Cell differentiation is a crucial and continuous process in multicellular organisms which allows for cell specialization. Both animals and plants have cells which can differentiate into all of the cells required by an adult organism. In animals these cells are embryonic stem cells and in higher plants these cells are termed meristematic cells. Furthermore, only the zygote of a mammal contains blastomeres, cells capable of differentiating into any cell type including placental tissue.
All of an organism’s cells contain the same DNA and this DNA sequence is not altered during cell differentiation. Rather, cells become different through various mechanisms controlled by genes. For example, in different tissues, different genes are expressed and this influences the types of cells present.
However, all cells do express identical genes, known as housekeeping genes. These genes are needed for processes such as metabolism and for producing proteins for mechanisms such as replication. Even though housekeeping genes are present in all cells, their level of expression can vary. For example, in red and white muscle cells, this difference in expression regulates their varying activity levels. Furthermore, the control of this gene expression occurs at a multitude of levels, such as the post-transcriptional level and/or mRNA degradation level, to name a few controls.
Additionally, in the mammalian system, three different cell types exist: germ-line cells, somatic cells and stem cells. Germ-line cells are needed to produce haploid gametes, somatic cells are diploid cells and stem cells are able to become very specialized over infinite periods of division.
Cell differentiation is an essential process because it allows for the production of cells capable of being used for various functions. Although the mechanisms of differentiation and gene control are rather complex, this discussion provides a basic overview on this subject matter.