Nuclear structure and the three-dimensional organization of DNA.

The organization of DNA within the nucleus has been demonstrated to be both cell and tissue specific and is arranged in a non-random fashion in both sperm and somatic cells. Nuclear structure has a pivotal role in this three-dimensional organization of DNA and RNA and contributes as well to forming fixed organizing sites for nuclear functions, such as DNA replication, transcription, and RNA processing. In sperm, DNA is also organized in a specific fashion by the nuclear matrix and DNA-protamine interactions. Within somatic cells, the nuclear matrix provides a three-dimensional framework for the tissue specific regulation of genes by directed interaction with transcriptional activators. This differential organization of the DNA by the nuclear matrix, in a tissue specific manner, contributes to tissue specific gene expression. The nuclear matrix is the first link from the DNA to the entire tissue matrix system and provides a direct structural linkage to the cytomatrix and extracellular matrix. In summary, the tissue matrix serves as a dynamic structural framework for the cell which interacts to organize and process spatial and temporal information to coordinate cellular functions and gene expression. The tissue matrix provides a structural system for integrating form and function.