Table 16-1 Examples of “classical” Growth Factors Egf - Epidermal Growth Factor Fgf - Fibroblast Growth Factor Ngf - Nerve Growth Factor Tgfβ - Transforming Growth Factor

Orderly development requires extensive coordination and communication between cells. Much of this is provided by extracellular proteins (growth factors) that positively and negatively regulate proliferation, differentiation, migration/pathfinding and survival/death. This is achieved via transmembrane receptors that transduce growth factor binding to a cascade of intracellular signaling events that culminate in both transcription-independent and transcription-dependent changes in target cell behavior. A number of growth factor superfamilies have been recognized along with their specific transmembrane receptors. Several specific examples are presented to illustrate the many roles of growth factors in promoting development. These reveal the complexity of feedback mechanisms by which growth factors coordinate embryogenesis. There are several distinct types of mechanisms by which growth factor signaling is accomplished.