A col10a1: NlGFP transgenic line displays putative osteoblast precursors at the medaka notochordal sheath prior to mineralization

Abstract

In teleosts, such as medaka, ossification of the vertebral column starts with the mineralization of the notochordal sheath in a segmental pattern. This establishes the chordal centrum, which serves as the basis for further ossifications by sclerotome derived osteoblasts generating the vertebral body. So far, it is unclear which cells produce the notochordal sheath and how a segmental pattern of mineralization is established in teleosts. Here, we use a transgenic medaka line that expresses nlGFP under the control of the col10. a1 promoter for in vivo analysis of vertebral body formation. We show that col10. a1. :nlGFP expression recapitulates endogenous col10. a1 expression. In the axial skeleton, col10. a1. :nlGFP cells appear prior to the mineralization of the notochordal sheath in a segmental pattern. These cells remain on the outer surface of the chordal centra during mineralization as well as subsequent perichordal ossification of the vertebral bodies. Using twist1. a1. :dsRed and osx:mCherry transgenic lines we show that a subset of col10. a1. :nlGFP cells is derived from sclerotomal precursors and differentiates into future osteoblasts. For the first time, this shows a segmental occurrence of putative osteoblast precursors in the vertebral centra prior to ossification of the notochordal sheath. This opens the possibility that sclerotome derived cells in teleosts are implicated in the establishment of the mineralized vertebral column in a similar manner as previously described for tetrapods. © 2013 Elsevier Inc.