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Abnormal nuclear shape and impaired mechanotransduction in emerin-deficient cells.

Lammerding J, Hsiao J, Schulze PC, Kozlov S, Stewart CL, Lee RT - J. Cell Biol. (2005)

Bottom Line: Clin.Invest. 113:370-378).Thus, emerin-deficient mouse embryo fibroblasts have apparently normal nuclear mechanics but impaired expression of mechanosensitive genes in response to strain, suggesting that emerin mutations may act through altered transcriptional regulation and not by increasing nuclear fragility.

View Article: PubMed Central - PubMed

Affiliation: Cardiovascular Division, Brigham and Women's Hospital, Boston, MA 02115, USA. jlammerding@rics.bwh.harvard.edu

ABSTRACT
Emery-Dreifuss muscular dystrophy can be caused by mutations in the nuclear envelope proteins lamin A/C and emerin. We recently demonstrated that A-type lamin-deficient cells have impaired nuclear mechanics and altered mechanotransduction, suggesting two potential disease mechanisms (Lammerding, J., P.C. Schulze, T. Takahashi, S. Kozlov, T. Sullivan, R.D. Kamm, C.L. Stewart, and R.T. Lee. 2004. J. Clin. Invest. 113:370-378). Here, we examined the function of emerin on nuclear mechanics and strain-induced signaling. Emerin-deficient mouse embryo fibroblasts have abnormal nuclear shape, but in contrast to A-type lamin-deficient cells, exhibit nuclear deformations comparable to wild-type cells in cellular strain experiments, and the integrity of emerin-deficient nuclear envelopes appeared normal in a nuclear microinjection assay. Interestingly, expression of mechanosensitive genes in response to mechanical strain was impaired in emerin-deficient cells, and prolonged mechanical stimulation increased apoptosis in emerin-deficient cells. Thus, emerin-deficient mouse embryo fibroblasts have apparently normal nuclear mechanics but impaired expression of mechanosensitive genes in response to strain, suggesting that emerin mutations may act through altered transcriptional regulation and not by increasing nuclear fragility.

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Emerin and A-type lamin-deficient cells have increased nuclear dynamics and decreased nuclear shape stability. (a) Time-lapse series of fibroblasts over an 8 h, 20 min time period. Images shown were acquired at 5 min, 4 h, and 8 h. Wild-type nuclei (top row) appear very stable over time and have only minor deformations, whereas A-type lamin-deficient nuclei (bottom row) show large nuclear deformations over time. Emerin-deficient nuclei (center row) display an intermediate phenotype, with some nuclei appearing very stable and other nuclei undergoing larger deformations. White crosses denote initial positions of nucleoli, green crosses positions according to the least-square fit assuming linear affine transformations (see Materials and methods), and black crosses the actual nucleoli centroid positions. Deviations between the black and green positions indicate nuclear deformations independent of translation, rotation, or uniform changes in nuclear size. Plots on the right show the average deviation between the actual nucleoli positions and the least-square fit. Time-lapse videos are available online at http://www.jcb.org/cgi/content/full/jcb.200502148/DC1. (b) Time courses of the nuclear deformations for wild-type (top), emerin-deficient (center), and A-type lamin-deficient (bottom) fibroblasts, 25 nuclei each. (c) Emerin-deficient cells have significantly increased time-averaged nuclear deformations compared with wild-type cells, but to a much lesser extent than A-type lamin-deficient cells (time-averaged nuclear deformation = 0.23 ± 0.015 μm, 0.42 ± 0.038 μm, and 1.11 ± 0.104 μm for wild-type, emerin-deficient, and A-type lamin-deficient cells, respectively; P < 0.0001 for emerin and A-type lamin-deficient vs. wild-type cells). (d) A-type lamin-deficient cells have significantly increased time-averaged nuclear size changes compared with wild-type and emerin-deficient cells (time-averaged normalized size change = 1.018 ± 0.006, 1.023 ± 0.010, and 1.058 ± 0.013 for wild-type, emerin-deficient, and A-type lamin-deficient cells, respectively; P < 0.01 for A-type lamin-deficient vs. wild-type cells).
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fig3: Emerin and A-type lamin-deficient cells have increased nuclear dynamics and decreased nuclear shape stability. (a) Time-lapse series of fibroblasts over an 8 h, 20 min time period. Images shown were acquired at 5 min, 4 h, and 8 h. Wild-type nuclei (top row) appear very stable over time and have only minor deformations, whereas A-type lamin-deficient nuclei (bottom row) show large nuclear deformations over time. Emerin-deficient nuclei (center row) display an intermediate phenotype, with some nuclei appearing very stable and other nuclei undergoing larger deformations. White crosses denote initial positions of nucleoli, green crosses positions according to the least-square fit assuming linear affine transformations (see Materials and methods), and black crosses the actual nucleoli centroid positions. Deviations between the black and green positions indicate nuclear deformations independent of translation, rotation, or uniform changes in nuclear size. Plots on the right show the average deviation between the actual nucleoli positions and the least-square fit. Time-lapse videos are available online at http://www.jcb.org/cgi/content/full/jcb.200502148/DC1. (b) Time courses of the nuclear deformations for wild-type (top), emerin-deficient (center), and A-type lamin-deficient (bottom) fibroblasts, 25 nuclei each. (c) Emerin-deficient cells have significantly increased time-averaged nuclear deformations compared with wild-type cells, but to a much lesser extent than A-type lamin-deficient cells (time-averaged nuclear deformation = 0.23 ± 0.015 μm, 0.42 ± 0.038 μm, and 1.11 ± 0.104 μm for wild-type, emerin-deficient, and A-type lamin-deficient cells, respectively; P < 0.0001 for emerin and A-type lamin-deficient vs. wild-type cells). (d) A-type lamin-deficient cells have significantly increased time-averaged nuclear size changes compared with wild-type and emerin-deficient cells (time-averaged normalized size change = 1.018 ± 0.006, 1.023 ± 0.010, and 1.058 ± 0.013 for wild-type, emerin-deficient, and A-type lamin-deficient cells, respectively; P < 0.01 for A-type lamin-deficient vs. wild-type cells).

