Accumulation of smooth tubular membrane aggregates in the vitellogenic oocytes of an insect, Dysdercus cingulatus

Abstract

The accumulation of vitellogenins in the oocytes of insects is a receptor-mediated endocytic process, which leads to the formation of yolk granules. We have been studying the hormonal regulation of vitellogenin accumulation and yolk granule formation in the red cotton stainer, Dysdercus cingulatus (Insecta, Hemiptera). During our investigation we observed the appearance of extensive aggregates of smooth tubular membranes in the vitellogenic oocytes. In this report we describe the ultrastructural features of these new cellular organelles.In D. cingulatus (as in other insects) the onset of vitellogenesis (i.e. yolk accumulation) is marked by the appearance of coated pits between the microvilli (Fig. 1). The coated pits transform into electron dense coated vesicles upon invagination into the cortical ooplasm and their subsequent fusion leads to the formation of yolk granules. At a later stage the fusion and continuous growth of yolk granules gives rise to large yolk platelets. During the early phase of yolk accumulation the cortical ooplasm also contains non-coated vesicles of different size in a large number (Fig. 1).