Day-night expression patterns of clock genes in the human pineal gland

Rhythm generation within the mammalian circadian system is achieved by clock genes and their protein products. As an integral part of this system, the pineal gland serves the need to tune the body to the temporal environment by the rhythmic synthesis and release of melatonin. A number of human disorders and syndromes are associated with alterations in circadian rhythms of clock genes and their protein products and/or a dysfunction in melatonin synthesis. In the human, little is known about the molecular signature of time management. Pineal tissue from regular autopsies was allocated to asserted time-of-death groups (dawn, day, dusk, night), and analyzed by RT-PCR, immunoblotting, immunohistochemistry, and confocal laser scanning microscopy for expression of clock genes. Despite the observed diurnal rhythms in activity of the arylalkylamine N-acetyltransferase and in melatonin content, mRNA levels for the clock genes Period1, Cryptochrome1, Clock, and Bmal1, and also amounts of corresponding clock gene proteins showed no differences between time- of-death groups. In contrast, a time-of-day-dependent nucleocytoplasmic shuttling of clock gene proteins was detected. These data confirm the minor importance of a transcriptional regulation for dynamics in the human pineal gland, and offer a novel twist in the molecular competence of clock gene proteins.