Daily oscillation of gene expression in the retina is phase-advanced with respect to the pineal gland

The photoreceptive retina and the non-photoreceptive pineal gland are components of the circadian and the melatonin forming system in mammals. To contribute to our understanding of the functional integrity of the circadian system and the melatonin forming system we have compared the daily oscillation of the two tissues under various seasonal lighting conditions. For this purpose, the 24-h profiles of the expression of the genes coding for arylalkylamine N-acetyltransferase (AA-NAT), nerve growth factor inducible gene-A (NGFI-A), nerve growth factor inducible gene-B (NGFI-B), retinoic acid related orphan receptor beta (ROR beta P), dopamine D4 receptor, and period2 (Per2) have been simultaneously recorded in the retina and the pineal gland of rats under short day (light/dark 8:16) and long day (light/dark 16:8) conditions. We have found that the cyclical patterns of all genes are phase-advanced in the retina, often with a lengthened temporal interval under short day conditions. In both tissues, the AA-NAT gene expression represents an indication of the output of the relevant pacemakers. The temporal phasing in the AA-NAT transcript amount between the retina and the pineal gland is retained under constant darkness suggesting that the intrinsic self-cycling clock of the retina oscillates in a phase-advanced manner with respect to the self-cycling clock in the suprachiasmatic nucleus, which controls the pineal gland. We therefore conclude that daily rhythms in gene expression in the retina are phase-advanced with respect to the pineal gland, and that the same temporal relationship appears to be valid for the self-cycling clocks influencing the tissues. (c) 2008 Elsevier B.V. All rights reserved.