Dynamic localisation of KR-H during an ecdysone response in Drosophila.

The propagation of a hormonal response following an increase in titre involves intensive cross-talk between the products of the key regulatory genes. The Kr-h gene of Drosophila is a modulator of both the embryonic and metamorphic hierarchies of ecdysone responsive genes, but its mode of action is puzzling as mutants have both quantitative and qualitative (timing) effects on the ecdysone responses. We have used an antibody against KR-H to follow its distribution in larval tissues as they prepare for metamorphosis. While in most tissues protein levels remain stable, its distribution within salivary gland cells changes throughout the late larval ecdysone response and the ensuing prepupal period. We show that, at the chromosomal level, KR-H localisation is dynamic and that the protein is recruited to, and released from, loci harbouring an important subset of the known regulatory genes as the response advances. Such behaviour is most likely a conserved characteristic of hormonal responses.