Date of Award

Spring 2010

Document Type

Restricted Thesis

Terms of Use

© 2010 James D. Robinson. 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


Biology Department

First Advisor

Scott F. Gilbert


The turtle plastron is a set of nine bones formed via intramembranous ossification in the ventral dermis of the embryonic turtle. Early work in the Gilbert laboratory showed cells staining positive for several neural crest cell markers in the plastron ossification sites, and recent work has identified a late-emerging population of trunk neural crest cells and can be seen forming intramembrous bone. Previous studies have shown that trunk neural crest from chick embryo left in culture gain chondrocyte forming capacities, in parallel with a loss of Hox gene expression (Abzhanov et al. 2003), suggest that the loss of Hox gene expression may respecify trunk neural crest cells as cranial neural crest cells. The studies discussed here are the first to compare the gene expression of the early and late emerging populations of trunk neural crest cells in the turtle Trachemys scripta. Shortly after emerging from the neural tube, late migrating trunk neural crest cells retained Hox gene expression, though preliminary results suggest that this expression is qualitatively lower than that of early migrating trunk neural crest. As these late migrating cells have been shown to migrate into the carapacial mesenchyme before reaching the plastron, future experiments should examine this region as a 'staging area' where these cells lose their inability to form bone.