ACTIVATION OF POSTERIOR PAIR-RULE STRIPE EXPRESSION IN RESPONSE TO MATERNAL CAUDAL AND ZYGOTIC KNIRPS ACTIVITIES

Drosophila pair-rule gene expression, in an array of seven evenly spac ed stripes along the anterior-posterior axis of the blastoderm embryo, is controlled by distinct cis-acting stripe elements. In the anterior region, such elements mediate transcriptional activation in response to the maternal concentration gradient of the anterior determinant BIC OID and repression by spatially distinct activities of zygotic gap gen es. In the posterior region, activation of hairy stripe 6 has been sho wn to depend on the activity of the gap gene knirps, suggesting that p osterior stripe expression is exclusively controlled by zygotic regula tors. Here we show that the zygotic activation of hairy stripe 6 expre ssion is preceded by activation in response to maternal caudal activit y. Thus, transcriptional activation of posterior stripe expression is likely to be controlled by maternal and zygotic factors as has been ob served for anterior stripes. The results suggest that activation and t he expression level mediated by the hairy stripe 6-element depend on t he number of activator binding sites, likely to involve additive rathe r than synergistic interactions. We found an identical transacting fac tor requirement for hairy stripe 6 and 7 expression. The arrangement o f the corresponding binding sites for the common factors involved in t he control of the two stripes share a high degree of similarity, but s ome of the factors exert opposite regulatory functions within the two enhancer elements. (C) 1998 Elsevier Science Ireland Ltd.