Wnt signals from the neural tube block ectopic cardiogenesis.

It has long been observed that repressive signals from the neural tube block cardiogenesis in vertebrates. Here we show that a signal from the neural tube that blocks cardiogenesis in the adjacent anterior paraxial mesoderm of stage 8-9 chick embryos can be mimicked by ectopic expression of either Wnt-3a or Wnt-1, both of which are expressed in the dorsal neural tube. Repression of cardiogenesis by the neural tube can be overcome by ectopic expression of a secreted Wnt antagonist. On the basis of both in vitro and in vivo results, we propose that Wnt signals from the neural tube normally act to block cardiogenesis in the adjacent anterior paraxial mesendoderm.