Mesenchymal stem cells (MSCs) are a heterogeneous subset of stromal stem cells isolated from many adult tissues. Previous studies reported that MSCs can differentiate to both mesodermal and neural lineages by a phenomenon referred to as "dedifferentiation" or "transdifferentiation". However, since MSCs have only been defined in vitro, Much of their development in Vivo is Still unknown. Here, we prospectively identified MSCs in the bone marrow from adult transgenic mice encoding neural crest-specific P0-Cre/FIoxed-EGFP and Wnt1-Cre/Floxed-EGFP. EGFP-positive MSCs formed spheres that expressed neural crest stem cell genes and differentiated into neurons, glial cells, and myofibroblasts. Interestingly, we observed MSCs both in the GFP(+) and GFP(-) fraction and found that there were no significant differences in the in vitro characteristics between these two populations. Our results suggest that MSCs in adult bone marrow have at least two developmental origins, one of which is the neural crest. (C) 2009 Elsevier Inc. All rights reserved.