HCK and medulloblastoma: Although both Gli1 and Hck are important for Shh target gene activation, they are not required for normal development.19, 37, 48, 49 During normal development, Gli2 is sufficient for Shh-induced gene activation.19 Gli1 is required for medulloblastoma formation and is more potent than Gli2 at inducing cell transformation.50 Thus Gli1 activity is important for the abnormally high transcription output of Shh signaling that are required for tumorigenesis.