Spatial repositioning of centromeric domains during regrowth of axons in nuclei of murine dorsal root ganglion neurons in vitro.

Specific chromatin domains within interphase nuclei are organized in cell type specific distributions and are rearranged in association with changes in cell function. Axotomy leads to changes in gene expression. Dorsal root ganglion (DRG) neurons in vitro are a model for axotomy because they are detached from their axons in preparation for the culturing procedure. In a test of the hypothesis that neurons regrowing in vitro undergo rearrangement of specific chromatin domains, changes in the distribution of centromere-associated kinetochores proteins within DRG neurons were assessed as a function of time in vitro. Camparison of the kinetochore distributions in neurons in situ to those 24 h after placement into culture showed that the mean proportion (+/-S.E.M.) of kinetochore signals in the karyoplasm decreased from 41.0 +/- 1.8% to 28.6 +/- 3.3%, while the proportion at the nucleolus increased from 35.2 +/- 2.0% to 48.4 +/- 2.9%. This indicated redistribution of centromeric domains to the nucleolus. Between 1 day and 16 days in vitro, signals were redistributed to the nuclear periphery, indicated by an increase in the proportion of signals in this nuclear compartment from 23.0 +/- 4.3% to 37.6 +/- 3.4% and a decrease in the proportion of signals from 48.4 +/- 2.9% to 23.0 +/- 2.3% at the nucleolus. The results indicate that neurite regrowth following axotomy is associated with changes in nuclear topology. The reorganization that occurs within 24 h is speculated to be associated with a recapitulation of a cytoskeletal development program, while later changes in centromeric distributions may be related to cues elicited by in vitro conditions.