Oxysterol-binding protein-related protein 6 regulates neuronal morphology and migration of cerebellar granule cells during cerebellar development in vivo.

Oxysterol-binding protein (OSBP)-related protein (ORP) 6, a member of subfamily III of the ORP family, localizes at endoplasmic reticulum-plasma membrane contact sites and is involved in regulating the turnover of the lipid composition of the plasma membrane through the counter-transport of phosphatidylinositol-4-phosphate and phosphatidylserine in neurons. However, the physiological functions of ORP6-mediated lipid counter-transport remain poorly understood. In the present study, we investigated the developmental expression of ORP6 protein in the mouse cerebellum and the role of ORP6 in neuronal differentiation and migration using Neuro-2A cells and primary cultured cerebellar granule cells (CGCs). The expression of the ORP6 protein increased from P7 to P21, coinciding with a key period of granule cell progenitor proliferation and immature CGC migration. Both ORP6 RNAi knockdown and overexpression of two different types of dominant-negative ORP6 constructs significantly increased the number and length of neurites in retinoic acid-induced differentiated Neuro-2A cells. Similarly, ORP6 knockdown in primary cultured CGCs increased neurite number and length and disrupted their migration in vitro. Furthermore, overexpression of a dominant-negative form of ORP6 in immature CGCs using in vivo electroporation impaired their migration into the granule layer. Taken together, these results suggest the possible involvement of lipid counter-transport by ORP6 in the regulation of neuronal morphology and migration of CGCs.