Meeting Abstract

135.1  Monday, Jan. 7  The origin and loss of periodic patterning in the turtle shell MOUSTAKAS-VERHO, JE*; ZIMM, R; CEBRA-THOMAS, J; SEPPäLä, NK; KALLONEN, A; MITCHELL, KL; HäMäLäINEN, K; SALAZAR-CIUDAD, I; JERNVALL, J; GILBERT, SF; Institute of Biotechnology, University of Helsinki; Institute of Biotechnology, University of Helsinki; Biology Department, Millersville University; Institute of Biotechnology, University of Helsinki; Department of Physics, University of Helsinki; Biology Department, Swarthmore College; Department of Physics, University of Helsinki; Departament de Genètica i Microbiologia, Universitat Autònoma de Barcelona; Institute of Biotechnology, University of Helsinki; Biology Department, Swarthmore College Jacqueline.Moustakas@helsinki.fi

Testudines (turtles and their relatives) originated in the Triassic Period and became one of the most successful groups of tetrapods, radiating into terrestrial, semiaquatic, and marine environments on all continents. The developmental mechanisms responsible for the formation of the turtle shell remain one of the great mysteries in evolutionary biology. The keratinous scutes of the turtle shell are novel epidermal structures, the patterns of which are diagnostic of different taxa. These scutes become the modular elements of turtle shell epidermal growth. We show that scutes develop from an earlier array of patterned placodal signaling centers and that these placodal signaling centers are absent from a soft-shelled turtle species in which scutes were lost evolutionarily. Furthermore, inhibiting Shh and BMP signaling experimentally results in the loss of these signaling centers and scutes. We propose that these signaling centers are formed by the reaction-diffusion dynamics of activator-inhibitor systems and show that both natural and abnormal variation can be modeled by changes in growth and timing. We propose that these signaling centers represent developmental modules responsible for the evolution of scutes in turtles and that the regulation of these centers have allowed for the diversification of the turtle shell.