In the developing nervous system many key proteins are modified or activated by proteolytic enzymes or proteases. These enzymes act both within the neuron as well as in the extracellular environment near growing processes and synapses. By cleaving key regulatory proteins the nervous system proteases influence the development of connections between nerve cells and their targets, and control the processing of secreted hormones and signaling molecules that are necessary for synapse function. The "serine proteases" are an important class of proteolytic enzymes in neurons. The serine proteases are widely conserved in evolution, and are important for both development as well as for changes associated with learning and memory. Understanding how these enzymes are controlled is the central goal of this project. Serine proteases are often regulated by a special class of proteins known as "serpins" (serine protease inhibitors). The serpins and serine proteases function as an interdependent system. In order to understand these proteins better Dr. Keshishian will examine their biological functions in a model genetic organism, Drosophila. In Drosophila Dr. Keshishian has already characterized the key serpins of the nervous system (Spn4), and has noted that Spn4 is expressed at connections between motoneurons and muscles. He has also discovered a second role for Spn4 in the enzymatic processing of precursor forms of secreted peptides and hormones. One variant of Spn4 binds to and regulates peptide processing serine proteases in vitro. When it is experimentally expressed in vivo the protein disrupts endogenous peptide hormone maturation, resulting in developmental abnormalities. A major goal will be to examine serpin functions at both developing neuromuscular connections, and in the processing of peptide hormones, and to test the effects of both its loss and overexpression. Studying Drosophila Spn4 will be of value in understanding how these regulatory molecules influence nervous system development and function in general.
