title: Development of the carapacial ridge: implications for the evolution of genetic networks in turtle shell development.
abstract: Paleontologists and neontologists have long looked to development to understand the homologies of the dermal bones that form the "armor" of turtles, crocodiles, armadillos, and other vertebrates. This study shows molecular evidence supporting a dermomyotomal identity for the mesenchyme of the turtle carapacial ridge. The mesenchyme of the carapace primordium expresses Pax3, Twist1, Dermo1, En1, Sim1, and Gremlin at early stages and before overt ossification expresses Pax1. A hypothesis is proposed that this mesenchyme forms dermal bone in the turtle carapace. A comparison of regulatory gene expression in the primordia of the turtle carapace, the vertebrate limb, and the vertebral column implies the exaptation of key genetic networks in the development of the turtle shell. This work establishes a new role for this mesodermal compartment and highlights the importance of changes in genetic regulation in the evolution of morphology.
authors.affiliation: Department of Integrative Biology and Museum of Paleontology, University of California, 1101 Valley Life Sciences Building, Berkeley, CA 94720, USA. moustakas@berkeley.edu
authors.forename: Jacqueline E
authors.initials: JE
authors.lastname: Moustakas
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004625:Embryo, Nonmammalian / Q000166:cytology; D047108:Embryonic Development; D005121:Extremities / Q000254:growth & development; D020869:Gene Expression Profiling; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism; D010012:Osteogenesis / Q000235:genetics; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism; D019170:Somites / Q000254:growth & development; D014426:Turtles / Q000196:embryology* / Q000235:genetics / Q000254:growth & development
chemical_list: D053823:Hedgehog Proteins; D051761:Paired Box Transcription Factors; C070835:PAX1 transcription factor