4.1G promotes arborization and tight junction formation of oligodendrocyte cell line OLN-93.

4.1G belongs to the membrane-associated band 4.1 protein family, which plays important roles in establishing and maintaining the links between transmembrane proteins and the cytoskeleton. Till date, expression and functions of 4.1G in the central nervous system (CNS) have not been fully elucidated. We investigated expression, cellular/subcellular distribution, and biological roles of 4.1G in the rat CNS and in cultured oligodendrocyte cell line OLN-93. Immunoblotting (IB) and immunoprecipitation revealed CNS 4.1G protein isoforms with molecular weights ranging from ∼80 to ∼180 kDa. In subconfluent OLN-93 cell culture, overexpression of full-length 4.1G and C-terminal-domain-deleted 4.1G, but not the FERM-domain-deleted 4.1G, promoted cellular arborization. In confluent cells, endogenous 4.1G was upregulated and clustered in the cytoplasmic periphery together with tight junction protein ZO-1. FERM domain seemed essential for this recruitment of 4.1G to OLN-93 cell periphery. Calcium switch experiment demonstrated that overexpressed 4.1G promoted tight junction reassembly, whereas siRNA knockdown of endogenous 4.1G inhibited tight junction formation among confluent OLN-93 cells. Together, these results suggest functional roles of 4.1G in cellular arborization and tight junction formation. In the CNS, 4.1G might be involved in maturation of host cells as well as in interaction among neurons/neuroglia.