[The intermediate filament-lamina-nuclear matrix system of ES-M13 cells]

Sequential extraction and DGD embedment-free section TEM techniques were used as new methods to study the intermediate filament-lamina-nuclear matrix (IF-L-NM) system of cells. Murine embryonic stem cells (ES-M13) were investigated by means of electron microscopy, immunofluorescence microscopy and Western-blot analysis. There existed a delicate nuclear matrix network in the nucleus domain of detergent-extracted ES cells. The filaments of the nuclear matrix were found in close association with the nuclear lamina. Some intermediate filaments were also observed in the cytoplasm. In immunofluorescence microscopy, a bright, slightly granular cytoplasmic fluorescence, showing no polar concentration, was revealed with keratin monoclonal antibody AF5. We could not detect any significant fibrillar staining in the ES cells by indirect immunofluorescence method. With antibodies to vimentin and desmin, the ES cells showed only a nonspecific, weak fluorescence, similar to that seen in the control. In Western-blot analysis of electrophoretically separated polypeptides, three polypeptides with molecular weight of 65 KD, 62 KD and 52 KD, reactive with keratin monoclonal antibody were detected in the ES cells.