cell differentiation
Meaning of cell differentiation: How one fertilized egg becomes hundreds of cell types without changing its genes, and the yardstick a pathologist uses to grade a tumor.
Definition of cell differentiation
Cell differentiation is the process by which an unspecialized cell takes on the structure and function of a particular tissue, becoming a muscle cell, a nerve cell or a skin cell rather than remaining a general one. The change is driven by switching sets of genes on and off, not by altering the genes themselves, so every cell keeps the same complete instructions.
If the genes stay the same, what changes?
Which genes are read. A liver cell and a nerve cell carry identical DNA and differ entirely in which parts of it are switched on. Master regulator proteins turn on the program for a tissue, and chemical marks laid onto the DNA and onto the proteins it wraps around lock the unused sections away. Those marks are copied when the cell divides, so a liver cell reliably produces liver cells. The state is stable, which is why the finding that a handful of introduced regulators can reset an adult cell to an unspecialized one was so unexpected.
Is it a one-way process?
Mostly, inside the body. Cells generally travel from unspecialized toward specialized, and the most specialized often stop dividing altogether, which is part of why heart muscle and nerve tissue repair so poorly after injury. Some tissues keep a reserve of unspecialized cells for renewal, so the lining of the gut and the blood are replaced continuously from stem cells that specialize as they mature. In the laboratory the direction can be reversed, and cells taken from skin can be returned to a flexible state and pushed down a different path.
Why does it matter in cancer?
| Grade | Appearance under the microscope |
|---|---|
| Well differentiated | Closely resembles the tissue it came from |
| Moderately differentiated | Recognizable but disordered |
| Poorly differentiated | Little resemblance to the parent tissue |
| Undifferentiated or anaplastic | Origin cannot be told from appearance alone |
Loss of differentiation generally tracks with faster growth and a worse outlook, and tumor grading is built on it. Setting a mature teratoma against an immature teratoma makes the point plainly. Both contain tissue from several lineages, and how far those tissues have matured is what separates a benign tumor from a malignant one.
Also known as
Used in a sentence
The report described a poorly differentiated tumor bearing little resemblance to the surrounding tissue.
Good to know
Differentiation changes which genes are active rather than which genes are present, so a tumor cell that has lost its specialized appearance still carries the full genetic instructions of the tissue it arose from.
Word origin
Where “cell differentiation” comes from
Differentiation comes from the Latin differre, meaning to carry apart or set apart; cell from cella, a small room.