Date of Award

2006

Document Type

Restricted Thesis

Terms of Use

© 2006 Erin A. Betters. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Biology Department

First Advisor

Scott F. Gilbert

Second Advisor

Judith Cebra-Thomas

Abstract

Previous research has provided evidence that the nuchal bone and plastron of the Trachemys scripta shell are derived from the neural crest (Clark et al. 2001; Bender et al., unpublished). In this study, we hypothesize that the nine bones of the plastron and the nuchal bone of the carapace are formed from the trunk neural crest. Two methods to test the contribution of trunk neural crest cells (NCCs) to the turtle shell were employed. First, T. scripta embryo sections were stained using the monoclonal HNK-1 antibody (a marker of NCCs), and any HNK-1 positive migrating cells were identified. To differentiate between melanoblasts, which are derived from the neural crest, and other potential NCCs, C5 antibody staining (which marks melanoblasts) was also performed. HNK-1 and C5 staining patterns were then compared. HNK-1 positive cells were observed in the neural tube, dorsal root ganglia, and craniofacial structures; NCCs are expected in all of these structures. HNK-1 staining was also observed in the carapacial mesenchyme in the presumptive region of the nuchal bone. C5 staining in similar anterior sections was seen only in the periphery of the carapace, indicating that the HNK-l positive cells in the carapacial mesenchyme are not presumptive melanoblasts, but are possibly NCCs contributing to the nuchal bone. HNK-1 staining between the neural tube and carapace in more posterior sections indicates the existence of a possible staging area of trunk NCCs. HNK-1 positive cells were also observed migrating ventrally through embryo sections. These cells may represent a population of late-migrating NCCs unique to turtles, which will eventually go on to form the plastron. In older T. scripta sections, HNK-1 staining of the presumptive plastron was seen. Second, T. scripta embryos were injected with DiI and then cultured to test for the existence of a possible late-migrating population of NCCs. Embryos were injected in the dorsal carapacial mesenchyme just lateral to the neural tube. Ventrally migrating DiI labeled cells were observed in whole injected embryos. In cryosections of DiI-injected embryos, DiI-positive cells were seen to have migrated both laterally and ventrally from the injection sites. Together, these results suggest that there exists a distinct population of NCCs that migrates ventrally to form the plastron and dorsally to form the nuchal bone.

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