eLife assessment
The microRNA lin-4, originally discovered in C. elegans, has a key role in controlling developmental timing across species, but how its expression is developmentally regulated is poorly understood. Here, the authors provide convincing evidence that two MYRF transcription factors are essential positive regulators of lin-4 during early C. elegans larval development. These results provide important insight into the molecular control of developmental timing that could have significant implications for understanding these processes in more complex systems.