Heterozygous Mutation of Sonic Hedgehog Receptor (Ptch1) Drives Cerebellar Overgrowth and Sex-specifically Alters Hippocampal and Cortical Layer Structure, Activity, and Social Behavior in Female Mice

Sonic hedgehog (SHH) signaling is essential for the differentiation and migration of early stem cell populations during cerebellar development. Dysregulation of SHH-signaling can result in cerebellar overgrowth and the formation of the brain tumor medulloblastoma. Treatment for medulloblastoma is extremely aggressive and patients suffer life-long side effects including behavioral deficits. Considering that other behavioral disorders including autism spectrum disorders, holoprosencephaly, and basal cell nevus syndrome are known to present with cerebellar abnormalities, it is proposed that some behavioral abnormalities could be inherent to the medulloblastoma sequalae rather than treatment. Using a haploinsufficient SHH receptor knockout mouse model (Ptch1), a partner preference task was used to explore activity, social behavior and neuroanatomical changes resulting from dysregulated SHH signaling. Compared to wild-type, Ptch1 females displayed increased activity by traveling a greater distance in both open-field and partner preference tasks. Social behavior was also sex-specifically modified in Ptch1 females that interacted more with both novel and familiar animals in the partner preference task compared to same-sex wild-type controls. Haploinsufficiency of PTCH1 resulted in cerebellar overgrowth in lobules IV/V and IX of both sexes, and female-specific decreases in hippocampal size and isocortical layer thickness. Taken together, neuroanatomical changes related to deficient SHH signaling may alter social behavior.