Cell differentiation Definition
“It is a biological process wherein cells gain specialised roles and switch from one cell type to another in an entity”
In human development, a fertilized egg undergoes differentiation into another type of specialized cell present in the body such as muscle, neurons and muscle cells. Undifferentiated cells are known as stem cells. These stem cells are located in the embryos and in adults.
Factors Influencing Cell Differentiation
In multicellular entities, the factors that stimulate the process of cell differentiation are environmental influences, cell signalling and the level of development of entities. The fundamental differentiation of a cell takes place when a sperm cell fertilizes an egg and the hence formed zygote arrives at a specific size. At this juncture, the zygote transforms various forms of cells requiring differentiated cells to undertake specialized roles.
Gene expression is said to be the reason. Gene set in all entities is identical as the genetic code is replicated from the actual egg cell that is fertilized by the sperm cell. To undertake a specific role, a cell from its genetic code only uses a few of the genes, ignoring the remaining.
Cell differentiation is primarily influenced by:
Structure of the gene – it is the prime factor for cell differentiation. Every viable gene possesses crucial instructions which decide the cell type and physical traits of the host. Any mistake here will influence the cell differentiation process and host-development.
Environmental determinants – temperature-change, oxygen supply and many other environmental factors have an impact on the working of hormones because of the different proteins dedicated to transforming information and stimulation of hormones. Any impact on these molecules will cause the cell differentiation and development process to get affected.
There are few instances leading to cell differentiation:
- Regular turnover of cells (blood cells in mature entities)
- Immature entity growing into an adult
- Damaged tissues undergoing repair when special cells are to be substituted
- Influence of cytoplasm
- Interaction between cells
Differentiated animal and plant cells tend to preserve all the genes necessary for programming the differentiation and development of a complex entity. Differentiated cells, in addition, possess a variety of proteins. Hence, cell differentiation can be ascribed to the pattern of gene expression which is to say that in each differentiating cell type, different genes are differently expressed.
Cell Differentiation – Mechanism
Transcription factors are key to the cell differentiation process. The chemicals and hormones involved determine the course of action revolving around the DNA, deciding the transcription. The body and cells in the proximity decide the factors found in cells right from the fetal developmental stage to death. Both the DNA constituted in a cell and the location of expression of DNA is pivotal. The cell differentiation process has a range of
The transcription factor has a direct influence on the proteins transcribing the DNA transforming it gradually to operating proteins and other cells. But, cells signal each other when they start to compress together indicating the action can no longer proceed.
Cell Differentiation – Examples
Examples in Plants
Although there is an involvement from various hormones, plants too emerge from one cell. Comparing the eggs in animals to seeds in plants, seeds harbours and nourishes its zygote just like the egg in animal cells. Cell division causes the zygote to divide, turning into an embryo. In the event of seed getting dispersed, stages of further development are ceased.
The embryo then forms into meristems, a specialized stem cell segment which differentiates outwards where one grows away and one towards the surface.
Root cap is formed in roots girdling meristems, which sheds when roots emerge through the soil, constantly replaced by meristems. Meristems are different on the surface creating both outward and inward cells. While the inward cells undergo similar differentiation as that seen in the root producing more vascular tissues, cells on the outside differentiate to leaves and stems. This can be compared to various organs in animals, where initial cells are not the same.
Examples in Animals
Process of fertilization in animals produces zygote which is totipotent (Totipotent cells are those cells that can be differentiated into any other cell type). All the complex tissues found in advanced animals arise from the zygote. In entities, cell differentiation commences early on.
Cell Differentiation – Errors
Abnormalities in cell differentiation can be categorized into three classes – anaplasia, dysplasia, and metaplasia.
Anaplasia – it refers to the loss of apparent differentiation which can take place in advanced stages of cancer. Early stages of cancer appear to mimic the tissue from which they originated and are organized by their differentiation pattern. With development further, variants of more irregular features are generated along with expanding malignancy. Ultimately, a highly anaplastic growth takes place where the cancerous cells have no association visibly to the parent tissue.
Dysplasia – refers to the cell arrangement typically emerging from distress in their regular growth pattern. While few are precursor lesions to cancer, some others are innocuous and relapse immediately. For instance CIN (cervical intraepithelial neoplasia).
Metaplasia – one cell type is converted into another. Typically, it occurs when chronic damage to the tissue is succeeded by extensive regeneration. For instance, squamous metaplasia of the bronchi.
Stem Cell Differentiation
Stem cells are specialized cells that can undergo self-renewal and differentiate into mature somatic cells in vitro and in vivo. Stem cells are the cells which cannot be differentiated. They are found in embryos typically referred to as embryonic stem cells which can either be pluripotent or totipotent. Adult cells too are stem cells and are multipotent.
Totipotent are those stem cells which can differentiate into every cell type in the body. Pluripotent are the stem cells which can be differentiated into most, not all cell types. These are found in the blastocysts in humans. While multipotent, are the stem cells found in adults which are capable of differentiating into restricted types of cells.
To sum it, adult cells are multipotent, while embryonic stem cells can either be pluripotent or totipotent.
Is Cell Differentiation Reversible?
The undifferentiated adult stem cells lead to the formation of specialized cells which can be differentiated. Such adult stem cells are found in large numbers in humans in their bone marrow, brain and skin.
Latest studies suggest that adult skin cells can be caused to reverse the process of differentiation and infer the many features of embryonic cells. Such results are known as iPS or induced pluripotent stem cells, which is the area of future interest in this stream.
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