Expression of BMP-2 and chordin transcripts during osteogenic differentiation of human mesenchymal stem cells. (a) Temporal progression of bone morphogenetic protein (BMP)-2 and chordin expression during osteogenic differentiation of human MSCs over a 10-day period. Human MSCs were cultured in basal media (BM) or osteogenic media (OM) for 5 or 10 days. (b) Effect of small interfering RNA (siRNA) on chordin expression. Mesenchymal stem cells (MSCs) were transfected with either control or chordin siRNA and then grown in OM for the 3 or 10 days. RNA was extracted and reverse transcribed, and PCR amplification of chordin, BMP-2 and GAPDH (glyceraldehyde 3-phosphate dehydrogenase) sequences was performed.