Somite fate mapping using GFP-transgenic axolotls
Nadine Piekarski, Lennart Olsson
1 Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität Jena
Single somite fate has been studied extensively using quail-chick chimeras. We are interested in to what degree somite fate is conserved despite the conspicuous differences in morphology seen among vertebrates. Therefore, we have focused our study on a urodele amphibian, the Mexican axolotl, in which long-term fate mapping is technically feasible. Compared to birds the axolotl is morphologically very different e.g. in many skeletal muscles and in skeletal elements of the occipital region, as well as in the shoulder girdle, all known to be somitic derivatives from quail-chick chimeras. Somites two to six were fate-mapped by transplantation of single somites from GFP-transgenic axolotls. Transplanted fluorescent somites and their derivatives were tracked in vivo, and cryosections were made. Our data reveal a highly conserved pattern of somitic derivatives among the two species. The shoulder girdle in axolotls for example has a segmental (more than one somite) and a composite (somites and lateral plate) origin exactly as in chicken. However, there are small differences that could be caused by the different position in which it is being formed in the two species. We also found differences in the specific formation of the hypobranchial chord that gives rise to hypobranchial muscles. Our results support a conserved pattern of somitic derivatives, however, the small differences observed could be the key to understand the developmental basis of evolutionary change in this system.