VISUALIZATION OF SLOW AXONAL-TRANSPORT IN-VIVO

In axons, cytoskeletal constituents move by slow transport, However, i t remains controversial whether axonal neurofilaments are dynamic stru ctures in which only subunits are transported or whether filaments ass emble in the proximal axon and are transported intact as polymers to t he axon terminus. To investigate the form neurofilament proteins rake during transport, neurons of transgenic mice lacking axonal neurofilam ents were infected with a recombinant adenoviral vector encoding epito pe-tagged neurofilament M. Confocal and electron microscopy revealed t hat the vitally encoded neurofilament M was transported in unpolymeriz ed form along axonal microtubules. Thus, neurofilament proteins are pr obably transported as subunits or small oligomers along microtubules, which are major routes for slow axonal transport.