Stem cell self-renewal is tightly controlled by the concerted actions of stem cell-intrinsic elements and indicators inside the market

Stem cell self-renewal is tightly controlled by the concerted actions of stem cell-intrinsic elements and indicators inside the market. and Crittenden, 2007). By contrast, in the ovary (Fig. 1B) and testis (Fig. 1C), two or three somatic cell types form the niche for GSCs: the female GSC niche is composed of terminal filament cells, cap cells and GSC-contacting escort cells, whereas the male niche consists of hub cells and cyst stem cells (CySCs) (de Cuevas and Matunis, 2011; Xie, LY2811376 2012). Sometimes, two different stem cell types in the same tissue share a LY2811376 common niche cell component. For example, cap cells in LY2811376 the ovary serve as a component of both the GSC and follicular stem cell (FSC) niches, whereas hub cells of the testis function as the common niche component that regulates GSCs and CySCs (de Cuevas LY2811376 and Matunis, 2011; Xie, 2012). Mammalian stem cell niches are generally more complex. The hematopoietic stem cell (HSC) niche contains at least four different cell types (Fig. 1D), including osteoblasts, vascular cells, mesenchymal stem cells and neuron-Schwann cells (Wang and Wagers, 2011). In addition to specialized cell types, the ECM is a crucial component of the stem cell niche; many stem cell Rabbit Polyclonal to ZNF460 types, such as mammalian spermatogonial stem cells (SSCs), epidermal stem cells and neural stem cells (NSCs) (Fig. 1E), express high levels of integrins and directly contact the ECM, highlighting the role of ECM as an integral part of the stem cell niche (Kanatsu-Shinohara et al., 2008; Kazanis et al., 2010; Shen et al., 2008; Watt, 2002). This complex nature of the stem cell niche allows the formation of distinct and specialized niche structures for different stem cell types in the same organism or for the same stem cell type in different organisms. Open in a separate window Fig. 1. Stem cell niches. Niche cells and stem cells are depicted in green and red, respectively. Differentiated stem cell progeny and their surrounding somatic cells are shown in yellow and gray, respectively. (A) The GSC niche in the hermaphrodite gonad. (B) The GSC niche in the ovary. (C) The GSC niche in the testis. (D) The mammalian HSC niche. (E) The NSC niche in the mammalian subventricular zone. ASC, astrocyte; CAR, CXCL12-abundant reticular cell; CPC, cap cell; CySC, cyst stem cell; DGCs, differentiated germ cells; DTC, distal tip cell; EPC, ependymal cell; GEC, GSC-contacting escort cell; GSC, germline stem cell; HSC, hematopoietic stem cell; LSC, leptin receptor+ perivascular stromal cell; MSC, mesenchymal stem cell; NBs, neuroblasts; NSC, neural stem cell; PEC, posterior escort cell; SNC-SC, sympathetic neuronal cell-Schwann cell; SNO, spindle-shaped N-cadherin+ osteoblast; TF, terminal filament. Individual stem cell niches also use distinct combinations of signaling molecules to control stem cell self-renewal and proliferation. For some stem cell types, the activation of LY2811376 a single signaling pathway by the niche is sufficient for promoting stem cell self-renewal. For example, bone morphogenetic protein (BMP) in the female GSC niche is necessary and sufficient for GSC self-renewal (Xie, 2012). This is also true for Notch in the GSC niche (Byrd and Kimble, 2009; Kimble and Crittenden, 2007). However, for most stem cell types, the simultaneous activation of several pathways is needed for continuous stem cell self-renewal. For example, the fibroblast development element (FGF), brain-derived neurotrophic element (BDNF) and sonic hedgehog (Shh) signaling pathways are necessary for long-term mammalian NSC self-renewal (Zhao et al., 2008). Although particular mixtures or indicators of indicators are essential by different niche categories to regulate stem cell self-renewal, most of them appear to work as short-range indicators. Therefore, stem cells must stay in the niche to be able to maintain long-term self-renewal. One of the most easy, and probably the most dependable probably, methods would be to anchor stem cells.