Krüppel expression regulated by:
Kruppel transcription factor gap gene shows bell-shaped expression centrally. Activation requires intermediate Bicoid and Hunchback co-activation; repression by high Hunchback anteriorly, Knirps and Giant posteriorly defines borders. Bicoid alone insufficient, high Hunchback represses. Combinatorial integration illustrates threshold model for morphogen interpretation. Wingless does not regulate Kruppel; instead regulates engrailed later. Dual activation ensures robust positioning of Kruppel stripe which then represses abdominal gap genes, forming mutually repressive network sharpening gap doma
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Kruppel regulated by Bicoid and Hunchback - gap gene network integration.
