Recent studies demonstrated that stromal cells isolated from adult bone marrow have the competence of differentiating into neuronal cells in vitro and in vivo. However, the capacity of marrow stromal cells or mesenchymal stem cells (MSCs) to differentiate into diverse neuronal cell populations and the identity of molecular factors that confer marrow stromal cells with the competence of a neuronal subtype have yet to be elucidated. Here, we show that Sonic hedgehog (Shh) and retinoic acid (RA), signaling molecules secreted from tissues in the vicinity of peripheral sensory ganglia during embryogenesis, exert synergistic effects on neural-competent MSCs to express a comprehensive set of glutamatergic sensory neuron markers. Application of Shh or RA alone had little or no effect on the expression of these neuronal subtype markers. In addition, incubation of MSCs with embryonic hindbrain/somite/otocyst conditioned medium or prenatal cochlea explants promoted up-regulation of additional sensory neuron markers and process outgrowth. These results identify Shh and RA as sensory competence factors for adult pluripotent cells and establish the importance of interactions between adult pluripotent cells and the host microenvironment in neuronal subtype specification.
Kondo et al. (2005) studied this question.