The orphan GPCR, Gpr161, regulates the retinoic acid and canonical Wnt pathways during neurulation.

Abstract The vacuolated lens ( vl ) mouse mutation arose on the C3H/HeSnJ background and results in lethality, neural tube defects (NTDs) and cataracts. The vl phenotypes are due to a deletion/frameshift mutation in the orphan GPCR, Gpr 161. A recent study using a null allele demonstrated that Gpr161 functions in primary cilia and represses the Shh pathway. We show the hypomorphic Gpr 161 vl allele does not severely affect the Shh pathway. To identify additional pathways regulated by Gpr161 during neurulation, we took advantage of naturally occurring genetic variation in the mouse. Previously Gpr 161 vl- C3H was crossed to different inbred backgrounds including MOLF/EiJ and the Gpr 161 vl mutant phenotypes were rescued. Five modifiers were mapped ( Modvl : Mod ifier of vl ) including Modvl 5 MOLF . In this study we demonstrate the Modvl 5 MOLF congenic rescues the Gpr 161 vl -associated lethality and NTDs but not cataracts. Bioinformatics determined the transcription factor, Cdx 1, is the only annotated gene within the Modvl 5 95% CI co-expressed with Gpr 161 during neurulation and not expressed in the eye. Using Cdx 1 as an entry point, we identified the retinoid acid (RA) and canonical Wnt pathways as downstream targets of Gpr 161. QRT-PCR, ISH and IHC determined that expression of RA and Wnt genes are down-regulated in Gpr 161 vl / vl but rescued by the Modvl 5 MOLF congenic during neurulation. Intraperitoneal RA injection restores expression of canonical Wnt markers and rescues Gpr 161 vl / vl NTDs. These results establish the RA and canonical Wnt as pathways downstream of Gpr 161 during neurulation, and suggest that Modvl 5 MOLF bypasses the Gpr 161 vl mutation by restoring the activity of these pathways.