Rhythmic melatonin secretion does not correlate with the expression of arylalkylamine N-ACETYLTRANSFERASE, inducible cyclic amp early repressor, period1 or cryptochrome1 mRNA in the sheep pineal

Mar 18, 2004Neuroscience

Melatonin rhythms in sheep are not linked to key enzyme and clock gene activity in the pineal gland

AI simplified

Circadian Biology on OpenScience ↗PubMed ↗DOI ↗

Abstract

No rhythmic expression of the genes ICER, AA-NAT, or Cryptochrome1 was found in the pineal glands of Soay sheep adapted to short days.

Melatonin synthesis in ungulates is primarily regulated by enzyme activity rather than gene transcription.
The expression of Period1 showed a low amplitude rhythm, peaking during the dark period.
Delaying lights out by 8 hours did not significantly affect the expression of key genes in the pineal gland.
Changes in gene expression due to photoperiod were observed in the hypothalamic suprachiasmatic nuclei and pituitary, but not in the pineal gland.
These findings suggest a reduction in circadian control of gene expression in the ovine pineal gland compared to other species.

AI simplified

The pineal gland, through nocturnal melatonin, acts as a neuroendocrine transducer of daily and seasonal time. Melatonin synthesis is driven by rhythmic activation of the rate-limiting enzyme, arylalkylamine N-acetyltransferase (AA-NAT). In ungulates, AA-NAT mRNA is constitutively high throughout the 24-h cycle, and melatonin production is primarily controlled through effects on AA-NAT enzyme activity; this is in contrast to dominant transcriptional control in rodents. To determine whether there has been a selective loss of circadian control of AA-NAT mRNA expression in the sheep pineal, we measured the expression of other genes known to be rhythmic in rodents (inducible cAMP early repressor ICER, the circadian clock genes Period1 and Cryptochrome1, as well as AA-NAT). We first assayed gene expression in pineal glands collected from Soay sheep adapted to short days (Light: dark, 8-h: 16-h), and killed at 4-h intervals through 24-h. We found no evidence for rhythmic expression of ICER, AA-NAT or Cryptochrome1 under these conditions, whilst Period1 showed a low amplitude rhythm of expression, with higher values during the dark period. In a second group of animals, lights out was delayed by 8-h during the final 24-h sampling period, a manipulation that causes an immediate shortening of the period of melatonin secretion. This did not significantly affect the expression of ICER, AA-NAT or Cryptochrome1 in the pineal, whilst a slight suppressive effect on overall Per1 levels was observed. The attenuated response to photoperiod change appears to be specific to the ovine pineal, as the first long day induced rapid changes of Period1 and ICER expression in the hypothalamic suprachiasmatic nuclei and pituitary pars tuberalis, respectively. Overall, our data suggest a general reduction of circadian control of transcript abundance in the ovine pineal gland, consistent with a marked evolutionary divergence in the mechanism regulating melatonin production between terrestrial ruminants and fossorial rodents.

Full Text

Full text is available at the source.

View full text (XML) ↗View full text ↗

Rhythmic melatonin secretion does not correlate with the expression of arylalkylamine N-ACETYLTRANSFERASE, inducible cyclic amp early repressor, period1 or cryptochrome1 mRNA in the sheep pineal

Abstract

Full Text

You found one interesting study. We’ll send the next 7.

what lands in your inbox each week:

Recent issues from the circadian biology brief

Abstract

Full Text

Related papers

You found one interesting study. We’ll send the next 7.

what lands in your inbox each week:

Recent issues from the circadian biology brief