Wood Shona, Loudon Andrew
Faculty of Biology, Medicine and Health, School of Medical Sciences, University of Manchester, A.V. Hill Building, Oxford Road, Manchester M13 9PT, UK.
Faculty of Biology, Medicine and Health, School of Medical Sciences, University of Manchester, A.V. Hill Building, Oxford Road, Manchester M13 9PT, UK.
Gen Comp Endocrinol. 2018 Mar 1;258:222-235. doi: 10.1016/j.ygcen.2017.06.029. Epub 2017 Jun 30.
Accurate timing and physiological adaptation to anticipate seasonal changes are an essential requirement for an organism's survival. In contrast to all other environmental cues, photoperiod offers a highly predictive signal that can be reliably used to activate a seasonal adaptive programme at the correct time of year. Coupled to photoperiod sensing, it is apparent that many organisms have evolved innate long-term timekeeping systems, allowing reliable anticipation of forthcoming environmental changes. The fundamental biological processes giving rise to innate long-term timing, with which the photoperiod-sensing pathway engages, are not known for any organism. There is growing evidence that the pars tuberalis (PT) of the pituitary, which acts as a primary transducer of photoperiodic input, may be the site of the innate long-term timer or "circannual clock". Current research has led to the proposition that the PT-specific thyrotroph may act as a seasonal calendar cell, driving both hypothalamic and pituitary endocrine circuits. Based on this research we propose that the mechanistic basis for the circannual rhythm appears to be deeply conserved, driven by a binary switching cell based accumulator, analogous to that proposed for development. We review the apparent conservation of function and pathways to suggest that these broad principles may apply across the vertebrate lineage and even share characteristics with processes driving seasonal adaptation in plants.
准确的时间安排和对季节性变化的生理适应是生物体生存的基本要求。与所有其他环境线索不同，光周期提供了一个高度可预测的信号，可在一年中的正确时间可靠地用于激活季节性适应程序。与光周期感知相结合，很明显许多生物体已经进化出天生的长期计时系统，从而能够可靠地预测即将到来的环境变化。对于任何生物体来说，引发天生长期计时的基本生物学过程以及光周期感知途径与之相关的过程都尚不清楚。越来越多的证据表明，作为光周期输入主要传感器的垂体结节部（PT）可能是天生长期计时器或“年节律钟”的所在位置。目前的研究提出，PT特异性促甲状腺细胞可能充当季节性日历细胞，驱动下丘脑和垂体的内分泌回路。基于这项研究，我们认为年节律的机制基础似乎高度保守，由基于二元开关细胞的累加器驱动，类似于发育过程中所提出的那样。我们回顾了功能和途径的明显保守性，以表明这些广泛的原则可能适用于整个脊椎动物谱系，甚至与驱动植物季节性适应的过程具有共同特征。
