Development and evolution of brain commissures

Orateur : Alain CHEDOTAL (Institut de la Vision, INSERM UMRS 968, Paris)

The central nervous system of most animal species contains special types of neurons, called commissural neurons, which extend their axons in commissures across the longitudinal axis of symmetry (or midline) to connect to target neurons located on the opposite side. The appearance of novel commissural systems or the modification of existing ones has accompanied the emergence of key neurobiological features in vertebrate evolution. We have discovered that Robo3 , a receptor of the roundabout family, is expressed in vertebrate embryos by developing commissural axons. Most brain commissures fail to develop in mice and humans lacking Robo3 . I will present results that suggest that Robo3 evolution was key to sculpting the mammalian brain by converting a receptor for commissural axon repulsion into one that primarily potentiates attraction. Our results illustrate how modest changes in sequence of an axon guidance receptor can lead to fundamental changes in its function that helps sculpt distinct circuits, and thereby help understand the emergence of specific sensory, motor and cognitive functions and why they differ between species.

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