Meeting Abstract

135.2  Monday, Jan. 7  Neural crest derivation of the bony skull of the Mexican axolotl and its implications for vertebrate skull evolution PIEKARSKI, N.*; HANKEN, J.; Harvard University; Harvard University npiekarski@oeb.harvard.edu

Cartilages and bones of the craniate skull are derived from two embryonic sources, neural crest and mesoderm. Contributions of these tissues to the skull have been revealed in great detail in one amniote model using the quail-chick chimeric system, and to lesser extent in a few other species. However, the degree to which patterns of embryonic derivation are evolutionary conserved or labile remains an intriguing question, given the extensive variability in skull morphology observed among craniates. Living amphibians are a non-amniote tetrapod group with a highly derived skull morphology and ontogeny. Recent technical advances enable us to derive fate maps at a level of detail previously known only from avian studies. We employed embryonic transplantations, using GFP-transgenic axolotls as donors, to document the nature and extent of neural crest contribution to the adult osteocranium. Comparisons between axolotl, chicken and mouse reveal a highly conserved embryonic origin of the tetrapod skull. Conversely, a comparison between axolotl and Xenopus reveals tremendous differences in the embryonic origin of skull bones between these two taxa. The unique features seen in Xenopus may be a consequence of the dramatic transformation of cranial morphology that is associated with the extreme posthatching metamorphosis characteristic of most anurans.