Molecular biology of peptide pheromone production and reception in mice

Fecundity difference is related to the production of reproductive pheromones in rats

In brief

Social and reproductive behaviors in mammals are regulated by pheromones. This study shows the possibility that male extraorbital lacrimal gland-derived pheromones are involved in reproductive efficiency in rats.

Abstract

In rodents, male-derived pheromones play fundamental roles in reproduction. The Hirosaki hairless rat (HHR) is a mutant strain derived from the Sprague-Dawley rat (SDR). While investigating the natural mating between single males and females, (SDR♂ × SDR♀) or (HHR♂ × HHR♀), the HHRs showed higher fecundity than the SDRs; the mean period between mating and delivery was shorter, and every HHR pair gave birth, whereas approximately half of the SDR pairs gave birth in the 3 months of experimental testing. By changing partners between the HHRs and SDRs, (SDR♂ × HHR♀) or (HHR♂ × SDR♀), we attributed the fecundity difference to the males. However, no significant difference was observed in the litter size, the concentration, morphology, or motility of sperm in the cauda epididymis, or the testosterone concentration in the serum between the SDR and HHR males. When an SDR and HHR male were simultaneously mated with a single female, the HHR males always succeeded in leaving progeny. Therefore, we assumed that the reason for the fecundity difference was the difference in copulation efficiency and focused on male-derived pheromones that may induce reproductive behaviors in females. Whereas Darcin (MUP20), one of the pheromones produced in the liver, did not appear to be involved, the extraorbital lacrimal gland (ELG) was heavier in the HHR males and showed larger amounts of pheromones, namely exocrine gland-secreting peptide 1 (ESP1) and cystatin-related protein 1 (CRP1). These results suggest that the fecundity difference is due to the difference in amounts of ELG-derived pheromones.

Sex Effects on Gene Expression in Lacrimal Glands of Mouse Models of Sjögren Syndrome

Purpose

Sjögren syndrome is an autoimmune disease that occurs primarily in women, and is associated with lacrimal gland inflammation and aqueous-deficient dry eye. We hypothesize that sex-associated differences in lacrimal gland gene expression are very important in promoting lymphocyte accumulation in this tissue and contribute to the onset, progression, and/or severity of the inflammatory disease process. To test our hypothesis, we explored the nature and extent of sex-related differences in gene expression in autoimmune lacrimal glands.

Methods

Lacrimal glands were collected from age-matched, adult, male and female MRL/MpJ-Tnfrsf6^lpr (MRL/lpr) and nonobese diabetic/LtJ (NOD) mice. Glands were processed for the analysis of differentially expressed mRNAs by using CodeLink Bioarrays and Affymetrix GeneChips. Data were evaluated with bioinformatics and statistical software.

Results

Our results show that sex significantly influences the expression of thousands of genes in lacrimal glands of MRL/lpr and NOD mice. The immune nature of this glandular response is very dependent on the Sjögren syndrome model. Lacrimal glands of female, as compared with male, MRL/lpr mice contain a significant increase in the expression of genes related to inflammatory responses, antigen processing, and chemokine pathways. In contrast, it is the lacrimal tissue of NOD males, and not females, that presents with a significantly greater expression of immune-related genes.

Conclusions

These data support our hypothesis that sex-related differences in gene expression contribute to lacrimal gland disease in Sjögren syndrome. Our findings also suggest that factors in the lacrimal gland microenvironment are critically important in mediating these sex-associated immune effects.

Self-Exposure to the Male Pheromone ESP1 Enhances Male Aggressiveness in Mice

Exocrine gland-secreting peptide 1 (ESP1) released into male tear fluids is a male pheromone that stimulates sexually receptive behavior in female mice via the vomeronasal sensory system. ESP1 also induces c-Fos expression in male brain regions distinct from those in females. However, behavior in males following ESP1 exposure has not been examined. In the present study, we show that ESP1, in conjunction with unfamiliar male urine, enhances male aggression via the specific vomeronasal receptor V2Rp5. In addition, male mice that secrete ESP1 but lack V2Rp5 exhibit a lower level of aggressiveness than do mice that express V2Rp5. These results suggest that ESP1 not only acts as a male pheromone in both sexes but also serves as an auto-stimulatory factor that enhances male aggressiveness by self-exposure. Finally, re-activation of ESP1-induced c-Fos-positive neurons by using the designer receptor exclusively activated by designer drug (DREADD) approach resulted in enhancement of sexual and aggressive behaviors in female and male mice, respectively, indicating that sexually dimorphic activation in the brain is a neural basis for the sex-specific behavioral responses to ESP1.

