The expression of the let-7 small regulatory RNA is controlled by ecdysone duriniz metamorphosis in Drosophila melanogaster

In Caenorhabditis elegans, the heterochronic pathway controls the timing of develop men tal events during the larval stages. A component of this pathway, the let-7 small regulatory RNA, is expressed at the late stages of development and promotes the transition from larval to adult (L/A) stages. The stage-specificity of let-7 expression, which is crucial for the proper timing of the worm L/A transition, is conserved in Drosophila melanogaster and other invertebrates. In Drosophila, pulses of the steroid hormone 20-hydroxyecdysone (ecdysone) control the timing of the transition from larval to pupal to adult stages. To test whether let-7 expression is regulated by ecdysone in Drosophila, we used Northern blot analysis to examine the effect of altered eedysone levels on let-7 expression in mutant animals, organ cultures, and S2 cultured cells. Experiments were conducted to test the role of Broad-Complex (BR-Q, an essential component in the ecdysone pathway, in let-7 expression. We show that eedysone and BR-C are required for let-7 expression, indicating that the eedysone pathway regulates the temporal expression of let-7 in Drosophila. These results demonstrate an interaction between steroid hormone signaling and the heterochronic pathway in insects. (C) 2002 Elsevier Science (USA).