Question: What is a main identifier of stem cells?
About the article "Stem cell", section "Identification".

Candidate passages:
Chorionic villi are a rich source of stem cells.
Biocell Center, a biotech company managed by Giuseppe Simoni, is studying and testing these types of stem cells.
Chorionic stem cells, like amniotic stem cells, are uncontroversial multipotent stem cells. 
The public in the United States has a general awareness of embryonic stem cells because of the stem cell controversy.
However, cord blood stem cells (hematopoietic stem cells) are not embryonic stem cells (pluripotent stem cells). 
Vertebrate Adult stem cell niches.A.
Hematopoietic stem cell niche.
Vertebrate hematopoietic stem cells niche in the bone marrow is formed by cells subendosteal osteoblasts, sinusoidal endothelial cells and bone marrow stromal (also sometimes called reticular) cells which includes a mix of fibroblastoid, monocytic and adipocytic cells. 
Thy-1 can be considered as a surrogate marker for various kind of stem cells (e.g.
hematopoietic stem cells or HSCs).
It is one of the popular combinatorial surface markers for FACS for stem cells in combination with other markers like CD34.
During sorting, mouse HSCs fall under Thy1hi subpopulation, while human HSCs fall under the Thy1lo subpopulation.
In humans, Thy-1 is expressed on neurons and HSCs among others.
It is considered a major marker of HSC pluripotency in concordance with CD34.
In human HSCs, Thy1 cells are all CD34 positive.
Thy 1 is also a marker of other kind of stem cells, for example: mesenchymal stem cells, hepatic stem cells ("oval cells"), keratinocyte stem cells, putative endometrial progenitor/(?
)stem cells. 
 Veterinary applications of stem cell therapy as a means of tissue regeneration have been largely shaped by research that began with the use of adult-derived mesenchymal stem cells to treat animals with injuries or defects affecting bone, cartilage, ligaments and/or tendons.
There are two main categories of stem cells used for treatments: allogeneic stem cells derived from a genetically different donor within the same species and autologous mesenchymal stem cells, derived from the patient prior to use in various treatments.
A third category, xenogenic stem cells, or stem cells derived from different species, are used primarily for research purposes, especially for human treatments.
Most stem cells intended for regenerative therapy are generally isolated either from the patient's bone marrow or from adipose tissue.
Mesenchymal stem cells can differentiate into the cells that make up bone, cartilage, tendons, and ligaments, as well as muscle, neural and other progenitor tissues, they have been the main type of stem cells studied in the treatment of diseases affecting these tissues.
The number of stem cells transplanted into damaged tissue may alter efficacy of treatment.
Accordingly, stem cells derived from bone marrow aspirates, for instance, are cultured in specialized laboratories for expansion to millions of cells.
Although adipose-derived tissue also requires processing prior to use, the culturing methodology for adipose-derived stem cells is not as extensive as that for bone marrow-derived cells.
While it is thought that bone-marrow derived stem cells are preferred for bone, cartilage, ligament, and tendon repair, others believe that the less challenging collection techniques and the multi-cellular microenvironment already present in adipose-derived stem cell fractions make the latter the preferred source for autologous transplantation.
New sources of mesenchymal stem cells are currently being researched, including stem cells present in the skin and dermis which are of interest because of the ease at which they can be harvested with minimal risk to the animal.
Hematopoetic stem cells have also been discovered to be travelling in the blood stream and possess equal differentiating ability as other mesenchymal stem cells, again with a very non-invasive harvesting technique.
There has been more recent interest in the use of extra embryonic mesenchymal stem cells.
Research is currently underway to examine the differentiating capabilities of stem cells found in the umbilical cord, yolk sac and placenta of different animals.
These stem cells are thought to have more differentiating ability than their adult counterparts, including the ability to more readily form tissues of endodermal and ectodermal origin.