Circadian expression of tryptophan hydroxylase mRNA in the chicken retina.
Many aspects of retinal physiology are controlled by a circadian clock located within the eye. This clock controls the rhythmic synthesis of melatonin, which results in elevated levels during the night and low levels during the day. The rate-limiting enzyme in melatonin biosynthesis in retina appears to be tryptophan hydroxylase (TPH)[G.M. Cahill and J.C. Besharse, Circadian regulation of melatonin in the retina of Xenopus laevis: Limitation by serotonin availability, J. Neurochem. 54 (1990) 716-719]. 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. The abundance of retinal TPH mRNA exhibits a circadian rhythm which persists in constant light or constant darkness. The phase of the rhythm can be reversed by reversing the light:dark cycle. In parallel experiments we found a similar pattern of expression in the chicken pineal gland. However, whereas a pulse of light at midnight suppressed retinal TPH mRNA by 25%, it did not alter pineal TPH mRNA, suggesting that there are tissue-specific differences in photic regulation of TPH mRNA. 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. These observations provide the first evidence that chick retinal TPH mRNA is under control of a circadian clock.
Chong
N W
NW
National Institutes of Health Section on Neuroendocrinology, Laboratory of Developmental Neurobiology, 49/5A38, National Institute of Child Health and Human Development, Bethesda, MD 20892, USA.
Cassone
V M
VM
Bernard
M
M
Klein
D C
DC
Iuvone
P M
PM
D000818:Animals; D002645:Chickens; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D003624:Darkness; D017403:In Situ Hybridization; D007608:Kainic Acid / Q000494:pharmacology; D008027:Light; D008297:Male; D008550:Melatonin / Q000096:biosynthesis; D010786:Photoreceptor Cells / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D010870:Pineal Gland / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis* / Q000187:drug effects; D012160:Retina / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D012165:Retinal Ganglion Cells / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D014365:Tryptophan Hydroxylase / Q000235:genetics*
D012333:RNA, Messenger; D014365:Tryptophan Hydroxylase; D008550:Melatonin; D007608:Kainic Acid