Department of Vertebrate Zoology and Ecology, Nicolaus Copernicus University in Toruń, Toruń, Poland.
Institute of Neurobiology, Ulm University, Ulm, Germany.
PLoS One. 2024 Oct 25;19(10):e0309591. doi: 10.1371/journal.pone.0309591. eCollection 2024.
Although the Djungarian hamster (Phodopus sungorus) is a seasonality model, it presents substantial variability in winter acclimation. In response to short photoperiod, some individuals express a suite of winter traits such as low body mass, regressed gonads, white fur, and daily torpor, while others develop only some adjustments or maintain a summer phenotype. Despite comprehensive research, the mechanisms underlying polymorphism of winter phenotype are still unknown. We compared key elements of the hypothalamic thyroid hormone system, as well as the tanycyte architecture in hamsters of both sexes. Individuals presented different responses to short photoperiod characterized either as phenotypes (non-responder, partial-responder and full-responder) or photoresponsive index. We measured the expression of genes coding iodothyronine deiodinase 2 and 3, monocarboxylate transporter 8, thyrotropin-releasing hormone, and somatostatin in 40 individuals and counted the number of immunolabeled tanycyte processes in standardized regions of interest around the third ventricle in 30 individuals. Animals acclimated to short photoperiod presented a downregulation of diodinase 2 and somatostatin and an upregulation of deiodinase 3, as well as a decreased number of tanycyte processes, compared to long photoperiod-exposed individuals. Although phenotypes did not differ in gene expression, the higher the photoresponsive index, the lower was the deiodinase 2 expression and the higher the deiodinase 3 expression. Partial-responders and full-responders had less tanycyte processes than non-responders, and the number of tanycyte processes correlated with the photoresponsive index. Sexes differed neither in their seasonal response, nor hypothalamic gene expression, but females had more tanycyte processes. Our results are in accordance with studies emphasizing the pivotal role of thyroid hormones in seasonal response. We suggest that the whole spectrum of winter phenotypes exists within the population of Djungarian hamsters and that it is reflected also at the level of neuroendocrine regulation. However, the neuroendocrine underpinnings of winter phenotype polymorphism require further investigation.
尽管沙鼠（Phodopus sungorus）是季节性模式动物，但它在冬季适应过程中表现出很大的可变性。为了应对短光照周期，一些个体表现出一系列冬季特征，如低体重、退化的性腺、白色的皮毛和日常休眠，而另一些个体只表现出一些调整或保持夏季表型。尽管进行了全面的研究，但冬季表型多态性的机制仍不清楚。我们比较了两性沙鼠下丘脑甲状腺激素系统的关键要素以及 tanycyte 结构。个体对短光照周期的反应不同，表现为表型（无反应者、部分反应者和完全反应者）或光反应指数。我们测量了 40 只个体中编码碘甲状腺原氨酸脱碘酶 2 和 3、单羧酸转运蛋白 8、促甲状腺激素释放激素和生长抑素的基因表达，并在 30 只个体的第三脑室周围标准化感兴趣区域中计数免疫标记的 tanycyte 过程数量。与长光照周期暴露的个体相比，适应短光照周期的动物表现出脱碘酶 2 和生长抑素下调以及脱碘酶 3 上调，以及 tanycyte 过程数量减少。尽管表型在基因表达上没有差异，但光反应指数越高，脱碘酶 2 表达越低，脱碘酶 3 表达越高。部分反应者和完全反应者的 tanycyte 过程比无反应者少，tanycyte 过程数量与光反应指数相关。性别在季节性反应或下丘脑基因表达方面没有差异，但雌性的 tanycyte 过程更多。我们的结果与强调甲状腺激素在季节性反应中的关键作用的研究一致。我们认为，冬季表型的整个范围存在于沙鼠种群中，并且在神经内分泌调节水平上也有所反映。然而，冬季表型多态性的神经内分泌基础需要进一步研究。
