Fig. 8. The effects of DHCR7 impinges on Smo. (A-F) Microinjection of DHCR7^R350W mutant inhibits endogenous Shh signaling. Embryos microinjected with 1 ng of DHCR7^R350W mRNA inhibits the expression of FoxA2, Shh and Ptc-1. (G-I) Microinjection of mRNA (500 pg) encoding dnPKA inhibits the cyclopic phenotype caused by DHCR7^R350W. (J) Control uninjected embryo. (K) Smo-M2 rescues DHCR7-mediated Hh signaling inhibition. Embryos were co-injected with 8x3'Gli-BS Luc together with Chordin, Shh-N, DHCR7 or Smo-M2 mRNA (0.5 ng), or in combination, and the reporter gene activity was measured. (L) DHCR7^IVS8-1G>C blocks Gli reporter activation mediated by Smo-M2. Embryos were co-injected with Gli reporter together with Chordin, DHCR7^IVS8-1G>C or Smo-M2 mRNA, or in combination, and reporter gene activity was measured. (M) Model for the role of DHCR7 in Shh signaling. Shh inactivates Ptc, thus permitting the activation of Smo. Activated Smo transmits a Shh signal to activate Gli protein. PKA inhibits Gli activation. DHCR7 inhibits Shh signaling either at the level of or downstream of Smo.