MEF2 Isotypes During Skeletal Myogenesis

Abstract

The MEF2 family of transcription factors (MEF2A, MEF2C, and MEF2D) are crucial during skeletal muscle differentiation. Although the roles of MEF2D isoforms are well established, the roles of MEF2A and MEF2C are not as well understood. This thesis, we investigated the expression, localization, and function of MEF2A and MEF2C, using specific antibodies. While MEF2A is expressed in both proliferating and differentiated myoblasts, protein levels of MEF2C were only detected during differentiation. During early stages of differentiation MEF2A is expressed in both the cytoplasm and the nucleus. However during later stages of differentiation, it is localized predominately in the nucleus. MEF2C appears to be localized differently depending on which isoform is being investigated. Using an affinity purification and mass spectrometry based approach we identified PRMT1 as a unique interacting protein with MEF2A during skeletal muscle differentiation. PRMT1 is a protein arginine methyltransferase which mediates the addition of methyl groups onto various proteins including histone H4 arginine 3 (H3R4) which is associated with gene activation. Both MEF2A and PRMT1 occupy genomic targets of MEF2A. Inhibition of PRMT1 with a specific inhibitor delays C2C12 myoblast differentiation in the early stages of differentiation but no effect was observed during late stage differentiation. The MEF2 family of transcription factors show distinct but overlapping function during skeletal muscle differentiation.