Circadian clock gene homolog shapes neural circuit development in C. elegans, but developmental sleep may not be essential
Sleep is widely assumed to be essential for brain development. Across the animal kingdom, from worms to humans, developing brains spend large portions of time in a sleep-like state, and disrupting sleep early in life has been linked to lasting cognitive and behavioral impairments. But a new study published in iScience challenges a core piece of that assumption. Researchers at the Weizmann Institute of Science and the Technion have found that in the microscopic roundworm Caenorhabditis elegans, developmentally timed sleep is surprisingly dispensable for the formation of a functional neural circuit. The real driver of proper circuit wiring, they report, is a gene with deep evolutionary roots: a homolog of the circadian clock machinery itself.
The clock gene and developmental timing
C. elegans passes through four larval stages as it matures from egg to adult. Between each stage, the worm enters a period of deep, reversible quiescence known as developmentally timed sleep, or DTS. In mammals, these sleep windows are regulated in part by circadian clock genes, and the same molecular machinery operates in worms: homologs of the circadian clock govern the timing of DTS and the broader developmental schedule.
The team, led by lead author Shiraz Nir Halber and senior author Meital Oren-Suissa of the Weizmann Institute’s Department of Brain Sciences, focused on one such clock gene homolog, ces-2. In mammals, the equivalent gene belongs to the PAR bZIP transcription factor family and plays a role in circadian rhythm regulation. In worms, ces-2 turned out to be a master coordinator of developmental tempo.
When the researchers disrupted ces-2, the consequences were dramatic. Development became both delayed and highly variable in both sexes. Some larvae stalled at early stages, while others took erratic paths to adulthood. The gene, it became clear, functions like a molecular timekeeper, ensuring that the progression through larval stages proceeds on a reliable schedule. Without it, the rhythm of development breaks down.
The role of sleep in circuit formation
To test whether this disrupted developmental timing, or the loss of sleep itself, was to blame for downstream neural problems, the researchers turned to the male mating circuit, one of the best-mapped neural circuits in any organism. Male C. elegans use a specialized set of neurons and muscles to locate mates, make physical contact, and transfer sperm. The wiring diagram is nearly entirely known, which makes it an ideal model for asking whether developmental sleep is necessary for building a working circuit.
The first finding was unexpected in its own right. Compared with hermaphrodites, males developed faster and showed altered DTS patterns, spending less time in quiescence. The sex difference hinted that developmental sleep might be flexible, not fixed.
Then came the critical experiment. The team perturbed DTS directly, without touching the clock gene machinery. They found that male worms deprived of normal developmental sleep still mated successfully. The neural circuit formed and functioned. Developmental sleep, at least for this circuit, was not essential.
But when they disrupted ces-2 instead, the picture changed completely. Males with a broken clock gene homolog showed marked deficits in mating behavior. When the researchers examined the underlying wiring, they found reduced synaptic connectivity within the mating circuitry. The neurons were there, but the connections between them were weaker or missing.
The dissociation is striking. Sleep loss alone did not impair the circuit. But the loss of proper developmental timing, driven by a clock gene homolog, did.
Why it matters
This study makes an important conceptual contribution by separating two things that are often lumped together: the role of sleep and the role of the molecular clock machinery that regulates it. Many studies that disrupt sleep also disrupt the genes that control sleep timing, making it impossible to tell which factor drives the observed effects on brain development.
By using the precise genetic toolkit available in C. elegans, the Halber team was able to tease these apart. The results suggest that the circadian clock gene homolog ces-2 plays a role in neural development that goes beyond simply controlling when the animal sleeps. The gene appears to coordinate developmental rhythms in a way that directly influences synaptic wiring. Sleep, at least in this context, may be a downstream consequence of that timing machinery rather than an active sculptor of neural connections.
The findings also highlight an intriguing evolutionary continuity. The same families of clock genes that govern daily sleep-wake cycles in mammals are at work in a worm with a nervous system of only a few hundred neurons, shaping how those neurons connect to each other. That conservation suggests the link between developmental timing and neural circuit assembly is ancient and fundamental.
Limits
Several caveats apply. The study was conducted entirely in C. elegans, and whether these findings translate to organisms with more complex nervous systems is unknown. The male mating circuit, while well-characterized, is a single, specialized circuit; other neural circuits in the worm may depend more heavily on developmental sleep. The authors note that their DTS perturbation methods, while effective, may not have eliminated every aspect of sleep-related physiology. And the specific molecular mechanisms by which CES-2 influences synaptic connectivity have not yet been identified.
Bottom line
A circadian clock gene homolog called ces-2 regulates developmental timing in C. elegans, and disrupting it impairs both the tempo of development and the synaptic wiring of the male mating circuit. But developmental sleep itself is not required for that circuit to form and function. The findings uncouple the role of sleep from the role of the clock genes that control it, suggesting that these genes influence neurodevelopment through mechanisms beyond sleep regulation.
Source
Shiraz Nir Halber, Eshkar Nir, Shay Stern, Meital Oren-Suissa. “A circadian clock gene homolog regulates developmental timing and male mating circuitry in C. elegans.” iScience 29, no. 7 (July 2, 2026): 116659. DOI: 10.1016/j.isci.2026.116659. PMID: 42437001.