Expression and purification of mouse peptide ESP4 in Escherichia coli

Pheromones are species-specific chemical signals that regulate a wide range of social and sexual behaviors in many animals. In mice, the male-specific peptide ESP1 (exocrine gland-secreting peptide 1) is secreted into tear fluids and enhances female sexual receptive behavior. ESP1 belongs to the ESP family, a multigene family with 38 genes in mice. ESP1 shares the highest homology with ESP4. ESP1 is expressed in the extraorbital lacrimal gland, whereas ESP4 is expressed in some exocrine glands. Thus, ESP4 is expected to have a function that has not been elucidated yet. Large amounts of the purified ESP4 protein are required for structural and biochemical studies. Here we present an expression and purification scheme for the recombinant ESP4 protein. The N-terminally histidine-tagged ESP4 fusion protein was expressed in Escherichia coli as inclusion bodies, which were solubilized and purified by nickel affinity chromatography. The histidine tag was cleaved with thrombin and removed by a second nickel affinity chromatography step. The ESP4 protein was isolated with high purity by reversed-phase chromatography. For NMR analyses, we prepared a stable isotope-labeled ESP4 protein. Three repeated freeze-drying steps after the reversed-phase chromatography were required, to remove a volatile contaminating compound and to obtain an NMR spectrum with a homogeneous line shape. AMS-modification and far-UV CD spectroscopic analyses suggested that ESP4 has an intramolecular disulfide bridge and a helical structure, respectively. The present study provides a powerful tool for structural and biochemical studies of ESP4, leading toward the elucidation of the roles of the ESP family members.

A sexually conditioned switch of chemosensory behavior in C. elegans

In sexually reproducing animals, mating is essential for transmitting genetic information to the next generation and therefore animals have evolved mechanisms for optimizing the chance of successful mate location. In the soil nematode C. elegans, males approach hermaphrodites via the ascaroside pheromones, recognize hermaphrodites when their tails contact the hermaphrodites' body, and eventually mate with them. These processes are mediated by sensory signals specialized for sexual communication, but other mechanisms may also be used to optimize mate location. Here we describe associative learning whereby males use sodium chloride as a cue for hermaphrodite location. Both males and hermaphrodites normally avoid sodium chloride after associative conditioning with salt and starvation. However, we found that males become attracted to sodium chloride after conditioning with salt and starvation if hermaphrodites are present during conditioning. For this conditioning, which we call sexual conditioning, hermaphrodites are detected by males through pheromonal signaling and additional cue(s). Sex transformation experiments suggest that neuronal sex of males is essential for sexual conditioning. Altogether, these results suggest that C. elegans males integrate environmental, internal and social signals to determine the optimal strategy for mate location.

Structure of the mouse sex peptide pheromone ESP1 reveals a molecular basis for specific binding to the class C G-protein-coupled vomeronasal receptor

Exocrine gland-secreting peptide 1 (ESP1) is a sex pheromone that is released in male mouse tear fluids and enhances female sexual receptive behavior. ESP1 is selectively recognized by a specific class C G-protein-coupled receptor (GPCR), V2Rp5, among the hundreds of receptors expressed in vomeronasal sensory neurons (VSNs). The specific sensing mechanism of the mammalian peptide pheromone by the class C GPCR remains to be elucidated. Here we identified the minimal functional region needed to retain VSN-stimulating activity in ESP1 and determined its three-dimensional structure, which adopts a helical fold stabilized by an intramolecular disulfide bridge with extensive charged patches. We then identified the amino acids involved in the activation of VSNs by a structure-based mutational analysis, revealing that the highly charged surface is crucial for the ESP1 activity. We also demonstrated that ESP1 specifically bound to an extracellular region of V2Rp5 by an in vitro pulldown assay. Based on homology modeling of V2Rp5 using the structure of the metabotropic glutamate receptor, we constructed a docking model of the ESP1-V2Rp5 complex in which the binding interface exhibited good electrostatic complementarity. These experimental results, supported by the molecular docking simulations, reveal that charge-charge interactions determine the specificity of ESP1 binding to V2Rp5 in the large extracellular region characteristic of class C GPCRs. The present study provides insights into the structural basis for the narrowly tuned sensing of mammalian peptide pheromones by class C GPCRs.

