[1][2] Zerknüllt codes for a homeoprotein regulates aspects of early embryogenesis in insects.
Unlike the canonical Hox genes which are expressed in precise zones along the anteroposterior (head to tail) body axis, zerknüllt expression is restricted along the dorsoventral (back to belly) body axis.
Expression of Zerknüllt is repressed in the ventral part of the embryo by a protein called Dorsal, and activated in the dorsal part of the embryo by the TGF beta signaling pathway.
[4] Zerknüllt has been found to undergo a number of gene duplications in certain insect lineages.
In this group, zen has duplicated at least four times resulting in the emergence of the additional divergent 'Special homeobox' (Shx) genes, named ShxA, ShxB, ShxC and ShxD.