Sociability genetically separable from social hierarchy in amniotes.

Sociability and social hierarchy are two essential features to form a social group. However, it remains unknown whether sociability and social hierarchy are genetically separable. In this study, we examined the social hierarchy, social and social novelty preference of PAS1 knock-out and knock-in mice. PAS1 (placental-accelerated sequence 1) is an enhancer that modulates social hierarchy. We found that PAS1 knock-out mice lack social hierarchy while wallaby/chicken PAS1 knock-in mice establish stable social ranks. Moreover, social and social novelty preference was observed in all PAS1-mutant mice. PAS1 knock-in mice have stronger preference to interact with other mice than wild-type mice (C57BL/6). All PAS1-mutants have neither stress/aggression-like behavior nor olfactory impairment. Overall, our results showed that PAS1 is an indispensable regulatory element in the formation of social hierarchy while PAS1 regulates one of pathways modulating sociability. Therefore, sociability should be genetically separable from social hierarchy in amniotes.