Structure And Function Of Cytoplasmic Motors

Neurological Disorders And Stroke

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Abstract

The squid giant axon has been established as an important model for understanding processes of axonal transport. Conventional kinesin, the founding member of a diverse and functionally important group of molecular motor proteins, was discovered in squid and it?s role there attributed to the transport of vesicles towards the plus ends of microtubules. Recently we have undertaken an EST (Expressed Sequence Tag) project aimed at identifying other motors that might be present within the squid nervous system. To date, 22,564 ESTs have been obtained that encode more than 3,000 unique genes. Of these ESTs, 83 overlapping sequences encode five cellular myosins (non-muscle), three dynein heavy chains, and six new kinesins. These findings suggest a more complex story of vesicle trafficking. Antibodies raised against one of the new kinesins (K-165) decorates axoplasmic vesicles washed in 600 mM potassium iodide as viewed by electron microscopy immunogold. This motor is therefore tightly associated with axonal organelles and may be, along with conventional kinesin, a major motor responsible for the transport of organelles within the axon. In addition to motors, the EST project has identified genes implicated in neurological disease. This includes Amyloid Precursor Protein (APP), a transmembrane protein with a role in Alzheimer's Disease (AD), and two genes involved in Niemann Pick Disease. This EST resource has been shared with seventeen laboratories working on squid to study basic and biomedical research. The surprising high degree of gene homology between human and squid sequences suggests that the squid may be a useful model for understanding the function of disease gene candidates. We also developed a new technique for labeling a subpopulation of the actin cytoskeleton using photoactivatable-EGFP-actin, We observed lateral motions of actin accompanied by synchronous lateral movement and clustering of beta 1 integrins. These results suggest that actin positioning activates integrins to provide a mechanism for cells to seek new adhesion sites and preferred directions of migration.