Key result
Developmental atrophy and programmed cell death in Manduca sexta resulted in a ~75-80% decline in muscle mass without reducing nuclear number, leading to a ~85% reduction in the myonuclear domain.
In a model lacking satellite cells, skeletal muscle nuclei persist during severe atrophy and programmed cell death, challenging the myonuclear domain hypothesis.
Challenges myonuclear domain hypothesis in satellite cell-free model; leaves open relevance to mammalian atrophy.
Skeletal muscle mass can increase during hypertrophy or decline dramatically in response to normal or pathological signals that trigger atrophy. Many reports have documented that the number of nuclei within these cells is also plastic. It has been proposed that a yet-to-be-defined regulatory mechanism functions to maintain a relatively stable relationship between the cytoplasmic volume and nuclear number within the cell, a phenomenon known as the "myonuclear domain" hypothesis. While it is accepted that hypertrophy is typically associated with the addition of new nuclei to the muscle fiber from stem cells such as satellite cells, the loss of myonuclei during atrophy has been controversial. The intersegmental muscles from the tobacco hawkmoth Manduca sexta are composed of giant syncytial cells that undergo sequential developmental programs of atrophy and programmed cell death at the end of metamorphosis. Since the intersegmental muscles lack satellite cells or regenerative capacity, the tissue is not "contaminated" by these nonmuscle nuclei. Consequently, we monitored muscle mass, cross-sectional area, nuclear number, and cellular DNA content during atrophy and the early phases of cell death. Despite a ∼75-80% decline in muscle mass and cross-sectional area during the period under investigation, there were no reductions in nuclear number or DNA content, and the myonuclear domain was reduced by ∼85%. These data suggest that the myonuclear domain is not an intrinsic property of skeletal muscle and that nuclei persist through atrophy and programmed cell death.
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Schwartz et al. (2016) studied Skeletal muscle atrophy and programmed cell death. Developmental programs of atrophy and programmed cell death was evaluated on Muscle mass, cross-sectional area, nuclear number, and cellular DNA content. Developmental atrophy and programmed cell death in Manduca sexta resulted in a ~75-80% decline in muscle mass without reducing nuclear number, leading to a ~85% reduction in the myonuclear domain.
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