Signal transduction pathways involved in myogenesis

Tushar Balkrishna Vaidya, Purdue University

Abstract

Although the inhibition of skeletal muscle differentiation by serum, purified growth factors and oncogenes is well documented, the intracellular signal transduction pathways used by these inhibitors remain poorly understood. My research has focused on understanding the signal transduction pathways which control muscle development with specific emphasis on the role of oncogenes and growth factors during myogenesis. My results have demonstrated that, like the activated H-ras oncogene, the growth factors, basic fibroblast growth factor and transforming growth factor $\beta,$ inhibit myogenesis in the established mouse myogenic cell line, 23A2. In each case, this inhibition was associated with a down-regulation of the myogenic regulatory gene, MyoD1. However, over-expression of the MyoD1 cDNA is able to overcome the inhibition by the H-ras oncogene but not the inhibition of myogenesis by either growth factor, suggesting that these inhibitory agents may be acting through multiple pathways to control muscle development. I have also shown that the differentiation-defective 23A2-ras cells contain elevated levels of the serine-threonine kinase, protein kinase C. While eliminating the high levels of protein kinase C activity does not lead to a reversal of the ras-mediated inhibition, elimination of protein kinase C prior to the introduction of the H-ras oncogene reduces the ability of the oncogene to inhibit myogenesis. This suggests that PKC activity is required to initiate, but not to maintain, the ras-mediated inhibition of myogenesis. In addition, we also have cloned and determined the nucleotide sequence of a genomic DNA fragment containing the rat MyoD1 gene. Mouse fibroblasts transfected with this DNA display a high degree of conversion to a muscle phenotype, suggesting that this genomic clone contains sufficient sequence information to allow the expression of the rat MyoD1 protein in these cells. My results with the effects of basic fibroblast growth factor and transforming growth factor $\beta$ and the involvement of protein kinase C in ras-mediated effects, as well as the cloning for the rat MyoD1 gene, should provide material for further experimentation on the signal transduction pathways involved in the developmental regulation of skeletal muscle differentiation.

Degree

Ph.D.

Advisors

Taparowsky, Purdue University.

Subject Area

Molecular biology

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