Molecular Characterization of the Long-Day Response in the Soay Sheep, a Seasonal Mammal

Melatonin influences clock gene expression and prolactin secretion in Soay sheep within 24 hours of a shift to long days.

• The expression of clock genes Cryptochrome1 (Cry1), Period1 (Per1), and RevErbalpha is regulated by melatonin signaling in response to changes in day length.
• Cry1 activation occurs at dusk when melatonin levels rise, while Per1 expression peaks at dawn, marking the end of melatonin secretion.
• The interval between Cry1 and Per1 expression adjusts rapidly to melatonin signals after the transition from short to long days.
• Prolactin secretion increases within 24 hours following the adjustment to long days and altered melatonin levels.
• RevErbalpha expression also responds to long days but does not immediately transition to a stable long-day pattern.

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