Two anatomically distinct niches regulate stem cell activity.
The niche microenvironment controls stem cell number, fate, and behavior. The bone marrow, intestine, and skin are organs with highly regenerative potential, and all produce a large number of mature cells daily. Here, focusing on adult stem cells in these organs, we compare the structures and cellular components of their niches and the factors they produce. We then define the niche as a functional unit for stem cell regulation. For example, the niche possibly maintains quiescence and regulates fate in stem cells. Moreover, we discuss our hypothesis that many stem cell types are regulated by both specialized and nonspecialized niches, although hematopoietic stem cells, as an exception, are regulated by a nonspecialized niche only. The specialized niche is composed of 1 or a few types of cells lying on the basement membrane in the epithelium. The nonspecialized niche is composed of various types of cells widely distributed in mesenchymal tissues. We propose that the specialized niche plays a role in local regulation of stem cells, whereas the nonspecialized niche plays a role in relatively broad regional or systemic regulation. Further work will verify this dual-niche model to understand mechanisms underlying stem cell regulation.
Department of Cell Differentiation, Sakaguchi Laboratory of Developmental Biology, Keio University School of Medicine, Tokyo, Japan. hema@a7.keio.jp
Hideo
H
Ema
Toshio
T
Suda
D000328:Adult; D053687:Adult Stem Cells / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001853:Bone Marrow / Q000378:metabolism; D002454:Cell Differentiation; D018859:Hair Follicle / Q000166:cytology / Q000378:metabolism; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism; D007421:Intestine, Small / Q000166:cytology / Q000378:metabolism; D009928:Organ Specificity; D055153:Stem Cell Niche