Cell surface proteins of Drosophila. II. A comparison of embryonic and ecdysone-induced proteins

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 biosynthesis of these hormones. Previous studies have suggested that production of 20-hydroxyecdysone in Drosophila and other arthropods involves a series of cytochrome P450 catalyzed hydroxylations of cholesterol. In this report, we show that the disembodied (dib) locus of Drosophila codes for a P450-like sequence. 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 hybridization studies reveal that dib is expressed in a complex pattern in the early embryo, which eventually gives way to restricted expression in the prothoracic portion of the ring gland. In larval and adult tissues, dib expression is observed in the prothoracic gland and follicle cells of the ovaries respectively, two tissues known to synthesize ecdysteroids. Phenotypic analysis reveals that dib mutant embryos produce little or no cuticle and exhibit severe defects in many late morphogenetic processes such as head involution, dorsal closure and gut development. In addition, we examined the phenotypes of several other mutants that produce defective embryonic cuticles. Like dib, mutations in the spook (spo) locus result in low embryonic ecdysteroid titers, severe late embryonic morphological defects, and a failure to induce IMP-E1. From these data, we conclude that dib and spo likely code for essential components in the ecdysone biosynthetic pathway and that ecdysteroids regulate many late embryonic morphogenetic processes such as cell movement and cuticle deposition.

26-[125I]iodoponasterone A is a potent ecdysone and a sensitive radioligand for ecdysone receptors

The effects of ecdysone, the steroid molting hormone of arthropods, are of considerable interest both to insect physiologists and to those studying steroid-regulated gene expression. Yet progress in understanding ecdysone receptors has been inhibited by the lack of a suitable highly radioactive hormone analog with high affinity for the receptor. Here we report that the synthetic ecdysteroid 26-iodoponasterone A is one of the most active ecdysones known, inducing half-maximal morphological transformation in Drosophila Kc167 cells when present at 0.5 nM. 26-[125I]Iodoponasterone A can be prepared at a specific activity of 2175 Ci/mmol (1 Ci = 37 GBq) by reaction of the precursor 26-mesylinokosterone with carrier-free Na125I. The radiolabeled material binds to Kc167 cell ecdysone receptors specifically and with affinity (Kd ca. 3.8 X 10(-10) M). Thus, 26-[125I]iodoponasterone A appears to be a superior radioligand for ecdysone receptors on grounds both of affinity and of specific activity. Its ready availability should greatly facilitate studies of these receptors.

Isolation of plasma membranes from Drosophila embryos

Cell surface components probably play an important role in early embryonic development. However, hardly any information is available on the structure or regulation of expression of the corresponding genes. As a first step in approaching this issue, we devised a procedure to obtain enriched plasma membranes from embryonic Drosophila cells. Membranes are fractionated according to two independent physical parameters: size, using velocity gradient centrifugation and density, using isopicnic gradient centrifugation. The final membrane fraction is enriched by 6 to 8 fold with respect to the plasma membrane enzyme marker Na+/K+ ATPase and substantially depleted of the mitochondrial enzyme marker cytochrome C oxidase. Two-dimensional polyacrylamide gel electrophoresis of the purified membranes reveals enrichment for specific proteins and electron microscopy reveals membrane vesicles in abundance. The enriched fraction should be suitable for the preparation of antibody probes that recognize cell surface components.