MEDAKA SPALT ACTS AS A TARGET GENE OF HEDGEHOG SIGNALING

In vertebrates, pattern formation in the eye, central nervous system, somites, and limb depends on hedgehog activity, but a general target g ene controlled by hedgehog in all these signaling centers has remained largely elusive. The medaka fish gene spalt encodes a zinc-finger tra nscription factor, which is expressed in all known hedgehog signaling centers of the embryo and in the organizer region at the midbrain-hind brain boundary. We show that the spalt expression domains expand in re sponse to ectopic hedgehog activity and narrow in the presence of prot ein kinase A activity, an antagonist of hedgehog signaling, indicating that spalt is a hedgehog target gene. Our results also suggest a sign aling mechanism for anterior-posterior patterning of the vertebrate br ain that controls spalt expression at the midbrain-hindbrain boundary in a protein kinase A dependent manner likely to involve an unknown me mber of the hedgehog family.