Stem Cell Microenvironments and Beyond.

Endogenous stem cells are indispensable to keep tissue homeostasis due to their unique ability to generate more specialized cell types in an organized way depending on the body needs. Precise control over stem cell differentiation is essential for organogenesis and tissue homeostasis. Stem cells reside in specialized microenvironments, also called niches, which maintain them in an undifferentiated and self-renewing state. The cellular and molecular mechanisms of stem cell maintenance are key to the regulation of homeostasis and likely contribute to several disorders when altered during adulthood. Extensive studies in a various tissues have shown the importance of the niche in modulating stem cell behavior, including bone marrow, skin, intestine, skeletal muscle, vocal cord, brain, spinal cord, stomach, esophagus, and others. In recent past, extraordinary advancement has been made in the identification and characterization of stem cell niches using modern state-of-art techniques. This progress lead to the definition of the main cellular components in the microenvironment where stem cells reside and the identification of molecular mechanisms by which stem cell behavior is controlled, revealing key niche signals involved in stem cell regulation. Similar to the ecological niche of an organism, a stem cell niche is exclusive to the specific type of stem cell and guides its dynamics. This book describes the major cellular and molecular components of various stem cells microenvironments in different organs and at distinct pathophysiological conditions, such as cell-cell interactions, extra-cellular matrix proteins, soluble factors, and physical forces. Although several advances have been made in our understanding of the signals that promote stem cell activation or quiescence, several components of the stem cells microenvironment remain unknown due to the complexity of niche composition and its dynamics. Further insights into these cellular and molecular mechanisms will have important implications for our understanding of organ homeostasis and disease. In this book, we present a selected collection of detailed chapters on what we know so far about the stem cell niches in various tissues and under distinct pathophysiological conditions. Twelve chapters written by experts in the field summarize the present knowledge about the physiological function and pathophysiological role of the stem cell regulation by the microenvironment.