Stem cells (SCs) are unspecialised cells with the ability to give rise to one or more type of mature specialised cell and also display extensive unlimited, self-renewal potential. They can be classified by the extent to which they can differentiate into different cell types, this is defined as potency. Totipotent SC is the cell with the greatest differentiation potential, able to produce extra embryonic tissue as well as every other cell type in a living organism. Spores and zygotes are examples of totipotent SCs.14 During human development, when totipotent SCs begin to specialize they become embryonic SCs. These SCs are isolated and cultivated from the inner cell mass of the blastocyst of a growing embryo, formed approximately 5 days after fertilization. These SCs are pluripotent, losing the ability to form extra embryonic tissue but still retaining the ability to differentiate into every type of adult cell.
Tissue specific non-embryonic stem cells (also referred to as somatic or adult stem cells) (ASC) are multipotent. They are more restricted in that they only differentiate into cells of a particular lineage; cells of the specific tissue/organ in which they reside. For example, blood forming (haematopoietic) SCs in bone marrow can only give rise to red blood cells, white blood cells and platelets but not neurons15.
SCs formed in different stages of life and in different places of the body.
More recently – induced pluripotent stem cells- pioneered by Shinya Yamanaka in 2006 – Adult cells that have been genetically reprogrammed to an ESC-like condition by being provoked to express genes and growth factors important for maintaining the properties of ESCs. This may pave the way… for era in the stem cell therapeutics.
Throughout life we continue to rely on capability of the stem cells to replace damaged tissues thereby facilitating their repair.
All in all, SCs are key tools helping researchers increase their knowledge about normal development, disease onset and progression, especially regarding cancers, useful for developing and testing new drugs and therapies for safety and effectiveness.