DISSERTATION RESEARCH: The role of Maternal Hormones in Programming Offspring Aggression

母亲对当前环境的荷尔蒙反应会对其正在发育的后代造成永久性的改变，这可能会决定这些后代在未来的环境中是生是死。在竞争更激烈的环境中繁殖的雌性往往会在产前将更多的睾丸激素传递给后代，从而使后代永久地更具攻击性。这种母性效应可能有助于后代适应竞争环境，但尚不清楚母性睾酮如何永久影响后代的行为。在不知道它是如何发生的情况下，很难描述这种母体效应的遗传性，以及它如何适应更大的进化框架。这项研究是第一个测试分子机制，如基因表达和控制的变化，是否介导母体睾酮对后代攻击性的影响的研究，在鸟类中，母体睾酮对后代攻击性的影响研究得最好。这项研究将采用一种新颖的方法，从几种大脑通路中探索与攻击相关的基因的差异。这项研究的结果将有助于澄清是什么导致了攻击行为的长期变化，以及为什么动物行为存在差异。研究人员还将对本科生进行实验室方法和生物信息学方面的培训。此外，这项研究还与美国各地的鸣鸟饲养者一起开展了一项公民科学项目，以探索影响鸟类繁殖的因素。具体来说，研究人员将通过实验确定表观遗传机制（即DNA甲基化）是否在鸣禽的母体激素对后代攻击的编程中起作用。鸟类是母性效应的极好模型，因为它们的幼崽在卵的外部发育，雌性将大量的睾丸激素分配到蛋黄中。研究人员将在斑胸草雀卵中注入对照物或睾丸激素，并测量由此产生的后代的攻击性和竞争行为（即生长速度和乞讨率）。在这些后代的一个子集中，研究人员将测试表观遗传编程的证据。攻击行为是通过许多相互作用的基因（即类固醇受体、组胺、多巴胺、生长抑素、精氨酸缩素等）发起的。因此，研究人员将使用RNA-seq和甲基化-seq分析来探索两个与社会相关的大脑区域（端脑和间脑）中攻击相关基因的mRNA表达和位点特异性甲基化模式的全基因组差异。这项研究将极大地扩展我们对不同基因网络如何在大脑区域相互作用以表达攻击性的认识，并将提供最早的鸟类DNA甲基化组之一。本项目产生的所有数据将存档在适当的电子存储库中。

A mother's hormonal response to her current environment can cause permanent changes in her developing offspring, potentially determining whether those offspring live or die in their future environment. Females breeding in more competitive environments tend to transfer more testosterone to their offspring prenatally, which permanently makes offspring more aggressive. This maternal effect may help offspring adapt to competitive environments, yet it is still unclear how maternally derived testosterone permanently impacts offspring behavior. Without knowing how it happens, it is difficult to characterize the heritability of this maternal effect and how it fits into larger evolutionary frameworks. This research is among the first to test if molecular mechanisms, such as changes in gene expression and control, mediate the effects of maternal testosterone on offspring aggression using birds, in which this maternal effect is best studied. This research will take a novel approach by exploring differences in aggression-related genes from several brain pathways. The results of this research will help clarify what contributes to long-lasting variation in aggressive behaviors and why differences in animal behaviors exist. The researchers will also train undergraduate students in laboratory methods and bioinformatics. Additionally, this research has lent itself to a citizen science project with songbird breeders throughout the United States to explore factors influencing avian reproduction. Specifically, the researchers will experimentally determine if an epigenetic mechanism (i.e., DNA methylation) underlies the programming of offspring aggression by maternal hormones in songbirds. Birds are excellent models for maternal effects because their young develop externally in eggs and females allocate substantial amounts of testosterone to their egg yolks. The researchers will inject zebra finch eggs with a control vehicle or testosterone and measure aggressive and competitive behaviors (i.e., growth rate and begging rate) in the resulting offspring. In a subset of these offspring, the researchers will test for evidence of epigenetic programming. Aggressive behaviors are initiated across many interacting genes (i.e., steroid receptors, histamine, dopamine, somatostatin, arginine vasotocin, etc.). Thus, the researchers will use RNA-seq and methyl-seq analyses to explore genome-wide differences in mRNA expression and site-specific methylation patterns of aggression-related genes in two socially-relevant brain regions, the telencephalon and diencephalon. This research will greatly expand our knowledge of how different gene networks interact across brain regions to express aggression and will provide one of the first avian DNA methylomes. All data generated in this project will be archived in appropriate electronic repositories.