Hope Sydney F, Buenaventura Christopher R, Husain Zahabiya, DuRant Sarah E, Kennamer Robert A, Hopkins William A, Thompson Christopher K
Department of Fish and Wildlife Conservation, Virginia Tech, Blacksburg, VA, United States.
School of Neuroscience, Virginia Tech, Blacksburg, VA, United States.
Front Physiol. 2019 Jul 5;10:857. doi: 10.3389/fphys.2019.00857. eCollection 2019.
The conditions that animals experience during early development can have profound consequences for health and fitness. In birds, one of the most important aspects of development is egg incubation temperature. A small decrease in average temperature leads to various impacts on offspring phenotype, such as smaller body sizes, slower growth rates, and less efficient metabolic activity. Little is known, however, about the proximate mechanisms underlying these incubation temperature-induced phenotypic changes. Two important hormones which could play a proximate role are thyroid hormone and corticosterone, which mobilize stored energy reserves and coordinate the normal growth of tissues, particularly in the brain. Previous research shows that circulating blood concentrations of both hormones are influenced by incubation temperature, but the mechanism by which incubation temperature may lead to these changes is unknown. We hypothesized that incubation temperature induces changes in thyroid hormone and corticosterone regulation, leading to changes in expression of hormone-sensitive genes in the brain. To test this, we incubated wood duck () eggs at three different temperatures within the natural range (35.0, 35.8, and 37.0°C). We measured mRNA expression of thyroid hormone-related neuroendocrine endpoints (deiodinase 2/3, thyroid hormone receptor α/β, neural regeneration related protein, and Krueppel-like factor 9) in newly hatched ducklings and corticosterone-related neuroendocrine endpoints (mineralocorticoid receptor, glucocorticoid receptor, cholecystokinin, and brain-derived neurotrophic factor) in 15 day-old ducklings using qPCR on brain tissue from the hippocampus and hypothalamus. Contrary to our predictions, we found that mRNA expression of thyroid hormone-related endpoints in both brain areas were largely unaffected by incubation temperature, although there was a trend for an inverse relationship between mRNA expression and incubation temperature for several genes in the hypothalamus. We also found that mineralocorticoid receptor mRNA expression in the hypothalamus was lower in ducklings incubated at the low relative to the high temperatures. This study is the first to evaluate the effects of incubation temperature on mRNA expression of neuroendocrine endpoints in the developing avian brain and suggests that these particular endpoints may be largely resistant to changes in incubation temperature. Thus, further research into the proximate mechanisms for incubation temperature-induced developmental plasticity is needed.
动物在早期发育过程中所经历的条件会对其健康和适应性产生深远影响。在鸟类中，发育的一个最重要方面是卵的孵化温度。平均温度的小幅下降会对后代表型产生各种影响，例如体型变小、生长速度减慢以及代谢活动效率降低。然而，对于这些由孵化温度引起的表型变化背后的直接机制，我们却知之甚少。两种可能起直接作用的重要激素是甲状腺激素和皮质酮，它们可调动储存的能量储备并协调组织的正常生长，尤其是在大脑中。先前的研究表明，这两种激素的循环血液浓度均受孵化温度影响，但孵化温度导致这些变化的机制尚不清楚。我们推测，孵化温度会引起甲状腺激素和皮质酮调节的变化，从而导致大脑中激素敏感基因表达的改变。为了验证这一点，我们在自然范围内的三个不同温度（35.0、35.8和37.0°C）下孵化林鸳鸯（）卵。我们使用qPCR检测了新孵化雏鸭大脑中甲状腺激素相关神经内分泌终点（脱碘酶2/3、甲状腺激素受体α/β、神经再生相关蛋白和类Krüppel因子9）的mRNA表达，以及15日龄雏鸭大脑中海马体和下丘脑组织中皮质酮相关神经内分泌终点（盐皮质激素受体、糖皮质激素受体、胆囊收缩素和脑源性神经营养因子）的mRNA表达。与我们的预测相反，我们发现两个脑区中甲状腺激素相关终点的mRNA表达在很大程度上不受孵化温度影响，尽管下丘脑中有几个基因的mRNA表达与孵化温度之间存在负相关趋势。我们还发现，相对于高温孵化的雏鸭，低温孵化的雏鸭下丘脑盐皮质激素受体mRNA表达较低。本研究首次评估了孵化温度对发育中的鸟类大脑神经内分泌终点mRNA表达的影响，并表明这些特定终点可能在很大程度上抵抗孵化温度的变化。因此，需要进一步研究孵化温度诱导发育可塑性的直接机制。
