Pluripotent stem cells and their niches

Abstract

The ability of stem cells to self-renew and to replace mature cells is fundamental to ontogeny and tissue regeneration. Stem cells of the adult organism can be categorized as mono-, bi-, or multipotent, based on the number of mature cell types to which they can give rise. In contrast, pluripotent stem cells of the early embryo have the ability to form every cell type of the adult body. Permanent lines of pluripotent stem cells have been derived from preimplantation embryos (embryonic stem cells), fetal primordial germ cells (embryonic germ cells), and malignant teratocarcinomas (embryonal carcinoma cells). Cultured pluripotent stem cells can easily be manipulated genetically, and they can be matured into adult-type stem cells and terminally differentiated cell types in vitro, thereby, providing powerful model systems for the study of mammalian embryogenesis and disease processes. In addition, human embryonic stem cell lines hold great promise for the development of novel regenerative therapies. To fully utilize the potential of these cells, we must first understand the mechanisms that control pluripotent stem cell fate and function. In recent decades, the microenvironment or niche has emerged as particularly critical for stem cell regulation. In this article, we review how pluripotent stem cell signal transduction mechanisms and transcription factor circuitries integrate information provided by the microenvironment. In addition, we consider the potential existence and location of adult pluripotent stem cell niches, based on the notion that a revealing feature indicating the presence of stem cells in a given tissue is the occurrence of tumors whose characteristics reflect the normal developmental potential of the cognate stem cells.

The induction of bone formation by coral-derived calcium carbonate/hydroxyapatite constructs

“…It is obvious that the rectus abdominis muscle of adult baboons is endowed with a stem cell niche [35] which provides a large number of differentiating cells including osteogenic progenitors which attach and differentiate onto the biomimetic matrices. The presence of a stem cell niche in adult rectus abdominis muscles is additionally supported by the recent identification of myogenic endothelial cells in human skeletal muscle [36].…”

Mechanical control of stem cell differentiation

“…Preliminary findings indicate that RhoA/ROCK signaling controls differentiation of embryonic stem cells (Peerani et al, 2007;Watanbe et al, 2007), although a specific role of tension/mechanical force remains wholly unexplored. Given the poor efficiency of forming induced pluripotent cells in vitro (Meissner et al, 2007;Takahashi et al, 2007) and the apparent importance of microenvironmental cues in forming "stem cell niches" (Lensch et al, 2006;Moore and Lemischka, 2006), it is tempting to speculate that the mechanical environment may hold the keys to engineering stemness, and represents an important opportunity and direction for future research.…”

Human mandible bone defect repair by the grafting of dental pulp stem/progenitor cells and collagen sponge biocomplexes

“…Dental pulp is a niche housing neural-crest-derived stem cells. This niche is easily accessible and there is limited morbidity after collection (Jo et al, 2007;Lensch et al, 2006;Mitsiadis et al, 2007). Previous studies have shown that dental pulp stem cells (DPSCs) are capable of differentiating into osteoblasts (Laino et al, 2005;Laino et al, 2006b) that secrete abundant extracellular matrix (ECM) and that can build a woven bone in vitro (Laino et al, 2006a).…”