Satellite Cells in Skeletal Muscle of the Hibernating Dormouse, a Natural Model of Quiescence and Re-Activation: Focus on the Cell Nucleus

Abstract

Satellite cells (SCs) participate in skeletal muscle plasticity/regeneration. Activation of SCs implies that nuclear changes underpin a new functional status. In hibernating mammals, periods of reduced metabolic activity alternate with arousals and resumption of bodily functions, thereby leading to repeated cell deactivation and reactivation. In hibernation, muscle fibers are preserved despite long periods of immobilization. The structural and functional characteristics of SC nuclei during hibernation have not been investigated yet. Using ultrastructural and immunocytochemical analysis, we found that the SCs of the hibernating edible dormouse, Glis glis, did not show apoptosis or necrosis. Moreover, their nuclei were typical of quiescent cells, showing similar amounts and distributions of heterochromatin, pre-mRNA transcription and processing factors, as well as paired box protein 7 (Pax7) and the myogenic differentiation transcription factor D (MyoD), as in euthermia. However, the finding of accumulated perichromatin granules (i.e., sites of storage/transport of spliced pre-mRNA) in SC nuclei of hibernating dormice suggested slowing down of the nucleus-to-cytoplasm transport. We conclude that during hibernation, SC nuclei maintain similar transcription and splicing activity as in euthermia, indicating an unmodified status during immobilization and hypometabolism. Skeletal muscle preservation during hibernation is presumably not due to SC activation, but rather to the maintenance of some functional activity in myofibers that is able to counteract muscle wasting.

MyoD is a 3D genome structure organizer for muscle cell identity

“…It will be interesting to determine which signals ultimately initiate MyoD's loop specification layer of genetic regulation at the earliest possible stage of myogenic-lineage-specific cell fate determination. It was recently reported that quiescent muscle stem cells (also known as satellite cells, SCs) have relatively dense heterochromatin [72][73][74][75] and depletion of the paired-box transcription factor, Pax7, significantly reduces heterochromatin condensation in rare surviving SCs 72,73 , indicating that Pax7 regulates heterochromatin structure in quiescent muscle cells. Pax7 also critically contributes to the ability of SCs to generate committed myogenic progenitors by directly regulating Myf5 and MyoD [76][77][78] .…”

Physical Training Chronically Stimulates the Motor Neuron Cell Nucleus in the Ts65Dn Mouse, a Model of Down Syndrome

“…Ultrathin sections were processed for immunocytochemistry by using mouse monoclonal antibodies directed against phosphorylated polymerase II (Abcam, Cambridge, MA, USA; ab24759), the activated form of the enzyme occurring at pre-mRNA transcription sites [37,38], (Sm)snRNP (small nuclear RiboNucleoProtein) core protein (Abcam, ab3138), involved in the early splicing of pre-mRNA [39] or rabbit polyclonal antibody directed against fibrillarin (Cytoskeleton Inc., Denver, CO, USA), an early splicing factor of pre-rRNA [40]. Sections were floated for 3 min on normal goat serum (NGS) diluted 1:100 in PBS and then incubated for 17 h at 4 • C with the primary antibodies, all diluted 1:10 in PBS containing 0.1% bovine serum albumin (Fluka, Buchs, Switzerland) and 0.05% Tween 20.…”

Contusion concomitant with ischemia injury aggravates skeletal muscle necrosis and hinders muscle functional recovery

“…SCs remain quiescent (in a nondividing state) in uninjured muscle and can be identified by the expression of Pax7. 38 After injury, quiescent SCs become activated and give rise to myogenic progenitors that massively proliferate, differentiate, and fuse to form new myofibers. This process is partially mediated by induced expression of MyoD and other myogenic regulatory factors (MRFs).…”