First observations of the nucleoplasmic lipid islets: "black holes: in the cell nucleus?

0426062 - ÚMG 2014 DE eng C - Conference Paper (international conference)
Sobol, Margaryta - Yildirim, Sukriye - Filimonenko, Vlada - Filimonenko, Anatolij - Hozák, Pavel
First observations of the nucleoplasmic lipid islets: "black holes: in the cell nucleus?
MC 2013 Regensburg. Regensburg: European Microscopy Society, 2013, s. 341-342.
[MC 2013 Regensburg. Regensburg (DE), 25.08.2013-30.08.2013]
R&D Projects: GA ČR GAP305/11/2232; GA TA ČR TE01020118; GA MŠMT LD12063; GA MŠMT LH12143
Institutional support: RVO:68378050
Keywords : cell nucleus * chromatin * PIP2 * 3D electron tomography * super-resolution microscopy
Subject RIV: EB - Genetics ; Molecular Biology

We describe novel structures containing phosphatidylinositol 4,5-bisphosphate (PIP2) which seem to contribute to spatial nuclear ordering. We carried out ultrastructural mapping of PIP2-containing structures using pre-embedding immunolabeling and 3D electron tomography. We showed that these structures propagate through the nucleolus where they connect individual fibrillar centers and the dense fibrillar component. Besides interchromatin granule clusters the PIP2-positive structures stretch into the nucleoplasm where they appear as previously undescribed 70-100 nm roundish “lipid islets”. We mapped the elemental content of these islets using electron energy-loss microscopy. They appear surrounded by chromatin and carbon mapping showed high density of organic compounds inside the islets indicating that lipids might be the main inner constituents of these structures. To reveal the plausible functions of these islets we mapped mutual localization of PIP2 with nuclear proteins involved in transcription, splicing, and higher order chromatin organization using advanced immunogold electron microscopy and super-resolution light microscopy. We show that at the islet periphery PIP2 co-localizes or is located in immediate vicinity with nascent transcripts, pre-lamin A, LAP2α, H3K4me2, and H3K9me2. Direct binding and mobility assays also showed nucleoplasmic interactions between PIP2 and nuclear myosin 1 (NM1), which is a part of chromatin remodelling complex B-WICH and promotes Pol I and Pol II transcription. Recruitment of lamin A into NM1-bound lipo-protein complex via interactions with PIP2 was also demonstrated, along with PIP2 association with core histones in pull-down experiments and the mobility of histone H2B depending on PIP2. We propose that PIP2 might modulate the state of chromatin by interactions with NM1, core histones and lamin A; PIP2 may thus play an important role in the organization of chromatin architecture and thus in regulation of gene transcription.
Permanent Link: http://hdl.handle.net/11104/0231826