Nuclear matrix

Abstract: The mammalian cell nucleus contains numerous sub-compartments, which have been implicated in essential processes such as transcription and splicing The mechanisms by which nuclear compartments are formed and maintained are unclear More fundamentally, it is not known how proteins move within the cell nucleus We have measured the kinetic properties of proteins in the nucleus of living cells using photobleaching techniques Here we show that proteins involved in diverse nuclear processes move rapidly throughout the entire nucleus Protein movement is independent of energy, which indicates that proteins may use a passive mechanism of movement Proteins rapidly associate and dissociate with nuclear compartments Using kinetic modelling, we determined residence times and steady-state fluxes of molecules in two main nuclear compartments These data show that many nuclear proteins roam the cell nucleus in vivo and that nuclear compartments are the reflection of the steady-state association/dissociation of its 'residents' with the nucleoplasmic space Our observations have conceptual implications for understanding nuclear architecture and how nuclear processes are organized in vivo

Abstract: Mammalian sperm DNA is the most tightly compacted eukaryotic DNA, being at least sixfold more highly condensed than the DNA in mitotic chromosomes. To achieve this high degree of packaging, sperm DNA interacts with protamines to form linear, side-by-side arrays of chromatin. This differs markedly from the bulkier DNA packaging of somatic cell nuclei and mitotic chromosomes, in which the DNA is coiled around histone octamers to form nucleosomes. The overall organization of mammalian sperm DNA, however, resembles that of somatic cells in that both the linear arrays of sperm chromatin and the 30-nm solenoid filaments of somatic cell chromatin are organized into loop domains attached at their bases to a nuclear matrix. In addition to the sperm nuclear matrix, sperm nuclei contain a unique structure termed the sperm nuclear annulus to which the entire complement of DNA appears to be anchored when the nuclear matrix is disrupted during decondensation. In somatic cells, proper function of DNA is dependent upon the structural organization of the DNA by the nuclear matrix, and the structural organization of sperm DNA is likely to be just as vital to the proper functioning of the spermatozoa.