We examined the distribution of nonlamin nuclear matrix antigens during the mitotic cell cycle in mouse 3T3 fibroblasts . Four monoclonal antibodies produced against isolated nuclear matrices were used to characterize antigens by the immunoblotting of isolated nuclear matrix preparations, and were used to localize the antigens by indirect immunofluorescence . For comparison, lamins and histones were localized using human autoimmune antibodies . At interphase, the monoclonal antibodies recognized non-nucleolar and nonheterochromatin nuclear components . Antibody Pl stained the nuclear periphery homogeneously, with some small invaginations toward the interior of the nucleus . Antibody 11 detected an antigen distributed as fine granules throughout the nuclear interior . Monoclonals PI1 and P12 stained both the nuclear periphery and interior, with some characteristic differences . During mitosis, P1 and 11 were chromosome-associated, whereas P11 and P12 dispersed in the cytoplasm . Antibody P1 heavily stained the periphery of the chromosome mass, and we suggest that the antigen may play a role in maintaining interphase and mitotic chromosome order . With antibody 11, bright granules were distributed along the chromosomes and there was also some diffuse internal staining. The antigen to 11 may be involved in chromatin/ chromosome higher-order organization throughout the cell cycle . Antibodies P11 and P12 were redistributed independently during prophase, and dispersed into the cytoplasm during prometaphase . Antibody P12 also detected antigen associated with the spindle poles.The nuclear matrix is a complex biochemical fraction consisting of nonhistone nuclear proteins and small quantities of DNA and RNA . It is obtained by sequential extraction of isolated interphase nuclei with low-and high-salt buffers, detergents, and DNAse and RNAse . Structurally, the nuclear matrix comprises the peripheral nuclear pore complex-lamina, an internal fibrogranular network and residual nucleoli . Part of the matrix has been envisaged as an interphase "nuclear skeleton" on which nuclear functions such as DNA replication, RNA transcription and processing, virus replication, and hormone response can be ordered (see references 1-3 for reviews).Several studies have suggested that the nuclear matrix is involved in mitosis (4-7). Recent work (8, 9) has also indicated a potential role for the nuclear matrix in the organization of mitotic chromosomes per se. To examine the distribution of individual nuclear matrix polypeptides throughout the cell cycle, we used monoclonal antibodies against isolated THE JOURNAL OF CELL BIOLOGY " VOLUME 99 AUGUST 1984 661-671 © The Rockefeller University Press -0021-9525/84/08/0661/11 $1 .00 nuclear matrices in an immunofluorescence study of mouse 3T3 fibroblasts . MATERIALS AND METHODSCell Culture: Mouse 3T3 fibroblasts were cultured at 37°C with 5% C02 in Dulbecco's modified Eagle's medium with 10% fetal calf serum, 100 U/ml penicillin, 100 Ag/ml streptomycin, and 0.25 lg/ml fungizone . Mouse myel...

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From previous immunofluorescent, immunohistochemical and ultrastructural studies, myoepithelial cells have been reported to be absent from the striated and excretory ducts of human salivary gland. Yet recently, certain anti-cytokeratin monoclonal antibodies which specifically label the myoepithelium of salivary gland acini and intercalated ducts have also been found to stain basally situated cells in both striated and excretory ducts. In this study, we have used eight samples of normal human parotid gland (methacarn-fixed and frozen sections) to establish if basal cells of striated and excretory ducts have the cytoskeletal protein complement (actin and cytokeratins) of myoepithelial cells. Using a muscle-specific actin, HHF35, not only is the myoepithelium of acini and intercalated ducts stained in all cases, but stellate and spindle shaped cells are also detected all along the inter- and intralobular striated ducts in four of the eight examples. With double-labeled frozen sections and fluorescent microscopy, the actin-specific probe, phalloidin, and the myoepithelial-selective anti-cytokeratin 14 antibody, 312C8-1, confirm that the striated duct does have a population of basal cells with the cytoskeletal protein make-up of myoepithelium. The monoclonal antibody 8.12 (specific for cytokeratin 13 and 16) also stains some basal cells of striated and excretory ducts, as well as luminal cells of ducts at all levels, but does not label the myoepithelium of acini and intercalated ducts. Both the anti-cytokeratin antibodies and the actin-detecting mechanisms reveal that the basal cell population of striated and excretory ducts is more heterogeneous, and likely functionally more complex, than has been realized previously. Such findings are not in agreement with certain aspects of current theories of the histogenesis of salivary gland tumours.

We have applied monoclonal antibodies generated against nuclear matrix in an immunofluorescence study of a variety of plant and animal species. Antibodies P1 and I1 detected antigens in all species examined, including higher and lower plants. Antibodies PI1 and PI2 stained only animal cells, and showed some tissue and/or species-specific variability in staining pattern. The presence of similar nuclear matrix components in such diverse species suggests that nuclear order may be maintained by similar mechanisms in all eukaryotes.