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

Abstract

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.

Mammalian hibernation: differential gene expression and novel application of epigenetic controls

“…Hence, the formation of nuclear bodies may be another effective method of global transcriptional suppression during hibernation. Interestingly, the delta opioid D-Ala2-D-Leu5 enkephalin, which mimics the activity of the hibernation induction trigger (Oeltgen et al, 1988), delayed the disassembly of nuclear bodies during in vitro studies with G. glis liver (Malatesta et al, 2001). This provides more evidence that nuclear body formation and protein SUMOylation has a physiological function in hibernation.…”

“…Nuclear body formation may regulate transcription in at least three ways: (1) by titrating the effective concentrations of nuclear transcription factors by sequestration/release, (2) by mediating post-translational modifications to transcription factors that may occur preferentially in the nuclear body, or (3) by acting as subnuclear compartmentalization centres (Zhong et al, 2000). The formation of several types of torpor phase-specific nuclear bodies has been extensively examined in hibernating dormice, Glis glis (summarized in Malatesta et al, 2001). These disappear rapidly upon arousal and, therefore, appear to be storage/assembly sites for molecules needed for the rapid and massive resumption of transcriptional and post-transcriptional activities upon arousal (Malatesta et al, 2001).…”

“…The formation of several types of torpor phase-specific nuclear bodies has been extensively examined in hibernating dormice, Glis glis (summarized in Malatesta et al, 2001). These disappear rapidly upon arousal and, therefore, appear to be storage/assembly sites for molecules needed for the rapid and massive resumption of transcriptional and post-transcriptional activities upon arousal (Malatesta et al, 2001). Storage of SUMOylated proteins may be one role of nuclear body formation during torpor (Lee et al, 2007).…”

The involvement of mRNA processing factors TIA-1, TIAR, and PABP-1 during mammalian hibernation

“…2b and Table 3). The presence of nuclei containing structural components in response to the hibernating phenotype has also been observed in the hazel dormouse (Muscardinus avellanarius) and the edible dormouse (Glis glis) (Malatesta et al 1994(Malatesta et al , 1999(Malatesta et al , 2001(Malatesta et al , 2008; however, the ground squirrel subnuclear structures presently described appear as single foci/nucleus with distinct characteristics, including size. Since nuclear TIA-1 and TIAR perform a range of functions including rendering mRNA translationally silent, modulating the rates of gene transcription, and regulating constitutive and alternative pre-mRNA splicing (Förch et al 2001;López de Silanes et al 2005;Suswam et al 2005), further studies were performed in order to better understand the function of subnuclear foci during torpor.…”

Regulation of hypometabolism: insights into epigenetic controls

“…Electron microscopy revealed condensed coiled bodies and amorphous bodies in nucleoplasm during torpor as well as changes in the shape of nucleoli (Malatesta et al, 1994;Malatesta et al, 1999); these disassembled during arousal (Malatesta et al, 2001). Tissue-specific differences in pre-mRNA handling were also apparent; hepatocytes showed a preferential accumulation of premRNAs at the splicing stage whereas brown adipocytes stored these at the cleavage stage (Malatesta et al, 2008).…”