THE DANCE OF THE GROWTH CONES - WHERE TO NEXT

Axon guidance in the developing nervous system is accomplished by a re markable structure, the axon growth cone. This structure navigates, of ten over long distances, to find and synapse with target cells. Transf ormation of the growth cone to a terminal arbor establishes functional circuitry The navigational properties of growth cones, and their inte ractions with target tissue, have been studied widely by examining ind ividual cells in vitro, and have also been inferred from histological sections. Recent advances in labelling techniques and imaging of livin g cells have enabled direct observation of the growing axon tip in int act embryos as well as in slice preparations. To understand how pathwa ys and terminal arbors are formed, the challenge now is to relate the dynamic morphology and behaviour of living growth canes to surrounding cues in the complex environment of the developing embryo.