Correlative changes in homoeotic and segmentation gene expression in Krüppel mutant embryos of Drosophila.

Mutations of the segmentation gene Krüppel (Kr) cause deletions of contiguous sets of body segments from the middle region of the Drosophila embryo. We have monitored expression in situ of three other genes implicated in the establishment of the body plan, namely hairy (h), fushi tarazu (ftz) and engrailed (en), in mutant Kr embryos. Our results show that the pattern of expression of all three genes depends upon Kr activity and are consistent with a hierarchical model of segmentation gene activity. In addition, we find that the initial expression of the homoeotic selector gene Ultrabithorax(Ubx) follows a novel pattern in Kr embroys indicating a close integration of the spatial control of homoeotic and segmantation gene expression.