Chromatin motion in neuronal interphase nuclei: Changes induced by disruption of intermediate filaments

Abstract

Motion of nucleoli within interphase nuclei, known as nuclear rotation, may be used as a measure of motion of chromatin domains within the global confines of the nucleus. Mechanisms by which chromatin domains are transposed remain enigmatic. It has been established that nuclei are anchored by a network of intermediate filaments, structural proteins which share epitopes with nuclear lamins and possibly representing a constraint on nuclear rotation. It is postulated that selective removal of this constraint, by acrylamide, would result in increased chromatin motion. Mean rates of nucleolar displacement were quantified in neurons, in vitro. Nuclear rotation increased from a mean control rate of 0.102 +/- 0.002 micron/min (n = 52) to a maximum mean rate of 0.207 +/- 0.026 micron/min (n = 11), after 23 hr of exposure to 4 mM acrylamide. Despite this significant increase in motion of intranuclear domains, cytoplasmic structures in the immediate juxtanuclear area did not exhibit increases in rates of motion. Immunocytochemistry was used to visualize cytoskeletal structures and to assay selective disruption of neurofilaments by acrylamide. Increased rates of chromatin motion coincided with breakdown of the intermediate filament network. Ultrastructural analyses showed that the increase in chromatin motion induced by acrylamide was also associated with a significant (P less than 0.005) change in the thickness of the nuclear lamina, decreasing from 20.9 +/- 5.10 nm (n = 159) in controls to 18.9 +/- 3.1 nm (n = 148), to 19.5 +/- 3.6 nm (n = 240) and to 16.1 +/- 4.4 nm (n = 103) at 4, 8 and 22 hr exposure, respectively. Moreover, the number of mitochondria per unit area changed significantly (P less than 0.0001) with exposure to acrylamide, increasing from 9.1 +/- 2.2 mitochondrial profiles in controls to 16.5 +/- 5.3 profiles after 22 hr exposure to acrylamide. Distribution of other cytoskeletal components, actin and microtubules, was not altered and does not appear to play a significant role in the observed increase in rates of nuclear rotation. We conclude that the removal of the damping effects on chromatin motion normally imposed by the nuclear lamina and by intermediate filaments results in increased chromatin motion.

Spatial coordination between cell and nuclear shape within micropatterned endothelial cells

“…Specific pharmacological agents were used to inhibit the polymerization of actin filaments 47 (latrunculin-A, Enzo Life Sciences, Zandhoven, Belgium), microtubules 48 (Colchicine, Enzo Life Sciences) and to collapse the intermediate filament network 49,50 (Acrylamide and Calyculin A, Sigma). Blebbistatin (Enzo Life Sciences) was used to inhibit myosin II contractility 51 .…”

Onset of Human Cytomegalovirus Replication in Fibroblasts Requires the Presence of an Intact Vimentin Cytoskeleton

“…To determine whether the integrity of the vimentin cytoskeleton is required to facilitate the onset of viral infection, HF were treated with a 5 mM ACR solution for 2, 4, 6, or 8 h prior to infection with either AD169 or TB40/E. ACR is a neurotoxin that has been extensively used to disrupt the organization of IF in neurons and in other cells types (2,20,21,33,75). ACR treatment of HF induced cell rounding and contraction, accompanied by the aggregation of vimentin IF in elongated bundles extending into the cells' retraction fibers (Fig.…”

“…Consistent with literature reports (20,47), actin stress fiber disassembly but no microtubule depolymerization was detected in ACR-treated cells (data not shown). As the emergence of nuclear folds has been described to occur in some vimentin null cells, in cells expressing vimentin mutants or containing thick IF bundles, and in ACRtreated neurons (33,43,76,78), we used the percentage of cells with nuclear invaginations as an estimate of the extent of IF disruption. As expected, an exposure time-dependent increase in percentage values was observed, from 1.5% Ϯ 1% after 2 h to 32% Ϯ 7% after 8 h of continual treatment (Fig.…”

Cell Nuclei Spin in the Absence of Lamin B1

“…Furthermore, there is evidence for docking of lamin B containing mitotic vesicles with vimentin filaments (49). Although we did not investigate disruption of the intermediate filament network in the present study, nuclear rotation has been reported in neuronal interphase nuclei following acrylamide treatment, which results in neurofilament disruption and a decrease in nuclear lamina thickness (50).…”