During the late cellular blastoderm stage of Drosophila embryogenesis the segmentation genes engrailed, en, and wingless, wg, become expressed in two series of 14 stripes1-4 which will subsequently coincide with the anterior5 and posterior4 limits of each parasegment 6. Previous studies7-10 have shown that the establishment of the pattern of en stripes depends upon the activity of the homoeobox-containing pair-rule genes11 fushi tarazu, ftz12 and even skipped, eve8,13. Here we show that these two genes also control the spatial expression of wg. Whereas ftz and eve behave as activators of en we find that both genes are required to repress wg expression, so that wg becomes expressed only in the narrow stripes of cells which come to separate the ftz and eve bands at the end of the blastoderm stage. In contrast, we propose that the precise positioning of the en stripes depends upon signals generated in a combinatorial manner14 by the overlaps between the ftz or eve domains and those of other pair rule genes, specifically odd paired, opa 15 and paired, prd11,16,17.
ASJC Scopus subject areas