ABSTRACT
BACKGROUND: Radial chromosome positioning in interphase nuclei is nonrandom and can alter according to developmental, differentiation, proliferation, or disease status. However, it is not yet clear when and how chromosome repositioning is elicited. RESULTS: By investigating the positioning of all human chromosomes in primary fibroblasts that have left the proliferative cell cycle, we have demonstrated that in cells made quiescent by reversible growth arrest, chromosome positioning is altered considerably. We found that with the removal of serum from the culture medium, chromosome repositioning took less than 15 minutes, required energy and was inhibited by drugs affecting the polymerization of myosin and actin. We also observed that when cells became quiescent, the nuclear distribution of nuclear myosin 1 beta was dramatically different from that in proliferating cells. If we suppressed the expression of nuclear myosin 1 beta by using RNA-interference procedures, the movement of chromosomes after 15 minutes in low serum was inhibited. When high serum was restored to the serum-starved cultures, chromosome repositioning was evident only after 24 to 36 hours, and this coincided with a return to a proliferating distribution of nuclear myosin 1 beta. CONCLUSIONS: These findings demonstrate that genome organization in interphase nuclei is altered considerably when cells leave the proliferative cell cycle and that repositioning of chromosomes relies on efficient functioning of an active nuclear motor complex that contains nuclear myosin 1 beta.
Subject(s)
Cell Nucleus/metabolism , Chromosomes/ultrastructure , Fibroblasts/metabolism , Actins/metabolism , Adenosine Triphosphatases/metabolism , Cell Cycle , Cell Proliferation , Chromosomes/metabolism , Fluorescent Antibody Technique, Indirect , GTP Phosphohydrolases/metabolism , Humans , In Situ Hybridization, Fluorescence , Models, Biological , Myosins/metabolism , RNA Interference , Ventricular Myosins/metabolismABSTRACT
Rapid interphase chromosome territory repositioning appears to function through the action of nuclear myosin and actin, in a nuclear motor complex. We have found that chromosome repositioning when cells leave the cell cycle is not apparent in cells that have mutant lamin A or that are lacking emerin. We discuss the possibility that there is a functional intranuclear complex comprising four proteins: nuclear actin, lamin A, emerin and nuclear myosin. If any of the components are lacking or aberrant, then the nuclear motor complex involved in moving chromosomes or genes will be dysfunctional, leading to an inability to move chromosomes in response to signalling events.
