The Drosophila disembodied gene controls late embryonic morphogenesis and codes for a cytochrome P450 enzyme that regulates embryonic ecdysone levels

Ecdysteroids regulate a wide variety of cellular processes during arthropod development, yet little is known about the genes involved in the biosynthe sis of these hormones. Previous studies have suggested that production of 2 0-hydroxyecdysone in Drosophila and other arthropods involves a series of c ytochrome P450 catalyzed hydroxylations of cholesterol, In this report, we show that the disembodied (dib) locus of Drosophila codes for a P450-like s equence. In addition, we find that dib mutant embryos have very low titers of ecdysone and 20-hydroxyecdysone (20E) and fail to express IMP-E1 and L1, two 20E-inducible genes, in certain tissues of the embryo. In situ hybridi zation studies reveal that dib is expressed in a complex pattern in the ear ly embryo, which eventually gives way to restricted expression in the proth oracic portion of the ring gland. In larval and adult tissues, dib expressi on is observed in the prothoracic gland and follicle cells of the ovaries r espectively, two tissues known to synthesize ecdysteroids. Phenotypic analy sis reveals that dib mutant embryos produce little or no cuticle and exhibi t severe defects in many late morphogenetic processes such as head involuti on, dorsal closure and gut development. In addition, we examined the phenot ypes of several other mutants that produce defective embryonic cuticles. Li ke dib, mutations in the spook (spo) locus result in low embryonic ecdyster oid titers, severe late embryonic morphological defects, and a failure to i nduce IMP-E1. From these data, we conclude that dib and spo likely code for essential components in the ecdysone biosynthetic pathway and that ecdyste roids regulate many late embryonic morphogenetic processes such as cell mov ement and cuticle deposition.