Neuronal and endocrine mechanisms underlying the circadian gating of eclosion: insights from Drosophila.

The circadian rhythm of adult emergence (aka eclosion) of the fruit fly Drosophila is a classic behavioural read-out that served in the first characterisation of the key features of circadian clocks and was also used for the identification of the first clock genes. Rhythmic eclosion requires the central clock in the brain, as well as a peripheral clock in the steroidogenic prothoracic gland. Here, we review recent findings on the timing and neuroendocrine coupling mechanisms of the two clocks. These findings identify rhythmic prothoracicotropic hormone and downstream ERK signalling as the main coupling pathway and show that the two clocks impose daily rhythmicity to the temporal pattern of eclosion by regulating the timing of the very last steps in metamorphosis.