Unraveling the Organization of the Internal Nuclear Matrix: RNA-Dependent Anchoring of NuMA to a Lamin Scaffold

The remodeling of nuclear organization during differentiation and the dramatic alteration of nuclear organization associated with cancer development are well documented. However, the importance of tissue architecture in the control of nuclear organization remains to be determined. Differentiation of mammary epithelial cells into functional tissue structures, in three-dimensional culture, is characterized by a specific tissue architecture (i.e. a basoapical polarity axis), cell cycle exit and maintenance of cell survival. Here we show that induction of partial differentiation (i.e. basal polarity only, cell cycle exit and cell survival) by epigenetic mechanisms in malignant breast cells is sufficient to restore features of differentiation-specific nuclear organization, including perinucleolar heterochromatin, large splicing factor speckles, and distinct nuclear mitotic apparatus protein (NuMA) foci. Upon alteration of nuclear organization using an antibody against NuMA, differentiated non-neoplastic cells undergo apoptosis, whereas partially differentiated malignant cells enter the cell cycle. Non-neoplastic cells cultured under conditions that prevent the establishment of apical polarity also enter the cell cycle upon NuMA antibody treatment. These findings demonstrate that the differentiation status rather than the non-neoplastic or neoplastic origin of cells controls nuclear organization and suggest a link between nuclear organization and epigenetic mechanisms dictated by tissue architecture for the control of cell behavior.

Section: Resultsmentioning

confidence: 99%

The control of tissue architecture over nuclear organization is crucial for epithelial cell fate

Chandramouly

Abad

Knowles

et al. 2007

“…Owing to its involvement in the formation and maintenance of the mitotic spindle (Compton and Cleveland, 1994;Compton, 1998), NuMA overexpression might lead to abnormal chromosome segregation and aneuploidy. Moreover, the suggested involvement of NuMA with various nuclear functions (Gribbon et al, 2002;Barboro et al, 2002) suggests that misregulated NuMA levels in NT embryos might also affect functions important for normal development. This hypothesis remains to be tested.…”

Section: Discussionmentioning

confidence: 99%

Architectural defects in pronuclei of mouse nuclear transplant embryos

Moreira

Robl

Collas

2003

Reprogramming somatic nuclear function by transplantation of nuclei into recipient oocytes is associated with a morphological remodeling of the somatic nucleus. Successful cloning of animals by nuclear transplantation (NT) demonstrates that reprogramming somatic cell function is possible. However, low pregnancy rates and high frequencies of lethal abnormalities in animals born suggest that reprogramming is rarely complete. To address this issue, we tested the hypothesis that nuclear transplantation leads to nuclear remodeling deficiencies. We report the identification of several markers of morphological remodeling, or lack thereof, of mouse cumulus cell nuclei after transplantation into oocytes. Notably, nuclear transplant mouse embryos exhibit nuclear assembly of the differentiated cell-specific A-type lamins at the one-cell stage, as a result of misregulation of lamin A gene expression. The transplanted nuclei also display enhanced concentration of the nuclear matrix-associated protein NuMA as a result of translation from maternal mRNA and de novo transcription. The A-kinase anchoring protein 95 (AKAP95), a marker of the nuclear envelope-chromatin interface, is of somatic origin. Furthermore, greater resistance of AKAP95 and DNA to in situ extractions of one-cell stage NT embryos with non-ionic detergent, DNase, RNase and NaCl reflects an enhanced proportion of heterochromatin in these embryos. Passage through first embryonic mitosis does not rescue the defects detected in one-cell stage embryos. We propose that somatic nuclear reprogramming deficiencies by NT might emanate from, at least in part, failure to remodel the somatic nucleus morphologically into a functional embryonic nucleus.

“…However, although there is some evidence for an internal nucleoskeleton containing B-type lamins (Hozak et al, 1995;Barboro et al, 2002), the significance of this is difficult to assess as so little is known about the structure of the peripheral and internal lamin networks (Gruenbaum et al, 2003;Broers et al, 2006).…”

Section: Chromatin Loops and The Nucleoskeleton In Human Cellsmentioning

confidence: 99%

The integrity of a lamin-B1-dependent nucleoskeleton is a fundamental determinant of RNA synthesis in human cells

Tang

Maya-Mendoza

Martin

et al. 2008

103

122

Spatial organisation of nuclear compartments is an important regulator of chromatin function, yet the molecular principles that maintain nuclear architecture remain ill-defined. We have used RNA interference to deplete key structural nuclear proteins, the nuclear lamins. In HeLa cells, we show that reduced expression of lamin B1, but not lamin A/C, severely inhibits RNA synthesis – first by RNA polymerase II and later by RNA polymerase I. Declining levels of transcription correlate with different morphological changes in major nuclear compartments, nucleoli and nuclear speckles. Ultimately, nuclear changes linked to the loss of synthetic activity result in expansion of the inter-chromatin domain and corresponding changes in the structure and spatial organisation of chromosome territories, which relocate towards the nuclear periphery. These results show that a lamin B1-containing nucleoskeleton is required to maintain RNA synthesis and that ongoing synthesis is a fundamental determinant of global nuclear architecture in mammalian cells.