DISSERTATION RESEARCH: The Homology of Dermal Ossifications in Reptiles

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Most bone forms in one of two ways: through a cartilage model (endochondral bone) or directly in the skin (dermal bone). Turtle shells and crocodile scutes are formed of dermal bone, and although some aspects of their development are well understood, it is not clear how their development is initiated. Some researchers have proposed that these bones come from a tissue called the neural crest; however, this origin has not been demonstrated. The neural crest is a tissue formed in the ectoderm of the vertebrate embryo that contributes the dermal bones of the skull. A separate embryonic tissue, the mesoderm, contributes endochondral bone to the skull and forms the rest of the skeleton. This study investigates gene expression as a means to trace the contribution of neural crest and mesoderm to turtle shells and crocodile scutes. Genes expressed in neural crest or mesoderm in other vertebrate animals will be studied as potential markers for these tissues in turtle and alligator embryos using RNA hybridization techniques. The importance of this study for systematics lies in its assessment of the evolutionary developmental origin of dermal bone. It may also aid in understanding the evolutionary relationships of turtles to other reptiles. This study harnesses approaches from evolutionary biology and molecular biology to analyze a very old problem in new terms. Normally, studies using these methods are performed on model systems, such as fruit flies, frogs, chickens, or mice. By using turtles and alligators, this study expands the knowledge and technical resources that can be used for the study of evolutionary history. The doctoral student is a Hispanic female, her training is broad, and she disseminates her work through seminars, courses, scientific meetings, and the worldwide web.