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Gene Review

TPH1  -  tryptophan hydroxylase 1

Gallus gallus

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Disease relevance of SERGEF

  • In this report, we found that TPH mRNA is strongly expressed in the photoreceptor layer and the vitread portion of the inner nuclear layer; the message is also expressed, but to a lesser extent, in the ganglion cell layer [1].

High impact information on SERGEF

  • Using quantitative two-dimensional polyacrylamide gel electrophoresis, we have examined the regulation of TPH by agents known to affect melatonin synthesis in the chick pineal [2].
  • The level of 35S incorporation into tryptophan hydroxylase (TPH) shows a circadian rhythm in cultured chick pineal cells [2].
  • We report here that 35S incorporation into TPH is induced by cyclic AMP and calcium, and partially inhibited by acute exposure to light [2].
  • Cyclic AMP also causes a proportional increase in the radiolabeling of one of the TPH isoforms and a concomitant decrease in another isoform, possibly reflecting a change in the phosphorylation state of TPH [2].
  • In this series of experiments, we compared levels of pinopsin and tryptophan 5-hydroxylase mRNA in the pineal glands of GUCY1*B (*B) and normal chickens housed under either cyclic light or constant dark conditions [3].

Biological context of SERGEF

  • We have previously shown that the level of [35S]methionine incorporation into tryptophan hydroxylase (TPH) shows a circadian rhythm in cultured chick pineal cells [4].
  • Because TPH mRNA are regulated by the endogenous pineal circadian clock, this provides a valuable system in which the molecular mechanism of clock control of gene expression [5].

Associations of SERGEF with chemical compounds

  • The TPH protein oscillation persists in constant darkness, peaks in the early night and can be phase-shifted by light, in parallel to the effect of these treatments on melatonin synthesis [4].
  • The latter antibody recognizes tryptophan 5-hydroxylase, one of the synthesizing enzymes for serotonin [6].
  • In retinas treated with kainic acid to destroy serotonin-containing amacrine and bipolar cells, a high amplitude rhythm of TPH mRNA was observed indicating that melatonin-synthesizing photoreceptors are the primary source of the rhythmic message [1].
  • The effect of 5-hydroxytryptophan is much greater at night, when TPH and AA-NAT activities are high, than during the day, when the enzyme activities are low [7].
  • Brainstem tryptophan 5-hydroxylase activity was unaltered by either lead or niacin [8].

Regulatory relationships of SERGEF

  • The rhythm in TPH mRNA also persists in constant darkness, suggesting that TPH mRNA synthesis and/or turnover is regulated by an endogenous circadian clock in cultured chick pineal cells [4].


  1. Circadian expression of tryptophan hydroxylase mRNA in the chicken retina. Chong, N.W., Cassone, V.M., Bernard, M., Klein, D.C., Iuvone, P.M. Brain Res. Mol. Brain Res. (1998) [Pubmed]
  2. Regulation of tryptophan hydroxylase by cyclic AMP, calcium, norepinephrine, and light in cultured chick pineal cells. Florez, J.C., Takahashi, J.S. J. Neurochem. (1996) [Pubmed]
  3. Pinopsin mRNA levels are significantly elevated in the pineal glands of chickens carrying a null mutation in guanylate cyclase-1. Semple-Rowland, S.L., Tepedino, M., Coleman, J.E. Brain Res. Mol. Brain Res. (2001) [Pubmed]
  4. Molecular cloning of chick pineal tryptophan hydroxylase and circadian oscillation of its mRNA levels. Florez, J.C., Seidenman, K.J., Barrett, R.K., Sangoram, A.M., Takahashi, J.S. Brain Res. Mol. Brain Res. (1996) [Pubmed]
  5. Tryptophan hydroxylase mRNA levels are regulated by the circadian clock, temperature, and cAMP in chick pineal cells. Green, C.B., Besharse, J.C., Zatz, M. Brain Res. (1996) [Pubmed]
  6. Immunocytochemical identification of serotonin-synthesizing neurons in the vertebrate retina: a comparative study. Wilhelm, M., Zhu, B., Gábriel, R., Straznicky, C. Exp. Eye Res. (1993) [Pubmed]
  7. Elevation of melatonin in chicken retina by 5-hydroxytryptophan: differential light/dark responses. Thomas, K.B., Brown, A.D., Iuvone, P.M. Neuroreport (1998) [Pubmed]
  8. Effects of lead and niacin on tryptophan and serotonin metabolism. Cupo, M.A., Donaldson, W.E. Drug-nutrient interactions. (1988) [Pubmed]
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