The status of Wnt signalling regulates neural and epidermal fates in the chick embryo

The acquisition of neural fate by embryonic ectodermal cells is a fundament al step in the formation of the vertebrate nervous system. Neural induction seems to involve signalling by fibroblast growth factors (FGFs) and attenu ation of the activity of bone morphogenetic protein (BMP)(1-4). But FGFs, e ither alone or in combination with BMP antagonists, are not sufficient to i nduce neural fate in prospective epidermal ectoderm of amniote embryos(1,3, 4). These findings suggest that additional signals are involved in the spec ification of neural fate. Here we show that the state of Wnt signalling is a critical determinant of neural and epidermal fates in the chick embryo. C ontinual Wnt signalling blocks the response of epiblast cells to FGF signal s, permitting the expression and signalling of BMP to direct an epidermal f ate. Conversely, a lack of exposure of epiblast cells to Wnt signals permit s FGFs to induce a neural fate.