Type 2 vomeronasal receptor-A4 subfamily: Potential predator sensors in mice.

Sensory signals detected by olfactory sensory organs are critical regulators of animal behavior. An accessory olfactory organ, the vomeronasal organ, detects cues from other animals and plays a pivotal role in intra- and inter-species interactions in mice. However, how ethologically relevant cues control mouse behavior through approximately 350 vomeronasal sensory receptor proteins largely remains elusive. The type 2 vomeronasal receptor-A4 (V2R-A4) subfamily members have been repeatedly detected from vomeronasal sensory neurons responsive to predator cues, suggesting a potential role of this receptor subfamily as a sensor for predators. This review focuses on this intriguing subfamily, delving into its receptor functions and genetic characteristics.

Epigenetic programming of stochastic olfactory receptor choice.

The mammalian sense of smell relies upon a vast array of receptor proteins to detect odorant compounds present in the environment. The proper deployment of these receptor proteins in olfactory sensory neurons is orchestrated by a suite of epigenetic processes that remodel the olfactory genes in differentiating neuronal progenitors. The goal of this review is to elucidate the central role of gene regulatory processes acting in neuronal progenitors of olfactory sensory neurons that lead to a singular expression of an odorant receptor in mature olfactory sensory neurons. We begin by describing the principal features of odorant receptor gene expression in mature olfactory sensory neurons. Next, we delineate our current understanding of how these features emerge from multiple gene regulatory mechanisms acting in neuronal progenitors. Finally, we close by discussing the key gaps in our understanding of how these regulatory mechanisms work and how they interact with each other over the course of differentiation.

Histological evaluation of the alpaca (Vicugna pacos) vomeronasal organ.

Little is known about the neuronal structure of the vomeronasal organ (VNO), a receptor organ responsible for pheromone perception, in the alpaca (Vicugna pacos). This study was performed to determine the localization of neuronal elements, including protein gene product 9.5 (PGP 9.5), a pan-neuronal marker, olfactory marker protein (OMP), a marker of mature olfactory receptor cells, and phospholipase C beta 2 (PLC-ß2), a marker of solitary chemoreceptor cells (SCCs), in the VNO. OMP was identified in receptor cells of the vomeronasal sensory epithelium (VSE), while PGP 9.5 and PLC-ß2 were localized in both the VSE and vomeronasal non-sensory epithelium. Collectively, these results suggested that the alpaca VNO possesses SCCs and olfactory receptor cells, which recognize both harmful substances and pheromones.

S100Z is expressed in a lateral subpopulation of olfactory receptor neurons in the main olfactory system of Xenopus laevis.

In contrast to other S100 protein members, the function of S100 calcium-binding protein Z (S100Z) remains largely uncharacterized. It is expressed in the olfactory epithelium of fish, and it is closely associated with the vomeronasal organ (VNO) in mammals. In this study, we analyzed the expression pattern of S100Z in the olfactory system of the anuran amphibian Xenopus laevis. Using immunohistochemistry in whole mount and slice preparations of the larval olfactory system, we found exclusive S100Z expression in a subpopulation of olfactory receptor neurons (ORNs) of the main olfactory epithelium (MOE). S100Z expression was not co-localized with TP63 and cytokeratin type II, ruling out basal cell and supporting cell identity. The distribution of S100Z-expressing ORNs was laterally biased, and their average number was significantly increased in the lateral half of the olfactory epithelium. The axons of S100Z-positive neurons projected exclusively into the lateral and intermediate glomerular clusters of the main olfactory bulb (OB). Even after metamorphic restructuring of the olfactory system, S100Z expression was restricted to a neuronal subpopulation of the MOE, which was then located in the newly formed middle cavity. An axonal projection into the ventro-lateral OB persisted also in postmetamorphic frogs. In summary, S100Z is exclusively associated with the main olfactory system in the amphibian Xenopus and not with the VNO as in mammals, despite the presence of a separate accessory olfactory system in both classes.

The vomeronasal system of the wolf (Canis lupus signatus): The singularities of a wild canid.

