AN AUTORADIOGRAPHIC AND IMMUNOCYTOCHEMICAL ANALYSIS OF ECDYSTEROIDS AND ECDYSTEROID BINDING-SITES IN TARGET-CELLS OF DROSOPHILA-MELANOGASTER

Ecdysteroid localization in target tissues of Drosophila melanogaster was demonstrated by the utilization of low temperature autoradiography and immunohistochemistry. Autoradiographic studies utilized high spec ific activity [H-3]ponasterone A, an ecdysteroid with exceptional molt ing hormone activity in Drosophila. The data revealed a selective nucl ear concentration of the labelled ligand in cells of the salivary glan d, corpus allatum (source of juvenile hormone), prothoracic gland (sou rce of ecdysone) and the central nervous system. Nuclear localization was also observed in epithelial cells of the esophagus and muscle cell s of the pharynx and mandibles, etc. The specific labelling of cell nu clei was prevented by incubation of the tissue with [H-3]ponasterone A in the presence of excess unlabelled ponasterone A. Nuclear localizat ion of ponasterone A in the salivary gland was also observed when usin g an antiserum against ecdysteroids and an avidin-biotin-complex (ABC) detection system. The staining showed two binding patterns, heavy and light, that agreed with the autoradiographic studies. The results cle arly demonstrate specific ponasterone A binding sites in nuclei of the target cells and support the dogma that ecdysteroids exert their effe cts at the level of the genome.