CD47 is involved in neurite differentiation in cultured neurons, but the function of CD47 in brain development is largely unknown. We determined that CD47 mRNA was robustly expressed in the developing cerebellum, especially in granule cells. CD47 protein was mainly expressed in the inner layer of the external granule layer (EGL), molecular layer, and internal granule layer (IGL), where granule cells individually become postmitotic and migrate, leading to neurite fasciculation. At postnatal day 8 (P8), CD47 knockout mice exhibited an increased number of proliferating granule cells in the EGL, whereas the CD47 agonist peptide 4N1K increased the number of postmitotic cells in primary granule cells. Knocking out the CD47 gene and anti-CD47 antibody impaired the radial migration of granule cells from the EGL to the IGL individually in mice and slice cultures. In primary granule cells, knocking out CD47 reduced the number of axonal collaterals and dendritic branches; by contrast, overexpressing CD47 or 4N1K treatment increased the axonal length and numbers of axonal collaterals and dendritic branches. Furthermore, the length of the fissure between Lobules VI and VII was decreased in CD47 knockout mice at P21 and at 14 wk after birth. Lastly, CD47 knockout mice exhibited increased social interaction at P21 and depressive-like behaviors at 10 wk after birth. Our study revealed that the cell adhesion molecule CD47 participates in multiple phases of granule cell development, including proliferation, migration, and neurite differentiation implying that aberrations of CD47 are risk factors that cause abnormalities in cerebellar development and atypical behaviors.
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