Ancient origin of amniote muscle development
- MLS, Curtin University, Kent street, Bentley, 6102 WA, Australia.
- ARMI, Monash University, 15 Innovation walk, Clayton, Vic 3800, Australia.
- PMCPO, Heidelberglaan 25, 3584 CS Utrecht, Netherlands.
- Harvard Medical school, Harvard University, 25 Shattuck St, Boston, MA 02115, USA.
- MCB, Kennesaw state university, 1000 Chastain Road Kennesaw, GA 30144, USA.
- Caltech, Caltech,1200 EAST CALIFORNIA BOULEVARD, PASADENA, CA 91125, USA.
Zebrafish (actinopterygians), mice and chicks (amniotes) are useful developmental models to understand muscle development and human diseases. However, their early development mechanisms are different in timing, morphology and mechanisms. In zebrafish, the first muscle fibers form prior to somite formation (adaxial cells), this is followed by somite rotation and the establishment of the external cell layer (single cell layer) which contributes to myoblasts for further muscle formation. In contrast, amniotes develop their first myoblasts from the dermomyome, a multicellular epithelial derivative of the somite. In order to understand the evolutionary origin of muscle development in vertebrates and reconcile the divergent developmental modes of extant vertebrates, we immunostained growth series of the elephant shark (basal jawed vertebrate), the lamprey (jawless vertebrate) and paddlefish (basal actinopterygian). Building on our results that elephant sharks display an amniote like dermomyotome with four epithelial lips expressing Pax7, we are presenting novel findings on lamprey muscle development. Our results suggest that muscle development in lamprey is preceded by a single celled simplified dermomyotome whereas muscle formation in paddlefish is very similar to that of zebrafish. This suggests that the amniote dermomyotome is an ancient feature of vertebrates which evolved from a single celled dermomyome present in lampreys. Early formation of myocytes adaxial to the notochord is a feature of actinopterygians and could have evolved at the base of the lineage to speed up development.