JNK signaling in pioneer neurons directs the architectural organization of the CNS and coordinates the motor activity of the Drosophila embryo

The Central Nervous System (CNS) organogenesis is a complex process that obeys precise architectural rules. Yet, both the mechanisms dictating CNS structural organization, and the impact that this may have on its functionality remain unknown. Analyzing the Drosophila embryo Ventral Nerve Cord (VNC) morphogenesis, we found that tight control of JNK signaling levels is essential for its stereotyped architectural organization. The JNK pathway is active in a specific subset of pioneer neurons, where it, autonomously, regulates the expression of cell adhesion molecules, the integrity of axons and dendrites, and motoneurons electrophysiological properties. Interfering during early embryogenesis in the activity of JNK signaling in these cells, it affects their pioneer functions and leads to cumulative scaffolding defects during the establishment of axonal networks. This global architectural disarray associates to the failure of the VNC condensation and the coordination of the embryonic motor activities required for hatching. Altogether, our data point to the JNK cascade in a subset of pioneer neurons as a key element underpinning VNC architecture, and reveal critical links between the structural organization of the VNC and its functional optimization. ### Competing Interest Statement The authors have declared no competing interest.