration of astrocytes in zebrafish, in particular this apparent attenuation of astrogliosis, has the potential to elucidate key differences in glial function between teleosts and mammals.

Role of Axonal Odorant Receptors in Olfactory Topography.

A unique feature in the organization of the olfactory system is the dual role of the odorant receptors: they detect odors in the nasal epithelium and they play an instructive role in the convergence of olfactory sensory neuron axons in specific loci, ie, glomeruli, in the olfactory bulb. The dual role is corroborated by the expression of the odorant receptors in 2 specific locations of the olfactory sensory neurons: the cilia that protrude in the nostril, where the odorant receptors interact with odors, and the axon terminal, a suitable location for a potential axon guidance molecule. The mechanism of activation and function of the odorant receptors expressed at the axon terminal remained unknown for almost 20 years. A recent study identified the first putative ligand of the axonal odorant receptors, phosphatidylethanolamine-binding protein1, a molecule expressed in the olfactory bulb. The distinctive mechanisms of activation of the odorant receptors expressed at the opposite locations in sensory neurons, by odors, at the cilia, and by molecules expressed in the olfactory bulb, at the axon terminal, explain the dual role of the odorant receptors and link the specificity of odor perception with its internal representation, in the topographic map.

Olfactory ensheathing cells from the nasal mucosa and olfactory bulb have distinct membrane properties.

Transplantation of olfactory ensheathing cells (OECs) is a potential therapy for the regeneration of damaged neurons. While they maintain tissue homeostasis in the olfactory mucosa (OM) and olfactory bulb (OB), their regenerative properties also support the normal sense of smell by enabling continual turnover and axonal regrowth of olfactory sensory neurons (OSNs). However, the molecular physiology of OECs is not fully understood, especially that of OECs from the mucosa. Here, we carried out whole-cell patch-clamp recordings from individual OECs cultured from the OM and OB of the adult rat, and from the human OM. A subset of OECs from the rat OM cultured 1-3days in vitro had large weakly rectifying K+ currents, which were sensitive to Ba2+ and desipramine, blockers of Kir4-family channels. Kir4.1 immunofluorescence was detectable in cultured OM cells colabeled for the OEC marker S100, and in S100-labeled cells found adjacent to OSN axons in mucosal sections. OECs cultured from rat OB had distinct properties though, displaying strongly rectifying inward currents at hyperpolarized membrane potentials and strongly rectifying outward currents at depolarized potentials. Kir4.1 immunofluorescence was not evident in OECs adjacent to axons of OSNs in the OB. A subset of human OECs cultured from the OM of adults had membrane properties comparable to those of the rat OM that is dominated by Ba2+ -sensitive weak inwardly rectifying currents. The membrane properties of peripheral OECs are different to those of central OECs, suggesting they may play distinct roles during olfaction.

Sequential Maturation of Olfactory Sensory Neurons in the Mature Olfactory Epithelium.

The formation of the olfactory nerve and olfactory bulb (OB) glomeruli begins embryonically in mice. However, the development of the olfactory system continues throughout life with the addition of new olfactory sensory neurons (OSNs) in the olfactory epithelium (OE). Much attention has been given to the perinatal innervation of the OB by OSN axons, but in the young adult the process of OSN maturation and axon targeting to the OB remains controversial. To address this gap in understanding, we used BrdU to label late-born OSNs in young adult mice at postnatal day 25 (P25-born OSNs) and timed their molecular maturation following basal cell division. We show that OSNs in young adults undergo a sequential molecular development with the expression of GAP 43 (growth-associated protein 43) > AC3 (adenylyl cyclase 3) > OMP (olfactory marker protein), consecutively, in a time frame of ∼8 d. To assess OSN axon development, we implemented an in vivo fate-mapping strategy to label P25-born OSNs with ZsGreen. Using sampling intervals of 24 h, we demonstrate the progressive extension of OSN axons in the OE, through the foramen of the cribriform plate, and onto the surface of the OB. OSN axons reached the OB and began to target and robustly innervate specific glomeruli ∼10 d following basal cell division, a time point at which OMP expression becomes evident. Our data demonstrate a sequential process of correlated axon extension and molecular maturation that is similar to that seen in the neonate, but on a slightly longer timescale and with regional differences in the OE.

