Time-of-day-dependent light-induction of gene expression in the chicken pineal gland

Light has a strong effect on whole organism physiology, such as the circadian rhythms that are phase delayed and advanced by light given at early and late subjective night, respectively. Despite the importance of the phase-dependent light responses, little is known about the underlying molecular mechanism. We performed a comprehensive analysis of genes induced by light in a phase-dependent manner in the chicken pineal gland, an organ that represents a unique vertebrate clock system harboring intrinsic light sensitivity. Newborn chicks were entrained to 12-h light/12-h dark cycle for 7 days then transferred to constant darkness for a day to be exposed to light for 1 h from CT (circadian time) 6 (representing subjective day), CT14 (early subjective night) or CT22 (late subjective night). Control animals were kept in the dark without light pulse. The pineal glands were isolated at the end of the 1-h light pulse for gene expression analysis by Affymetrix GeneChip. Each condition contains 2 biological samples.