Reptilian Tooth and Jaw Development

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Reptiles and mammals share a common ancestor dating back more than 300 million years but during evolution significant specializations in the skull and teeth have arisen. Our goal is to determine how and when in development these differences arose. For example, skulls of the majority of reptiles have more openings than mammals. Mammals always have closed palates that separate the oral and nasal cavities. In contrast snakes, lizards and birds have open palates, turtles have a primitive palate and surprisingly alligators have a closed palate like mammals. In the dentition, there are also striking differences in tooth anatomy and replacement capacity. Most snakes, lizards and crocodilians replace their teeth continuously throughout life (polyphyodonty), whereas mammals can only replace their teeth once.***The embryos of reptiles and mammals are remarkably similar at early stages reflecting their common origins. At key stages of development genes involved in skull and palate development will be examined in turtles, lizards, birds and alligators to determine subtle differences that correlate with later skull anatomy. The shape of the head and palate will also be analyzed to measure precisely when differences in morphology can be detected. To test the function of key genes, retroviruses will be placed into the chicken to change gene expression to resemble that of non-avian reptiles. We hypothesize that some of these genes will convert the bird anatomy into that of other reptiles.***We will investigate tooth replacement in longitudinal studies on leopard geckos as well as historical data collected on iguanas. We will test whether there are global cues that regulate the timing and pattern of tooth replacement and whether these are set up prior to hatching. We will also test the role of the environment on tooth replacement by removing teeth, injecting chemicals next to the teeth or injuring the tooth replacement apparatus. Wax bites will be taken weekly to record the shedding of teeth. We will also inject a fluorescent dye that is incorporated into mineralizing teeth at the time the experiments are conducted. The shedding and eruption of fluorescent teeth over time will be recorded with a fluorescence microscope. Follow-up experiments will analyze the fixed tissues for gene expression and cell proliferation changes. The reptile research group at UBC is unique in Canada and the world. Our innovative studies on molecular evolution of the skull and teeth will provide the insights into how animals adapted to environmental changes. Our results are of great interest to paleobiologists, developmental biologists and the broad scientific community.********