Stem cells

Stem cells are undifferentiated cells with the ability to divide through mitosis to produce more stem cells (self-renewal) and that can differentiate into specialized cells. 

The relevance of stem cells in biomedical research was reflected in the decision to award Sir John B. Gurdon (Dippenhall, United Kingdom, 1933) and Professor Shinya Yamanaka (Osaka, Japan, 1962) the Nobel Prize of Medicine in 2012 for their findings in this research topic.

 

 Taken from the Official Website of the Nobel Prize.

Stem cells are widely studied, due to their potential therapeutic use and for their inherent interest. As explained during the lesson, stem cell research is now focused on regenerative medicine as well as on the treatment of a wide variety of diseases, including cancer, Parkinson disease, multiple sclerosis, and spinal cord injuries, among others. However, most of the clinical trials using stem cells as therapy are still in early clinical phases. The following video explains what stem cells are and how scientists are harnessing their medical potential:

 

Classification of stem cells according to developmental potentials

• Totipotent stem cells derive from the fusion of a sperm cell with an egg cell (zygote) or from the first few divisions of the fertilized egg (morula). Totipotent stem cells can give rise to an entire functional organism or to any cell type of the body, including the extraembryonic tissues (i.e. placenta, umbilical cord, amniotic sac).
• Pluripotent stem cells derive from the inner cell mass of the blastocyst. Pluripotent stem cells can differentiate into nearly all cell types of the three embryonic germ layers (endoderm, mesoderm, ectoderm), but not into an entire functional organism.
• Multipotent stem cells can develop into more than one cell type, but only those of a closely related family of cells (i.e. multipotent blood stem cells are capable of differentiating into erythrocytes, lymphocytes or platelets).
• Unipotent stem cells can produce only one cell type, their own, but have the property of self-renewal, which distinguishes them from non-stem cells.

 Taken from Eckfeldt et al. Nature Reviews Molecular Cell Biology 2005;6:726-737

Classification of stem cells according to their origin

• Embryonic stem cells derive from the embryonic stage of morula (totipotent stem cells) or from the inner cell mass blastocyst (pluripotent stem cells). Due to their high developmental potential, embryonic stem cells can give rise to teratomas, that are tumors containing differentiated elements of all three embryonic germ layers. Isolation of human embryonic stem cells results in the destruction of the fertilized embryo, which raises ethical issues.
• Adult or somatic stem cells originate from adult tissues and they have the ability to divide or self-renew indefinitely and generate the cell types from the tissue from which they originate. This type of cells are multipotent stem cells.
• Induced pluripotent stem cells (iPS): Professor Shinya Yamanaka (University of Kyoto, Japan) reprogrammed, for the first time, murine skin fibroblasts into multipotent stem cells that could develop into all cell types of an adult mouse by introducing four factors Oct3/4, Sox2, c-Myc and Klf4. He named the cells induced pluripotent stem cells (iPS) and these results were published in the prestigious Cell journal in 2006. In the present video, you can see the methods used to obtain iPS cells:

 

You will have to know the:

• Classification and characteristics of stem cells according to their developmental potential (totipotent, pluripotent, multipotent and unipotent stem cells).
• Classification and characteristics of stem cells according to their origin (embryonic, adult and inducible pluripotent stem cells).
• Genes implicated in the induction of iPS cells.