Adult skeletal muscles have remarkable regenerative capacity. Muscle regeneration occurs when muscle tissue experiences injury, causing a population of normally quiescent muscle-resident stem cells, called satellite cells, to become activated. The CCAAT/enhancer binding proteins known as C/EBPs are transcription factors belonging to the bZIP family. Previous work from our lab has identified C/EBPβ as an important negative regulator of myogenesis. C/EBPβ expression is localized to muscle satellite cells and is downregulated upon induction to differentiate, mirroring the loss of Pax7 expression in early myogenesis. C/EBPβ expression also negatively regulates MyoD protein expression. Leaky ribosomal scanning of the Cebpb mRNA produces three C/EBPβ isoforms: LAP*, LAP and LIP, though the individual role of each of these isoforms has not been investigated in myoblasts. This thesis focuses on determining the role of each of the C/EBPβ isoforms during skeletal muscle differentiation. Forced expression of the C/EBPβ-LIP isoform in myoblasts led to a decrease in Myf5, MyoD, and myogenin expression under differentiation conditions when compared to empty vector controls. Further, the fusion of cells was greatly reduced following differentiation. C/EBPβ-LIP expressing cells also demonstrated a growth defect, with pronounced G1 arrest and features of senescence. In contrast, myoblasts expressing the C/EBPβ-LAP isoform has impaired differentiation, though this was not as pronounced as in C/EBPβ-LIP expressing cells and proliferated normally. While LIP is not normally expressed in primary myoblasts from healthy muscle, the ratio of LIP:LAP was increased in primary myoblasts isolated from mdx mice, an animal model for Duchenne muscular dystrophy. These findings suggest that the regulation of C/EBPβ isoform expression could regulate stem cell stamina and may contribute to defects in muscle regeneration in disease.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/32787 |
| Date | January 2015 |
| Creators | Lee, Hwabin |
| Contributors | Wiper-Bergeron, Nadine |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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