幹細胞ニッチ

Summary The multipotentiality and self-renewal ability are the two main characteristics of stem cells. Stem cells are maintained in a microenvironment called the stem cell niche, and start to cycle upon exit from the niche. Drosophila germline stem cells employ a simple niche system, where they attach to single niche cells: cap cells in the ovary and hub cells in the testis. The more complicated hematopoietic stem cell (HSC) niches are broadly classified into two categories, osteoblastic and vascular. While the osteoblasts on the endosteal surface maintain HSCs, sinusoidal endothelial cells and perivascular cells support their proliferation and differentiation. The two niches cooperate with each other in the maintenance of hematopoietic homeostasis. Recently other cells have been identified as components of the HSC niches, such as CAR cells (CXCL12 Abundant Reticular cells) and Nestins⁺ mesenchymal stem cells. The understanding of these mesenchymal stem/progenitor cells may provide a novel insight into the relationship between the two main HSC niches.