Mentions: Liu et al. (2000) previously demonstrated that nuclei of lamin-deficient Caenorhabditis elegans cells display significant shape changes over time. To assess dynamic changes in nuclear shape in A-type lamin-deficient and emerin-deficient mouse embryo fibroblasts, we analyzed nuclear shape stability using time-lapse imaging. Phase-contrast images were acquired every 5 min over an 8 h, 20 min period of time for a total of 100 frames. Nuclear motion and deformation were quantified by tracking individual nucleoli within a given nucleus over time (Fig. 3 a) and subsequently computing the translation, rotation, and deformation from these measurements. Cells that underwent mitosis during the observation period were excluded from the analysis. We defined the nuclear deformation as the average deviation from a linear affine transformation, i.e., a change in geometry that can be reduced to a combination of translation, rotation, and scaling in which relative positions to each other are maintained.


Abnormal nuclear shape and impaired mechanotransduction in emerin-deficient cells.

Lammerding J, Hsiao J, Schulze PC, Kozlov S, Stewart CL, Lee RT - J. Cell Biol. (2005)

Emerin and A-type lamin-deficient cells have increased nuclear dynamics and decreased nuclear shape stability. (a) Time-lapse series of fibroblasts over an 8 h, 20 min time period. Images shown were acquired at 5 min, 4 h, and 8 h. Wild-type nuclei (top row) appear very stable over time and have only minor deformations, whereas A-type lamin-deficient nuclei (bottom row) show large nuclear deformations over time. Emerin-deficient nuclei (center row) display an intermediate phenotype, with some nuclei appearing very stable and other nuclei undergoing larger deformations. White crosses denote initial positions of nucleoli, green crosses positions according to the least-square fit assuming linear affine transformations (see Materials and methods), and black crosses the actual nucleoli centroid positions. Deviations between the black and green positions indicate nuclear deformations independent of translation, rotation, or uniform changes in nuclear size. Plots on the right show the average deviation between the actual nucleoli positions and the least-square fit. Time-lapse videos are available online at http://www.jcb.org/cgi/content/full/jcb.200502148/DC1. (b) Time courses of the nuclear deformations for wild-type (top), emerin-deficient (center), and A-type lamin-deficient (bottom) fibroblasts, 25 nuclei each. (c) Emerin-deficient cells have significantly increased time-averaged nuclear deformations compared with wild-type cells, but to a much lesser extent than A-type lamin-deficient cells (time-averaged nuclear deformation = 0.23 ± 0.015 μm, 0.42 ± 0.038 μm, and 1.11 ± 0.104 μm for wild-type, emerin-deficient, and A-type lamin-deficient cells, respectively; P < 0.0001 for emerin and A-type lamin-deficient vs. wild-type cells). (d) A-type lamin-deficient cells have significantly increased time-averaged nuclear size changes compared with wild-type and emerin-deficient cells (time-averaged normalized size change = 1.018 ± 0.006, 1.023 ± 0.010, and 1.058 ± 0.013 for wild-type, emerin-deficient, and A-type lamin-deficient cells, respectively; P < 0.01 for A-type lamin-deficient vs. wild-type cells).
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fig3: Emerin and A-type lamin-deficient cells have increased nuclear dynamics and decreased nuclear shape stability. (a) Time-lapse series of fibroblasts over an 8 h, 20 min time period. Images shown were acquired at 5 min, 4 h, and 8 h. Wild-type nuclei (top row) appear very stable over time and have only minor deformations, whereas A-type lamin-deficient nuclei (bottom row) show large nuclear deformations over time. Emerin-deficient nuclei (center row) display an intermediate phenotype, with some nuclei appearing very stable and other nuclei undergoing larger deformations. White crosses denote initial positions of nucleoli, green crosses positions according to the least-square fit assuming linear affine transformations (see Materials and methods), and black crosses the actual nucleoli centroid positions. Deviations