Meeting Abstract

21.4  Tuesday, Jan. 4  How The Turtle Got Its Spots MOUSTAKAS, J. E.*; CEBRA-THOMAS, N. K.; KALLONEN, A.; LEWIS, K.; HÄMÄLÄINEN, K.; JERNVALL, J.; GILBERT, S. F.; Institute of Biotechnology, University of Helsinki, Finland; Swarthmore College, PA; Department of Physics, University of Helsinki, Finland; Swarthmore College, PA; Department of Physics, University of Helsinki, Finland; Institute of Biotechnology, University of Helsinki, Finland; Swarthmore College, PA and Institute of Biotechnology, University of Helsinki, Finland Jacqueline.Moustakas@helsinki.fi

The turtle shell is a classic case of morphological novelty, yet the developmental biology of the turtle shell is principally known through descriptive embryology. We examined the growth dynamics of the turtle shell in an ontogenetic series using genetic markers for scute placodes as landmarks. The turtle shell is composed of endochondral axial skeletal elements overlain by plates of dermal bone and keratinous scutes. As in the development of several other ectodermal organs, the keratinous scutes form by an epithelial-mesenchymal interaction and express several placodal markers, including Shh and Bmp2. We used the expression of these genes in the placodes to construct a distance map in a time-series of embryonic development in the red-eared slider turtle Trachemys scripta to visualize the growth of the shell. We then used computer tomography to generate three-dimensional reconstructions of the growing shell to examine the relation of the expanding carapacial ridge to the ribs, and to the dynamic expression of Bmp2, Bmp4, Shh, and Gremlin. Lastly, we consider the roles of these genes in the growth of the shell and the patterning of the epidermal scutes by examining their expression in the softshell turtle Pelodiscus sinensis, which does not form keratinous scutes, but rather a leathery skin.