Figure 4

Model of Hedgehog signaling In the absence of Hh signal, Cos2 and Su(fu) binding to Ci prevents Ci activation and retain it in the cytoplasm. Most of Ci is available for cleavage in a process which is dependent upon its phosphorylation by the PKA and which involves Cos2 and Slimb. Uncleaved, full-length Ci, is actively exported from the nucleus. Upon Hh reception, Fused is activated and acts on Cos2 and Sufu, alleviating thus their negative effect on Ci. As a result, Ci cleavage is reduced, Ci155 nuclear import overcomes its export and Ci is activated. Ci activation requires Cos2 and Fu to antagonize Su(fu) negative effect. Activated nuclear Ci interact with the CBP to fully activate the transcription of Hh target genes.