Editorial – Friedrich Bonhoeffer (1932–2021)

Friedrich Bonhoeffer was a real hero for us molecular neurobiologists studying nervous system development. He had laid the groundwork for the search and characterization of molecular guidance cues with his decade-long work on the topographic wiring of the chick retinotectal system. His invention of the microfluidics stripe assay in which retinal axons grow on stripes of tectal membranes, was very powerful, as it demonstrated that the posterior tectum contained a repulsive membrane-anchored protein which retinal growth cones used for guidance. These findings corroborated Roger Sperry’s chemoaffinity hypothesis, but revealed that the underlying mechanism was repulsion rather than attraction. Moreover, his work also highlighted the beauty of biochemical gradients which provide directional information for navigating growth cones and help position the axonal connections by the concentration of the guidance cue.