Osteogenic and chondrogenic differentiation of human MSC (A-H). On day 21, alkaline phosphatase staining of osteogenically induced MSC cultures demonstrated an enhanced AP activity (A) when compared to control cultures (B). On this day, von Kossa staining of osteogenically induced cultures was positive indicating a formation of mineralized bone matrix (C), whereas control cultures stained negative (D). TGFβ3 - induction of chondrogenesis, on day 21, resulted in the secretion of cartilage proteoglycans as shown by alcian blue staining (E), and of cartilage specific collagen type II (G). Control cultures showed no secretion of both extracellular matrix molecules (F, H).