Until recently adult somatic stem cells were thought to differentiate only into cells of their resident tissues. Several reports have suggested that adult stem cells are more plastic than previously appreciated, even differentiating into cell types developmentally derived from different germ layers. We reported that Marrow Stromal Cells (MSCs), which normally differentiate into mesenchymal derivatives (bone, cartilage, muscle, tendon and fat) are able to differentiate into neurons, classical ectodermal cells. To begin characterizing mechanisms regulating transgerminal differentiation of MSCs, we previously examined gene expression in undifferentiated populations in dissociated culture. Surprisingly, the CD11b-/CD34-/CD45-/CD44+/CD77+/CD91+ population expressed genes representing all primary embryonic germ layers (SFN Abstract, 2001) Since the MSCs most probably comprise a heterogeneous population, we performed clonal analysis in the present studies. A clonal population, derived from a single cell, express ...