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. Author manuscript; available in PMC: 2017 May 1.
Published in final edited form as: Trends Mol Med. 2016 Apr 13;22(5):404–413. doi: 10.1016/j.molmed.2016.03.006

Figure 5. The Sonic Hedgehog (Shh) pathway is critical for cerebellar development.

Figure 5

During cerebellar development, Purkinje cells secrete Sonic Hedgehog (Shh) and other mitogens that stimulate the granule cells to proliferate. RORα is a transcription factor that upregulates Shh gene expression. Shh binds to the Patched receptor (Ptch1) on the surface of granule cells. This relieves Ptch1-mediated inhibition of Smoothened (Smo). Smo signaling leads to activation of Gli2 as a transcription factor and thus expression of genes encoding transcription factors (such as Gli1) and proteins needed for cell proliferation (such as Cyclin D1), among others. Atoh1 is a transcription factor expressed in immature granule cells that regulates basal gene expression of Gli2. This contributes to the sensitivity to proliferative signals coming from Purkinje cells.