NATURES KNOCKOUT - THE MEL(1B) RECEPTOR IS NOT NECESSARY FOR REPRODUCTIVE AND CIRCADIAN RESPONSES TO MELATONIN IN SIBERIAN HAMSTERS

The pineal hormone melatonin regulates seasonal reproduction and influ ences the timing of circadian rhythms. The Mel(1a) and Mel(1b) recepto rs are the high-affinity melatonin receptors present in mammals. Unexp ectedly, the Mel(1b) receptor gene of the Siberian hamster, Phodopus s ungorus, cannot encode a functional receptor; two nonsense mutations a re present within the coding region. Southern blot analysis indicates that this is a single copy gene. The Mel(1b) receptor gene is nonfunct ional in outbred populations of P. sungorus and Phodopus campbelli. Si berian hamsters lacking a functional Mel(1b) receptor nevertheless sho w seasonal reproductive and circadian responses to melatonin, indicati ng that the Mel(1b) receptor is not necessary for these responses. The se data support the hypothesis that the Mel(1a) receptor, which does e ncode a functional receptor in this species, mediates reproductive and circadian responses to melatonin.