Glycogen stores in mature ovarian follicles and young embryos of Drosophila: ultrastructural changes and some biochemical correlates.

During the last phase of oogenesis in Drosophila, large amounts of carbohydrates are taken up by the oocyte and become stored in the so-called beta-spheres whose ultrastructure and histochemical properties indicate that glycogen is the predominant storage form. The ultrastructure of the beta-spheres changes at the onset of embryogenesis: they become irregular in shape and the spacing of the granular substructures (beta-particles) increases. During the first 2 h of embryonic development, the total carbohydrate content decreases sharply while at the same time the protein content increases. Presumably the carbohydrate store is used to generate energy at this phase of development. Using monoclonal antibodies against an ecdysteroid-related antigen we showed that this antigen is mostly located in the beta-spheres. The asymmetrical distribution of the antigen in the egg (more concentrated near the posterior end) correlates with the same asymmetrical distribution of the beta-spheres in the mature follicle.