Regulation of Myogenin Activation during Skeletal Muscle Differentiation and Reprogramming

Cell differentiation is the foundation for tissue development and regeneration, disease modeling, and cell-based therapies. The differentiation of skeletal myoblasts has been well-studied, and expression of the transcription factor myogenin is recognized as an early indicator of a cell committed to the myogenic differentiation. Not as much is known regarding how individual cells activate myogenin, the dynamics with which this happens, or the genomic regions that regulate this activation beyond the promoter. This research tested the following hypotheses: 1) The single-cell expression profile of myogenin could reveal distinct subpopulations of myogenic cells and indicate unique cell states. 2) The dynamic evolution of myogenin expression is indicative of the processes regulating differentiation. 3) There exist other genomic loci beyond the immediate promoter of myogenin that regulate the expression of myogenin. The primary conclusions of this dissertation are as follows: 1) Differentiating or reprogrammed cells activating myogenin show a bimodal distribution, with cells either expressing low or high levels of myogenin, and there is a critical dose of MyoD required to transition to differentiate. 2) Myogenic lineage commitment can be delayed but not prevented by serum, and myogenic reprogramming can be accelerated by increasing the forced expression of MyoD. 3) In addition to the promoter, there are additional enhancer sites that regulate the expression of myogenin in differentiating myoblasts.