MSCs are multipotent stem cells, multipotent progenitor cells, or myeloid stromal cells found in bone marrow, lungs, adipose tissue, and other body tissues.
When cultured as aggregates in suspension, embryonic stem cells form three-dimensional, multicellular complexes called embryoid bodies. These spherical structures resemble the egg cylinders of embryos 6 to 8 days post-fertilization.
After approximately 4 to 8 days, these embryoid bodies typically contain skeletal structures between the inner mesenchymal cells and outer epithelial cells, which begin to contract spontaneously.