Detection of apoptosis in the ovarian follicle cells of ecdyonurus venosus (ephemeroptera, heptageniidae)

Abstract

Programmed cell death, or apoptosis, occurs in ovarian follicle cells of Ecdyonurus venosus (Ephemeroptera, Heptageniidae) nymphs in the developmental phase characterized by pale wing‐pads. Follicle cells are responsible for egg vitelline and chorionic envelope synthesis. Apoptosis was detected in these cells both on the basis of their ultrastructural morphological characteristics and immunocytochemically by the TUNEL reaction, which proves nuclear DNA fragmentation. Cells showed structural changes after the synthesis of chorionic knob‐terminated coiled threads (KCTs), which typically perform an adhesive function in these insects. The morphological characteristics of apoptosis were evident under transmission electron microscopy after the completion of choriogenesis and consisted in: a) the lobated nucleus; b) chromatin forming small clumps close to the nuclear envelope; c) vacuoles increasing in size in the cell cytoplasm, which was filled with rough endoplasmic reticulum. Apoptotic follicle cells were particularly evident at one egg pole, thus reflecting the polar concentration of these cells in order to synthesize the KCTs. At the end stage of oogenesis in this insect group, as in many other multicellular organisms, apoptosis appears to be a common fate for cells that have fulfilled their role.