Stem Cell Adhesion Molecules
Stem cells reside within distinct microenvironments known as stem cell niches. Within the niche, stem cells may be in contact with their daughter cells, the extracellular matrix (ECM), and stromal cells. Adhesion molecules, such as Cadherins and Integrins, mediate stem cell contacts with other cells and ECM proteins, respectively. E-Cadherin-based cell adhesion is important for embryonic stem cell self-renewal and maintenance of pluripotency. In the developing mammalian embryonic brain, the loss of Integrin molecules and subsequent neural stem cell detachment from the ECM results in apoptosis. Integrins are also thought to regulate hematopoietic stem cell homing and retention in the bone marrow niche. In addition, adhesion molecules may influence asymmetric stem cell division by interacting with microtubules of the mitotic spindle and directing the plane of cell division. The daughter cell that maintains contact with the niche receives self-renewal signals, while the sister cell inherits differentiation factors and lacks potency signals from the niche. Pathologically, the loss of cell-cell adhesion molecules in cancer stem cells is thought to contribute to an epithelial to mesenchymal transition and an invasive, migratory phenotype.