Circadian clock neurons in the silkmoth Antheraea pernyi: novel mechanisms of Period protein regulation.

We examined Period (PER) protein regulation in the brain of the silkmoth Antheraea pernyi. PER expression is restricted to the cytoplasm and axons of eight neurons, with no evidence of temporal movement into the nucleus. These neurons appear to be circadian clock cells, because PER and per mRNA are colocalized and their levels oscillate in these cells, Timeless protein immunoreactivity is coexpressed in each PER-positive neuron, and clock protein and mRNA oscillations are all suppressed in these neurons by constant light. A per antisense RNA oscillation was detected that is spatially restricted to PER-expressing cells, suggesting a novel mechanism of PER regulation. PER-positive neurons and their projections are strategically positioned for regulating prothoracicotropic hormone and eclosion hormone, two neurohormones under circadian control. Differences in the molecular details of PER expression and regulation between the brains of silkmoths and fruitflies provide insights into the mechanisms of clock gene regulation.