Cell body clustering drives gap junction-mediated synchronous activity in command neurons.

The nervous system contains densely packed cell bodies, yet the role of neuronal cell body position in circuit function is poorly understood. Here we show that four Drosophila Moonwalker Descending Neurons (MDNs), command neurons for backward locomotion, must maintain cell body contact to allow gap junction-dependent synchronous activity necessary to initiate backward walking. MDNs express the transcription factor Hunchback, which drives expression of the Lar cell adhesion molecule; Hunchback, Lar, and its ligand Dlp promote MDN cell body clustering and backward walking. When clustered, the gap junction protein Inx8 allows synchronous firing of MDNs, which is required to initiate backward walking. These findings reveal a previously unappreciated role for cell body clustering and synchronous firing in neural circuit function.