Directional Cues for Retinal Axons

  1. B. Stahl,
  2. Y. von Boxberg,
  3. B. Müller,
  4. J. Walter,
  5. U. Schwarz, and
  6. F. Bonhoeffer
  1. Max-Planck-Institut für Entwicklungsbiologie, D-7400 Tübingen, Federal Republic of Germany

This extract was created in the absence of an abstract.

Excerpt

The elucidation of the mechanisms that govern the development of topographic projections in the central nervous system has been a challenge for neurobiologists for quite some time. Since the pioneering work of Sperry (1956, 1963) on the formation of neural connections in the retinotectal system of amphibia and fish, many speculations have been put forward and dismissed. One of them, which is still a tenable hypothesis, is that the axons are guided to their target site by directional cues expressed on the surface of the target organ given by the graded distribution of substances either diffusible or membrane-bound. As documented in many systems, there are in vivo directional cues for incoming axons at the target surface.

Conceptually, it is very easy to see how a gradient may determine direction. In fact, it appears almost impossible to consider directional cues without thinking of gradients. However, it is a fascinating question of...

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