Morphogens, Embryonic Patterning and Axis Formation

Growth factors and morphogens regulate embryonic patterning, cell fate specification, cell migration, and morphogenesis. The activity and behavior of these signaling molecules are regulated in the extracellular space through interactions with proteoglycans.The formation of morphogen concentration gradients directs the biological responses of surrounding cells. Graded responses occur as a result of morphogens binding to specific cell surface receptors that subsequently activate intracellular signaling pathways and promote or repress gene expression at specific threshold concentrations. Activation or inactivation of these signaling pathways provides positional information that ultimately determines cell fate decisions, tissue organization, and morphology. Research in model organisms has revealed that morphogenetic fields are involved in many aspects of development. Research in higher organisms has demonstrated that homologues of these same signaling molecules regulate vertebrate axis formation, anterior/posterior polarity during limb development, mesoderm patterning, and numerous other processes that establish an organism's basic body structure.