Studies of synaptic vesicle endocytosis in the nematode C. elegans.

After synaptic vesicle exocytosis, synaptic vesicle proteins must be retrieved from the plasma membrane, sorted away from other membrane proteins, and reconstituted into a functional synaptic vesicle. The nematode Caenorhabditis elegans is an organism well suited for a genetic analysis of this process. In particular, three types of genetic studies have contributed to our understanding of synaptic vesicle endocytosis. First, screens for mutants defective in synaptic vesicle recycling have identified new proteins that function specifically in neurons. Second, RNA interference has been used to quickly confirm the roles of known proteins in endocytosis. Third, gene targeting techniques have elucidated the roles of genes thought to play modulatory or subtle roles in synaptic vesicle recycling. We describe a molecular model for synaptic vesicle recycling and discuss how protein disruption experiments in C. elegans have contributed to this model.

Mutations in synaptojanin disrupt synaptic vesicle recycling.

Synaptojanin is a polyphosphoinositide phosphatase that is found at synapses and binds to proteins implicated in endocytosis. For these reasons, it has been proposed that synaptojanin is involved in the recycling of synaptic vesicles. Here, we demonstrate that the unc-26 gene encodes the Caenorhabditis elegans ortholog of synaptojanin. unc-26 mutants exhibit defects in vesicle trafficking in several tissues, but most defects are found at synaptic termini. Specifically, we observed defects in the budding of synaptic vesicles from the plasma membrane, in the uncoating of vesicles after fission, in the recovery of vesicles from endosomes, and in the tethering of vesicles to the cytoskeleton. Thus, these results confirm studies of the mouse synaptojanin 1 mutants, which exhibit defects in the uncoating of synaptic vesicles (Cremona, O., G. Di Paolo, M.R. Wenk, A. Luthi, W.T. Kim, K. Takei, L. Daniell, Y. Nemoto, S.B. Shears, R.A. Flavell, D.A. McCormick, and P. De Camilli. 1999. Cell. 99:179-188), and further demonstrate that synaptojanin facilitates multiple steps of synaptic vesicle recycling.

Affinity of 10-(4-methylpiperazino)dibenz[b,f]oxepins for clozapine and spiroperidol binding sites in rat brain.

10-(4-Methylpiperazino)dibenz[b,f]oxepins were prepared and evaluated as potential antipsychotic agents using specific clozapine [8-chloro-11-(4-methylpiperazino)-5H-dibenzo[b,e][1,4]diazepine] binding sites in rat forebrain that are noncholinergic and nondopaminergic in nature and from which [3H]clozapine is displaced by known antipsychotic agents. [3H]Clozapine binding in the presence of atropine represents nonmuscarinic binding, while binding in the absence of atropine represents muscarinic (cholinergic) plus nonmuscarinic binding. The relative affinity for dopamine binding sites was determined by displacement of [3H]spiroperidol from binding sites in rat caudate nuclei. Thus, clozapine, its 2-chloro isomer, its dechloro analogue, and their 5H-dibenzo[a,d]cycloheptene and dibenz[b,f]oxepine analogues have about the same relative affinity for the nonmuscarinic clozapine binding sites. At the spiroperidol (dopaminergic) sites, both the nature of the tricyclic system and the presence of a chlorine atom on the tricyclic system have a substantial effect on the binding affinity. Within each series, shift or a chlorine atom from the position distal to the piperazino group to the proximal position increases the binding affinity by a factor of about nine, but removal of the chlorine atom substantially decreases the binding affinity. Nevertheless, 10-(4-methylpiperazino)dibenz[b,f]oxepin has a threefold greater affinity for the dopaminergic binding sites than does clozapine itself.