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

Abstract

The role of compartmentalized signaling in primary cilia during tissue morphogenesis is not well understood. The cilia localized G protein-coupled receptor, Gpr161, represses hedgehog pathway via cAMP signaling. We engineered a knock-in at the <i>Gpr161</i> locus in mice to generate a variant (Gpr161^mut1), which was ciliary localization defective but cAMP signaling competent. Tissue phenotypes from hedgehog signaling depend on downstream bifunctional Gli transcriptional factors functioning as activators or repressors. Compared to knockout (ko), <i>Gpr161^mut1/ko</i> had delayed embryonic lethality, moderately increased hedgehog targets, and partially down-regulated Gli3 repressor. Unlike ko, the <i>Gpr161^mut1/</i>^ko neural tube did not show Gli2 activator-dependent expansion of ventral-most progenitors. Instead, the intermediate neural tube showed progenitor expansion that depends on loss of Gli3 repressor. Increased extraciliary receptor levels in <i>Gpr161^mut1/mut1</i> prevented ventralization. Morphogenesis in limb buds and midface requires Gli repressor; these tissues in <i>Gpr161^mut1/mut1</i> manifested hedgehog hyperactivation phenotypes-polydactyly and midfacial widening. Thus, ciliary and extraciliary Gpr161 pools likely establish tissue-specific Gli repressor thresholds in determining morpho-phenotypic outcomes.