During development, precursor cells can become more specialized by cellular differentiation. The newly synthesized cells therefore can develop into one cell type or another. A single cell can differentiate to function as a neurone or a epithelial cell. In multicelluar organisms, cell differentiation occurs multiple times to form complex system of tissues with specific functions. This process is seen during embryonic development, renewal of tissues, regeneration of missing tissues and cells, etc. Totipotent cells are the only cells that can differentiate into any cell type.