Mishra I, Singh D, Kumar V
Department of Zoology, IndoUS Center for Biological Timing, University of Delhi, Delhi, India.
J Neuroendocrinol. 2017 May;29(5). doi: 10.1111/jne.12469.
The present study investigated seasonal alterations in the daily rhythms of hypothalamic expression of genes involved in the photoperiodic regulation of annual cycles in birds. We measured the 4-hourly mRNA expression of genes involved in the photoperiodic transduction (OPN5, EYA3, CGA, TSHβ, DIO2, DIO3) and neurosteroid-dependent processes (AR, CYP19, ERα, ERβ) in the hypothalamus of migratory blackheaded buntings photoinduced with photosensitive, photostimulated (early and late stimulated) and photorefractory seasonal states. There were significant differences in daily mRNA profiles between the photoperiodic states. Particularly, increased CGA, TSHβ and DIO2 and decreased DIO3 mRNA levels in the early photostimulated state, compared to the photosensitive state, suggest that thyroid hormones have a role in photostimulation in buntings. Similar differences in the expression of genes coding for the aromatase enzyme (CYP19) and receptors for oestrogen (ERα, ERβ) (but not androgen; AR) indicate that there is seasonal alteration in the neuro-oestrogen-mediated functions. Furthermore, peak expression times of CGA, TSHβ and DIO2 genes at hours 14-15 of the day in the early stimulated state indicated molecular regulation of the daily rhythm of photoinducibility in buntings. Most significantly, however, we found an attenuated daily rhythm in thyroid hormone modulatory genes and a switch of peak expression time from day to night in CYP19 mRNA rhythm in the subsequent late photostimulated state, although testicular maturation still persisted. These alterations in daily rhythms may have signalled the initiation of processes underlying other seasonal phenologies in parallel with the gonadal response, such as a manifestation of the night-time flight in buntings. These results show alterations in daily rhythms underlying the transcriptional regulation of the photoperiod-induced seasonal states in migratory blackheaded buntings.
本研究调查了参与鸟类年周期光周期调节的基因在下丘脑表达的日节律中的季节性变化。我们测量了光敏感、光刺激（早期和晚期刺激）及光不应性季节性状态下，经光诱导的迁徙黑头鹀下丘脑内参与光周期转导（OPN5、EYA3、CGA、TSHβ、DIO2、DIO3）和神经甾体依赖性过程（AR、CYP19、ERα、ERβ）的基因每4小时的mRNA表达。光周期状态之间的每日mRNA谱存在显著差异。特别是，与光敏感状态相比，早期光刺激状态下CGA、TSHβ和DIO2的mRNA水平升高，DIO3的mRNA水平降低，这表明甲状腺激素在鹀类的光刺激中起作用。编码芳香化酶（CYP19）和雌激素受体（ERα、ERβ）（而非雄激素受体；AR）的基因表达存在类似差异，表明神经雌激素介导的功能存在季节性变化。此外，早期刺激状态下CGA、TSHβ和DIO2基因在一天中的14 - 15小时达到表达峰值，这表明鹀类光诱导能力的日节律存在分子调控。然而，最显著的是，我们发现在随后的晚期光刺激状态下，甲状腺激素调节基因的日节律减弱，CYP19 mRNA节律的表达峰值时间从白天转换到了夜晚，尽管睾丸成熟仍在持续。这些日节律的变化可能标志着与性腺反应同时发生的其他季节性物候现象背后的过程开始启动，比如鹀类夜间飞行的表现。这些结果显示了迁徙黑头鹀光周期诱导的季节性状态转录调控背后的日节律变化。