Experience‐dependent axon targeting in the olfactory system

Olfactory sensory neurons that express the same olfactory receptors are scattered in the olfactory epithelium (OE) and their axons coalesce into a few bundles of axons or glomeruli on each olfactory bulb. A single odorant particle binds to specific olfactory receptors (OR) and activates a pattern of glomeruli, facilitating the ability to smell. The mechanism wherein these OSN coalesce is still unclear. As a step toward understanding glomeruli map formation, we determined the effect of postnatal odor experience on OSN axon targeting of two related ORs, muscarinic type 71 (M71) and type 72 (M72) using a cognate ligand, 2‐hydroxyacetophenone. M71 and M72 differ in only 11 amino acid sequences and therefore respond to an overlapping set of odorants.We obtained mice that express both M71 and M72 receptors and exposed them to 1/1000 of 2‐hydroxyacetophone for 16 hours intervals daily from birth to day 21. Mice were sacrificed at day 21 and dissected to view their olfactory bulb under fluorescence microscope that highlighted M71 glomeruli with green signal and M72 glomeruli with red signal. M71 and M72 glomeruli were categorized as intermingling, adjacent, or separate based on their proximity on the olfactory bulb.Mice stimulated with 1/1000 2‐hydroxyacetophone had M71 and M72 glomeruli at closer distances in the olfactory bulb than control. The distance was analyzed according to minimum distances between each glomerulus, which was done by collecting the pixel coordinates of each object and determining the pair of coordinates between the two glomeruli with a minimum distance. We found that odor experience affected M71 and M72 olfactory sensory neurons (OSNs) that their axons coalesced onto closer glomeruli in the olfactory bulb compared to control mice.Support or Funding InformationFunding Acknowledgements: Research Supplement to Promote Diversity in Health‐Related Research, National Institute of Deafness and other Communication Disorders (NIDCD).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Selective Cre-mediated gene deletion identifies connexin 43 as the main connexin channel supporting olfactory ensheathing cell networks.

Many functions of glial cells depend on the formation of selective glial networks mediated by gap junctions formed by members of the connexin family. Olfactory ensheathing cells (OECs) are specialized glia associated with olfactory sensory neuron axons. Like other glia, they form selective networks, however, the connexins that support OEC connectivity in vivo have not been identified. We used an in vivo mouse model to selectively delete candidate connexin genes with temporal control from OECs and address the physiological consequences. Using this model, we effectively abolished the expression of connexin 43 (Cx43) in OECs in both juvenile and adult mice. Cx43-deleted OECs exhibited features consistent with the loss of gap junctions including reduced membrane conductance, largely reduced sensitivity to the gap junction blocker meclofenamic acid and loss of dye coupling. This indicates that Cx43, a typically astrocytic connexin, is the main connexin forming functional channels in OECs. Despite these changes in functional properties, the deletion of Cx43 deletion did not alter the density of OECs. The strategy used here may prove useful to delete other candidate genes to better understand the functional roles of OECs in vivo.

Primary dendrites of mitral cells synapse unto neighboring glomeruli independent of their odorant receptor identity

In the mouse olfactory bulb, neural map topography is largely established by axon–axon interactions of olfactory sensory neurons (OSNs). However, to make the map functional, the OSNs must make proper connections to second-order neurons, the mitral cells. How do the mitral-cell dendrites find their partner glomeruli for synapse formation with OSN axons? Here, we analyze dendrite connections of mitral cells in various mutant mice in which glomerular formation is perturbed. Our present results support the proximity model, whereby mitral cells tend to connect primary dendrites to the nearest neighboring glomeruli regardless of their odorant receptor identities. The physical location of glomeruli rather than the odorant-receptor specificity appears to play a key role in matching mitral cells with their partner OSN axons.

Kirrel2 is differentially required in populations of olfactory sensory neurons for the targeting of axons in the olfactory bulb.

The formation of olfactory maps in the olfactory bulb (OB) is crucial for the control of innate and learned mouse behaviors. Olfactory sensory neurons (OSNs) expressing a specific odorant receptor project axons into spatially conserved glomeruli within the OB and synapse onto mitral cell dendrites. Combinatorial expression of members of the Kirrel family of cell adhesion molecules has been proposed to regulate OSN axonal coalescence; however, loss-of-function experiments have yet to establish their requirement in this process. We examined projections of several OSN populations in mice that lacked either Kirrel2 alone, or both Kirrel2 and Kirrel3. Our results show that Kirrel2 and Kirrel3 are dispensable for the coalescence of MOR1-3-expressing OSN axons to the most dorsal region (DI) of the OB. In contrast, loss of Kirrel2 caused MOR174-9- and M72-expressing OSN axons, projecting to the DII region, to target ectopic glomeruli. Our loss-of-function approach demonstrates that Kirrel2 is required for axonal coalescence in subsets of OSNs that project axons to the DII region and reveals that Kirrel2/3-independent mechanisms also control OSN axonal coalescence in certain regions of the OB.

Olfactory marker protein (OMP) regulates formation and refinement of the olfactory glomerular map

Inputs from olfactory sensory neuron (OSN) axons expressing the same type of odorant receptor (OR) converge in the glomerulus of the main olfactory bulb. A key marker of mature OSNs is olfactory marker protein (OMP), whose deletion has been associated with deficits in OSN signal transduction and odor discrimination. Here, we investigate glomerular odor responses and anatomical architecture in mice in which one or both alleles of OMP are replaced by the fluorescent synaptic activity reporter, synaptopHluorin. Functionally heterogeneous glomeruli, that is, ones with microdomains with distinct odor responses, are rare in OMP+/– mice, but occur frequently in OMP–/– mice. Genetic targeting of single ORs reveals that these microdomains arise from co-innervation of individual glomeruli by OSNs expressing different ORs. This glomerular mistargeting is locally restricted to a few glomerular diameters. Our studies document functional heterogeneity in sensory input within individual glomeruli and uncover its anatomical correlate, revealing an unexpected role for OMP in the formation and refinement of the glomerular map.

