El Allali Khalid, Sinitskaya Natalia, Bothorel Béatrice, Achaaban Rachid, Pévet Paul, Simonneaux Valérie
Unite d'Anatomie Comparee, Institut Agronomique et Veterinaire Hassan II, Rabat, Morocco.
Chronobiol Int. 2008 Sep;25(5):800-7. doi: 10.1080/07420520802384085.
Arylalkylamine N-acetyltransferase (AA-NAT) is the rhythm-generating enzyme for the synthesis of pineal melatonin. Molecular investigations have revealed two biological models for the activation of AA-NAT. In rodent species, Aa-nat gene transcription is turned off during the daytime and markedly activated at night. In primates, sheep, and cows, the Aa-nat gene is constitutively transcripted with no visible daily variations. This inter-species difference in Aa-nat gene regulation leads to different daily profiles in melatonin synthesis and release. Thus, the nighttime onset of the rise in circulating melatonin is delayed and slow in rodents, whereas it is fast and sharp in sheep. In the camel (Camelus dromedarius), we have observed that circulating melatonin rises immediately after sunset, suggesting AA-NAT activity is regulated at the post-transcriptional level. In agreement with this hypothesis, we report herein the amount of Aa-nat mRNA in the camel pineal gland is high, during both the day and night with no daily variations, while melatonin concentration in the same pineal tissue is five times higher during the night than daytime.
芳基烷基胺N - 乙酰基转移酶（AA - NAT）是合成松果体褪黑素的节律产生酶。分子研究揭示了两种激活AA - NAT的生物学模型。在啮齿动物中，Aa - nat基因转录在白天关闭，在夜间显著激活。在灵长类动物、绵羊和奶牛中，Aa - nat基因持续转录，没有明显的每日变化。Aa - nat基因调控的这种种间差异导致褪黑素合成和释放的每日模式不同。因此，啮齿动物循环褪黑素升高的夜间起始延迟且缓慢，而在绵羊中则快速且急剧。在骆驼（单峰驼）中，我们观察到循环褪黑素在日落后立即升高，表明AA - NAT活性在转录后水平受到调节。与该假设一致，我们在此报告骆驼松果体中Aa - nat mRNA的量在白天和夜间均很高，没有每日变化，而同一松果体组织中的褪黑素浓度在夜间比白天高五倍。
