Regulation of the expression of serotonin N-acetyltransferase gene in Japanese quail (Coturnix japonica): II. Effect of vitamin A deficiency

Levels of serotonin N-acetyltransferase [arylalkylamine N-acetyltransferase (AANAT); EC2.3.1.87] mRNA, AANAT activity, and melatonin display a rhythmi c pattern in both the pineal gland and the retina. It has been shown that v itamin A is required to maintain the rhythm of melatonin synthesis in the p ineal gland of Japanese quail. To understand the mechanism underlying the d irect relationship among these factors, we developed an assay system sensit ive enough to determine AANAT mRNA, AANAT activity, and melatonin content f rom a single pineal gland of Japanese quail. Positive direct relationships were found among these three parameters. We next deprived Japanese quail of vitamin A by feeding them a vitamin A-free diet supplemented with retinoic acid, and examined the effects of vitamin A deficiency on the expression o f AANAT mRNA in the pineal gland and the retina. Vitamin A deficiency reduc ed both the expression of AANAT mRNA and melatonin content in the pineal gl and. Retinal AANAT mRNA rhythm disappeared in vitamin A-deficient quails. M oreover, the responsiveness of the pineal gland and the retina to light was reduced by vitamin A deficiency when compared with the control group.