The segmentation gene Krüppel of Drosophila melanogaster has homeotic properties.

In Drosophila hindgut, Malpighian tubules and posterior midgut develop from the most posterior region of the blastoderm. One of the genes that influences the differentiation of the Malpighian tubules is Krüppel (Kr), a segmentation gene of the gap class. Kr homozygous embryos lack thoracic and abdominal segments and, depending on the allele, develop nearly normal Malpighian tubules or do not differentiate them at all. In the wild type, injection of horseradish peroxidase (HRP) into cells of the early gastrula at various posterior positions results in labeling of hindgut (93%), Malpighian tubules (46%), and posterior midgut (20%). Malpighian tubules were labeled only in combination with hindgut. In Kr1 homozygous embryos that lack Malpighian tubules, the label was restricted to hindgut (84%) and posterior midgut (24%). Because we could not find significant cell death in the posterior region of Kr1 embryos, we counted the cell nuclei in the hindguts of wild-type and mutant embryos. The results show that the hindgut in Kr1 embryos contains those cells that would differentiate into Malpighian tubules in wild type. Therefore, we conclude that the Krüppel gene exhibits a homeotic function in addition to its role as a segmentation gene and is involved in separating hindgut and Malpighian tubule cells and in the elongation process as well.