Protocadherin γC4 regulates neuronal survival and dendritic self-avoidance

Animal models of human disease syndromes are useful for elucidating disease causes and developing treatments. The protocadherin γC4 (Pcdh-γC4) among the 22 isoforms encoded by the protocadherin-γ (Pcdh-γ) gene cluster causes a human neurodevelopmental syndrome with progressive microcephaly, seizures, and intellectual disorder. Here, we successfully established a useful mouse model of human Pcdh-γC4 neurodevelopmental syndrome, which exhibited motor disfunctions, seizures, brain size reduction, massive neuronal apoptosis and impaired dendritic development of Purkinje cells. At the same times, we generated Pcdh-γC4 only mice that express only full-length Pcdh-γC4 and truncated forms of the other 21 Pcdh-γ isoforms by using a two-step CRISPR/Cas9-based genome editing strategy, DOMINO (Double Mutation Inducing Open reading frame switch). These mice were viable and fertile, unlike Pcdh-γ cluster knockout mice. Biochemical analyses revealed that Pcdh-γC4 significantly regulates phosphorylation of FAK and PYK2, implicating its γ-constant domain in intracellular signaling. Furthermore, we found that Pcdh-γC4 is sufficient to restore normal dendritic self-avoidance of Purkinje cells observed in Pcdh-γ full-cluster knockouts. These findings demonstrate that Pcdh-γC4 is both necessary and sufficient for neuronal survival, dendritic patterning, and signaling, highlighting it as a functionally dominant isoform within the Pcdh-γ gene cluster.