GROWTH-FACTORS DURING EARLY EVENTS IN AVIAN EMBRYO DEVELOPMENT

Peptide growth factors and cytokines play important roles in the ontog eny and maintenance of tissue form and function. Recent data indicate that growth factors mediate crucial events during early vertebrate dev elopment. This review highlights the data on the function of growth fa ctors during the development of the avian embryo prior to and through gastrulation with an emphasis on axial development and the development of the germ cell lineage. Cytokines from the transforming growth fact or-beta and fibroblast growth factor superfamilies clearly have defini tive roles in the specification of the axis. In this context, relative ly little is known about the regulatory events governing the segregati on of the germ cell lineage prior to gastrulation. Nevertheless, recen t work suggests the existence of a founder population of the germ cell lineage on the hypoblast of the pre-primitive streak embryo and that fibroblast growth factor and stem cell factor may be involved in the p rocess of germ cell segregation. Although germ cell development procee ds independent of a normal embryonic axis, it is speculated that the t emporal development of the two processes might be linked.