RUI:Formation of the Turtle Plastron by Re-specified Trunk Neural Crest Cells

Millersville University, Millersville PA

Investigators

Abstract

This research investigates how new types of animals evolve through changes in their body plan. The turtle shell evolved about 220 million years ago, and it is the defining character of an entire order of animals, turtles and tortoises. This research examines the developmental origin of the cells that form the bones of the turtle plastron (the bottom portion of the shell). The plastron bones form in the same way as those of the face and much of the skull; they form without a cartilage intermediate from a stem cell-like population known as neural crest cells. Importantly, this means that cells that do not produce bones of the body in mice and chicks, do so in turtles. Previous work demonstrated that a unique subpopulation of neural crest cells found only in turtles migrates into the plastron region. The experiments use specific dyes to study the migration of the unique neural crest cells, and test the prediction that if they can make bone, they should express a set of genes similar to those neural crest cells that form the head and skull bones. This research will help to explain the mechanism by which cells "choose" their developmental fate from a variety of options, and provide insight into how this process can be altered to produce a novel structure such as the turtle shell. This research is focused on the characterization of a unique osteogenic population of trunk neural crest cells that appear to give rise to the turtle plastron, an evolutionary novelty that defines the vertebrate order Testudines. One goal is to investigate the developmental origin of the plastron bones in red-eared slider turtle (T. scripta) embryos using lineage-tracing experiments to follow the movement of labeled cells from the dorsal neural tube. The second goal is to investigate the temporal and spatial pattern of expression of neural crest inducers and specifiers in and around the neural tube in turtle and chick embryos. The final goal is to compare the differentiation potential, gene expression pattern and transcriptional profile of early (conventional) and late (unique) trunk neural crest cells, and cranial neural crest cells. This will test the hypothesis that a portion of the trunk neural crest cells in turtle embryos has been respecified, or has reactivated or recruited the skeletogenic transcriptional program. These activities will enhance the research environment at a public liberal arts college where many students are economically disadvantaged and/or first generation college students, and provide research opportunities for women and under-represented minorities. The students work in research teams, and receive training in embryology, cell and organ culture, antibody staining, in situ hybridization and bioinformatics. Over 60 undergraduates have already begun their careers working on earlier stages of this project, and more than a dozen of them have subsequently received their PhDs or MD/PhDs. This project has been used in numerous outreach programs, and the results have helped unite developmental biology and paleontology in seeking explanations for the origin of new body plans.