Cry1 expression in the chicken pineal gland: Effects of changes in the light/dark conditions

Cryptochromes (Cry) are core components in the gene regulation of circadian rhythmic processes. It was shown earlier, that Cry1 mRNA content of the avian pineal gland was increased after a 4 h exposure to light during subjective night; however, a 30 min exposure was ineffective. In this study, changes in pineal Cry1 expression were detected in chickens during and after being placed into reversed light/dark environment. Cry1 mRNA content was higher if light was on during the night; however, in the first 2 h of light exposure at night, Cry1 mRNA contents were decreased. Following the first overnight light exposure, the peak of the mRNA expression was delayed for 12 h compared to controls. Our results suggest that environmental illumination activates a complex regulatory cascade that includes both up- and down-regulation of the Cry1 gene which inverses the 24 h pattern of Cry1 mRNA expression within one period.