Gene expression profiling of the olfactory tissues of sex-separated and sex-combined female and male mice

In mice, discrete odors can selectively promote the neurogenesis of sensory neuron subtypes that they stimulate

In mammals, olfactory sensory neurons (OSNs) are born throughout life, presumably solely to replace neurons lost via turnover or injury. This assumption follows from the hypothesis that olfactory neurogenesis is strictly stochastic with respect to neuron subtype, as defined by the single odorant receptor allele that each neural precursor stochastically chooses out of hundreds of possibilities. This hypothesis is challenged by recent findings that the birthrates of a fraction of subtypes are selectively diminished by olfactory deprivation. These findings raise questions about how, and why, olfactory stimuli are required to promote the neurogenesis of some OSN subtypes, including whether the stimuli are generic (e.g., broadly activating odors or mechanical stimuli) or specific (e.g., discrete odorants). Based on RNA-seq and scRNA-seq analyses, we hypothesized that the neurogenic stimuli are specific odorants that selectively activate the same OSN subtypes whose birthrates are accelerated. In support of this, we have found, using subtype-specific OSN birthdating, that exposure to male and musk odors can accelerate the birthrates of responsive OSNs. Collectively, our findings reveal that certain odor experiences can selectively "amplify" specific OSN subtypes, and that persistent OSN neurogenesis may serve, in part, an adaptive function.

Behavioral evidence of the functional interaction between the main and accessory olfactory system suggests a large olfactory system with a high plastic capability

Olfaction is fundamental in many species of mammals. In rodents, the integrity of this system is required for the expression of parental and sexual behavior, mate recognition, identification of predators, and finding food. Different anatomical and physiological evidence initially indicated the existence of two anatomically distinct chemosensory systems: The main olfactory system (MOS) and the accessory olfactory system (AOS). It was originally conceived that the MOS detected volatile odorants related to food, giving the animal information about the environment. The AOS, on the other hand, detected non-volatile sexually relevant olfactory cues that influence reproductive behaviors and neuroendocrine functions such as intermale aggression, sexual preference, maternal aggression, pregnancy block (Bruce effect), puberty acceleration (Vandenbergh effect), induction of estrous (Whitten effect) and sexual behavior. Over the last decade, several lines of evidence have demonstrated that although these systems could be anatomically separated, there are neuronal areas in which they are interconnected. Moreover, it is now clear that both the MOS and the AOS process both volatile and no-volatile odorants, indicating that they are also functionally interconnected. In the first part of the review, we will describe the behavioral evidence. In the second part, we will summarize data from our laboratory and other research groups demonstrating that sexual behavior in male and female rodents induces the formation of new neurons that reach the main and accessory olfactory bulbs from the subventricular zone. Three factors are essential for the neurons to reach the AOS and the MOS: The stimulation frequency, the stimulus's temporal presentation, and the release of opioids induced by sexual behavior. We propose that the AOS and the MOS are part of a large olfactory system with a high plastic capability, which favors the adaptation of species to different environmental signals.

Variation in mouse chemical signals is genetically controlled and environmentally modulated

In most mammals and particularly in mice, chemical communication relies on the detection of ethologically relevant fitness-related cues from other individuals. In mice, urine is the primary source of these signals, so we employed proteomics and metabolomics to identify key components of chemical signalling. We show that there is a correspondence between urinary volatiles and proteins in the representation of genetic background, sex and environment in two house mouse subspecies Mus musculus musculus and M. m. domesticus. We found that environment has a strong influence upon proteomic and metabolomic variation and that volatile mixtures better represent males while females have surprisingly more sex-biased proteins. Using machine learning and combined-omics techniques, we identified mixtures of metabolites and proteins that are associated with biological features.

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.

Prolactin-sensitive olfactory sensory neurons regulate male preference in female mice by modulating responses to chemosensory cues

Chemosensory cues detected in the nose need to be integrated with the hormonal status to trigger appropriate behaviors, but the neural circuits linking the olfactory and the endocrine system are insufficiently understood. Here, we characterize olfactory sensory neurons in the murine nose that respond to the pituitary hormone prolactin. Deletion of prolactin receptor in these cells results in impaired detection of social odors and blunts male preference in females. The prolactin-responsive olfactory sensory neurons exhibit a distinctive projection pattern to the brain that is similar across different individuals and express a limited subset of chemosensory receptors. Prolactin modulates the responses within these neurons to discrete chemosensory cues contained in male urine, providing a mechanism by which the hormonal status can be directly linked with distinct olfactory cues to generate appropriate behavioral responses.

