Stem cells

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Stem cells are undifferentiated cells, which self-renew via mitosis, and are able to differentiate in order to obtain a variety of functions.

Embryonic stem cells are totipotent, as they have the potential to differentiate into any cell lineage, including the germ line and placental types[1]. They can also proliferate indefinitely before they differentiate[2]. One example of where they can be found is in the inner mass of a blastocyst[3].

Once a cell has begun to differentiate down a specific lineage, it become pluripotent, and then multipotent, untill reaching the terminal differentiation point as a unipotent cell as it's determined fate. Differentiation occurs via asymmetric cell division, whereas the proliferation of stem cells occurs by symmetric cell division.

An example of as pluripotent stem cell would be haematopoietic stem cells, which are the common ancestor to all blood cells in the body and are found in the bone marrow [4]. These cells that give rise to all blood cells are pluripotent stem cells. Differentiation of these cells begins during the development of the foetus and continues throughout life. The pluripotent stem cell differentiates into stem cells, sometimes referred to as colony forming units, for different lineages of blood cells, including the lymphoid (T and B cells), myeloid, erythrocytic and megakaryoblastic lineages. Along with being primarily found in the bone marrow, stem cells can also be isolated from foetal blood in umbilical cords.Stem cells which express embryonic stem cell markers have been isolated in dental pulp[5]. Differentiation of stem cells into the functional blood cells is triggered by specific cell surface interactions with the stromal cells of the marrow and specific cytokines produced by these and other cells. Specific cytokines that promote hematopoietic cell growth and terminal differentiation are released by helper T cells, dendritic cells, macrophages, and other cells in response to infections and on activation[6].

Some cytoplasmic factors are known to induce somatic cells nuclei into a pluripotent state[7]. This has been proven in research using cytoplasmic factors from oocytes and using these factors on transplanted somatic cells[8].

References

  1. Becker, W. M., Kleinsmith L. J., Hardin, J., Bertoni, G. P., (2009) The World of the Cell, 7th edition, San Francisco: Pearson Education
  2. H.J. Rippon and A.E. Bishop; Embryonic stem cells; Tissue Engineering and Regenerative Medicine Centre, Investigative Science, Imperial College London, London, UK; January 2004; pages 23-34
  3. James A. Thomson*, Joseph Itskovitz-Eldor, Sander S. Shapiro, Michelle A. Waknitz, Jennifer J. Swiergiel, Vivienne S. Marshall, Jeffrey M. Jones; Embryonic Stem Cell Lines Derived from Human Blastocysts; Science; Science 06 Nov 1998; Vol. 282, Issue 5391, pp. 1145-1147; 1998
  4. Alberts, B., Bray, D., Hopkin, K., Johnson, A., Lewis, J., Raff, M., Roberts, K., Walter, P., (2008) Essential Cell Biology, 5th edition, New York: Garland Science
  5. Kerkis, Irina; Kerkis, Alexandre; Dozortsev, Dmitri; Stukart-Parsons, GaËlle Chopin; Gomes Massironi, SÍLvia Maria; Pereira, Lygia V.; Caplan, Arnold I.; Cerruti, Humberto F. (2006). "Isolation and Characterization of a Population of Immature Dental Pulp Stem Cells Expressing OCT-4 and Other Embryonic Stem Cell Markers". Cells Tissues Organs 184 (3–4): 105–16
  6. Murray P R, Rosenthal K S, Pfaller M A et al. 2013, Medical Microbiology, Seventh Edition, Philadelphia PA, Elsevier Saunders
  7. Human Embryonic Stem Cells Derived By Somatic Cell Nuclear Transfer. (2013). Cell, [online] 153(6), pp.1228-1238. Available at: http://www.sciencedirect.com/science/article/pii/S0092867413005710 [Accessed 22 Oct. 2015].
  8. Human Embryonic Stem Cells Derived By Somatic Cell Nuclear Transfer. (2013). Cell, [online] 153(6), pp.1228-1238. Available at: http://www.sciencedirect.com/science/article/pii/S0092867413005710 [Accessed 22 Oct. 2015].
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