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Fig. 2. Possible ways in which megalin might influence N-Shh trafficking and
signaling. The mechanisms include direct signaling via megalin [the asterisk
indicates megalin-binding adaptor proteins of the fetal brain
(Petersen et al., 2003)],
megalin-mediated endocytosis and trafficking of N-Shh leading to N-Shh
transcytosis and megalin-mediated trafficking of the N-Shh receptors Ptc and
Smo. Not depicted in the model are heparan sulfate proteoglycans, which have
been shown to cooperate with megalin in N-Shh endocytosis
(McCarthy et al., 2002).