Wolves, akin to their fellow canids, extensively employ chemical signals for various aspects of communication, including territory maintenance, reproductive synchronisation and social hierarchy signalling. Pheromone-mediated chemical communication operates unconsciously among individuals, serving as an innate sensory modality that regulates both their physiology and behaviour. Despite its crucial role in the life of the wolf, there is a lacuna in comprehensive research on the neuroanatomical and physiological underpinnings of chemical communication within this species. This study investigates the vomeronasal system (VNS) of the Iberian wolf, simultaneously probing potential alterations brought about by dog domestication. Our findings demonstrate the presence of a fully functional VNS, vital for pheromone-mediated communication, in the Iberian wolf. While macroscopic similarities between the VNS of the wolf and the domestic dog are discernible, notable microscopic differences emerge. These distinctions include the presence of neuronal clusters associated with the sensory epithelium of the vomeronasal organ (VNO) and a heightened degree of differentiation of the accessory olfactory bulb (AOB). Immunohistochemical analyses reveal the expression of the two primary families of vomeronasal receptors (V1R and V2R) within the VNO. However, only the V1R family is expressed in the AOB. These findings not only yield profound insights into the VNS of the wolf but also hint at how domestication might have altered neural configurations that underpin species-specific behaviours. This understanding holds implications for the development of innovative strategies, such as the application of semiochemicals for wolf population management, aligning with contemporary conservation goals.

Hair from sexually active bucks strongly activates olfactory sensory inputs but fails to trigger early first ovulation in prepubescent does.

Early exposure of does to sexually active bucks triggers early puberty onset correlating with neuroendocrine changes. However, the sensory pathways that are stimulated by the male are still unknown. Here, we assessed whether responses to olfactory stimuli are modulated by social experience (exposure to males or not) and/or endocrine status (prepubescent or pubescent). We used a calcium imaging approach on goat sensory cells from the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). For both cell types, we observed robust responses to active male hair in females under three physiological conditions: prepubescent females isolated from males (ISOL PrePub), pubescent females exposed to males (INT Pub) and isolated females (ISOL Pub). Response analysis showed overall greater proportion of responses to buck hair in ISOL PrePub. We hypothesized that females would be more responsive to active buck hair during the prepubertal period, with numerous responses perhaps originating from immature neurons. We also observed a greater proportion of mature olfactory neurons in the MOE and VNO of INT Pub females suggesting that male exposure can induce plastic changes on olfactory cell function and organization. To determine whether stimulation by male odor can advance puberty, we exposed prepubescent does to active buck hair (ODOR). In both ODOR and females isolated from males (ISOL) groups, puberty was reached one month after females exposed to intact bucks (INT), suggesting that olfactory stimulation is not sufficient to trigger puberty.

Connectivity and molecular profiles of Foxp2- and Dbx1-lineage neurons in the accessory olfactory bulb and medial amygdala.

In terrestrial vertebrates, the olfactory system is divided into main (MOS) and accessory (AOS) components that process both volatile and nonvolatile cues to generate appropriate behavioral responses. While much is known regarding the molecular diversity of neurons that comprise the MOS, less is known about the AOS. Here, focusing on the vomeronasal organ (VNO), the accessory olfactory bulb (AOB), and the medial amygdala (MeA), we reveal that populations of neurons in the AOS can be molecularly subdivided based on their ongoing or prior expression of the transcription factors Foxp2 or Dbx1, which delineate separate populations of GABAergic output neurons in the MeA. We show that a majority of AOB neurons that project directly to the MeA are of the Foxp2 lineage. Using single-neuron patch-clamp electrophysiology, we further reveal that in addition to sex-specific differences across lineage, the frequency of excitatory input to MeA Dbx1- and Foxp2-lineage neurons differs between sexes. Together, this work uncovers a novel molecular diversity of AOS neurons, and lineage and sex differences in patterns of connectivity.

Expression patterns of the transcription factors Fezf1, Fezf2, and Bcl11b in the olfactory organs of turtle embryos.

