Fig. 3 Processes regulating axial straightening and notochord integrity underlie defects of spine morphogenesis. Beginning at the curved tailbud stage, generating a straight body axis requires the function of motile cilia components, which drives the formation of the Reissner fiber (top). Once axial straightening occurs, defects of the Reissner fiber, disrupted motile cilia or CSF flow, which are revealed during larval development in zebrafish, can lead to more subtle curvatures of the notochord. Alternatively, defects in the notochord sheath or in vacuolated cell morphogenesis can contribute to severe bends or kinks of the notochord, which directly arise into regions of vertebral malformations and fusion, and sometimes scoliosis.