Date of Award

Winter 1-1-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy In Regulatory Biology Degree

Department

Biological, Geological and Environmental Sciences

First Advisor

Weyman, Crystal M.

Second Advisor

Dr. Alexandru Almasan

Third Advisor

Dr. Anton A. Komar, BGES

Abstract

The formation of functional skeletal muscle is the consequence of both the differentiation and apoptosis of skeletal myoblasts. Ex vivo culture of skeletal myoblasts provides a tractable model for the study of these two coordinately regulated processes. We have previously reported that 23A2 myoblasts stably expressing a dominant negative Death Receptor 5 (A2:dnDR5 myoblasts) exhibit decreased basal mRNA and protein expression of the master muscle regulatory transcription factor MyoD. This decrease at the mRNA level is not a consequence of altered stability. Binding of the transcription factor SRF to a non-canonical CArG box within a serum response element (SRE) in the distal regulatory region (DRR) of the MyoD gene is required for basal MyoD expression. Herein, we report that A2:dnDR5 myoblasts exhibit a decrease in the amount of SRF bound at this CArG box. Additionally, in A2:dnDR5 myoblasts, we observe a decrease in the phosphorylation indicative of activation of SRF as well as a decrease in the phosphorylation indicative of activation of the mitogen-activated protein kinase p38, which is known to activate SRF. Pharmacological inhibition of p38, or of caspase-3, in parental 23A2 myoblasts mimics the decreased activation of SRF and p38, the decreased binding of SRF to the MyoD CArG box, and the decreased levels of MyoD mRNA and protein detected in the A2:dnDR5 myoblasts. Taken together, these results suggest that v basal signaling through DR5 to caspase 3 leads to the activation of p38 and subsequently SRF to maintain basal expression of MyoD

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