Formation of the karyosome in developing oocytes of weevils (Coleoptera, Curculionidae)

A complex structure termed the karyosome forms in the nuclei of the develop ing oocytes of Anthonomus pomorum, Hylobius abietis and Phyllobius sp, (Col eoptera: Curculionidae). It is composed of highly condensed chromosomes, fu sed with an electron-dense granular material. There are two types of nuclea r body associated with the karyosome. The smaller bodies are found in the i mmediate vicinity of the karyosome, The larger, and more electron-dense, bo dies originate next to the condensing chromosomes. During vitellogenesis, t he latter bodies disperse in the karyoplasm, and at least some of them loca te in the characteristic irregular projections of the germinal vesicle. Mor phologically, these projections resemble the accessory nuclei described in other insects. In the studied species, a proteinaceous sheath, the so-calle d karyosome capsule, surrounds the karyosome, The formation of the karyosom e and its capsule occurs during previtellogenesis, so that these structures are fully formed at the onset of vitellogenesis. An extraction of the oocy te cytoplasm with Triton X-100 showed that the material constituting the ka ryosome capsule is filamentous. Staining with rhodamine-conjugated phalloid in reveals large amount of F-actin in the karyosome capsule. (C) 1999 Harco urt Publishers Ltd.