Many tetrapod vertebrates have two distinct olfactory organs, the olfactory epithelium (OE) and vomeronasal organ (VNO). In turtles, the olfactory organ consists of two types of sensory epithelia, the upper chamber epithelium (UCE; corresponding to the OE) and the lower chamber epithelium (LCE; corresponding to the VNO). In many turtle species, the UCE contains ciliated olfactory receptor cells (ORCs) and the LCE contains microvillous ORCs. To date, several transcription factors involved in the development of the OE and VNO have been identified in mammals. Fez family zinc-finger protein 1 and 2 (Fezf1 and 2) are expressed in the OE and VNO, respectively, of mouse embryos, and are involved in the development and maintenance of ORCs. B-cell lymphoma/leukemia 11B (Bcl11b) is expressed in the mouse embryo OE except the dorsomedial parts of the nasal cavity, and regulates the expression of odorant receptors in the ORCs. In this study, we examined the expression of Fezf1, Fezf2, and Bcl11b in the olfactory organs of embryos in three turtle species, Pelodiscus sinensis, Trachemys scripta elegans, and Centrochelys sulcata, to evaluate their involvement in the development of reptile olfactory organs. In all three turtle species, Bcl11b was expressed in the UCE, Fezf2 in the LCE, and Fezf1 in both the UCE and LCE. These results imply that the roles of the transcription factors Fezf1, Fezf2, and Bcl11b in olfactory organ development are conserved among mammals and turtles.

Sexual discrimination and attraction through scents in the water vole, Arvicola terrestris.

In mammals, especially rodents, social behaviours, such as parenting, territoriality or mate attraction, are largely based on olfactory communication through chemosignals. These behaviours are mediated by species-specific chemosignals, including small organic molecules and proteins that are secreted in the urine or in various fluids from exocrine glands. Chemosignal detection is mainly ensured by olfactory neurons in two specific sensory organs, the vomeronasal organ (VNO) and the main olfactory epithelium (MOE). This study aimed to characterise the olfactory communication in the fossorial ecotype of the water voles, Arvicola terrestris. We first measured the olfactory investigation of urine and lateral scent gland secretions from conspecifics. Our results showed that water voles can discriminate the sex of conspecifics based on the smell of urine, and that urinary male odour is attractive for female voles. Then, we demonstrated the ability of the VNO and MOE to detect volatile organic compounds (VOCs) found in water vole secretions using live-cell calcium imaging in dissociated cells. Finally, we evaluated the attractiveness of two mixtures of VOCs from urine or lateral scent glands in the field during a cyclical outbreak of vole populations.

Expression of type 1 vomeronasal receptors in the olfactory organ of the African lungfish, Protopterus dolloi.

The vomeronasal organ is an olfactory organ found in amphibians and higher vertebrates. Type 1 vomeronasal receptors, one of the major olfactory receptors in vertebrates, are expressed in the vomeronasal organ in mammals. In amphibians and fish, they are expressed in the olfactory epithelium. The lungfish, which is the species of fish most closely related to amphibians, has a primitive vomeronasal organ: the recess epithelium. Expression of type 1 vomeronasal receptors has been reported in both the olfactory epithelium and the recess epithelium in three species of African lungfish and one species of South American lungfish. However, a previous study suggested that in the African lungfish Protopterus dolloi these receptors are expressed only in the olfactory epithelium. In this study, we identified 21 type 1 vomeronasal receptor genes in P. dolloi and examined the expression sites in the olfactory organ. In P. dolloi, most cells expressing the type 1 vomeronasal receptor were distributed in the olfactory epithelium, but a few were also found in the recess epithelium. This implies that the functions of the olfactory epithelium and the primitive vomeronasal organ are incompletely separated, and that all extant African and South American lungfish share this trait.

Sensing and avoiding sick conspecifics requires Gαi2+ vomeronasal neurons.

