Spatial control of the gap gene knirps in the Drosophila embryo by posterior morphogen system.

The gap genes of Drosophila are the first zygotic genes to respond to the maternal positional signals and establish the body pattern along the anterior-posterior axis. The gap gene knirps, required for patterning in the posterior region of the embryo, can be activated throughout the wild-type embryo and is normally repressed from the anterior and posterior sides. These results provide direct molecular evidence that the posterior morphogen system interacts in a fundamentally different manner than do hunchback and bicoid, which are responsible for anterior pattern formation.