Developmental expression of the 25-kDa synaptosomal-associated protein (SNAP-25) in rat brain.

The developmental expression and subcellular distribution of the neuron-specific 25-kDa synaptosomal protein (SNAP-25) were investigated by using Northern (RNA) blots, immunoblots, and immunocytochemistry. Both SNAP-25 protein and mRNA were present at low levels in embryonic day 15 rat brain, and levels of both increased during early postnatal maturation. Developmental immunoblots with antipeptide antisera demonstrated that a 25-kDa peptide was the major isoform in brain, and this form increased steadily from embryonic day 15 through adulthood. A second 27-kDa immunoreactive isoform was present in brain only during early development. Immunoblots of two-dimensional SDS/polyacrylamide gels revealed the presence of a predominant 25-kDa isoform of SNAP-25 in adult brain. Immunocytochemical studies indicated that as immunoreactivity for SNAP-25 increased during development, the cellular localization of SNAP-25 immunoreactivity concomitantly shifted from axons and cell bodies to presynaptic terminals. These data suggest that the SNAP-25 protein shifts in subcellular localization during development and may play a role in the establishment and stabilization of specific presynaptic terminals in brain.