Blood Stem Cell Self-Renewal and Differentiation

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Abstract

The mammalian blood system is made of more than ten different cell types. One of the distinct cells in the blood or hematopoietic stem cell (HSC). HSC has the ability of differentiation and self-renewal. According to research studies, mature blood cells have a short life span. Due to this, HSC is required to continuously generate the right number of each type of blood cell to sustain the body. While generating the cells, HSC must ensure a balance between self-renewal and differentiation. In this paper, the author will provide an in-depth analysis of blood stem cells’ self-renewal and differentiation.

Introduction

Blood cell’s primary responsibility is the maintenance and immune protection of all types of cells in the body (Orkin & Zon, 2008). Due to this functionality, the blood and skin cells’ pose the greatest ability of differentiation and self-renewal. The blood stem cells are also referred to as hematopoietic stem cells (HSC). Apart from the ability to self-renew and differentiate, HSC produce a number of specialized components such as red and white blood cells through haematopoiesis.

The Stem cell concept was initially proposed by McCulloch and Till in the early 1960s. The two were analyzing the bone marrow to determine which components were responsible for blood regeneration. Ten days after transplanting syngeneic bone marrow cells in experimental mice, the duo discovered the formation of cellular colonies in the specimens’ spleens. Examination of the colonies showed that a minute sub-population of the bone marrow cells had two distinct characteristics (Kelly, 2007). The properties include the ability to self-renew and produce multiple myeloerythroid cells. The findings paved way for the two defining features of stem cells.

Since the initial success studies by Till and McCulloch, the field of blood stem cell research has undergone great expansion. Numerous experiments over the decades have led to an in-depth understanding of the stem cell concept. For example, findings from different studies reveal HSCs are the only cells within the hematopoietic structure with the ability to differentiate and self-renew (Roeder, Horn, Sieburg, Cho, Muller-Sieburg, & Loeffler, 2008). In addition, experts in the field have been able to discover that HSCs are responsible for generating lymphoid and myeloid lineages of blood cells.

Today, researchers continue to study more about blood stem cell self-renew and differentiation with the aim of discovering new ways in which stem cells can be used in the medical field.

Characteristics of Blood Stem Cells

Blood stem cells have two primary characteristics. The features include multi-potency and self-renewal.

Self-Renewal

Self-renewal refers to the process by which at least one of the two daughter cells remains identical to the mother during division. The procedure is used by blood stem cells to generate more tissues and ensure the required population is maintained (Davis & Halton, 2011). Scientists’ reports reveal self-renewal occurs in the stem cell recess in the bone marrow. Due to this, the signals present in this spot are considered to be essential in duplication.

The process of division takes place in two ways. According to Tang (2012) the mechanisms include obligatory asymmetric replication and stochastic differentiation. Obligatory asymmetric replication is a process where a stem cell splits into one mother cell indistinguishable to the original. On its part, stochastic differentiation is characterized by the development of one stem cell into two differentiated daughter cells.

Self-renewal is controlled by the interactions of cell intrinsic molecular pathways (Kolonin & Simmons, 2012). The conduits contain extrinsic signals exhibited by the cell’s microenvironment. Due to this, the natural environment for the blood stem cells is referred to as the niche. The spot is the tissue-specific anatomical habitation. Roeder et al. (2008) note the dwelling changes within the cell development course. In addition, the niche offers the required milieu for regulated alterations between self-renewal, multi-potency, and stem cell quiescence. When exposed to the right signals, stem cells move from the dormant state and undergo through symmetrical or asymmetrical cell divisions. During the development stage, numerous tissue stem cells are often generated. The cells attain the ability of self-renewal and maintain the aptitude during the sturdy period of an adult organ (Taupin, 2011). Once in a steady state, the process of blood stem cell replication can only be triggered during regeneration when there is a tissue injury.

Differentiation

Stem cell differentiation is also referred to as potency. The process is termed as the ability to split into dissimilar cell types. There are different methods of differentiation. Orkin and Zon (2008) claim the appropriate technique is determined by the type of stem cell, the species, somatic cell type, and lineages. When separating Blood stem cells, it is important to monitor the progress and analyze the phenotype of the cells. Identities and lineages of differentiated cells can be examined using various PCR methods. The techniques include western blotting, cell sorting, and biomarker analysis.

