MOLECULAR-CLONING OF CHICK PINEAL TRYPTOPHAN-HYDROXYLASE AND CIRCADIAN OSCILLATION OF ITS MESSENGER-RNA LEVELS

We have previously shown that the level of [S-35]methionine incorporat ion into tryptophan hydroxylase (TPH) shows a circadian rhythm in cult ured chick pineal cells. The TPH pro-rein oscillation persists in cons tant darkness, peaks in the early night and can be phase-shifted by li ght, in parallel to the effect of these treatments on melatonin synthe sis. We have cloned and sequenced a full-length cDNA for chick pineal TPH. Levels of TPH mRNA. show a robust diurnal oscillation both in viv o and in vitro. The rhythm in TPH mRNA also persists in constant darkn ess, suggesting that TPH mRNA synthesis and/or turnover is regulated b y an endogenous circadian clock in cultured chick pineal cells. The ci rcadian oscillation of TPH constitutes the first described circadian r hythm of a chick pineal gene at the mRNA level.