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, Gpr161. A recent study using a null allele demonstrated that Gpr161 functions in primary cilia and represses the Shh pathway. We show the hypomorphic Gpr161(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 Gpr161(vl-C3H) was crossed to different inbred backgrounds including MOLF/EiJ and the Gpr161(vl) mutant phenotypes were rescued. Five modifiers were mapped (Modvl: Modifier of vl) including Modvl5(MOLF). In this study we demonstrate the Modvl5(MOLF) congenic rescues the Gpr161(vl)-associated lethality and NTDs but not cataracts. Bioinformatics determined the transcription factor, Cdx1, is the only annotated gene within the Modvl5 95% CI co-expressed with Gpr161 during neurulation and not expressed in the eye. Using Cdx1 as an entry point, we identified the retinoid acid (RA) and canonical Wnt pathways as downstream targets of Gpr161. QRT-PCR, ISH and IHC determined that expression of RA and Wnt genes are down-regulated in Gpr161(vl/vl) but rescued by the Modvl5(MOLF) congenic during neurulation. Intraperitoneal RA injection restores expression of canonical Wnt markers and rescues Gpr161(vl/vl) NTDs. These results establish the RA and canonical Wnt as pathways downstream of Gpr161 during neurulation, and suggest that Modvl5(MOLF) bypasses the Gpr161(vl) mutation by restoring the activity of these pathways.

The primary cilium as a cellular receiver: organizing ciliary GPCR signaling

“…Similarly, ciliary GPCRs can activate different downstream pathways depending on the cellular context. Indeed, a recent study uncovered a role of Gpr161 in activating canonical Wnt signaling in addition to its known role in mediating Shh signaling [52]. …”

Genome-wide CRISPR screening identifies new regulators of glycoprotein secretion

“…GPR161 is a G-protein coupled receptor (GPCR) that is involved in neural tube development and acts as a regulator of cell signalling pathways, including Shh signalling, PKA signalling, retinoic acid signalling and Wnt signalling 31,32 . This was a particularly interesting hit as it has recently become clear that GPCRs function at membranes other than the plasma membrane 33 , and previous work has suggested that a Golgi-resident GPCR regulates transport from the Golgi, although the specific GPCR involved remains unknown 34 .…”

Primary Cilia and Coordination of Receptor Tyrosine Kinase (RTK) and Transforming Growth Factor β (TGF-β) Signaling

“…These include mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K)-AKT, Hippo, nuclear factor k light-chain enhancer of activated B cells (NF-kB), and mammalian target of rapamycin (mTOR) pathways (Boehlke et al 2010;Christensen et al 2012;Wann et al 2014;Hansen et al 2015;Umberger and Caspary 2015). In addition, primary cilia were proposed to play a critical role in coordinating the balanced regulation of WNT/b-catenin versus WNT/PCP ( planar cell polarity) pathways (Lienkamp et al 2012;Oh and Katsanis 2013;Veland et al 2013;Li et al 2015;Saito et al 2015), which extensively cross talk with SHH, TGF-b, RTK, MAPK, Hippo, and Notch signaling (Bernascone and Martin-Belmonte 2013;Zhang et al 2014;Borggrefe et al 2016;Zhang et al 2016).…”