LETTER Evidence for the Neural Crest Origin of Turtle Plastron Bones Karen Clark, 1 Gu ¨ nes Bender, 2 B. Patrick Murray, 2 Kristen Panﬁlio, 2 Steven Cook, 2 Raquel Davis, 2 Katherine Murnen, 2 Rocky S. Tuan, 1 and Scott F. Gilbert 2 * 1 Department of Orthopedic Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania 2 Department of Biology, Martin Research Laboratories, Swarthmore College, Swarthmore, Pennsylvania Received 6 August 2001; Revised 26 September 2001 Summary: The migrating cranial neural crest cells of birds, ﬁsh, and mammals have been shown to form the membranous bones of the cranium and face. These ﬁnd- ings have been extrapolated to suggest that all the der- mal bones of the vertebrate exoskeleton are derived from the neural crest ectomesenchyme. However, only one group of extant animals, the Chelonians, has an extensive bony exoskeleton in the trunk. We have previ- ously shown that the autapomorphic carapacial and plastron bones of the turtle shell arise from dermal in- tramembranous ossiﬁcation. Here, we show that the bones of the plastron stain positively for HNK-1 and PDGFR and are therefore most likely of neural crest origin. This extends the hypothesis of the neural crest origin of the exoskeleton to include the turtle plastron. genesis 31:111–117, 2001. © 2001 Wiley-Liss, Inc. Key words: neural crest; plastron; turtle Cell labeling studies of ﬁsh, amphibians, birds, and mam- mals have demonstrated that the membranous cranial and facial bones of the vertebrate exoskeleton (as well as the dentine of the teeth) come from the cranial region of the neural crest (Patterson, 1977; Noden, 1991; Couly et al., 1992, 1993; Smith and Hall, 1990, 1993). These studies have been extrapolated to suggest that (a) the entire vertebrate exoskeleton is derived from neural crest cells, and (b) only cranial neural crest cells, not trunk neural crest cells, have the ability to form bone. While conﬁrming the hypothesis that the cranial ex- oskeleton is neural crest derived, Smith and Hall (1993) have challenged the view that only the cranial region of the neural crest can form the exoskeleton. They note that many groups of fossil ﬁshes have extensive exoskel- etons, that certain extant ﬁsh have dermal denticles on their postcranial skeleton, that trunk neural crests ap- pear to contribute to the medial ray ﬁns in extant ﬁsh (Smith et al., 1994), and that neural crest cells from the head would have to migrate prodigious distances to form such bones and denticles. It is not known whether the neural crest (either trunk or cranial) contributes to the postcranial exoskeleton of *Correspondence to: Scott Gilbert, Department of Biology, Martin Re- search Laboratories, Swarthmore College, 500 College Ave., Swarthmore, PA 19081. E-mail: sgilber1@swarthmore.edu FIG. 1. Ossiﬁcation centers of Trachemys scripta. Whole-mount alcian blue/alizarin red staining of a turtle hatchling, 78 days after egg deposition (about 15 days posthatching), shows nine centers of ossiﬁcation in the plastron. The lighter red staining shows the pri- mary centers; the secondary spread can be seen by the darker red stain. e, entoplastron; E, epiplastron; H, hyoplastron; h, hypoplas- tron; X, xiphiplastron. © 2001 Wiley-Liss, Inc. DOI 10.1002/gene.10012 genesis 31:111–117 (2001)