TY - JOUR
T1 - The origin and loss of periodic patterning in the turtle shell
AU - Moustakas-Verho, Jacqueline E.
AU - Zimm, Roland
AU - Cebra-Thomas, Judith
AU - Lempiäinen, Netta K.
AU - Kallonen, Aki
AU - Mitchell, Katherine L.
AU - Häma, Keijöläinen
AU - Salazar-Ciudad, Isaac
AU - Jernvall, Jukka
AU - Gilbert, Scott F.
PY - 2014/1/1
Y1 - 2014/1/1
N2 - The origin of the turtle shell over 200 million years ago greatly modified the amniote body plan, and the morphological plasticity of the shell has promoted the adaptive radiation of turtles. The shell, comprising a dorsal carapace and a ventral plastron, is a layered structure formed by basal endochondral axial skeletal elements (ribs, vertebrae) and plates of bone, which are overlain by keratinous ectodermal scutes. Studies of turtle development have mostly focused on the bones of the shell; however, the genetic regulation of the epidermal scutes has not been investigated. Here, we show that scutes develop from an array of patterned placodes and that these placodes are absent from a softshelled turtle in which scutes were lost secondarily. Experimentally inhibiting Shh, Bmp or Fgf signaling results in the disruption of the placodal pattern. Finally, a computational model is used to show how two coupled reaction-diffusion systems reproduce both natural and abnormal variation in turtle scutes. Taken together, these placodal signaling centers are likely to represent developmental modules that are responsible for the evolution of scutes in turtles, and the regulation of these centers has allowed for the diversification of the turtle shell. © 2014. Published by The Company of Biologists Ltd.
AB - The origin of the turtle shell over 200 million years ago greatly modified the amniote body plan, and the morphological plasticity of the shell has promoted the adaptive radiation of turtles. The shell, comprising a dorsal carapace and a ventral plastron, is a layered structure formed by basal endochondral axial skeletal elements (ribs, vertebrae) and plates of bone, which are overlain by keratinous ectodermal scutes. Studies of turtle development have mostly focused on the bones of the shell; however, the genetic regulation of the epidermal scutes has not been investigated. Here, we show that scutes develop from an array of patterned placodes and that these placodes are absent from a softshelled turtle in which scutes were lost secondarily. Experimentally inhibiting Shh, Bmp or Fgf signaling results in the disruption of the placodal pattern. Finally, a computational model is used to show how two coupled reaction-diffusion systems reproduce both natural and abnormal variation in turtle scutes. Taken together, these placodal signaling centers are likely to represent developmental modules that are responsible for the evolution of scutes in turtles, and the regulation of these centers has allowed for the diversification of the turtle shell. © 2014. Published by The Company of Biologists Ltd.
KW - Ectodermal appendage
KW - Placode
KW - Scute
KW - Shh
KW - Turtle
U2 - 10.1242/dev.109041
DO - 10.1242/dev.109041
M3 - Article
VL - 141
SP - 3033
EP - 3039
IS - 15
ER -