The adhesion G protein-coupled receptor GPR56 is a cell-autonomous regulator of oligodendrocyte development

Stefanie Giera,Yiyu Deng,Rong Luo,Gabriel Corfas,Allison R Bialas,Kelly R Monk,Yanqin Ying,Manabu Makinodan,Bernard S Chang,Sarah D Ackerman,Beth Stevens,Sung-Jin Jeong,Amit Mogha,Xianhua Piao

doi:10.1038/ncomms7121

Abstract

Mutations in GPR56, a member of the adhesion G protein-coupled receptor family, cause a human brain malformation called bilateral frontoparietal polymicrogyria (BFPP). Magnetic resonance imaging (MRI) of BFPP brains reveals myelination defects in addition to brain malformation. However, the cellular role of GPR56 in oligodendrocyte development remains unknown. Here, we demonstrate that loss of Gpr56 leads to hypomyelination of the central nervous system in mice. GPR56 levels are abundant throughout early stages of oligodendrocyte development, but are downregulated in myelinating oligodendrocytes. Gpr56-knockout mice manifest with decreased oligodendrocyte precursor cell (OPC) proliferation and diminished levels of active RhoA, leading to fewer mature oligodendrocytes and a reduced number of myelinated axons in the corpus callosum and optic nerves. Conditional ablation of Gpr56 in OPCs leads to a reduced number of mature oligodendrocytes as seen in constitutive knockout of Gpr56. Together, our data define GPR56 as a cell-autonomous regulator of oligodendrocyte development.

Highlights

Mutations in GPR56, a member of the adhesion G protein-coupled receptor family, cause a human brain malformation called bilateral frontoparietal polymicrogyria (BFPP)
Immunohistochemistry (IHC) and western blot analysis of myelin basic protein (MBP) and proteolipid protein (PLP), two markers for mature OLs and central nervous system (CNS) myelin, showed significant reductions of the two proteins in Gpr[56] À / À mice compared with controls (Fig. 1c–e and Supplementary Fig. 3)
After culturing for 4 days in the presence of PDGF-AA, a major oligodendrocyte precursor cell (OPC) mitogen, we found that the percentage of dividing OPCs, represented by Ki67 þ in total PDGFRa þ population, was significantly reduced in OPCs derived from Gpr[56] À / À mouse brains compared with controls (Fig. 5c,d)

Summary

Results

Loss of GPR56 results in CNS myelination defects. CNS white matter abnormalities, manifesting as bilateral foci of T2 signal intensity change within the cerebral white matter on brain MRIs (Supplementary Fig. 1, right panel), is one of the hallmarks of BFPP brains[12,13,22,23]. To test whether the reduced number of OPCs and mature OLs observed in Gpr[56] knockouts is due to decreased OPC proliferation, we performed double immunostaining of NG2 and Ki67, markers for OPCs and proliferating cells, respectively, on postnatal brains of Gpr[56] À / À and their littermate controls. A significantly reduced number of dual-positive cells was detected in Gpr[56] À / À brains, compared with the controls (Fig. 5a,b), suggesting that GPR56 has a role in regulating OPC proliferation, either directly or indirectly. A significantly fewer number of Plp þ mature OLs was found in the CC of Gpr56fl/fl; Pdgfra-cre þ / À , compared with the controls (Fig. 7e), demonstrating that GPR56 regulates OL development in a cell-autonomous manner

Discussion

20 Total RhoA

E Null allele