Diffusible and bound actin nuclei of Xenopus laevis oocytes

Several criteria have been used to identify actin in hand-isolated nuclei of Xenopus laevis oocytes; these include co-migration with actin on SDS-polyacrylamide gels, immunological cross-reactivity with antiserum against actin, binding to DNAase I and peptide mapping on SDS gels. The use of hand-isolated nuclei precludes the possibility of contamination from cytoplasmic actin or the leakage of significant amounts of actin from nuclei during isolation. Actin constitutes roughly 6% of the total nuclear protein. Approximately 75% of the actin is diffusible under the conditions of nuclear isolation used. About 25%, however, is stably associated with an insoluble nuclear gel, in which chromosomes, nucleoli and other nuclear granules are embedded. Actin is the single most promient component of the nuclear gel, comprising roughly 16% of the total protein of the complex. The possible significance of diffusible and bound actin in these nuclei is discussed.     

Nuclear structures in the telotrophic ovarioles of nocturnal ground beetles (Tenebrionidae, Polyphaga). II. The oocyte nucleus of Blaps lethifera and Gnaptor spinimanus. Light optical data]

Changes in the nuclear structures and their participation in RNA synthesis in the growing oocytes were followed in two species of beetles Blaps lethifera and Gnaptor spinimanus. In the oocytes of both the species, the chromosomes join into the karyosphere following the short-term lampbrush stage. A large capsule appears around the karayosphere which consists of the fibrous substance, granules and karyosphere nucleoli. The latter form in the karyosphere and contain RNP but they are not true nucleoli since they do not include 3H-uridine. RNA synthesis on the chromosomes, active at the lampbrush stage, falls markedly following their joining into the karyosphere. The oocyte nuclei of these beetles are, thus, characterized by the absence of RNA synthesizing nucleolar system and, as compared with the trophocytes, by the low level of RNA synthesis on the chromosomes.     

Intranuclear actin microfilaments in the oocytes of the common frog

For identification and distribution of actin microfilaments in hand-isolated nuclei of R. temporaria oocytes (stage 6, according to Dumont, 1972) different methods were used: heavy meromyosin decoration, antiactin immunofluorescence with monoclonal antibodies, staining with rhodamine phalloidin, and electrophoresis in polyacrylamide gel. The nuclei of R. temporaria oocytes contain a considerable quantities of actin microfilaments which form intranuclear meshwork. Microfilaments are connected with the nucleoli, nucleolar RNP-complexes and nuclear envelope. Immunofluorescence with antiactin monoclonal antibodies reveals a strong staining of microfilaments and nucleoli. A slight staining of nucleoli is observed after the treatment of nuclei with rhodamine phalloidin. A specific role of intranuclear microfilaments in direct transport of nucleolar material from the nucleus into the oocyte cytoplasm, in stabilization of the karyosphere (the late diplotene oocyte complex of chromosomes with numerous nucleoli) is discussed in addition to its keeping in a definite region of the nucleus. A supposition is drawn on the functional significance of the connection between microfilaments and nuclear matrix. Based on our own and literature data, a conclusion is drawn, that the intranuclear filament actin may be one of the leading components in morpho-functional organization of the nucleus as the whole.