BACKGROUND: Rodents utilize chemical cues to recognize and avoid other conspecifics infected with pathogens. Infection with pathogens and acute inflammation alter the repertoire and signature of olfactory stimuli emitted by a sick individual. These cues are recognized by healthy conspecifics via the vomeronasal or accessory olfactory system, triggering an innate form of avoidance behavior. However, the molecular identity of the sensory neurons and the higher neural circuits involved in the detection of sick conspecifics remain poorly understood. RESULTS: We employed mice that are in an acute state of inflammation induced by systemic administration of lipopolysaccharide (LPS). Through conditional knockout of the G-protein Gαi2 and deletion of other key sensory transduction molecules (Trpc2 and a cluster of 16 vomeronasal type 1 receptors), in combination with behavioral testing, subcellular Ca2+ imaging, and pS6 and c-Fos neuronal activity mapping in freely behaving mice, we show that the Gαi2+ vomeronasal subsystem is required for the detection and avoidance of LPS-treated mice. The active components underlying this avoidance are contained in urine whereas feces extract and two selected bile acids, although detected in a Gαi2-dependent manner, failed to evoke avoidance behavior. Our analyses of dendritic Ca2+ responses in vomeronasal sensory neurons provide insight into the discrimination capabilities of these neurons for urine fractions from LPS-treated mice, and how this discrimination depends on Gαi2. We observed Gαi2-dependent stimulation of multiple brain areas including medial amygdala, ventromedial hypothalamus, and periaqueductal grey. We also identified the lateral habenula, a brain region implicated in negative reward prediction in aversive learning, as a previously unknown target involved in these tasks. CONCLUSIONS: Our physiological and behavioral analyses indicate that the sensing and avoidance of LPS-treated sick conspecifics depend on the Gαi2 vomeronasal subsystem. Our observations point to a central role of brain circuits downstream of the olfactory periphery and in the lateral habenula in the detection and avoidance of sick conspecifics, providing new insights into the neural substrates and circuit logic of the sensing of inflammation in mice.

Vomeronasal Receptors Associated with Circulating Estrogen Processing Chemosensory Cues in Semi-Aquatic Mammals.

In numerous animals, one essential chemosensory organ that detects chemical signals is the vomeronasal organ (VNO), which is involved in species-specific behaviors, including social and sexual behaviors. The purpose of this study is to investigate the mechanism underlying the processing of chemosensory cues in semi-aquatic mammals using muskrats as the animal model. Muskrat (Ondatra zibethicus) has a sensitive VNO system that activates seasonal breeding behaviors through receiving specific substances, including pheromones and hormones. Vomeronasal organ receptor type 1 (V1R) and type 2 (V2R) and estrogen receptor α and ß (ERα and ERß) were found in sensory epithelial cells, non-sensory epithelial cells and lamina propria cells of the female muskrats' VNO. V2R and ERα mRNA levels in the VNO during the breeding period declined sharply, in comparison to those during the non-breeding period, while V1R and ERß mRNA levels were detected reversely. Additionally, transcriptomic study in the VNO identified that differently expressed genes might be related to estrogen signal and metabolic pathways. These findings suggested that the seasonal structural and functional changes in the VNO of female muskrats with different reproductive status and estrogen was regulated through binding to ERα and ERß in the female muskrats' VNO.

An updated synthesis of and outstanding questions in the olfactory and vomeronasal systems in bats: Genetics asks questions only anatomy can answer.

The extensive diversity observed in bat nasal chemosensory systems has been well-documented at the histological level. Understanding how this diversity evolved and developing hypotheses as to why particular patterns exist require a phylogenetic perspective, which was first outlined in the work of anatomist Kunwar Bhatnagar. With the onset of genetics and genomics, it might be assumed that the puzzling patterns observed in the morphological data have been clarified. However, there is still a widespread mismatch of genetic and morphological correlations among bat chemosensory systems. Novel genomic evidence has set up new avenues to explore that demand more evidence from anatomical structures. Here, we outline the progress that has been made in both morphological and molecular studies on the olfactory and vomeronasal systems in bats since the work of Bhatnagar. Genomic data of olfactory and vomeronasal receptors demonstrate the strong need for further morphological sampling, with a particular focus on receiving brain regions, glands, and ducts.

Does the Environmental Air Impact the Condition of the Vomeronasal Organ? A Mouse Model for Intensive Farming.

