SELECTIVE IMAGING AND ABLATION OF TARGETED CELLS AND SUBCELLULAR STRUCTURES AT THE MOUSE NEUROMUSCULAR JUNCTION

The neuromuscular junction (NMJ) is the ultimate synapse in the somatic motor system, allowing skeletal muscle to be controlled by the central nervous system. It is a classic model synapse because of its large size and accessibility, and as such, cellular components of the NMJ have been selectively ablated without damaging the other elements to determine the role of that component in the healthy system as well as providing details on whether and how the system recovers from injury. For the past two decades, researchers have developed new methods of monitoring specific cell types, and now more recently, genetically ablating specific cell types. These new methods have allowed researchers to perform previously impossible experimental paradigms, and have further increased our knowledge about the biology of the mammalian synapse. Here, I have combined molecular tools in new ways to address hypotheses previously too difficult to pursue. One way in which I have done so is to combine selective, vital labeling of Schwann cells (SCs) with the ability to genetically ablate those SCs. I found that the motor axons largely survive and maintain innervation until SCs regenerate their former position of capping the axon terminal. Additionally, the SCs, upon return, remodel the NMJ in such a way that suggests they are repeating certain developmental functions. I have also bred together a mouse line that has allowed for the selective, vital imaging of myonuclei, which can be useful for studying myonuclear dynamics in myopathic conditions, such as sarcopenia or muscular dystrophy. I have used this myonuclear label mouse line along with a mouse line with transgenic labelingiii of axons and Schwann cells to assess cellular damage after cardiotoxin exposure finding that it causes acute but extensive retraction of axon terminals one day after exposure, suggesting a relationship between the extent of muscle damage and the extent of motor axon withdrawal. The results described here provide new information about the consequences of damage to individual cellular compartments of the NMJ, and may provide insights into treating disease states that involve injury to one or more aspects of the neuromuscular system