The evolutionary origins of our own phylum, the chordates, have been a topic of intense debate for the past 200 years. Despite broad interest in the issue, little consensus has emerged from this intense research scrutiny. Recent advances in our understanding of the relationships between the groups of animals closely related to chordates, and the technological advances from molecular genetics, make this key issue much more experimentally tractable. This work investigates the developmental biology of a phylum called hemichordates, which is one of the most closely related groups to chordates. Approach: This project examines how the mesoderm and endoderm are set up in this phylum. The mesoderm is a tissue layer that gives rise to many of the key innovations of our own phylum such as skeleton and the associated complex musculature. The endoderm gives rise to our complex gut and associated glands. Expected results: Investigating the role of genes with conserved roles in inducing and patterning chordate endoderm and mesoderm will help reconstruct the early evolution of these tissue layers and how they were modified and diversified to produce the critical morphological structures that define our phylum. A comparative study of the gene networks involved in endoderm and mesoderm development will give additional insights into how they function in vertebrates. Broader impacts: This project will involve the training and participation of undergraduate and graduate students at the University of Chicago. The PI and graduate students will present the results at a broad range of institutions and internally conferences.
This grant funded work in my lab to investigate the early evolutionary origins of the developmental decisions defining the differences between the three layers of cells that define our bodies – ectoderm, endoderm and mesoderm. Ectoderm gives rise to our skin and nervous system, endoderm gives rise to our gut and associated organs, and mesoderm gives rise to our muscles and vasculature. In vertebrates, a large body of research has focused on determining how the endoderm and mesoderm are established during the early development of embryos. Insights into the complex developmental mechanisms of our own development can often be aided by studies in much simpler animals that have to make similar developmental decisions. Almost all animals carve their embryos into these three types of cells and studying how these decisions are made in simpler animals can give key insights into our own development, and the molecular mechanisms involved in determining the ectoderm, endoderm and mesoderm. We investigated what genes are responsible for making the early decisions during the development of a hemichordate embryo to define the embryonic regions that will form the endoderm and mesoderm. We chose to work on a representative species of the phylum Hemichordata, as they are closely related to our own phylum, the chordates. Much of our previous work has revealed extensive genetic and developmental similarities with chordates and given some key insights into developmental and evolutionary origins of our nervous system and brain. In order to define the basic mechanisms of endoderm and mesoderm formation similar comparative approaches have been carried out in other phyla such as arthropods and echinoderms, but for the most part, many of the mechanisms that define their endoderm and mesoderm seem quite different from our own group of animals. We selected three main pathways that play important roles in mesoderm and endoderm development in vertebrates; Nodal, FGF (Fibroblast growth factor) and Wnt. Our findings reveal some similarities with echinoderms in the role of the Wnt pathway in the formation of the endoderm that are different to those in vertebrates, but both Nodal and FGF signaling share come conserved roles with vertebrates not present in echinoderms. The simple development and genomic simplicity of hemichordates makes it a good candidate for helping understand the more complex mechanisms of vertebrate development. In addition, this work not only gives us mechanistic insights into our own development, but the details of hemichordate development will help us ultimately to understand the evolutionary origins of our own phylum. The approach that we take in our research and the value of using comparative developmental biology to address fundamental questions in animal and human biology has been presented to a wide range of scientists from a wide range of disciplines at international and domestic meetings. We have also presented our work to the general public and to high school teachers in various outreach projects at Hopkins Marine Station and the Monterey Bay Aquarium.
