Mechanism of an Evolutionary Change in Development

点击翻译按钮获取中文摘要

The purpose of this project is to understand the mechanisms underlying evolutionary changes in the chordate body plan. For these studies, the PI has developed a model system consisting of two closely-related ascidian species with different larvae. The ascidian tadpole larva exhibits all the hallmarks of a chordate yet contains only 2500 cells and six different tissues. Molgula oculata (the tailed species) has a swimming tadpole larva with a tail containing a notochord and striated muscle cells, whereas Molgula occulta (the tailless species) has an immotile larva lacking these features. Fertilization of tailless species' eggs with tailed species' sperm results in restoration of the notochord and tail in the hybrid larvae, suggesting that they were lost in part by changes in zygotic tail-forming genes. In previous funding periods the PI has identified some of the tail forming genes. This project extends those studies in focusing on the Manx and bobcat genes, which encode a putative transcription factor and an RNA helicase respectively. Preliminary studies show that Manx and bobcat are present in an operon-like cluster in the tailed species' genome. Here the PI proposes to determine how these linked genes regulate ascidian evolution and development. First, the PI will characterize the entire Manx/bobcat gene complex to determine whether other tail-forming genes are present and whether these genes are indeed part of an operon in the tailed species. Second, the PI will determine the roles of the Manx and bobcat genes in tail development, particularly in mediating cell proliferation and programmed cell death. Third, the PI will characterize the Manx/bobcat genes in the tailless species to determine what mutations may have accumulated to result in tail regression. Finally, the PI will study the potential interactions between Manx and bobcat and the forkhead and Brachyury (T) genes, which are known to be involved in axis and notochord development in ascidians. Thus, by studying tail forming genes in ascidian larvae, the PI hopes to shed light on the mechanisms underlying the origin of the chordate body plan during evolution.