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 affected.
As previously mentioned cell differentiation is a process through which a generic cell evolves into a given type of cell 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 functional animal.
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. Research is still ongoing to ensure that this type of treatment is both safe and effective.
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 irreversible commitment.
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.
These include:
Cytoplasmic localization
Induction
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).
Once the 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 development.
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).
In 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.
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 cells.
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 higher plants).
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.
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 be possible.
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.
You, as a human being, are made from trillions of cells, but only of about 250 different types
A specialised cell is a cell that has a particular structure and composition of subcellular structures
Structural differences between different types of cells enable them to perform specific functions within the organism
Cells specialise by undergoing a process known as differentiation
Specialised Cells in Animals
The nerve cell
Nerve cells (neurones) have a characteristically elongated structure which allows them to coordinate information from the brain and spinal cord with the rest of the body
Function: conduction of impulses
Adaptations:
Has a cell body where most of the cellular structures are located and most protein synthesis occurs
Extensions of the cytoplasm from the cell body form dendrites (which receive signals) and axons (which transmit signals), allowing the neurone to communicate with other nerve cells, muscles and glands
The axon (the main extension of cytoplasm away from the cell body) is covered with a fatty sheath, which speeds up nerve impulses. Axons can be up to 1m long in some animals
Muscle cells
Muscle cells contain layers of fibres which allow them to contract. The image above shows skeletal muscle cells
Function: contraction for movement
Adaptations:
There are three different types of muscle in animals: skeletal, smooth and cardiac (heart)
All muscle cells have layers of protein filaments in them. These layers can slide over each other causing muscle contraction
Muscle cells have a high density of mitochondria to provide sufficient energy (via respiration) for muscle contraction
Skeletal muscle cells fuse together during development to form multinucleated cells that contract in unison
A sperm cell
Sperm cells are mobile – their tail helps propel them forward in search of an egg to fertilise
Function: reproduction (pass on fathers genes)
Adaptations:
The head contains a nucleus which contains half the normal number of chromosomes (haploid, no chromosome pairs)
The acrosome in the head contains digestive enzymes that can break down the outer layer of an egg cell so that the haploid nucleus can enter to fuse with the egg’s nucleus
The mid-piece is packed with mitochondria to release energy (via respiration) for the tail
The tail rotates, propelling the sperm cell forwards (allowing it to move/swim)
Specialised Cells in Plants
A root hair cell
The root hair is an extension of the cytoplasm, increasing the surface area of the cell in contact with the soil to maximise absorption of water and minerals
Function: absorption of water and mineral ions from soil
Adaptations:
Root hair to increase surface area (SA) so the rate of water uptake by osmosis is greater (can absorb more water and ions than if SA were lower)
Thinner walls than other plant cells so that water can move through easily (due to shorter diffusion distance)
Permanent vacuole contains cell sap which is more concentrated than soil water, maintaining a water potential gradient
Mitochondria for active transport of mineral ions
Remember that chloroplasts are not found in these cells – there’s no light for photosynthesis underground!
A xylem vessel
Xylem cells lose their top and bottom walls to form a continuous tube through which water moves through from the roots to the leaves
Function: transport tissue for water and dissolved ions
Adaptations:
No top and bottom walls between cells to form continuous hollow tubes through which water is drawn upwards towards the leaves by transpiration
Cells are essentially dead, without organelles or cytoplasm, to allow free passage of water
Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant
Phloem cells
Phloem cells form tubes similar to xylem vessels, except the cells still retain some subcellular structures and are therefore living
Function: transport of dissolved sugars and amino acids
Adaptations:
Made of living cells (as opposed to xylem vessels which are made of dead cells) which are supported by companion cells
Cells are joined end-to-end and contain holes in the end cell walls (sieve plates) forming tubes which allow sugars and amino acids to flow easily through (by translocation)
Cells also have very few subcellular structures to aid the flow of materials
![Blood Cells Differentiation By パタゴニア [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons](https://www.microscopemaster.com/images/Blood_cells_differentiation_chart.jpg "Blood Cells Differentiation By パタゴニア [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons")
