Canonical Wnt signaling instructively promotes sensory neurogenesis in early neural crest stem cells (eNCSCs) (Lee, H. -catenin fail to generate both sensory and autonomic neuronal cells after BMP2 treatment (E). Bar, 10 m. BMP signaling counteracts Wnt/-catenin-dependent sensory neurogenesis Canonical Wnt signaling is both required and Fluorouracil cell signaling sufficient for sensory neuronal fate specification in eNCSCs (Hari et al., 2002; Lee Syk et al., 2004). Accordingly, as in BMP2-treated cultures, the formation of Brn-3ACpositive sensory neurons was abolished in explants of in mice results in the reduction of most neural crest lineages (Ikeya et al., 1997), and Wnt signal inhibition at the onset of neural crest emigration in zebrafish leads to reduced expression of several neural crest markers, including Sox10 (Lewis et al., 2004). However, numbers of Sox10-positive cells appear normal and neural crest cells still contribute to multiple lineages after neural crestCspecific deletion of and of (Hari et al., 2002; Stottmann et al., 2004). This could point to stage- or signaling componentCspecific requirements for Wnt/BMP signaling in stem cell maintenance, which has to be addressed in future studies. Although Wnt in combination with BMP signaling maintains multipotency of NCSCs and supports cell division in many of these cells, their responsiveness to instructive growth factors changes as time passes. Most intriguingly, extended NCSCs reduce their sensitivity towards the sensory neuronCinducing activity of canonical Wnt signaling while staying responsive to additional instructive growth elements including BMP2, NRG1, and TGF. The increased loss of Wnt responsiveness can’t be explained from the selective eradication of cells with sensory potential, as proven by clonal evaluation of cells which have been taken care of in the current presence of Wnt1 and BMP2 (Figs. 5 and ?and6).6). Rather, during maintenance in tradition individual NCSCs possess acquired intrinsic variations in comparison with eNCSCs emigrating from the neural pipe. Strikingly, these adjustments correspond to procedures happening in vivo: Although regarding sciatic nerve cells improved cell death may have masked an impact of Wnt on sensory neurogenesis, postmigratory NCSCs within both sciatic nerve as well as the DRG shown an modified Wnt response in comparison with migratory NCSCs and didn’t generate sensory neurons (Fig. 6). Identical adjustments happen in response to additional development elements also, both in NCSCs isolated at different period factors and in postmigratory NCSCs produced from different PNS areas (Bixby et al., 2002; Kruger et al., Fluorouracil cell signaling 2002). Therefore, adjustments in cell-intrinsic determinants impact cell destiny decisions by changing the level of sensitivity of neural crest cells to particular extracellular indicators (White colored et al., 2001; Fluorouracil cell signaling Kubu et al., 2002). For example, the amount of the transcription element Sox10 determines how neural crest cells interpret their environment and which destiny they adopt (Paratore et al., 2001). Such adjustments acquired as time passes might also clarify the various features related to Wnts and BMPs during neural crest advancement, which range from neural crest induction, delamination, and NCSC development to melanocyte development and neurogenesis (Ikeya et al., 1997; Dorsky et al., 1998; Garcia-Castro et al., 2002; Burstyn-Cohen et al., 2004; Lee et al., 2004). Certainly, obstructing Wnt signaling at different time factors in zebrafish embryogenesis indicated its reiterated but specific tasks in neural crest advancement (Lewis et al., 2004). Neural stem cells through the CNS also go through intrinsic adjustments during advancement, biasing a cell to self-renew, to generate either neurons or glia, or to produce specific neuronal cell types (Alvarez-Buylla et al., 2001). In particular, canonical Wnt signaling promotes stem cell expansion at early stages of cortical development, whereas it induces neuronal lineage commitment at later stages (Hirabayashi et al., 2004). Thus, as is the case with NCSCs found at different stages of PNS development, the proposed transition from neural stem cells present in the embryo to adult neural stem cells is accompanied by alterations in the stem cell’s genetic program (Alvarez-Buylla et al., 2001). It follows that continuous self-renewal used as a key feature of stem cells might Fluorouracil cell signaling not apply in its strictest sense to neural (and conceivably other) stem cells during development. Rather, although maintaining their multipotency, stem cells adapt to signals present in their extracellular environment. The environment, however, also changes with time. In the PNS, canonical Wnt activity is observed only at early development stages, when neural crest cells emigrate from the neural tube (Fig. 6). At later stages, Wnt/-catenin activity was no longer detectable in neural crestCderived tissues, such as DRG, peripheral nerves, and sympathetic ganglia. Thus, not only do NCSCs lose their Wnt responsiveness with time, but also postmigratory neural crest cells are not exposed to canonical Wnt signaling any more. We propose that this.