The function of B9D1 (B9 domain containing 1, Ensembl gene identifier ENSG00000108641) is as follows. Component of the tectonic-like complex, a complex localized at the transition zone of primary cilia and acting as a barrier that prevents diffusion of transmembrane proteins between the cilia and plasma membranes. Required for ciliogenesis and sonic hedgehog/SHH signaling (By similarity). .