The squid giant axon has been and remains an important model system for studying neuronal function. Recently, we have initiated an EST (Expressed Sequence Tag) project aimed at obtaining genomic information on the squid nervous system. To date, we have sequenced 6,912 randomly selected cDNA clones and identified 1,935 unique genes expressed in the stellate ganglion, which contains the cell bodies for the giant axons. So far four additional motor proteins, including a second kinesin and three myosins previously unknown in squid have been identified. Additionally, we have found an EST for Amyloid Precursor Protein (APP), a transmembrane protein with a role in Alzheimer?s Disease (AD). Using this sequence to synthesize peptides it was possible to show that a particular cytoplasmic domain of squid (and human) APP is sufficient to induce anterograde transport of fluorescent beads injected into the squid giant axon. This finding suggests a crucial role for APP in axonal transport. Other EST data is being utilized by three separate groups at NINDS as well as by investigators at the Marine Biological Laboratory, Woods Hole, for gene identification, peptide sequence analysis, antibody production and proteomics. Work in progress is expected to create a nearly complete library of proteins expressed in the squid nervous system. This information directly linked to a library of clones will be made readily and openly available to the scientific community, where it is expected to be broadly useful. With the help of antibodies developed in our laboratory against a variety of myosins in the squid giant axon we have been able to isolate the specific myosin, myosin II, responsible for the purse string contraction in axons following transection. The purse string contraction is thought to minimize degeneration and loss of function after axonal injury. Using the myosin II antibodies we are currently visualizing the location and time course of the myosins as the axon reduces its diameter, In collaboration with Dr. Catherine Galbraith of NIDCR we are also investigating axonal pathfinding and guidance in cultures. By developing a new technique for labeling a subpopulation of the actin cytoskeleton using photoactivatable-EGFP-actin, we were able to visualize previously unobserved lateral movement of newly polymerized actin filaments. We have observed that this newly described motion of actin is accompanied by synchronous lateral movement and clustering of beta 1 integrins. The integrin clustering produces primed but unligated beta1 integrins along the leading edge of fibroblast lamella and growth cone filipodia. These results suggest that actin positioning activates integrins to provide a mechanism for cells to seek new adhesion sites and preferred directions of migration.
| Galbraith, Catherine G; Yamada, Kenneth M; Galbraith, James A (2007) Polymerizing actin fibers position integrins primed to probe for adhesion sites. Science 315:992-5 |
| Colina, Claudia; Rosenthal, Joshua J C; DeGiorgis, Joseph A et al. (2007) Structural basis of Na(+)/K(+)-ATPase adaptation to marine environments. Nat Struct Mol Biol 14:427-31 |
| Satpute-Krishnan, Prasanna; DeGiorgis, Joseph A; Conley, Michael P et al. (2006) A peptide zipcode sufficient for anterograde transport within amyloid precursor protein. Proc Natl Acad Sci U S A 103:16532-7 |
| DeGiorgis, Joseph A; Reese, Thomas S; Bearer, Elaine L (2002) Association of a nonmuscle myosin II with axoplasmic organelles. Mol Biol Cell 13:1046-57 |
| Galbraith, J A; Reese, T S; Schlief, M L et al. (1999) Slow transport of unpolymerized tubulin and polymerized neurofilament in the squid giant axon. Proc Natl Acad Sci U S A 96:11589-94 |
