Cysteine string proteins (CSPs): To be able ot study the function of these new synaptic vesicle components that were discovered in our laboratory, we have generated, in collaboration with two groups in Swizerland and the USA, "knock-out" flies which lack the csp gene. The detailed analysis of the phenotype of these mutants, in combination with biochemical properties of vertebrate cysteine string proteins that were cloned independently by colleagues in the USA and Great Britain, allows us now to propose a hypothesis for the molecular function of these proteins. Cysteine string proteins contain a "J" domain that is known to interact with Hsp70 heat shock proteins. The CSP-Hsp70 complex presumably acts as a molecular chaperone. We speculate that this chaperone relieves the inactivation of presynaptic, voltage sensitive calcium channels at those sites of the presynaptic membrane where synaptic vesicles have docked. By such a mechanism calcium entry can be restricted to the actual sites of exocytosis, and the intracellular accumulation of physiologically ineffective calcium is prevented. Fig. 1 shows two larval body wall muscles with the associated segmental nerve. Synaptic boutons have been stained immunochemically by using an antibody against CSPs.

Synapsins: These phosphoproteins have been studied in vertebrates for many years and intensive efforts to clone a homologous gene in Drosophila have been unsuccessful. By an antibody crossreaction we have accidentally discovered the gene and have subsequently generated "knock-out" flies. We are now in a position to characterize functional defects in the mutants and compare them to the described phenotypes of synapsin "knock-out" mice. One focus of our investigations will be a quantitative analysis of plastic phenomena related to learning and memory. Our preliminary data show that deletion of this abundant synaptic vesicle protein in flies fails to lead to dramatic disruptions of synaptic transmission, an observation previously already noted in mice. In collaboration with Prof. Hoppe (Physiological Chemistry Department) we have identified a translation start site of the Syn gene. The pattern of synapsin phosporylation is presently investigated in Drosophila and the possible function of these posttranslational modifications will be analyzed by molecular genetic techniques.

Synapse-associated protein of 47kD (SAP47): This novel synaptic protein of Drosophila displays no significant homologies to known proteins. Recently, we have identified in the genetic data base an "expressed sequence tag" clone coding for a human homologue of SAP47. In collaboration with Prof. Weber and Prof. Schmid (Human Genetics Department) we have cloned the corresponding human gene and localized it on the X chromosome. The generation of "knock-out" flies is presently attempted in order to analyze the function of this new protein family. The phenotype of such mutants may provide first hints to human diseases that may possibly be related to a defect in the human sap47 gene.

For details see Projects list.