Although actin monomers polymerize into filaments in the cytoplasm, the form of actin in the nucleus remains elusive. We searched for the form and function of β-actin fused to nuclear localization signal and to enhanced yellow fluorescent protein (EN-actin). Our results reveal that EN-actin is either dispersed in the nucleoplasm (homogenous EN-actin) or forms bundled filaments in the nucleus (EN-actin filaments). Formation of such filaments was not connected with increased EN-actin levels. Among numerous actin-binding proteins tested, only cofilin is recruited to the EN-actin filaments. Overexpression of EN-actin causes increase in the nuclear levels of actin-related protein 3 (Arp3). Although Arp3, a member of actin nucleation complex Arp2/3, is responsible for EN-actin filament nucleation and bundling, the way cofilin affects nuclear EN-actin filaments dynamics is not clear. While cells with homogenous EN-actin maintained unaffected mitosis during which EN-actin re-localizes to the plasma membrane, generation of nuclear EN-actin filaments severely decreases cell proliferation and interferes with mitotic progress. The introduction of EN-actin manifests in two mitotic-inborn defects-formation of binucleic cells and generation of micronuclei-suggesting that cells suffer aberrant cytokinesis and/or impaired chromosomal segregation. In interphase, nuclear EN-actin filaments passed through chromatin region, but do not co-localize with either chromatin remodeling complexes or RNA polymerases I and II. Surprisingly presence of EN-actin filaments was connected with increase in the overall transcription levels in the S-phase by yet unknown mechanism. Taken together, EN-actin can form filaments in the nucleus which affect important cellular processes such as transcription and mitosis.

• MeSH
• Actins metabolism   MeSH
• Bacterial Proteins metabolism   MeSH
• Cell Nucleus metabolism   MeSH
• Actin Depolymerizing Factors MeSH
• Transcription, Genetic MeSH
• HEK293 Cells MeSH
• Humans MeSH
• Luminescent Proteins metabolism   MeSH
• Actin Cytoskeleton metabolism   MeSH
• Mitosis genetics   MeSH
• Cell Line, Tumor MeSH
• Actin-Related Protein 3 biosynthesis   metabolism   MeSH
• Chromatin Assembly and Disassembly MeSH
• RNA Polymerase I genetics   MeSH
• RNA Polymerase II genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Actins MeSH
• Bacterial Proteins MeSH
• Actin Depolymerizing Factors MeSH
• Luminescent Proteins MeSH
• Actin-Related Protein 3 MeSH
• RNA Polymerase I MeSH
• RNA Polymerase II MeSH
• yellow fluorescent protein, Bacteria MeSH Browser

Simultaneous detection of biological molecules by means of indirect immunolabeling provides valuable information about their localization in cellular compartments and their possible interactions in macromolecular complexes. While fluorescent microscopy allows for simultaneous detection of multiple antigens, the sensitive electron microscopy immunodetection is limited to only two antigens. In order to overcome this limitation, we prepared a set of novel, shape-coded metal nanoparticles readily discernible in transmission electron microscopy which can be conjugated to antibodies or other bioreactive molecules. With the use of novel nanoparticles, various combinations with commercial gold nanoparticles can be made to obtain a set for simultaneous labeling. For the first time in ultrastructural histochemistry, up to five molecular targets can be identified simultaneously. We demonstrate the usefulness of the method by mapping of the localization of nuclear lipid phosphatidylinositol-4,5-bisphosphate together with four other molecules crucial for genome function, which proves its suitability for a wide range of biomedical applications.

• MeSH
• Actins metabolism   MeSH
• Staining and Labeling methods   MeSH
• Cell Nucleus MeSH
• Microscopy, Electron MeSH
• Phosphatidylinositol 4,5-Diphosphate metabolism   MeSH
• HeLa Cells MeSH
• Immunohistochemistry methods   MeSH
• Nuclear Proteins metabolism   MeSH
• Metal Nanoparticles chemistry   MeSH
• Humans MeSH
• Cell Line, Tumor MeSH
• Nucleophosmin MeSH
• Cell Cycle Proteins MeSH
• Antibodies immunology   MeSH
• Ribonucleoproteins, Small Nuclear metabolism   MeSH
• Carrier Proteins metabolism   MeSH
• Gold chemistry   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Actins MeSH
• Phosphatidylinositol 4,5-Diphosphate MeSH
• Nuclear Proteins MeSH
• Nucleophosmin MeSH
• Cell Cycle Proteins MeSH
• Antibodies MeSH
• Ribonucleoproteins, Small Nuclear MeSH
• SMC2 protein, human MeSH Browser
• Carrier Proteins MeSH
• Gold MeSH

Actin is a well-known protein that has shown a myriad of activities in the cytoplasm. However, recent findings of actin involvement in nuclear processes are overwhelming. Actin complexes in the nucleus range from very dynamic chromatin-remodeling complexes to structural elements of the matrix with single partners known as actin-binding proteins (ABPs). This review summarizes the recent findings of actin-containing complexes in the nucleus. Particular attention is given to key processes like chromatin remodeling, transcription, DNA replication, nucleocytoplasmic transport and to actin roles in nuclear architecture. Understanding the mechanisms involving ABPs will definitely lead us to the principles of the regulation of gene expression performed via concerting nuclear and cytoplasmic processes.

• MeSH
• Actins chemistry   metabolism   MeSH
• Models, Biological MeSH
• Cell Nucleus chemistry   metabolism   MeSH
• Humans MeSH
• Microfilament Proteins chemistry   metabolism   MeSH
• DNA Repair MeSH
• DNA Replication MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Actins MeSH
• Microfilament Proteins MeSH