Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
Gen Comp Endocrinol. 2019 Nov 1;283:113224. doi: 10.1016/j.ygcen.2019.113224. Epub 2019 Jul 16.
Glucocorticoid hormones are important intermediates between an organism and its environment. They enable an organism to adjust its behavioural and physiological processes in response to environmental changes by binding to mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) expressed in many tissues, including the integument. The regulation of glucocorticoids co-varies with melanin-based colouration in numerous species, an association that might result from pleiotropic effects of genes in the melanocortin system and evolve within a signalling context. Most studies have focused on the circulating levels of glucocorticoids disregarding the receptors that mediate their action, and that might partly account for the covariation between the regulation of stress and melanin-based colouration. We investigated the association of the expression levels of GR and MR genes with melanin-based colouration in the growing feathers of nestling barn owls (Tyto alba). We also explored the association between GR and MR expression levels and the expression of genes related to the melanocortin system and melanogenesis to better understand the origin of the link between the expression of receptors to which corticosterone binds and melanin-based colouration. Nestling barn owls displaying larger eumelanic black feather spots expressed GR and MR at lower levels than smaller-spotted individuals. However, we found that the expression of the GR and MR genes was positively rather than negatively correlated with the expression of genes involved in the deposition of melanin pigments at the time we sampled the nestlings. This provides mixed evidence of the association between melanin-based traits and MR and GR gene expression. The finding that the expression of GR and MR was positively associated with the expression of the PCSK2 gene (encoding one of the protein convertase responsible for the production of hormone peptide ACTH and α-MSH) suggests that the melanocortin system may be implicated in the establishment of the covariation between melanin-based colour and the expression of receptors to which glucocorticoids bind. However, further studies investigating the expression of melanin-based traits with stress-related endpoints at different time points of feather development will be necessary to understand better the proximate mechanism linking melanin-based traits with stress.
糖皮质激素是生物与环境之间的重要中介。它们使生物体能够通过结合在许多组织（包括表皮）中表达的盐皮质激素受体（MR）和糖皮质激素受体（GR），对环境变化做出行为和生理过程的调整。在许多物种中，糖皮质激素的调节与基于黑色素的颜色变化密切相关，这种关联可能是由于黑素皮质素系统中的基因的多效性效应，并在信号转导的背景下进化而来。大多数研究都集中在循环中的糖皮质激素水平上，而忽略了介导其作用的受体，这可能部分解释了应激调节和基于黑色素的颜色变化之间的共变。我们研究了生长中的雏鸟Barn 猫头鹰（Tyto alba）的羽毛中 GR 和 MR 基因的表达水平与基于黑色素的颜色之间的关联。我们还探索了 GR 和 MR 表达水平与黑素皮质素系统和黑色素生成相关基因的表达之间的关联，以更好地理解结合皮质酮的受体的表达与基于黑色素的颜色变化之间的联系的起源。表现出较大的真黑色素黑色羽毛斑点的雏鸟 Barn 猫头鹰的 GR 和 MR 表达水平低于斑点较小的个体。然而，我们发现，在我们采样雏鸟时，GR 和 MR 基因的表达与参与黑色素颜料沉积的基因的表达呈正相关，而不是负相关。这为黑素皮质素性状与 MR 和 GR 基因表达之间的关联提供了混合证据。GR 和 MR 表达与 PCSK2 基因（编码一种负责产生激素肽 ACTH 和 α-MSH 的蛋白转化酶）的表达呈正相关的发现表明，黑素皮质素系统可能与基于黑色素的颜色与糖皮质激素结合的受体表达之间的共变有关。然而，为了更好地理解将基于黑色素的特征与应激相关的末端联系起来的近因机制，还需要进一步研究在羽毛发育的不同时间点具有应激相关终点的基于黑色素的特征的表达。
