A New LIVE MOUSE Tracking System Reveals That SHANK2 and SHANK3 Mutant MICE Display Opposite Abnormal Behaviours in Object Exploration and HOME-Cage Social Conditions

Background: Mutations in genes coding for synaptic proteins were shown to increase susceptibility to autism spectrum disorder (ASD). Among the causative proteins, cell adhesion molecules such as neuroligins and neurexins as well as scaffolding proteins such as SHANK3 and SHANK2 were robustly associated with ASD in independent patients. We previously analysed transgenic knockout mice lacking Shank2. These mice displayed abnormal glutamatergic receptor expression and neurotransmission, as well as hyperactivity, longer grooming bouts and subtle abnormalities in social interactions and communication.

Objectives: The aim of the present project was to develop new protocols to investigate further the behavioural deficits in Shank2 mutant mice in object exploration and in the home cage. We conducted a comparative study in Shank3 mutant mice. Such new ways of phenotyping within the home cage allow to characterise behavioural abnormalities at a finer level of details and in a more comprehensive way than the classical tests, that trigger a high level of stress in the mice. Testing mice together without intervention also permits to better control experimental conditions.

Methods: Comparisons were drawn between Shank2^-/- (deletion of exon 16), Shank3^-/- (deletion of exon 11) and their respective wild-type adult female littermates (generated on a C57BL/6J background). We tested 12-18 animals per genotype. We tested locomotor activity and reactions to a novel object in a single mouse, as well as mixed-genotype group home cage behaviour. We used a newly developed tracking system (Live Mouse Tracker). This system allows to follow individually each mouse within a group over several days and to record its individual behaviours and social interactions.

Results: We were able to show that later generations of Shank2 mutant mice still displayed a high hyperactivity in comparison with their wild-type littermates, while Shank3^-/- mice displayed a reduced activity in comparison with their wild-type littermates. Shank2^-/- mice lacked risk assessment behaviour when confronted with a novel object, in contrast to their wild-type littermates and to Shank3^-/- mice. Home cage behaviour was minimally affected in Shank3 mutant mice while social behaviours were significantly perturbed in Shank2 mutant mice.

Conclusions: In conclusion, the Live Mouse Tracker system allows to describe fine behavioural specificities in mouse models of autism. Indeed, both models display abnormal locomotor activity and social behaviour, but not in the same direction. These results highlight that in mice carrying mutations in similar synaptic genes associated with ASD like SHANK2 and SHANK3 can impact social behaviour but with apparently different mechanisms and consequences.