About 360 million years ago, vertebrates divorced themselves completely from the water. This evolution required changes in eggs, so that they could develop on land. These changes were fundamentally important in generating the type of egg and embryo, now present in humans. Development of frogs with large eggs provides opportunities to consider how the land egg originated. One such frog, a Puerto Rican tree frog popularly called the coquÃ, no longer has a tadpole and has radically changed the development of its endoderm, the tissue that becomes the gut. Some of its endoderm becomes stomach, intestine, liver, and so on, and some is used only for nutrition. The goal of this project is to determine the mechanisms involved in this novel setting aside of cells for nutrition only. Based on gut development in other animals, the hypothesis will be tested that this evolutionary change in coquà was due to alterations of particular signals, called nodals. The molecules involved in nodal signaling will be compared between coquà and other animals, and these molecules will be manipulated in the coquà embryo to see whether gut development can be altered in predictable ways. The experiments will not only shed light on a critical evolutionary change in embryonic development, but they also will provide a novel context for examining nodal signals, which play many important roles in embryos. In addition to these basic questions, the coquà itself is an important animal in natural environments and knowledge derived from maintaining a coquà reproductive colony may contribute both to rescuing endangered frogs and managing invasive populations.
