
The Proliferation of Cells in Development and Differentiation - benniebio
https://www.creative-bioarray.com/Services/cell-proliferation-assay-services.htm
======
benniebio
Blood cell differentiation provides a good example of the continued
proliferation of stem cells. There are several different types of blood cells
with special functions: red blood cells (red blood cells) transport O 2 and CO
2 ; granulocytes and macrophages are phagocytic cells; platelets (fragment of
megakaryocytes) play a role in blood coagulation; and responsible for the
immune response with lymphocytes. All of these cells have a limited life span,
ranging from less than one day to several months, and are constantly produced
by the division of common stem cells (pluripotent stem cells) in the bone
marrow. The progeny of pluripotent stem cells then become committed to
specific differentiation pathways. These cells continue to proliferate upon
differentiation and undergo several rounds of division. However, once they are
fully differentiated, the proliferation will stop, so the maintenance of
differentiated blood cell populations depends on the continued proliferation
of pluripotent stem cells.

Because stem cells can replicate and differentiate to produce a variety of
cell types, they have considerable potential for further medical applications.
For example, stem cells can be used to treat human disease and repair damaged
tissue. Stem cells with the broadest differentiation ability are embryonic
stem cells (ES cells) present in early embryos and can produce differentiated
cell types of all adult organisms. These cells can be cultured from mouse
embryos for introduction of altered genes into mice.

------
benniebio
Early development is characterized by rapid proliferation of embryonic cells,
which are then differentiated to produce many specific types of cells that
make up the tissues and organs of multicellular animals. The cell
proliferation will generally decrease with the differentiation of cells, and
most cells in adult animals are blocked in the G 0 phase of the cell cycle.
Some types of differentiated cells will not divide again, but most cells can
regain proliferation as needed to replace cells that are lost due to injury or
cell death. In addition, some cells divide throughout life to replace cells
with high conversion rates in adult animals. Thus, cell proliferation and cell
death are carefully balanced to maintain a constant number of cells in adult
tissues and organs.

In terms of cell proliferation, the cells of adult animals can be classified
into three major categories. Some types of differentiated cells will not be
able to divide, such as human cardiomyocytes. These cells are produced during
embryonic development, differentiated, and then retained throughout life.

In contrast, most cells in adult animals enter the G0 phase of the cell cycle,
but regain proliferation as needed to replace cells that have been injured or
have died. Cells of this type include skin fibroblasts, smooth muscle cells,
endothelial cells that line the blood vessels, and most internal organs of the
epithelial cells, such as the liver, pancreas, kidneys, lungs, prostate, and
breasts. An example of controlled proliferation of these cells discussed above
is the rapid proliferation of dermal fibroblasts to repair damage caused by
cutting or wounds. Hepatocytes provide another striking example, with
hepatocytes usually rarely dividing.

------
benniebio
However, if a large number of hepatocytes are lost (eg, by surgical removal of
a portion of the liver), the remaining cells are stimulated to proliferate to
replace the missing tissue. For example, two-thirds of the liver of a
surgically resected rat is followed by rapid cell proliferation, resulting in
regeneration of the entire liver within a few days.

Other types of differentiated cells, including blood cells, epithelial skin
and epithelial cells line the digestive tract, have a short life cycle and
must be replaced by continuous cell proliferation of adult animals. In these
cases, fully differentiated cells will not proliferate, instead, they are
replaced by cell proliferation called stem cells that are less differentiated.
Stem cell division produces daughter cells that can differentiate or remain as
stem cells, thereby serving as a source of lifelong differentiated cells.

------
benniebio
In 1998, two groups of researchers reported the isolation of ES cells from
human embryos, increasing the likelihood that these human stem cells could be
used in medical applications. It is therefore theoretically possible that the
nuclei of an adult cell can be used to produce ES cells, which can then
provide a tissue source for treating the individual. In addition, stem cells
have been isolated from adult tissues, producing not only blood cells, but
also many other cell types, including neurons and connective tissue cells such
as bone, cartilage, fat and muscle. The therapeutic application of these adult
stem cells avoids the ethical issues associated with the use of embryos as a
source of ES cells. Therefore, ongoing research on stem cells can open up new
ways to treat a wide range of human diseases.

