Intranuclear Actin Distribution at the Four- and Eight-Cell Stages of Mouse Embryo Development

Abstract

Intranuclear distribution of actin was studied in mouse embryos in the middle and end of the four-cell stage of development, as well as in the blastomeres of uncompacted eight-cell embryos. Actin was visualized with direct fluorescence, indirect immunofluorescence and confocal microscopy. It was found that nuclei at these stages of development contained monomeric, as well as polymeric actin, differing from conventional filamentous. The pattern of actin distribution in the nuclei at the middle-stage four-cell embryos and uncompacted eight-cell embryos was similar. Comparison of this pattern with nuclear actin distribution in the two-cell embryos that we examined previously showed that at the early stages of embryo cleavage the intranuclear actin localization was not stage-specific and was stably reproduced in the nuclei of the embryos during transition from earlier to later stage of embryogenesis. Filamentous actin that had not been found in the nuclei of middle-stage four-cell embryos was detected by fluorescent phalloidin in the nuclei of the embryos at the end of a four-cell stage of development, shortly before the beginning of the third cleavage division. The appearance of nuclear filamentous actin is possibly related to the preparation of embryos to the following cleavage division.