Process and Steps, Specification/Determination
Cell differentiation may simply be described as
the process through which a young and immature cell evolves in to a specialized
cell, reaching its mature form and function. For such unicellular organisms
like bacteria, various life functions occur within a single cell.
That is, such
processes as the transport of molecules, metabolism and reproduction all take
place within a single cell given that they are single celled. However,
multicellular organisms require different types of cells for these processes to
Here, different types of cells play a specific function given that they have varied structures. For instance, whereas the nerve cells play a crucial role in the transmission of signals to different parts of the body, blood cells play an important role carrying oxygen to different parts of the body.
The differences in structure and functions between the cells mean that they are specialized cells. To be able to perform different functions, cells have to become specialized. This becomes possible through the process referred to as cell specialization.
Process and Steps of Cell Differentiation
A cell capable of differentiating into any type
of cell is known as "totipotent". For mammals, totipotent includes
the zygote and products of the first few cell divisions. There are also certain
types of cells that can differentiate into many types of cells. These cells are
known as "pluripotent" or stem cells in animals (meristemic cells in
While this type of cell can divide to produce new
differentiated generations, they retain the ability to divide and maintain the
stem cell population making them some of the most important cells.
Examples of stem and
progenitor cells include:
Hematopoietic Stem Cells - These are from the bone
marrow and are involved in the production of red and white blood cells as well
as the platelets.
Mesenchymal Stem Cells - Also from the bone
marrow, these cells are involved in the production of fat cells, stromal cells
as well as a given type of bone cell.
Epithelial Stem Cells - These are progenitor
cells and are involved in the production of certain skin cells.
Muscle Satellite Cells - These are progenitor
cells that contribute to differentiated muscle tissue.
The process of cell differentiation starts with
the fertilization of the female egg. As soon as the egg is fertilized, cell
multiplication is initiated resulting in the formation of a sphere of cells
known as the blastocyst. It's this sphere of cells that attach to the uterine
wall and continues to differentiate.
As the blastocyst differentiates, it
divides and specializes to form a zygote that attaches to the womb for
nutrients. As it continues to multiply and increase in size, the
differentiation process results in the formation of different organs.
DNA and Cell Differentiation
Once the female egg has been fertilized, the
cells formed after cell division contain DNA that is identical. That is, the
DNA in all the cells will be identical. However, different regions of a
chromosome (DNA is wound in to a chromosome) code for different functions and
cell type. Here, it's only the regions that are required to perform a given
function that are expressed in each cell.
The regions (genes) that are
expressed determine the type of cell that will be created. While the different
types of cells that are formed contain the same DNA, it's the expression of
different genes that results in different types of cells. This is to say that
not all genes are expressed during differentiation.
* Gene expression is the process through which
information from a given gene is used to develop the structures of specific
Specification and Determination
During the differentiation process, cells
gradually become committed towards developing into a given cell type. Here, the
state of commitment may be described as "specification" representing
a reversible type of commitment or "determination" representing
Although the two represent differential gene activity,
the properties of cells in this stage is not completely similar to that of fully
differentiated cells. For instance, in the specification state, cells are not
stable over a long period of time.
There are two mechanisms that bring about
altered commitments in the different regions of the early embryo.
Cytoplasmic Localization - This occurs during the
earliest stage of embryo development. Here, the embryo divides without growth
and undergoes cleavage divisions that produce blastomeres (separate cells). Each
of these cells inherit a given region of the cytoplasm of the original cell
that may contain cytoplasmic determinants (reuratory substances).
embryo becomes a morula (solid mass of blastomeres) it is composed of two or
more differently committed cell populations. The cytoplasmic determinants may
contain mRNA or protein a given state of activation that influence specific
Induction - In induction, a
substance secreted by one group of cells causes changes in the development of
another group. During early development, induction tends to be instructive in
that tissue assumes a given state of commitment in the presence of the signal.
In induction, inductive signals also evoke various responses at varying concentrations
which results in the formation of a sequence of groups of cells, each being in
a different state of specification.
During the final phase of cell differentiation,
there is formation of several types of differentiated cells from one population
of stem cells of the precursor. Here, terminal differentiation occurs both in
embryonic development as well as in tissues during postnatal life.
Control of the process largely depends on a system of lateral inhibition.
That is, cells differentiating along a given pathway send out signals which
repress similar differentiation by the neighboring cells. A good example of
this is with the developing CNS of vertebrates (central nervous system).
this system, neurons cells from the tube of neuropithelium possess a surface
receptor known as Notch and a cell surface molecule known as Delta that can
bind to the Notch of adjacent cells and activate them.
This activation results
in a cascade of intracellular events that ultimately result in the suppression of
Delta production as well as the suppression of neuronal differentiation. As a
result, the neuropithelium ends up only generating a few cells with high expression
of Delta surrounded by a larger number of cells with low expression of Delta.
Cell Differentiation Significance
As previously mentioned cell differentiation is
a process through which a generic cell evolves into a given type of cell (cell
type) and ultimately allowing the zygote to gradually evolve in to a
multicellular adult organism.
Cell differentiation is an important process
through which a single cell gradually evolves allowing for development that not
only results in various organs and tissues being formed, but also a fully
While it plays a significant role in embryonic development,
the process of cell differentiation is also very important when it comes to
complex organisms throughout their lives. This is because of the
fact that it causes changes in size, shape, metabolic activities as well as
signal responsiveness of cells.
In cell differentiation, gene expression is particular
important given that there are vital control systems that only ensure certain differentiation. Here, the process proves beneficial by controlling
certain activities to guarantee both normal functioning tissues and organs, but
also a full functional animal.
Knowledge of cell differentiation has also
influenced stem cell research. Today, scientists and researchers are working to
determine the best way they can use stem cells for the purposes of
regenerating and repairing cellular damage.
As mentioned earlier, stem cells are
important in that they can develop to any cell type. This makes them very
special in that they can differentiate and be used for given treatment
purposes. A good example of this is with cells among the older adults. In older
years, many of the cells experience wear and tear. As a result, they lose their
ability to divide or repair themselves.
Stem cells can continue
differentiating into a number of specialized cells to renew and repair the
tissue in question. In theory, it is supposed that there is no limit as to the
type of diseases that can be treated using stem cell therapy. However, research
is still ongoing to ensure that this type of treatment is both safe and
Primary Factors Influencing Cell Differentiation
Gene Structure - This is the most important factor when it
comes to cell differentiation. Each of the viable genes contains important
information that determine the cell type and physical attributes of the animal
(host). Any problem in the genetic material ultimately affects cell
differentiation and the development of the host.
Environmental Factors - Various environmental
factors as changes in temperature and supply of oxygen etc can affect the
release and production of hormones given that various proteins are involved in
the transmission of information as well as triggering of hormones. If these
molecules are affected, then cell differentiation and development is also
Here, learn more about Cell Culture, Cell Division, Cell Proliferation and Cell Staining as well as Gram Stain.
Check out information on Cell Theory.
Take a look at different types of Organelles in the cell
And more advanced: Cytochemistry
Take a look at White Blood Cells Main Page and Platelets
Interesting and Related Articles:
Return to learning more about Stem Cells
Return from Cell Differentiation to Cell Biology Main Page
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Bora Zivkovic (2001) From Two Cells To Many:
Cell Differentiation and Embryonic Development.
Browder, L. W. 1996. Cell determination and
differentiation: The muscle paradigm. In L. W. Browder (ed.), Advanced
Developmental Biology. The University of Calgary. Retrieved November 15, 2007.