Читать книгу The SAGE Encyclopedia of Stem Cell Research - Группа авторов - Страница 226

The identification a specific cell that could regenerate the entire epithelial breast lineage with intact morphological features such as ducts and glands occurred in 2006. Researchers were able to isolate a single mouse breast cell based on its specific surface proteins, visualize it under a microscope, and demonstrate its capacity to regenerate a complete functional mammary gland when transplanted into a cleared fat pad of a recipient mouse. Clonal outgrowths obtained from the recipient mouse were further transplanted into another recipient and were once again shown to regenerate a complete functional gland, which meant that the outgrowth must been generated from the self-renewing mammary stem cell. These cells were found to be localized to the basal cell population in the gland where the myoepithelial cells are present. MaSCs are difficult to identify with precision because they represent a small percentage of the basal cells, and markers to identify them are still being researched. Advances in cell dissection, isolation, and sorting techniques will also enable more accurate separation of MaSCs from other cell types in the basal cell population. Identification of lineage-restricted luminal and myoepithelial progenitors has had significantly more success, with a specific population of progenitors having been identified based both on cell surface markers and the presence or absence of receptors for the hormones estrogen and progesterone. After the identification of MaSCs in the mouse in 2006, distinct luminal progenitor cell populations were also identified. Following this, MaSCs and luminal progenitors have also been identified in humans by various research groups.

More recently, a study published in 2013 has identified a small population of cells in the human breast that exhibit significant multilineage differentiation capacity. When these cells were isolated from a larger population of mammary epithelial cells and cultured in the lab, they exhibited a capacity to differentiate into both luminal and myoepithelial cells. They were also shown to be capable of forming alveolar structures in culture. When these human cells were transplanted on to the cleared fat pads of immunodeficient mice, they also formed glandular and ductal outgrowths, showing a distinct capacity to repopulate the breast with all three cell types present. These cells were termed endogenous plastic somatic (ePS) cells. Further study demonstrated that when ePS cells were isolated from this epithelial population each of these cells were capable of differentiating into all three germ layers, indicating the presence of pluripotency characteristics. However, these cells were shown to be distinct from embryonic stem cells, induced pluripotent stem cells, or multipotent mesenchymal stem cells in that they cannot proliferate indefinitely.