Biol. Bull. 207: 164. (October 2004)
© 2004 Marine Biological Laboratory
Anterograde Transport of Peptide-Conjugated Fluorescent Beads in the Squid Giant Axon Identifies a Zip-Code for the Synapse
Michael P. Conley1,2,
Marcus K. Jang1,2,
Joseph A. DeGiorgis1,3 and
Elaine L. Bearer1,2
1 Marine Biological Laboratory, Woods Hole, Massachusetts
2 Brown University, Providence, Rhode Island
3 NIH, NINDS, Bethesda, Maryland
The giant axon of the squid has long served as a model system to study physiological events common to neuronal systems in many species and also active in most other eukaryotic cells. These physiological events include ion currents and vesicular transport. Endogenous transport vesicles move in the axon for up to six hours after dissection. Mid-size squid organelles 0.2–0.53 µm in diameter are transported in axoplasm at average velocities of 1.1 µm/s, whereas larger particles (>0.5 µm diameter), mostly mitochondria, move more slowly (0.2 µm/s). A major question in neurophysiology is how synaptic components are transported to the pre-synaptic terminal. The giant axon of the squid provides an assay for the molecular requirements of this transport that are highly conserved at the sequence level across species. The first microtubule-based motor, kinesin, was discovered in the squid axon and subsequently found in most other organisms. We are using the giant axon to uncover the molecular mechanisms of cargo/motor interactions. First, using GFP-labeled human herpes virus (HSV1) as a tool, we reconstituted HSV transport in both directions in the squid axon. Then we discovered that HSV particles moving in the anterograde direction are associated with cellular amyloid precursor protein (APP). Two summers ago we discovered that a peptide from the cytoplasmic C-terminus of APP (C-APP) is sufficient to move 100 nm beads in the axon towards the synapse at fast transport rates (0.9 µm/s), whereas uncoated negatively charged beads move rarely and slower (0.08 µm/s); and beads coated with other peptides do not move. This summer we are using multi-spectral imaging to observe many different colored beads simultaneously to screen a peptide library for transport activity in the giant axon. Thus the giant axon of the squid serves as a reliable assay to identify the molecular mechanisms of motor recruitment.
Supported by NINDS (E.L.B.).
