Comprehensive analysis of expression, subcellular localization, and cognate pairing of SNARE proteins in oligodendrocytes

Abstract

Oligodendrocytes form the central nervous system myelin sheath by spiral wrapping of their plasma membrane around axons, necessitating a high rate of exocytic membrane addition to the growing myelin membrane. Membrane fusion is mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptor proteins (SNAREs), which act by specific pairing of vesicle (R)- and target (Q)-SNAREs. To characterize oligodendroglial SNAREs and their trafficking pathways, we performed a detailed expression analysis of SNAREs in differentiating cultured oligodendrocytes and myelin and determined their subcellular localization. Expression of the plasma membrane Q-SNAREs syntaxin 3, syntaxin 4, SNAP23, and the endosomal R-SNARE VAMP3/cellubrevin increased with oligodendroglial maturation, while the expression of SNAP29 decreased. Interestingly, syntaxin 3, syntaxin 4, and VAMP7/tetanustoxin-insensitive VAMP accumulated in myelin during development, suggesting a role in myelin membrane fusion. Coimmunoprecipitation from oligodendroglial cell lysates elucidated interactions between SNAREs: for example, Golgi-localized VAMP4 associated with syntaxin 6 and SNAP29. Furthermore, we identified a cognate core complex composed of VAMP3, syntaxin 4, and SNAP23, which may mediate fusion of endosome-derived vesicles with the plasma membrane. This study provides a comprehensive analysis of SNARE proteins in oligodendrocytes and assigns defined SNAREs to putative vesicle trafficking pathways in myelinating oligodendrocytes, thus facilitating future functional analysis of distinct SNAREs in oligodendroglial membrane traffic and myelination.