The many functions of phosphoinositides in cytosolic signaling were extensively studied; however, their activities in the cell nucleus are much less clear. In this review, we summarize data about their nuclear localization and metabolism, and review the available literature on their involvements in chromatin remodeling, gene transcription, and RNA processing. We discuss the molecular mechanisms via which nuclear phosphoinositides, in particular phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2), modulate nuclear processes. We focus on PI(4,5)P2's role in the modulation of RNA polymerase I activity, and functions of the nuclear lipid islets-recently described nucleoplasmic PI(4,5)P2-rich compartment involved in RNA polymerase II transcription. In conclusion, the high impact of the phosphoinositide-protein complexes on nuclear organization and genome functions is only now emerging and deserves further thorough studies.

• Klíčová slova
• cell nucleus, gene expression, genome, phosphoinositides,
• MeSH
• buněčné jádro genetika   metabolismus   MeSH
• Eukaryota genetika   metabolismus   MeSH
• fosfatidylinositol-4,5-difosfát metabolismus   MeSH
• genetická transkripce MeSH
• genom * MeSH
• posttranskripční úpravy RNA MeSH
• restrukturace chromatinu MeSH
• RNA-polymerasa I metabolismus   MeSH
• RNA-polymerasa II metabolismus   MeSH
• vazba proteinů fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• fosfatidylinositol-4,5-difosfát MeSH
• RNA-polymerasa I MeSH
• RNA-polymerasa II MeSH

In biomedical studies, the colocalization is commonly understood as the overlap between distinctive labelings in images. This term is usually associated especially with quantitative evaluation of the immunostaining in fluorescence microscopy. On the other hand, the evaluation of the immunolabeling colocalization in the electron microscopy images is still under-investigated and biased by the subjective and non-quantitative interpretation of the image data. We introduce a novel computational technique for quantifying the level of colocalization in pointed patterns. Our approach follows the idea included in the widely used Manders' colocalization coefficients in fluorescence microscopy and represents its counterpart for electron microscopy. In presented methodology, colocalization is understood as the product of the spatial interactions at the single-particle (single-molecule) level. Our approach extends the current significance testing in the immunoelectron microscopy images and establishes the descriptive colocalization coefficients. To demonstrate the performance of the proposed coefficients, we investigated the level of spatial interactions of phosphatidylinositol 4,5-bisphosphate with fibrillarin in nucleoli. We compared the electron microscopy colocalization coefficients with Manders' colocalization coefficients for confocal microscopy and super-resolution structured illumination microscopy. The similar tendency of the values obtained using different colocalization approaches suggests the biological validity of the scientific conclusions. The presented methodology represents a good basis for further development of the quantitative analysis of immunoelectron microscopy data and can be used for studying molecular interactions at the ultrastructural level. Moreover, this methodology can be applied also to the other super-resolution microscopy techniques focused on characterization of discrete pointed structures.

• Klíčová slova
• Colocalization, Immunohistochemistry, Manders’ coefficients, Pointed patterns, Quantitative analysis, Transmission electron microscopy,
• MeSH
• algoritmy * MeSH
• fluorescenční mikroskopie MeSH
• imunoelektronová mikroskopie MeSH
• konfokální mikroskopie MeSH
• počítačové zpracování obrazu * MeSH
• Publikační typ
• časopisecké články MeSH

Nuclear actin and nuclear myosin I (NMI) are important players in transcription of ribosomal genes. Transcription of rDNA takes place in highly organized intranuclear compartment, the nucleolus. In this study, we characterized the localization of these two proteins within the nucleolus of HeLa cells with high structural resolution by means of electron microscopy and gold-immunolabeling. We demonstrate that both actin and NMI are localized in specific compartments within the nucleolus, and the distribution of NMI is transcription-dependent. Moreover, a pool of NMI is present in the foci containing nascent rRNA transcripts. Actin, in turn, is present both in transcriptionally active and inactive regions of the nucleolus and colocalizes with RNA polymerase I and UBF. Our data support the involvement of actin and NMI in rDNA transcription and point out to other functions of these proteins in the nucleolus, such as rRNA maturation and maintenance of nucleolar architecture.

• MeSH
• aktiny metabolismus   MeSH
• buněčné jadérko metabolismus   MeSH
• genetická transkripce fyziologie   MeSH
• HeLa buňky MeSH
• imunohistochemie MeSH
• lidé MeSH
• myosin typu I metabolismus   MeSH
• ribozomální DNA metabolismus   MeSH
• RNA ribozomální metabolismus   MeSH
• RNA-polymerasa I metabolismus   MeSH
• transkripční iniciační komplex Pol1 - proteiny metabolismus   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• aktiny MeSH
• myosin typu I MeSH
• ribozomální DNA MeSH
• RNA ribozomální MeSH
• RNA-polymerasa I MeSH
• transcription factor UBF MeSH Prohlížeč
• transkripční iniciační komplex Pol1 - proteiny MeSH

Nuclear actin plays an important role in such processes as chromatin remodeling, transcriptional regulation, RNA processing, and nuclear export. Recent research has demonstrated that actin in the nucleus probably exists in dynamic equilibrium between monomeric and polymeric forms, and some of the actin-binding proteins, known to regulate actin dynamics in cytoplasm, have been also shown to be present in the nucleus. In this paper, we present ultrastructural data on distribution of actin and various actin-binding proteins (alpha-actinin, filamin, p190RhoGAP, paxillin, spectrin, and tropomyosin) in nuclei of HeLa cells and resting human lymphocytes. Probing extracts of HeLa cells for the presence of actin-binding proteins also confirmed their presence in nuclei. We report for the first time the presence of tropomyosin and p190RhoGAP in the cell nucleus, and the spatial colocalization of actin with spectrin, paxillin, and alpha-actinin in the nucleolus.

