PEPTIDE GROWTH-FACTOR INTERACTIONS IN EMBRYONIC AND FETAL GROWTH

Peptide growth factors are expressed by multiple tissues in the animal and human embryo and fetus. They undergo specific interactions which control the rate of cellular proliferation, tissue differentiation and the induction of specific morphogenic events such as mesoderm formation in the embryo. Biologic control may not only be exerted at the level of growth factor synthesis and receptor expression but by the sequestration and storage of growth factors by extracellular matrix molecules. In the case- of insulin-like growth factors (IGFs), storage maybe mediated by attachment to specific IGF-binding proteins which may additionally modulate biological potency. Basic fibroblast growth factor (basic FGF) and transforming growth factor-beta (TGFbeta) directly bind to glycosaminoglycan molecules. Release of growth factors from these stores may be by local proteolytic action. A sequential expression of basic FGF, IGF-II and TGFbeta occurs in the ovine fetal epiphyseal growth plate as chondrocytes progress from a proliferative to a postmitotic, hypertrophic state. Cellular phenotype may be largely explained by the relative amounts of these autocrine growth factors within the growth plate.