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Neurons and glia are thought to arise from multipotent and self-renewing stem cells, which comprise the majority of neuroepithelial cells in the ventricular zone (VZ) of the early embryonic CNS. However, this idea remains to be tested rigorously, because CNS stem cells have been identified only by using in vitro assays, from which their abundance in vivo cannot be directly inferred. In the hematopoietic system, stem cells are characterized by using prospective isolation and direct in vivo transplantation. Here we have used this approach to ask whether most VZ progenitors behave as stem cells in vivo. The best-studied region of the embryonic CNS for addressing this problem is, arguably, the ventral spinal cord, within which progenitors in the motoneuron progenitor (pMN) domain sequentially generate motoneurons (MNs) and oligodendrocyte precursors (OPs). Virtually all VZ cells in pMN express the transcription factor Olig2. If most of these cells are stem cells, then they should maintain neurogenic potential, even at later, gliogenic stages. To test this hypothesis, we have prospectively isolated [Olig2.sup.+] cells from murine embryonic day (E)9.5 and E13.5 spinal cord and directly transplanted them to E2 chick spinal cord. Transplanted E9.5 cells generate both neurons, including MNs and OPs, whereas E13.5 cells generate. The observation that most [Olig2.sup.+] progenitors do not maintain neurogenic potential into the period of gliogenesis argues that they do not self-renew. These results do not support the commonly held view that most neuroepithelial cells in the embryonic CNS VZ are stem cells in vivo. CNS stem cells | neuroepithelial cells | in vivo transplantation

The link between basal cell carcinoma (BCC) and aberrant activation of the Hedgehog (Hh) signaling pathway has been well established in humans and in mouse models. Here we report the development of assays, including two novel in vitro BCC models, which allowed us to screen for Hh inhibitors and test their validity as potential treatments for BCC. We identified a novel small molecule Hh inhibitor (CUR61414) that can block elevated Hh signaling activity resulting from oncogenic mutations in Patched-1. Moreover, CUR61414 can suppress proliferation and induce apoptosis of basaloid nests in the BCC model systems, whereas having no effect on normal skin cells. These findings directly demonstrate that the use of Hh inhibitors could be a valid therapeutic approach for treating BCC. cancer | medulloblastoma | patched | smoothened

Young neurons born in the medial ganglionic eminence (MGE) migrate a long distance dorsally, giving rise to several types of interneurons in neocortex. The mechanisms that facilitate selective dorsal dispersion of MGE cells while restricting their movement ventrally into neighboring regions are not known. Using microtransplantation into fetal brain slices and onto dissociated substrate cells on floating filters (spot assay), we demonstrate that ventral forebrain regions neighboring the MGE are nonpermissive for MGE cell migration, whereas the dorsal regions leading to the neocortex are increasingly permissive. Spot assay experiments using filters with different pore sizes indicate that the permissive factors are not diffusible. We also show that MGE cells respond to chemoattractive and inhibitory factors diffusing from the neocortex and ventromedial forebrain, respectively. We propose that the final extent and regional specificity of MGE cell dispersion is largely dictated by contact guidance through a selectively permissive environment, flanked by nonpermissive tissues. In addition, we propose that chemotactic guidance cues superimposed over the permissive corridor facilitate efficient dorsal migration of MGE cells.

Research has been conducted on the embryonic stem cells. The hypothesis that these cells can be directed to a motor neuron fate has been tested and the results demonstrate that the signaling factors can induce mouse embryonic stem cells to differentiate into spinal progenitor cells and then into motor neurons.