this include regulation of gene expression and the cell cycle. The role of PI3K has been investigated by several laboratories. Accumulating data suggests that, while this molecule is, in general, part of growth signaling complex, it plays a more profound role in controlling cell migration. The different ligand isoforms have variable affinities for the receptor isoforms, and the receptor isoforms may variably form hetero- or homo- dimers. This leads to specificity of downstream signaling. It has been shown that the sis oncogene is derived from the PDGF B-chain gene. PDGF-BB is the highest-affinity ligand for the PDGFR-beta; PDGFR-beta is a key marker of hepatic stellate cell activation in the process of fibrogenesis. Function PDGFs are mitogenic during early developmental stages, driving the proliferation of undifferentiated mesenchyme and some progenitor populations. During later maturation stages, PDGF signalling has been implicated in tissue remodelling and cellular differentiation, and in inductive events involved in patterning and morphogenesis. In addition to driving mesenchymal proliferation, PDGFs have been shown to direct the migration, differentiation and function of a variety of specialised mesenchymal and migratory cell types, both during development and in the adult animal. Other growth factors in this family include vascular endothelial growth factors B and C (VEGF-B, VEGF-C) which are active in angiogenesis and endothelial cell growth, and placenta growth factor (PlGF) which is also active in angiogenesis. PDGF plays a role in embryonic development, cell proliferation, cell migration, and angiogenesis. Over-expression of PDGF has been linked to several diseases such as atherosclerosis, fibrotic disorders and malignancies. Synthesis occurs due to external stimuli such as thrombin, low oxygen tension, or other cytokines and growth factors. PDGF is a required element in cellular division for fibroblasts, a type of connective tissue cell that is especially prevalent in wound healing. In essence, the PDGFs allow a cell to skip the G1 checkpoints in order to divide. It has been shown that in monocytes-macrophages and fibroblasts, exogenously administered PDGF stimulates chemotaxis, proliferation, and gene expression and significantly augmented the influx of inflammatory cells and fibroblasts, accelerating extracellular matrix and collagen formation and thus reducing the time for the healing process to occur. In terms of osteogenic differentiation of mesenchymal stem cells, comparing PDGF to epidermal growth factor (EGF), which is also implicated in stimulating cell growth, proliferation, and differentiation, MSCs were shown to have stronger osteogenic differentiation into bone-forming cells when stimulated by epidermal growth factor