• MeSH
• aktinin MeSH
• aktiny analýza   MeSH
• buněčné jádro chemie   ultrastruktura   MeSH
• HeLa buňky MeSH
• jaderné proteiny analýza   MeSH
• lidé MeSH
• lymfocyty chemie   ultrastruktura   MeSH
• mikrofilamentové proteiny analýza   MeSH
• paxilin MeSH
• proteiny aktivující GTPasu MeSH
• spektrin MeSH
• tropomyosin MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• aktinin MeSH
• aktiny MeSH
• jaderné proteiny MeSH
• mikrofilamentové proteiny MeSH
• paxilin MeSH
• proteiny aktivující GTPasu MeSH
• rho GTPase-activating protein MeSH Prohlížeč
• spektrin MeSH
• tropomyosin MeSH

Early leukemic granulocytic and plasmacytic precursors were studied in vitro and in vivo to provide an information on the intranucleolar distribution of AgNORs (silver stained nucleolus organizer regions). In most of these cells AgNORs appeared as clusters of silver stained particles distributed in the whole nucleolar body. On the other hand, in some leukemic early granulocytic precursors, i.e., in myeloblasts and promyelocytes enlarged AgNORs were translocated in the nucleolar peripheral part. In addition, the number of translocated AgNORs at the nucleolar periphery was significantly smaller. Such translocation of a reduced number of AgNORs was easily produced by experimental aging, i.e., starving of cultured leukemic early granulocytic precursors (HL-60 and K562 cells) in vitro and seems to be reversible. Similar translocation of a reduced number of AgNORs was also produced by aging of leukemic plasmacytic precursors. Thus, the translocation of the reduced number of AgNORs to the nucleolar periphery in some blastic leukemic hematopoietic cells might be an useful marker of their aging at the single cell level. However, more studies in this direction are required in the future.

• MeSH
• barvení stříbrem MeSH
• buněčné jadérko metabolismus   MeSH
• buněčný cyklus fyziologie   MeSH
• buňky K562 MeSH
• buňky kostní dřeně metabolismus   MeSH
• DNA nádorová metabolismus   MeSH
• granulocyty metabolismus   ultrastruktura   MeSH
• HL-60 buňky MeSH
• leukemie metabolismus   MeSH
• lidé MeSH
• organizátor jadérka metabolismus   MeSH
• plazmatické buňky metabolismus   ultrastruktura   MeSH
• RNA nádorová metabolismus   MeSH
• stárnutí buněk fyziologie   MeSH
• transport proteinů MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA nádorová MeSH
• RNA nádorová MeSH

As previous studies suggested, nuclear myosin I (NMI) and actin have important roles in DNA transcription. In this study, we characterized the dynamics of these two proteins during transcriptional activation in phytohemagglutinin (PHA) stimulated human lymphocytes. The stimulation led to strong up-regulation of NMI both on the mRNA and protein level, while actin was relatively stably expressed. The intranuclear distribution of actin and NMI was evaluated using immunogold labeling. In nucleoli of resting cells, actin was localized predominantly to fibrillar centers (FCs), while NMI was located mainly to the dense fibrillar component (DFC). Upon stimulation, FCs remained the main site of actin localization, however, an accumulation of both actin and NMI in the DFC and in the granular component was observed. In the nucleoplasm of resting lymphocytes, both actin and NMI were localized mostly in condensed chromatin. Following stimulation, the majority of both proteins shifted towards the decondensed chromatin. In transcriptionally active cells, both actin and NMI colocalized with nucleoplasmic transcription sites. These results demonstrate that actin and NMI are compartmentalized in the nuclei where they can dynamically translocate depending on transcriptional activity of the cells.

• MeSH
• aktiny metabolismus   MeSH
• buněčné jadérko účinky léků   metabolismus   ultrastruktura   MeSH
• buněčné jádro účinky léků   metabolismus   ultrastruktura   MeSH
• fytohemaglutininy farmakologie   MeSH
• genetická transkripce genetika   MeSH
• lidé MeSH
• lymfocyty účinky léků   metabolismus   ultrastruktura   MeSH
• messenger RNA metabolismus   MeSH
• myosin typu I metabolismus   MeSH
• polymerázová řetězová reakce s reverzní transkripcí MeSH
• transmisní elektronová mikroskopie MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• aktiny MeSH
• fytohemaglutininy MeSH
• messenger RNA MeSH
• myosin typu I MeSH