Scientists differentiate blood stem cells in various ways. The techniques used include signal inhibition and three-dimensional culture. Other methods entail analyzing growth factors, cell culture substrate, and co-culture environments. In Cell Culture Substrate, stem cells are cultured on extracellular matrix proteins to trigger differentiation (Tang, 2012). Cells are known to generate signals that neighboring cells can respond to. Due to this, scientists grow blood stem cells together with other tissues that produce growth factors responsible for activating differentiation process.

According to Kelly (2007) blood stem differentiation processes produces a number of different cells. They include omnipotent, multipotent, unipotent, pluripotent, and oligopotent. Each form of cell produced exhibits unique characteristics.

Omnipotent are cells produced during the initial division of the fertilized egg. The blood stem cells can separate into extra-embryonic and embryonic cell types (Davis & Halton, 2011). In addition, omnipotent have the ability to form an absolute, feasible organism. The cells are also generated from the blending of an egg and sperm cell.

Multipotent blood stem cells differentiate into various cell types. However, they separate into cells which share almost similar traits.

Unipotent blood stem cells produce one kind of cell (Roeder et al., 2008). However, they have the ability to self-renew themselves and appear different from non-stem cells.

Pluripotent stem cells are linked to totipotents. Tang (2012) claim the tissues can differentiate into just about all cells in the body except placenta. However, the cells cannot sustain a full organism development. The pluripotents instigate as inner cell mass (ICM) tissues inside a blastocyst. Research findings reveal scientists lay bare pluripotency by offering evidence of steady developmental prospective in cases of protracted culture. Oligopotent blood stem cells can only separate into a small number of tissue types (Orkin & Zon, 2008). The cell forms include lymphoid and myeloid.

Essential Niche for Blood Stem Cells

Extensive research studies reveal there are three different sources of blood stem cells. The sources are bone marrow, peripheral blood, and umbilical cord. The three areas have been proved to support proper self-renewal and differentiation of blood stem cells.

Bone Marrow

The bone marrow was the first source of Blood stem cells (Taupin, 2011). Experiments on specimen such as mice proved the marrow to be an ideal spot for stem cell production. After successful studies on mice, doctors started performing bone marrow transplants on humans by drawing out marrow cells from donors. The collected blood stem cells take over the responsibility of generating blood cells when injected in the patient’s body (Kolonin & Simmons, 2012).

Peripheral Blood

Blood stem cells can be acquired from the bloodstream. To make the blood stream an ideal niche for self-renewal and differentiation, certain proteins are used to move stem cells from the bone marrow into the blood (Kelly, 2007). The process allows isolation of enough cells to sustain the body.

Umbilical Cord

In the late 1980 and early 1990s the umbilical cord was discovered to be a rich source of blood stem cells. The cells self-renew and differentiate supporting the fetus during pregnancy (Davis & Halton, 2011).

Conclusion

HSCs were the initial stem cells to be discovered. Since the first test by Till and McCulloch majors steps have been witnessed in stem cell field. More areas where the cells can be found in the human body have been detected. In addition numerous methods of activating cell self-renewal and differentiation have been formulated. The progress in the field by biologists has helped to control a number of diseases such as Leukemia and anemia. Today, scientists are striving to develop new ways of producing large amounts of blood stem cells in the laboratories. The experts are developing means of growing specialized cells with the ability of self-renewal and differentiation.

References

Davis, B., & Halton, C. (2011). Perspectives in stem cell research. New York: Nova Science.

Kelly, E. (2007). Stem cells. Westport, CT: Greenwood Press.

Kolonin, M., & Simmons, P. (2012). Stem cell mobilization: Methods and protocols. New York: Humana Press.

Orkin, S., & Zon, L. (2008). Hematopoiesis: An evolving paradigm for stem cell biology. Cell, 132(4), 631-644.

Roeder, I., Horn, K., Sieburg, H., Cho, R., Muller-Sieburg, C., & Loeffler, M. (2008). Characterization and quantification of clonal heterogeneity among hematopoietic stem cells: A model-based approach. Blood, 112(13), 4874-4883.

Tang, Y. (2012). Genetics of stem cells. Amsterdam: Elsevier/Academic Press.

Taupin, P. (2011). Stem cells & regenerative medicine. Hauppauge, NY: Nova Science.

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