Nuclear antigens follow different pathways into daughter nuclei during mitosis in early Drosophila embryos.

In the early embryonic development of Drosophila melanogaster, there is a series of 13 rapid and highly synchronous nuclear divisions. We have used a collection of monoclonal antibodies to follow the re-distribution of nuclear antigens into daughter nuclei at this developmental stage by indirect immunofluorescence microscopy. The antigens fall into several categories in terms of the pathways that are followed at mitosis. At one extreme is a group of antigens that remains continuously associated with the DNA throughout all the mitotic phases. At the other extreme, another group of antigens is excluded from the nucleus at prophase, and does not associate with the nucleus again until late telophase. One antigen, which becomes incorporated into the nucleolus at cellularization after the thirteenth division, becomes associated with the chromosomes during mitosis, but not until anaphase. Several different antibodies stain a diamond-shaped compartment that develops over the spindle at anaphase. The distribution of antigens within this spindle compartment shows some variation: one antigen appears to be present at higher concentrations in the central region of the spindle; others appear in three quite distinct areas corresponding to the positions of the new daughter nuclei and the old parental nucleus. Yet another antibody gives uniform staining of the spindle compartment. This antibody also recognizes a protein present in centrosomes.