Читать книгу The SAGE Encyclopedia of Stem Cell Research - Группа авторов - Страница 225

The search for mammary stem and progenitor cells is based on the understanding of a differentiation hierarchy that is present in the mammary epithelial cells. This differentiation hierarchy gives rise to three adult cell types: the myoepithelial cell, the ductal cell, and the alveolar cell. Currently there are two modes of differentiation that have been proposed to explain the origin of these cells based upon the techniques used. In both cases, the primary cell of origin is a stem cell with self-renewing capacity and multipotency, termed mammary stem cell. In the first model, the stem cell gives rise to a single progenitor that is long lived but not self-renewing, which in turn gives rise to both luminal (ductal, alveolar) and myoepithelial progenitor cells, which are more restricted in their differentiation capacity. These are termed bipotent progenitors. In the second model, proposed based on lineage tracing studies, cell maintenance in the adult breast is proposed to occur from unipotent progenitor cells (which in turn arise from the single progenitor). These cells are capable of producing cells of only a single lineage (luminal, alveolar, or myoepithelial). In both cases, the restricted progenitor cells give rise to the adult cells. The existence of bipotent progenitor cells was initially thought to occur only during development, with a switch to unipotent cells occurring at birth. However, recent studies have shown that bipotent progenitors continue to exist in the adult and may contribute to the long-term maintenance of the breast. This is an active area of study that is currently determining the roles of each of these modes of differentiation in the developing and adult breast.