Biological Roles of Lipocalins in Chemical Communication, Reproduction, and Regulation of Microbiota

Major evolutionary transitions were always accompanied by genetic remodelling of phenotypic traits. For example, the vertebrate transition from water to land was accompanied by rapid evolution of olfactory receptors and by the expansion of genes encoding lipocalins, which - due to their transporting functions - represent an important interface between the external and internal organic world of an individual and also within an individual. Similarly, some lipocalin genes were lost along other genes when this transition went in the opposite direction leading, for example, to cetaceans. In terrestrial vertebrates, lipocalins are involved in the transport of lipophilic substances, chemical signalling, odour reception, antimicrobial defence and background odour clearance during ventilation. Many ancestral lipocalins have clear physiological functions across the vertebrate taxa while many other have - due to pleiotropic effects of their genes - multiple or complementary functions within the body homeostasis and development. The aim of this review is to deconstruct the physiological functions of lipocalins in light of current OMICs techniques. We concentrated on major findings in the house mouse in comparison to other model taxa (e.g., voles, humans, and birds) in which all or most coding genes within their genomes were repeatedly sequenced and their annotations are sufficiently informative.

A Subset of Olfactory Sensory Neurons Express Forkhead Box J1-Driven eGFP

Forkhead box protein J1 (FOXJ1), a member of the forkhead family transcription factors, is a transcriptional regulator of motile ciliogenesis. The nasal respiratory epithelium, but not olfactory epithelium, is lined with FOXJ1-expressing multiciliated epithelial cells with motile cilia. In a transgenic mouse where an enhanced green fluorescent protein (eGFP) transgene is driven by the human FOXJ1 promoter, robust eGFP expression is observed not only in the multiciliated cells of the respiratory epithelium but in a distinctive small subset of olfactory sensory neurons in the olfactory epithelium. These eGFP-positive cells lie at the extreme apical part of the neuronal layer and are most numerous in dorsal-medial regions of olfactory epithelium. Interestingly, we observed a corresponding small number of glomeruli in the olfactory bulb wherein eGFP-labeled axons terminate, suggesting that the population of eGFP+ receptor cells expresses a limited number of olfactory receptors. Similarly, a subset of vomeronasal sensory neurons expresses eGFP and is distributed throughout the full height of the vomeronasal sensory epithelium. In keeping with this broad distribution of labeled vomeronasal receptor cells, eGFP-labeled axons terminate in many glomeruli in both anterior and posterior portions of the accessory olfactory bulb. These findings suggest that Foxj1-driven eGFP marks a specific population of olfactory and vomeronasal sensory neurons, although neither receptor cell population possess motile cilia.

A database for using machine learning and data mining techniques for coronary artery disease diagnosis

We present the coronary artery disease (CAD) database, a comprehensive resource, comprising 126 papers and 68 datasets relevant to CAD diagnosis, extracted from the scientific literature from 1992 and 2018. These data were collected to help advance research on CAD-related machine learning and data mining algorithms, and hopefully to ultimately advance clinical diagnosis and early treatment. To aid users, we have also built a web application that presents the database through various reports.

Sex separation induces differences in the olfactory sensory receptor repertoires of male and female mice

Within the mammalian olfactory sensory epithelium, experience-dependent changes in the rate of neuronal turnover can alter the relative abundance of neurons expressing specific chemoreceptors. Here we investigate how the mouse olfactory sensory receptor repertoire changes as a function of exposure to odors emitted from members of the opposite sex, which are highly complex and sexually dimorphic. Upon housing mice either sex-separated or sex-combined until six months of age, we find that sex-separated mice exhibit significantly more numerous differentially expressed genes within their olfactory epithelia. A subset of these chemoreceptors exhibit altered expression frequencies following both sex-separation and olfactory deprivation. We show that several of these receptors detect either male- or female-specific odors. We conclude that the distinct odor experiences of sex-separated male and female mice induce sex-specific differences in the abundance of neurons that detect sexually dimorphic odors.