Figure 41.4 The Mouse Vomeronasal Organ Identifies Gender
The use of gene knockouts is a commonly used tool to understand gene function. In this study, Stowers et al. (2002) examined the function of the mouse vomeronasal organ (VNO). Previous research had investigated the VNO’s function by physically removing the organ, and results of these studies had suggested that the VNO was necessary for initiating mating behavior. Stowers and colleagues studied the function of this organ by creating knockout mutant mice that do not produce TRP2, a protein necessary for the sensory activation of the VNO. They then exposed both the knockout and wild-type male mice to wild-type females. In contrast to previous studies, they found that there was no difference in the mating behavior of the knockout and wild-type mice. However, the researchers then exposed the knockout male mice to wild-type males. What they observed was surprising; instead of the usual aggression, the knockout males exhibited the same mating behavior shown towards female mice. Thus, Stowers et al. hypothesized that in mice the VNO functions not in the initiation of mating behavior, but in gender discrimination. To definitely demonstrate this, the researchers first had to disprove the alternative explanations for their results. Specifically, perhaps the lack of VNO function creates animals that have an overactive sexual drive, resulting in mating behavior towards males in the absence of females. Alternatively, knockout males may have a different sexual preference, only mating with females in the absence of males. To rule-out these alternative explanations, the researchers introduced knockout males to both wild-type males and females simultaneously. In this experiment the knockout males exhibited mating behavior towards males and females at equal frequency. As a result of this additional experiment, the researchers were able to conclude that the mouse VNO does indeed function in gender recognition.
Original Paper
Stowers, L., T. E. Holy, M. Meister, C. Dulac, and G. Koentges. 2002. Loss of sex discrimination and male–male aggression in mice deficient for TRP2. Science 295: 1493–1500.
Links
Beckman, M. 2002. Pheromone reception: When in Doubt, Mice Mate Rather Than Hate. Science 295: 782.
iBioSeminars: Catherine Dulac Part I: Sex and Smell: Chemosensory Detection
Scitable by Nature Education: Scientists Can Analyze Gene Function by Deleting Gene Sequences
Kimball’s Biology Pages: Pheromones
Dulac, C., and A. T. Torello. 2003. Molecular detection of pheromone signals in mammals: from genes to behaviour. Nature Reviews Neuroscience 4: 551–562.