A 2.5kb XbaI-SacI spacer element (from the Antp eighth exon), is fused upstream of a ftz 5' regulatory fragment that includes the zebra element, promoter and leader sequence up to codon 2, fused in frame to lacZ.
In germ-band extended embryos, strong expression in the mesoderm, but characteristic ftz expression in the ectoderm is greatly reduced. Expressed in even parasegments. In later embryos, no expression observed in the CNS.