Functional aspects of a tyrosine kinase encoding protooncogene, the c-src gene

To date the src gene family consists of at least 9 closely related protein tyrosine kinases belonging to the non-receptor type of kinases: c-src, c-yes, c-fgr, fyn, lyn, lck, hck, tkl and bkl. We have intensively studied the expression of the c-src gene during evolution and with respect to its possible functions in the processes of cellular differentiation and proliferation. From our results we conclude, that the c-src encoded tyrosine kinase could play a role in the development and/or maintenance of the multicellular organisation of primitive organisms like sponges or coelenterates. With respect to its tissue-specific expression pattern with neuronal cells always displaying elevated levels of pp60c-src and the observation that synaptophysin, the major constituent of the synaptic vesicle membrane protein, is phosphorylated by the c-src encoded tyrosinekinase in vitro and in intact synaptic vesicles, we suggest an essential role for pp60c-src in signal transduction pathways and/or axonal transport mechanisms in neurons.