Cell differentiation is a process in which a generic cell develops into a specific type of cell in response to specific triggers from the body or the cell itself. This is the process which allows a single celled zygote to develop into a multicellular adult organism which can contain hundreds of different types of cells. In addition to being critical to embryonic development, cell differentiation also plays a role in the function of many organisms, especially complex mammals, throughout their lives.
When a single cell has the capability of developing into any kind of cell, it is known as totipotent. In mammals, the zygote and the embryo during early stages of development are totipotent, for example. Cells which can differentiate into several different cell types, but not all, are considered to be pluripotent. In both cases, the nucleus is the same, containing all of the genetic information needed to encode the entire organism, but only certain genes are activated.
When an embryo develops, cell differentiation is critical, because it allows the developing organism to create numerous different needed cell types, from neurons which will make up the brain to epidermal cells which will create the upper layers of skin. Once mature, the organism will have germ cells, somatic cells, and adult stem cells. Germ cells are haploid cells which are used in reproduction, while somatic cells make up most of the cells in the body, with over 250 known kinds of cell in the human body alone.
Adult stem cells which are able to engage in cell differentiation are found in several areas of the body. One of the most important sites for adult stem cells is the bone marrow. The stem cells in the bone marrow have the capability of developing into several different types of blood cell to meet the body's demand for new blood. The balance of blood cells in the body signals the bone marrow to produce more or less of a particular time to keep the proportions appropriate.
Some organisms are capable of de-differentiation, in which specialized cells become more basic. This process is involved in the regeneration of limbs in animals which are capable of this feat, with the basic cells differentiating again to construct the needed tissues, bones, and other types of cells for the replacement. The exact processes behind cell differentiation and de-differentiation are not fully understood, although researchers have studied cells capable of these feats extensively, as the mechanics of this process could have valuable implications for the medical field.