Grant: Discovery Grants Program - Individual

The nucleolus, initially reported in the 1800's, is a phase separated, membraneless sub-nuclear compartment primarily specialized for ribosome biogenesis. The nucleolus exhibits dynamic changes in its architecture depending on a variety of cellular conditions that are intrinsically linked with changes in Pol I mediated transcription of rRNA genes and ultimately to a change in the protein translational capacity of the cell. Thus, modulation of nucleolar morphology may be functionally linked to adaptations in gene expression and cellular function. In the process of muscle cell differentiation (myogenesis), the formation of multinucleated muscle cells (myotubes (MTs)) from committed progenitor cells (myoblasts (MBs)) requires a vast orchestration of gene expression. The transcriptional regulatory program(s) underlying the production of Pol II mediated mRNA transcriptome changes has been well characterized. Conversely, the large changes in protein synthesis necessary to translate the altered transcriptome leading to differentiation and/or post-natal structural changes in muscle tissue are less well understood. Consistent with the idea that changes in nucleolar morphology are linked with changes in protein translational capacity of the cell, in our recent NSERC funded studies we have documented profound changes in nucleolar morphology during the differentiation of myogenic progenitor cells. We have also reported that rRNA production and protein translation are markedly upregulated during myogenesis. In addition, we recently made the novel observation that cJun (a nuclear transcription factor that is part of the AP1 complex) translocates into the nucleolus and can modulate nucleolar morphology (NSERC funded). Thus, these data potentially implicate cJun in nucleolar morphology changes that may also be associated with ribosome biogenesis and protein translational capacity during myogenesis. These observations are the foundation of the current proposal which will assess the following major questions: a) what is the role and regulation of nucleolar morphology changes in the myogenic differentiation program ?; and b) what is the function of cJun in nucleolar function and morphology in myogenic cells ? The experimental strategies to answer these questions will be based on (a)visualization of the effects of perturbation of nucleolar morphology changes on the myogenic differentiation program, and (b) documenting the effects on myogenesis of mutated cJun expression that affect its nucleolar localization. These research questions will be addressed using (i) state of the art cellular/live cell imaging and (ii) next-gen sequencing based genomic methods (ATAC seq, ChIP seq) in cultured myogenic cells. Building on current progress, this experimentation will further define the novel role of nucleolar function and morphology in myogenic cells and the potential role of cJun in this process.