In the embryo, axon elongation is guided by chemoattractant and chemorepulsive molecules. In the years 1990, four canonical families of proteins involved in the orientation of growing axons were discovered : netrins, semaphorins, ephrins and slit proteins. These molecules are evolutionarily conserved, and can be bifunctional, attracting some axons and repelling others. Morphogens (members of the Hedgehog, Wnt and BMP families) and growth factors are also involved. Other axon guidance signals continue to be identified (notably members of the immunoglobulin superfamily), but all these molecules cannot fully account for the path of an axon from its origin to its target, indicating that our knowledge of these signals is still incomplete. Mutations in genes coding for axon guidance molecules have been identified in several familial neurological diseases. To travel long distances, axons must cross intermediate targets. The axon is first attracted to the target, then, when it reaches it, repelled by it, enabling it to continue its journey. The mechanisms by which axons are alternately attracted to and repelled by an intermediate target are still poorly understood, but they are the subject of very active research, as their understanding could be put to good use in attempts to repair axonal lesions.
17:00 - 18:00
Guest lecturer
Not recorded
Assembly of brain neurons : logic and mechanisms of axonal guidance
Marc Tessier-Lavigne
