TGF-beta and BMP mediated gene expression in cultured sclerotome.

Very little is known about how intervertebral disc (IVD) is formed or maintained. Members of the TGF-ß superfamily are secreted signaling proteins that regulate many aspects of development including cellular differentiation. We recently showed that deletion of Tgfbr2 in Col2a expressing tissue results in alterations in development of IVD annulus fibrosus. The results suggested TGF-ß has an important role in regulating development of the axial skeleton, however, the mechanistic basis of TGF-ß action in these specialized joints is not known. To understand the mechanism of TGF-ß action in IVD development, we undertook a global analysis of gene expression comparing gene expression profiles in sclerotome cultures treated with TGF-ß or BMP4. As expected, treatment with BMP4 resulted in up-regulation of cartilage marker genes including Acan, Sox 5, Sox6, and Sox9. In contrast, treatment with TGF-ß1 did not regulate expression of cartilage markers but instead resulted in up-regulation of many IVD markers including Fmod and Adamtsl2. We propose TGF-ß has two functions in IVD development: 1) to prevent chondrocyte differentiation in the presumptive IVD and 2) to promote differentiation of annulus fibrosus from sclerotome. We have identified genes that are enriched in the IVD and regulated by TGF-ß that warrant further investigation as regulators of IVD development. Nine samples were analyzed. Three biological replicates of untreated sclerotome grown in micromass culture. Three biological replicates of cells treated with 50 ng/ml BMP4 for 8 hours and three biological replicates of cells treated with 5 ng/ ml TGF-ß1 for 8 hours.