Cilium proteomics reveals Numb as a positive regulator of the Hedgehog signaling pathway

The transduction of Hedgehog (Hh) signaling relies on the primary cilium, a cell surface organelle acting as a signaling hub for the cell. Using proximity labeling and quantitative proteomics, we identified Numb as a new ciliary protein that positively regulates Hh signaling. Numb localizes to the ciliary pocket and acts as an endocytic adaptor to incorporate Ptch1 into clathrin-coated vesicles, thereby promoting Ptch1 exit from the cilium, a key step in Hh signaling activation. Numb loss impaired Sonic Hedgehog-induced Ptch1 departure from the cilium, resulting in severe attenuation of Hh signaling. Genetic ablation of Numb and its homolog Numblike in the developing cerebellum impaired the proliferation of granule cell precursors, a Hh-dependent process, resulting in reduced cerebellar size. This study demonstrates a key function of Numb in controlling protein levels in the cilium, and highlights Numb's critical role in the regulation of Hh signaling. ### Competing Interest Statement The authors have declared no competing interest.