Subcellular localisation of 14-3-3 isoforms in rat brain using specific antibodies

The 14-3-3 protein family, which is present at particularly high concentrations in mammalian brain, is known to be involved in various cellular functions, including protein kinase C regulation and exocytosis. Despite the fact that most of the 14-3-3 proteins are cytosolic, a small but significant proportion of 14-3-3 in brain is tightly and selectively associated with some membranes. Using a panel of isoform-specific antisera we find that the epsilon, eta, gamma, beta, and zeta isoforms are all present in purified synaptic membranes but absent from mitochondrial and myelin membranes. In addition, the eta, epsilon, and gamma isoforms but not the beta and zeta isoforms are associated with isolated synaptic junctions. When different populations of synaptosomes were fractionated by a nonequilibrium Percoll gradient procedure, the epsilon and gamma isoforms were present and the beta and zeta isoforms were absent from the membranes of synaptosomes sedimenting in the more dense parts of the gradient. The finding that these proteins are associated with different populations of synaptic membranes suggests that they are selectively expressed in different classes of neurones and raises the possibility that some or all of them may influence neurotransmission by regulating exocytosis and/or phosphorylation.