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 an as 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 (ISMs) 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 ISMs lack satellite cells or regenerative capacity, the tissue is not "contaminated" by these non-muscle 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 either nuclear number or DNA content and the myonuclear domain was reduced by about 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.
- Manduca sexta
- Copyright © 2016, American Journal of Physiology-Cell Physiology