between the black and green positions indicate nuclear deformations independent of translation, rotation, or uniform changes in nuclear size. Plots on the right show the average deviation between the actual nucleoli positions and the least-square fit. Time-lapse videos are available online at http://www.jcb.org/cgi/content/full/jcb.200502148/DC1. (b) Time courses of the nuclear deformations for wild-type (top), emerin-deficient (center), and A-type lamin-deficient (bottom) fibroblasts, 25 nuclei each. (c) Emerin-deficient cells have significantly increased time-averaged nuclear deformations compared with wild-type cells, but to a much lesser extent than A-type lamin-deficient cells (time-averaged nuclear deformation = 0.23 ± 0.015 μm, 0.42 ± 0.038 μm, and 1.11 ± 0.104 μm for wild-type, emerin-deficient, and A-type lamin-deficient cells, respectively; P < 0.0001 for emerin and A-type lamin-deficient vs. wild-type cells). (d) A-type lamin-deficient cells have significantly increased time-averaged nuclear size changes compared with wild-type and emerin-deficient cells (time-averaged normalized size change = 1.018 ± 0.006, 1.023 ± 0.010, and 1.058 ± 0.013 for wild-type, emerin-deficient, and A-type lamin-deficient cells, respectively; P < 0.01 for A-type lamin-deficient vs. wild-type cells).
Mentions: Liu et al. (2000) previously demonstrated that nuclei of lamin-deficient Caenorhabditis elegans cells display significant shape changes over time. To assess dynamic changes in nuclear shape in A-type lamin-deficient and emerin-deficient mouse embryo fibroblasts, we analyzed nuclear shape stability using time-lapse imaging. Phase-contrast images were acquired every 5 min over an 8 h, 20 min period of time for a total of 100 frames. Nuclear motion and deformation were quantified by tracking individual nucleoli within a given nucleus over time (Fig. 3 a) and subsequently computing the translation, rotation, and deformation from these measurements. Cells that underwent mitosis during the observation period were excluded from the analysis. We defined the nuclear deformation as the average deviation from a linear affine transformation, i.e., a change in geometry that can be reduced to a combination of translation, rotation, and scaling in which relative positions to each other are maintained.

Bottom Line: Clin.Invest. 113:370-378).Thus, emerin-deficient mouse embryo fibroblasts have apparently normal nuclear mechanics but impaired expression of mechanosensitive genes in response to strain, suggesting that emerin mutations may act through altered transcriptional regulation and not by increasing nuclear fragility.

View Article: PubMed Central - PubMed

Affiliation: Cardiovascular Division, Brigham and Women's Hospital, Boston, MA 02115, USA. jlammerding@rics.bwh.harvard.edu

ABSTRACT
Emery-Dreifuss muscular dystrophy can be caused by mutations in the nuclear envelope proteins lamin A/C and emerin. We recently demonstrated that A-type lamin-deficient cells have impaired nuclear mechanics and altered mechanotransduction, suggesting two potential disease mechanisms (Lammerding, J., P.C. Schulze, T. Takahashi, S. Kozlov, T. Sullivan, R.D. Kamm, C.L. Stewart, and R.T. Lee. 2004. J. Clin. Invest. 113:370-378). Here, we examined the function of emerin on nuclear mechanics and strain-induced signaling. Emerin-deficient mouse embryo fibroblasts have abnormal nuclear shape, but in contrast to A-type lamin-deficient cells, exhibit nuclear deformations comparable to wild-type cells in cellular strain experiments, and the integrity of emerin-deficient nuclear envelopes appeared normal in a nuclear microinjection assay. Interestingly, expression of mechanosensitive genes in response to mechanical strain was impaired in emerin-deficient cells, and prolonged mechanical stimulation increased apoptosis in emerin-deficient cells. Thus, emerin-deficient mouse embryo fibroblasts have apparently normal nuclear mechanics but impaired expression of mechanosensitive genes in response to strain, suggesting that emerin mutations may act through altered transcriptional regulation and not by increasing nuclear fragility.

Show MeSH
Related in: MedlinePlus