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Protein Tpr is required for establishing nuclear pore-associated zones of heterochromatin exclusion.

Krull S, Dörries J, Boysen B, Reidenbach S, Magnius L, Norder H, Thyberg J, Cordes VC - EMBO J. (2010)

Bottom Line: HEZ occurrence depended on the NPC-associated protein Tpr and its large coiled coil-forming domain.RNAi-mediated loss of Tpr allowed condensing chromatin to occur all along the NE's nuclear surface, resulting in HEZs no longer being established and NPCs covered by heterochromatin.These results assign a central function to Tpr as a determinant of perinuclear organization, with a direct role in forming a morphologically distinct nuclear sub-compartment and delimiting heterochromatin distribution.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institut für Biophysikalische Chemie, Göttingen, Germany.

ABSTRACT
Amassments of heterochromatin in somatic cells occur in close contact with the nuclear envelope (NE) but are gapped by channel- and cone-like zones that appear largely free of heterochromatin and associated with the nuclear pore complexes (NPCs). To identify proteins involved in forming such heterochromatin exclusion zones (HEZs), we used a cell culture model in which chromatin condensation induced by poliovirus (PV) infection revealed HEZs resembling those in normal tissue cells. HEZ occurrence depended on the NPC-associated protein Tpr and its large coiled coil-forming domain. RNAi-mediated loss of Tpr allowed condensing chromatin to occur all along the NE's nuclear surface, resulting in HEZs no longer being established and NPCs covered by heterochromatin. These results assign a central function to Tpr as a determinant of perinuclear organization, with a direct role in forming a morphologically distinct nuclear sub-compartment and delimiting heterochromatin distribution.

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NPC-associated HEZs of distinct size and shape withstand the expansion of condensed chromatin after PV infection. (A1) TEM of a perpendicular NE cross-section of a non-infected HeLa cell in mid-interphase, with a thin layer of NE-associated heterochromatin between the NPCs. (B1) A PV-infected HeLa cell (assembled from two micrographs) at 12 h post-infection, illustrating the characteristic nuclear distortion and emergence of NPC-associated HEZs (arrows). (A2, B2) Higher magnification views of NE cross-sections of non-infected HeLa cells (A2) and of cells 12 h after PV infection (B2), illustrating the contouring of NPC-associated HEZs by condensed chromatin (cc). Nucleolar materials (no) were excluded from these zones too. Chromatin hyper-condensation was also accompanied by gradual loss of the electron-dense NPC midplanes seen in non-infected cells (white arrowhead), and often by dilation of the NE lumen (arrow) late in the infection process. Bars: 200 nm; same magnification for panels A1 and B1, and panels A2 and B2.
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f1: NPC-associated HEZs of distinct size and shape withstand the expansion of condensed chromatin after PV infection. (A1) TEM of a perpendicular NE cross-section of a non-infected HeLa cell in mid-interphase, with a thin layer of NE-associated heterochromatin between the NPCs. (B1) A PV-infected HeLa cell (assembled from two micrographs) at 12 h post-infection, illustrating the characteristic nuclear distortion and emergence of NPC-associated HEZs (arrows). (A2, B2) Higher magnification views of NE cross-sections of non-infected HeLa cells (A2) and of cells 12 h after PV infection (B2), illustrating the contouring of NPC-associated HEZs by condensed chromatin (cc). Nucleolar materials (no) were excluded from these zones too. Chromatin hyper-condensation was also accompanied by gradual loss of the electron-dense NPC midplanes seen in non-infected cells (white arrowhead), and often by dilation of the NE lumen (arrow) late in the infection process. Bars: 200 nm; same magnification for panels A1 and B1, and panels A2 and B2.

Mentions: In cell lines such as HeLa, only small amounts of heterochromatin are aligned along the NE between neighbouring NPCs (Figure 1A). Local amassments of such heterochromatin occur only sporadically (Supplementary Figure S1A). Furthermore, the frequency of NPCs in these contact regions between heterochromatin clusters and the NE can be notably lower than that in the neighbouring areas (see also Maul, 1977; Garcia-Segura et al, 1989). Therefore, ultrathin sections of such cells only infrequently include perpendicular sections through NPCs juxtaposed to heterochromatin amassments. The few present, however, generally reveal an NPC-associated heterochromatin-free zone, often with seemingly hyperbolic contours or shaped like an isosceles triangle or trapezium with its basis next to the NPC. Similar clearance zones are also seen when the granular, pre-ribosomal material of the nucleolus is positioned directly in front of an NPC (Supplementary Figure S1A). Again though, NPCs are comparatively rare in such contact regions (Maul, 1977).


