Arrangement of kinetochore proteins and satellite DNA in neuronal interphase nuclei: changes induced by gamma-aminobutyric acid (GABA).

Discrete chromatin domains occupy specific nuclear compartments in neuronal interphase nuclei. Nuclear rotation, defined as the motion of interphase chromatin domains, has been proposed to function in the placement of specific chromatin domains to nuclear compartments which are appropriate to the physiological state or the state of differentiation of the cell. Rates of this chromatin motion may be increased by agents, including gamma-amino butyric acid (GABA), which may cause changes in gene expression. To test whether GABA also causes a spatial rearrangement of specific chromatin domains, the three-dimensional distribution of kinetochores in nuclei of mouse dorsal root ganglion neurons was determined by immunofluorescence. In addition, centromeric satellite DNA sequences were localized by in situ hybridization using a biotinylated mouse satellite DNA probe followed by immunofluorescence. Kinetochores occurred in clusters, associated with nucleoli or in intermediate nucleoplasmic regions, between the nucleolus and the nuclear membrane. Clusters of satellite DNA sequences were found either associated with nucleoli or throughout the nucleoplasm. Strikingly, nucleoplasmic kinetochores consistently occupied a 5-microns distance from the nuclear center, representing 70% of the spherical nuclear radius. Exposure of neurons to GABA induced a significant reorganization of kinetochores which may represent movement of chromosomes to alternate nuclear compartments to accommodate a new transcriptional state.