TRENDS IN COMPARATIVE ENDOCRINOLOGY AND NEUROBIOLOGY Expression of Cry2 in the Chicken Pineal Gland Effects of Changes in Light–Dark Conditions Andras D. Nagy, Karishma Seomangal, Siri Kommedal, and Valer J. Csernus University of P´ ecs, Medical School, Department of Anatomy, P´ ecs, Hungary Pineal expression of Cry2 mRNA has been examined in chickens under normal (LD) and reversed (DL) light–dark conditions. In vivo the peak of Cry2 mRNA content at late subjective day under LD diminished after switching to a DL schedule. In vitro, Cry2 mRNA levels showed a steady decrease during light exposure at subjective night. Our data show that light-sensitive clock components in the pinealocytes may be involved in the repression of Cry2 transcription at night, which may contribute to resetting the phase of the clock within 24 h. Key words: circadian rhythms; Cry2; pineal gland; chicken; light Introduction Cryptochromes (Cry1, Cry2) are core compo- nents in the molecular oscillator of vertebrate circadian clocks. 7 In the mammalian suprachi- asmatic nucleus (SCN), Cry1 and Cry2 mRNAs show similar circadian rhythm in vivo under normal light–dark conditions (LD) and also under constant dark conditions (DD). 7 Un- like Per1 and Per2, Cry expression in the mam- malian SCN is not induced by light pulses. 3 In the mammalian pineal gland, daily rhythms of clock gene expression are delayed by 8 h with respect to those in the SCN. 6,7 In the rat pineal in vivo, the expression of Cry2 but not Cry1 is regulated by the clock-driven changes in norepinephrine, suggesting different roles in peripheral clocks. 8 Unlike mammals, avian pinealocytes contain a circadian clockwork with functioning photoreceptors, indicated also by the absence of phase delay between pineal and SCN patterns of clock gene expression. 10 Furthermore, chicken pineal cryptochromes Address for correspondence: Andras D. Nagy, MD, Department of Anatomy, University of P´ ecs, Medical School, Szigeti ut 12. P´ ecs, 7624. Hungary. Voice: +36-30-668-6451; fax: +36-72-536-393. andras.d.nagy@aok.pte.hu inhibit the activation of circadian-regulated genes by BMAL:CLOCK heterodimers, 9 as do their mouse counterparts in the SCN that form the basis of a similar oscillator. While shift- ing the LD schedule, Cry1 mRNA pattern in the chicken pineal gland in vivo corresponds well with that seen in the mammalian SCN. 4 Whether Cry2 and Cry1 expression show simi- lar patterns in the chicken pineal gland, avail- able data were found to be inconsistent. 1,2,9,10 To clarify this, we collected in vivo and in vitro data on Cry2 expression in the chicken pineal gland under both LD and reversed LD (DL) conditions. Materials and Methods Animals Newly hatched white Leghorn chickens were kept under normal 14/10 h LD schedule (lights on at 06:00 h) for 6 weeks. In the in vivo exper- iments, chickens were placed at 20:00 h to a 10/14 h DL environment (lights on at 20:00 h). Chickens were sacrificed by decapitation every 4 h throughout a day beginning at 06:00 h and pineal glands were collected. Trends in Comparative Endocrinology and Neurobiology: Ann. N.Y. Acad. Sci. 1163: 488–490 (2009). doi: 10.1111/j.1749-6632.2008.03640.x C  2009 New York Academy of Sciences. 488