Evolution of cis-regulation of the engrailed gene in relation to evolution of the chordate body plan: amphioxus as a model for the ancestral vertebrate

6亿年前，文昌鱼从脊椎动物谱系中分化出来，本研究的长期目标是阐明形成脊椎动物胚胎的模式机制的进化起源。文昌鱼是脊椎动物，但与脊椎动物不同的是，文昌鱼既没有复制也没有丢失很多基因。即便如此，文昌鱼和人类基因组之间仍保留着许多可能的基因调控序列（增强子）。基因调控的进化变化被认为是影响动物身体结构大规模变化的一种方式。目前的研究重点是“嵌入”基因。在文文鱼中，嵌入的表达表明在神经元身份的规范和肌肉体的分割中都有功能。文昌鱼的腹肌、七鳃鳗的腭肌和一些脊椎动物的颚肌中的基因表达导致了一种假设，即脊椎动物的颚肌是从类似文昌鱼的无颌祖先的前肌体进化而来的。先前nsf支持的研究表明，从文文鱼（amphioxus）中获得的1.2 kb肌肉增强子与小鼠engrailed-2 （en-2）颌骨肌肉增强子高度保守。本研究有三个具体目的：(1)全面表征文昌鱼肌肉中直接表达文昌鱼的调控元件；(2)确定脊索肌中遗传调控的进化保护程度；(3)研究文昌鱼肌肉分割相关基因网络的进化保护。这些结果不仅可以让我们深入了解嵌入基因的进化过程，还可以深入了解基因调控的进化过程。此外，它还解决了基因功能如何随着新的解剖结构的演变而变化的问题。就更广泛的影响而言，这项工作在基因组进化如何导致无脊椎动物向脊椎动物过渡的发育机制进化的一般概念中很重要。研究结果将发表在同行评议的期刊上，并在科学研讨会上发表。本研究将为一名博士后提供培训，并将培养动手研究的本科生，他们将成为研究论文的共同作者。将继续向学生，特别是来自拉丁美洲的学生提供服务。

The long term goal of this research on the basal chordate amphioxus, which diverged from the vertebrate lineage over 600 million years ago, is to elucidate the evolutionary origins of the patterning mechanisms that shape the vertebrate embryo. Amphioxus is vertebrate-like, but, unlike vertebrates, has neither duplicated nor lost many genes. Even so, many likely gene-regulatory sequences (enhancers) are conserved between the amphioxus and human genomes. Evolutionary changes in gene regulation are thought to be one way of effecting large-scale changes in animal body plans. The present research focuses on the 'engrailed' gene. In amphioxus, engrailed expression suggests functions in both specification of neuronal identity and in segmentation of the muscular somites. Engrailed expression in the amphioxus somites, lamprey velar muscles and some vertebrate jaw muscles led to the hypothesis that vertebrate jaw muscles evolved from the anterior muscular somites of an amphioxus-like jawless ancestor. Previous NSF-supported research revealed a 1.2 kb muscle enhancer from amphioxus engrailed that is highly conserved with the mouse engrailed-2 (en-2) jaw muscle enhancer. The present research has three specific aims: (1) to fully characterize the regulatory elements responsible for directing expression of amphioxus engrailed to muscle in amphioxus; (2) to determine the extent of evolutionary conservation of engrailed regulation in chordate muscle; and (3) to investigate evolutionary conservation of the gene network involving engrailed in segmentation of the muscles in amphioxus. The results should permit insights not only into the evolution of the engrailed gene but also into the evolution of gene regulation in general. In addition, it addresses the question of how gene function changes as new anatomical structures evolve. In terms of Broader Impacts the work is important in the general concept of how genome evolution leads to evolution of developmental mechanisms at the invertebrate to vertebrate transition. The results will be published in peer-reviewed journals and presented at scientific symposia. This research will provide training for one postdoctoral fellow, and will train undergraduates in hands-on research, who will be co-authors on research papers. Outreach to students, particularly those from Latin America, will be continued.