Understanding the role of JARID2 in skeletal muscle proliferation and differentiation

Author

Pramish Mainali, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2016

Degree Name

Master of Science

Department

Molecular Biology Microbiology and Biochemistry

First Advisor

Davie, Judith

Abstract

JARID2 is the founding member of Jumonji family of proteins, which are characterized by their ability to demethylate histone proteins, mainly histone H3. Methylation or demethylation of histone tails has profound effect on transcriptional activity of chromatin. Interestingly, JARID2 is found to be unable to execute demethylation due to alterations in its amino acid sequence in its C terminal domain, JmjC. However, this modified C terminal domain is highly conserved throughout vertebrates like human, mouse, chicken, frog and zebrafish along with non-vertebrate like drosophila. While Jarid2 apparently lacks demethylase activity, it has been shown to be required for appropriate targeting of the polycomb repressor complex (PRC2), which methylates H3K27 and represses gene expression. Jarid2 and the PCR2 complex are required for early embryonic development in mice. On the other hand, studies in mice have shown increased proliferation of cardiomyocytes and fibroblasts upon Jarid2 knockdown, which indicates that JARID2 might also be required for promoting cell differentiation in some cells. JARID2 has also been found to be overexpressed in Rhabdomyosarcoma (RMS), which is the most common soft tissue sarcoma afflicting children. RMS is thought to arise from skeletal muscle precursor cells and RMS cells share many features of skeletal muscle. Loss of JARID2 in RMS cell lines has been shown to decrease proliferation of these cancer cells, suggesting the role of JARID2 in driving cell proliferation. The aim of my study was to understand how JARID2 functions in normal skeletal muscle, which had been unexplored. I performed overexpression and depletion of JARID2 in C2C12 cells (immortalized mouse myoblast cells) to find that, in both cases, it leads to increase in cell proliferation and impaired differentiation. In addition, downregulation in expression of Myogenin, a muscle regulatory factor (MRF) required for skeletal muscle differentiation, several muscle specific genes, p21(a cyclin dependent kinase inhibitor gene) and Rb (a tumor suppressor gene) were observed in both conditions. I concluded that JARID2 is required to maintain a fine balance of proliferation and differentiation in skeletal muscles. Increasing or decreasing JARID2 expression leads to the maintenance of a proliferative stage.