DHR3, AN ECDYSONE-INDUCIBLE EARLY-LATE GENE ENCODING A DROSOPHILA NUCLEAR RECEPTOR, IS REQUIRED FOR EMBRYOGENESIS

Response to the steroid hormone ecdysone in Drosophila is controlled b y genetic regulatory hierarchies that include eight members of the nuc lear receptor protein family, The DHR3 gene, located within the 46F ea rly-late ecdysone-inducible chromosome puff; encodes an orphan nuclear receptor that recently has been shown to exert both positive and nega tive regulatory effects in the ecdysone-induced genetic hierarchies at metamorphosis. We used a reverse genetics approach to identify 11 DHR 3 mutants from a pool of lethal mutations in the 46F region on the sec ond chromosome, Two DHR3 mutations result in amino acid substitutions within the conserved DIVA binding domain, Analysis of DHR3 mutants rev eals that DHR3 function is required to complete embryogenesis, All DHR 3 alleles examined result in nervous system defects in the embryo.