The Role of FgF2 in Skeletal Myogenesis of Chick Presomitic Mesoderm Lyudmila Kruzhkova & Peter Burgess, Franklin & Marshall College, Lancaster, PA

Objective
To test the role of the FgF2 in the skeletal muscle cell differentiation of the presomitic mesoderm of stage 14 chick embryos.

Introduction
Differentiation of muscle cells occurs in three stages. During the first stage the cells are withdrawn from the cell cycle, and the genes associated with myosin synthesis are expressed. The mononucleated cells that engage in myosin synthesis are the myoblasts proper [4]. If growth factors (ex. FgF2) are present at this stage, the cells will proliferate, but will not differentiate. If the growth factors are depleted or absent, myoblasts will secretfibronectin into the extracellular matrix and bind to the fibronectin receptor a5b1 integrin. If this adhesion is blocked, muscle development ceases. Thus, the integrin- fibronection attachment is critical for initiating the myoblast to differentiate into muscle cell. During the second stage, the myoblasts are aligned together into chains. Identity of species is not important as long as both cells are myoblasts. The third stage, cell fusion, is mediated by metalloproteins called meltrins [3].

Basic Fibroblast growth Factor 2 (FgF2) promotes myoblast cell division, but inhibits myoblast differentiation by suppressing MyoD and myogenin. The MyoD gene encodes a nuclear DNA-binding protein that can bind to regions of the DNA adjacent to muscle-specific genes and activate these genes. The MyoD gene is expressed only in cells of the muscle lineage [3]. Most FgFs are capable of blocking the myoblast surface FGF recetors, resulting in undifferentiation [5]. Also, FGF receptors are lost after myoblast differentiation due to the downregulation of FGF receptor mRNA[5].