Lymphocytic Choriomeningitis Virus Alters the Expression of Male Mouse Scent Proteins

Intestinal colonization regulates systemic anti-commensal immune sensitivity and hyperreactivity

Healthy host-microbial mutualism with our intestinal microbiota relies to a large degree on compartmentalization and careful regulation of adaptive mucosal and systemic anti-microbial immune responses. However, commensal intestinal bacteria are never exclusively or permanently restricted to the intestinal lumen and regularly reach the systemic circulation. This results in various degrees of commensal bacteremia that needs to be appropriately dealt with by the systemic immune system. While most intestinal commensal bacteria, except for pathobionts or opportunistic pathogen, have evolved to be non-pathogenic, this does not mean that they are non-immunogenic. Mucosal immune adaptation is carefully controlled and regulated to avoid an inflammatory response, but the systemic immune system usually responds differently and more vigorously to systemic bacteremia. Here we show that germ-free mice have increased systemic immune sensitivity and display anti-commensal hyperreactivity in response to the addition of a single defined T helper cell epitope to the outer membrane porin C (OmpC) of a commensal Escherichia coli strain demonstrated by increased E. coli-specific T cell-dependent IgG responses following systemic priming. This increased systemic immune sensitivity was not observed in mice colonized with a defined microbiota at birth indicating that intestinal commensal colonization also regulates systemic, and not only mucosal, anti-commensal responses. The observed increased immunogenicity of the E. coli strain with the modified OmpC protein was not due to a loss of function and associated metabolic changes as a control E. coli strain without OmpC did not display increased immunogenicity.

Infection of Trichinella spiralis Affects the Reproductive Capacity of ICR/CD-1 Male Mice by Reducing the Urine Pheromone Contents and Sperm Quality

Female mice can discriminate the urinary odors of male mice due to their olfactory acuity. Parasitic infection or subclinical infection can decrease the odor attractiveness of male mice and finally lead to aversion or avoidance responses in odor selection for female mice. Trichinella spiralis is a kind of tissue-parasitizing nematode that causes trichinellosis, a zoonotic parasitic disease that spreads throughout the world. However, the reproductive injury caused by Trichinella spiralis infection was not fully revealed. In this study, we explored the effect of Trichinella spiralis infection on the reproductive capacity in ICR/CD-1 male mice. We identified eight volatile compounds in urine by GC-MS analysis, and the results indicated that the contents of dimethyl sulfone, Z-7-tetradecen-1-ol, 6-Hydroxy-6-methyl-3-heptanone and (S)-2-sec-butyl-4,5-dihydrothiazole were significantly downregulated after parasitic infection, which might lead to the reduction of attractiveness of male mice urine to females. On the other hand, parasitic infection decreased sperm quality and downregulated the expression levels of Herc4, Ipo11, and Mrto4, and these genes were strongly related to spermatogenesis. In summary, this study revealed that the reproductive injury caused by Trichinella spiralis infection in ICR/CD-1 male mice could be associated with a decrease in urine pheromone content and sperm quality.

Infection with Cryptosporidium parvum Affects Secondary Sexual Characteristics of Male Mice by Altering the Pheromone Content in Preputial Gland

The olfactory acuity of female mice allows them to discriminate the urinary odors of males. Parasitic infection can reduce the odor attractiveness of male mice to females and result in female aversion or avoidance responses in odor selection. However, the chemical signaling changes in the pheromone contents produced by the foreskin gland were not fully revealed after parasitic infection. Cryptosporidium parvum (C. parvum) is a common zoonotic intestinal parasite and has a wide range of hosts, including human, domestic animals, and wild animals. In this study, we immunosuppressed ICR/CD-1 male mice by dexamethasone sodium phosphate treatment. After C. parvum infection, physiological indexes such as body weight and organ weight were significantly decreased. Furthermore, the gene expression level of MUP (major urinary protein) in liver and urine were significantly down-regulated, which could be the reason for the decrease in urine attractiveness to females. GC-MS was performed to analyze the changes in the pheromone produced by the preputial gland before and after parasitic infection, and the results indicated that the levels of different pheromones were significantly reduced after parasitic infection. In summary, this study reveals that C. parvum infection damages the secondary sexual characteristics of male ICR/CD-1 male mice and decreases the pheromone content produced by the foreskin gland.

Regulation of Sexually Dimorphic Expression of Major Urinary Proteins

Male house mice excrete large amounts of protein in their urinary scent marks, mainly composed of Major Urinary Proteins (MUPs), and these lipocalins function as pheromones and pheromone carriers. Here, we review studies on sexually dimorphic MUP expression in house mice, including the proximate mechanisms controlling MUP gene expression and their adaptive functions. Males excrete 2 to 8 times more urinary protein than females, though there is enormous variation in gene expression across loci in both sexes. MUP expression is dynamically regulated depending upon a variety of factors. Males regulate MUP expression according to social status, whereas females do not, and males regulate expression depending upon health and condition. Male-biased MUP expression is regulated by pituitary secretion of growth hormone (GH), which binds receptors in the liver, activating the JAK2-STAT5 signaling pathway, chromatin accessibility, and MUP gene transcription. Pulsatile male GH secretion is feminized by several factors, including caloric restriction, microbiota depletion, and aging, which helps explain condition-dependent MUP expression. If MUP production has sex-specific fitness optima, then this should generate sexual antagonism over allelic expression (intra-locus sexual conflict) selectively favoring sexually dimorphic expression. MUPs influence the sexual attractiveness of male urinary odor and increased urinary protein excretion is correlated with the reproductive success of males but not females. This finding could explain the selective maintenance of sexually dimorphic MUP expression. Producing MUPs entails energetic costs, but increased excretion may reduce the net energetic costs and predation risks from male scent marking as well as prolong the release of chemical signals. MUPs may also provide physiological benefits, including regulating metabolic rate and toxin removal, which may have sex-specific effects on survival. A phylogenetic analysis on the origins of male-biased MUP gene expression in Mus musculus suggests that this sexual dimorphism evolved by increasing male MUP expression rather than reducing female expression.