Insufficiency of BUBR1, a mitotic spindle checkpoint regulator, causes impaired ciliogenesis in vertebrates

BUBR1 is a central molecule of the spindle assembly checkpoint. Germline mutations in the BUB1B gene encoding BUBR1 cause Premature Chromatid Separation (PCS) / Mosaic Variegated Aneuploidy (MVA) syndrome, which is characterized by constitutional aneuploidy and a high risk of childhood cancer. Patients with the syndrome often develop Dandy-Walker complex and polycystic kidneys; implying a critical role of BUBR1 in morphogenesis. However, little is known about the function of BUBR1 other than mitotic control. Here, we report that BUBR1 is essential for the primary cilium formation, and that PCS (MVA) syndrome is thus a novel ciliopathy. Morpholino knockdown of bubr1 in medaka fish also caused ciliary dysfunction characterized by defects in cerebellar development and perturbed left-right asymmetry of the embryo. Biochemical analyses demonstrated that BUBR1 is required for ubiquitin-mediated proteasomal degradation of CDC20 in the G0 phase and maintains anaphase promoting complex/cyclosome-CDH1 (APC/CCDH1) activity that regulates the optimal level of Dishevelled for ciliogenesis.