Transcriptomes of mouse olfactory epithelium reveal sexual differences in odorant detection

To sense numerous odorants and chemicals, animals have evolved a large number of olfactory receptor genes (Olfrs) in their genome. In particular, the house mouse has ∼1,100 genes in the Olfr gene family. This makes the mouse a good model organism to study Olfr genes and olfaction-related genes. To date, whether male and female mice possess the same ability in detecting environmental odorants is still unknown. Using the next generation sequencing technology (paired-end mRNA-seq), we detected 1,088 expressed Olfr genes in both male and female olfactory epithelium. We found that not only Olfr genes but also odorant-binding protein (Obp) genes have evolved rapidly in the mouse lineage. Interestingly, Olfr genes tend to express at a higher level in males than in females, whereas the Obp genes clustered on the X chromosome show the opposite trend. These observations may imply a more efficient odorant-transporting system in females, whereas a more active Olfr gene expressing system in males. In addition, we detected the expression of two genes encoding major urinary proteins, which have been proposed to bind and transport pheromones or act as pheromones in mouse urine. This observation suggests a role of main olfactory system (MOS) in pheromone detection, contrary to the view that only accessory olfactory system (AOS) is involved in pheromone detection. This study suggests the sexual differences in detecting environmental odorants in MOS and demonstrates that mRNA-seq provides a powerful tool for detecting genes with low expression levels and with high sequence similarities.

The male mouse pheromone ESP1 enhances female sexual receptive behaviour through a specific vomeronasal receptor

Various social behaviours in mice are regulated by chemical signals called pheromones that act through the vomeronasal system. Exocrine gland-secreting peptide 1 (ESP1) is a 7-kDa peptide that is released into male tear fluids and stimulates vomeronasal sensory neurons in female mice. Here, we describe the molecular and neural mechanisms that are involved in the decoding of ESP1 signals in the vomeronasal system, which leads to behavioural output in female mice. ESP1 is recognized by a specific vomeronasal receptor, V2Rp5, and the ligand-receptor interaction results in sex-specific signal transmission to the amygdaloid and hypothalamic nuclei via the accessory olfactory bulb. Consequently, ESP1 enhances female sexual receptive behaviour upon male mounting (lordosis), allowing successful copulation. In V2Rp5-deficient mice, ESP1 induces neither neural activation nor sexual behaviour. These findings show that ESP1 is a crucial male pheromone that regulates female reproductive behaviour through a specific receptor in the mouse vomeronasal system.

Dual control by a single gene of secondary sexual characters and mating preferences in medaka

Background

Animals utilize a wide variety of tactics to attract reproductive partners. Behavioral experiments often indicate an important role for visual cues in fish, but their molecular basis remains almost entirely unknown. Studies on model species (such as zebrafish and medaka) allow investigations into this fundamental question in behavioral and evolutionary biology.

Results

Through mate-choice experiences using several laboratory strains of various body colors, we successfully identified one medaka mutant (color interfere; ci) that is distinctly unattractive to reproductive partners. This unattractiveness seems to be due to reduced orange pigment cells (xanthophores) in the skin. The ci strain carries a mutation on the somatolactin alpha (SLa) gene, therefore we expected over-expression of SLa to make medaka hyper-attractive. Indeed, extremely strong mating preferences were detected in a choice between the ci and SLa-transgenic (Actb-SLa:GFP) medaka. Intriguingly, however, the strains showed opposite biases; that is, the mutant and transgenic medaka liked to mate with partners from their own strain, similar to becoming sexually isolated.

Conclusion

This study spotlighted SLa as a novel mate-choice gene in fish. In addition, these results are the first demonstration of a single gene that can pleiotropically and harmoniously change both secondary sexual characters and mating preferences. Although theoretical models have long suggested joint evolution of linked genes on a chromosome, a mutation on a gene-regulatory region (that is, switching on/off of a single gene) might be sufficient to trigger two 'runaway' processes in different directions to promote (sympatric) speciation.

