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International audience; The growth of axons is a key step in neuronal circuit assembly. The axon starts elongating with the migration of its growth cone in response to molecular signals present in the surrounding embryonic tissues. Following the formation of a synapse between the axon and the target cell, the distance which separates the cell body from the synapse continues to increase to accommodate the growth of the organism. This second phase of elongation, which is universal and crucial since it contributes to an important proportion of the final axon size, has been historically referred to as “stretch-induced axon growth”. It is indeed likely to result from a mechanical tension generated by the growth of the body, but the underlying mechanisms remain poorly characterized. This article reviews the experimental studies of this process, mainly analysed on cultured neurons so far. The recent development of in vivo imaging techniques and tools to probe and perturb mechanical forces within embryos will shed new light on this universal mode of axonal growth. This knowledge may inspire the design of novel tissue engineering strategies dedicated to brain and spinal cord repair.; La croissance des axones est une étape clef dans l'assemblage des circuits neuronaux. L'axone commence par grandir grâce à la migration de son cône de croissance en réponse à des signaux moléculaires présents dans les tissus de l'embryon. Après la formation d'un contact synaptique entre l'axone et la cellule-cible, la distance qui sépare le corps cellulaire de la synapse continue d'augmenter au même rythme que la croissance de l'organisme. Cette seconde phase d'élongation, universelle et cruciale puisqu'elle est responsable d'une part importante de la taille finale des axones, a été historiquement qualifiée de croissance « par étirement ». Il est en effet vraisemblable d'imaginer qu'elle résulte d'une tension mécanique générée par la croissance des tissus de l'organisme, mais les mécanismes sous-jacents restent encore mal caractérisés. Dans cette revue, nous présentons les études expérimentales de ce processus, analysé principalement sur des neurones en culture. Le développement récent de techniques d'imagerie in vivo et d'outils de mesure et de perturbation des forces mécaniques au sein des embryons permettra de mieux comprendre ce mode universel de croissance axonale. Ces connaissances pourraient être exploitées pour développer de nouvelles stratégies d'ingénierie tissulaire dédiées à la réparation des lésions du système nerveux.

The growth of axons is a key step in neuronal circuit assembly. The axon starts elongating with the migration of its growth cone in response to molecular signals present in the surrounding embryonic tissues. Following the formation of a synapse between the axon and the target cell, the distance which separates the cell body from the synapse continues to increase to accommodate the growth of the organism. This second phase of elongation, which is universal and crucial since it contributes to an important proportion of the final axon size, has been historically referred to as "stretch-induced axon growth". It is indeed likely to result from a mechanical tension generated by the growth of the body, but the underlying mechanisms remain poorly characterized. This article reviews the experimental studies of this process, mainly analysed on cultured neurons so far. The recent development of in vivo imaging techniques and tools to probe and perturb mechanical forces within embryos will shed new light on this universal mode of axonal growth. This knowledge may inspire the design of novel tissue engineering strategies dedicated to brain and spinal cord repair.