Meeting Abstract

135.4  Monday, Jan. 7  A dual embryonic origin of the vertebrate pharyngeal skeleton SEFTON, E.M.*; PIEKARSKI, N.; HANKEN, J.; Harvard University esefton@oeb.harvard.edu

The pharyngeal-arch skeleton is a hallmark of vertebrates. In basal taxa, it supports the gills and muscles of the pharynx, whereas in more derived groups it surrounds the larynx and trachea. That most of the pharyngeal-arch skeleton is derived from embryonic neural crest was first demonstrated in the mudpuppy in the late 19th century, and this result has since been confirmed in additional species. Yet, the evolution and extent of neural crest contributions to the pharyngeal skeleton is incompletely understood. In this study, we fate map neural crest in the axolotl, Ambystoma mexicanum, using transplantations from GFP-transgenic donors into wild-type hosts. We found that neural crest does not contribute to all elements of the pharyngeal skeleton: the ventral midline element basibranchial 2 was never labeled. Based on this result we also constructed a fate map of cranial mesoderm. Our results positively demonstrate for the first time a mesodermal contribution to the pharyngeal skeleton. Cranial mesoderm contributes to basibranchial 2, suggesting distinct patterning mechanisms in this region. Our results demonstrate a dual embryonic origin of the pharyngeal skeleton, from both neural crest and cranial mesoderm, and shed new light on its development and evolution.