Adult neural stem cells are rare, and little is known about their unique characteristics, leaving their in vivo identity enigmatic. We show that Lewis X (LeX), a carbohydrate expressed by embryonic pluripotent stem cells, is made by adult mouse subventricular zone (SVZ) stem cells and shed into their environment. Only 4% of acutely isolated SVZ cells are LeX(+); this subpopulation, purified by FACS, contains the SVZ stem cells. Ependymal cells are LeX(-), and purified ependymal cells do not make neurospheres, resolving the controversial claim that these are stem cells. Thus, LeX expression by adult CNS stem cells aids their in vivo identification, allows their enrichment, and raises new questions about the role of this unusual carbohydrate in stem cell biology.

Noninvasive monitoring of stem cells, using high-resolution molecular imaging, will be instrumental to improve clinical neural transplantation strategies. We show that labeling of human central nervous system stem cells grown as neurospheres with magnetic nanoparticles does not adversely affect survival, migration, and differentiation or alter neuronal electrophysiological characteristics. Using MRI, we show that human central nervous system stem cells transplanted either to the neonatal, the adult, or the injured rodent brain respond to cues characteristic for the ambient microenvironment resulting in distinct migration patterns. Nanoparticlelabeled human central nervous system stem cells survive long-term and differentiate in a site-specific manner identical to that seen for transplants of unlabeled cells. We also demonstrate the impact of graft location on cell migration and describe magnetic resonance characteristics of graft cell death and subsequent clearance. Knowledge of migration patterns and implementation of noninvasive stem cell tracking might help to improve the design of future clinical neural stem cell transplantation.superparamagnetic iron oxide ͉ stem cell biology A dvances in neural transplantation have paved the way for clinical trials aimed at restoring brain function in diseases, such as Parkinson's (1-3) and Huntington's (4), and stroke (5). The success of these trials for neurological diseases will depend not only on patient selection criteria and on choosing the right cell type, but also on the timing and site of transplantation. Both variables can influence the transplanted stem cells' migration pattern and subsequent differentiation (6, 7). Therefore, long-term monitoring of the graft in relation to the evolving lesion will be crucial. MRI, with its high spatial resolution, is the ideal modality for in vivo cell tracking. Tagging cells with superparamagnetic iron oxide (SPIO) nanocomposites has been shown to induce sufficient MR cell contrast for in vivo imaging of neural cell migration (8,9). Previous studies have demonstrated its application to track stem cells after stroke, but these were done with non-human stem cells and lacked in-depth analysis of the SPIO effect on stem cell biology (10, 11).Before this method can be considered to label human neural stem cells for clinical application, further analysis of the effects of SPIO on the biology of human stem cells are needed. For example, it has been described that Feridex, a SPIO reagent approved by the United States Food and Drug Administration for human use, inhibits mesenchymal stem cells from differentiating into chondrocytes (12), emphasizing the need for in-depth analysis of the influence of magnetic labeling on stem cell biology.We investigated the effects of SPIO labeling on human central nervous system stem cells grown as neurospheres (hCNS-SCns) (6, 13-15) in vitro and in vivo. We show that SPIO-labeled hCNS-SCns proliferate and differentiate normally in vitro and exhibit neuronal electrophysiological characteristics. We th...

Multipotent stem cells that generate both neurons and glia are widespread components of the early neuroepithelium. During CNS development, neurogenesis largely precedes gliogenesis: how is this timing achieved? Using clonal cell culture combined with long-term time-lapse video microscopy, we show that isolated stem cells from the embryonic mouse cerebral cortex exhibit a distinct order of cell-type production: neuroblasts first and glioblasts later. This is accompanied by changes in their capacity to make neurons versus glia and in their response to the mitogen EGF. Hence, multipotent stem cells alter their properties over time and undergo distinct phases of development that play a key role in scheduling production of diverse CNS cells.

Since their discovery twenty years ago and prospective isolation a decade later, neural stem cells (NSCs), their progenitors, and differentiated cell derivatives along with other stem-cell based strategies have advanced steadily toward clinical trials, spurred by the immense need to find reparative therapeutics for central nervous system (CNS) diseases and injury. Current phase I/II trials using stem cells in the CNS are the vanguard for the widely anticipated next generation of regenerative therapies and as such are pioneering the stem cell therapy process. While translation has typically been the purview of industry, academic researchers are increasingly driven to bring their findings toward treatments and face challenges in knowledge gap and resource access that are accentuated by the unique financial, manufacturing, scientific, and regulatory aspects of cell therapy. Solutions are envisioned that both address the significant unmet medical need and lead to increased funding for basic and translational research.

LeX/SSEA1/CD15 is an extracellular matrix-associated carbohydrate expressed by ES cells and by adult neural and bone marrow stem cells. It is important for cell adhesion, compaction and FGF2 responses of early embryonic stem cells; however, its function at later stages is not clear. We now show that LeX is expressed by primary mouse neural progenitor cells, including neural stem cells, neuroblasts and glioblasts, but not by their more differentiated products. LeX distinguishes highly proliferative cells even in the primitive neuroepithelium, demonstrating heterogeneity in cell potential before radial glia arise. At later stages, LeX expressing progenitors are frequently radial in morphology. Surface LeX expression can be used to enrich neural stem and progenitor cells from different CNS regions throughout development by FACS. We found that LeX expression is particularly strong in neural regions with prolonged neurogenesis, e.g., the olfactory epithelium, hippocampus, basal forebrain and cerebellum. These regions also express high levels of the growth factors FGF8 and/or Wnt-1. We show here that LeX-containing molecules in the developing nervous system bind Wnt-1. Our findings suggest that LeX, which is present on the surface of principle neural progenitors and secreted into their extracellular niche, may bind and present growth factors important for their proliferation and self-renewal.