Process+of+Cell+Differentiation

** Cell Differentiation **

** What is cell differentiation? **
The process starts from a single celled zygote to a mature multicellular organism and so the cell should undergo mitosis countless times. However, if a zygote keeps undergoing mitosis, human beings would end up as clumps of zygotes rather than a particular organism with specific parts like organs and tissues; and so, something in the process must allow cells to mature and take form of an organism.

Cell differentiation is the process in which a cell becomes specialized and is able to perform a particular function. It takes place during the embryological process when unspecialized cells become specialized into one of the 250 general types of cells in the human body. The process of cell differentiation has been a recent focus of modern research for many years now because researchers are fascinated by the embryonic stem cells’ ability to undergo differentiation from one cell into any type of cell in the body.

Before cell differentiation can occur, fertilization, the joining of a sperm and egg to form a zygote, must take place. All of the cells of an organism develop from the zygote, the original cell. Once the zygote forms, a series of mitotic divisions take place. Eventually, the cells become more specialized. Most of the cells in a multicellular organism contain the same DNA; this is due to the fact that they all develop from the same one cell. However, it is obvious that there are many different cell types in multicellular organisms. This is possible due to the selective expression of certain genes to create different types of cell from the same DNA.

**Prior to cell differentiation: Cell Determination**
A zygote is considered to have great potential for development so it is said to be in totipotent phase. As the zygote divides to produce more cells, the resulting cells are more limited to a particular type of cell. This process of a cell becoming increasingly destined to a particular type of cell is called cell determination. Cell determination occurs before the cell is in its final mature form.

**Cell Differentiation**
The cells in different stages in cell differentiation are categorized as totipotent, pluripotent, multipotent and specialized. Cells that are totipotent are able to differentiate into all different types of cells. In mammals, only the zygote and the products of the first few cell divisions are totipotent. The following stage is pluripotent, in which cells are capable of differentiating into many types of cells. The cells undergo further specialization to become stem cells that give rise to cells with a particular function. For example, blood stem cells give rise to red blood cells, white blood cells and platelets. The next stage of cell differentiation is called multipotent, in which the cells are able to give rise to only several kinds of cells, tissues and structures.

During the process of normal cell differentiation, the shape and anatomy of the cell changes drastically yet the genetic makeup generally stays the same. In other words, while the single fertilized egg cell starts with one set of DNA components and differentiates into hundreds of cell types, each cell contains the same genetic makeup. Researchers have found that the genetic expression of the developing cells causes changes.

**Process of Cell Differentiation**
1. Cytoplasmic segregation is apparent in the earliest stages of embryonic development. During this time, the embryo divides without growing, and undergoes cleavage divisions to produce individual blastomere cells. The embryo then develops into a solid mass of blastomeres, called a morula. mRNA or proteins are capable of determining the future cell type of the cell. Differential gene expression determines which proteins are used in which phase. Next, proteins from one phase regulate the activity of the genes of the next phase. Most cells are determined by the end of these early stages, and the future layout of the cell has been made.

2. In induction, a substance secreted by one group of cells influences the maturity of another group. Signals from the environment and other cells induce a number of different responses. This leads to the formation of different, specialized cells. Cells have developed complex ways of receiving and responding to signals from other cells and from their environment. Cells undergo a process called signal transduction, in which signals are received by cells and translated into a cellular response. Cells receive signals at the cell membrane or within the cytoplasm, amplify the signals, and finally respond to the signal. Cell signaling plays a role in the determination and differentiation of totipotent cells and in the regulation and activity of mature cells and tissues.

Differentiation forms several types of different cells from one precursor cell. In response to an exterior signal, cells can change the way they function and develop by regulating what genes are expressed at what time. A cell becomes differentiated by expressing certain genes and producing specific proteins from its DNA template; this allows it to develop into its mature form. All organisms have similar developmental processes and controls. The different structures develop based on the concentration of a type of signal.

**Example of Normal Cell Differentiation: Hematopoiesis**
Hematopoiesis is the process in which immature cells eventually develop into mature blood cells. A modern theory of how this process works is Monophyletic Theory, which states that a single type of stem cell can produce all the functioning blood cells in the body. According to this theory, some pluripotent stem cells will produce more pluripotent stem cells to ensure a stable and lasting supply of stem cells. The other cells will differentiate into cells that will produce mature blood cells. As previously mentioned, pluripotent stem cells in the bone marrow are capable of dividing and differentiating. During their development, they undergo transitional steps to produce red blood cells, platelets, white blood cells, and other different types of blood cells. These transitions are stimulated by growth factors.

Normal hematopoietic stem cells multiply rapidly and differentiate into different unipotential cells such as monocytes, granulocytes, red blood cells and platelets that have a specific limited life span. When cells don’t have this ability to terminally differentiate, they produce mass amounts of immature cells that don’t function properly but have a prolonged life span. Such cells in the bone marrow are referred to as leukemia cells.



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