IBSP and atrial fibrillation: Figure 1C and 1D shows a typical field observed in these cultures. CA12, which was recently decribed by Minogue et al as a marker gene for human NP cells, was found to have significantly higher levels of expression in NP cells and NP tissue than in AF tissue and chondrocytes (Fig. 1D). IBSP and FBN1, which were also recently decribed by Minogue et al as negative markers gene for human NP cells, was found to have significantly low levels of expression in NP cells and NP tissue than in AF tissue and chondrocytes (Fig. 1E and 1F).