Axonal myosins.

The myosin super family is an extended family of actin-based motor proteins that can be divided into 15-18 structurally distinct classes (Sellers, J. R (2000) Biochemica et Biophysica Acta, 1496, 3-22; Hodge, T. & Cope, M. J. T. V. (2000) Journal of Cell Science, 113, 3353-3354; Berg, J. S., Powell, B. C. & Cheney, R. E. (2001) Molecular Biology of the Cell, 12, 780-794). Many myosin classes contain multiple members, including different isoforms within the same species as well as homologous proteins from different species. A number of the myosin classes are expressed in multiple cell types in vertebrates, including neurons. Surprisingly little is known about the neuronal function of these different myosins. In this review we concentrate on the vertebrate myosins known to be present in neuronal axons. We take a simplistic view of this topic, addressing a number of specific questions. (1) Which myosins are present in neurons? (2) Do their levels change during development? (3) Are the neuronal forms unique in any way? (4) Which neuronal myosins are located in axons and how are they distributed? (5) What do these myosins do and are they essential for a specific neuronal function?