Bentz Alexandra B, Dossey Emma K, Rosvall Kimberly A
Department of Biology, Indiana University, Bloomington, IN 47405, USA; Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN 47405, USA.
Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Gen Comp Endocrinol. 2019 Jan 1;270:26-34. doi: 10.1016/j.ygcen.2018.10.001. Epub 2018 Oct 3.
Testosterone (T) is a sex steroid hormone that often varies seasonally and mediates trade-offs between territorial aggression and parental care. Prior work has provided key insights into the 'top-down' hypothalamic control of this seasonal plasticity in T, yet mechanisms acting outside of the brain may also influence circulating T levels. We hypothesized that peripheral mechanisms may be especially critical for females, because peripheral regulation may mitigate the costs of systemically elevated T. Here, we begin to test this hypothesis using a seasonal comparative approach, measuring gene expression in peripheral tissues in tree swallows (Tachycineta bicolor), a songbird with intense female-female competition and T-mediated aggression. We focused on the gonad and liver for their role in T production and metabolism, respectively, and we contrasted females captured during territory establishment versus incubation. During territory establishment, when T levels are highest, we found elevated gene expression of the hepatic steroid metabolizing enzyme CYP2C19 along with several ovarian steroidogenic enzymes, including the androgenic 5α-reductase. Despite these seasonal changes in gene expression along the steroidogenic pathway, we did not observe seasonal changes in sensitivity to upstream signals, measured as ovarian mRNA abundance of luteinizing hormone receptor. Together, these data suggest that differential regulation of steroidogenic gene expression in the ovary is a potentially major contributor to seasonal changes in T levels in females. Furthermore, these data provide a unique and organismal glimpse into tissue-specific gene regulation and its potential role in hormonal plasticity in females.
睾酮（T）是一种性类固醇激素，其水平常常随季节变化，并在领地攻击行为和亲代抚育之间进行权衡。先前的研究已经对下丘脑对T这种季节性可塑性的“自上而下”控制提供了关键见解，但大脑之外的作用机制也可能影响循环中的T水平。我们推测，外周机制对雌性可能尤为关键，因为外周调节可能会减轻全身T水平升高带来的代价。在此，我们开始使用季节性比较方法来验证这一假设，测量树燕（双色树燕）外周组织中的基因表达，树燕是一种具有激烈雌性间竞争且存在T介导攻击行为的鸣禽。我们分别关注性腺和肝脏在T产生和代谢中的作用，并对比了在领地建立期与孵卵期捕获的雌性。在领地建立期，当T水平最高时，我们发现肝脏类固醇代谢酶CYP2C19以及几种卵巢类固醇生成酶（包括雄激素5α -还原酶）的基因表达升高。尽管沿着类固醇生成途径存在这些基因表达的季节性变化，但我们并未观察到对上游信号敏感性的季节性变化，以上游信号敏感性以促黄体生成素受体的卵巢mRNA丰度来衡量。总之，这些数据表明卵巢中类固醇生成基因表达的差异调节可能是雌性T水平季节性变化的一个潜在主要因素。此外，这些数据为组织特异性基因调节及其在雌性激素可塑性中的潜在作用提供了独特的、从生物体角度的观察。
