Ultrastructural analysis of coiled body assembly and disassembly in cell nuclei of hibernating dormice
Hibernating mammals are characterised by intense periodic changes of their metabolic activity through quiescence-reactivation cycles. During these transitions, the structural constituents of the cell nucleus undergo various modifications. In particular, large number of coiled bodies (CBs) accumulate during the hibernation bouts and disappear upon arousal in cell nuclei of different tissues. CBs are enigmatic nuclear organelles occasionally occurring in cells of non-hibernating species, they shuttle between nucleoplasm and nucleolus, and are thought to play a role in the storage and intranuclear transport of nucleoplasmic and nucleolar splicing factors as well as in the regulation of chromatin organization and transcriptome activity. However, CB origin, formation and disassembly is still unclear, and hibernating mammals may represent a suitable model to study these phenomena under physiological conditions. In this work, we investigated by transmission electron microscopy the structural evolution of CBs and their content in their marker protein p80-coilin in liver and brown adipose tissue of the hazel dormouse Muscardinus avellanarius during the euthermic-hibernating-arousal cycle. We found that CBs form in the nucleoplasm at early hibernation as aggregates of threads already containing p80-coilin and other splicing factors, and only in deep hibernation they move to the nucleolus; at arousal, CBs undergo rapid disaggregation in both the nucleoplasm and nucleolus, thus releasing their molecular components in the intranuclear milieu.
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