Satellite cells (SCs) are muscle stem cells that are required to repair tissue damage upon injury or disease. In resting muscles, majority of satellite cells stay in a quiescent state. In response to injury, SCs will be activated and will go through proliferation and differentiation process. They will further differentiate and fuse to form muscle fibers. This whole process is tightly regulated by many myogenic regulatory factors (MRFs), such as MyoD, Myf5, MRF4 and Myogenin. Apart from these factors, recent discoveries of thousands of large intergenic non-coding RNAs (lincRNAs) that possess regulatory functions indicate the participation of these RNAs in gene regulation. Many of these RNAs are evolutionarily conserved and take parts in many biological processes. Our group has previousl...[ Read more ]

Satellite cells (SCs) are muscle stem cells that are required to repair tissue damage upon injury or disease. In resting muscles, majority of satellite cells stay in a quiescent state. In response to injury, SCs will be activated and will go through proliferation and differentiation process. They will further differentiate and fuse to form muscle fibers. This whole process is tightly regulated by many myogenic regulatory factors (MRFs), such as MyoD, Myf5, MRF4 and Myogenin. Apart from these factors, recent discoveries of thousands of large intergenic non-coding RNAs (lincRNAs) that possess regulatory functions indicate the participation of these RNAs in gene regulation. Many of these RNAs are evolutionarily conserved and take parts in many biological processes. Our group has previously profiled the transcriptomes of quiescent and activated muscle stem cells, and has identified a long non-coding RNA, named lincMyoD, that serves as a positive regulator of myogenic differentiation. By knocking down lincMyoD, we observed down-regulation of Myogenin but no change for MyoD. We thus hypothesize that lincMyoD binds with MyoD to regulate Myogenin expression and promote myogenic differentiation. To further investigate the role of this lincRNA during myogenesis, we tested the interaction between lincMyoD and the 4 myogenic regulatory factors. Only the recruitment of both lincMyoD and MyoD to the proximity of a promoter could trans-activate the downstream reporter. We also used recombinant GST-MRFs to test the physical interactions between lincMyoD and MRFs. Our results show that lincMyoD could bind with MyoD and target downstream gene expression but not other MRFs.

Notch signaling pathway is one of the most important signaling pathways which can define the fate of one cell by its relationship with neighboring cells. For muscle stem cells, previous studies have shown that inhibition of Notch pathway will lead to loss of maintenance of quiescent state and stem cells will lack the ability to self-renew. Characterization of Notch pathway dependent elements can be of great help for the understanding the maintenance of quiescent state of muscle stem cells. Recent whole transcriptome sequencing has revealed a large number of lincRNAs which play important roles in diverse cellular processes. After analyzing sequencing data of Dll1 treated SCs, we were able to determine Notch-dependent lincRNAs. To validate data analysis results, we performed Dll1 treatment on FACS sorted SCs and checked the expression pattern by RT-PCR. Our results showed that there are several Notch-dependent lincRNA candidates that might play essential roles either in quiescence maintenance or activation and we are interested in investigating their roles during myogenic lineage.