Neuroplastic changes in the olfactory bulb associated with nasal inflammation in mice

Rhinitis and rhinosinusitis are olfactory disorders caused by inflammation of the nasal passage and paranasal sinuses. Although patients with chronic rhinosinusitis have smaller olfactory bulbs (OBs), there is limited knowledge regarding the influence of chronic nasal inflammation on OB neurons. Repeated intranasal administration of LPS that induced persistent nasal inflammation in mice caused a loss of olfactory sensory neurons (OSNs) and gliosis and synaptic loss in the OBs within 3weeks. The present study aimed to clarify the effects of long-term LPS treatment on the OB neurocircuit. LPS was repeatedly administered into a mouse nostril for up to 24weeks. For the recovery analyses, the mice received LPS for 10weeks and were subsequently maintained without additional treatment for another 10weeks. The effects of these treatments on the OBs were examined histologically. Three or more mice were analyzed per group. Long-term repeated LPS administration caused OB atrophy, particularly in the layers along which OSN axons travel and in the superficial external plexiform layer, in which tufted cells form synapses with interneurons. Interestingly, the OBs recovered from atrophy after cessation of LPS administration: OB volume and superficial external plexiform layer thickness returned to pretreatment levels after the nontreatment period. In contrast, OSN regeneration was incomplete. These results suggest that chronic nasal inflammation induces structural changes in a specific OB circuit related to tufted cells, whereas tufted cells retain a high degree of plasticity that enables recovery from structural damages after inflammation subsides.

Low survival rate of young adult-born olfactory sensory neurons in the undamaged mouse olfactory epithelium.

Olfactory sensory neurons (OSNs) are generated throughout life from progenitor cells in the olfactory epithelium. OSN axons project in an odorant receptor-specific manner to the olfactory bulb (OB), forming an ordered array of glomeruli where they provide sensory input to OB neurons. The tetracycline transactivator (tTA) system permits developmental stage-specific expression of reporter genes in OSNs and has been widely used for structural and functional studies of the development and plasticity of the mouse olfactory system. However, the cellular ages at which OSNs stop expressing reporters driven by the immature OSN-specific Gγ8-tTA driver line and begin to express reporters driven by the mature OSN-specific OMP-tTA driver line have not been directly determined. We pulse-labeled terminally dividing cells in the olfactory epithelium of 28-day-old (P28) mice with EdU and analyzed EdU labeling in OSNs expressing fluorescent reporter proteins under control of either the Gγ8-tTA or OMP-tTA driver line 5-14days later. Expression of OMP-tTA-driven reporters began in 6-day-old OSNs, while the vast majority of newborn OSNs did not express Gγ8-tTA-driven fluorescent proteins beyond 8days of cellular age. Surprisingly, we also found a low survival rate for P28-born OSNs, very few of which survived for more than 14days. We propose that OSN survival requires the formation of stable synaptic connections and hence may be dependent on organismal age.

Peripheral Gene Therapeutic Rescue of an Olfactory Ciliopathy Restores Sensory Input, Axonal Pathfinding, and Odor-Guided Behavior.

Cilia of olfactory sensory neurons (OSNs) are the primary site of odor binding; hence, their loss results in anosmia, a clinical manifestation of pleiotropic ciliopathies for which there are no curative therapies. We used OSN-specific Ift88 knock-out mice (Ift88osnKO) of both sexes to examine the mechanisms of ciliopathy-induced olfactory dysfunction and the potential for gene replacement to rescue odorant detection, restore olfactory circuitry, and restore odor-guided behaviors. Loss of OSN cilia in Ift88osnKO mice resulted in substantially reduced odor detection and odor-driven synaptic activity in the olfactory bulb (OB). Defects in OSN axon targeting to the OB were also observed in parallel with aberrant odor-guided behavior. Intranasal gene delivery of wild-type IFT88 to Ift88osnKO mice rescued OSN ciliation and peripheral olfactory function. Importantly, this recovery of sensory input in a limited number of mature OSNs was sufficient to restore axonal targeting in the OB of juvenile mice, and with delayed onset in adult mice. In addition, restoration of sensory input re-established course odor-guided behaviors. These findings highlight the spare capacity of the olfactory epithelium and the plasticity of primary synaptic input into the central olfactory system. The restoration of peripheral and central neuronal function supports the potential for treatment of ciliopathy-related anosmia using gene therapy.SIGNIFICANCE STATEMENT Ciliopathies, for which there are no curative therapies, are genetic disorders that alter cilia morphology and/or function in numerous tissue types, including the olfactory system, leading to sensory dysfunction. We show that in vivo intranasal gene delivery restores peripheral olfactory function in a ciliopathy mouse model, including axonal targeting in the juvenile and adult olfactory bulb. Gene therapy also demonstrated restoration of olfactory perception by rescuing odor-guided behaviors. Understanding the therapeutic window and viability for gene therapy to restore odor detection and perception may facilitate translation of therapies to ciliopathy patients with olfactory dysfunctions.