Chemical communication in mammals is ensured by exchanging chemical signals through the vomeronasal organ (VNO) and its ability to detect pheromones. The alteration of this organ has been proven to impact animal life, participating in the onset of aggressive behaviors in social groups. To date, few studies have highlighted the possible causes leading to these alterations, and the farming environment has not been investigated, even though irritant substances such as ammonia are known to induce serious damage in the respiratory tract. The goal of this study was to investigate the environmental impact on the VNO structure. Thirty mice were split into three groups, one housed in normal laboratory conditions and the other two in confined environments, with or without the release of litter ammonia. VNOs were analyzed using histology and immunohistochemistry to evaluate the effect of different environments on their condition. Both restricted conditions induced VNO alterations (p = 0.0311), soft-tissue alteration (p = 0.0480), and nonsensory epithelium inflammation (p = 0.0024). There was glycogen accumulation (p < 0.0001), the olfactory marker protein was underexpressed (p < 0.0001), and Gαi2 positivity remained unchanged while Gαo expression was upregulated in confined conditions. VNO conditions seemed to worsen with ammonia, even if not always significantly. These murine model results suggest that the housing environment can strongly impact VNO conditions, providing novel insights for improving indoor farming systems.

Type 1 vomeronasal receptor expression in juvenile and adult lungfish olfactory organ.

Lungfish are the most closely related fish to tetrapods. The olfactory organ of lungfish contains lamellae and abundant recesses at the base of lamellae. Based on the ultrastructural and histochemical characteristics, the lamellar olfactory epithelium (OE), covering the surface of lamellae, and the recess epithelium, contained in the recesses, are thought to correspond to the OE of teleosts and the vomeronasal organ (VNO) of tetrapods. With increasing body size, the recesses increase in number and distribution range in the olfactory organ. In tetrapods, the expression of olfactory receptors is different between the OE and VNO; for instance, the type 1 vomeronasal receptor (V1R) is expressed only in the OE in amphibians and mainly in the VNO in mammals. We recently reported that V1R-expressing cells are contained mainly in the lamellar OE but also rarely in the recess epithelium in the olfactory organ of lungfish of approximately 30 cm body length. However, it is unclear whether the distribution of V1R-expressing cells in the olfactory organ varies during development. In this study, we compared the expression of V1Rs in the olfactory organs between juveniles and adults of the African lungfish Protopterus aethiopicus and South American lungfish, Lepidosiren paradoxa. The density of V1R-expressing cells was higher in the lamellae than in the recesses in all specimens evaluated, and this pattern was more pronounced in juveniles than adults. In addition, the juveniles showed a higher density of V1R-expressing cells in the lamellae compared with the adults. Our results imply that differences in lifestyle between juveniles and adults are related to differences in the density of V1R-expressing cells in the lamellae of lungfish.

The clinical significance of the human vomeronasal organ.

OBJECTIVE: To find out whether the vomeronasal organ (VNO) can be identified in the nose as a mucosal pit in the anterior nasal septum, to elucidate its function in man and to determine whether it is important to preserve the VNO during septal surgery. METHODS: Literature review. RESULTS AND CONCLUSION: The VNO is histologically present in almost all humans, but a macroscopically visible septal pit does not necessarily correspond with the actual VNO. The human VNO is probably a vestigial organ with a non-operational sensory function. It is not necessary to take particular care not to damage the VNO during septal surgery.

Type 1 vomeronasal receptors expressed in the olfactory organs of two African lungfish, Protopterus annectens and Protopterus amphibius.

