Stem Cell definitions
Stem cells (SCs) are defined as cells that show self-renewal either with or without differentiation, depending on the symmetry of the division. After fertilization of the oocyte, symmetric cell divisions (SD) followed by asymmetric cell divisions (AD) form a blastocyst. The inner cell mass (ICM) contains pluripotent embryonic stem cells (ESCs) which are able to differentiate into every cell type of the three germ layers (endoderm, mesoderm, and ectoderm) of the embryo (Figure).
After the gastrulation process, the pluripotent SCs give rise to multipotent SCs which continue the developmental process with more specific tasks (Figure, adapted from Spaas et al., 2012a). The blood contains 2 types of multipotent SCs: mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs).
In Global Stem cell Technology, we work with MSCs which have the capacity to form cartilage, bone, fat, muscle and tendon. This is in contrast with HSCs which have the ability to form all the different types of blood cells.
In 2006, the International Society for Cellular Therapy (ISCT) has carefully determined the qualities which human cells must possess in order to be defined as mesenchymal stem cells (MSCs) (Dominici et al., 2006).
These qualities are as follows: human MSCs have to be (i) plastic-adherent; (ii) positive for MSC markers and negative for adult blood cell markers; and (iii) able to differentiate into different cell types of the mesodermal germ layer such as osteoblasts (bone cells), chondroblasts (cartilage cells) and adipocytes (fat cells). Although no such strict definitions for veterinary stem cells have been established to date, the MSCs used in Global Stem cell Technology possess all these properties.
The origin of stem cells
Adapted from: Spaas, J.H., Guest, D., Van de Walle, G.,R. (2012). Tendon Regeneration in Human and Equine Athletes. Sports Medicine. 42. 871-890. 10.1007/BF03262300.