The B1C8 protein is in the dense assemblies of the nuclear matrix and relocates to the spindle and pericentriolar filaments at mitosis.

Abstract

The B1C8 monoclonal antibody detects a 180-kDa nuclear matrix-specific protein. The protein is a component of the dense, metabolically active bodies or assemblies revealed by resinless section electron microscopy of the nuclear matrix. These assemblies are scattered through the nuclear interior, enmeshed in a complex network of 11-nm filaments. Resinless section electron microscopy of immunogold-stained nuclear matrix preparations shows B1C8 located in many but apparently not all the assemblies. In this regard, the B1C8 antigen resembles previously studied nuclear matrix proteins such as the H1B2 protein. The speckled pattern of nuclear immunofluorescence by B1C8 reflects this labeling of the dense assemblies in the nuclear matrix. Somewhat unusual is the faint staining of cytoplasmic microtubules by B1C8, which appears to be due to a weakly cross-reacting protein. During cell division, the B1C8 antigen redistributed drastically, showing the dispersion of nuclear matrix assemblies at mitosis. Speckles of B1C8 fluorescence first coalesced at prophase within the nuclear interior and then scattered into numerous cytoplasmic speckles by prometaphase. At metaphase, the B1C8 speckled cytoplasmic staining had become even more widely distributed and finely grained. Also, intense labeling appeared at the mitotic pole and on the spindle fibers themselves. The reassembly of BiC8 antigens into larger cytoplasmic speckles began at anaphase and finally, at telophase, most B1C8 labeling redistributed into speckles in the re-forming nuclei.There is increasing evidence that most, and probably all, nuclear macromolecular metabolism is closely associated with the nuclear matrix. More recent evidence indicates that nuclear events are highly localized into metabolically active centers. DNA synthesis takes place in replication sites (1-3), heterogeneous nuclear RNA (hnRNA) processing, and RNA transport in spliceosomes that process hnRNA (4-6), while nucleoli have long been known as dense bodies that synthesize and process rRNA (7).We have previously shown that the nuclear matrix is composed of a profuse network of "core filaments" that enmesh many dense bodies ofdiverse sizes and morphologies (8-10). Conventional electron micrographs of the nucleus show mostly the dense chromatin. Removal of the chromatin reveals an extensive nonchromatin nuclear structure consisting of filaments and dense bodies. While visible in conventional micrographs, only resinless section electron microscopy shows the filaments and dense bodies with great clarity in three dimensions. Immunolocalization with monoclonal antibodies shows the dense bodies to be of complex protein composition and to be the principal sites of nuclear metabolism. Because of their various types, complex compositionThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.and variety of functions, we suggest that these dense b...

Binding of ATP to UAP56 is necessary for mRNA export

“…By metaphase, UAP56 had moved to the poles of the mitotic spindle and to foci distributed throughout the cytoplasm, but more concentrated around the periphery of the chromosomes. This same distribution is observed for SRm160 at metaphase (Wan et al, 1994), when it might interact with cohesin (McCracken et al, 2005). UAP56 remained at the poles of the mitotic spindle and in smaller cytoplasmic foci through anaphase and into telophase.…”

The Dynamic Association of RCC1 with Chromatin Is Modulated by Ran-dependent Nuclear Transport

“…SRm160 is a pre-mRNA splicing factor (Blencowe et al, 1998). Like the majority of mRNA splicing factors, SRm160 is not localized at sites of transcription but is instead enriched in nuclear domains called speckles (Wan et al, 1994;Misteli, 2000). When cells are treated with RNA pol II inhibitors, splicing activity is reduced and the speckles become fewer in number, enlarged, and rounded (Misteli et al, 1997).…”

“…The antibodies used were: mouse anti-Ran (Transduction Laboratories, Lexington, KY), rabbit anti-Crm1 (from M. Yoshida) (Kudo et al, 1997), mouse anti-nucleophosmin/B23 (from P.K. Chan) (Yung et al, 1985), and mouse (IgM) anti-SRm160 (from J. Nickerson) (Wan et al, 1994). The labeled second antibodies were tetramethylrhodamine B isothiocyanate (TRITC)-labeled donkey anti-mouse or anti-rabbit (Jackson ImmunoResearch Laboratories, West Grove, PA) and Texas Red-labeled goat anti-mouse IgM (Southern Biotechnologies, Birmingham, AL).…”

Association of Lyn Tyrosine Kinase with the Nuclear Matrix and Cell‐Cycle‐Dependent Changes in Matrix‐Associated Tyrosine Kinase Activity

“…Numerous procedures have been used in the isolation of the nuclear matrix and extensive studies by H e et al [25] have shown that low salt extraction gives rise to complete nuclear matrices; 2 M salt extraction after DNase digestion and low-salt treatment of nuclei give rise only to the core filaments of the matrix. Wan et al [36] have more recently stated that high-salt extraction is necessary to obtain the most native nuclear matrix morphology. For our experiments we used three different methods and found that Lyn polypeptides are reproducibly associated with nuclear matrix preparations.…”