Subsystem organization of the mammalian sense of smell

The mammalian olfactory system senses an almost unlimited number of chemical stimuli and initiates a process of neural recognition that influences nearly every aspect of life. This review examines the organizational principles underlying the recognition of olfactory stimuli. The olfactory system is composed of a number of distinct subsystems that can be distinguished by the location of their sensory neurons in the nasal cavity, the receptors they use to detect chemosensory stimuli, the signaling mechanisms they employ to transduce those stimuli, and their axonal projections to specific regions of the olfactory forebrain. An integrative approach that includes gene targeting methods, optical and electrophysiological recording, and behavioral analysis has helped to elucidate the functional significance of this subsystem organization for the sense of smell.

Sensing odorants and pheromones with chemosensory receptors

Olfaction is a critical sensory modality that allows living things to acquire chemical information from the external world. The olfactory system processes two major classes of stimuli: (a) general odorants, small molecules derived from food or the environment that signal the presence of food, fire, or predators, and (b) pheromones, molecules released from individuals of the same species that convey social or sexual cues. Chemosensory receptors are broadly classified, by the ligands that activate them, into odorant or pheromone receptors. Peripheral sensory neurons expressing either odorant or pheromone receptors send signals to separate odor- and pheromone-processing centers in the brain to elicit distinct behavioral and neuroendocrinological outputs. General odorants activate receptors in a combinatorial fashion, whereas pheromones activate narrowly tuned receptors that activate sexually dimorphic neural circuits in the brain. We review recent progress on chemosensory receptor structure, function, and circuitry in vertebrates and invertebrates from the point of view of the molecular biology and physiology of these sensory systems.

Pheromone communication in amphibians and reptiles

This selective review considers herpetological papers that feature the use of chemical cues, particularly pheromones involved in reproductive interactions between potential mates. Primary examples include garter snake females that attract males, lacertid lizards and the effects of their femoral gland secretions, aquatic male newts that chemically attract females, and terrestrial salamander males that chemically persuade a female to mate. Each case study spans a number of research approaches (molecular, biochemical, behavioral) and is related to sensory processing and the physiological effects of pheromone delivery. These and related studies show that natural pheromones can be identified, validated with behavioral tests, and incorporated in research on vomeronasal functional response.

Candidate chemoreceptor subfamilies differentially expressed in the chemosensory organs of the mollusc Aplysia

Background

Marine molluscs, as is the case with most aquatic animals, rely heavily on olfactory cues for survival. In the mollusc Aplysia californica, mate-attraction is mediated by a blend of water-borne protein pheromones that are detected by sensory structures called rhinophores. The expression of G protein and phospholipase C signaling molecules in this organ is consistent with chemosensory detection being via a G-protein-coupled signaling mechanism.

Results

Here we show that novel multi-transmembrane proteins with similarity to rhodopsin G-protein coupled receptors are expressed in sensory epithelia microdissected from the Aplysia rhinophore. Analysis of the A. californica genome reveals that these are part of larger multigene families that possess features found in metazoan chemosensory receptor families (that is, these families chiefly consist of single exon genes that are clustered in the genome). Phylogenetic analyses show that the novel Aplysia G-protein coupled receptor-like proteins represent three distinct monophyletic subfamilies. Representatives of each subfamily are restricted to or differentially expressed in the rhinophore and oral tentacles, suggesting that they encode functional chemoreceptors and that these olfactory organs sense different chemicals. Those expressed in rhinophores may sense water-borne pheromones. Secondary signaling component proteins Gα_q, Gα_i, and Gα_o are also expressed in the rhinophore sensory epithelium.

Conclusion

The novel rhodopsin G-protein coupled receptor-like gene subfamilies identified here do not have closely related identifiable orthologs in other metazoans, suggesting that they arose by a lineage-specific expansion as has been observed in chemosensory receptor families in other bilaterians. These candidate chemosensory receptors are expressed and often restricted to rhinophores and oral tentacles, lending support to the notion that water-borne chemical detection in Aplysia involves species- or lineage-specific families of chemosensory receptors.

