Ciliary and extraciliary Gpr161 pools repress hedgehog signaling in a tissue-specific manner

The role of compartmentalized cAMP signaling in primary cilia is not well understood. The cilia-localized G-protein-coupled receptor—Gpr161 represses hedgehog pathway via cAMP signaling. Here, by generating knock-in mutant mouse at endogenous Gpr161 locus ( mut1 ), we show that ciliary and extraciliary receptor pools repress hedgehog signaling in a tissue-specific manner. Gpr161 ^mut1 was competent in generating cAMP but did not transit through cilia. Compared to knockout, Gpr161 ^mut1 had delayed embryonic lethality, less upregulation of hedgehog targets and partially down-regulated Gli3-repressor. Ventral-most progenitor expansion in neural tube of Gpr161 knockout occurred in a Gli2-activator-dependent manner but was not seen in Gpr161 ^mut1 . Intermediate-level ventralization occurred from Gpr161 lack specifically in cilia but was restored by increased extraciliary mutant generating Gli3-repressor. Morphogenesis in limb buds and midface that require Gli-repressor manifested hedgehog hyperactivation phenotypes— polydactyly and midfacial widening—in Gpr161 ^mut1 . Thus, ciliary and extraciliary cAMP signaling establishes tissue-specific Gli-repressor thresholds in dictating morpho-phenotypic outcomes.