This determines differences in gene expression and cell differentiation. AP-1 controls a number of cellular processes including differentiation, proliferation, and apoptosis. EGF results effective in cellular proliferation, differentiation and survival. It is well known that DNA methylation is associated with cell differentiation and proliferation. It effects transcription of genes required for mesoderm formation and cellular differentiation. IL-4 is the positive feedback cytokine for T2 cells differentiation. It activates genes in Sertoli cells, which promote differentiation of spermatogonia. Epigenetic mechanisms were a necessary part of the evolutionary origin of cell differentiation. They play an important role in regulating cell division, cellular differentiation, and morphogenesis. This is done through controlling the expression of the transcription factors which regulate hair differentiation. It is essential for osteoblastic differentiation and skeletal morphogenesis. Processes of tension such as stretching and relaxing increased differentiation into muscle cells. Growth factors comprise the second major set of candidates of epigenetic regulators of cellular differentiation. RNA molecules are an important type of intracellular differentiation control signal. Myostatin is a protein responsible for inhibiting muscle differentiation and growth.