Inhalation exposure to acetone induces selective damage on olfactory neuroepithelium in mice

Due to their specific position in the nasal cavity, the cells of olfactory neuroepithelium can be damaged by exposure to environmental airborne chemicals. However, few studies have been focused on selective damage, i.e. olfactory sensory neurons, basal cells, supporting and duct cells. As solvents are known to induce critical effects on olfactory neuroepithelium (OE), this study was designed to characterize histological and immunohistological effects induced by acetone exposure on OE in mice. Behavioral tests were conducted to evaluate olfactory sensitivity. Moreover, olfactory neuroepithelium was examined to evaluate the thickness and the total number of cells. Finally, different markers, olfactory marker protein (OMP) and proliferating cell nuclear antigen (PCNA), were used to characterize respectively olfactory sensory neurons and basal cells, and secondly to evaluate the dynamic of the tissue turnover. Results showed structural modifications, since the thickness and the number of cells in the OE were modified according to the time course of the exposure. Additionally, no changes for OMP-positive cells were observed whereas significant differences appeared for the density of PCNA-positive cells in relation to their location (main-body or basal layer of OE). These findings indicate that acetone exposure induces selective damage in olfactory neuroepithelium.

Better smelling through genetics: mammalian odor perception

The increasing availability of genomic and genetic tools to study olfaction-the sense of smell-has brought important new insights into how this chemosensory modality functions in different species. Newly sequenced mammalian genomes-from platypus to dog-have made it possible to infer how smell has evolved to suit the needs of a given species and how variation within a species may affect individual olfactory perception. This review will focus on recent advances in the genetics and genomics of mammalian smell, with a primary focus on rodents and humans.

Sexual communication via peptide and protein pheromones

Pheromones are specific substances utilized by various organisms for intraspecific communication about sex, strain, or species. Although pheromones in terrestrial animals tend to be volatile airborne chemicals, large non-volatile molecules such as peptides and proteins are also utilized for sociosexual communication. Peptide pheromones are recognized by specific receptors expressed in the vertebrate vomeronasal organ that comprises a unique chemosensory system. The information is sent to the hypothalamic area wherein the signal is further integrated, leading to various pheromonal outputs. In this review, current knowledge on the structure and function of peptide and protein pheromones in vertebrates as well as the mechanisms underlying receptor-mediated signal processing will be summarized. The present review will also discuss why, from chemical and ecological points of view, peptide pheromones evolved.

Sex differences in expression and differential regulation by androgen and estrogen of two odorant-binding tear lipocalins in lacrimal glands of immature hamsters

In adults of several mammalian species, lacrimal glands (LG) have sex differences but there is no report of any sexual dimorphism in LG of immatures. In LG and tears of adult hamsters, we found female-specific expression of two closely related odorant-/pheromone-binding lipocalins, FLP (female lacrimal protein) and MSP (male-specific protein; initially identified in salivary glands of males). Although, both androgens and estrogens markedly repress FLP and MSP in LG of adults, the expression of these lipocalins in females is due to their incomplete repression by endogenous estrogens. Here we report a marked sexual dimorphism in the expression of FLP and MSP in LG and tears of 20-day-old immature hamsters. The age-dependant expression of these lipocalins and effect of neonatal-gonadectomy and sex hormone treatments on their expression in immatures was investigated. FLP and MSP are detectable in LG at 10-day age in both sexes of hamster but by 20-day age levels of both lipocalins show sex differences wherein FLP is several fold higher in males and MSP is obliterated in males. Thereafter, FLP declines in male LG and is obliterated by 36-day age, resulting in female-specific expression of both LG lipocalins as seen in adults. In LG of 20-day-old immatures, FLP and MSP are insensitive to repression by androgen and estrogen, respectively, which was unlike the androgen/estrogen-repressed regulation of both lipocalins in adult LG. The estrogenic repression of FLP and androgenic repression of MSP in LG of immature hamsters could be prevented by treatment with tamoxifen and flutamide, respectively. Our studies indicate that (i) presence of gonads in immatures can have significant effects on LG lipocalins resulting in their sexually dimorphic expression, (ii) in immatures, unlike adults, the repressive effects of estrogen and androgen on LG lipocalins are selective for FLP and MSP, respectively, and (iii) these repressions are likely to be mediated by sex hormone receptors.