Figure 3. Model of Hh signal activation.

Figure 3

Model of Hh signal activation. 1) In the absence of Hh (left panel), Ptc is constantly recycling from the plasma membrane to vesicles inside the cells. Occasionally, these vesicles enter the proteolytic pathway. 2) At the same time, Smo is kept inactive in an intracellular compartment, unable to signal. Smo enters as well the degradative pathway under this situation. 3) Upon the reception of Hh (right panel), the receptor-ligand complex is internalized, contributing to the slope of the gradient of Hh. 4) At the same time, Ptc no longer represses Smo, which is stabilized and traffics to the plasma membrane preferentially. This plasma membrane stabilization of Smo correlates with signal activation.

From: The Patched Receptor: Switching On/Off the Hedgehog Signaling Pathway

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