Evolutionary Changes in Early Brain Development

人类的前脑比其他哺乳动物的大。同样，鹦鹉和鸣禽的前脑也比其他鸟类的大。 成年人大脑比例的这些物种差异已经得到了很好的描述，并被认为是行为复杂性和智力的物种差异。 然而，几乎完全未知的是产生这种物种差异的发育机制。Striedter实验室以前的工作表明，鹦鹉和鸣禽的前脑扩大是因为这些物种的前脑前体细胞增殖时间更长，从而产生更大的前脑前体库。虽然这是扩大大脑区域的强大机制，但其他物种可能通过其他机制扩大大脑区域，例如改变年轻胚胎中基因表达的空间模式或改变前体细胞分裂的速率。这项拟议中的研究通过比较不同鸟类（包括长尾小鹦鹉、鹌鹑、鸡和鸭）的大脑区域大小、基因表达模式和细胞分裂速率来探索这些替代机制。如果这些参数中的一个或多个在所研究的物种之间存在差异，那么进化就可以通过几种不同的发育机制自由地改变大脑的比例，而不是只限于使用一种。更一般地说，这些发现将澄清一些控制大脑进化的规则。一个重要的长期目标是以遵循这些规则的方式操纵大脑发育，从而模仿自然的进化变化。这样的实验是令人兴奋的，因为它们将允许测试进化假说。 总体而言，拟议的工作将激励和培训至少一名研究生和几名本科生进行独立研究。它还将激发和教育公众，他们将通过公开讲座和与学生团体的外联接触到它。

The forebrain is proportionately larger in humans than in other mammals. Similarly, the forebrain is proportionately larger in parrots and songbirds than in other birds. These species differences in adult brain proportions have been well described and are thought to account for species differences in behavioral complexity and intelligence. Almost completely unknown, however, are the developmental mechanisms that generate such species differences. Previous work from the Striedter laboratory has shown that forebrain enlargement in parrots and songbirds occurs because the forebrain's precursor cells in these species proliferate for a longer period of time, thereby generating a larger forebrain precursor pool. Although this is a powerful mechansim for enlarging a brain region, other species may enlarge a brain region by other mechanisms, such as changing the spatial patterns of gene expression in young embryos or changing the rates at which precursor cells divide. The proposed research explores these alternative mechanisms by comparing brain region sizes, patterns of gene expression, and rates of cell division across young embryos of different bird species, including parakeets, quail, chickens, and ducks. If one or more of these parameters differs between the examined species, then evolution is free to vary brain proportions through several different developmental mechanisms, rather than constrained to utilize just one. More generally, the findings will clarify some of the rules that govern brain evolution. An important long-term goal is to manipulate brain development in ways that follow these rules and, thus, mimic the natural evolutionary changes. Such experiments are exciting because they will allow for the testing of evolutionary hypotheses. Overall, the proposed work will motivate and train at least one graduate student and several undergraduates performing independent research. It will also excite and educate the general public, who will be exposed to it through public lectures and outreach to student groups.