Disassembly of nuclear bodies during arousal from hibernation: an in vitro study

In previous studies we demonstrated that during hibernation cell nuclei contain structural constituents usually absent in euthermia. The rapid disappearance of such nuclear bodies upon arousal makes very difficult the in vivo investigation of the disassembly process, which could clarify their functions in nuclear metabolism in the hibernator. In the present study we subjected liver samples taken from hibernating edible dormice ( Glis glis) to different in vitro experimental conditions: at 4 degrees C, to preserve the hypothermic state of the hibernating organism; at 37 degrees C, to simulate the drastic increase in body temperature occurring during arousal; at 37 degrees C, in culture medium containing 10(-5) M delta opioid D-Ala2- D-Leu5 enkephalin, which mimics the activity of the hibernation induction trigger in hibernators. Electron microscopic analysis of hepatocyte nuclei at increasing incubation times revealed the subsequent steps of disassembly of coiled bodies, amorphous bodies and fibro-granular material, the unusual structural constituents accumulating during hibernation in these nuclei. We demonstrated that: (1) a temperature of 37 degrees C induces the disappearance of all nuclear bodies typical of hibernation in a few minutes; (2) both low temperature and hibernation-triggering opioid are able to slow down, although to different extents, the process of disassembly of nuclear bodies; (3) the fibro-granular material rapidly disappears during the early phases of incubation; while (4) coiled bodies and amorphous bodies progressively disassemble as fibrous material. Our results support previous hypotheses based on in vivo observations about a possible role for coiled bodies, amorphous bodies and fibro-granular material as storage/assembly sites of molecules needed for the rapid and massive resumption of transcriptional and post-transcriptional activities upon arousal and suggest a strict correlation between the dynamics and metabolic rate of nuclear bodies.