Nuclear matrix

In biology, the nuclear matrix is the network of fibres found throughout the inside of a cell nucleus and is somewhat analogous to the cell cytoskeleton. However, in contrast to the cytoskeleton, the nuclear matrix has been proposed to be a highly dynamic structure, perhaps more like a dynamic sponge with open compartments for free diffusion of molecules in the nucleus. The nuclear matrix, along with the nuclear lamina aid in organizing the genetic information within the cell.

The exact function of this matrix is still disputed, and its very existence has recently been called into question. Evidence for such a structure was recognised as long ago as 1948 (Zbarskii and Debov), and consequently many proteins associated with the matrix have been discovered. The presence of intra-cellular proteins is largely indisputable, and it is well recognized that proteins such as the Scaffold, or Matrix Associated Proteins (SAR or MAR) have some role in the organisation of chromatins. There is evidence that the nuclear matrix is involved in regulation of gene expression in Arabidopsis thaliana.

For a long time the question whether a polymer meshwork, a “nuclear matrix” or “nuclear-scaffold” is an essential component of the in vivo nuclear architecture has remained a matter of debate. While there are arguments that the relative position of chromosome territories (CTs), the equivalent of condensed metaphase chromosomes at interphase, may be maintained due to steric hindrance or electrostatic repulsion forces between the apparently highly structured CT surfaces, this concept has to be reconciled with observations according to which cells treated with the classical matrix-extraction procedures maintain defined territories up to the point where a minor subset of acidic nuclear matrix proteins is released – very likely those proteins that governed their association with the nuclear skeleton.

S/MARs (scaffold/matrix attachment elements), the DNA regions that are thought to attach genomic DNA to the nuclear skeleton, show an ever increasing spectrum of established biological activities. All these activities are in agreement with (or most easily explained by) the nuclear matrix hypothesis. This is one justification for maintaining this concept before equally plausible alternative models emerge.

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