JNK signaling activity in pioneer neurons modulates the architectural organization of the CNS of Drosophila embryos

Abstract Morphogenesis of the Central Nervous System (CNS) is a complex process that obeys precise architectural rules. Yet, the mechanisms dictating these rules remain unknown. Analyzing morphogenesis of the Drosophila embryo Ventral Nerve Cord (VNC), we found that a tight control of JNK signaling is essential to attain the final VNC architecture. JNK signaling in a specific subset of pioneer neurons autonomously regulates the expression of Fasciclin 2 (Fas 2) and Neurexin IV (Nrx IV) adhesion molecules via the transcription factor zfh1. Interfering at any step in this cascade affects the fasciculation of axons and the dendritic make up of primary neurons. This leads to secondary cumulative scaffolding defects during the structural organization of the axonal network, revealed in aberrant spatial correlations along the Antero-Posterior (AP) axis of the VNC. The global loss of architectural robustness and tensional balance ultimately influences nervous system condensation. In summary, our data point to the JNK cascade in a subset of pioneer neurons as a key element underpinning VNC architecture, revealing critical milestones on the mechanism of control of its structural organization