Constitutive activation of canonical Wnt signaling disrupts choroid plexus epithelial fate

The choroid plexus (ChP) secretes cerebrospinal fluid and is critical for the development and function of the brain. In the telencephalon, the ChP epithelium (ChPe) arises from the Wnt- expressing cortical hem. Embryonic mouse and human ChPe both express nuclear β-CATENIN, a canonical Wnt signaling pathway effector, indicating that this pathway is active during ChPe development. Point mutations in human β-CATENIN result in the constitutive activation of canonical Wnt signaling. In a mouse model that recapitulates this perturbation, we report a loss of ChPe identity and an apparent transformation of the ChPe to a neuronal identity. Aspects of this phenomenon are recapitulated in human embryonic stem cell (hESC)-derived organoids. The ChPe is also disrupted when β-Catenin is conditionally inactivated in the mouse. Together, our results indicate that canonical Wnt signaling is required in a precise and regulated manner for normal ChPe development in the mammalian brain.