[Molecular aspects of vertebral chondrogenesis].

In this article, we review the data showing that dorso-ventral polarization of the vertebral cartilage involves two distinct molecular pathways, acting sequentially during development. The first one is mediated by the notochord and the ventral part of the neural tube, by the action of the Sonic Hedghehog protein (SHH): it directs the formation of the cartilaginous pieces located in a deep position within the embryo. The second one is responsible for the differentiation of the dorsal parts of the vertebra, differentiating under the ectoderm; it is initiated by the roof plate of the neural tube, by the action of the secreted protein BMP4. Those two pathways cannot be exchanged, rather they are antagonists. These data allow us to draw a new model for vertebral chondrogenesis.