Cell differentiation

Cell differentiation is how a single fertilized egg ends up as a body with many distinct kinds of cells. As cells differentiate they change in shape, size, metabolism and function, and they generally lose developmental potential: a pluripotent embryonic cell can become almost anything, while a mature neuron or muscle fiber is locked into its role.

Nearly every cell in the body carries the same DNA, so differentiation is not about gaining or losing genes but about using them selectively. Transcription factors bind DNA and turn particular genes on or off, and epigenetic marks such as DNA methylation help keep those choices stable through later divisions. The decisions are triggered by signals from neighboring cells, by gradients of signaling molecules called morphogens and by a cell's own history. Differentiation usually runs one way, although reprogramming adult cells into induced pluripotent stem cells shows it can be reversed in the lab.

The process shapes the embryo, keeps blood and skin supplied with new cells from adult stem cells throughout life, and matters in cancer, where poorly differentiated tumor cells tend to grow more aggressively.