While each cell in your body contains the same genetic starting material, specialized cell types are dictated by the expression of a particular set of genes. During development, the regulation of these genes changes rapidly in response to morphogen gradients and other biological signaling mechanisms as cells become specialized. In the context of skeletal muscle differentiation, the mesoderm arises from the primitive streak where it splits into the lateral plate, which forms heart muscle and parts of the circulatory system, and paraxial mesoderm, which forms skeletal muscle, smooth muscle, bone, and brown fat [Figure 2].