Lungfish are the fish related most closely to tetrapods. The olfactory organ of lungfish contains two distinct sensory epithelia: the lamellar olfactory epithelium (OE) and the recess epithelium (RecE). Based on their ultrastructural and histological characteristics, the lamellar OE and the RecE are considered to correspond respectively to the teleost OE and a primitive vomeronasal organ (VNO). In tetrapods, the OE and VNO have been shown to express different families of olfactory receptors; for example, in mammals, the OE expresses odorant receptors and trace amine-associated receptors, while the VNO expresses type 1 (V1Rs) and type 2 (V2Rs) vomeronasal receptors. In the present study, we examined the expression of V1Rs in the olfactory organs of two African lungfish, Protopterus annectens and Protopterus amphibius. RNA sequencing and phylogenetic analyses identified 29 V1R genes in P. annectens and 50 V1R genes in P. amphibius. Most V1Rs identified in these lungfish were classified as the tetrapod-type V1Rs initially found in tetrapods and distinct from fish-type V1Rs. In teleost, which all lack a VNO, all olfactory receptors are expressed in the OE, while in Xenopus V1Rs are expressed exclusively in the OE, and not in the VNO. In situ hybridization analysis indicated that lungfish V1Rs were expressed mainly in the lamellar OE and rarely in the RecE. These results imply that V1R expression in lungfish represents an intermediate step toward the complete segregation of V1R expression between the OE and VNO, reflecting the phylogenetic position of lungfish between teleosts and amphibians.

Pheromones, binding proteins, and olfactory systems in the pig (Sus scrofa): An updated review.

Pigs utilize multimodal communication for reproductive and other behaviors, and chemical communication is one of the key components. The success of reproduction relies on chemical communication favored by the steroid pheromones from boar saliva. These steroids were proven to be involved in advancing puberty in gilts (the boar effect) and in promoting estrus behaviors in gilts/sows, thereby helping to detect estrus and facilitating the timing of artificial insemination. The steroid pheromones bound with carrier proteins are evidenced in the mandibular (submandibular) salivary secretions of the boar. These salivary steroids bind with carrier proteins in the nasal mucus and vomeronasal organ (VNO) of the sows, eventually triggering a cascade of activities at the olfactory and endocrine levels. Besides steroid pheromones, pig appeasing pheromones (from mammary skin secretions of sows) have also been demonstrated to bind with carrier proteins in the nasal mucus and VNO of the piglets. Thus far, four different proteins have been identified and confirmed in the nasal mucus and VNO of pigs, including odorant binding proteins (OBPs), salivary lipocalin (SAL), pheromaxein, and Von Ebner's Gland Protein (VEGP). The critical roles of the chemosensory systems, main olfactory systems and VNO, have been comprehensively reported for pigs. This review summarizes the current knowledge on pheromones, their receptor proteins, and the olfactory systems of porcine species.

Sex separation unveils the functional plasticity of the vomeronasal organ in rabbits.

Chemosensory cues are vital for social and sexual behaviours and are primarily detected and processed by the vomeronasal system (VNS), whose plastic capacity has been investigated in mice. However, studying chemosensory plasticity outside of laboratory conditions may give a more realistic picture of how the VNS adapts to a changing environment. Rabbits are a well-described model of chemocommunication since the discovery of the rabbit mammary pheromone and their vomeronasal organ (VNO) transcriptome was recently characterised, a first step to further study plasticity-mediated transcriptional changes. In this study, we assessed the plastic capacity of the rabbit male and female VNO under sex-separation vs. sex-combined scenarios, including adults and juveniles, to determine whether the rabbit VNO is plastic and, if so, whether such plasticity is already established at early stages of life. First, we characterised the number of differentially expressed genes (DEGs) between the VNO of rabbit male and female under sex-separation and compared it to sex-combined individuals, both in adults and juveniles, finding that differences between male and female were larger in a sex-separated scenario. Secondly, we analysed the number of DEGs between sex-separated and sex-combined scenarios, both in males and females. In adults, both sexes showed a high number of DEGs while in juveniles only females showed differences. Additionally, the vomeronasal receptor genes were strikingly downregulated in sex-separated adult females, whereas in juveniles upregulation was shown for the same condition, suggesting a role of VRs in puberty onset. Finally, we described the environment-modulated plastic capacity of genes involved in reproduction, immunity and VNO functional activity, including G-protein coupled receptors. Our results show that sex-separation induces sex- and stage-specific gene expression differences in the VNO of male and female rabbit, both in adults and juveniles. These results bring out for the first time the plastic capacity of the rabbit VNO, supporting its functional adaptation to specifically respond to a continuous changing environment. Finally, species-specific differences and individual variability should always be considered in VNO studies and overall chemocommunication research.