The dance of the growth cones--where to next?

Axon guidance in the developing nervous system is accomplished by a remarkable structure, the axon growth cone. This structure navigates, often over long distances, to find and synapse with target cells. Transformation of the growth cone to a terminal arbor establishes functional circuitry. The navigational properties of growth cones, and their interactions with target tissue, have been studied widely by examining individual cells in vitro, and have also been inferred from histological sections. Recent advances in labelling techniques and imaging of living cells have enabled direct observation of the growing axon tip in intact embryos as well as in slice preparations. To understand how pathways and terminal arbors are formed, the challenge now is to relate the dynamic morphology and behaviour of living growth cones to surrounding cues in the complex environment of the developing embryo.