First described in 1948, the Nuclear Matrix refers to a network of fibres found inside the nucleus of all animal, plant, fungi and bacterial (etc.) cells, It has also been termed the “Nuclear-Scaffold” or "NuMat".

The function of the matrix is disputed. Some theorists suggest that it's an active structure involved in biochemical and genetic transport - as it contains proteins, chaperones, DNA/RNA-binding proteins, chromatin remodeling and transcription factors (Source : Wikipedia).

Others say it's simply an artifact of cell-extraction techniques.

When cell nuclei (or cells) are extracted in certain ways, an extensive array of filaments is observed in the remnant nucleus: “the nuclear matrix.” Onto this framework virtually every step in gene readout has been conceptually draped. Some investigators worshipfully attribute to this envisioned nuclear scaffold the same biochemically enabling attributes that the cytoskeleton (demonstrably) conveys for cell shape, cell locomotion, intracellular vesicular traffic, and chromosome movement during cell division. But many other investigators consider this nuclear matrix fraction to be a global aggregation phenomenon. Few aspects of contemporary eukaryotic cell biology have been more contentious."

Source : Half a Century of “The Nuclear Matrix”Molecular Biology of the Cell. 11(3): 799–805.