Protein Tpr is required for establishing nuclear pore-associated zones of heterochromatin exclusion.

Krull S, Dörries J, Boysen B, Reidenbach S, Magnius L, Norder H, Thyberg J, Cordes VC - EMBO J. (2010)

NPC-associated HEZs of distinct size and shape withstand the expansion of condensed chromatin after PV infection. (A1) TEM of a perpendicular NE cross-section of a non-infected HeLa cell in mid-interphase, with a thin layer of NE-associated heterochromatin between the NPCs. (B1) A PV-infected HeLa cell (assembled from two micrographs) at 12 h post-infection, illustrating the characteristic nuclear distortion and emergence of NPC-associated HEZs (arrows). (A2, B2) Higher magnification views of NE cross-sections of non-infected HeLa cells (A2) and of cells 12 h after PV infection (B2), illustrating the contouring of NPC-associated HEZs by condensed chromatin (cc). Nucleolar materials (no) were excluded from these zones too. Chromatin hyper-condensation was also accompanied by gradual loss of the electron-dense NPC midplanes seen in non-infected cells (white arrowhead), and often by dilation of the NE lumen (arrow) late in the infection process. Bars: 200 nm; same magnification for panels A1 and B1, and panels A2 and B2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2876962&req=5

f1: NPC-associated HEZs of distinct size and shape withstand the expansion of condensed chromatin after PV infection. (A1) TEM of a perpendicular NE cross-section of a non-infected HeLa cell in mid-interphase, with a thin layer of NE-associated heterochromatin between the NPCs. (B1) A PV-infected HeLa cell (assembled from two micrographs) at 12 h post-infection, illustrating the characteristic nuclear distortion and emergence of NPC-associated HEZs (arrows). (A2, B2) Higher magnification views of NE cross-sections of non-infected HeLa cells (A2) and of cells 12 h after PV infection (B2), illustrating the contouring of NPC-associated HEZs by condensed chromatin (cc). Nucleolar materials (no) were excluded from these zones too. Chromatin hyper-condensation was also accompanied by gradual loss of the electron-dense NPC midplanes seen in non-infected cells (white arrowhead), and often by dilation of the NE lumen (arrow) late in the infection process. Bars: 200 nm; same magnification for panels A1 and B1, and panels A2 and B2.
Mentions: In cell lines such as HeLa, only small amounts of heterochromatin are aligned along the NE between neighbouring NPCs (Figure 1A). Local amassments of such heterochromatin occur only sporadically (Supplementary Figure S1A). Furthermore, the frequency of NPCs in these contact regions between heterochromatin clusters and the NE can be notably lower than that in the neighbouring areas (see also Maul, 1977; Garcia-Segura et al, 1989). Therefore, ultrathin sections of such cells only infrequently include perpendicular sections through NPCs juxtaposed to heterochromatin amassments. The few present, however, generally reveal an NPC-associated heterochromatin-free zone, often with seemingly hyperbolic contours or shaped like an isosceles triangle or trapezium with its basis next to the NPC. Similar clearance zones are also seen when the granular, pre-ribosomal material of the nucleolus is positioned directly in front of an NPC (Supplementary Figure S1A). Again though, NPCs are comparatively rare in such contact regions (Maul, 1977).

Bottom Line: HEZ occurrence depended on the NPC-associated protein Tpr and its large coiled coil-forming domain.RNAi-mediated loss of Tpr allowed condensing chromatin to occur all along the NE's nuclear surface, resulting in HEZs no longer being established and NPCs covered by heterochromatin.These results assign a central function to Tpr as a determinant of perinuclear organization, with a direct role in forming a morphologically distinct nuclear sub-compartment and delimiting heterochromatin distribution.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institut für Biophysikalische Chemie, Göttingen, Germany.

ABSTRACT
Amassments of heterochromatin in somatic cells occur in close contact with the nuclear envelope (NE) but are gapped by channel- and cone-like zones that appear largely free of heterochromatin and associated with the nuclear pore complexes (NPCs). To identify proteins involved in forming such heterochromatin exclusion zones (HEZs), we used a cell culture model in which chromatin condensation induced by poliovirus (PV) infection revealed HEZs resembling those in normal tissue cells. HEZ occurrence depended on the NPC-associated protein Tpr and its large coiled coil-forming domain. RNAi-mediated loss of Tpr allowed condensing chromatin to occur all along the NE's nuclear surface, resulting in HEZs no longer being established and NPCs covered by heterochromatin. These results assign a central function to Tpr as a determinant of perinuclear organization, with a direct role in forming a morphologically distinct nuclear sub-compartment and delimiting heterochromatin distribution.

Show MeSH
Related in: MedlinePlus