Periodic Reporting for period 3 - DRIVE (GUIDANCE AND FUNCTION OF REGENERATIVE FIBERS IN ADULT CNS) Reporting period: 2021-03-01 to 2022-08-31 Summary of the context and overall objectives of the project Mature neurons from the central nervous system (CNS) are not able to regenerate, unlike the young ones, leading to irreversible loss of motor and/or cognitive functions. Understanding the detailed mechanisms of axonal growth and repair remains a major neurobiological and neurological challenge. Manipulating neuronal molecular pathways has recently shown promising results when external factors fail to trigger regeneration. Particularly, my work has demonstrated that the simultaneous activation of mTOR, JAK/STAT and c-myc pathways leads to unprecedented extent of regeneration and provides an exciting avenue for functional studies and therapeutical strategies. However, such combined activation may also exacerbate axon guidance defects leading to potential aberrant circuit formation. This unique concept of strong regeneration offers the possibility to explore fundamental questions of CNS regeneration. Here, I propose to address the guidance of regenerating axons in adult CNS. Studying this yet unexplored question should increase our understanding of the formation of a functional new circuit after injury. More specifically, my goals are to understand (i) guidance modalities in adult CNS, (ii) whether axons are still responsive to developmental guidance cues, (iii) whether regenerative axons can form connections with their targets and (iv) if these connections are functional?Results generated by DRIVE should lead to major breakthroughs in the mechanism of axon guidance during regeneration of adult neurons and in the functioning of de novo formed circuits. They will open up new ways for innovative therapeutic development after CNS insult but also to the large spectrum of neurodegenerative diseases. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far We performed a candidate and a large scale approach to define the actors potentially involved in axon guidance during the regeneration of the central nervous system. We focused on one specific brain target. Regenerating axons avoid this brain region and we found out that a repulsive molecule is expressed by this tissue.We are currently manipulating this signalling in vivo and using organotypic cultures to modulate axon guidance choices of regenerating axons. We have currently an article in press describing the organotypic culture. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) We found out that axon guidance molecules are still expressed in the mature nervous system. We are currently manipulating those signalling to drive regenerating axons to their proper targets.We expect to find new modalities to form functional neuronal circuit upon central nervous system injury.