Deep Phenotyping Reveals Movement Phenotypes in Mouse Neurodevelopmental Models

Abstract

Background: Repetitive action, resistance to environmental change, and fine motor disruptions are hallmarks of autism spectrum disorder (ASD) and other neurodevelopmental disorders, and vary considerably from individual to individual. In animal models, conventional behavioral phenotyping captures such fine-scale variations incompletely. Here, we aimed at investigating behavioral consequences of a cerebellum-specific deletion in Tsc1 protein and a whole-brain knockout in Cntnap2 protein in mice, both mutations are found in the clinical conditions and have been associated with ASD. We observed male and female C57BL/6J mice to methodically catalog adaptive movement over multiple days and examined two rodent models of developmental disorders against this dynamic baseline. Methods: Here, we use advances in computer vision and deep learning, a generalized form of high-dimensional statistical analysis, to develop a framework for characterizing mouse movement on multiple time scales using a single popular behavioral assay, the open field test. The pipeline takes virtual markers from pose estimation to find behavior clusters and generate wavelet signatures of behavior classes. We measured spatial and temporal habituation to a new environment across minutes and days, different types of self-grooming, locomotion and gait. Results: Both Cntnap2 knockout and L7-Tsc1 mutants showed forelimb lag during gait. L7-Tsc1 mutants showed complex defects in multi-day adaptation, lacking the tendency of wild-type mice to spend progressively more time in corners of the arena. In L7-Tsc1 mutant mice, failure-to-adapt took the form of maintained ambling, turning, and locomotion, and an overall decrease in grooming. Adaptation in Cntnap2 knockout mice more broadly resembled that of wild-type. L7-Tsc1 mutant and Cntnap2 knockout mouse models showed different patterns of behavioral state occupancy. Limitations: Genetic risk factors for autism are numerous, and here we tested only two. Our pipeline was only applied to conditions of free behavior. Testing under task or social conditions would reveal more information about behavioral dynamics and variability. Conclusions: Our automated pipeline for deep phenotyping successfully captures model-specific deviations in adaptation and movement as well as differences in the detailed structure of behavioral dynamics. The reported deficits indicate that deep phenotyping constitutes a robust set of ASD symptoms that may be considered for implementation in clinical settings as a quantitative diagnosis criteria.

Neural mechanisms underlying the temporal organization of naturalistic animal behavior

“…Comparison of state usage and transition rates can also reveal subtle phenotypical changes in the structure of ongoing behavior in genetically modified mice compared to wildtype ones. This phenotypic fingerprinting has led to insights into the behavior of mouse models of autism spectrum disorder ( Wiltschko et al, 2015 ; Wiltschko et al, 2020 ; Klibaite et al, 2021 ).…”

“…Earlier studies of contextual modulations of rodent freely moving behavior by pharmacological or genetic manipulations were mostly confined to comparison of usage statistics of single actions ( Wiltschko et al, 2015 ). However, more recent studies ( Marshall et al, 2021 ; Klibaite et al, 2021 ), which mapped the rodent behavioral hierarchy, allowed a multiscale assessment of contextual effects. In a rat model of the fragile X syndrome, while mutant and wildtype rats had similar locomotor behavior, the former showed abnormally long grooming epochs, characterized by different behavioral sequences and states compared to wildtypes ( Figure 7C ).…”