The proper wiring of neuronal circuits during development is essential for the neuronal control of behavior. Across animal species, sleep/wake cycle rhythms, as well as many other behavioral and physiological rhythms, are controlled by the circadian timekeeping system, a network of neurons that maintains endogenous molecular oscillations and rhythmic behavior with a ~24 hour period. The proper functioning of this circadian network requires the formation of synaptic and peptidergic connections during development. The Drosophila circadian clock neurons offer an excellent model for exploring the non-circadian roles of canonical clock genes such as cycle. Our results show that downregulating cyc specifically in the Pdf-expressing cells and observed pronounced defasciculation of the sLNv projections. cyc downregulation in these cells during development is sufficient to prevent the fasciculation and results in the loss of behavioral rhythms in adult flies. We are studying the mechanisms by which cyc and other clock components control neuronal development beyond the clock neuron network.