Download What types of cells do not undergo mitosis?

What types of cells do not undergo mitosis?
Neurons
(adapted from HHMI’s “Ask a Scientist”)
The classic teaching is that we are born with all the neurons we will ever have. This idea was based on the
observation that after a stroke, the brain undergoes a process called gliosis, whereby the supporting cells in the
brain (glial cells) proliferate and replace neurons that have died during the hypoxic (stroke) episode.
You may have heard, however, that recently scientists have been identifying certain populations of neurons that
may indeed retain the ability to divide well into adulthood. Certain areas of the brain seem to preferentially
contain neurons that can still divide—namely, the subventricular region and the hippocampus. We're still not sure
whether neuronal mitosis can help recovery after an incident such as a stroke.
Cardiac muscle
The story of cardiac muscle is remarkably similar to that of neurons. Traditionally, we have thought that the
cardiac muscle, like skeletal muscle, can only undergo hypertrophy, not hyperplasia. That is, each individual cell
can get bigger and generate more contractile units, but the cells cannot increase in number. That is probably true
for mature cardiac muscle cells. Recently, however, evidence has been mounting for a population of so-called
cardiac stem cells, which may indeed be able to divide to replace myocardium that has been infracted because of
an episode of cardiac ischemia.
Red and white blood cells
Red blood cells (RBCs) fall into a somewhat easier category. Mature RBCs do not divide. In fact, because mature
RBCs don't even have a nucleus, these cells really can't do much of anything other than act as vessels for the
hemoglobin with which they are jam-packed. New RBCs are made in the marrow in the mature human. In the
marrow, there is a population of erythropoietic stem cells. These are the precursors to RBCs, and they do have
nuclei (which get expelled before they leave the marrow) and the ability to respond to growth factors (in
particular, erythropoietin) by undergoing mitosis.
A similar system exists in the marrow for the different kinds of white blood cells (WBCs). While WBCs do retain
their nucleus while in peripheral circulation, most are also what we call terminally differentiated, since they can
no longer undergo mitosis.
Skeletal muscle
Skeletal muscle can undergo hypertrophy, as each cell gets bigger. But skeletal muscle cells do undergo
hyperplasia, since no new cells are generated. As you can imagine, scientists have searched long and hard for a
way to get around this in order to repair muscle damaged by trauma or disease. Recent evidence suggests that this
might be possible because of a population of cells within the muscle termed satellite cells.
Smooth muscle
We have now discussed two out of three of the body's major types of muscle: cardiac and skeletal. The third type
is smooth muscle, which makes up the walls of our internal organs, such as the gastrointestinal tract and the
bladder, and the walls of our blood vessels. Smooth muscle holds the unique distinction of being the only type
with clear physiological as well as pathological predilections toward hyperplasia. For instance, the muscle cells in
the uterus of a pregnant woman undergo a huge amount of mitosis in response to a normal pregnancy. This
potential for division that smooth muscles retain can be a source of pathology, though: 25 percent of women of
reproductive age harbor symptomatic fibroids, also called leiomyomas. These are essentially benign tumors of the
smooth muscle. When mitosis happens where it's not needed, an uncomfortable and disabling disease can result.
Further reading:
http://www.hhmi.org/askascientist/answers/what_types_of_cells_do_not_undergo_mitosis_i_know_the_obvious_
answers_sex_cells_and_neurons_but_i.html
McKinnell, I.W., Parise, G., Rudnicki, M.A. Muscle stem cells and regenerative myogenesis. Current Topics in
Developmental Biology 71: 113-30, 2005.
Urbanek, K., et al. Myocardial regeneration by activation of multipotent cardiac stem cells in ischemic heart
failure. Proceedings of the National Academy of Sciences USA 102 (24): 8692-97, 2005.