Krüppel-homolog is essential for the coordination of regulatory gene hierarchies in early Drosophila development.

Drosophila development is marked by two major morphogenetic processes: embryogenesis and metamorphosis. While insect metamorphosis is known to be controlled by the steroid hormone ecdysone, relatively little is known concerning the hormonal control of embryogenesis. Here we show that many ecdysone-regulated transcripts of metamorphosis are also expressed in a wavelike manner during embryogenesis, suggesting that these genes also participate in an embryonic ecdysone response. At metamorphosis, the Krüppel-homolog (Kr-h) gene, coding for a zinc finger protein, is required during the prepupal ecdysone response. Kr-h mutants die at the prepupal-pupal transition. In these mutants, the expression of several ecdysone-regulated genes is disrupted and we concluded that Kr-h was a key modulator of the hormonal response [Dev. Biol. 221 (2000) 53]. While Kr-h is expressed in many tissues at metamorphosis, in embryos expression is restricted to neurons. Here, we investigate its role during early Drosophila development using new alleles with an earlier lethality than those previously described. Although we detect only minor morphological defects in these mutants, we show that Kr-h expression is necessary for the early development of Drosophila and that, during metamorphosis, Kr-h acts as a modulator of the expression of many of these ecdysone-regulated genes.