Nuclear matrix

Multicellular organisms are characterized by differentiated, that is, specialized cells that in turn have a characteristic architecture, as well as ways to communicate with each other. Both components - structure and interaction - are mediated by protein networks that are available on contact points with each other. From the outside ( extracellular ) to the inside ( nucleus ) these networks are:

• The extracellular matrix, mostly specialized collagen braids, which are produced and secreted by the cell itself embedded,
• The cytoskeleton of microtubules, actin microfilaments and intermediate filaments or,
• As well as the core skeleton, also called nuclear matrix. Outstanding components here are the lamins, which are located in the nuclear envelope and, as we know now inside the cell nucleus, and SAF -A ( scaffold attachment factor A, also described as hnRNP -U). In addition, cell-specific factors are included, which recently assigned meaning in the diagnosis of malignant degeneration.

This nucleated cells of higher organisms ( eukaryotes ) are much more complicated structured as bacterial cells. The basic difference is the nuclear membrane, which separates the DNA from the cytoplasm. Each of the 46 chromosomes of a human cell contains 48-240 million base pairs, which corresponds to a length of 1.6 to 8.2 cm, ( a total of 2 m of DNA ). How can a thread of this length disappear in a core with 5-30 micron diameter? The secret are the organizing principles of chromatin, a complex of DNA, RNA and proteins, which together can legitimate folding in several stages, and thus a variety of epigenetic regulation of gene expression. Lower levels include the nucleosome 1974 discovered a protein complex to which the DNA is wound about two turns. The total of 25 million nucleosomes of a mammalian cell in turn are organized in the form of 30 000 loops -shaped chromatin (Figure). A classical model suggests that this loop organization by attachment of specific DNA elements, which are called S / MARs ( scaffold / matrix attachment regions), to the protein backbone of the nucleus ( the nuclear matrix; gray fields) maintained.

Recent studies indicate a considerable dynamics of this complex structure, which is influenced by the type and differentiation state of the cell.