Interrelationship and modularity of notochord and somites: a comparative view on zebrafish and chicken vertebral body development

Abstract

Tetrapod vertebrae are sclerotome-derived metameric structures. Cells from this tissue provide cartilage that surrounds the notochord and give rise to the vertebral centrum as well as the vertebral arches. Eventually, later on, the cartilage is remodeled into bone. Vertebral body development in teleost fish is different, since the mineralization of the notochord sheath is the first step of vertebral centrum formation and no cartilage is involved in this process. Thus, the sclerotomal contribution to early teleost vertebral centrum formation has been questioned. In contrast, teleost vertebral arches are sclerotome-derived and often have cartilaginous precursors. In this short review we compare the development of vertebral bodies in chicken and teleost fish, analyzing the role of the notochord and the somites in vertebral body development and addressing two interesting questions: (i) Could the vertebral bodies and arches arise and function as separate developmental modules? (ii) Could the most medial presomitic mesoderm (PSM) cells and the notochord form a common developmental module? Finally we suggest (iii) that this developmental module is physically grouped in the teleost notochord but spatially subdivided in the chick where the medial PSM is responsible for vertebral body formation.