Laboratoire Matière et Systèmes Complexes

Marie Breau, Institut de Biologie, Paris Seine, Unité de Biologie du Développement, Jussieu

Cell movements and axon emergence during olfactory placode morphogenesis

Abstract : To form functional sensory neuronal circuits, neurons have to assemble into compact clusters to shape sensory organs and ganglia, and send out axons transmitting information to the brain. Very little is known about how these two processes are regulated and coordinated in vivo. We use the olfactory placode in zebrafish as a system to address the underlying mechanisms. We find that cell death and proliferation are dispensable for olfactory placode morphogenesis. Live imaging demonstrates that it is rather achieved through coordinated and directed cell movements.

Interestingly, axon formation is concomitant with placode morphogenesis and is also driven by cell movements. Instead of resulting from the expected outgrowth of axons from static cell bodies towards the brain, it occurs by displacement of cell bodies away from axon tips attached to the brain surface. This work unravels a novel mechanism of sensory organ formation, whereby directed cell movements drive both the morphogenesis of a neuronal cluster and the emergence of axonal contacts with the brain.

We are currently analysing cell protrusions (lamellipodia, filopodia) and actomyosin dynamics in placodal neurons. Our results suggest that some of the observed movements are active, ie powered by internal forces, whereas others rather represent passive displacements, likely triggered by external pulling or pushing forces.

We plan to map the mechanical forces exerted within the rearranging placodal tissue, and to probe the influence of external mechanical stimuli on cell behaviours. This will be essential to fully understand the mechanisms of olfactory placode assembly and its coordination with axon formation.