EMBRYONIC STEM-CELLS DIFFERENTIATED IN-VITRO AS A NOVEL SOURCE OF CELLS FOR TRANSPLANTATION

The controlled differentiation of mouse embryonic stem (ES) cells into near homogeneous populations of both neurons and skeletal muscle cell s that can survive and function in vivo after transplantation is repor ted, We show that treatment of pluripotent ES cells with retinoic acid (RA) and dimethylsulfoxide (DMSO) induce differentiation of these cel ls into highly enriched populations of gamma-aminobutyric acid (GABA) expressing neurons and skeletal myoblasts, respectively. For neuronal differentiation, RA alone is sufficient to induce ES cells to differen tiate into neuronal cells that show properties of postmitotic neurons both in vitro and in vivo, In vivo function of RA-induced neuronal cel ls was demonstrated by transplantation into the quinolinic acid lesion ed striatum of rats (a rat model for Huntington's disease), where cell s integrated and survived for up to 6 wk, The response of embryonic st em cells to DMSO to form muscle was less dramatic than that observed f or RA, DMSO-induced ES cells formed mixed populations of muscle cells composed of cardiac, smooth, and skeletal muscle instead of homogeneou s populations of a single muscle cell type, To determine whether the r esponse of ES cells to DMSO induction could be further controlled, ES cells were stably transfected with a gene coding for the muscle-specif ic regulatory factor, MyoD, When induced with DMSO, ES cells constitut ively expressing high levels of MyoD differentiated exclusively into s keletal myoblasts (no cardiac or smooth muscle cells) that fused to fo rm myotubes capable of spontaneous contraction, Thus, the specific mus cle cell type formed was controlled by the expression of MyoD, These r esults provided evidence that the specific cell type formed (whether i t be muscle, neuronal, or other cell types) can be controlled in vitro , Further, these results demonstrated that ES cells can provide a sour ce of multiple differentiated cell types that can be used for transpla ntation.