In invertebrates, just as in "Drosophila", the binding of Hedgehog to PTCH leads to internalisation and sequestration of the ligand. Consequently, "in vivo" the passage of hedgehog over a receptive field that expresses the receptor leads to attenuation of the signal, an effect called ligand-dependent antagonism (LDA). In contrast to "Drosophila", vertebrates possess another level of hedgehog regulation through LDA mediated by Hh-interacting protein 1 (HHIP1). HHIP1 also sequesters hedgehog ligands, but unlike PTCH, it has no effect on the activity of SMO.