Genetically engineered mice reveal how pheromones drive mating behavior

Pheromones—chemicals produced by animals—are well-known for influencing the social and sexual behavior of members of the same species. These chemical signals convey vital information, such as gender and reproductive status. Detection of pheromones by the vomeronasal organ (VNO) triggers a behavioral response in other members of the same species.

Vomeronasal receptors (VRs), sensory receptors found in the nerve cells of the VNO, are key for the detection of pheromones in land mammals. While VRs are categorized into type-1 (V1Rs) and type-2 (V2Rs), the precise role and function of the genetically conserved VR gene sequence encoding the ancient VR type-1 (ancV1R) receptor remains poorly understood.

To elucidate the role of ancV1R in pheromone detection, a team of researchers led by Professor Junji Hirota from Institute of Science Tokyo, Japan, has conducted a series of experiments using an ancV1R-deficient mouse model. Their findings were published online on November 21, 2024, in Current Biology.

Sharing the motivation behind the present research, Hirota states, “The recent coelacanth genome project revealed that coelacanths or lobe-finned fishes have an unidentified genetic sequence belonging to the V1R family. Interestingly, this novel V1R gene is found across a variety of organisms, from bony and ray-finned fishes to mammals, and we named it ancV1R denoting its ‘ancient’ origin. These conserved evolutionary links inspired our research team to investigate the role of ancV1R in VNO-mediated pheromone detection.”

Initially, the researchers used the CRISPR-Cas9 system—a genome editing technology—to delete the ancV1R gene from the mouse genome. They then conducted behavioral experiments involving ancV1R-deficient female mice and observed frequent rejection of sexual advances by male mice. Hirota and the team hypothesized that ancV1R-deficient females were unable to recognize the male mice due to an impaired pheromone response.

To validate their findings, the scientists developed a two-choice preference test to study the response of ancV1R-deficient female mice to male and female urine. Interestingly, the mice displayed no preference for male urinary pheromones. Further experiments examining nerve cell activation in response to male urine revealed decreased neural activity in the VNO of the female mice.

The researchers also examined the effects of exocrine gland-secreting peptide 1 (ESP1), a pheromone known to enhance female sexual receptivity, in both wild-type female mice (with functional ancV1R) and ancV1R-deficient mice. They observed that sensory neuron activation by ESP1 was significantly reduced in the ancV1R-deficient females. Moreover, even after pre-exposure to ESP1, these females continued to reject male advances and mating attempts.

Notably, findings from analyses of neuronal responses to various pheromones further support these observations. AncV1R-deficient females displayed increased neural activity in the lateral septum—the brain region associated with stress—following interactions with male mice.

Hirota says, “Our findings demonstrated that ancV1R is crucial for detecting pheromone cues in the VNO, and its loss impairs the ability of female mice to perceive males and exhibit sexual behaviors.”

This study paves the way for future research on VRs, pheromone sensing, and related social behaviors in animals with VNOs.