Progenitor cell

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The concept of a progenitor cell is difficult to define. Like stem cells, progenitor cells have a capacity to differentiate into a specific type of cell. In contrast to stem cells, however, they are already far more specific than stem cells: they are pushed to differentiate into their "target" cell. Controversy about the exact definition remains and the concept is still evolving, since it is only a decade old. Despite the difficulty of defining progenitors, the term is frequently used in research. Thus the importance of progenitors cannot be ignored.

1 Properties of Progenitor Cells
2 Function of Progenitor Cells
3 Examples of Progenitor Cells
4 References

[edit] Properties of Progenitor Cells

Most progenitors are described as unipotent or multipotent. In this point of view, they may be compared to adult stem cells. But progenitors are said to be in a farther stage of cell differentiation. They are in the “center” between stem cells and fully differentiated cell. The kind of potency they have, depends on the type of their "parent" stem cell and also on their niche. Like stem cells, mostly, they are formed and transported in a colony, with the right conditions for them to grow and differentiate into their target tissues. In contrast, some progenitor cells were found during research, and were isolated. After their marker was found, it was proven that these progenitor could move through the body and migrate towards the tissue where they are needed. Lots of properties are shared by adult stem cells and progenitor cells. But still, controversy remains because Embryonic stem cells are true stem cells in that they are pluripotent and show unlimited capacity for self-renewal. In contrast, many cells termed adult stem cells would be better defined as progenitor cells, as their capacities for unlimited self renewal and plasticity have not been comprehensively demonstrated.

	Stem Cell	Progenitor Cell
Self Renewal in vivo	Unlimited	Limited
Self Renewal in vitro	Unlimited	Limited
Potentiality	Multipotent	Unipotent, sometimes multipotent
Maintenance of Self Renewal	Yes	No
Population	Reaches maximum amount of cells before differentiating	Does not reach maximum population

[edit] Function of Progenitor Cells

The majority of progenitor cells lie dormant or possess little activity in the tissue in which they reside. They exhibit slow growth and their main role is to replace cells lost by normal attrition. In case of tissue injury, damaged or dead cells, progenitor cells can be activated. growth factors or cytokines are two substances which trigger the progenitors to mobilize towards the damaged tissue. At the same time, they start to differentiate into the target cells. Not all progenitors are mobile and are situated near the tissue of their target differentiation. When the cytokines, growth factors and other cell division enhancing stimulators take on the progenitors, a higher rate of cell division is introduced. It leads to the recovery of the tissue.

[edit] Examples of Progenitor Cells

The characterization or the defining principle of progenitor cells, in order to separate them from others, are rather based on the different cell markers than their morphological appearance.

Satellite cells found in muscles. They play a major role in muscle cell differentiaton and injury recoveries.
The transit amplifying neural progenitors of the rostral migratory stream.These cells are formed in the subventricular zone, they migrate to the olfactory bulb and differentiate further into specific types of neural cells.
Bone marrow stromal cells, basal cell of epidermis have 10% of progenitor cell, although they are often classed as stem cells due to their high plasticity and potentially unlimited capacity for self renewal.
Periosteum contains progenitor cells that develop into osteoblasts and chondroblasts.
Pancreatic progenitor cells are among the most studied progenitors. They are used in research to develop a cure against diabetes type-1.
Angioblasts or Endothelial progenitor cells(EPC). These are very important for research on fracture and wounds healing.

[edit] References

Barber CL, Iruela-Arispe ML(2006). The ever-elusive endothelial progenitor cell: identities, functions and clinical implications. Pediatric Researc 59, 722

I. Todorov, , I. Nair, K. Ferreri, J. Rawson, A. Kuroda, M. Pascual, K. Omori, L. Valiente, C. Orr, I. Al-Abdullah, A. Riggs, F. Kandeel(2005). Multipotent Progenitor Cells Isolated From Adult Human Pancreatic Tissue. Transplant Proceedings 37, 3420-3421

Raewyn M. Seaberg and Derek van der Kooy(2003). Stem and progenitor cells: the premature desertion of rigorous definitions. Trends in Neurosciences 26, 125-131