Final Report Summary - SEX-DIMOR-REP-BEHAV (Characterization of pheromone-evoked sexually dimorphic social and reproductive responses in wild-caught TRPC2 mutant mice, under semi-natural conditions)
From invertebrates to humans, males and females of a given species display identifiable differences in behaviors, mostly but not exclusively pertaining to sexual and social behaviors, which is crucial to the reproductive success of the animal and the survival of the species. A long-standing and fundamental neurobiological question is ‘how are sex-specific behaviors, such as courtship, mating, nursing, and aggression encoded by neural circuits?’
These dimorphic behaviors include a robust set of species-specific fixed action patterns that can be elicited in socially naïve animals, suggesting that the underlying neuronal substrates necessary for their execution are likely to be genetically determined and developmentally programmed. The olfactory system of most mammals is activated by pheromone signals that play an essential role in eliciting and regulating characteristic arrays of sexually dimorphic innate reproductive and social behaviors. Pheromones are generally defined as chemosensory substances that are released to the outside by one individual and elicit species-specific innate behavioral and long-lasting neuro-endocrinological responses in other individuals. Information being delivered via pheromone signals includes social, biologically relevant information such as species, gender, individual identity, age, and reproductive status.
The project main objectives are: 1. To develop new experimental design to study pheromone-mediated responses under natural biologically relevant context. 2. To use this model (i.e. aim 1) in order to identify novel behavioral, physiological and neurobiochemical pheromone-mediated social and sexual responses, in freely socially-interacting mice.
In this project we performed a genetic back-crossing of laboratory knockout mouse model with wild-caught mice; hence, transferring the specific mutation involve in pheromone detection from a standard inbred laboratory mouse strain onto an outbred wild-caught genetic background. Next, we performed a comprehensive phenotypic characterizations in term of morphology, physiology and behavior, of wild-caught mice, laboratory inbred mice and the wild-backcrossed mice, in males and females. This large scale phenotypic analysis (>25 quantified parameters) demonstrate that: 1. unexpectedly, there is a profound female-bias in the effects of domestication on mouse behavioral traits. Specifically, in females, but not in males, a large number of complex behaviors including anxiety-related responses, inter-females aggression and pup-directed behaviors were found to be dramatically different between the laboratory and the wild-caught mice. 2. The backcrossed mouse model displays similar phenotypic traits to wild-caught mice, including social and reproductive behaviors presented by wild-caught females but are absent in the laboratory mice.
This novel mouse model, in contrast to any other wild-backcrossed laboratory strains generated to date, allows the study of the genetic and neuronal basis of ecological relevant behavioral traits, as well as physiological and morphological traits, that were profoundly altered or even lost in all classical laboratory (domesticated) mouse strains.
As a proof of concept, to demonstrate the applicability and potential of the wild-backcrossed model system, we assessed the role of TrpC2 – a gene that was shown to mediate pheromone-evoked social behaviors in laboratory mice – in female social and reproductive behaviors in TrpC2 mutant laboratory and wild-backcrossed mice.
We revealed a novel role of TrpC2 gene in wild-backcrossed females, in which female aggressive behavior toward pups is activated by TrpC2-mediated signals, a behavioral phenotype which was absent in the TrpC2 mutant laboratory females. Furthermore, we also showed that previously reported phenotype observed in the laboratory TrpC2 mutant strain, i.e. lost of sexual preference and elevation of male-typical sexual behavior, is retained in the wild-backcrossed TrpC2 mutant females.
Lastly we have developed and constructed semi-natural enclosures equipped with an automated tacking system for multiple mice. We have developed large panel of mathematic algorithms that allow to automatically identified and quantified varies mouse behavior parameters. Next, we have performed a series of assay to validate the accuracy of the behavioral phenotyping of the automated system by studying the mice behavior in our novel system and compared it to the mice behavior as quantified by human observer and using commercially available systems.
We found that the system allowing automated recording of the precise spatial position and wide range of behaviors with high accuracy of freely-interacting mice of different genotype, age or sex. Specifically, we found that this automatic behavioral phenotyping system can precisely and robustly identify and quantify of pheromone-evoked social behaviors including chasing behavior, sexual behavior, aggressive, sociability level, social hierarchy and social discrimination. Our innovative tracking and behavioral characterization provides an integrative solution for multi-purposes and an interdisciplinary applicable framework for studying the mechanisms underlying social interactions of animal colonies, collective animal behaviors and autistic-related behaviors within naturalistic, complex environments and diverse animal models.
Together these project devolved and applied novel ethologically-relevant behavioral approaches, costume-designed experimental set-ups and combine it with the power of advance mouse genetic techniques. This allowed to deeper our understanding on the effects of pheromone signals on behavioral and neuroendocrinology responses and better understanding of the neuronal mechanisms controlling sex-typical reproductive and social responses in mammals. Also, since the research program places an emphasis on understanding both reproductive and social behaviors discoveries it provide a platform to future studies defining the mechanism underlying sex-related mental and social disorders, such as autism spectrum disorders.
Website:
http://www.weizmann.ac.il/neurobiology/labs/kimchi/