A nuclear dot-like structure that has a relationship with perinuclear intermediate filaments.

A new type of nuclear dot-like structure was found that seems to associate with perinuclear intermediate filaments (IFs). A monoclonal antibody AP435 MAb (IgM), reactive with desmin and vimentin, recognized from several to dozens of small nuclear dots (AP435 dots) as well as cytoplasmic IFs in various mammalian cells under immunofluorescence microscopy. AP435 dots were sensitive to treatment with 0.5% Triton X-100 while IFs were resistant. The dots disappeared during mitosis in some cells. They colocalized with neither centromeres nor structures involved in RNA processing. Many AP435 dots seem to associate with perinuclear IFs, though they were observed even in cells with no IFs. In cells possessing IFs AP435 dots separated from the bulk of the IFs and remained in the nuclear region both after treatment with colchicin and after treatment with cytochalasin B followed by centrifugation. Confocal laser-scanning fluorescence microscopy revealed the dots to be inside the nucleus. AP435 dots are small intranuclear structures that seem to interact directly or indirectly with perinuclear IFs.